1 /*
2 * Copyright 2001-2008 Sun Microsystems, Inc. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
24
25 # include "incls/_precompiled.incl"
26 # include "incls/_concurrentMarkSweepGeneration.cpp.incl"
27
28 // statics
29 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
30 bool CMSCollector::_full_gc_requested = false;
31
32 //////////////////////////////////////////////////////////////////
33 // In support of CMS/VM thread synchronization
34 //////////////////////////////////////////////////////////////////
35 // We split use of the CGC_lock into 2 "levels".
36 // The low-level locking is of the usual CGC_lock monitor. We introduce
37 // a higher level "token" (hereafter "CMS token") built on top of the
38 // low level monitor (hereafter "CGC lock").
39 // The token-passing protocol gives priority to the VM thread. The
40 // CMS-lock doesn't provide any fairness guarantees, but clients
41 // should ensure that it is only held for very short, bounded
42 // durations.
43 //
44 // When either of the CMS thread or the VM thread is involved in
45 // collection operations during which it does not want the other
46 // thread to interfere, it obtains the CMS token.
47 //
48 // If either thread tries to get the token while the other has
49 // it, that thread waits. However, if the VM thread and CMS thread
50 // both want the token, then the VM thread gets priority while the
51 // CMS thread waits. This ensures, for instance, that the "concurrent"
52 // phases of the CMS thread's work do not block out the VM thread
53 // for long periods of time as the CMS thread continues to hog
54 // the token. (See bug 4616232).
55 //
56 // The baton-passing functions are, however, controlled by the
57 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
58 // and here the low-level CMS lock, not the high level token,
59 // ensures mutual exclusion.
60 //
61 // Two important conditions that we have to satisfy:
62 // 1. if a thread does a low-level wait on the CMS lock, then it
63 // relinquishes the CMS token if it were holding that token
64 // when it acquired the low-level CMS lock.
65 // 2. any low-level notifications on the low-level lock
66 // should only be sent when a thread has relinquished the token.
67 //
68 // In the absence of either property, we'd have potential deadlock.
69 //
70 // We protect each of the CMS (concurrent and sequential) phases
71 // with the CMS _token_, not the CMS _lock_.
72 //
73 // The only code protected by CMS lock is the token acquisition code
74 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
75 // baton-passing code.
76 //
77 // Unfortunately, i couldn't come up with a good abstraction to factor and
78 // hide the naked CGC_lock manipulation in the baton-passing code
79 // further below. That's something we should try to do. Also, the proof
80 // of correctness of this 2-level locking scheme is far from obvious,
81 // and potentially quite slippery. We have an uneasy supsicion, for instance,
82 // that there may be a theoretical possibility of delay/starvation in the
83 // low-level lock/wait/notify scheme used for the baton-passing because of
84 // potential intereference with the priority scheme embodied in the
85 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
86 // invocation further below and marked with "XXX 20011219YSR".
87 // Indeed, as we note elsewhere, this may become yet more slippery
88 // in the presence of multiple CMS and/or multiple VM threads. XXX
89
90 class CMSTokenSync: public StackObj {
91 private:
92 bool _is_cms_thread;
93 public:
94 CMSTokenSync(bool is_cms_thread):
95 _is_cms_thread(is_cms_thread) {
96 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
97 "Incorrect argument to constructor");
98 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
99 }
100
101 ~CMSTokenSync() {
102 assert(_is_cms_thread ?
103 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
104 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
105 "Incorrect state");
106 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
107 }
108 };
109
110 // Convenience class that does a CMSTokenSync, and then acquires
111 // upto three locks.
112 class CMSTokenSyncWithLocks: public CMSTokenSync {
113 private:
114 // Note: locks are acquired in textual declaration order
115 // and released in the opposite order
116 MutexLockerEx _locker1, _locker2, _locker3;
117 public:
118 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
119 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
120 CMSTokenSync(is_cms_thread),
121 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
122 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
123 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
124 { }
125 };
126
127
128 // Wrapper class to temporarily disable icms during a foreground cms collection.
129 class ICMSDisabler: public StackObj {
130 public:
131 // The ctor disables icms and wakes up the thread so it notices the change;
132 // the dtor re-enables icms. Note that the CMSCollector methods will check
133 // CMSIncrementalMode.
134 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
135 ~ICMSDisabler() { CMSCollector::enable_icms(); }
136 };
137
138 //////////////////////////////////////////////////////////////////
139 // Concurrent Mark-Sweep Generation /////////////////////////////
140 //////////////////////////////////////////////////////////////////
141
142 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
143
144 // This struct contains per-thread things necessary to support parallel
145 // young-gen collection.
146 class CMSParGCThreadState: public CHeapObj {
147 public:
148 CFLS_LAB lab;
149 PromotionInfo promo;
150
151 // Constructor.
152 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
153 promo.setSpace(cfls);
154 }
155 };
156
157 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
158 ReservedSpace rs, size_t initial_byte_size, int level,
159 CardTableRS* ct, bool use_adaptive_freelists,
160 FreeBlockDictionary::DictionaryChoice dictionaryChoice) :
161 CardGeneration(rs, initial_byte_size, level, ct),
162 _dilatation_factor(((double)MinChunkSize)/((double)(oopDesc::header_size()))),
163 _debug_collection_type(Concurrent_collection_type)
164 {
165 HeapWord* bottom = (HeapWord*) _virtual_space.low();
166 HeapWord* end = (HeapWord*) _virtual_space.high();
167
168 _direct_allocated_words = 0;
169 NOT_PRODUCT(
170 _numObjectsPromoted = 0;
171 _numWordsPromoted = 0;
172 _numObjectsAllocated = 0;
173 _numWordsAllocated = 0;
174 )
175
176 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
177 use_adaptive_freelists,
178 dictionaryChoice);
179 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
180 if (_cmsSpace == NULL) {
181 vm_exit_during_initialization(
182 "CompactibleFreeListSpace allocation failure");
183 }
184 _cmsSpace->_gen = this;
185
186 _gc_stats = new CMSGCStats();
187
188 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
189 // offsets match. The ability to tell free chunks from objects
190 // depends on this property.
191 debug_only(
192 FreeChunk* junk = NULL;
193 assert(UseCompressedOops ||
194 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
195 "Offset of FreeChunk::_prev within FreeChunk must match"
196 " that of OopDesc::_klass within OopDesc");
197 )
198 if (ParallelGCThreads > 0) {
199 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
200 _par_gc_thread_states =
201 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads);
202 if (_par_gc_thread_states == NULL) {
203 vm_exit_during_initialization("Could not allocate par gc structs");
204 }
205 for (uint i = 0; i < ParallelGCThreads; i++) {
206 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
207 if (_par_gc_thread_states[i] == NULL) {
208 vm_exit_during_initialization("Could not allocate par gc structs");
209 }
210 }
211 } else {
212 _par_gc_thread_states = NULL;
213 }
214 _incremental_collection_failed = false;
215 // The "dilatation_factor" is the expansion that can occur on
216 // account of the fact that the minimum object size in the CMS
217 // generation may be larger than that in, say, a contiguous young
218 // generation.
219 // Ideally, in the calculation below, we'd compute the dilatation
220 // factor as: MinChunkSize/(promoting_gen's min object size)
221 // Since we do not have such a general query interface for the
222 // promoting generation, we'll instead just use the mimimum
223 // object size (which today is a header's worth of space);
224 // note that all arithmetic is in units of HeapWords.
225 assert(MinChunkSize >= oopDesc::header_size(), "just checking");
226 assert(_dilatation_factor >= 1.0, "from previous assert");
227 }
228
229
230 // The field "_initiating_occupancy" represents the occupancy percentage
231 // at which we trigger a new collection cycle. Unless explicitly specified
232 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
233 // is calculated by:
234 //
235 // Let "f" be MinHeapFreeRatio in
236 //
237 // _intiating_occupancy = 100-f +
238 // f * (CMSTrigger[Perm]Ratio/100)
239 // where CMSTrigger[Perm]Ratio is the argument "tr" below.
240 //
241 // That is, if we assume the heap is at its desired maximum occupancy at the
242 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
243 // space be allocated before initiating a new collection cycle.
244 //
245 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
246 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
247 if (io >= 0) {
248 _initiating_occupancy = (double)io / 100.0;
249 } else {
250 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
251 (double)(tr * MinHeapFreeRatio) / 100.0)
252 / 100.0;
253 }
254 }
255
256
257 void ConcurrentMarkSweepGeneration::ref_processor_init() {
258 assert(collector() != NULL, "no collector");
259 collector()->ref_processor_init();
260 }
261
262 void CMSCollector::ref_processor_init() {
263 if (_ref_processor == NULL) {
264 // Allocate and initialize a reference processor
265 _ref_processor = ReferenceProcessor::create_ref_processor(
266 _span, // span
267 _cmsGen->refs_discovery_is_atomic(), // atomic_discovery
268 _cmsGen->refs_discovery_is_mt(), // mt_discovery
269 &_is_alive_closure,
270 ParallelGCThreads,
271 ParallelRefProcEnabled);
272 // Initialize the _ref_processor field of CMSGen
273 _cmsGen->set_ref_processor(_ref_processor);
274
275 // Allocate a dummy ref processor for perm gen.
276 ReferenceProcessor* rp2 = new ReferenceProcessor();
277 if (rp2 == NULL) {
278 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
279 }
280 _permGen->set_ref_processor(rp2);
281 }
282 }
283
284 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
285 GenCollectedHeap* gch = GenCollectedHeap::heap();
286 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
287 "Wrong type of heap");
288 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
289 gch->gen_policy()->size_policy();
290 assert(sp->is_gc_cms_adaptive_size_policy(),
291 "Wrong type of size policy");
292 return sp;
293 }
294
295 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
296 CMSGCAdaptivePolicyCounters* results =
297 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
298 assert(
299 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
300 "Wrong gc policy counter kind");
301 return results;
302 }
303
304
305 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
306
307 const char* gen_name = "old";
308
309 // Generation Counters - generation 1, 1 subspace
310 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
311
312 _space_counters = new GSpaceCounters(gen_name, 0,
313 _virtual_space.reserved_size(),
314 this, _gen_counters);
315 }
316
317 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
318 _cms_gen(cms_gen)
319 {
320 assert(alpha <= 100, "bad value");
321 _saved_alpha = alpha;
322
323 // Initialize the alphas to the bootstrap value of 100.
324 _gc0_alpha = _cms_alpha = 100;
325
326 _cms_begin_time.update();
327 _cms_end_time.update();
328
329 _gc0_duration = 0.0;
330 _gc0_period = 0.0;
331 _gc0_promoted = 0;
332
333 _cms_duration = 0.0;
334 _cms_period = 0.0;
335 _cms_allocated = 0;
336
337 _cms_used_at_gc0_begin = 0;
338 _cms_used_at_gc0_end = 0;
339 _allow_duty_cycle_reduction = false;
340 _valid_bits = 0;
341 _icms_duty_cycle = CMSIncrementalDutyCycle;
342 }
343
344 // If promotion failure handling is on use
345 // the padded average size of the promotion for each
346 // young generation collection.
347 double CMSStats::time_until_cms_gen_full() const {
348 size_t cms_free = _cms_gen->cmsSpace()->free();
349 GenCollectedHeap* gch = GenCollectedHeap::heap();
350 size_t expected_promotion = gch->get_gen(0)->capacity();
351 if (HandlePromotionFailure) {
352 expected_promotion = MIN2(
353 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(),
354 expected_promotion);
355 }
356 if (cms_free > expected_promotion) {
357 // Start a cms collection if there isn't enough space to promote
358 // for the next minor collection. Use the padded average as
359 // a safety factor.
360 cms_free -= expected_promotion;
361
362 // Adjust by the safety factor.
363 double cms_free_dbl = (double)cms_free;
364 cms_free_dbl = cms_free_dbl * (100.0 - CMSIncrementalSafetyFactor) / 100.0;
365
366 if (PrintGCDetails && Verbose) {
367 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
368 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
369 cms_free, expected_promotion);
370 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
371 cms_free_dbl, cms_consumption_rate() + 1.0);
372 }
373 // Add 1 in case the consumption rate goes to zero.
374 return cms_free_dbl / (cms_consumption_rate() + 1.0);
375 }
376 return 0.0;
377 }
378
379 // Compare the duration of the cms collection to the
380 // time remaining before the cms generation is empty.
381 // Note that the time from the start of the cms collection
382 // to the start of the cms sweep (less than the total
383 // duration of the cms collection) can be used. This
384 // has been tried and some applications experienced
385 // promotion failures early in execution. This was
386 // possibly because the averages were not accurate
387 // enough at the beginning.
388 double CMSStats::time_until_cms_start() const {
389 // We add "gc0_period" to the "work" calculation
390 // below because this query is done (mostly) at the
391 // end of a scavenge, so we need to conservatively
392 // account for that much possible delay
393 // in the query so as to avoid concurrent mode failures
394 // due to starting the collection just a wee bit too
395 // late.
396 double work = cms_duration() + gc0_period();
397 double deadline = time_until_cms_gen_full();
398 if (work > deadline) {
399 if (Verbose && PrintGCDetails) {
400 gclog_or_tty->print(
401 " CMSCollector: collect because of anticipated promotion "
402 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
403 gc0_period(), time_until_cms_gen_full());
404 }
405 return 0.0;
406 }
407 return work - deadline;
408 }
409
410 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
411 // amount of change to prevent wild oscillation.
412 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
413 unsigned int new_duty_cycle) {
414 assert(old_duty_cycle <= 100, "bad input value");
415 assert(new_duty_cycle <= 100, "bad input value");
416
417 // Note: use subtraction with caution since it may underflow (values are
418 // unsigned). Addition is safe since we're in the range 0-100.
419 unsigned int damped_duty_cycle = new_duty_cycle;
420 if (new_duty_cycle < old_duty_cycle) {
421 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
422 if (new_duty_cycle + largest_delta < old_duty_cycle) {
423 damped_duty_cycle = old_duty_cycle - largest_delta;
424 }
425 } else if (new_duty_cycle > old_duty_cycle) {
426 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
427 if (new_duty_cycle > old_duty_cycle + largest_delta) {
428 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
429 }
430 }
431 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
432
433 if (CMSTraceIncrementalPacing) {
434 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
435 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
436 }
437 return damped_duty_cycle;
438 }
439
440 unsigned int CMSStats::icms_update_duty_cycle_impl() {
441 assert(CMSIncrementalPacing && valid(),
442 "should be handled in icms_update_duty_cycle()");
443
444 double cms_time_so_far = cms_timer().seconds();
445 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
446 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
447
448 // Avoid division by 0.
449 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
450 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
451
452 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
453 if (new_duty_cycle > _icms_duty_cycle) {
454 // Avoid very small duty cycles (1 or 2); 0 is allowed.
455 if (new_duty_cycle > 2) {
456 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
457 new_duty_cycle);
458 }
459 } else if (_allow_duty_cycle_reduction) {
460 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
461 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
462 // Respect the minimum duty cycle.
463 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
464 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
465 }
466
467 if (PrintGCDetails || CMSTraceIncrementalPacing) {
468 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
469 }
470
471 _allow_duty_cycle_reduction = false;
472 return _icms_duty_cycle;
473 }
474
475 #ifndef PRODUCT
476 void CMSStats::print_on(outputStream *st) const {
477 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
478 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
479 gc0_duration(), gc0_period(), gc0_promoted());
480 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
481 cms_duration(), cms_duration_per_mb(),
482 cms_period(), cms_allocated());
483 st->print(",cms_since_beg=%g,cms_since_end=%g",
484 cms_time_since_begin(), cms_time_since_end());
485 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
486 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
487 if (CMSIncrementalMode) {
488 st->print(",dc=%d", icms_duty_cycle());
489 }
490
491 if (valid()) {
492 st->print(",promo_rate=%g,cms_alloc_rate=%g",
493 promotion_rate(), cms_allocation_rate());
494 st->print(",cms_consumption_rate=%g,time_until_full=%g",
495 cms_consumption_rate(), time_until_cms_gen_full());
496 }
497 st->print(" ");
498 }
499 #endif // #ifndef PRODUCT
500
501 CMSCollector::CollectorState CMSCollector::_collectorState =
502 CMSCollector::Idling;
503 bool CMSCollector::_foregroundGCIsActive = false;
504 bool CMSCollector::_foregroundGCShouldWait = false;
505
506 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
507 ConcurrentMarkSweepGeneration* permGen,
508 CardTableRS* ct,
509 ConcurrentMarkSweepPolicy* cp):
510 _cmsGen(cmsGen),
511 _permGen(permGen),
512 _ct(ct),
513 _ref_processor(NULL), // will be set later
514 _conc_workers(NULL), // may be set later
515 _abort_preclean(false),
516 _start_sampling(false),
517 _between_prologue_and_epilogue(false),
518 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
519 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
520 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
521 -1 /* lock-free */, "No_lock" /* dummy */),
522 _modUnionClosure(&_modUnionTable),
523 _modUnionClosurePar(&_modUnionTable),
524 // Adjust my span to cover old (cms) gen and perm gen
525 _span(cmsGen->reserved()._union(permGen->reserved())),
526 // Construct the is_alive_closure with _span & markBitMap
527 _is_alive_closure(_span, &_markBitMap),
528 _restart_addr(NULL),
529 _overflow_list(NULL),
530 _preserved_oop_stack(NULL),
531 _preserved_mark_stack(NULL),
532 _stats(cmsGen),
533 _eden_chunk_array(NULL), // may be set in ctor body
534 _eden_chunk_capacity(0), // -- ditto --
535 _eden_chunk_index(0), // -- ditto --
536 _survivor_plab_array(NULL), // -- ditto --
537 _survivor_chunk_array(NULL), // -- ditto --
538 _survivor_chunk_capacity(0), // -- ditto --
539 _survivor_chunk_index(0), // -- ditto --
540 _ser_pmc_preclean_ovflw(0),
541 _ser_pmc_remark_ovflw(0),
542 _par_pmc_remark_ovflw(0),
543 _ser_kac_ovflw(0),
544 _par_kac_ovflw(0),
545 #ifndef PRODUCT
546 _num_par_pushes(0),
547 #endif
548 _collection_count_start(0),
549 _verifying(false),
550 _icms_start_limit(NULL),
551 _icms_stop_limit(NULL),
552 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
553 _completed_initialization(false),
554 _collector_policy(cp),
555 _should_unload_classes(false),
556 _concurrent_cycles_since_last_unload(0),
557 _sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
558 {
559 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
560 ExplicitGCInvokesConcurrent = true;
561 }
562 // Now expand the span and allocate the collection support structures
563 // (MUT, marking bit map etc.) to cover both generations subject to
564 // collection.
565
566 // First check that _permGen is adjacent to _cmsGen and above it.
567 assert( _cmsGen->reserved().word_size() > 0
568 && _permGen->reserved().word_size() > 0,
569 "generations should not be of zero size");
570 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
571 "_cmsGen and _permGen should not overlap");
572 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
573 "_cmsGen->end() different from _permGen->start()");
574
575 // For use by dirty card to oop closures.
576 _cmsGen->cmsSpace()->set_collector(this);
577 _permGen->cmsSpace()->set_collector(this);
578
579 // Allocate MUT and marking bit map
580 {
581 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
582 if (!_markBitMap.allocate(_span)) {
583 warning("Failed to allocate CMS Bit Map");
584 return;
585 }
586 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
587 }
588 {
589 _modUnionTable.allocate(_span);
590 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
591 }
592
593 if (!_markStack.allocate(CMSMarkStackSize)) {
594 warning("Failed to allocate CMS Marking Stack");
595 return;
596 }
597 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
598 warning("Failed to allocate CMS Revisit Stack");
599 return;
600 }
601
602 // Support for multi-threaded concurrent phases
603 if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) {
604 if (FLAG_IS_DEFAULT(ParallelCMSThreads)) {
605 // just for now
606 FLAG_SET_DEFAULT(ParallelCMSThreads, (ParallelGCThreads + 3)/4);
607 }
608 if (ParallelCMSThreads > 1) {
609 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
610 ParallelCMSThreads, true);
611 if (_conc_workers == NULL) {
612 warning("GC/CMS: _conc_workers allocation failure: "
613 "forcing -CMSConcurrentMTEnabled");
614 CMSConcurrentMTEnabled = false;
615 }
616 } else {
617 CMSConcurrentMTEnabled = false;
618 }
619 }
620 if (!CMSConcurrentMTEnabled) {
621 ParallelCMSThreads = 0;
622 } else {
623 // Turn off CMSCleanOnEnter optimization temporarily for
624 // the MT case where it's not fixed yet; see 6178663.
625 CMSCleanOnEnter = false;
626 }
627 assert((_conc_workers != NULL) == (ParallelCMSThreads > 1),
628 "Inconsistency");
629
630 // Parallel task queues; these are shared for the
631 // concurrent and stop-world phases of CMS, but
632 // are not shared with parallel scavenge (ParNew).
633 {
634 uint i;
635 uint num_queues = (uint) MAX2(ParallelGCThreads, ParallelCMSThreads);
636
637 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
638 || ParallelRefProcEnabled)
639 && num_queues > 0) {
640 _task_queues = new OopTaskQueueSet(num_queues);
641 if (_task_queues == NULL) {
642 warning("task_queues allocation failure.");
643 return;
644 }
645 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
646 if (_hash_seed == NULL) {
647 warning("_hash_seed array allocation failure");
648 return;
649 }
650
651 // XXX use a global constant instead of 64!
652 typedef struct OopTaskQueuePadded {
653 OopTaskQueue work_queue;
654 char pad[64 - sizeof(OopTaskQueue)]; // prevent false sharing
655 } OopTaskQueuePadded;
656
657 for (i = 0; i < num_queues; i++) {
658 OopTaskQueuePadded *q_padded = new OopTaskQueuePadded();
659 if (q_padded == NULL) {
660 warning("work_queue allocation failure.");
661 return;
662 }
663 _task_queues->register_queue(i, &q_padded->work_queue);
664 }
665 for (i = 0; i < num_queues; i++) {
666 _task_queues->queue(i)->initialize();
667 _hash_seed[i] = 17; // copied from ParNew
668 }
669 }
670 }
671
672 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
673 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
674
675 // Clip CMSBootstrapOccupancy between 0 and 100.
676 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
677 /(double)100;
678
679 _full_gcs_since_conc_gc = 0;
680
681 // Now tell CMS generations the identity of their collector
682 ConcurrentMarkSweepGeneration::set_collector(this);
683
684 // Create & start a CMS thread for this CMS collector
685 _cmsThread = ConcurrentMarkSweepThread::start(this);
686 assert(cmsThread() != NULL, "CMS Thread should have been created");
687 assert(cmsThread()->collector() == this,
688 "CMS Thread should refer to this gen");
689 assert(CGC_lock != NULL, "Where's the CGC_lock?");
690
691 // Support for parallelizing young gen rescan
692 GenCollectedHeap* gch = GenCollectedHeap::heap();
693 _young_gen = gch->prev_gen(_cmsGen);
694 if (gch->supports_inline_contig_alloc()) {
695 _top_addr = gch->top_addr();
696 _end_addr = gch->end_addr();
697 assert(_young_gen != NULL, "no _young_gen");
698 _eden_chunk_index = 0;
699 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
700 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
701 if (_eden_chunk_array == NULL) {
702 _eden_chunk_capacity = 0;
703 warning("GC/CMS: _eden_chunk_array allocation failure");
704 }
705 }
706 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
707
708 // Support for parallelizing survivor space rescan
709 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
710 size_t max_plab_samples = MaxNewSize/((SurvivorRatio+2)*MinTLABSize);
711 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
712 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
713 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
714 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
715 || _cursor == NULL) {
716 warning("Failed to allocate survivor plab/chunk array");
717 if (_survivor_plab_array != NULL) {
718 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
719 _survivor_plab_array = NULL;
720 }
721 if (_survivor_chunk_array != NULL) {
722 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
723 _survivor_chunk_array = NULL;
724 }
725 if (_cursor != NULL) {
726 FREE_C_HEAP_ARRAY(size_t, _cursor);
727 _cursor = NULL;
728 }
729 } else {
730 _survivor_chunk_capacity = 2*max_plab_samples;
731 for (uint i = 0; i < ParallelGCThreads; i++) {
732 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
733 if (vec == NULL) {
734 warning("Failed to allocate survivor plab array");
735 for (int j = i; j > 0; j--) {
736 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
737 }
738 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
739 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
740 _survivor_plab_array = NULL;
741 _survivor_chunk_array = NULL;
742 _survivor_chunk_capacity = 0;
743 break;
744 } else {
745 ChunkArray* cur =
746 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
747 max_plab_samples);
748 assert(cur->end() == 0, "Should be 0");
749 assert(cur->array() == vec, "Should be vec");
750 assert(cur->capacity() == max_plab_samples, "Error");
751 }
752 }
753 }
754 }
755 assert( ( _survivor_plab_array != NULL
756 && _survivor_chunk_array != NULL)
757 || ( _survivor_chunk_capacity == 0
758 && _survivor_chunk_index == 0),
759 "Error");
760
761 // Choose what strong roots should be scanned depending on verification options
762 // and perm gen collection mode.
763 if (!CMSClassUnloadingEnabled) {
764 // If class unloading is disabled we want to include all classes into the root set.
765 add_root_scanning_option(SharedHeap::SO_AllClasses);
766 } else {
767 add_root_scanning_option(SharedHeap::SO_SystemClasses);
768 }
769
770 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
771 _gc_counters = new CollectorCounters("CMS", 1);
772 _completed_initialization = true;
773 _sweep_timer.start(); // start of time
774 }
775
776 const char* ConcurrentMarkSweepGeneration::name() const {
777 return "concurrent mark-sweep generation";
778 }
779 void ConcurrentMarkSweepGeneration::update_counters() {
780 if (UsePerfData) {
781 _space_counters->update_all();
782 _gen_counters->update_all();
783 }
784 }
785
786 // this is an optimized version of update_counters(). it takes the
787 // used value as a parameter rather than computing it.
788 //
789 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
790 if (UsePerfData) {
791 _space_counters->update_used(used);
792 _space_counters->update_capacity();
793 _gen_counters->update_all();
794 }
795 }
796
797 void ConcurrentMarkSweepGeneration::print() const {
798 Generation::print();
799 cmsSpace()->print();
800 }
801
802 #ifndef PRODUCT
803 void ConcurrentMarkSweepGeneration::print_statistics() {
804 cmsSpace()->printFLCensus(0);
805 }
806 #endif
807
808 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
809 GenCollectedHeap* gch = GenCollectedHeap::heap();
810 if (PrintGCDetails) {
811 if (Verbose) {
812 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
813 level(), short_name(), s, used(), capacity());
814 } else {
815 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
816 level(), short_name(), s, used() / K, capacity() / K);
817 }
818 }
819 if (Verbose) {
820 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
821 gch->used(), gch->capacity());
822 } else {
823 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
824 gch->used() / K, gch->capacity() / K);
825 }
826 }
827
828 size_t
829 ConcurrentMarkSweepGeneration::contiguous_available() const {
830 // dld proposes an improvement in precision here. If the committed
831 // part of the space ends in a free block we should add that to
832 // uncommitted size in the calculation below. Will make this
833 // change later, staying with the approximation below for the
834 // time being. -- ysr.
835 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
836 }
837
838 size_t
839 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
840 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
841 }
842
843 size_t ConcurrentMarkSweepGeneration::max_available() const {
844 return free() + _virtual_space.uncommitted_size();
845 }
846
847 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(
848 size_t max_promotion_in_bytes,
849 bool younger_handles_promotion_failure) const {
850
851 // This is the most conservative test. Full promotion is
852 // guaranteed if this is used. The multiplicative factor is to
853 // account for the worst case "dilatation".
854 double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes;
855 if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t
856 adjusted_max_promo_bytes = (double)max_uintx;
857 }
858 bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes);
859
860 if (younger_handles_promotion_failure && !result) {
861 // Full promotion is not guaranteed because fragmentation
862 // of the cms generation can prevent the full promotion.
863 result = (max_available() >= (size_t)adjusted_max_promo_bytes);
864
865 if (!result) {
866 // With promotion failure handling the test for the ability
867 // to support the promotion does not have to be guaranteed.
868 // Use an average of the amount promoted.
869 result = max_available() >= (size_t)
870 gc_stats()->avg_promoted()->padded_average();
871 if (PrintGC && Verbose && result) {
872 gclog_or_tty->print_cr(
873 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
874 " max_available: " SIZE_FORMAT
875 " avg_promoted: " SIZE_FORMAT,
876 max_available(), (size_t)
877 gc_stats()->avg_promoted()->padded_average());
878 }
879 } else {
880 if (PrintGC && Verbose) {
881 gclog_or_tty->print_cr(
882 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
883 " max_available: " SIZE_FORMAT
884 " adj_max_promo_bytes: " SIZE_FORMAT,
885 max_available(), (size_t)adjusted_max_promo_bytes);
886 }
887 }
888 } else {
889 if (PrintGC && Verbose) {
890 gclog_or_tty->print_cr(
891 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
892 " contiguous_available: " SIZE_FORMAT
893 " adj_max_promo_bytes: " SIZE_FORMAT,
894 max_contiguous_available(), (size_t)adjusted_max_promo_bytes);
895 }
896 }
897 return result;
898 }
899
900 CompactibleSpace*
901 ConcurrentMarkSweepGeneration::first_compaction_space() const {
902 return _cmsSpace;
903 }
904
905 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
906 // Clear the promotion information. These pointers can be adjusted
907 // along with all the other pointers into the heap but
908 // compaction is expected to be a rare event with
909 // a heap using cms so don't do it without seeing the need.
910 if (ParallelGCThreads > 0) {
911 for (uint i = 0; i < ParallelGCThreads; i++) {
912 _par_gc_thread_states[i]->promo.reset();
913 }
914 }
915 }
916
917 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
918 blk->do_space(_cmsSpace);
919 }
920
921 void ConcurrentMarkSweepGeneration::compute_new_size() {
922 assert_locked_or_safepoint(Heap_lock);
923
924 // If incremental collection failed, we just want to expand
925 // to the limit.
926 if (incremental_collection_failed()) {
927 clear_incremental_collection_failed();
928 grow_to_reserved();
929 return;
930 }
931
932 size_t expand_bytes = 0;
933 double free_percentage = ((double) free()) / capacity();
934 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
935 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
936
937 // compute expansion delta needed for reaching desired free percentage
938 if (free_percentage < desired_free_percentage) {
939 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
940 assert(desired_capacity >= capacity(), "invalid expansion size");
941 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
942 }
943 if (expand_bytes > 0) {
944 if (PrintGCDetails && Verbose) {
945 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
946 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
947 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
948 gclog_or_tty->print_cr(" Desired free fraction %f",
949 desired_free_percentage);
950 gclog_or_tty->print_cr(" Maximum free fraction %f",
951 maximum_free_percentage);
952 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
953 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
954 desired_capacity/1000);
955 int prev_level = level() - 1;
956 if (prev_level >= 0) {
957 size_t prev_size = 0;
958 GenCollectedHeap* gch = GenCollectedHeap::heap();
959 Generation* prev_gen = gch->_gens[prev_level];
960 prev_size = prev_gen->capacity();
961 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
962 prev_size/1000);
963 }
964 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
965 unsafe_max_alloc_nogc()/1000);
966 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
967 contiguous_available()/1000);
968 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
969 expand_bytes);
970 }
971 // safe if expansion fails
972 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
973 if (PrintGCDetails && Verbose) {
974 gclog_or_tty->print_cr(" Expanded free fraction %f",
975 ((double) free()) / capacity());
976 }
977 }
978 }
979
980 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
981 return cmsSpace()->freelistLock();
982 }
983
984 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
985 bool tlab) {
986 CMSSynchronousYieldRequest yr;
987 MutexLockerEx x(freelistLock(),
988 Mutex::_no_safepoint_check_flag);
989 return have_lock_and_allocate(size, tlab);
990 }
991
992 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
993 bool tlab) {
994 assert_lock_strong(freelistLock());
995 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
996 HeapWord* res = cmsSpace()->allocate(adjustedSize);
997 // Allocate the object live (grey) if the background collector has
998 // started marking. This is necessary because the marker may
999 // have passed this address and consequently this object will
1000 // not otherwise be greyed and would be incorrectly swept up.
1001 // Note that if this object contains references, the writing
1002 // of those references will dirty the card containing this object
1003 // allowing the object to be blackened (and its references scanned)
1004 // either during a preclean phase or at the final checkpoint.
1005 if (res != NULL) {
1006 collector()->direct_allocated(res, adjustedSize);
1007 _direct_allocated_words += adjustedSize;
1008 // allocation counters
1009 NOT_PRODUCT(
1010 _numObjectsAllocated++;
1011 _numWordsAllocated += (int)adjustedSize;
1012 )
1013 }
1014 return res;
1015 }
1016
1017 // In the case of direct allocation by mutators in a generation that
1018 // is being concurrently collected, the object must be allocated
1019 // live (grey) if the background collector has started marking.
1020 // This is necessary because the marker may
1021 // have passed this address and consequently this object will
1022 // not otherwise be greyed and would be incorrectly swept up.
1023 // Note that if this object contains references, the writing
1024 // of those references will dirty the card containing this object
1025 // allowing the object to be blackened (and its references scanned)
1026 // either during a preclean phase or at the final checkpoint.
1027 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1028 assert(_markBitMap.covers(start, size), "Out of bounds");
1029 if (_collectorState >= Marking) {
1030 MutexLockerEx y(_markBitMap.lock(),
1031 Mutex::_no_safepoint_check_flag);
1032 // [see comments preceding SweepClosure::do_blk() below for details]
1033 // 1. need to mark the object as live so it isn't collected
1034 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1035 // 3. need to mark the end of the object so sweeper can skip over it
1036 // if it's uninitialized when the sweeper reaches it.
1037 _markBitMap.mark(start); // object is live
1038 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1039 _markBitMap.mark(start + size - 1);
1040 // mark end of object
1041 }
1042 // check that oop looks uninitialized
1043 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1044 }
1045
1046 void CMSCollector::promoted(bool par, HeapWord* start,
1047 bool is_obj_array, size_t obj_size) {
1048 assert(_markBitMap.covers(start), "Out of bounds");
1049 // See comment in direct_allocated() about when objects should
1050 // be allocated live.
1051 if (_collectorState >= Marking) {
1052 // we already hold the marking bit map lock, taken in
1053 // the prologue
1054 if (par) {
1055 _markBitMap.par_mark(start);
1056 } else {
1057 _markBitMap.mark(start);
1058 }
1059 // We don't need to mark the object as uninitialized (as
1060 // in direct_allocated above) because this is being done with the
1061 // world stopped and the object will be initialized by the
1062 // time the sweeper gets to look at it.
1063 assert(SafepointSynchronize::is_at_safepoint(),
1064 "expect promotion only at safepoints");
1065
1066 if (_collectorState < Sweeping) {
1067 // Mark the appropriate cards in the modUnionTable, so that
1068 // this object gets scanned before the sweep. If this is
1069 // not done, CMS generation references in the object might
1070 // not get marked.
1071 // For the case of arrays, which are otherwise precisely
1072 // marked, we need to dirty the entire array, not just its head.
1073 if (is_obj_array) {
1074 // The [par_]mark_range() method expects mr.end() below to
1075 // be aligned to the granularity of a bit's representation
1076 // in the heap. In the case of the MUT below, that's a
1077 // card size.
1078 MemRegion mr(start,
1079 (HeapWord*)round_to((intptr_t)(start + obj_size),
1080 CardTableModRefBS::card_size /* bytes */));
1081 if (par) {
1082 _modUnionTable.par_mark_range(mr);
1083 } else {
1084 _modUnionTable.mark_range(mr);
1085 }
1086 } else { // not an obj array; we can just mark the head
1087 if (par) {
1088 _modUnionTable.par_mark(start);
1089 } else {
1090 _modUnionTable.mark(start);
1091 }
1092 }
1093 }
1094 }
1095 }
1096
1097 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1098 {
1099 size_t delta = pointer_delta(addr, space->bottom());
1100 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1101 }
1102
1103 void CMSCollector::icms_update_allocation_limits()
1104 {
1105 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1106 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1107
1108 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1109 if (CMSTraceIncrementalPacing) {
1110 stats().print();
1111 }
1112
1113 assert(duty_cycle <= 100, "invalid duty cycle");
1114 if (duty_cycle != 0) {
1115 // The duty_cycle is a percentage between 0 and 100; convert to words and
1116 // then compute the offset from the endpoints of the space.
1117 size_t free_words = eden->free() / HeapWordSize;
1118 double free_words_dbl = (double)free_words;
1119 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1120 size_t offset_words = (free_words - duty_cycle_words) / 2;
1121
1122 _icms_start_limit = eden->top() + offset_words;
1123 _icms_stop_limit = eden->end() - offset_words;
1124
1125 // The limits may be adjusted (shifted to the right) by
1126 // CMSIncrementalOffset, to allow the application more mutator time after a
1127 // young gen gc (when all mutators were stopped) and before CMS starts and
1128 // takes away one or more cpus.
1129 if (CMSIncrementalOffset != 0) {
1130 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1131 size_t adjustment = (size_t)adjustment_dbl;
1132 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1133 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1134 _icms_start_limit += adjustment;
1135 _icms_stop_limit = tmp_stop;
1136 }
1137 }
1138 }
1139 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1140 _icms_start_limit = _icms_stop_limit = eden->end();
1141 }
1142
1143 // Install the new start limit.
1144 eden->set_soft_end(_icms_start_limit);
1145
1146 if (CMSTraceIncrementalMode) {
1147 gclog_or_tty->print(" icms alloc limits: "
1148 PTR_FORMAT "," PTR_FORMAT
1149 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1150 _icms_start_limit, _icms_stop_limit,
1151 percent_of_space(eden, _icms_start_limit),
1152 percent_of_space(eden, _icms_stop_limit));
1153 if (Verbose) {
1154 gclog_or_tty->print("eden: ");
1155 eden->print_on(gclog_or_tty);
1156 }
1157 }
1158 }
1159
1160 // Any changes here should try to maintain the invariant
1161 // that if this method is called with _icms_start_limit
1162 // and _icms_stop_limit both NULL, then it should return NULL
1163 // and not notify the icms thread.
1164 HeapWord*
1165 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1166 size_t word_size)
1167 {
1168 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1169 // nop.
1170 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1171 if (top <= _icms_start_limit) {
1172 if (CMSTraceIncrementalMode) {
1173 space->print_on(gclog_or_tty);
1174 gclog_or_tty->stamp();
1175 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1176 ", new limit=" PTR_FORMAT
1177 " (" SIZE_FORMAT "%%)",
1178 top, _icms_stop_limit,
1179 percent_of_space(space, _icms_stop_limit));
1180 }
1181 ConcurrentMarkSweepThread::start_icms();
1182 assert(top < _icms_stop_limit, "Tautology");
1183 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1184 return _icms_stop_limit;
1185 }
1186
1187 // The allocation will cross both the _start and _stop limits, so do the
1188 // stop notification also and return end().
1189 if (CMSTraceIncrementalMode) {
1190 space->print_on(gclog_or_tty);
1191 gclog_or_tty->stamp();
1192 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1193 ", new limit=" PTR_FORMAT
1194 " (" SIZE_FORMAT "%%)",
1195 top, space->end(),
1196 percent_of_space(space, space->end()));
1197 }
1198 ConcurrentMarkSweepThread::stop_icms();
1199 return space->end();
1200 }
1201
1202 if (top <= _icms_stop_limit) {
1203 if (CMSTraceIncrementalMode) {
1204 space->print_on(gclog_or_tty);
1205 gclog_or_tty->stamp();
1206 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1207 ", new limit=" PTR_FORMAT
1208 " (" SIZE_FORMAT "%%)",
1209 top, space->end(),
1210 percent_of_space(space, space->end()));
1211 }
1212 ConcurrentMarkSweepThread::stop_icms();
1213 return space->end();
1214 }
1215
1216 if (CMSTraceIncrementalMode) {
1217 space->print_on(gclog_or_tty);
1218 gclog_or_tty->stamp();
1219 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1220 ", new limit=" PTR_FORMAT,
1221 top, NULL);
1222 }
1223 }
1224
1225 return NULL;
1226 }
1227
1228 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1229 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1230 // allocate, copy and if necessary update promoinfo --
1231 // delegate to underlying space.
1232 assert_lock_strong(freelistLock());
1233
1234 #ifndef PRODUCT
1235 if (Universe::heap()->promotion_should_fail()) {
1236 return NULL;
1237 }
1238 #endif // #ifndef PRODUCT
1239
1240 oop res = _cmsSpace->promote(obj, obj_size);
1241 if (res == NULL) {
1242 // expand and retry
1243 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1244 expand(s*HeapWordSize, MinHeapDeltaBytes,
1245 CMSExpansionCause::_satisfy_promotion);
1246 // Since there's currently no next generation, we don't try to promote
1247 // into a more senior generation.
1248 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1249 "is made to pass on a possibly failing "
1250 "promotion to next generation");
1251 res = _cmsSpace->promote(obj, obj_size);
1252 }
1253 if (res != NULL) {
1254 // See comment in allocate() about when objects should
1255 // be allocated live.
1256 assert(obj->is_oop(), "Will dereference klass pointer below");
1257 collector()->promoted(false, // Not parallel
1258 (HeapWord*)res, obj->is_objArray(), obj_size);
1259 // promotion counters
1260 NOT_PRODUCT(
1261 _numObjectsPromoted++;
1262 _numWordsPromoted +=
1263 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1264 )
1265 }
1266 return res;
1267 }
1268
1269
1270 HeapWord*
1271 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1272 HeapWord* top,
1273 size_t word_sz)
1274 {
1275 return collector()->allocation_limit_reached(space, top, word_sz);
1276 }
1277
1278 // Things to support parallel young-gen collection.
1279 oop
1280 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1281 oop old, markOop m,
1282 size_t word_sz) {
1283 #ifndef PRODUCT
1284 if (Universe::heap()->promotion_should_fail()) {
1285 return NULL;
1286 }
1287 #endif // #ifndef PRODUCT
1288
1289 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1290 PromotionInfo* promoInfo = &ps->promo;
1291 // if we are tracking promotions, then first ensure space for
1292 // promotion (including spooling space for saving header if necessary).
1293 // then allocate and copy, then track promoted info if needed.
1294 // When tracking (see PromotionInfo::track()), the mark word may
1295 // be displaced and in this case restoration of the mark word
1296 // occurs in the (oop_since_save_marks_)iterate phase.
1297 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1298 // Out of space for allocating spooling buffers;
1299 // try expanding and allocating spooling buffers.
1300 if (!expand_and_ensure_spooling_space(promoInfo)) {
1301 return NULL;
1302 }
1303 }
1304 assert(promoInfo->has_spooling_space(), "Control point invariant");
1305 HeapWord* obj_ptr = ps->lab.alloc(word_sz);
1306 if (obj_ptr == NULL) {
1307 obj_ptr = expand_and_par_lab_allocate(ps, word_sz);
1308 if (obj_ptr == NULL) {
1309 return NULL;
1310 }
1311 }
1312 oop obj = oop(obj_ptr);
1313 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1314 // Otherwise, copy the object. Here we must be careful to insert the
1315 // klass pointer last, since this marks the block as an allocated object.
1316 // Except with compressed oops it's the mark word.
1317 HeapWord* old_ptr = (HeapWord*)old;
1318 if (word_sz > (size_t)oopDesc::header_size()) {
1319 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1320 obj_ptr + oopDesc::header_size(),
1321 word_sz - oopDesc::header_size());
1322 }
1323
1324 if (UseCompressedOops) {
1325 // Copy gap missed by (aligned) header size calculation above
1326 obj->set_klass_gap(old->klass_gap());
1327 }
1328
1329 // Restore the mark word copied above.
1330 obj->set_mark(m);
1331
1332 // Now we can track the promoted object, if necessary. We take care
1333 // To delay the transition from uninitialized to full object
1334 // (i.e., insertion of klass pointer) until after, so that it
1335 // atomically becomes a promoted object.
1336 if (promoInfo->tracking()) {
1337 promoInfo->track((PromotedObject*)obj, old->klass());
1338 }
1339
1340 // Finally, install the klass pointer (this should be volatile).
1341 obj->set_klass(old->klass());
1342
1343 assert(old->is_oop(), "Will dereference klass ptr below");
1344 collector()->promoted(true, // parallel
1345 obj_ptr, old->is_objArray(), word_sz);
1346
1347 NOT_PRODUCT(
1348 Atomic::inc(&_numObjectsPromoted);
1349 Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()),
1350 &_numWordsPromoted);
1351 )
1352
1353 return obj;
1354 }
1355
1356 void
1357 ConcurrentMarkSweepGeneration::
1358 par_promote_alloc_undo(int thread_num,
1359 HeapWord* obj, size_t word_sz) {
1360 // CMS does not support promotion undo.
1361 ShouldNotReachHere();
1362 }
1363
1364 void
1365 ConcurrentMarkSweepGeneration::
1366 par_promote_alloc_done(int thread_num) {
1367 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1368 ps->lab.retire();
1369 #if CFLS_LAB_REFILL_STATS
1370 if (thread_num == 0) {
1371 _cmsSpace->print_par_alloc_stats();
1372 }
1373 #endif
1374 }
1375
1376 void
1377 ConcurrentMarkSweepGeneration::
1378 par_oop_since_save_marks_iterate_done(int thread_num) {
1379 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1380 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1381 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1382 }
1383
1384 // XXXPERM
1385 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1386 size_t size,
1387 bool tlab)
1388 {
1389 // We allow a STW collection only if a full
1390 // collection was requested.
1391 return full || should_allocate(size, tlab); // FIX ME !!!
1392 // This and promotion failure handling are connected at the
1393 // hip and should be fixed by untying them.
1394 }
1395
1396 bool CMSCollector::shouldConcurrentCollect() {
1397 if (_full_gc_requested) {
1398 assert(ExplicitGCInvokesConcurrent, "Unexpected state");
1399 if (Verbose && PrintGCDetails) {
1400 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1401 " gc request");
1402 }
1403 return true;
1404 }
1405
1406 // For debugging purposes, change the type of collection.
1407 // If the rotation is not on the concurrent collection
1408 // type, don't start a concurrent collection.
1409 NOT_PRODUCT(
1410 if (RotateCMSCollectionTypes &&
1411 (_cmsGen->debug_collection_type() !=
1412 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1413 assert(_cmsGen->debug_collection_type() !=
1414 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1415 "Bad cms collection type");
1416 return false;
1417 }
1418 )
1419
1420 FreelistLocker x(this);
1421 // ------------------------------------------------------------------
1422 // Print out lots of information which affects the initiation of
1423 // a collection.
1424 if (PrintCMSInitiationStatistics && stats().valid()) {
1425 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1426 gclog_or_tty->stamp();
1427 gclog_or_tty->print_cr("");
1428 stats().print_on(gclog_or_tty);
1429 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1430 stats().time_until_cms_gen_full());
1431 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1432 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1433 _cmsGen->contiguous_available());
1434 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1435 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1436 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1437 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1438 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1439 }
1440 // ------------------------------------------------------------------
1441
1442 // If the estimated time to complete a cms collection (cms_duration())
1443 // is less than the estimated time remaining until the cms generation
1444 // is full, start a collection.
1445 if (!UseCMSInitiatingOccupancyOnly) {
1446 if (stats().valid()) {
1447 if (stats().time_until_cms_start() == 0.0) {
1448 return true;
1449 }
1450 } else {
1451 // We want to conservatively collect somewhat early in order
1452 // to try and "bootstrap" our CMS/promotion statistics;
1453 // this branch will not fire after the first successful CMS
1454 // collection because the stats should then be valid.
1455 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1456 if (Verbose && PrintGCDetails) {
1457 gclog_or_tty->print_cr(
1458 " CMSCollector: collect for bootstrapping statistics:"
1459 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1460 _bootstrap_occupancy);
1461 }
1462 return true;
1463 }
1464 }
1465 }
1466
1467 // Otherwise, we start a collection cycle if either the perm gen or
1468 // old gen want a collection cycle started. Each may use
1469 // an appropriate criterion for making this decision.
1470 // XXX We need to make sure that the gen expansion
1471 // criterion dovetails well with this. XXX NEED TO FIX THIS
1472 if (_cmsGen->should_concurrent_collect()) {
1473 if (Verbose && PrintGCDetails) {
1474 gclog_or_tty->print_cr("CMS old gen initiated");
1475 }
1476 return true;
1477 }
1478
1479 // We start a collection if we believe an incremental collection may fail;
1480 // this is not likely to be productive in practice because it's probably too
1481 // late anyway.
1482 GenCollectedHeap* gch = GenCollectedHeap::heap();
1483 assert(gch->collector_policy()->is_two_generation_policy(),
1484 "You may want to check the correctness of the following");
1485 if (gch->incremental_collection_will_fail()) {
1486 if (PrintGCDetails && Verbose) {
1487 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1488 }
1489 return true;
1490 }
1491
1492 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1493 bool res = update_should_unload_classes();
1494 if (res) {
1495 if (Verbose && PrintGCDetails) {
1496 gclog_or_tty->print_cr("CMS perm gen initiated");
1497 }
1498 return true;
1499 }
1500 }
1501 return false;
1502 }
1503
1504 // Clear _expansion_cause fields of constituent generations
1505 void CMSCollector::clear_expansion_cause() {
1506 _cmsGen->clear_expansion_cause();
1507 _permGen->clear_expansion_cause();
1508 }
1509
1510 // We should be conservative in starting a collection cycle. To
1511 // start too eagerly runs the risk of collecting too often in the
1512 // extreme. To collect too rarely falls back on full collections,
1513 // which works, even if not optimum in terms of concurrent work.
1514 // As a work around for too eagerly collecting, use the flag
1515 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1516 // giving the user an easily understandable way of controlling the
1517 // collections.
1518 // We want to start a new collection cycle if any of the following
1519 // conditions hold:
1520 // . our current occupancy exceeds the configured initiating occupancy
1521 // for this generation, or
1522 // . we recently needed to expand this space and have not, since that
1523 // expansion, done a collection of this generation, or
1524 // . the underlying space believes that it may be a good idea to initiate
1525 // a concurrent collection (this may be based on criteria such as the
1526 // following: the space uses linear allocation and linear allocation is
1527 // going to fail, or there is believed to be excessive fragmentation in
1528 // the generation, etc... or ...
1529 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1530 // the case of the old generation, not the perm generation; see CR 6543076):
1531 // we may be approaching a point at which allocation requests may fail because
1532 // we will be out of sufficient free space given allocation rate estimates.]
1533 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1534
1535 assert_lock_strong(freelistLock());
1536 if (occupancy() > initiating_occupancy()) {
1537 if (PrintGCDetails && Verbose) {
1538 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1539 short_name(), occupancy(), initiating_occupancy());
1540 }
1541 return true;
1542 }
1543 if (UseCMSInitiatingOccupancyOnly) {
1544 return false;
1545 }
1546 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1547 if (PrintGCDetails && Verbose) {
1548 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1549 short_name());
1550 }
1551 return true;
1552 }
1553 if (_cmsSpace->should_concurrent_collect()) {
1554 if (PrintGCDetails && Verbose) {
1555 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1556 short_name());
1557 }
1558 return true;
1559 }
1560 return false;
1561 }
1562
1563 void ConcurrentMarkSweepGeneration::collect(bool full,
1564 bool clear_all_soft_refs,
1565 size_t size,
1566 bool tlab)
1567 {
1568 collector()->collect(full, clear_all_soft_refs, size, tlab);
1569 }
1570
1571 void CMSCollector::collect(bool full,
1572 bool clear_all_soft_refs,
1573 size_t size,
1574 bool tlab)
1575 {
1576 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1577 // For debugging purposes skip the collection if the state
1578 // is not currently idle
1579 if (TraceCMSState) {
1580 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1581 Thread::current(), full, _collectorState);
1582 }
1583 return;
1584 }
1585
1586 // The following "if" branch is present for defensive reasons.
1587 // In the current uses of this interface, it can be replaced with:
1588 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1589 // But I am not placing that assert here to allow future
1590 // generality in invoking this interface.
1591 if (GC_locker::is_active()) {
1592 // A consistency test for GC_locker
1593 assert(GC_locker::needs_gc(), "Should have been set already");
1594 // Skip this foreground collection, instead
1595 // expanding the heap if necessary.
1596 // Need the free list locks for the call to free() in compute_new_size()
1597 compute_new_size();
1598 return;
1599 }
1600 acquire_control_and_collect(full, clear_all_soft_refs);
1601 _full_gcs_since_conc_gc++;
1602
1603 }
1604
1605 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1606 GenCollectedHeap* gch = GenCollectedHeap::heap();
1607 unsigned int gc_count = gch->total_full_collections();
1608 if (gc_count == full_gc_count) {
1609 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1610 _full_gc_requested = true;
1611 CGC_lock->notify(); // nudge CMS thread
1612 }
1613 }
1614
1615
1616 // The foreground and background collectors need to coordinate in order
1617 // to make sure that they do not mutually interfere with CMS collections.
1618 // When a background collection is active,
1619 // the foreground collector may need to take over (preempt) and
1620 // synchronously complete an ongoing collection. Depending on the
1621 // frequency of the background collections and the heap usage
1622 // of the application, this preemption can be seldom or frequent.
1623 // There are only certain
1624 // points in the background collection that the "collection-baton"
1625 // can be passed to the foreground collector.
1626 //
1627 // The foreground collector will wait for the baton before
1628 // starting any part of the collection. The foreground collector
1629 // will only wait at one location.
1630 //
1631 // The background collector will yield the baton before starting a new
1632 // phase of the collection (e.g., before initial marking, marking from roots,
1633 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1634 // of the loop which switches the phases. The background collector does some
1635 // of the phases (initial mark, final re-mark) with the world stopped.
1636 // Because of locking involved in stopping the world,
1637 // the foreground collector should not block waiting for the background
1638 // collector when it is doing a stop-the-world phase. The background
1639 // collector will yield the baton at an additional point just before
1640 // it enters a stop-the-world phase. Once the world is stopped, the
1641 // background collector checks the phase of the collection. If the
1642 // phase has not changed, it proceeds with the collection. If the
1643 // phase has changed, it skips that phase of the collection. See
1644 // the comments on the use of the Heap_lock in collect_in_background().
1645 //
1646 // Variable used in baton passing.
1647 // _foregroundGCIsActive - Set to true by the foreground collector when
1648 // it wants the baton. The foreground clears it when it has finished
1649 // the collection.
1650 // _foregroundGCShouldWait - Set to true by the background collector
1651 // when it is running. The foreground collector waits while
1652 // _foregroundGCShouldWait is true.
1653 // CGC_lock - monitor used to protect access to the above variables
1654 // and to notify the foreground and background collectors.
1655 // _collectorState - current state of the CMS collection.
1656 //
1657 // The foreground collector
1658 // acquires the CGC_lock
1659 // sets _foregroundGCIsActive
1660 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1661 // various locks acquired in preparation for the collection
1662 // are released so as not to block the background collector
1663 // that is in the midst of a collection
1664 // proceeds with the collection
1665 // clears _foregroundGCIsActive
1666 // returns
1667 //
1668 // The background collector in a loop iterating on the phases of the
1669 // collection
1670 // acquires the CGC_lock
1671 // sets _foregroundGCShouldWait
1672 // if _foregroundGCIsActive is set
1673 // clears _foregroundGCShouldWait, notifies _CGC_lock
1674 // waits on _CGC_lock for _foregroundGCIsActive to become false
1675 // and exits the loop.
1676 // otherwise
1677 // proceed with that phase of the collection
1678 // if the phase is a stop-the-world phase,
1679 // yield the baton once more just before enqueueing
1680 // the stop-world CMS operation (executed by the VM thread).
1681 // returns after all phases of the collection are done
1682 //
1683
1684 void CMSCollector::acquire_control_and_collect(bool full,
1685 bool clear_all_soft_refs) {
1686 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1687 assert(!Thread::current()->is_ConcurrentGC_thread(),
1688 "shouldn't try to acquire control from self!");
1689
1690 // Start the protocol for acquiring control of the
1691 // collection from the background collector (aka CMS thread).
1692 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1693 "VM thread should have CMS token");
1694 // Remember the possibly interrupted state of an ongoing
1695 // concurrent collection
1696 CollectorState first_state = _collectorState;
1697
1698 // Signal to a possibly ongoing concurrent collection that
1699 // we want to do a foreground collection.
1700 _foregroundGCIsActive = true;
1701
1702 // Disable incremental mode during a foreground collection.
1703 ICMSDisabler icms_disabler;
1704
1705 // release locks and wait for a notify from the background collector
1706 // releasing the locks in only necessary for phases which
1707 // do yields to improve the granularity of the collection.
1708 assert_lock_strong(bitMapLock());
1709 // We need to lock the Free list lock for the space that we are
1710 // currently collecting.
1711 assert(haveFreelistLocks(), "Must be holding free list locks");
1712 bitMapLock()->unlock();
1713 releaseFreelistLocks();
1714 {
1715 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1716 if (_foregroundGCShouldWait) {
1717 // We are going to be waiting for action for the CMS thread;
1718 // it had better not be gone (for instance at shutdown)!
1719 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1720 "CMS thread must be running");
1721 // Wait here until the background collector gives us the go-ahead
1722 ConcurrentMarkSweepThread::clear_CMS_flag(
1723 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1724 // Get a possibly blocked CMS thread going:
1725 // Note that we set _foregroundGCIsActive true above,
1726 // without protection of the CGC_lock.
1727 CGC_lock->notify();
1728 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1729 "Possible deadlock");
1730 while (_foregroundGCShouldWait) {
1731 // wait for notification
1732 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1733 // Possibility of delay/starvation here, since CMS token does
1734 // not know to give priority to VM thread? Actually, i think
1735 // there wouldn't be any delay/starvation, but the proof of
1736 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1737 }
1738 ConcurrentMarkSweepThread::set_CMS_flag(
1739 ConcurrentMarkSweepThread::CMS_vm_has_token);
1740 }
1741 }
1742 // The CMS_token is already held. Get back the other locks.
1743 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1744 "VM thread should have CMS token");
1745 getFreelistLocks();
1746 bitMapLock()->lock_without_safepoint_check();
1747 if (TraceCMSState) {
1748 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1749 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1750 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1751 }
1752
1753 // Check if we need to do a compaction, or if not, whether
1754 // we need to start the mark-sweep from scratch.
1755 bool should_compact = false;
1756 bool should_start_over = false;
1757 decide_foreground_collection_type(clear_all_soft_refs,
1758 &should_compact, &should_start_over);
1759
1760 NOT_PRODUCT(
1761 if (RotateCMSCollectionTypes) {
1762 if (_cmsGen->debug_collection_type() ==
1763 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1764 should_compact = true;
1765 } else if (_cmsGen->debug_collection_type() ==
1766 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1767 should_compact = false;
1768 }
1769 }
1770 )
1771
1772 if (PrintGCDetails && first_state > Idling) {
1773 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1774 if (GCCause::is_user_requested_gc(cause) ||
1775 GCCause::is_serviceability_requested_gc(cause)) {
1776 gclog_or_tty->print(" (concurrent mode interrupted)");
1777 } else {
1778 gclog_or_tty->print(" (concurrent mode failure)");
1779 }
1780 }
1781
1782 if (should_compact) {
1783 // If the collection is being acquired from the background
1784 // collector, there may be references on the discovered
1785 // references lists that have NULL referents (being those
1786 // that were concurrently cleared by a mutator) or
1787 // that are no longer active (having been enqueued concurrently
1788 // by the mutator).
1789 // Scrub the list of those references because Mark-Sweep-Compact
1790 // code assumes referents are not NULL and that all discovered
1791 // Reference objects are active.
1792 ref_processor()->clean_up_discovered_references();
1793
1794 do_compaction_work(clear_all_soft_refs);
1795
1796 // Has the GC time limit been exceeded?
1797 check_gc_time_limit();
1798
1799 } else {
1800 do_mark_sweep_work(clear_all_soft_refs, first_state,
1801 should_start_over);
1802 }
1803 // Reset the expansion cause, now that we just completed
1804 // a collection cycle.
1805 clear_expansion_cause();
1806 _foregroundGCIsActive = false;
1807 return;
1808 }
1809
1810 void CMSCollector::check_gc_time_limit() {
1811
1812 // Ignore explicit GC's. Exiting here does not set the flag and
1813 // does not reset the count. Updating of the averages for system
1814 // GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC.
1815 GCCause::Cause gc_cause = GenCollectedHeap::heap()->gc_cause();
1816 if (GCCause::is_user_requested_gc(gc_cause) ||
1817 GCCause::is_serviceability_requested_gc(gc_cause)) {
1818 return;
1819 }
1820
1821 // Calculate the fraction of the CMS generation was freed during
1822 // the last collection.
1823 // Only consider the STW compacting cost for now.
1824 //
1825 // Note that the gc time limit test only works for the collections
1826 // of the young gen + tenured gen and not for collections of the
1827 // permanent gen. That is because the calculation of the space
1828 // freed by the collection is the free space in the young gen +
1829 // tenured gen.
1830
1831 double fraction_free =
1832 ((double)_cmsGen->free())/((double)_cmsGen->max_capacity());
1833 if ((100.0 * size_policy()->compacting_gc_cost()) >
1834 ((double) GCTimeLimit) &&
1835 ((fraction_free * 100) < GCHeapFreeLimit)) {
1836 size_policy()->inc_gc_time_limit_count();
1837 if (UseGCOverheadLimit &&
1838 (size_policy()->gc_time_limit_count() >
1839 AdaptiveSizePolicyGCTimeLimitThreshold)) {
1840 size_policy()->set_gc_time_limit_exceeded(true);
1841 // Avoid consecutive OOM due to the gc time limit by resetting
1842 // the counter.
1843 size_policy()->reset_gc_time_limit_count();
1844 if (PrintGCDetails) {
1845 gclog_or_tty->print_cr(" GC is exceeding overhead limit "
1846 "of %d%%", GCTimeLimit);
1847 }
1848 } else {
1849 if (PrintGCDetails) {
1850 gclog_or_tty->print_cr(" GC would exceed overhead limit "
1851 "of %d%%", GCTimeLimit);
1852 }
1853 }
1854 } else {
1855 size_policy()->reset_gc_time_limit_count();
1856 }
1857 }
1858
1859 // Resize the perm generation and the tenured generation
1860 // after obtaining the free list locks for the
1861 // two generations.
1862 void CMSCollector::compute_new_size() {
1863 assert_locked_or_safepoint(Heap_lock);
1864 FreelistLocker z(this);
1865 _permGen->compute_new_size();
1866 _cmsGen->compute_new_size();
1867 }
1868
1869 // A work method used by foreground collection to determine
1870 // what type of collection (compacting or not, continuing or fresh)
1871 // it should do.
1872 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1873 // and CMSCompactWhenClearAllSoftRefs the default in the future
1874 // and do away with the flags after a suitable period.
1875 void CMSCollector::decide_foreground_collection_type(
1876 bool clear_all_soft_refs, bool* should_compact,
1877 bool* should_start_over) {
1878 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1879 // flag is set, and we have either requested a System.gc() or
1880 // the number of full gc's since the last concurrent cycle
1881 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1882 // or if an incremental collection has failed
1883 GenCollectedHeap* gch = GenCollectedHeap::heap();
1884 assert(gch->collector_policy()->is_two_generation_policy(),
1885 "You may want to check the correctness of the following");
1886 // Inform cms gen if this was due to partial collection failing.
1887 // The CMS gen may use this fact to determine its expansion policy.
1888 if (gch->incremental_collection_will_fail()) {
1889 assert(!_cmsGen->incremental_collection_failed(),
1890 "Should have been noticed, reacted to and cleared");
1891 _cmsGen->set_incremental_collection_failed();
1892 }
1893 *should_compact =
1894 UseCMSCompactAtFullCollection &&
1895 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1896 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1897 gch->incremental_collection_will_fail());
1898 *should_start_over = false;
1899 if (clear_all_soft_refs && !*should_compact) {
1900 // We are about to do a last ditch collection attempt
1901 // so it would normally make sense to do a compaction
1902 // to reclaim as much space as possible.
1903 if (CMSCompactWhenClearAllSoftRefs) {
1904 // Default: The rationale is that in this case either
1905 // we are past the final marking phase, in which case
1906 // we'd have to start over, or so little has been done
1907 // that there's little point in saving that work. Compaction
1908 // appears to be the sensible choice in either case.
1909 *should_compact = true;
1910 } else {
1911 // We have been asked to clear all soft refs, but not to
1912 // compact. Make sure that we aren't past the final checkpoint
1913 // phase, for that is where we process soft refs. If we are already
1914 // past that phase, we'll need to redo the refs discovery phase and
1915 // if necessary clear soft refs that weren't previously
1916 // cleared. We do so by remembering the phase in which
1917 // we came in, and if we are past the refs processing
1918 // phase, we'll choose to just redo the mark-sweep
1919 // collection from scratch.
1920 if (_collectorState > FinalMarking) {
1921 // We are past the refs processing phase;
1922 // start over and do a fresh synchronous CMS cycle
1923 _collectorState = Resetting; // skip to reset to start new cycle
1924 reset(false /* == !asynch */);
1925 *should_start_over = true;
1926 } // else we can continue a possibly ongoing current cycle
1927 }
1928 }
1929 }
1930
1931 // A work method used by the foreground collector to do
1932 // a mark-sweep-compact.
1933 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1934 GenCollectedHeap* gch = GenCollectedHeap::heap();
1935 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1936 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1937 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1938 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1939 }
1940
1941 // Sample collection interval time and reset for collection pause.
1942 if (UseAdaptiveSizePolicy) {
1943 size_policy()->msc_collection_begin();
1944 }
1945
1946 // Temporarily widen the span of the weak reference processing to
1947 // the entire heap.
1948 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1949 ReferenceProcessorSpanMutator x(ref_processor(), new_span);
1950
1951 // Temporarily, clear the "is_alive_non_header" field of the
1952 // reference processor.
1953 ReferenceProcessorIsAliveMutator y(ref_processor(), NULL);
1954
1955 // Temporarily make reference _processing_ single threaded (non-MT).
1956 ReferenceProcessorMTProcMutator z(ref_processor(), false);
1957
1958 // Temporarily make refs discovery atomic
1959 ReferenceProcessorAtomicMutator w(ref_processor(), true);
1960
1961 ref_processor()->set_enqueuing_is_done(false);
1962 ref_processor()->enable_discovery();
1963 // If an asynchronous collection finishes, the _modUnionTable is
1964 // all clear. If we are assuming the collection from an asynchronous
1965 // collection, clear the _modUnionTable.
1966 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1967 "_modUnionTable should be clear if the baton was not passed");
1968 _modUnionTable.clear_all();
1969
1970 // We must adjust the allocation statistics being maintained
1971 // in the free list space. We do so by reading and clearing
1972 // the sweep timer and updating the block flux rate estimates below.
1973 assert(_sweep_timer.is_active(), "We should never see the timer inactive");
1974 _sweep_timer.stop();
1975 // Note that we do not use this sample to update the _sweep_estimate.
1976 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
1977 _sweep_estimate.padded_average());
1978
1979 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1980 ref_processor(), clear_all_soft_refs);
1981 #ifdef ASSERT
1982 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1983 size_t free_size = cms_space->free();
1984 assert(free_size ==
1985 pointer_delta(cms_space->end(), cms_space->compaction_top())
1986 * HeapWordSize,
1987 "All the free space should be compacted into one chunk at top");
1988 assert(cms_space->dictionary()->totalChunkSize(
1989 debug_only(cms_space->freelistLock())) == 0 ||
1990 cms_space->totalSizeInIndexedFreeLists() == 0,
1991 "All the free space should be in a single chunk");
1992 size_t num = cms_space->totalCount();
1993 assert((free_size == 0 && num == 0) ||
1994 (free_size > 0 && (num == 1 || num == 2)),
1995 "There should be at most 2 free chunks after compaction");
1996 #endif // ASSERT
1997 _collectorState = Resetting;
1998 assert(_restart_addr == NULL,
1999 "Should have been NULL'd before baton was passed");
2000 reset(false /* == !asynch */);
2001 _cmsGen->reset_after_compaction();
2002 _concurrent_cycles_since_last_unload = 0;
2003
2004 if (verifying() && !should_unload_classes()) {
2005 perm_gen_verify_bit_map()->clear_all();
2006 }
2007
2008 // Clear any data recorded in the PLAB chunk arrays.
2009 if (_survivor_plab_array != NULL) {
2010 reset_survivor_plab_arrays();
2011 }
2012
2013 // Adjust the per-size allocation stats for the next epoch.
2014 _cmsGen->cmsSpace()->endSweepFLCensus(sweepCount() /* fake */);
2015 // Restart the "sweep timer" for next epoch.
2016 _sweep_timer.reset();
2017 _sweep_timer.start();
2018
2019 // Sample collection pause time and reset for collection interval.
2020 if (UseAdaptiveSizePolicy) {
2021 size_policy()->msc_collection_end(gch->gc_cause());
2022 }
2023
2024 // For a mark-sweep-compact, compute_new_size() will be called
2025 // in the heap's do_collection() method.
2026 }
2027
2028 // A work method used by the foreground collector to do
2029 // a mark-sweep, after taking over from a possibly on-going
2030 // concurrent mark-sweep collection.
2031 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2032 CollectorState first_state, bool should_start_over) {
2033 if (PrintGC && Verbose) {
2034 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2035 "collector with count %d",
2036 _full_gcs_since_conc_gc);
2037 }
2038 switch (_collectorState) {
2039 case Idling:
2040 if (first_state == Idling || should_start_over) {
2041 // The background GC was not active, or should
2042 // restarted from scratch; start the cycle.
2043 _collectorState = InitialMarking;
2044 }
2045 // If first_state was not Idling, then a background GC
2046 // was in progress and has now finished. No need to do it
2047 // again. Leave the state as Idling.
2048 break;
2049 case Precleaning:
2050 // In the foreground case don't do the precleaning since
2051 // it is not done concurrently and there is extra work
2052 // required.
2053 _collectorState = FinalMarking;
2054 }
2055 if (PrintGCDetails &&
2056 (_collectorState > Idling ||
2057 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2058 gclog_or_tty->print(" (concurrent mode failure)");
2059 }
2060 collect_in_foreground(clear_all_soft_refs);
2061
2062 // For a mark-sweep, compute_new_size() will be called
2063 // in the heap's do_collection() method.
2064 }
2065
2066
2067 void CMSCollector::getFreelistLocks() const {
2068 // Get locks for all free lists in all generations that this
2069 // collector is responsible for
2070 _cmsGen->freelistLock()->lock_without_safepoint_check();
2071 _permGen->freelistLock()->lock_without_safepoint_check();
2072 }
2073
2074 void CMSCollector::releaseFreelistLocks() const {
2075 // Release locks for all free lists in all generations that this
2076 // collector is responsible for
2077 _cmsGen->freelistLock()->unlock();
2078 _permGen->freelistLock()->unlock();
2079 }
2080
2081 bool CMSCollector::haveFreelistLocks() const {
2082 // Check locks for all free lists in all generations that this
2083 // collector is responsible for
2084 assert_lock_strong(_cmsGen->freelistLock());
2085 assert_lock_strong(_permGen->freelistLock());
2086 PRODUCT_ONLY(ShouldNotReachHere());
2087 return true;
2088 }
2089
2090 // A utility class that is used by the CMS collector to
2091 // temporarily "release" the foreground collector from its
2092 // usual obligation to wait for the background collector to
2093 // complete an ongoing phase before proceeding.
2094 class ReleaseForegroundGC: public StackObj {
2095 private:
2096 CMSCollector* _c;
2097 public:
2098 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2099 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2100 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2101 // allow a potentially blocked foreground collector to proceed
2102 _c->_foregroundGCShouldWait = false;
2103 if (_c->_foregroundGCIsActive) {
2104 CGC_lock->notify();
2105 }
2106 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2107 "Possible deadlock");
2108 }
2109
2110 ~ReleaseForegroundGC() {
2111 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2112 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2113 _c->_foregroundGCShouldWait = true;
2114 }
2115 };
2116
2117 // There are separate collect_in_background and collect_in_foreground because of
2118 // the different locking requirements of the background collector and the
2119 // foreground collector. There was originally an attempt to share
2120 // one "collect" method between the background collector and the foreground
2121 // collector but the if-then-else required made it cleaner to have
2122 // separate methods.
2123 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2124 assert(Thread::current()->is_ConcurrentGC_thread(),
2125 "A CMS asynchronous collection is only allowed on a CMS thread.");
2126
2127 GenCollectedHeap* gch = GenCollectedHeap::heap();
2128 {
2129 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2130 MutexLockerEx hl(Heap_lock, safepoint_check);
2131 FreelistLocker fll(this);
2132 MutexLockerEx x(CGC_lock, safepoint_check);
2133 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2134 // The foreground collector is active or we're
2135 // not using asynchronous collections. Skip this
2136 // background collection.
2137 assert(!_foregroundGCShouldWait, "Should be clear");
2138 return;
2139 } else {
2140 assert(_collectorState == Idling, "Should be idling before start.");
2141 _collectorState = InitialMarking;
2142 // Reset the expansion cause, now that we are about to begin
2143 // a new cycle.
2144 clear_expansion_cause();
2145 }
2146 // Decide if we want to enable class unloading as part of the
2147 // ensuing concurrent GC cycle.
2148 update_should_unload_classes();
2149 _full_gc_requested = false; // acks all outstanding full gc requests
2150 // Signal that we are about to start a collection
2151 gch->increment_total_full_collections(); // ... starting a collection cycle
2152 _collection_count_start = gch->total_full_collections();
2153 }
2154
2155 // Used for PrintGC
2156 size_t prev_used;
2157 if (PrintGC && Verbose) {
2158 prev_used = _cmsGen->used(); // XXXPERM
2159 }
2160
2161 // The change of the collection state is normally done at this level;
2162 // the exceptions are phases that are executed while the world is
2163 // stopped. For those phases the change of state is done while the
2164 // world is stopped. For baton passing purposes this allows the
2165 // background collector to finish the phase and change state atomically.
2166 // The foreground collector cannot wait on a phase that is done
2167 // while the world is stopped because the foreground collector already
2168 // has the world stopped and would deadlock.
2169 while (_collectorState != Idling) {
2170 if (TraceCMSState) {
2171 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2172 Thread::current(), _collectorState);
2173 }
2174 // The foreground collector
2175 // holds the Heap_lock throughout its collection.
2176 // holds the CMS token (but not the lock)
2177 // except while it is waiting for the background collector to yield.
2178 //
2179 // The foreground collector should be blocked (not for long)
2180 // if the background collector is about to start a phase
2181 // executed with world stopped. If the background
2182 // collector has already started such a phase, the
2183 // foreground collector is blocked waiting for the
2184 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2185 // are executed in the VM thread.
2186 //
2187 // The locking order is
2188 // PendingListLock (PLL) -- if applicable (FinalMarking)
2189 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2190 // CMS token (claimed in
2191 // stop_world_and_do() -->
2192 // safepoint_synchronize() -->
2193 // CMSThread::synchronize())
2194
2195 {
2196 // Check if the FG collector wants us to yield.
2197 CMSTokenSync x(true); // is cms thread
2198 if (waitForForegroundGC()) {
2199 // We yielded to a foreground GC, nothing more to be
2200 // done this round.
2201 assert(_foregroundGCShouldWait == false, "We set it to false in "
2202 "waitForForegroundGC()");
2203 if (TraceCMSState) {
2204 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2205 " exiting collection CMS state %d",
2206 Thread::current(), _collectorState);
2207 }
2208 return;
2209 } else {
2210 // The background collector can run but check to see if the
2211 // foreground collector has done a collection while the
2212 // background collector was waiting to get the CGC_lock
2213 // above. If yes, break so that _foregroundGCShouldWait
2214 // is cleared before returning.
2215 if (_collectorState == Idling) {
2216 break;
2217 }
2218 }
2219 }
2220
2221 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2222 "should be waiting");
2223
2224 switch (_collectorState) {
2225 case InitialMarking:
2226 {
2227 ReleaseForegroundGC x(this);
2228 stats().record_cms_begin();
2229
2230 VM_CMS_Initial_Mark initial_mark_op(this);
2231 VMThread::execute(&initial_mark_op);
2232 }
2233 // The collector state may be any legal state at this point
2234 // since the background collector may have yielded to the
2235 // foreground collector.
2236 break;
2237 case Marking:
2238 // initial marking in checkpointRootsInitialWork has been completed
2239 if (markFromRoots(true)) { // we were successful
2240 assert(_collectorState == Precleaning, "Collector state should "
2241 "have changed");
2242 } else {
2243 assert(_foregroundGCIsActive, "Internal state inconsistency");
2244 }
2245 break;
2246 case Precleaning:
2247 if (UseAdaptiveSizePolicy) {
2248 size_policy()->concurrent_precleaning_begin();
2249 }
2250 // marking from roots in markFromRoots has been completed
2251 preclean();
2252 if (UseAdaptiveSizePolicy) {
2253 size_policy()->concurrent_precleaning_end();
2254 }
2255 assert(_collectorState == AbortablePreclean ||
2256 _collectorState == FinalMarking,
2257 "Collector state should have changed");
2258 break;
2259 case AbortablePreclean:
2260 if (UseAdaptiveSizePolicy) {
2261 size_policy()->concurrent_phases_resume();
2262 }
2263 abortable_preclean();
2264 if (UseAdaptiveSizePolicy) {
2265 size_policy()->concurrent_precleaning_end();
2266 }
2267 assert(_collectorState == FinalMarking, "Collector state should "
2268 "have changed");
2269 break;
2270 case FinalMarking:
2271 {
2272 ReleaseForegroundGC x(this);
2273
2274 VM_CMS_Final_Remark final_remark_op(this);
2275 VMThread::execute(&final_remark_op);
2276 }
2277 assert(_foregroundGCShouldWait, "block post-condition");
2278 break;
2279 case Sweeping:
2280 if (UseAdaptiveSizePolicy) {
2281 size_policy()->concurrent_sweeping_begin();
2282 }
2283 // final marking in checkpointRootsFinal has been completed
2284 sweep(true);
2285 assert(_collectorState == Resizing, "Collector state change "
2286 "to Resizing must be done under the free_list_lock");
2287 _full_gcs_since_conc_gc = 0;
2288
2289 // Stop the timers for adaptive size policy for the concurrent phases
2290 if (UseAdaptiveSizePolicy) {
2291 size_policy()->concurrent_sweeping_end();
2292 size_policy()->concurrent_phases_end(gch->gc_cause(),
2293 gch->prev_gen(_cmsGen)->capacity(),
2294 _cmsGen->free());
2295 }
2296
2297 case Resizing: {
2298 // Sweeping has been completed...
2299 // At this point the background collection has completed.
2300 // Don't move the call to compute_new_size() down
2301 // into code that might be executed if the background
2302 // collection was preempted.
2303 {
2304 ReleaseForegroundGC x(this); // unblock FG collection
2305 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2306 CMSTokenSync z(true); // not strictly needed.
2307 if (_collectorState == Resizing) {
2308 compute_new_size();
2309 _collectorState = Resetting;
2310 } else {
2311 assert(_collectorState == Idling, "The state should only change"
2312 " because the foreground collector has finished the collection");
2313 }
2314 }
2315 break;
2316 }
2317 case Resetting:
2318 // CMS heap resizing has been completed
2319 reset(true);
2320 assert(_collectorState == Idling, "Collector state should "
2321 "have changed");
2322 stats().record_cms_end();
2323 // Don't move the concurrent_phases_end() and compute_new_size()
2324 // calls to here because a preempted background collection
2325 // has it's state set to "Resetting".
2326 break;
2327 case Idling:
2328 default:
2329 ShouldNotReachHere();
2330 break;
2331 }
2332 if (TraceCMSState) {
2333 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2334 Thread::current(), _collectorState);
2335 }
2336 assert(_foregroundGCShouldWait, "block post-condition");
2337 }
2338
2339 // Should this be in gc_epilogue?
2340 collector_policy()->counters()->update_counters();
2341
2342 {
2343 // Clear _foregroundGCShouldWait and, in the event that the
2344 // foreground collector is waiting, notify it, before
2345 // returning.
2346 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2347 _foregroundGCShouldWait = false;
2348 if (_foregroundGCIsActive) {
2349 CGC_lock->notify();
2350 }
2351 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2352 "Possible deadlock");
2353 }
2354 if (TraceCMSState) {
2355 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2356 " exiting collection CMS state %d",
2357 Thread::current(), _collectorState);
2358 }
2359 if (PrintGC && Verbose) {
2360 _cmsGen->print_heap_change(prev_used);
2361 }
2362 }
2363
2364 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2365 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2366 "Foreground collector should be waiting, not executing");
2367 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2368 "may only be done by the VM Thread with the world stopped");
2369 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2370 "VM thread should have CMS token");
2371
2372 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2373 true, gclog_or_tty);)
2374 if (UseAdaptiveSizePolicy) {
2375 size_policy()->ms_collection_begin();
2376 }
2377 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2378
2379 HandleMark hm; // Discard invalid handles created during verification
2380
2381 if (VerifyBeforeGC &&
2382 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2383 Universe::verify(true);
2384 }
2385
2386 bool init_mark_was_synchronous = false; // until proven otherwise
2387 while (_collectorState != Idling) {
2388 if (TraceCMSState) {
2389 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2390 Thread::current(), _collectorState);
2391 }
2392 switch (_collectorState) {
2393 case InitialMarking:
2394 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2395 checkpointRootsInitial(false);
2396 assert(_collectorState == Marking, "Collector state should have changed"
2397 " within checkpointRootsInitial()");
2398 break;
2399 case Marking:
2400 // initial marking in checkpointRootsInitialWork has been completed
2401 if (VerifyDuringGC &&
2402 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2403 gclog_or_tty->print("Verify before initial mark: ");
2404 Universe::verify(true);
2405 }
2406 {
2407 bool res = markFromRoots(false);
2408 assert(res && _collectorState == FinalMarking, "Collector state should "
2409 "have changed");
2410 break;
2411 }
2412 case FinalMarking:
2413 if (VerifyDuringGC &&
2414 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2415 gclog_or_tty->print("Verify before re-mark: ");
2416 Universe::verify(true);
2417 }
2418 checkpointRootsFinal(false, clear_all_soft_refs,
2419 init_mark_was_synchronous);
2420 assert(_collectorState == Sweeping, "Collector state should not "
2421 "have changed within checkpointRootsFinal()");
2422 break;
2423 case Sweeping:
2424 // final marking in checkpointRootsFinal has been completed
2425 if (VerifyDuringGC &&
2426 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2427 gclog_or_tty->print("Verify before sweep: ");
2428 Universe::verify(true);
2429 }
2430 sweep(false);
2431 assert(_collectorState == Resizing, "Incorrect state");
2432 break;
2433 case Resizing: {
2434 // Sweeping has been completed; the actual resize in this case
2435 // is done separately; nothing to be done in this state.
2436 _collectorState = Resetting;
2437 break;
2438 }
2439 case Resetting:
2440 // The heap has been resized.
2441 if (VerifyDuringGC &&
2442 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2443 gclog_or_tty->print("Verify before reset: ");
2444 Universe::verify(true);
2445 }
2446 reset(false);
2447 assert(_collectorState == Idling, "Collector state should "
2448 "have changed");
2449 break;
2450 case Precleaning:
2451 case AbortablePreclean:
2452 // Elide the preclean phase
2453 _collectorState = FinalMarking;
2454 break;
2455 default:
2456 ShouldNotReachHere();
2457 }
2458 if (TraceCMSState) {
2459 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2460 Thread::current(), _collectorState);
2461 }
2462 }
2463
2464 if (UseAdaptiveSizePolicy) {
2465 GenCollectedHeap* gch = GenCollectedHeap::heap();
2466 size_policy()->ms_collection_end(gch->gc_cause());
2467 }
2468
2469 if (VerifyAfterGC &&
2470 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2471 Universe::verify(true);
2472 }
2473 if (TraceCMSState) {
2474 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2475 " exiting collection CMS state %d",
2476 Thread::current(), _collectorState);
2477 }
2478 }
2479
2480 bool CMSCollector::waitForForegroundGC() {
2481 bool res = false;
2482 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2483 "CMS thread should have CMS token");
2484 // Block the foreground collector until the
2485 // background collectors decides whether to
2486 // yield.
2487 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2488 _foregroundGCShouldWait = true;
2489 if (_foregroundGCIsActive) {
2490 // The background collector yields to the
2491 // foreground collector and returns a value
2492 // indicating that it has yielded. The foreground
2493 // collector can proceed.
2494 res = true;
2495 _foregroundGCShouldWait = false;
2496 ConcurrentMarkSweepThread::clear_CMS_flag(
2497 ConcurrentMarkSweepThread::CMS_cms_has_token);
2498 ConcurrentMarkSweepThread::set_CMS_flag(
2499 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2500 // Get a possibly blocked foreground thread going
2501 CGC_lock->notify();
2502 if (TraceCMSState) {
2503 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2504 Thread::current(), _collectorState);
2505 }
2506 while (_foregroundGCIsActive) {
2507 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2508 }
2509 ConcurrentMarkSweepThread::set_CMS_flag(
2510 ConcurrentMarkSweepThread::CMS_cms_has_token);
2511 ConcurrentMarkSweepThread::clear_CMS_flag(
2512 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2513 }
2514 if (TraceCMSState) {
2515 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2516 Thread::current(), _collectorState);
2517 }
2518 return res;
2519 }
2520
2521 // Because of the need to lock the free lists and other structures in
2522 // the collector, common to all the generations that the collector is
2523 // collecting, we need the gc_prologues of individual CMS generations
2524 // delegate to their collector. It may have been simpler had the
2525 // current infrastructure allowed one to call a prologue on a
2526 // collector. In the absence of that we have the generation's
2527 // prologue delegate to the collector, which delegates back
2528 // some "local" work to a worker method in the individual generations
2529 // that it's responsible for collecting, while itself doing any
2530 // work common to all generations it's responsible for. A similar
2531 // comment applies to the gc_epilogue()'s.
2532 // The role of the varaible _between_prologue_and_epilogue is to
2533 // enforce the invocation protocol.
2534 void CMSCollector::gc_prologue(bool full) {
2535 // Call gc_prologue_work() for each CMSGen and PermGen that
2536 // we are responsible for.
2537
2538 // The following locking discipline assumes that we are only called
2539 // when the world is stopped.
2540 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2541
2542 // The CMSCollector prologue must call the gc_prologues for the
2543 // "generations" (including PermGen if any) that it's responsible
2544 // for.
2545
2546 assert( Thread::current()->is_VM_thread()
2547 || ( CMSScavengeBeforeRemark
2548 && Thread::current()->is_ConcurrentGC_thread()),
2549 "Incorrect thread type for prologue execution");
2550
2551 if (_between_prologue_and_epilogue) {
2552 // We have already been invoked; this is a gc_prologue delegation
2553 // from yet another CMS generation that we are responsible for, just
2554 // ignore it since all relevant work has already been done.
2555 return;
2556 }
2557
2558 // set a bit saying prologue has been called; cleared in epilogue
2559 _between_prologue_and_epilogue = true;
2560 // Claim locks for common data structures, then call gc_prologue_work()
2561 // for each CMSGen and PermGen that we are responsible for.
2562
2563 getFreelistLocks(); // gets free list locks on constituent spaces
2564 bitMapLock()->lock_without_safepoint_check();
2565
2566 // Should call gc_prologue_work() for all cms gens we are responsible for
2567 bool registerClosure = _collectorState >= Marking
2568 && _collectorState < Sweeping;
2569 ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar
2570 : &_modUnionClosure;
2571 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2572 _permGen->gc_prologue_work(full, registerClosure, muc);
2573
2574 if (!full) {
2575 stats().record_gc0_begin();
2576 }
2577 }
2578
2579 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2580 // Delegate to CMScollector which knows how to coordinate between
2581 // this and any other CMS generations that it is responsible for
2582 // collecting.
2583 collector()->gc_prologue(full);
2584 }
2585
2586 // This is a "private" interface for use by this generation's CMSCollector.
2587 // Not to be called directly by any other entity (for instance,
2588 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2589 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2590 bool registerClosure, ModUnionClosure* modUnionClosure) {
2591 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2592 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2593 "Should be NULL");
2594 if (registerClosure) {
2595 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2596 }
2597 cmsSpace()->gc_prologue();
2598 // Clear stat counters
2599 NOT_PRODUCT(
2600 assert(_numObjectsPromoted == 0, "check");
2601 assert(_numWordsPromoted == 0, "check");
2602 if (Verbose && PrintGC) {
2603 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2604 SIZE_FORMAT" bytes concurrently",
2605 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2606 }
2607 _numObjectsAllocated = 0;
2608 _numWordsAllocated = 0;
2609 )
2610 }
2611
2612 void CMSCollector::gc_epilogue(bool full) {
2613 // The following locking discipline assumes that we are only called
2614 // when the world is stopped.
2615 assert(SafepointSynchronize::is_at_safepoint(),
2616 "world is stopped assumption");
2617
2618 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2619 // if linear allocation blocks need to be appropriately marked to allow the
2620 // the blocks to be parsable. We also check here whether we need to nudge the
2621 // CMS collector thread to start a new cycle (if it's not already active).
2622 assert( Thread::current()->is_VM_thread()
2623 || ( CMSScavengeBeforeRemark
2624 && Thread::current()->is_ConcurrentGC_thread()),
2625 "Incorrect thread type for epilogue execution");
2626
2627 if (!_between_prologue_and_epilogue) {
2628 // We have already been invoked; this is a gc_epilogue delegation
2629 // from yet another CMS generation that we are responsible for, just
2630 // ignore it since all relevant work has already been done.
2631 return;
2632 }
2633 assert(haveFreelistLocks(), "must have freelist locks");
2634 assert_lock_strong(bitMapLock());
2635
2636 _cmsGen->gc_epilogue_work(full);
2637 _permGen->gc_epilogue_work(full);
2638
2639 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2640 // in case sampling was not already enabled, enable it
2641 _start_sampling = true;
2642 }
2643 // reset _eden_chunk_array so sampling starts afresh
2644 _eden_chunk_index = 0;
2645
2646 size_t cms_used = _cmsGen->cmsSpace()->used();
2647 size_t perm_used = _permGen->cmsSpace()->used();
2648
2649 // update performance counters - this uses a special version of
2650 // update_counters() that allows the utilization to be passed as a
2651 // parameter, avoiding multiple calls to used().
2652 //
2653 _cmsGen->update_counters(cms_used);
2654 _permGen->update_counters(perm_used);
2655
2656 if (CMSIncrementalMode) {
2657 icms_update_allocation_limits();
2658 }
2659
2660 bitMapLock()->unlock();
2661 releaseFreelistLocks();
2662
2663 _between_prologue_and_epilogue = false; // ready for next cycle
2664 }
2665
2666 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2667 collector()->gc_epilogue(full);
2668
2669 // Also reset promotion tracking in par gc thread states.
2670 if (ParallelGCThreads > 0) {
2671 for (uint i = 0; i < ParallelGCThreads; i++) {
2672 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2673 }
2674 }
2675 }
2676
2677 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2678 assert(!incremental_collection_failed(), "Should have been cleared");
2679 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2680 cmsSpace()->gc_epilogue();
2681 // Print stat counters
2682 NOT_PRODUCT(
2683 assert(_numObjectsAllocated == 0, "check");
2684 assert(_numWordsAllocated == 0, "check");
2685 if (Verbose && PrintGC) {
2686 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2687 SIZE_FORMAT" bytes",
2688 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2689 }
2690 _numObjectsPromoted = 0;
2691 _numWordsPromoted = 0;
2692 )
2693
2694 if (PrintGC && Verbose) {
2695 // Call down the chain in contiguous_available needs the freelistLock
2696 // so print this out before releasing the freeListLock.
2697 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2698 contiguous_available());
2699 }
2700 }
2701
2702 #ifndef PRODUCT
2703 bool CMSCollector::have_cms_token() {
2704 Thread* thr = Thread::current();
2705 if (thr->is_VM_thread()) {
2706 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2707 } else if (thr->is_ConcurrentGC_thread()) {
2708 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2709 } else if (thr->is_GC_task_thread()) {
2710 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2711 ParGCRareEvent_lock->owned_by_self();
2712 }
2713 return false;
2714 }
2715 #endif
2716
2717 // Check reachability of the given heap address in CMS generation,
2718 // treating all other generations as roots.
2719 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2720 // We could "guarantee" below, rather than assert, but i'll
2721 // leave these as "asserts" so that an adventurous debugger
2722 // could try this in the product build provided some subset of
2723 // the conditions were met, provided they were intersted in the
2724 // results and knew that the computation below wouldn't interfere
2725 // with other concurrent computations mutating the structures
2726 // being read or written.
2727 assert(SafepointSynchronize::is_at_safepoint(),
2728 "Else mutations in object graph will make answer suspect");
2729 assert(have_cms_token(), "Should hold cms token");
2730 assert(haveFreelistLocks(), "must hold free list locks");
2731 assert_lock_strong(bitMapLock());
2732
2733 // Clear the marking bit map array before starting, but, just
2734 // for kicks, first report if the given address is already marked
2735 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2736 _markBitMap.isMarked(addr) ? "" : " not");
2737
2738 if (verify_after_remark()) {
2739 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2740 bool result = verification_mark_bm()->isMarked(addr);
2741 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2742 result ? "IS" : "is NOT");
2743 return result;
2744 } else {
2745 gclog_or_tty->print_cr("Could not compute result");
2746 return false;
2747 }
2748 }
2749
2750 ////////////////////////////////////////////////////////
2751 // CMS Verification Support
2752 ////////////////////////////////////////////////////////
2753 // Following the remark phase, the following invariant
2754 // should hold -- each object in the CMS heap which is
2755 // marked in markBitMap() should be marked in the verification_mark_bm().
2756
2757 class VerifyMarkedClosure: public BitMapClosure {
2758 CMSBitMap* _marks;
2759 bool _failed;
2760
2761 public:
2762 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2763
2764 bool do_bit(size_t offset) {
2765 HeapWord* addr = _marks->offsetToHeapWord(offset);
2766 if (!_marks->isMarked(addr)) {
2767 oop(addr)->print();
2768 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2769 _failed = true;
2770 }
2771 return true;
2772 }
2773
2774 bool failed() { return _failed; }
2775 };
2776
2777 bool CMSCollector::verify_after_remark() {
2778 gclog_or_tty->print(" [Verifying CMS Marking... ");
2779 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2780 static bool init = false;
2781
2782 assert(SafepointSynchronize::is_at_safepoint(),
2783 "Else mutations in object graph will make answer suspect");
2784 assert(have_cms_token(),
2785 "Else there may be mutual interference in use of "
2786 " verification data structures");
2787 assert(_collectorState > Marking && _collectorState <= Sweeping,
2788 "Else marking info checked here may be obsolete");
2789 assert(haveFreelistLocks(), "must hold free list locks");
2790 assert_lock_strong(bitMapLock());
2791
2792
2793 // Allocate marking bit map if not already allocated
2794 if (!init) { // first time
2795 if (!verification_mark_bm()->allocate(_span)) {
2796 return false;
2797 }
2798 init = true;
2799 }
2800
2801 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2802
2803 // Turn off refs discovery -- so we will be tracing through refs.
2804 // This is as intended, because by this time
2805 // GC must already have cleared any refs that need to be cleared,
2806 // and traced those that need to be marked; moreover,
2807 // the marking done here is not going to intefere in any
2808 // way with the marking information used by GC.
2809 NoRefDiscovery no_discovery(ref_processor());
2810
2811 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2812
2813 // Clear any marks from a previous round
2814 verification_mark_bm()->clear_all();
2815 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2816 assert(overflow_list_is_empty(), "overflow list should be empty");
2817
2818 GenCollectedHeap* gch = GenCollectedHeap::heap();
2819 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2820 // Update the saved marks which may affect the root scans.
2821 gch->save_marks();
2822
2823 if (CMSRemarkVerifyVariant == 1) {
2824 // In this first variant of verification, we complete
2825 // all marking, then check if the new marks-verctor is
2826 // a subset of the CMS marks-vector.
2827 verify_after_remark_work_1();
2828 } else if (CMSRemarkVerifyVariant == 2) {
2829 // In this second variant of verification, we flag an error
2830 // (i.e. an object reachable in the new marks-vector not reachable
2831 // in the CMS marks-vector) immediately, also indicating the
2832 // identify of an object (A) that references the unmarked object (B) --
2833 // presumably, a mutation to A failed to be picked up by preclean/remark?
2834 verify_after_remark_work_2();
2835 } else {
2836 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2837 CMSRemarkVerifyVariant);
2838 }
2839 gclog_or_tty->print(" done] ");
2840 return true;
2841 }
2842
2843 void CMSCollector::verify_after_remark_work_1() {
2844 ResourceMark rm;
2845 HandleMark hm;
2846 GenCollectedHeap* gch = GenCollectedHeap::heap();
2847
2848 // Mark from roots one level into CMS
2849 MarkRefsIntoClosure notOlder(_span, verification_mark_bm(), true /* nmethods */);
2850 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2851
2852 gch->gen_process_strong_roots(_cmsGen->level(),
2853 true, // younger gens are roots
2854 true, // collecting perm gen
2855 SharedHeap::ScanningOption(roots_scanning_options()),
2856 NULL, ¬Older);
2857
2858 // Now mark from the roots
2859 assert(_revisitStack.isEmpty(), "Should be empty");
2860 MarkFromRootsClosure markFromRootsClosure(this, _span,
2861 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2862 false /* don't yield */, true /* verifying */);
2863 assert(_restart_addr == NULL, "Expected pre-condition");
2864 verification_mark_bm()->iterate(&markFromRootsClosure);
2865 while (_restart_addr != NULL) {
2866 // Deal with stack overflow: by restarting at the indicated
2867 // address.
2868 HeapWord* ra = _restart_addr;
2869 markFromRootsClosure.reset(ra);
2870 _restart_addr = NULL;
2871 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2872 }
2873 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2874 verify_work_stacks_empty();
2875 // Should reset the revisit stack above, since no class tree
2876 // surgery is forthcoming.
2877 _revisitStack.reset(); // throwing away all contents
2878
2879 // Marking completed -- now verify that each bit marked in
2880 // verification_mark_bm() is also marked in markBitMap(); flag all
2881 // errors by printing corresponding objects.
2882 VerifyMarkedClosure vcl(markBitMap());
2883 verification_mark_bm()->iterate(&vcl);
2884 if (vcl.failed()) {
2885 gclog_or_tty->print("Verification failed");
2886 Universe::heap()->print();
2887 fatal(" ... aborting");
2888 }
2889 }
2890
2891 void CMSCollector::verify_after_remark_work_2() {
2892 ResourceMark rm;
2893 HandleMark hm;
2894 GenCollectedHeap* gch = GenCollectedHeap::heap();
2895
2896 // Mark from roots one level into CMS
2897 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2898 markBitMap(), true /* nmethods */);
2899 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2900 gch->gen_process_strong_roots(_cmsGen->level(),
2901 true, // younger gens are roots
2902 true, // collecting perm gen
2903 SharedHeap::ScanningOption(roots_scanning_options()),
2904 NULL, ¬Older);
2905
2906 // Now mark from the roots
2907 assert(_revisitStack.isEmpty(), "Should be empty");
2908 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2909 verification_mark_bm(), markBitMap(), verification_mark_stack());
2910 assert(_restart_addr == NULL, "Expected pre-condition");
2911 verification_mark_bm()->iterate(&markFromRootsClosure);
2912 while (_restart_addr != NULL) {
2913 // Deal with stack overflow: by restarting at the indicated
2914 // address.
2915 HeapWord* ra = _restart_addr;
2916 markFromRootsClosure.reset(ra);
2917 _restart_addr = NULL;
2918 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2919 }
2920 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2921 verify_work_stacks_empty();
2922 // Should reset the revisit stack above, since no class tree
2923 // surgery is forthcoming.
2924 _revisitStack.reset(); // throwing away all contents
2925
2926 // Marking completed -- now verify that each bit marked in
2927 // verification_mark_bm() is also marked in markBitMap(); flag all
2928 // errors by printing corresponding objects.
2929 VerifyMarkedClosure vcl(markBitMap());
2930 verification_mark_bm()->iterate(&vcl);
2931 assert(!vcl.failed(), "Else verification above should not have succeeded");
2932 }
2933
2934 void ConcurrentMarkSweepGeneration::save_marks() {
2935 // delegate to CMS space
2936 cmsSpace()->save_marks();
2937 for (uint i = 0; i < ParallelGCThreads; i++) {
2938 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2939 }
2940 }
2941
2942 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2943 return cmsSpace()->no_allocs_since_save_marks();
2944 }
2945
2946 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2947 \
2948 void ConcurrentMarkSweepGeneration:: \
2949 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2950 cl->set_generation(this); \
2951 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2952 cl->reset_generation(); \
2953 save_marks(); \
2954 }
2955
2956 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2957
2958 void
2959 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
2960 {
2961 // Not currently implemented; need to do the following. -- ysr.
2962 // dld -- I think that is used for some sort of allocation profiler. So it
2963 // really means the objects allocated by the mutator since the last
2964 // GC. We could potentially implement this cheaply by recording only
2965 // the direct allocations in a side data structure.
2966 //
2967 // I think we probably ought not to be required to support these
2968 // iterations at any arbitrary point; I think there ought to be some
2969 // call to enable/disable allocation profiling in a generation/space,
2970 // and the iterator ought to return the objects allocated in the
2971 // gen/space since the enable call, or the last iterator call (which
2972 // will probably be at a GC.) That way, for gens like CM&S that would
2973 // require some extra data structure to support this, we only pay the
2974 // cost when it's in use...
2975 cmsSpace()->object_iterate_since_last_GC(blk);
2976 }
2977
2978 void
2979 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2980 cl->set_generation(this);
2981 younger_refs_in_space_iterate(_cmsSpace, cl);
2982 cl->reset_generation();
2983 }
2984
2985 void
2986 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
2987 if (freelistLock()->owned_by_self()) {
2988 Generation::oop_iterate(mr, cl);
2989 } else {
2990 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2991 Generation::oop_iterate(mr, cl);
2992 }
2993 }
2994
2995 void
2996 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
2997 if (freelistLock()->owned_by_self()) {
2998 Generation::oop_iterate(cl);
2999 } else {
3000 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3001 Generation::oop_iterate(cl);
3002 }
3003 }
3004
3005 void
3006 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3007 if (freelistLock()->owned_by_self()) {
3008 Generation::object_iterate(cl);
3009 } else {
3010 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3011 Generation::object_iterate(cl);
3012 }
3013 }
3014
3015 void
3016 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3017 }
3018
3019 void
3020 ConcurrentMarkSweepGeneration::post_compact() {
3021 }
3022
3023 void
3024 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3025 // Fix the linear allocation blocks to look like free blocks.
3026
3027 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3028 // are not called when the heap is verified during universe initialization and
3029 // at vm shutdown.
3030 if (freelistLock()->owned_by_self()) {
3031 cmsSpace()->prepare_for_verify();
3032 } else {
3033 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3034 cmsSpace()->prepare_for_verify();
3035 }
3036 }
3037
3038 void
3039 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) {
3040 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3041 // are not called when the heap is verified during universe initialization and
3042 // at vm shutdown.
3043 if (freelistLock()->owned_by_self()) {
3044 cmsSpace()->verify(false /* ignored */);
3045 } else {
3046 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3047 cmsSpace()->verify(false /* ignored */);
3048 }
3049 }
3050
3051 void CMSCollector::verify(bool allow_dirty /* ignored */) {
3052 _cmsGen->verify(allow_dirty);
3053 _permGen->verify(allow_dirty);
3054 }
3055
3056 #ifndef PRODUCT
3057 bool CMSCollector::overflow_list_is_empty() const {
3058 assert(_num_par_pushes >= 0, "Inconsistency");
3059 if (_overflow_list == NULL) {
3060 assert(_num_par_pushes == 0, "Inconsistency");
3061 }
3062 return _overflow_list == NULL;
3063 }
3064
3065 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3066 // merely consolidate assertion checks that appear to occur together frequently.
3067 void CMSCollector::verify_work_stacks_empty() const {
3068 assert(_markStack.isEmpty(), "Marking stack should be empty");
3069 assert(overflow_list_is_empty(), "Overflow list should be empty");
3070 }
3071
3072 void CMSCollector::verify_overflow_empty() const {
3073 assert(overflow_list_is_empty(), "Overflow list should be empty");
3074 assert(no_preserved_marks(), "No preserved marks");
3075 }
3076 #endif // PRODUCT
3077
3078 // Decide if we want to enable class unloading as part of the
3079 // ensuing concurrent GC cycle. We will collect the perm gen and
3080 // unload classes if it's the case that:
3081 // (1) an explicit gc request has been made and the flag
3082 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3083 // (2) (a) class unloading is enabled at the command line, and
3084 // (b) (i) perm gen threshold has been crossed, or
3085 // (ii) old gen is getting really full, or
3086 // (iii) the previous N CMS collections did not collect the
3087 // perm gen
3088 // NOTE: Provided there is no change in the state of the heap between
3089 // calls to this method, it should have idempotent results. Moreover,
3090 // its results should be monotonically increasing (i.e. going from 0 to 1,
3091 // but not 1 to 0) between successive calls between which the heap was
3092 // not collected. For the implementation below, it must thus rely on
3093 // the property that concurrent_cycles_since_last_unload()
3094 // will not decrease unless a collection cycle happened and that
3095 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3096 // themselves also monotonic in that sense. See check_monotonicity()
3097 // below.
3098 bool CMSCollector::update_should_unload_classes() {
3099 _should_unload_classes = false;
3100 // Condition 1 above
3101 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3102 _should_unload_classes = true;
3103 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3104 // Disjuncts 2.b.(i,ii,iii) above
3105 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3106 CMSClassUnloadingMaxInterval)
3107 || _permGen->should_concurrent_collect()
3108 || _cmsGen->is_too_full();
3109 }
3110 return _should_unload_classes;
3111 }
3112
3113 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3114 bool res = should_concurrent_collect();
3115 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3116 return res;
3117 }
3118
3119 void CMSCollector::setup_cms_unloading_and_verification_state() {
3120 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3121 || VerifyBeforeExit;
3122 const int rso = SharedHeap::SO_Symbols | SharedHeap::SO_Strings
3123 | SharedHeap::SO_CodeCache;
3124
3125 if (should_unload_classes()) { // Should unload classes this cycle
3126 remove_root_scanning_option(rso); // Shrink the root set appropriately
3127 set_verifying(should_verify); // Set verification state for this cycle
3128 return; // Nothing else needs to be done at this time
3129 }
3130
3131 // Not unloading classes this cycle
3132 assert(!should_unload_classes(), "Inconsitency!");
3133 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3134 // We were not verifying, or we _were_ unloading classes in the last cycle,
3135 // AND some verification options are enabled this cycle; in this case,
3136 // we must make sure that the deadness map is allocated if not already so,
3137 // and cleared (if already allocated previously --
3138 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3139 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3140 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3141 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3142 "permanent generation verification disabled");
3143 return; // Note that we leave verification disabled, so we'll retry this
3144 // allocation next cycle. We _could_ remember this failure
3145 // and skip further attempts and permanently disable verification
3146 // attempts if that is considered more desirable.
3147 }
3148 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3149 "_perm_gen_ver_bit_map inconsistency?");
3150 } else {
3151 perm_gen_verify_bit_map()->clear_all();
3152 }
3153 // Include symbols, strings and code cache elements to prevent their resurrection.
3154 add_root_scanning_option(rso);
3155 set_verifying(true);
3156 } else if (verifying() && !should_verify) {
3157 // We were verifying, but some verification flags got disabled.
3158 set_verifying(false);
3159 // Exclude symbols, strings and code cache elements from root scanning to
3160 // reduce IM and RM pauses.
3161 remove_root_scanning_option(rso);
3162 }
3163 }
3164
3165
3166 #ifndef PRODUCT
3167 HeapWord* CMSCollector::block_start(const void* p) const {
3168 const HeapWord* addr = (HeapWord*)p;
3169 if (_span.contains(p)) {
3170 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3171 return _cmsGen->cmsSpace()->block_start(p);
3172 } else {
3173 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3174 "Inconsistent _span?");
3175 return _permGen->cmsSpace()->block_start(p);
3176 }
3177 }
3178 return NULL;
3179 }
3180 #endif
3181
3182 HeapWord*
3183 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3184 bool tlab,
3185 bool parallel) {
3186 assert(!tlab, "Can't deal with TLAB allocation");
3187 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3188 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3189 CMSExpansionCause::_satisfy_allocation);
3190 if (GCExpandToAllocateDelayMillis > 0) {
3191 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3192 }
3193 return have_lock_and_allocate(word_size, tlab);
3194 }
3195
3196 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3197 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3198 // to CardGeneration and share it...
3199 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3200 return CardGeneration::expand(bytes, expand_bytes);
3201 }
3202
3203 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3204 CMSExpansionCause::Cause cause)
3205 {
3206
3207 bool success = expand(bytes, expand_bytes);
3208
3209 // remember why we expanded; this information is used
3210 // by shouldConcurrentCollect() when making decisions on whether to start
3211 // a new CMS cycle.
3212 if (success) {
3213 set_expansion_cause(cause);
3214 if (PrintGCDetails && Verbose) {
3215 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3216 CMSExpansionCause::to_string(cause));
3217 }
3218 }
3219 }
3220
3221 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3222 HeapWord* res = NULL;
3223 MutexLocker x(ParGCRareEvent_lock);
3224 while (true) {
3225 // Expansion by some other thread might make alloc OK now:
3226 res = ps->lab.alloc(word_sz);
3227 if (res != NULL) return res;
3228 // If there's not enough expansion space available, give up.
3229 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3230 return NULL;
3231 }
3232 // Otherwise, we try expansion.
3233 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3234 CMSExpansionCause::_allocate_par_lab);
3235 // Now go around the loop and try alloc again;
3236 // A competing par_promote might beat us to the expansion space,
3237 // so we may go around the loop again if promotion fails agaion.
3238 if (GCExpandToAllocateDelayMillis > 0) {
3239 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3240 }
3241 }
3242 }
3243
3244
3245 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3246 PromotionInfo* promo) {
3247 MutexLocker x(ParGCRareEvent_lock);
3248 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3249 while (true) {
3250 // Expansion by some other thread might make alloc OK now:
3251 if (promo->ensure_spooling_space()) {
3252 assert(promo->has_spooling_space(),
3253 "Post-condition of successful ensure_spooling_space()");
3254 return true;
3255 }
3256 // If there's not enough expansion space available, give up.
3257 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3258 return false;
3259 }
3260 // Otherwise, we try expansion.
3261 expand(refill_size_bytes, MinHeapDeltaBytes,
3262 CMSExpansionCause::_allocate_par_spooling_space);
3263 // Now go around the loop and try alloc again;
3264 // A competing allocation might beat us to the expansion space,
3265 // so we may go around the loop again if allocation fails again.
3266 if (GCExpandToAllocateDelayMillis > 0) {
3267 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3268 }
3269 }
3270 }
3271
3272
3273
3274 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3275 assert_locked_or_safepoint(Heap_lock);
3276 size_t size = ReservedSpace::page_align_size_down(bytes);
3277 if (size > 0) {
3278 shrink_by(size);
3279 }
3280 }
3281
3282 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3283 assert_locked_or_safepoint(Heap_lock);
3284 bool result = _virtual_space.expand_by(bytes);
3285 if (result) {
3286 HeapWord* old_end = _cmsSpace->end();
3287 size_t new_word_size =
3288 heap_word_size(_virtual_space.committed_size());
3289 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3290 _bts->resize(new_word_size); // resize the block offset shared array
3291 Universe::heap()->barrier_set()->resize_covered_region(mr);
3292 // Hmmmm... why doesn't CFLS::set_end verify locking?
3293 // This is quite ugly; FIX ME XXX
3294 _cmsSpace->assert_locked();
3295 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3296
3297 // update the space and generation capacity counters
3298 if (UsePerfData) {
3299 _space_counters->update_capacity();
3300 _gen_counters->update_all();
3301 }
3302
3303 if (Verbose && PrintGC) {
3304 size_t new_mem_size = _virtual_space.committed_size();
3305 size_t old_mem_size = new_mem_size - bytes;
3306 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3307 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3308 }
3309 }
3310 return result;
3311 }
3312
3313 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3314 assert_locked_or_safepoint(Heap_lock);
3315 bool success = true;
3316 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3317 if (remaining_bytes > 0) {
3318 success = grow_by(remaining_bytes);
3319 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3320 }
3321 return success;
3322 }
3323
3324 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3325 assert_locked_or_safepoint(Heap_lock);
3326 assert_lock_strong(freelistLock());
3327 // XXX Fix when compaction is implemented.
3328 warning("Shrinking of CMS not yet implemented");
3329 return;
3330 }
3331
3332
3333 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3334 // phases.
3335 class CMSPhaseAccounting: public StackObj {
3336 public:
3337 CMSPhaseAccounting(CMSCollector *collector,
3338 const char *phase,
3339 bool print_cr = true);
3340 ~CMSPhaseAccounting();
3341
3342 private:
3343 CMSCollector *_collector;
3344 const char *_phase;
3345 elapsedTimer _wallclock;
3346 bool _print_cr;
3347
3348 public:
3349 // Not MT-safe; so do not pass around these StackObj's
3350 // where they may be accessed by other threads.
3351 jlong wallclock_millis() {
3352 assert(_wallclock.is_active(), "Wall clock should not stop");
3353 _wallclock.stop(); // to record time
3354 jlong ret = _wallclock.milliseconds();
3355 _wallclock.start(); // restart
3356 return ret;
3357 }
3358 };
3359
3360 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3361 const char *phase,
3362 bool print_cr) :
3363 _collector(collector), _phase(phase), _print_cr(print_cr) {
3364
3365 if (PrintCMSStatistics != 0) {
3366 _collector->resetYields();
3367 }
3368 if (PrintGCDetails && PrintGCTimeStamps) {
3369 gclog_or_tty->date_stamp(PrintGCDateStamps);
3370 gclog_or_tty->stamp();
3371 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3372 _collector->cmsGen()->short_name(), _phase);
3373 }
3374 _collector->resetTimer();
3375 _wallclock.start();
3376 _collector->startTimer();
3377 }
3378
3379 CMSPhaseAccounting::~CMSPhaseAccounting() {
3380 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3381 _collector->stopTimer();
3382 _wallclock.stop();
3383 if (PrintGCDetails) {
3384 gclog_or_tty->date_stamp(PrintGCDateStamps);
3385 if (PrintGCTimeStamps) {
3386 gclog_or_tty->stamp();
3387 gclog_or_tty->print(": ");
3388 }
3389 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3390 _collector->cmsGen()->short_name(),
3391 _phase, _collector->timerValue(), _wallclock.seconds());
3392 if (_print_cr) {
3393 gclog_or_tty->print_cr("");
3394 }
3395 if (PrintCMSStatistics != 0) {
3396 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3397 _collector->yields());
3398 }
3399 }
3400 }
3401
3402 // CMS work
3403
3404 // Checkpoint the roots into this generation from outside
3405 // this generation. [Note this initial checkpoint need only
3406 // be approximate -- we'll do a catch up phase subsequently.]
3407 void CMSCollector::checkpointRootsInitial(bool asynch) {
3408 assert(_collectorState == InitialMarking, "Wrong collector state");
3409 check_correct_thread_executing();
3410 ReferenceProcessor* rp = ref_processor();
3411 SpecializationStats::clear();
3412 assert(_restart_addr == NULL, "Control point invariant");
3413 if (asynch) {
3414 // acquire locks for subsequent manipulations
3415 MutexLockerEx x(bitMapLock(),
3416 Mutex::_no_safepoint_check_flag);
3417 checkpointRootsInitialWork(asynch);
3418 rp->verify_no_references_recorded();
3419 rp->enable_discovery(); // enable ("weak") refs discovery
3420 _collectorState = Marking;
3421 } else {
3422 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3423 // which recognizes if we are a CMS generation, and doesn't try to turn on
3424 // discovery; verify that they aren't meddling.
3425 assert(!rp->discovery_is_atomic(),
3426 "incorrect setting of discovery predicate");
3427 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3428 "ref discovery for this generation kind");
3429 // already have locks
3430 checkpointRootsInitialWork(asynch);
3431 rp->enable_discovery(); // now enable ("weak") refs discovery
3432 _collectorState = Marking;
3433 }
3434 SpecializationStats::print();
3435 }
3436
3437 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3438 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3439 assert(_collectorState == InitialMarking, "just checking");
3440
3441 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3442 // precede our marking with a collection of all
3443 // younger generations to keep floating garbage to a minimum.
3444 // XXX: we won't do this for now -- it's an optimization to be done later.
3445
3446 // already have locks
3447 assert_lock_strong(bitMapLock());
3448 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3449
3450 // Setup the verification and class unloading state for this
3451 // CMS collection cycle.
3452 setup_cms_unloading_and_verification_state();
3453
3454 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3455 PrintGCDetails && Verbose, true, gclog_or_tty);)
3456 if (UseAdaptiveSizePolicy) {
3457 size_policy()->checkpoint_roots_initial_begin();
3458 }
3459
3460 // Reset all the PLAB chunk arrays if necessary.
3461 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3462 reset_survivor_plab_arrays();
3463 }
3464
3465 ResourceMark rm;
3466 HandleMark hm;
3467
3468 FalseClosure falseClosure;
3469 // In the case of a synchronous collection, we will elide the
3470 // remark step, so it's important to catch all the nmethod oops
3471 // in this step; hence the last argument to the constrcutor below.
3472 MarkRefsIntoClosure notOlder(_span, &_markBitMap, !asynch /* nmethods */);
3473 GenCollectedHeap* gch = GenCollectedHeap::heap();
3474
3475 verify_work_stacks_empty();
3476 verify_overflow_empty();
3477
3478 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3479 // Update the saved marks which may affect the root scans.
3480 gch->save_marks();
3481
3482 // weak reference processing has not started yet.
3483 ref_processor()->set_enqueuing_is_done(false);
3484
3485 {
3486 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3487 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3488 gch->gen_process_strong_roots(_cmsGen->level(),
3489 true, // younger gens are roots
3490 true, // collecting perm gen
3491 SharedHeap::ScanningOption(roots_scanning_options()),
3492 NULL, ¬Older);
3493 }
3494
3495 // Clear mod-union table; it will be dirtied in the prologue of
3496 // CMS generation per each younger generation collection.
3497
3498 assert(_modUnionTable.isAllClear(),
3499 "Was cleared in most recent final checkpoint phase"
3500 " or no bits are set in the gc_prologue before the start of the next "
3501 "subsequent marking phase.");
3502
3503 // Temporarily disabled, since pre/post-consumption closures don't
3504 // care about precleaned cards
3505 #if 0
3506 {
3507 MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(),
3508 (HeapWord*)_virtual_space.high());
3509 _ct->ct_bs()->preclean_dirty_cards(mr);
3510 }
3511 #endif
3512
3513 // Save the end of the used_region of the constituent generations
3514 // to be used to limit the extent of sweep in each generation.
3515 save_sweep_limits();
3516 if (UseAdaptiveSizePolicy) {
3517 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3518 }
3519 verify_overflow_empty();
3520 }
3521
3522 bool CMSCollector::markFromRoots(bool asynch) {
3523 // we might be tempted to assert that:
3524 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3525 // "inconsistent argument?");
3526 // However that wouldn't be right, because it's possible that
3527 // a safepoint is indeed in progress as a younger generation
3528 // stop-the-world GC happens even as we mark in this generation.
3529 assert(_collectorState == Marking, "inconsistent state?");
3530 check_correct_thread_executing();
3531 verify_overflow_empty();
3532
3533 bool res;
3534 if (asynch) {
3535
3536 // Start the timers for adaptive size policy for the concurrent phases
3537 // Do it here so that the foreground MS can use the concurrent
3538 // timer since a foreground MS might has the sweep done concurrently
3539 // or STW.
3540 if (UseAdaptiveSizePolicy) {
3541 size_policy()->concurrent_marking_begin();
3542 }
3543
3544 // Weak ref discovery note: We may be discovering weak
3545 // refs in this generation concurrent (but interleaved) with
3546 // weak ref discovery by a younger generation collector.
3547
3548 CMSTokenSyncWithLocks ts(true, bitMapLock());
3549 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3550 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3551 res = markFromRootsWork(asynch);
3552 if (res) {
3553 _collectorState = Precleaning;
3554 } else { // We failed and a foreground collection wants to take over
3555 assert(_foregroundGCIsActive, "internal state inconsistency");
3556 assert(_restart_addr == NULL, "foreground will restart from scratch");
3557 if (PrintGCDetails) {
3558 gclog_or_tty->print_cr("bailing out to foreground collection");
3559 }
3560 }
3561 if (UseAdaptiveSizePolicy) {
3562 size_policy()->concurrent_marking_end();
3563 }
3564 } else {
3565 assert(SafepointSynchronize::is_at_safepoint(),
3566 "inconsistent with asynch == false");
3567 if (UseAdaptiveSizePolicy) {
3568 size_policy()->ms_collection_marking_begin();
3569 }
3570 // already have locks
3571 res = markFromRootsWork(asynch);
3572 _collectorState = FinalMarking;
3573 if (UseAdaptiveSizePolicy) {
3574 GenCollectedHeap* gch = GenCollectedHeap::heap();
3575 size_policy()->ms_collection_marking_end(gch->gc_cause());
3576 }
3577 }
3578 verify_overflow_empty();
3579 return res;
3580 }
3581
3582 bool CMSCollector::markFromRootsWork(bool asynch) {
3583 // iterate over marked bits in bit map, doing a full scan and mark
3584 // from these roots using the following algorithm:
3585 // . if oop is to the right of the current scan pointer,
3586 // mark corresponding bit (we'll process it later)
3587 // . else (oop is to left of current scan pointer)
3588 // push oop on marking stack
3589 // . drain the marking stack
3590
3591 // Note that when we do a marking step we need to hold the
3592 // bit map lock -- recall that direct allocation (by mutators)
3593 // and promotion (by younger generation collectors) is also
3594 // marking the bit map. [the so-called allocate live policy.]
3595 // Because the implementation of bit map marking is not
3596 // robust wrt simultaneous marking of bits in the same word,
3597 // we need to make sure that there is no such interference
3598 // between concurrent such updates.
3599
3600 // already have locks
3601 assert_lock_strong(bitMapLock());
3602
3603 // Clear the revisit stack, just in case there are any
3604 // obsolete contents from a short-circuited previous CMS cycle.
3605 _revisitStack.reset();
3606 verify_work_stacks_empty();
3607 verify_overflow_empty();
3608 assert(_revisitStack.isEmpty(), "tabula rasa");
3609
3610 bool result = false;
3611 if (CMSConcurrentMTEnabled && ParallelCMSThreads > 0) {
3612 result = do_marking_mt(asynch);
3613 } else {
3614 result = do_marking_st(asynch);
3615 }
3616 return result;
3617 }
3618
3619 // Forward decl
3620 class CMSConcMarkingTask;
3621
3622 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3623 CMSCollector* _collector;
3624 CMSConcMarkingTask* _task;
3625 bool _yield;
3626 protected:
3627 virtual void yield();
3628 public:
3629 // "n_threads" is the number of threads to be terminated.
3630 // "queue_set" is a set of work queues of other threads.
3631 // "collector" is the CMS collector associated with this task terminator.
3632 // "yield" indicates whether we need the gang as a whole to yield.
3633 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set,
3634 CMSCollector* collector, bool yield) :
3635 ParallelTaskTerminator(n_threads, queue_set),
3636 _collector(collector),
3637 _yield(yield) { }
3638
3639 void set_task(CMSConcMarkingTask* task) {
3640 _task = task;
3641 }
3642 };
3643
3644 // MT Concurrent Marking Task
3645 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3646 CMSCollector* _collector;
3647 YieldingFlexibleWorkGang* _workers; // the whole gang
3648 int _n_workers; // requested/desired # workers
3649 bool _asynch;
3650 bool _result;
3651 CompactibleFreeListSpace* _cms_space;
3652 CompactibleFreeListSpace* _perm_space;
3653 HeapWord* _global_finger;
3654 HeapWord* _restart_addr;
3655
3656 // Exposed here for yielding support
3657 Mutex* const _bit_map_lock;
3658
3659 // The per thread work queues, available here for stealing
3660 OopTaskQueueSet* _task_queues;
3661 CMSConcMarkingTerminator _term;
3662
3663 public:
3664 CMSConcMarkingTask(CMSCollector* collector,
3665 CompactibleFreeListSpace* cms_space,
3666 CompactibleFreeListSpace* perm_space,
3667 bool asynch, int n_workers,
3668 YieldingFlexibleWorkGang* workers,
3669 OopTaskQueueSet* task_queues):
3670 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3671 _collector(collector),
3672 _cms_space(cms_space),
3673 _perm_space(perm_space),
3674 _asynch(asynch), _n_workers(n_workers), _result(true),
3675 _workers(workers), _task_queues(task_queues),
3676 _term(n_workers, task_queues, _collector, asynch),
3677 _bit_map_lock(collector->bitMapLock())
3678 {
3679 assert(n_workers <= workers->total_workers(),
3680 "Else termination won't work correctly today"); // XXX FIX ME!
3681 _requested_size = n_workers;
3682 _term.set_task(this);
3683 assert(_cms_space->bottom() < _perm_space->bottom(),
3684 "Finger incorrectly initialized below");
3685 _restart_addr = _global_finger = _cms_space->bottom();
3686 }
3687
3688
3689 OopTaskQueueSet* task_queues() { return _task_queues; }
3690
3691 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3692
3693 HeapWord** global_finger_addr() { return &_global_finger; }
3694
3695 CMSConcMarkingTerminator* terminator() { return &_term; }
3696
3697 void work(int i);
3698
3699 virtual void coordinator_yield(); // stuff done by coordinator
3700 bool result() { return _result; }
3701
3702 void reset(HeapWord* ra) {
3703 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3704 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3705 assert(ra < _perm_space->end(), "ra too large");
3706 _restart_addr = _global_finger = ra;
3707 _term.reset_for_reuse();
3708 }
3709
3710 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3711 OopTaskQueue* work_q);
3712
3713 private:
3714 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3715 void do_work_steal(int i);
3716 void bump_global_finger(HeapWord* f);
3717 };
3718
3719 void CMSConcMarkingTerminator::yield() {
3720 if (ConcurrentMarkSweepThread::should_yield() &&
3721 !_collector->foregroundGCIsActive() &&
3722 _yield) {
3723 _task->yield();
3724 } else {
3725 ParallelTaskTerminator::yield();
3726 }
3727 }
3728
3729 ////////////////////////////////////////////////////////////////
3730 // Concurrent Marking Algorithm Sketch
3731 ////////////////////////////////////////////////////////////////
3732 // Until all tasks exhausted (both spaces):
3733 // -- claim next available chunk
3734 // -- bump global finger via CAS
3735 // -- find first object that starts in this chunk
3736 // and start scanning bitmap from that position
3737 // -- scan marked objects for oops
3738 // -- CAS-mark target, and if successful:
3739 // . if target oop is above global finger (volatile read)
3740 // nothing to do
3741 // . if target oop is in chunk and above local finger
3742 // then nothing to do
3743 // . else push on work-queue
3744 // -- Deal with possible overflow issues:
3745 // . local work-queue overflow causes stuff to be pushed on
3746 // global (common) overflow queue
3747 // . always first empty local work queue
3748 // . then get a batch of oops from global work queue if any
3749 // . then do work stealing
3750 // -- When all tasks claimed (both spaces)
3751 // and local work queue empty,
3752 // then in a loop do:
3753 // . check global overflow stack; steal a batch of oops and trace
3754 // . try to steal from other threads oif GOS is empty
3755 // . if neither is available, offer termination
3756 // -- Terminate and return result
3757 //
3758 void CMSConcMarkingTask::work(int i) {
3759 elapsedTimer _timer;
3760 ResourceMark rm;
3761 HandleMark hm;
3762
3763 DEBUG_ONLY(_collector->verify_overflow_empty();)
3764
3765 // Before we begin work, our work queue should be empty
3766 assert(work_queue(i)->size() == 0, "Expected to be empty");
3767 // Scan the bitmap covering _cms_space, tracing through grey objects.
3768 _timer.start();
3769 do_scan_and_mark(i, _cms_space);
3770 _timer.stop();
3771 if (PrintCMSStatistics != 0) {
3772 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3773 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3774 }
3775
3776 // ... do the same for the _perm_space
3777 _timer.reset();
3778 _timer.start();
3779 do_scan_and_mark(i, _perm_space);
3780 _timer.stop();
3781 if (PrintCMSStatistics != 0) {
3782 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3783 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3784 }
3785
3786 // ... do work stealing
3787 _timer.reset();
3788 _timer.start();
3789 do_work_steal(i);
3790 _timer.stop();
3791 if (PrintCMSStatistics != 0) {
3792 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3793 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3794 }
3795 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3796 assert(work_queue(i)->size() == 0, "Should have been emptied");
3797 // Note that under the current task protocol, the
3798 // following assertion is true even of the spaces
3799 // expanded since the completion of the concurrent
3800 // marking. XXX This will likely change under a strict
3801 // ABORT semantics.
3802 assert(_global_finger > _cms_space->end() &&
3803 _global_finger >= _perm_space->end(),
3804 "All tasks have been completed");
3805 DEBUG_ONLY(_collector->verify_overflow_empty();)
3806 }
3807
3808 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3809 HeapWord* read = _global_finger;
3810 HeapWord* cur = read;
3811 while (f > read) {
3812 cur = read;
3813 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3814 if (cur == read) {
3815 // our cas succeeded
3816 assert(_global_finger >= f, "protocol consistency");
3817 break;
3818 }
3819 }
3820 }
3821
3822 // This is really inefficient, and should be redone by
3823 // using (not yet available) block-read and -write interfaces to the
3824 // stack and the work_queue. XXX FIX ME !!!
3825 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3826 OopTaskQueue* work_q) {
3827 // Fast lock-free check
3828 if (ovflw_stk->length() == 0) {
3829 return false;
3830 }
3831 assert(work_q->size() == 0, "Shouldn't steal");
3832 MutexLockerEx ml(ovflw_stk->par_lock(),
3833 Mutex::_no_safepoint_check_flag);
3834 // Grab up to 1/4 the size of the work queue
3835 size_t num = MIN2((size_t)work_q->max_elems()/4,
3836 (size_t)ParGCDesiredObjsFromOverflowList);
3837 num = MIN2(num, ovflw_stk->length());
3838 for (int i = (int) num; i > 0; i--) {
3839 oop cur = ovflw_stk->pop();
3840 assert(cur != NULL, "Counted wrong?");
3841 work_q->push(cur);
3842 }
3843 return num > 0;
3844 }
3845
3846 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3847 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3848 int n_tasks = pst->n_tasks();
3849 // We allow that there may be no tasks to do here because
3850 // we are restarting after a stack overflow.
3851 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3852 int nth_task = 0;
3853
3854 HeapWord* aligned_start = sp->bottom();
3855 if (sp->used_region().contains(_restart_addr)) {
3856 // Align down to a card boundary for the start of 0th task
3857 // for this space.
3858 aligned_start =
3859 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3860 CardTableModRefBS::card_size);
3861 }
3862
3863 size_t chunk_size = sp->marking_task_size();
3864 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3865 // Having claimed the nth task in this space,
3866 // compute the chunk that it corresponds to:
3867 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3868 aligned_start + (nth_task+1)*chunk_size);
3869 // Try and bump the global finger via a CAS;
3870 // note that we need to do the global finger bump
3871 // _before_ taking the intersection below, because
3872 // the task corresponding to that region will be
3873 // deemed done even if the used_region() expands
3874 // because of allocation -- as it almost certainly will
3875 // during start-up while the threads yield in the
3876 // closure below.
3877 HeapWord* finger = span.end();
3878 bump_global_finger(finger); // atomically
3879 // There are null tasks here corresponding to chunks
3880 // beyond the "top" address of the space.
3881 span = span.intersection(sp->used_region());
3882 if (!span.is_empty()) { // Non-null task
3883 HeapWord* prev_obj;
3884 assert(!span.contains(_restart_addr) || nth_task == 0,
3885 "Inconsistency");
3886 if (nth_task == 0) {
3887 // For the 0th task, we'll not need to compute a block_start.
3888 if (span.contains(_restart_addr)) {
3889 // In the case of a restart because of stack overflow,
3890 // we might additionally skip a chunk prefix.
3891 prev_obj = _restart_addr;
3892 } else {
3893 prev_obj = span.start();
3894 }
3895 } else {
3896 // We want to skip the first object because
3897 // the protocol is to scan any object in its entirety
3898 // that _starts_ in this span; a fortiori, any
3899 // object starting in an earlier span is scanned
3900 // as part of an earlier claimed task.
3901 // Below we use the "careful" version of block_start
3902 // so we do not try to navigate uninitialized objects.
3903 prev_obj = sp->block_start_careful(span.start());
3904 // Below we use a variant of block_size that uses the
3905 // Printezis bits to avoid waiting for allocated
3906 // objects to become initialized/parsable.
3907 while (prev_obj < span.start()) {
3908 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3909 if (sz > 0) {
3910 prev_obj += sz;
3911 } else {
3912 // In this case we may end up doing a bit of redundant
3913 // scanning, but that appears unavoidable, short of
3914 // locking the free list locks; see bug 6324141.
3915 break;
3916 }
3917 }
3918 }
3919 if (prev_obj < span.end()) {
3920 MemRegion my_span = MemRegion(prev_obj, span.end());
3921 // Do the marking work within a non-empty span --
3922 // the last argument to the constructor indicates whether the
3923 // iteration should be incremental with periodic yields.
3924 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3925 &_collector->_markBitMap,
3926 work_queue(i),
3927 &_collector->_markStack,
3928 &_collector->_revisitStack,
3929 _asynch);
3930 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3931 } // else nothing to do for this task
3932 } // else nothing to do for this task
3933 }
3934 // We'd be tempted to assert here that since there are no
3935 // more tasks left to claim in this space, the global_finger
3936 // must exceed space->top() and a fortiori space->end(). However,
3937 // that would not quite be correct because the bumping of
3938 // global_finger occurs strictly after the claiming of a task,
3939 // so by the time we reach here the global finger may not yet
3940 // have been bumped up by the thread that claimed the last
3941 // task.
3942 pst->all_tasks_completed();
3943 }
3944
3945 class Par_ConcMarkingClosure: public OopClosure {
3946 private:
3947 CMSCollector* _collector;
3948 MemRegion _span;
3949 CMSBitMap* _bit_map;
3950 CMSMarkStack* _overflow_stack;
3951 CMSMarkStack* _revisit_stack; // XXXXXX Check proper use
3952 OopTaskQueue* _work_queue;
3953 protected:
3954 DO_OOP_WORK_DEFN
3955 public:
3956 Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue,
3957 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3958 _collector(collector),
3959 _span(_collector->_span),
3960 _work_queue(work_queue),
3961 _bit_map(bit_map),
3962 _overflow_stack(overflow_stack) { } // need to initialize revisit stack etc.
3963 virtual void do_oop(oop* p);
3964 virtual void do_oop(narrowOop* p);
3965 void trim_queue(size_t max);
3966 void handle_stack_overflow(HeapWord* lost);
3967 };
3968
3969 // Grey object scanning during work stealing phase --
3970 // the salient assumption here is that any references
3971 // that are in these stolen objects being scanned must
3972 // already have been initialized (else they would not have
3973 // been published), so we do not need to check for
3974 // uninitialized objects before pushing here.
3975 void Par_ConcMarkingClosure::do_oop(oop obj) {
3976 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
3977 HeapWord* addr = (HeapWord*)obj;
3978 // Check if oop points into the CMS generation
3979 // and is not marked
3980 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3981 // a white object ...
3982 // If we manage to "claim" the object, by being the
3983 // first thread to mark it, then we push it on our
3984 // marking stack
3985 if (_bit_map->par_mark(addr)) { // ... now grey
3986 // push on work queue (grey set)
3987 bool simulate_overflow = false;
3988 NOT_PRODUCT(
3989 if (CMSMarkStackOverflowALot &&
3990 _collector->simulate_overflow()) {
3991 // simulate a stack overflow
3992 simulate_overflow = true;
3993 }
3994 )
3995 if (simulate_overflow ||
3996 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3997 // stack overflow
3998 if (PrintCMSStatistics != 0) {
3999 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4000 SIZE_FORMAT, _overflow_stack->capacity());
4001 }
4002 // We cannot assert that the overflow stack is full because
4003 // it may have been emptied since.
4004 assert(simulate_overflow ||
4005 _work_queue->size() == _work_queue->max_elems(),
4006 "Else push should have succeeded");
4007 handle_stack_overflow(addr);
4008 }
4009 } // Else, some other thread got there first
4010 }
4011 }
4012
4013 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4014 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4015
4016 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4017 while (_work_queue->size() > max) {
4018 oop new_oop;
4019 if (_work_queue->pop_local(new_oop)) {
4020 assert(new_oop->is_oop(), "Should be an oop");
4021 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4022 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4023 assert(new_oop->is_parsable(), "Should be parsable");
4024 new_oop->oop_iterate(this); // do_oop() above
4025 }
4026 }
4027 }
4028
4029 // Upon stack overflow, we discard (part of) the stack,
4030 // remembering the least address amongst those discarded
4031 // in CMSCollector's _restart_address.
4032 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4033 // We need to do this under a mutex to prevent other
4034 // workers from interfering with the work done below.
4035 MutexLockerEx ml(_overflow_stack->par_lock(),
4036 Mutex::_no_safepoint_check_flag);
4037 // Remember the least grey address discarded
4038 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4039 _collector->lower_restart_addr(ra);
4040 _overflow_stack->reset(); // discard stack contents
4041 _overflow_stack->expand(); // expand the stack if possible
4042 }
4043
4044
4045 void CMSConcMarkingTask::do_work_steal(int i) {
4046 OopTaskQueue* work_q = work_queue(i);
4047 oop obj_to_scan;
4048 CMSBitMap* bm = &(_collector->_markBitMap);
4049 CMSMarkStack* ovflw = &(_collector->_markStack);
4050 int* seed = _collector->hash_seed(i);
4051 Par_ConcMarkingClosure cl(_collector, work_q, bm, ovflw);
4052 while (true) {
4053 cl.trim_queue(0);
4054 assert(work_q->size() == 0, "Should have been emptied above");
4055 if (get_work_from_overflow_stack(ovflw, work_q)) {
4056 // Can't assert below because the work obtained from the
4057 // overflow stack may already have been stolen from us.
4058 // assert(work_q->size() > 0, "Work from overflow stack");
4059 continue;
4060 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4061 assert(obj_to_scan->is_oop(), "Should be an oop");
4062 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4063 obj_to_scan->oop_iterate(&cl);
4064 } else if (terminator()->offer_termination()) {
4065 assert(work_q->size() == 0, "Impossible!");
4066 break;
4067 }
4068 }
4069 }
4070
4071 // This is run by the CMS (coordinator) thread.
4072 void CMSConcMarkingTask::coordinator_yield() {
4073 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4074 "CMS thread should hold CMS token");
4075
4076 // First give up the locks, then yield, then re-lock
4077 // We should probably use a constructor/destructor idiom to
4078 // do this unlock/lock or modify the MutexUnlocker class to
4079 // serve our purpose. XXX
4080 assert_lock_strong(_bit_map_lock);
4081 _bit_map_lock->unlock();
4082 ConcurrentMarkSweepThread::desynchronize(true);
4083 ConcurrentMarkSweepThread::acknowledge_yield_request();
4084 _collector->stopTimer();
4085 if (PrintCMSStatistics != 0) {
4086 _collector->incrementYields();
4087 }
4088 _collector->icms_wait();
4089
4090 // It is possible for whichever thread initiated the yield request
4091 // not to get a chance to wake up and take the bitmap lock between
4092 // this thread releasing it and reacquiring it. So, while the
4093 // should_yield() flag is on, let's sleep for a bit to give the
4094 // other thread a chance to wake up. The limit imposed on the number
4095 // of iterations is defensive, to avoid any unforseen circumstances
4096 // putting us into an infinite loop. Since it's always been this
4097 // (coordinator_yield()) method that was observed to cause the
4098 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4099 // which is by default non-zero. For the other seven methods that
4100 // also perform the yield operation, as are using a different
4101 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4102 // can enable the sleeping for those methods too, if necessary.
4103 // See 6442774.
4104 //
4105 // We really need to reconsider the synchronization between the GC
4106 // thread and the yield-requesting threads in the future and we
4107 // should really use wait/notify, which is the recommended
4108 // way of doing this type of interaction. Additionally, we should
4109 // consolidate the eight methods that do the yield operation and they
4110 // are almost identical into one for better maintenability and
4111 // readability. See 6445193.
4112 //
4113 // Tony 2006.06.29
4114 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4115 ConcurrentMarkSweepThread::should_yield() &&
4116 !CMSCollector::foregroundGCIsActive(); ++i) {
4117 os::sleep(Thread::current(), 1, false);
4118 ConcurrentMarkSweepThread::acknowledge_yield_request();
4119 }
4120
4121 ConcurrentMarkSweepThread::synchronize(true);
4122 _bit_map_lock->lock_without_safepoint_check();
4123 _collector->startTimer();
4124 }
4125
4126 bool CMSCollector::do_marking_mt(bool asynch) {
4127 assert(ParallelCMSThreads > 0 && conc_workers() != NULL, "precondition");
4128 // In the future this would be determined ergonomically, based
4129 // on #cpu's, # active mutator threads (and load), and mutation rate.
4130 int num_workers = ParallelCMSThreads;
4131
4132 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4133 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4134
4135 CMSConcMarkingTask tsk(this, cms_space, perm_space,
4136 asynch, num_workers /* number requested XXX */,
4137 conc_workers(), task_queues());
4138
4139 // Since the actual number of workers we get may be different
4140 // from the number we requested above, do we need to do anything different
4141 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4142 // class?? XXX
4143 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4144 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4145
4146 // Refs discovery is already non-atomic.
4147 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4148 // Mutate the Refs discovery so it is MT during the
4149 // multi-threaded marking phase.
4150 ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1);
4151
4152 conc_workers()->start_task(&tsk);
4153 while (tsk.yielded()) {
4154 tsk.coordinator_yield();
4155 conc_workers()->continue_task(&tsk);
4156 }
4157 // If the task was aborted, _restart_addr will be non-NULL
4158 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4159 while (_restart_addr != NULL) {
4160 // XXX For now we do not make use of ABORTED state and have not
4161 // yet implemented the right abort semantics (even in the original
4162 // single-threaded CMS case). That needs some more investigation
4163 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4164 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4165 // If _restart_addr is non-NULL, a marking stack overflow
4166 // occured; we need to do a fresh marking iteration from the
4167 // indicated restart address.
4168 if (_foregroundGCIsActive && asynch) {
4169 // We may be running into repeated stack overflows, having
4170 // reached the limit of the stack size, while making very
4171 // slow forward progress. It may be best to bail out and
4172 // let the foreground collector do its job.
4173 // Clear _restart_addr, so that foreground GC
4174 // works from scratch. This avoids the headache of
4175 // a "rescan" which would otherwise be needed because
4176 // of the dirty mod union table & card table.
4177 _restart_addr = NULL;
4178 return false;
4179 }
4180 // Adjust the task to restart from _restart_addr
4181 tsk.reset(_restart_addr);
4182 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4183 _restart_addr);
4184 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4185 _restart_addr);
4186 _restart_addr = NULL;
4187 // Get the workers going again
4188 conc_workers()->start_task(&tsk);
4189 while (tsk.yielded()) {
4190 tsk.coordinator_yield();
4191 conc_workers()->continue_task(&tsk);
4192 }
4193 }
4194 assert(tsk.completed(), "Inconsistency");
4195 assert(tsk.result() == true, "Inconsistency");
4196 return true;
4197 }
4198
4199 bool CMSCollector::do_marking_st(bool asynch) {
4200 ResourceMark rm;
4201 HandleMark hm;
4202
4203 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4204 &_markStack, &_revisitStack, CMSYield && asynch);
4205 // the last argument to iterate indicates whether the iteration
4206 // should be incremental with periodic yields.
4207 _markBitMap.iterate(&markFromRootsClosure);
4208 // If _restart_addr is non-NULL, a marking stack overflow
4209 // occured; we need to do a fresh iteration from the
4210 // indicated restart address.
4211 while (_restart_addr != NULL) {
4212 if (_foregroundGCIsActive && asynch) {
4213 // We may be running into repeated stack overflows, having
4214 // reached the limit of the stack size, while making very
4215 // slow forward progress. It may be best to bail out and
4216 // let the foreground collector do its job.
4217 // Clear _restart_addr, so that foreground GC
4218 // works from scratch. This avoids the headache of
4219 // a "rescan" which would otherwise be needed because
4220 // of the dirty mod union table & card table.
4221 _restart_addr = NULL;
4222 return false; // indicating failure to complete marking
4223 }
4224 // Deal with stack overflow:
4225 // we restart marking from _restart_addr
4226 HeapWord* ra = _restart_addr;
4227 markFromRootsClosure.reset(ra);
4228 _restart_addr = NULL;
4229 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4230 }
4231 return true;
4232 }
4233
4234 void CMSCollector::preclean() {
4235 check_correct_thread_executing();
4236 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4237 verify_work_stacks_empty();
4238 verify_overflow_empty();
4239 _abort_preclean = false;
4240 if (CMSPrecleaningEnabled) {
4241 _eden_chunk_index = 0;
4242 size_t used = get_eden_used();
4243 size_t capacity = get_eden_capacity();
4244 // Don't start sampling unless we will get sufficiently
4245 // many samples.
4246 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4247 * CMSScheduleRemarkEdenPenetration)) {
4248 _start_sampling = true;
4249 } else {
4250 _start_sampling = false;
4251 }
4252 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4253 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4254 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4255 }
4256 CMSTokenSync x(true); // is cms thread
4257 if (CMSPrecleaningEnabled) {
4258 sample_eden();
4259 _collectorState = AbortablePreclean;
4260 } else {
4261 _collectorState = FinalMarking;
4262 }
4263 verify_work_stacks_empty();
4264 verify_overflow_empty();
4265 }
4266
4267 // Try and schedule the remark such that young gen
4268 // occupancy is CMSScheduleRemarkEdenPenetration %.
4269 void CMSCollector::abortable_preclean() {
4270 check_correct_thread_executing();
4271 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4272 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4273
4274 // If Eden's current occupancy is below this threshold,
4275 // immediately schedule the remark; else preclean
4276 // past the next scavenge in an effort to
4277 // schedule the pause as described avove. By choosing
4278 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4279 // we will never do an actual abortable preclean cycle.
4280 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4281 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4282 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4283 // We need more smarts in the abortable preclean
4284 // loop below to deal with cases where allocation
4285 // in young gen is very very slow, and our precleaning
4286 // is running a losing race against a horde of
4287 // mutators intent on flooding us with CMS updates
4288 // (dirty cards).
4289 // One, admittedly dumb, strategy is to give up
4290 // after a certain number of abortable precleaning loops
4291 // or after a certain maximum time. We want to make
4292 // this smarter in the next iteration.
4293 // XXX FIX ME!!! YSR
4294 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4295 while (!(should_abort_preclean() ||
4296 ConcurrentMarkSweepThread::should_terminate())) {
4297 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4298 cumworkdone += workdone;
4299 loops++;
4300 // Voluntarily terminate abortable preclean phase if we have
4301 // been at it for too long.
4302 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4303 loops >= CMSMaxAbortablePrecleanLoops) {
4304 if (PrintGCDetails) {
4305 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4306 }
4307 break;
4308 }
4309 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4310 if (PrintGCDetails) {
4311 gclog_or_tty->print(" CMS: abort preclean due to time ");
4312 }
4313 break;
4314 }
4315 // If we are doing little work each iteration, we should
4316 // take a short break.
4317 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4318 // Sleep for some time, waiting for work to accumulate
4319 stopTimer();
4320 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4321 startTimer();
4322 waited++;
4323 }
4324 }
4325 if (PrintCMSStatistics > 0) {
4326 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4327 loops, waited, cumworkdone);
4328 }
4329 }
4330 CMSTokenSync x(true); // is cms thread
4331 if (_collectorState != Idling) {
4332 assert(_collectorState == AbortablePreclean,
4333 "Spontaneous state transition?");
4334 _collectorState = FinalMarking;
4335 } // Else, a foreground collection completed this CMS cycle.
4336 return;
4337 }
4338
4339 // Respond to an Eden sampling opportunity
4340 void CMSCollector::sample_eden() {
4341 // Make sure a young gc cannot sneak in between our
4342 // reading and recording of a sample.
4343 assert(Thread::current()->is_ConcurrentGC_thread(),
4344 "Only the cms thread may collect Eden samples");
4345 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4346 "Should collect samples while holding CMS token");
4347 if (!_start_sampling) {
4348 return;
4349 }
4350 if (_eden_chunk_array) {
4351 if (_eden_chunk_index < _eden_chunk_capacity) {
4352 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4353 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4354 "Unexpected state of Eden");
4355 // We'd like to check that what we just sampled is an oop-start address;
4356 // however, we cannot do that here since the object may not yet have been
4357 // initialized. So we'll instead do the check when we _use_ this sample
4358 // later.
4359 if (_eden_chunk_index == 0 ||
4360 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4361 _eden_chunk_array[_eden_chunk_index-1])
4362 >= CMSSamplingGrain)) {
4363 _eden_chunk_index++; // commit sample
4364 }
4365 }
4366 }
4367 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4368 size_t used = get_eden_used();
4369 size_t capacity = get_eden_capacity();
4370 assert(used <= capacity, "Unexpected state of Eden");
4371 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4372 _abort_preclean = true;
4373 }
4374 }
4375 }
4376
4377
4378 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4379 assert(_collectorState == Precleaning ||
4380 _collectorState == AbortablePreclean, "incorrect state");
4381 ResourceMark rm;
4382 HandleMark hm;
4383 // Do one pass of scrubbing the discovered reference lists
4384 // to remove any reference objects with strongly-reachable
4385 // referents.
4386 if (clean_refs) {
4387 ReferenceProcessor* rp = ref_processor();
4388 CMSPrecleanRefsYieldClosure yield_cl(this);
4389 assert(rp->span().equals(_span), "Spans should be equal");
4390 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4391 &_markStack);
4392 CMSDrainMarkingStackClosure complete_trace(this,
4393 _span, &_markBitMap, &_markStack,
4394 &keep_alive);
4395
4396 // We don't want this step to interfere with a young
4397 // collection because we don't want to take CPU
4398 // or memory bandwidth away from the young GC threads
4399 // (which may be as many as there are CPUs).
4400 // Note that we don't need to protect ourselves from
4401 // interference with mutators because they can't
4402 // manipulate the discovered reference lists nor affect
4403 // the computed reachability of the referents, the
4404 // only properties manipulated by the precleaning
4405 // of these reference lists.
4406 stopTimer();
4407 CMSTokenSyncWithLocks x(true /* is cms thread */,
4408 bitMapLock());
4409 startTimer();
4410 sample_eden();
4411 // The following will yield to allow foreground
4412 // collection to proceed promptly. XXX YSR:
4413 // The code in this method may need further
4414 // tweaking for better performance and some restructuring
4415 // for cleaner interfaces.
4416 rp->preclean_discovered_references(
4417 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4418 &yield_cl);
4419 }
4420
4421 if (clean_survivor) { // preclean the active survivor space(s)
4422 assert(_young_gen->kind() == Generation::DefNew ||
4423 _young_gen->kind() == Generation::ParNew ||
4424 _young_gen->kind() == Generation::ASParNew,
4425 "incorrect type for cast");
4426 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4427 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4428 &_markBitMap, &_modUnionTable,
4429 &_markStack, &_revisitStack,
4430 true /* precleaning phase */);
4431 stopTimer();
4432 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4433 bitMapLock());
4434 startTimer();
4435 unsigned int before_count =
4436 GenCollectedHeap::heap()->total_collections();
4437 SurvivorSpacePrecleanClosure
4438 sss_cl(this, _span, &_markBitMap, &_markStack,
4439 &pam_cl, before_count, CMSYield);
4440 dng->from()->object_iterate_careful(&sss_cl);
4441 dng->to()->object_iterate_careful(&sss_cl);
4442 }
4443 MarkRefsIntoAndScanClosure
4444 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4445 &_markStack, &_revisitStack, this, CMSYield,
4446 true /* precleaning phase */);
4447 // CAUTION: The following closure has persistent state that may need to
4448 // be reset upon a decrease in the sequence of addresses it
4449 // processes.
4450 ScanMarkedObjectsAgainCarefullyClosure
4451 smoac_cl(this, _span,
4452 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4453
4454 // Preclean dirty cards in ModUnionTable and CardTable using
4455 // appropriate convergence criterion;
4456 // repeat CMSPrecleanIter times unless we find that
4457 // we are losing.
4458 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4459 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4460 "Bad convergence multiplier");
4461 assert(CMSPrecleanThreshold >= 100,
4462 "Unreasonably low CMSPrecleanThreshold");
4463
4464 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4465 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4466 numIter < CMSPrecleanIter;
4467 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4468 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4469 if (CMSPermGenPrecleaningEnabled) {
4470 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4471 }
4472 if (Verbose && PrintGCDetails) {
4473 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4474 }
4475 // Either there are very few dirty cards, so re-mark
4476 // pause will be small anyway, or our pre-cleaning isn't
4477 // that much faster than the rate at which cards are being
4478 // dirtied, so we might as well stop and re-mark since
4479 // precleaning won't improve our re-mark time by much.
4480 if (curNumCards <= CMSPrecleanThreshold ||
4481 (numIter > 0 &&
4482 (curNumCards * CMSPrecleanDenominator >
4483 lastNumCards * CMSPrecleanNumerator))) {
4484 numIter++;
4485 cumNumCards += curNumCards;
4486 break;
4487 }
4488 }
4489 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4490 if (CMSPermGenPrecleaningEnabled) {
4491 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4492 }
4493 cumNumCards += curNumCards;
4494 if (PrintGCDetails && PrintCMSStatistics != 0) {
4495 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4496 curNumCards, cumNumCards, numIter);
4497 }
4498 return cumNumCards; // as a measure of useful work done
4499 }
4500
4501 // PRECLEANING NOTES:
4502 // Precleaning involves:
4503 // . reading the bits of the modUnionTable and clearing the set bits.
4504 // . For the cards corresponding to the set bits, we scan the
4505 // objects on those cards. This means we need the free_list_lock
4506 // so that we can safely iterate over the CMS space when scanning
4507 // for oops.
4508 // . When we scan the objects, we'll be both reading and setting
4509 // marks in the marking bit map, so we'll need the marking bit map.
4510 // . For protecting _collector_state transitions, we take the CGC_lock.
4511 // Note that any races in the reading of of card table entries by the
4512 // CMS thread on the one hand and the clearing of those entries by the
4513 // VM thread or the setting of those entries by the mutator threads on the
4514 // other are quite benign. However, for efficiency it makes sense to keep
4515 // the VM thread from racing with the CMS thread while the latter is
4516 // dirty card info to the modUnionTable. We therefore also use the
4517 // CGC_lock to protect the reading of the card table and the mod union
4518 // table by the CM thread.
4519 // . We run concurrently with mutator updates, so scanning
4520 // needs to be done carefully -- we should not try to scan
4521 // potentially uninitialized objects.
4522 //
4523 // Locking strategy: While holding the CGC_lock, we scan over and
4524 // reset a maximal dirty range of the mod union / card tables, then lock
4525 // the free_list_lock and bitmap lock to do a full marking, then
4526 // release these locks; and repeat the cycle. This allows for a
4527 // certain amount of fairness in the sharing of these locks between
4528 // the CMS collector on the one hand, and the VM thread and the
4529 // mutators on the other.
4530
4531 // NOTE: preclean_mod_union_table() and preclean_card_table()
4532 // further below are largely identical; if you need to modify
4533 // one of these methods, please check the other method too.
4534
4535 size_t CMSCollector::preclean_mod_union_table(
4536 ConcurrentMarkSweepGeneration* gen,
4537 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4538 verify_work_stacks_empty();
4539 verify_overflow_empty();
4540
4541 // strategy: starting with the first card, accumulate contiguous
4542 // ranges of dirty cards; clear these cards, then scan the region
4543 // covered by these cards.
4544
4545 // Since all of the MUT is committed ahead, we can just use
4546 // that, in case the generations expand while we are precleaning.
4547 // It might also be fine to just use the committed part of the
4548 // generation, but we might potentially miss cards when the
4549 // generation is rapidly expanding while we are in the midst
4550 // of precleaning.
4551 HeapWord* startAddr = gen->reserved().start();
4552 HeapWord* endAddr = gen->reserved().end();
4553
4554 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4555
4556 size_t numDirtyCards, cumNumDirtyCards;
4557 HeapWord *nextAddr, *lastAddr;
4558 for (cumNumDirtyCards = numDirtyCards = 0,
4559 nextAddr = lastAddr = startAddr;
4560 nextAddr < endAddr;
4561 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4562
4563 ResourceMark rm;
4564 HandleMark hm;
4565
4566 MemRegion dirtyRegion;
4567 {
4568 stopTimer();
4569 CMSTokenSync ts(true);
4570 startTimer();
4571 sample_eden();
4572 // Get dirty region starting at nextOffset (inclusive),
4573 // simultaneously clearing it.
4574 dirtyRegion =
4575 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4576 assert(dirtyRegion.start() >= nextAddr,
4577 "returned region inconsistent?");
4578 }
4579 // Remember where the next search should begin.
4580 // The returned region (if non-empty) is a right open interval,
4581 // so lastOffset is obtained from the right end of that
4582 // interval.
4583 lastAddr = dirtyRegion.end();
4584 // Should do something more transparent and less hacky XXX
4585 numDirtyCards =
4586 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4587
4588 // We'll scan the cards in the dirty region (with periodic
4589 // yields for foreground GC as needed).
4590 if (!dirtyRegion.is_empty()) {
4591 assert(numDirtyCards > 0, "consistency check");
4592 HeapWord* stop_point = NULL;
4593 {
4594 stopTimer();
4595 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4596 bitMapLock());
4597 startTimer();
4598 verify_work_stacks_empty();
4599 verify_overflow_empty();
4600 sample_eden();
4601 stop_point =
4602 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4603 }
4604 if (stop_point != NULL) {
4605 // The careful iteration stopped early either because it found an
4606 // uninitialized object, or because we were in the midst of an
4607 // "abortable preclean", which should now be aborted. Redirty
4608 // the bits corresponding to the partially-scanned or unscanned
4609 // cards. We'll either restart at the next block boundary or
4610 // abort the preclean.
4611 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4612 (_collectorState == AbortablePreclean && should_abort_preclean()),
4613 "Unparsable objects should only be in perm gen.");
4614
4615 stopTimer();
4616 CMSTokenSyncWithLocks ts(true, bitMapLock());
4617 startTimer();
4618 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4619 if (should_abort_preclean()) {
4620 break; // out of preclean loop
4621 } else {
4622 // Compute the next address at which preclean should pick up;
4623 // might need bitMapLock in order to read P-bits.
4624 lastAddr = next_card_start_after_block(stop_point);
4625 }
4626 }
4627 } else {
4628 assert(lastAddr == endAddr, "consistency check");
4629 assert(numDirtyCards == 0, "consistency check");
4630 break;
4631 }
4632 }
4633 verify_work_stacks_empty();
4634 verify_overflow_empty();
4635 return cumNumDirtyCards;
4636 }
4637
4638 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4639 // below are largely identical; if you need to modify
4640 // one of these methods, please check the other method too.
4641
4642 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4643 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4644 // strategy: it's similar to precleamModUnionTable above, in that
4645 // we accumulate contiguous ranges of dirty cards, mark these cards
4646 // precleaned, then scan the region covered by these cards.
4647 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4648 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4649
4650 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4651
4652 size_t numDirtyCards, cumNumDirtyCards;
4653 HeapWord *lastAddr, *nextAddr;
4654
4655 for (cumNumDirtyCards = numDirtyCards = 0,
4656 nextAddr = lastAddr = startAddr;
4657 nextAddr < endAddr;
4658 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4659
4660 ResourceMark rm;
4661 HandleMark hm;
4662
4663 MemRegion dirtyRegion;
4664 {
4665 // See comments in "Precleaning notes" above on why we
4666 // do this locking. XXX Could the locking overheads be
4667 // too high when dirty cards are sparse? [I don't think so.]
4668 stopTimer();
4669 CMSTokenSync x(true); // is cms thread
4670 startTimer();
4671 sample_eden();
4672 // Get and clear dirty region from card table
4673 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4674 MemRegion(nextAddr, endAddr),
4675 true,
4676 CardTableModRefBS::precleaned_card_val());
4677
4678 assert(dirtyRegion.start() >= nextAddr,
4679 "returned region inconsistent?");
4680 }
4681 lastAddr = dirtyRegion.end();
4682 numDirtyCards =
4683 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4684
4685 if (!dirtyRegion.is_empty()) {
4686 stopTimer();
4687 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4688 startTimer();
4689 sample_eden();
4690 verify_work_stacks_empty();
4691 verify_overflow_empty();
4692 HeapWord* stop_point =
4693 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4694 if (stop_point != NULL) {
4695 // The careful iteration stopped early because it found an
4696 // uninitialized object. Redirty the bits corresponding to the
4697 // partially-scanned or unscanned cards, and start again at the
4698 // next block boundary.
4699 assert(CMSPermGenPrecleaningEnabled ||
4700 (_collectorState == AbortablePreclean && should_abort_preclean()),
4701 "Unparsable objects should only be in perm gen.");
4702 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4703 if (should_abort_preclean()) {
4704 break; // out of preclean loop
4705 } else {
4706 // Compute the next address at which preclean should pick up.
4707 lastAddr = next_card_start_after_block(stop_point);
4708 }
4709 }
4710 } else {
4711 break;
4712 }
4713 }
4714 verify_work_stacks_empty();
4715 verify_overflow_empty();
4716 return cumNumDirtyCards;
4717 }
4718
4719 void CMSCollector::checkpointRootsFinal(bool asynch,
4720 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4721 assert(_collectorState == FinalMarking, "incorrect state transition?");
4722 check_correct_thread_executing();
4723 // world is stopped at this checkpoint
4724 assert(SafepointSynchronize::is_at_safepoint(),
4725 "world should be stopped");
4726 verify_work_stacks_empty();
4727 verify_overflow_empty();
4728
4729 SpecializationStats::clear();
4730 if (PrintGCDetails) {
4731 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4732 _young_gen->used() / K,
4733 _young_gen->capacity() / K);
4734 }
4735 if (asynch) {
4736 if (CMSScavengeBeforeRemark) {
4737 GenCollectedHeap* gch = GenCollectedHeap::heap();
4738 // Temporarily set flag to false, GCH->do_collection will
4739 // expect it to be false and set to true
4740 FlagSetting fl(gch->_is_gc_active, false);
4741 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4742 PrintGCDetails && Verbose, true, gclog_or_tty);)
4743 int level = _cmsGen->level() - 1;
4744 if (level >= 0) {
4745 gch->do_collection(true, // full (i.e. force, see below)
4746 false, // !clear_all_soft_refs
4747 0, // size
4748 false, // is_tlab
4749 level // max_level
4750 );
4751 }
4752 }
4753 FreelistLocker x(this);
4754 MutexLockerEx y(bitMapLock(),
4755 Mutex::_no_safepoint_check_flag);
4756 assert(!init_mark_was_synchronous, "but that's impossible!");
4757 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4758 } else {
4759 // already have all the locks
4760 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4761 init_mark_was_synchronous);
4762 }
4763 verify_work_stacks_empty();
4764 verify_overflow_empty();
4765 SpecializationStats::print();
4766 }
4767
4768 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4769 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4770
4771 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4772
4773 assert(haveFreelistLocks(), "must have free list locks");
4774 assert_lock_strong(bitMapLock());
4775
4776 if (UseAdaptiveSizePolicy) {
4777 size_policy()->checkpoint_roots_final_begin();
4778 }
4779
4780 ResourceMark rm;
4781 HandleMark hm;
4782
4783 GenCollectedHeap* gch = GenCollectedHeap::heap();
4784
4785 if (should_unload_classes()) {
4786 CodeCache::gc_prologue();
4787 }
4788 assert(haveFreelistLocks(), "must have free list locks");
4789 assert_lock_strong(bitMapLock());
4790
4791 if (!init_mark_was_synchronous) {
4792 // We might assume that we need not fill TLAB's when
4793 // CMSScavengeBeforeRemark is set, because we may have just done
4794 // a scavenge which would have filled all TLAB's -- and besides
4795 // Eden would be empty. This however may not always be the case --
4796 // for instance although we asked for a scavenge, it may not have
4797 // happened because of a JNI critical section. We probably need
4798 // a policy for deciding whether we can in that case wait until
4799 // the critical section releases and then do the remark following
4800 // the scavenge, and skip it here. In the absence of that policy,
4801 // or of an indication of whether the scavenge did indeed occur,
4802 // we cannot rely on TLAB's having been filled and must do
4803 // so here just in case a scavenge did not happen.
4804 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4805 // Update the saved marks which may affect the root scans.
4806 gch->save_marks();
4807
4808 {
4809 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4810
4811 // Note on the role of the mod union table:
4812 // Since the marker in "markFromRoots" marks concurrently with
4813 // mutators, it is possible for some reachable objects not to have been
4814 // scanned. For instance, an only reference to an object A was
4815 // placed in object B after the marker scanned B. Unless B is rescanned,
4816 // A would be collected. Such updates to references in marked objects
4817 // are detected via the mod union table which is the set of all cards
4818 // dirtied since the first checkpoint in this GC cycle and prior to
4819 // the most recent young generation GC, minus those cleaned up by the
4820 // concurrent precleaning.
4821 if (CMSParallelRemarkEnabled && ParallelGCThreads > 0) {
4822 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4823 do_remark_parallel();
4824 } else {
4825 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4826 gclog_or_tty);
4827 do_remark_non_parallel();
4828 }
4829 }
4830 } else {
4831 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4832 // The initial mark was stop-world, so there's no rescanning to
4833 // do; go straight on to the next step below.
4834 }
4835 verify_work_stacks_empty();
4836 verify_overflow_empty();
4837
4838 {
4839 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4840 refProcessingWork(asynch, clear_all_soft_refs);
4841 }
4842 verify_work_stacks_empty();
4843 verify_overflow_empty();
4844
4845 if (should_unload_classes()) {
4846 CodeCache::gc_epilogue();
4847 }
4848
4849 // If we encountered any (marking stack / work queue) overflow
4850 // events during the current CMS cycle, take appropriate
4851 // remedial measures, where possible, so as to try and avoid
4852 // recurrence of that condition.
4853 assert(_markStack.isEmpty(), "No grey objects");
4854 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4855 _ser_kac_ovflw;
4856 if (ser_ovflw > 0) {
4857 if (PrintCMSStatistics != 0) {
4858 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4859 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4860 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4861 _ser_kac_ovflw);
4862 }
4863 _markStack.expand();
4864 _ser_pmc_remark_ovflw = 0;
4865 _ser_pmc_preclean_ovflw = 0;
4866 _ser_kac_ovflw = 0;
4867 }
4868 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4869 if (PrintCMSStatistics != 0) {
4870 gclog_or_tty->print_cr("Work queue overflow (benign) "
4871 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4872 _par_pmc_remark_ovflw, _par_kac_ovflw);
4873 }
4874 _par_pmc_remark_ovflw = 0;
4875 _par_kac_ovflw = 0;
4876 }
4877 if (PrintCMSStatistics != 0) {
4878 if (_markStack._hit_limit > 0) {
4879 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4880 _markStack._hit_limit);
4881 }
4882 if (_markStack._failed_double > 0) {
4883 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4884 " current capacity "SIZE_FORMAT,
4885 _markStack._failed_double,
4886 _markStack.capacity());
4887 }
4888 }
4889 _markStack._hit_limit = 0;
4890 _markStack._failed_double = 0;
4891
4892 if ((VerifyAfterGC || VerifyDuringGC) &&
4893 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4894 verify_after_remark();
4895 }
4896
4897 // Change under the freelistLocks.
4898 _collectorState = Sweeping;
4899 // Call isAllClear() under bitMapLock
4900 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
4901 " final marking");
4902 if (UseAdaptiveSizePolicy) {
4903 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
4904 }
4905 }
4906
4907 // Parallel remark task
4908 class CMSParRemarkTask: public AbstractGangTask {
4909 CMSCollector* _collector;
4910 WorkGang* _workers;
4911 int _n_workers;
4912 CompactibleFreeListSpace* _cms_space;
4913 CompactibleFreeListSpace* _perm_space;
4914
4915 // The per-thread work queues, available here for stealing.
4916 OopTaskQueueSet* _task_queues;
4917 ParallelTaskTerminator _term;
4918
4919 public:
4920 CMSParRemarkTask(CMSCollector* collector,
4921 CompactibleFreeListSpace* cms_space,
4922 CompactibleFreeListSpace* perm_space,
4923 int n_workers, WorkGang* workers,
4924 OopTaskQueueSet* task_queues):
4925 AbstractGangTask("Rescan roots and grey objects in parallel"),
4926 _collector(collector),
4927 _cms_space(cms_space), _perm_space(perm_space),
4928 _n_workers(n_workers),
4929 _workers(workers),
4930 _task_queues(task_queues),
4931 _term(workers->total_workers(), task_queues) { }
4932
4933 OopTaskQueueSet* task_queues() { return _task_queues; }
4934
4935 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4936
4937 ParallelTaskTerminator* terminator() { return &_term; }
4938
4939 void work(int i);
4940
4941 private:
4942 // Work method in support of parallel rescan ... of young gen spaces
4943 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
4944 ContiguousSpace* space,
4945 HeapWord** chunk_array, size_t chunk_top);
4946
4947 // ... of dirty cards in old space
4948 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4949 Par_MarkRefsIntoAndScanClosure* cl);
4950
4951 // ... work stealing for the above
4952 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4953 };
4954
4955 void CMSParRemarkTask::work(int i) {
4956 elapsedTimer _timer;
4957 ResourceMark rm;
4958 HandleMark hm;
4959
4960 // ---------- rescan from roots --------------
4961 _timer.start();
4962 GenCollectedHeap* gch = GenCollectedHeap::heap();
4963 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4964 _collector->_span, _collector->ref_processor(),
4965 &(_collector->_markBitMap),
4966 work_queue(i), &(_collector->_revisitStack));
4967
4968 // Rescan young gen roots first since these are likely
4969 // coarsely partitioned and may, on that account, constitute
4970 // the critical path; thus, it's best to start off that
4971 // work first.
4972 // ---------- young gen roots --------------
4973 {
4974 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
4975 EdenSpace* eden_space = dng->eden();
4976 ContiguousSpace* from_space = dng->from();
4977 ContiguousSpace* to_space = dng->to();
4978
4979 HeapWord** eca = _collector->_eden_chunk_array;
4980 size_t ect = _collector->_eden_chunk_index;
4981 HeapWord** sca = _collector->_survivor_chunk_array;
4982 size_t sct = _collector->_survivor_chunk_index;
4983
4984 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4985 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4986
4987 do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0);
4988 do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct);
4989 do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect);
4990
4991 _timer.stop();
4992 if (PrintCMSStatistics != 0) {
4993 gclog_or_tty->print_cr(
4994 "Finished young gen rescan work in %dth thread: %3.3f sec",
4995 i, _timer.seconds());
4996 }
4997 }
4998
4999 // ---------- remaining roots --------------
5000 _timer.reset();
5001 _timer.start();
5002 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5003 false, // yg was scanned above
5004 true, // collecting perm gen
5005 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5006 NULL, &par_mrias_cl);
5007 _timer.stop();
5008 if (PrintCMSStatistics != 0) {
5009 gclog_or_tty->print_cr(
5010 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5011 i, _timer.seconds());
5012 }
5013
5014 // ---------- rescan dirty cards ------------
5015 _timer.reset();
5016 _timer.start();
5017
5018 // Do the rescan tasks for each of the two spaces
5019 // (cms_space and perm_space) in turn.
5020 do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl);
5021 do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl);
5022 _timer.stop();
5023 if (PrintCMSStatistics != 0) {
5024 gclog_or_tty->print_cr(
5025 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5026 i, _timer.seconds());
5027 }
5028
5029 // ---------- steal work from other threads ...
5030 // ---------- ... and drain overflow list.
5031 _timer.reset();
5032 _timer.start();
5033 do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i));
5034 _timer.stop();
5035 if (PrintCMSStatistics != 0) {
5036 gclog_or_tty->print_cr(
5037 "Finished work stealing in %dth thread: %3.3f sec",
5038 i, _timer.seconds());
5039 }
5040 }
5041
5042 void
5043 CMSParRemarkTask::do_young_space_rescan(int i,
5044 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5045 HeapWord** chunk_array, size_t chunk_top) {
5046 // Until all tasks completed:
5047 // . claim an unclaimed task
5048 // . compute region boundaries corresponding to task claimed
5049 // using chunk_array
5050 // . par_oop_iterate(cl) over that region
5051
5052 ResourceMark rm;
5053 HandleMark hm;
5054
5055 SequentialSubTasksDone* pst = space->par_seq_tasks();
5056 assert(pst->valid(), "Uninitialized use?");
5057
5058 int nth_task = 0;
5059 int n_tasks = pst->n_tasks();
5060
5061 HeapWord *start, *end;
5062 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5063 // We claimed task # nth_task; compute its boundaries.
5064 if (chunk_top == 0) { // no samples were taken
5065 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5066 start = space->bottom();
5067 end = space->top();
5068 } else if (nth_task == 0) {
5069 start = space->bottom();
5070 end = chunk_array[nth_task];
5071 } else if (nth_task < (jint)chunk_top) {
5072 assert(nth_task >= 1, "Control point invariant");
5073 start = chunk_array[nth_task - 1];
5074 end = chunk_array[nth_task];
5075 } else {
5076 assert(nth_task == (jint)chunk_top, "Control point invariant");
5077 start = chunk_array[chunk_top - 1];
5078 end = space->top();
5079 }
5080 MemRegion mr(start, end);
5081 // Verify that mr is in space
5082 assert(mr.is_empty() || space->used_region().contains(mr),
5083 "Should be in space");
5084 // Verify that "start" is an object boundary
5085 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5086 "Should be an oop");
5087 space->par_oop_iterate(mr, cl);
5088 }
5089 pst->all_tasks_completed();
5090 }
5091
5092 void
5093 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5094 CompactibleFreeListSpace* sp, int i,
5095 Par_MarkRefsIntoAndScanClosure* cl) {
5096 // Until all tasks completed:
5097 // . claim an unclaimed task
5098 // . compute region boundaries corresponding to task claimed
5099 // . transfer dirty bits ct->mut for that region
5100 // . apply rescanclosure to dirty mut bits for that region
5101
5102 ResourceMark rm;
5103 HandleMark hm;
5104
5105 OopTaskQueue* work_q = work_queue(i);
5106 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5107 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5108 // CAUTION: This closure has state that persists across calls to
5109 // the work method dirty_range_iterate_clear() in that it has
5110 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5111 // use of that state in the imbedded UpwardsObjectClosure instance
5112 // assumes that the cards are always iterated (even if in parallel
5113 // by several threads) in monotonically increasing order per each
5114 // thread. This is true of the implementation below which picks
5115 // card ranges (chunks) in monotonically increasing order globally
5116 // and, a-fortiori, in monotonically increasing order per thread
5117 // (the latter order being a subsequence of the former).
5118 // If the work code below is ever reorganized into a more chaotic
5119 // work-partitioning form than the current "sequential tasks"
5120 // paradigm, the use of that persistent state will have to be
5121 // revisited and modified appropriately. See also related
5122 // bug 4756801 work on which should examine this code to make
5123 // sure that the changes there do not run counter to the
5124 // assumptions made here and necessary for correctness and
5125 // efficiency. Note also that this code might yield inefficient
5126 // behaviour in the case of very large objects that span one or
5127 // more work chunks. Such objects would potentially be scanned
5128 // several times redundantly. Work on 4756801 should try and
5129 // address that performance anomaly if at all possible. XXX
5130 MemRegion full_span = _collector->_span;
5131 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5132 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5133 MarkFromDirtyCardsClosure
5134 greyRescanClosure(_collector, full_span, // entire span of interest
5135 sp, bm, work_q, rs, cl);
5136
5137 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5138 assert(pst->valid(), "Uninitialized use?");
5139 int nth_task = 0;
5140 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5141 MemRegion span = sp->used_region();
5142 HeapWord* start_addr = span.start();
5143 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5144 alignment);
5145 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5146 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5147 start_addr, "Check alignment");
5148 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5149 chunk_size, "Check alignment");
5150
5151 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5152 // Having claimed the nth_task, compute corresponding mem-region,
5153 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5154 // The alignment restriction ensures that we do not need any
5155 // synchronization with other gang-workers while setting or
5156 // clearing bits in thus chunk of the MUT.
5157 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5158 start_addr + (nth_task+1)*chunk_size);
5159 // The last chunk's end might be way beyond end of the
5160 // used region. In that case pull back appropriately.
5161 if (this_span.end() > end_addr) {
5162 this_span.set_end(end_addr);
5163 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5164 }
5165 // Iterate over the dirty cards covering this chunk, marking them
5166 // precleaned, and setting the corresponding bits in the mod union
5167 // table. Since we have been careful to partition at Card and MUT-word
5168 // boundaries no synchronization is needed between parallel threads.
5169 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5170 &modUnionClosure);
5171
5172 // Having transferred these marks into the modUnionTable,
5173 // rescan the marked objects on the dirty cards in the modUnionTable.
5174 // Even if this is at a synchronous collection, the initial marking
5175 // may have been done during an asynchronous collection so there
5176 // may be dirty bits in the mod-union table.
5177 _collector->_modUnionTable.dirty_range_iterate_clear(
5178 this_span, &greyRescanClosure);
5179 _collector->_modUnionTable.verifyNoOneBitsInRange(
5180 this_span.start(),
5181 this_span.end());
5182 }
5183 pst->all_tasks_completed(); // declare that i am done
5184 }
5185
5186 // . see if we can share work_queues with ParNew? XXX
5187 void
5188 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5189 int* seed) {
5190 OopTaskQueue* work_q = work_queue(i);
5191 NOT_PRODUCT(int num_steals = 0;)
5192 oop obj_to_scan;
5193 CMSBitMap* bm = &(_collector->_markBitMap);
5194 size_t num_from_overflow_list =
5195 MIN2((size_t)work_q->max_elems()/4,
5196 (size_t)ParGCDesiredObjsFromOverflowList);
5197
5198 while (true) {
5199 // Completely finish any left over work from (an) earlier round(s)
5200 cl->trim_queue(0);
5201 // Now check if there's any work in the overflow list
5202 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5203 work_q)) {
5204 // found something in global overflow list;
5205 // not yet ready to go stealing work from others.
5206 // We'd like to assert(work_q->size() != 0, ...)
5207 // because we just took work from the overflow list,
5208 // but of course we can't since all of that could have
5209 // been already stolen from us.
5210 // "He giveth and He taketh away."
5211 continue;
5212 }
5213 // Verify that we have no work before we resort to stealing
5214 assert(work_q->size() == 0, "Have work, shouldn't steal");
5215 // Try to steal from other queues that have work
5216 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5217 NOT_PRODUCT(num_steals++;)
5218 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5219 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5220 // Do scanning work
5221 obj_to_scan->oop_iterate(cl);
5222 // Loop around, finish this work, and try to steal some more
5223 } else if (terminator()->offer_termination()) {
5224 break; // nirvana from the infinite cycle
5225 }
5226 }
5227 NOT_PRODUCT(
5228 if (PrintCMSStatistics != 0) {
5229 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5230 }
5231 )
5232 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5233 "Else our work is not yet done");
5234 }
5235
5236 // Return a thread-local PLAB recording array, as appropriate.
5237 void* CMSCollector::get_data_recorder(int thr_num) {
5238 if (_survivor_plab_array != NULL &&
5239 (CMSPLABRecordAlways ||
5240 (_collectorState > Marking && _collectorState < FinalMarking))) {
5241 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5242 ChunkArray* ca = &_survivor_plab_array[thr_num];
5243 ca->reset(); // clear it so that fresh data is recorded
5244 return (void*) ca;
5245 } else {
5246 return NULL;
5247 }
5248 }
5249
5250 // Reset all the thread-local PLAB recording arrays
5251 void CMSCollector::reset_survivor_plab_arrays() {
5252 for (uint i = 0; i < ParallelGCThreads; i++) {
5253 _survivor_plab_array[i].reset();
5254 }
5255 }
5256
5257 // Merge the per-thread plab arrays into the global survivor chunk
5258 // array which will provide the partitioning of the survivor space
5259 // for CMS rescan.
5260 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) {
5261 assert(_survivor_plab_array != NULL, "Error");
5262 assert(_survivor_chunk_array != NULL, "Error");
5263 assert(_collectorState == FinalMarking, "Error");
5264 for (uint j = 0; j < ParallelGCThreads; j++) {
5265 _cursor[j] = 0;
5266 }
5267 HeapWord* top = surv->top();
5268 size_t i;
5269 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5270 HeapWord* min_val = top; // Higher than any PLAB address
5271 uint min_tid = 0; // position of min_val this round
5272 for (uint j = 0; j < ParallelGCThreads; j++) {
5273 ChunkArray* cur_sca = &_survivor_plab_array[j];
5274 if (_cursor[j] == cur_sca->end()) {
5275 continue;
5276 }
5277 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5278 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5279 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5280 if (cur_val < min_val) {
5281 min_tid = j;
5282 min_val = cur_val;
5283 } else {
5284 assert(cur_val < top, "All recorded addresses should be less");
5285 }
5286 }
5287 // At this point min_val and min_tid are respectively
5288 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5289 // and the thread (j) that witnesses that address.
5290 // We record this address in the _survivor_chunk_array[i]
5291 // and increment _cursor[min_tid] prior to the next round i.
5292 if (min_val == top) {
5293 break;
5294 }
5295 _survivor_chunk_array[i] = min_val;
5296 _cursor[min_tid]++;
5297 }
5298 // We are all done; record the size of the _survivor_chunk_array
5299 _survivor_chunk_index = i; // exclusive: [0, i)
5300 if (PrintCMSStatistics > 0) {
5301 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5302 }
5303 // Verify that we used up all the recorded entries
5304 #ifdef ASSERT
5305 size_t total = 0;
5306 for (uint j = 0; j < ParallelGCThreads; j++) {
5307 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5308 total += _cursor[j];
5309 }
5310 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5311 // Check that the merged array is in sorted order
5312 if (total > 0) {
5313 for (size_t i = 0; i < total - 1; i++) {
5314 if (PrintCMSStatistics > 0) {
5315 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5316 i, _survivor_chunk_array[i]);
5317 }
5318 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5319 "Not sorted");
5320 }
5321 }
5322 #endif // ASSERT
5323 }
5324
5325 // Set up the space's par_seq_tasks structure for work claiming
5326 // for parallel rescan of young gen.
5327 // See ParRescanTask where this is currently used.
5328 void
5329 CMSCollector::
5330 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5331 assert(n_threads > 0, "Unexpected n_threads argument");
5332 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5333
5334 // Eden space
5335 {
5336 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5337 assert(!pst->valid(), "Clobbering existing data?");
5338 // Each valid entry in [0, _eden_chunk_index) represents a task.
5339 size_t n_tasks = _eden_chunk_index + 1;
5340 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5341 pst->set_par_threads(n_threads);
5342 pst->set_n_tasks((int)n_tasks);
5343 }
5344
5345 // Merge the survivor plab arrays into _survivor_chunk_array
5346 if (_survivor_plab_array != NULL) {
5347 merge_survivor_plab_arrays(dng->from());
5348 } else {
5349 assert(_survivor_chunk_index == 0, "Error");
5350 }
5351
5352 // To space
5353 {
5354 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5355 assert(!pst->valid(), "Clobbering existing data?");
5356 pst->set_par_threads(n_threads);
5357 pst->set_n_tasks(1);
5358 assert(pst->valid(), "Error");
5359 }
5360
5361 // From space
5362 {
5363 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5364 assert(!pst->valid(), "Clobbering existing data?");
5365 size_t n_tasks = _survivor_chunk_index + 1;
5366 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5367 pst->set_par_threads(n_threads);
5368 pst->set_n_tasks((int)n_tasks);
5369 assert(pst->valid(), "Error");
5370 }
5371 }
5372
5373 // Parallel version of remark
5374 void CMSCollector::do_remark_parallel() {
5375 GenCollectedHeap* gch = GenCollectedHeap::heap();
5376 WorkGang* workers = gch->workers();
5377 assert(workers != NULL, "Need parallel worker threads.");
5378 int n_workers = workers->total_workers();
5379 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5380 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5381
5382 CMSParRemarkTask tsk(this,
5383 cms_space, perm_space,
5384 n_workers, workers, task_queues());
5385
5386 // Set up for parallel process_strong_roots work.
5387 gch->set_par_threads(n_workers);
5388 gch->change_strong_roots_parity();
5389 // We won't be iterating over the cards in the card table updating
5390 // the younger_gen cards, so we shouldn't call the following else
5391 // the verification code as well as subsequent younger_refs_iterate
5392 // code would get confused. XXX
5393 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5394
5395 // The young gen rescan work will not be done as part of
5396 // process_strong_roots (which currently doesn't knw how to
5397 // parallelize such a scan), but rather will be broken up into
5398 // a set of parallel tasks (via the sampling that the [abortable]
5399 // preclean phase did of EdenSpace, plus the [two] tasks of
5400 // scanning the [two] survivor spaces. Further fine-grain
5401 // parallelization of the scanning of the survivor spaces
5402 // themselves, and of precleaning of the younger gen itself
5403 // is deferred to the future.
5404 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5405
5406 // The dirty card rescan work is broken up into a "sequence"
5407 // of parallel tasks (per constituent space) that are dynamically
5408 // claimed by the parallel threads.
5409 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5410 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5411
5412 // It turns out that even when we're using 1 thread, doing the work in a
5413 // separate thread causes wide variance in run times. We can't help this
5414 // in the multi-threaded case, but we special-case n=1 here to get
5415 // repeatable measurements of the 1-thread overhead of the parallel code.
5416 if (n_workers > 1) {
5417 // Make refs discovery MT-safe
5418 ReferenceProcessorMTMutator mt(ref_processor(), true);
5419 workers->run_task(&tsk);
5420 } else {
5421 tsk.work(0);
5422 }
5423 gch->set_par_threads(0); // 0 ==> non-parallel.
5424 // restore, single-threaded for now, any preserved marks
5425 // as a result of work_q overflow
5426 restore_preserved_marks_if_any();
5427 }
5428
5429 // Non-parallel version of remark
5430 void CMSCollector::do_remark_non_parallel() {
5431 ResourceMark rm;
5432 HandleMark hm;
5433 GenCollectedHeap* gch = GenCollectedHeap::heap();
5434 MarkRefsIntoAndScanClosure
5435 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5436 &_markStack, &_revisitStack, this,
5437 false /* should_yield */, false /* not precleaning */);
5438 MarkFromDirtyCardsClosure
5439 markFromDirtyCardsClosure(this, _span,
5440 NULL, // space is set further below
5441 &_markBitMap, &_markStack, &_revisitStack,
5442 &mrias_cl);
5443 {
5444 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5445 // Iterate over the dirty cards, setting the corresponding bits in the
5446 // mod union table.
5447 {
5448 ModUnionClosure modUnionClosure(&_modUnionTable);
5449 _ct->ct_bs()->dirty_card_iterate(
5450 _cmsGen->used_region(),
5451 &modUnionClosure);
5452 _ct->ct_bs()->dirty_card_iterate(
5453 _permGen->used_region(),
5454 &modUnionClosure);
5455 }
5456 // Having transferred these marks into the modUnionTable, we just need
5457 // to rescan the marked objects on the dirty cards in the modUnionTable.
5458 // The initial marking may have been done during an asynchronous
5459 // collection so there may be dirty bits in the mod-union table.
5460 const int alignment =
5461 CardTableModRefBS::card_size * BitsPerWord;
5462 {
5463 // ... First handle dirty cards in CMS gen
5464 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5465 MemRegion ur = _cmsGen->used_region();
5466 HeapWord* lb = ur.start();
5467 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5468 MemRegion cms_span(lb, ub);
5469 _modUnionTable.dirty_range_iterate_clear(cms_span,
5470 &markFromDirtyCardsClosure);
5471 verify_work_stacks_empty();
5472 if (PrintCMSStatistics != 0) {
5473 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5474 markFromDirtyCardsClosure.num_dirty_cards());
5475 }
5476 }
5477 {
5478 // .. and then repeat for dirty cards in perm gen
5479 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5480 MemRegion ur = _permGen->used_region();
5481 HeapWord* lb = ur.start();
5482 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5483 MemRegion perm_span(lb, ub);
5484 _modUnionTable.dirty_range_iterate_clear(perm_span,
5485 &markFromDirtyCardsClosure);
5486 verify_work_stacks_empty();
5487 if (PrintCMSStatistics != 0) {
5488 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5489 markFromDirtyCardsClosure.num_dirty_cards());
5490 }
5491 }
5492 }
5493 if (VerifyDuringGC &&
5494 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5495 HandleMark hm; // Discard invalid handles created during verification
5496 Universe::verify(true);
5497 }
5498 {
5499 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5500
5501 verify_work_stacks_empty();
5502
5503 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5504 gch->gen_process_strong_roots(_cmsGen->level(),
5505 true, // younger gens as roots
5506 true, // collecting perm gen
5507 SharedHeap::ScanningOption(roots_scanning_options()),
5508 NULL, &mrias_cl);
5509 }
5510 verify_work_stacks_empty();
5511 // Restore evacuated mark words, if any, used for overflow list links
5512 if (!CMSOverflowEarlyRestoration) {
5513 restore_preserved_marks_if_any();
5514 }
5515 verify_overflow_empty();
5516 }
5517
5518 ////////////////////////////////////////////////////////
5519 // Parallel Reference Processing Task Proxy Class
5520 ////////////////////////////////////////////////////////
5521 class CMSRefProcTaskProxy: public AbstractGangTask {
5522 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5523 CMSCollector* _collector;
5524 CMSBitMap* _mark_bit_map;
5525 const MemRegion _span;
5526 OopTaskQueueSet* _task_queues;
5527 ParallelTaskTerminator _term;
5528 ProcessTask& _task;
5529
5530 public:
5531 CMSRefProcTaskProxy(ProcessTask& task,
5532 CMSCollector* collector,
5533 const MemRegion& span,
5534 CMSBitMap* mark_bit_map,
5535 int total_workers,
5536 OopTaskQueueSet* task_queues):
5537 AbstractGangTask("Process referents by policy in parallel"),
5538 _task(task),
5539 _collector(collector), _span(span), _mark_bit_map(mark_bit_map),
5540 _task_queues(task_queues),
5541 _term(total_workers, task_queues)
5542 {
5543 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5544 "Inconsistency in _span");
5545 }
5546
5547 OopTaskQueueSet* task_queues() { return _task_queues; }
5548
5549 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5550
5551 ParallelTaskTerminator* terminator() { return &_term; }
5552
5553 void do_work_steal(int i,
5554 CMSParDrainMarkingStackClosure* drain,
5555 CMSParKeepAliveClosure* keep_alive,
5556 int* seed);
5557
5558 virtual void work(int i);
5559 };
5560
5561 void CMSRefProcTaskProxy::work(int i) {
5562 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5563 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5564 _mark_bit_map, work_queue(i));
5565 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5566 _mark_bit_map, work_queue(i));
5567 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5568 _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
5569 if (_task.marks_oops_alive()) {
5570 do_work_steal(i, &par_drain_stack, &par_keep_alive,
5571 _collector->hash_seed(i));
5572 }
5573 assert(work_queue(i)->size() == 0, "work_queue should be empty");
5574 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5575 }
5576
5577 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5578 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5579 EnqueueTask& _task;
5580
5581 public:
5582 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5583 : AbstractGangTask("Enqueue reference objects in parallel"),
5584 _task(task)
5585 { }
5586
5587 virtual void work(int i)
5588 {
5589 _task.work(i);
5590 }
5591 };
5592
5593 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5594 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5595 _collector(collector),
5596 _span(span),
5597 _bit_map(bit_map),
5598 _work_queue(work_queue),
5599 _mark_and_push(collector, span, bit_map, work_queue),
5600 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5601 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5602 { }
5603
5604 // . see if we can share work_queues with ParNew? XXX
5605 void CMSRefProcTaskProxy::do_work_steal(int i,
5606 CMSParDrainMarkingStackClosure* drain,
5607 CMSParKeepAliveClosure* keep_alive,
5608 int* seed) {
5609 OopTaskQueue* work_q = work_queue(i);
5610 NOT_PRODUCT(int num_steals = 0;)
5611 oop obj_to_scan;
5612 size_t num_from_overflow_list =
5613 MIN2((size_t)work_q->max_elems()/4,
5614 (size_t)ParGCDesiredObjsFromOverflowList);
5615
5616 while (true) {
5617 // Completely finish any left over work from (an) earlier round(s)
5618 drain->trim_queue(0);
5619 // Now check if there's any work in the overflow list
5620 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5621 work_q)) {
5622 // Found something in global overflow list;
5623 // not yet ready to go stealing work from others.
5624 // We'd like to assert(work_q->size() != 0, ...)
5625 // because we just took work from the overflow list,
5626 // but of course we can't, since all of that might have
5627 // been already stolen from us.
5628 continue;
5629 }
5630 // Verify that we have no work before we resort to stealing
5631 assert(work_q->size() == 0, "Have work, shouldn't steal");
5632 // Try to steal from other queues that have work
5633 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5634 NOT_PRODUCT(num_steals++;)
5635 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5636 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5637 // Do scanning work
5638 obj_to_scan->oop_iterate(keep_alive);
5639 // Loop around, finish this work, and try to steal some more
5640 } else if (terminator()->offer_termination()) {
5641 break; // nirvana from the infinite cycle
5642 }
5643 }
5644 NOT_PRODUCT(
5645 if (PrintCMSStatistics != 0) {
5646 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5647 }
5648 )
5649 }
5650
5651 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5652 {
5653 GenCollectedHeap* gch = GenCollectedHeap::heap();
5654 WorkGang* workers = gch->workers();
5655 assert(workers != NULL, "Need parallel worker threads.");
5656 int n_workers = workers->total_workers();
5657 CMSRefProcTaskProxy rp_task(task, &_collector,
5658 _collector.ref_processor()->span(),
5659 _collector.markBitMap(),
5660 n_workers, _collector.task_queues());
5661 workers->run_task(&rp_task);
5662 }
5663
5664 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5665 {
5666
5667 GenCollectedHeap* gch = GenCollectedHeap::heap();
5668 WorkGang* workers = gch->workers();
5669 assert(workers != NULL, "Need parallel worker threads.");
5670 CMSRefEnqueueTaskProxy enq_task(task);
5671 workers->run_task(&enq_task);
5672 }
5673
5674 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5675
5676 ResourceMark rm;
5677 HandleMark hm;
5678 ReferencePolicy* soft_ref_policy;
5679
5680 assert(!ref_processor()->enqueuing_is_done(), "Enqueuing should not be complete");
5681 // Process weak references.
5682 if (clear_all_soft_refs) {
5683 soft_ref_policy = new AlwaysClearPolicy();
5684 } else {
5685 #ifdef COMPILER2
5686 soft_ref_policy = new LRUMaxHeapPolicy();
5687 #else
5688 soft_ref_policy = new LRUCurrentHeapPolicy();
5689 #endif // COMPILER2
5690 }
5691 verify_work_stacks_empty();
5692
5693 ReferenceProcessor* rp = ref_processor();
5694 assert(rp->span().equals(_span), "Spans should be equal");
5695 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5696 &_markStack);
5697 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5698 _span, &_markBitMap, &_markStack,
5699 &cmsKeepAliveClosure);
5700 {
5701 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5702 if (rp->processing_is_mt()) {
5703 CMSRefProcTaskExecutor task_executor(*this);
5704 rp->process_discovered_references(soft_ref_policy,
5705 &_is_alive_closure,
5706 &cmsKeepAliveClosure,
5707 &cmsDrainMarkingStackClosure,
5708 &task_executor);
5709 } else {
5710 rp->process_discovered_references(soft_ref_policy,
5711 &_is_alive_closure,
5712 &cmsKeepAliveClosure,
5713 &cmsDrainMarkingStackClosure,
5714 NULL);
5715 }
5716 verify_work_stacks_empty();
5717 }
5718
5719 if (should_unload_classes()) {
5720 {
5721 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5722
5723 // Follow SystemDictionary roots and unload classes
5724 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5725
5726 // Follow CodeCache roots and unload any methods marked for unloading
5727 CodeCache::do_unloading(&_is_alive_closure,
5728 &cmsKeepAliveClosure,
5729 purged_class);
5730
5731 cmsDrainMarkingStackClosure.do_void();
5732 verify_work_stacks_empty();
5733
5734 // Update subklass/sibling/implementor links in KlassKlass descendants
5735 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5736 oop k;
5737 while ((k = _revisitStack.pop()) != NULL) {
5738 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5739 &_is_alive_closure,
5740 &cmsKeepAliveClosure);
5741 }
5742 assert(!ClassUnloading ||
5743 (_markStack.isEmpty() && overflow_list_is_empty()),
5744 "Should not have found new reachable objects");
5745 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5746 cmsDrainMarkingStackClosure.do_void();
5747 verify_work_stacks_empty();
5748 }
5749
5750 {
5751 TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty);
5752 // Now clean up stale oops in SymbolTable and StringTable
5753 SymbolTable::unlink(&_is_alive_closure);
5754 StringTable::unlink(&_is_alive_closure);
5755 }
5756 }
5757
5758 verify_work_stacks_empty();
5759 // Restore any preserved marks as a result of mark stack or
5760 // work queue overflow
5761 restore_preserved_marks_if_any(); // done single-threaded for now
5762
5763 rp->set_enqueuing_is_done(true);
5764 if (rp->processing_is_mt()) {
5765 CMSRefProcTaskExecutor task_executor(*this);
5766 rp->enqueue_discovered_references(&task_executor);
5767 } else {
5768 rp->enqueue_discovered_references(NULL);
5769 }
5770 rp->verify_no_references_recorded();
5771 assert(!rp->discovery_enabled(), "should have been disabled");
5772
5773 // JVMTI object tagging is based on JNI weak refs. If any of these
5774 // refs were cleared then JVMTI needs to update its maps and
5775 // maybe post ObjectFrees to agents.
5776 JvmtiExport::cms_ref_processing_epilogue();
5777 }
5778
5779 #ifndef PRODUCT
5780 void CMSCollector::check_correct_thread_executing() {
5781 Thread* t = Thread::current();
5782 // Only the VM thread or the CMS thread should be here.
5783 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5784 "Unexpected thread type");
5785 // If this is the vm thread, the foreground process
5786 // should not be waiting. Note that _foregroundGCIsActive is
5787 // true while the foreground collector is waiting.
5788 if (_foregroundGCShouldWait) {
5789 // We cannot be the VM thread
5790 assert(t->is_ConcurrentGC_thread(),
5791 "Should be CMS thread");
5792 } else {
5793 // We can be the CMS thread only if we are in a stop-world
5794 // phase of CMS collection.
5795 if (t->is_ConcurrentGC_thread()) {
5796 assert(_collectorState == InitialMarking ||
5797 _collectorState == FinalMarking,
5798 "Should be a stop-world phase");
5799 // The CMS thread should be holding the CMS_token.
5800 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5801 "Potential interference with concurrently "
5802 "executing VM thread");
5803 }
5804 }
5805 }
5806 #endif
5807
5808 void CMSCollector::sweep(bool asynch) {
5809 assert(_collectorState == Sweeping, "just checking");
5810 check_correct_thread_executing();
5811 verify_work_stacks_empty();
5812 verify_overflow_empty();
5813 incrementSweepCount();
5814 _sweep_timer.stop();
5815 _sweep_estimate.sample(_sweep_timer.seconds());
5816 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
5817
5818 // PermGen verification support: If perm gen sweeping is disabled in
5819 // this cycle, we preserve the perm gen object "deadness" information
5820 // in the perm_gen_verify_bit_map. In order to do that we traverse
5821 // all blocks in perm gen and mark all dead objects.
5822 if (verifying() && !should_unload_classes()) {
5823 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
5824 "Should have already been allocated");
5825 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
5826 markBitMap(), perm_gen_verify_bit_map());
5827 if (asynch) {
5828 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5829 bitMapLock());
5830 _permGen->cmsSpace()->blk_iterate(&mdo);
5831 } else {
5832 // In the case of synchronous sweep, we already have
5833 // the requisite locks/tokens.
5834 _permGen->cmsSpace()->blk_iterate(&mdo);
5835 }
5836 }
5837
5838 if (asynch) {
5839 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5840 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5841 // First sweep the old gen then the perm gen
5842 {
5843 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5844 bitMapLock());
5845 sweepWork(_cmsGen, asynch);
5846 }
5847
5848 // Now repeat for perm gen
5849 if (should_unload_classes()) {
5850 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5851 bitMapLock());
5852 sweepWork(_permGen, asynch);
5853 }
5854
5855 // Update Universe::_heap_*_at_gc figures.
5856 // We need all the free list locks to make the abstract state
5857 // transition from Sweeping to Resetting. See detailed note
5858 // further below.
5859 {
5860 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5861 _permGen->freelistLock());
5862 // Update heap occupancy information which is used as
5863 // input to soft ref clearing policy at the next gc.
5864 Universe::update_heap_info_at_gc();
5865 _collectorState = Resizing;
5866 }
5867 } else {
5868 // already have needed locks
5869 sweepWork(_cmsGen, asynch);
5870
5871 if (should_unload_classes()) {
5872 sweepWork(_permGen, asynch);
5873 }
5874 // Update heap occupancy information which is used as
5875 // input to soft ref clearing policy at the next gc.
5876 Universe::update_heap_info_at_gc();
5877 _collectorState = Resizing;
5878 }
5879 verify_work_stacks_empty();
5880 verify_overflow_empty();
5881
5882 _sweep_timer.reset();
5883 _sweep_timer.start();
5884
5885 update_time_of_last_gc(os::javaTimeMillis());
5886
5887 // NOTE on abstract state transitions:
5888 // Mutators allocate-live and/or mark the mod-union table dirty
5889 // based on the state of the collection. The former is done in
5890 // the interval [Marking, Sweeping] and the latter in the interval
5891 // [Marking, Sweeping). Thus the transitions into the Marking state
5892 // and out of the Sweeping state must be synchronously visible
5893 // globally to the mutators.
5894 // The transition into the Marking state happens with the world
5895 // stopped so the mutators will globally see it. Sweeping is
5896 // done asynchronously by the background collector so the transition
5897 // from the Sweeping state to the Resizing state must be done
5898 // under the freelistLock (as is the check for whether to
5899 // allocate-live and whether to dirty the mod-union table).
5900 assert(_collectorState == Resizing, "Change of collector state to"
5901 " Resizing must be done under the freelistLocks (plural)");
5902
5903 // Now that sweeping has been completed, if the GCH's
5904 // incremental_collection_will_fail flag is set, clear it,
5905 // thus inviting a younger gen collection to promote into
5906 // this generation. If such a promotion may still fail,
5907 // the flag will be set again when a young collection is
5908 // attempted.
5909 // I think the incremental_collection_will_fail flag's use
5910 // is specific to a 2 generation collection policy, so i'll
5911 // assert that that's the configuration we are operating within.
5912 // The use of the flag can and should be generalized appropriately
5913 // in the future to deal with a general n-generation system.
5914
5915 GenCollectedHeap* gch = GenCollectedHeap::heap();
5916 assert(gch->collector_policy()->is_two_generation_policy(),
5917 "Resetting of incremental_collection_will_fail flag"
5918 " may be incorrect otherwise");
5919 gch->clear_incremental_collection_will_fail();
5920 gch->update_full_collections_completed(_collection_count_start);
5921 }
5922
5923 // FIX ME!!! Looks like this belongs in CFLSpace, with
5924 // CMSGen merely delegating to it.
5925 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5926 double nearLargestPercent = 0.999;
5927 HeapWord* minAddr = _cmsSpace->bottom();
5928 HeapWord* largestAddr =
5929 (HeapWord*) _cmsSpace->dictionary()->findLargestDict();
5930 if (largestAddr == 0) {
5931 // The dictionary appears to be empty. In this case
5932 // try to coalesce at the end of the heap.
5933 largestAddr = _cmsSpace->end();
5934 }
5935 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5936 size_t nearLargestOffset =
5937 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5938 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5939 }
5940
5941 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5942 return addr >= _cmsSpace->nearLargestChunk();
5943 }
5944
5945 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5946 return _cmsSpace->find_chunk_at_end();
5947 }
5948
5949 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5950 bool full) {
5951 // The next lower level has been collected. Gather any statistics
5952 // that are of interest at this point.
5953 if (!full && (current_level + 1) == level()) {
5954 // Gather statistics on the young generation collection.
5955 collector()->stats().record_gc0_end(used());
5956 }
5957 }
5958
5959 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
5960 GenCollectedHeap* gch = GenCollectedHeap::heap();
5961 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
5962 "Wrong type of heap");
5963 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
5964 gch->gen_policy()->size_policy();
5965 assert(sp->is_gc_cms_adaptive_size_policy(),
5966 "Wrong type of size policy");
5967 return sp;
5968 }
5969
5970 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
5971 if (PrintGCDetails && Verbose) {
5972 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
5973 }
5974 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
5975 _debug_collection_type =
5976 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
5977 if (PrintGCDetails && Verbose) {
5978 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
5979 }
5980 }
5981
5982 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
5983 bool asynch) {
5984 // We iterate over the space(s) underlying this generation,
5985 // checking the mark bit map to see if the bits corresponding
5986 // to specific blocks are marked or not. Blocks that are
5987 // marked are live and are not swept up. All remaining blocks
5988 // are swept up, with coalescing on-the-fly as we sweep up
5989 // contiguous free and/or garbage blocks:
5990 // We need to ensure that the sweeper synchronizes with allocators
5991 // and stop-the-world collectors. In particular, the following
5992 // locks are used:
5993 // . CMS token: if this is held, a stop the world collection cannot occur
5994 // . freelistLock: if this is held no allocation can occur from this
5995 // generation by another thread
5996 // . bitMapLock: if this is held, no other thread can access or update
5997 //
5998
5999 // Note that we need to hold the freelistLock if we use
6000 // block iterate below; else the iterator might go awry if
6001 // a mutator (or promotion) causes block contents to change
6002 // (for instance if the allocator divvies up a block).
6003 // If we hold the free list lock, for all practical purposes
6004 // young generation GC's can't occur (they'll usually need to
6005 // promote), so we might as well prevent all young generation
6006 // GC's while we do a sweeping step. For the same reason, we might
6007 // as well take the bit map lock for the entire duration
6008
6009 // check that we hold the requisite locks
6010 assert(have_cms_token(), "Should hold cms token");
6011 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6012 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6013 "Should possess CMS token to sweep");
6014 assert_lock_strong(gen->freelistLock());
6015 assert_lock_strong(bitMapLock());
6016
6017 assert(!_sweep_timer.is_active(), "Was switched off in an outer context");
6018 gen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
6019 _sweep_estimate.padded_average());
6020 gen->setNearLargestChunk();
6021
6022 {
6023 SweepClosure sweepClosure(this, gen, &_markBitMap,
6024 CMSYield && asynch);
6025 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6026 // We need to free-up/coalesce garbage/blocks from a
6027 // co-terminal free run. This is done in the SweepClosure
6028 // destructor; so, do not remove this scope, else the
6029 // end-of-sweep-census below will be off by a little bit.
6030 }
6031 gen->cmsSpace()->sweep_completed();
6032 gen->cmsSpace()->endSweepFLCensus(sweepCount());
6033 if (should_unload_classes()) { // unloaded classes this cycle,
6034 _concurrent_cycles_since_last_unload = 0; // ... reset count
6035 } else { // did not unload classes,
6036 _concurrent_cycles_since_last_unload++; // ... increment count
6037 }
6038 }
6039
6040 // Reset CMS data structures (for now just the marking bit map)
6041 // preparatory for the next cycle.
6042 void CMSCollector::reset(bool asynch) {
6043 GenCollectedHeap* gch = GenCollectedHeap::heap();
6044 CMSAdaptiveSizePolicy* sp = size_policy();
6045 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6046 if (asynch) {
6047 CMSTokenSyncWithLocks ts(true, bitMapLock());
6048
6049 // If the state is not "Resetting", the foreground thread
6050 // has done a collection and the resetting.
6051 if (_collectorState != Resetting) {
6052 assert(_collectorState == Idling, "The state should only change"
6053 " because the foreground collector has finished the collection");
6054 return;
6055 }
6056
6057 // Clear the mark bitmap (no grey objects to start with)
6058 // for the next cycle.
6059 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6060 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6061
6062 HeapWord* curAddr = _markBitMap.startWord();
6063 while (curAddr < _markBitMap.endWord()) {
6064 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6065 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6066 _markBitMap.clear_large_range(chunk);
6067 if (ConcurrentMarkSweepThread::should_yield() &&
6068 !foregroundGCIsActive() &&
6069 CMSYield) {
6070 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6071 "CMS thread should hold CMS token");
6072 assert_lock_strong(bitMapLock());
6073 bitMapLock()->unlock();
6074 ConcurrentMarkSweepThread::desynchronize(true);
6075 ConcurrentMarkSweepThread::acknowledge_yield_request();
6076 stopTimer();
6077 if (PrintCMSStatistics != 0) {
6078 incrementYields();
6079 }
6080 icms_wait();
6081
6082 // See the comment in coordinator_yield()
6083 for (unsigned i = 0; i < CMSYieldSleepCount &&
6084 ConcurrentMarkSweepThread::should_yield() &&
6085 !CMSCollector::foregroundGCIsActive(); ++i) {
6086 os::sleep(Thread::current(), 1, false);
6087 ConcurrentMarkSweepThread::acknowledge_yield_request();
6088 }
6089
6090 ConcurrentMarkSweepThread::synchronize(true);
6091 bitMapLock()->lock_without_safepoint_check();
6092 startTimer();
6093 }
6094 curAddr = chunk.end();
6095 }
6096 _collectorState = Idling;
6097 } else {
6098 // already have the lock
6099 assert(_collectorState == Resetting, "just checking");
6100 assert_lock_strong(bitMapLock());
6101 _markBitMap.clear_all();
6102 _collectorState = Idling;
6103 }
6104
6105 // Stop incremental mode after a cycle completes, so that any future cycles
6106 // are triggered by allocation.
6107 stop_icms();
6108
6109 NOT_PRODUCT(
6110 if (RotateCMSCollectionTypes) {
6111 _cmsGen->rotate_debug_collection_type();
6112 }
6113 )
6114 }
6115
6116 void CMSCollector::do_CMS_operation(CMS_op_type op) {
6117 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6118 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6119 TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
6120 TraceCollectorStats tcs(counters());
6121
6122 switch (op) {
6123 case CMS_op_checkpointRootsInitial: {
6124 checkpointRootsInitial(true); // asynch
6125 if (PrintGC) {
6126 _cmsGen->printOccupancy("initial-mark");
6127 }
6128 break;
6129 }
6130 case CMS_op_checkpointRootsFinal: {
6131 checkpointRootsFinal(true, // asynch
6132 false, // !clear_all_soft_refs
6133 false); // !init_mark_was_synchronous
6134 if (PrintGC) {
6135 _cmsGen->printOccupancy("remark");
6136 }
6137 break;
6138 }
6139 default:
6140 fatal("No such CMS_op");
6141 }
6142 }
6143
6144 #ifndef PRODUCT
6145 size_t const CMSCollector::skip_header_HeapWords() {
6146 return FreeChunk::header_size();
6147 }
6148
6149 // Try and collect here conditions that should hold when
6150 // CMS thread is exiting. The idea is that the foreground GC
6151 // thread should not be blocked if it wants to terminate
6152 // the CMS thread and yet continue to run the VM for a while
6153 // after that.
6154 void CMSCollector::verify_ok_to_terminate() const {
6155 assert(Thread::current()->is_ConcurrentGC_thread(),
6156 "should be called by CMS thread");
6157 assert(!_foregroundGCShouldWait, "should be false");
6158 // We could check here that all the various low-level locks
6159 // are not held by the CMS thread, but that is overkill; see
6160 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6161 // is checked.
6162 }
6163 #endif
6164
6165 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6166 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6167 "missing Printezis mark?");
6168 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6169 size_t size = pointer_delta(nextOneAddr + 1, addr);
6170 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6171 "alignment problem");
6172 assert(size >= 3, "Necessary for Printezis marks to work");
6173 return size;
6174 }
6175
6176 // A variant of the above (block_size_using_printezis_bits()) except
6177 // that we return 0 if the P-bits are not yet set.
6178 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6179 if (_markBitMap.isMarked(addr)) {
6180 assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?");
6181 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6182 size_t size = pointer_delta(nextOneAddr + 1, addr);
6183 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6184 "alignment problem");
6185 assert(size >= 3, "Necessary for Printezis marks to work");
6186 return size;
6187 } else {
6188 assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?");
6189 return 0;
6190 }
6191 }
6192
6193 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6194 size_t sz = 0;
6195 oop p = (oop)addr;
6196 if (p->klass_or_null() != NULL && p->is_parsable()) {
6197 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6198 } else {
6199 sz = block_size_using_printezis_bits(addr);
6200 }
6201 assert(sz > 0, "size must be nonzero");
6202 HeapWord* next_block = addr + sz;
6203 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6204 CardTableModRefBS::card_size);
6205 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6206 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6207 "must be different cards");
6208 return next_card;
6209 }
6210
6211
6212 // CMS Bit Map Wrapper /////////////////////////////////////////
6213
6214 // Construct a CMS bit map infrastructure, but don't create the
6215 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6216 // further below.
6217 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6218 _bm(),
6219 _shifter(shifter),
6220 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6221 {
6222 _bmStartWord = 0;
6223 _bmWordSize = 0;
6224 }
6225
6226 bool CMSBitMap::allocate(MemRegion mr) {
6227 _bmStartWord = mr.start();
6228 _bmWordSize = mr.word_size();
6229 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6230 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6231 if (!brs.is_reserved()) {
6232 warning("CMS bit map allocation failure");
6233 return false;
6234 }
6235 // For now we'll just commit all of the bit map up fromt.
6236 // Later on we'll try to be more parsimonious with swap.
6237 if (!_virtual_space.initialize(brs, brs.size())) {
6238 warning("CMS bit map backing store failure");
6239 return false;
6240 }
6241 assert(_virtual_space.committed_size() == brs.size(),
6242 "didn't reserve backing store for all of CMS bit map?");
6243 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6244 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6245 _bmWordSize, "inconsistency in bit map sizing");
6246 _bm.set_size(_bmWordSize >> _shifter);
6247
6248 // bm.clear(); // can we rely on getting zero'd memory? verify below
6249 assert(isAllClear(),
6250 "Expected zero'd memory from ReservedSpace constructor");
6251 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6252 "consistency check");
6253 return true;
6254 }
6255
6256 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6257 HeapWord *next_addr, *end_addr, *last_addr;
6258 assert_locked();
6259 assert(covers(mr), "out-of-range error");
6260 // XXX assert that start and end are appropriately aligned
6261 for (next_addr = mr.start(), end_addr = mr.end();
6262 next_addr < end_addr; next_addr = last_addr) {
6263 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6264 last_addr = dirty_region.end();
6265 if (!dirty_region.is_empty()) {
6266 cl->do_MemRegion(dirty_region);
6267 } else {
6268 assert(last_addr == end_addr, "program logic");
6269 return;
6270 }
6271 }
6272 }
6273
6274 #ifndef PRODUCT
6275 void CMSBitMap::assert_locked() const {
6276 CMSLockVerifier::assert_locked(lock());
6277 }
6278
6279 bool CMSBitMap::covers(MemRegion mr) const {
6280 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6281 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6282 "size inconsistency");
6283 return (mr.start() >= _bmStartWord) &&
6284 (mr.end() <= endWord());
6285 }
6286
6287 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6288 return (start >= _bmStartWord && (start + size) <= endWord());
6289 }
6290
6291 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6292 // verify that there are no 1 bits in the interval [left, right)
6293 FalseBitMapClosure falseBitMapClosure;
6294 iterate(&falseBitMapClosure, left, right);
6295 }
6296
6297 void CMSBitMap::region_invariant(MemRegion mr)
6298 {
6299 assert_locked();
6300 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6301 assert(!mr.is_empty(), "unexpected empty region");
6302 assert(covers(mr), "mr should be covered by bit map");
6303 // convert address range into offset range
6304 size_t start_ofs = heapWordToOffset(mr.start());
6305 // Make sure that end() is appropriately aligned
6306 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6307 (1 << (_shifter+LogHeapWordSize))),
6308 "Misaligned mr.end()");
6309 size_t end_ofs = heapWordToOffset(mr.end());
6310 assert(end_ofs > start_ofs, "Should mark at least one bit");
6311 }
6312
6313 #endif
6314
6315 bool CMSMarkStack::allocate(size_t size) {
6316 // allocate a stack of the requisite depth
6317 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6318 size * sizeof(oop)));
6319 if (!rs.is_reserved()) {
6320 warning("CMSMarkStack allocation failure");
6321 return false;
6322 }
6323 if (!_virtual_space.initialize(rs, rs.size())) {
6324 warning("CMSMarkStack backing store failure");
6325 return false;
6326 }
6327 assert(_virtual_space.committed_size() == rs.size(),
6328 "didn't reserve backing store for all of CMS stack?");
6329 _base = (oop*)(_virtual_space.low());
6330 _index = 0;
6331 _capacity = size;
6332 NOT_PRODUCT(_max_depth = 0);
6333 return true;
6334 }
6335
6336 // XXX FIX ME !!! In the MT case we come in here holding a
6337 // leaf lock. For printing we need to take a further lock
6338 // which has lower rank. We need to recallibrate the two
6339 // lock-ranks involved in order to be able to rpint the
6340 // messages below. (Or defer the printing to the caller.
6341 // For now we take the expedient path of just disabling the
6342 // messages for the problematic case.)
6343 void CMSMarkStack::expand() {
6344 assert(_capacity <= CMSMarkStackSizeMax, "stack bigger than permitted");
6345 if (_capacity == CMSMarkStackSizeMax) {
6346 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6347 // We print a warning message only once per CMS cycle.
6348 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6349 }
6350 return;
6351 }
6352 // Double capacity if possible
6353 size_t new_capacity = MIN2(_capacity*2, CMSMarkStackSizeMax);
6354 // Do not give up existing stack until we have managed to
6355 // get the double capacity that we desired.
6356 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6357 new_capacity * sizeof(oop)));
6358 if (rs.is_reserved()) {
6359 // Release the backing store associated with old stack
6360 _virtual_space.release();
6361 // Reinitialize virtual space for new stack
6362 if (!_virtual_space.initialize(rs, rs.size())) {
6363 fatal("Not enough swap for expanded marking stack");
6364 }
6365 _base = (oop*)(_virtual_space.low());
6366 _index = 0;
6367 _capacity = new_capacity;
6368 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6369 // Failed to double capacity, continue;
6370 // we print a detail message only once per CMS cycle.
6371 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6372 SIZE_FORMAT"K",
6373 _capacity / K, new_capacity / K);
6374 }
6375 }
6376
6377
6378 // Closures
6379 // XXX: there seems to be a lot of code duplication here;
6380 // should refactor and consolidate common code.
6381
6382 // This closure is used to mark refs into the CMS generation in
6383 // the CMS bit map. Called at the first checkpoint. This closure
6384 // assumes that we do not need to re-mark dirty cards; if the CMS
6385 // generation on which this is used is not an oldest (modulo perm gen)
6386 // generation then this will lose younger_gen cards!
6387
6388 MarkRefsIntoClosure::MarkRefsIntoClosure(
6389 MemRegion span, CMSBitMap* bitMap, bool should_do_nmethods):
6390 _span(span),
6391 _bitMap(bitMap),
6392 _should_do_nmethods(should_do_nmethods)
6393 {
6394 assert(_ref_processor == NULL, "deliberately left NULL");
6395 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6396 }
6397
6398 void MarkRefsIntoClosure::do_oop(oop obj) {
6399 // if p points into _span, then mark corresponding bit in _markBitMap
6400 assert(obj->is_oop(), "expected an oop");
6401 HeapWord* addr = (HeapWord*)obj;
6402 if (_span.contains(addr)) {
6403 // this should be made more efficient
6404 _bitMap->mark(addr);
6405 }
6406 }
6407
6408 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6409 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6410
6411 // A variant of the above, used for CMS marking verification.
6412 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6413 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6414 bool should_do_nmethods):
6415 _span(span),
6416 _verification_bm(verification_bm),
6417 _cms_bm(cms_bm),
6418 _should_do_nmethods(should_do_nmethods) {
6419 assert(_ref_processor == NULL, "deliberately left NULL");
6420 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6421 }
6422
6423 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6424 // if p points into _span, then mark corresponding bit in _markBitMap
6425 assert(obj->is_oop(), "expected an oop");
6426 HeapWord* addr = (HeapWord*)obj;
6427 if (_span.contains(addr)) {
6428 _verification_bm->mark(addr);
6429 if (!_cms_bm->isMarked(addr)) {
6430 oop(addr)->print();
6431 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6432 fatal("... aborting");
6433 }
6434 }
6435 }
6436
6437 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6438 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6439
6440 //////////////////////////////////////////////////
6441 // MarkRefsIntoAndScanClosure
6442 //////////////////////////////////////////////////
6443
6444 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6445 ReferenceProcessor* rp,
6446 CMSBitMap* bit_map,
6447 CMSBitMap* mod_union_table,
6448 CMSMarkStack* mark_stack,
6449 CMSMarkStack* revisit_stack,
6450 CMSCollector* collector,
6451 bool should_yield,
6452 bool concurrent_precleaning):
6453 _collector(collector),
6454 _span(span),
6455 _bit_map(bit_map),
6456 _mark_stack(mark_stack),
6457 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6458 mark_stack, revisit_stack, concurrent_precleaning),
6459 _yield(should_yield),
6460 _concurrent_precleaning(concurrent_precleaning),
6461 _freelistLock(NULL)
6462 {
6463 _ref_processor = rp;
6464 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6465 }
6466
6467 // This closure is used to mark refs into the CMS generation at the
6468 // second (final) checkpoint, and to scan and transitively follow
6469 // the unmarked oops. It is also used during the concurrent precleaning
6470 // phase while scanning objects on dirty cards in the CMS generation.
6471 // The marks are made in the marking bit map and the marking stack is
6472 // used for keeping the (newly) grey objects during the scan.
6473 // The parallel version (Par_...) appears further below.
6474 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6475 if (obj != NULL) {
6476 assert(obj->is_oop(), "expected an oop");
6477 HeapWord* addr = (HeapWord*)obj;
6478 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6479 assert(_collector->overflow_list_is_empty(),
6480 "overflow list should be empty");
6481 if (_span.contains(addr) &&
6482 !_bit_map->isMarked(addr)) {
6483 // mark bit map (object is now grey)
6484 _bit_map->mark(addr);
6485 // push on marking stack (stack should be empty), and drain the
6486 // stack by applying this closure to the oops in the oops popped
6487 // from the stack (i.e. blacken the grey objects)
6488 bool res = _mark_stack->push(obj);
6489 assert(res, "Should have space to push on empty stack");
6490 do {
6491 oop new_oop = _mark_stack->pop();
6492 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6493 assert(new_oop->is_parsable(), "Found unparsable oop");
6494 assert(_bit_map->isMarked((HeapWord*)new_oop),
6495 "only grey objects on this stack");
6496 // iterate over the oops in this oop, marking and pushing
6497 // the ones in CMS heap (i.e. in _span).
6498 new_oop->oop_iterate(&_pushAndMarkClosure);
6499 // check if it's time to yield
6500 do_yield_check();
6501 } while (!_mark_stack->isEmpty() ||
6502 (!_concurrent_precleaning && take_from_overflow_list()));
6503 // if marking stack is empty, and we are not doing this
6504 // during precleaning, then check the overflow list
6505 }
6506 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6507 assert(_collector->overflow_list_is_empty(),
6508 "overflow list was drained above");
6509 // We could restore evacuated mark words, if any, used for
6510 // overflow list links here because the overflow list is
6511 // provably empty here. That would reduce the maximum
6512 // size requirements for preserved_{oop,mark}_stack.
6513 // But we'll just postpone it until we are all done
6514 // so we can just stream through.
6515 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6516 _collector->restore_preserved_marks_if_any();
6517 assert(_collector->no_preserved_marks(), "No preserved marks");
6518 }
6519 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6520 "All preserved marks should have been restored above");
6521 }
6522 }
6523
6524 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6525 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6526
6527 void MarkRefsIntoAndScanClosure::do_yield_work() {
6528 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6529 "CMS thread should hold CMS token");
6530 assert_lock_strong(_freelistLock);
6531 assert_lock_strong(_bit_map->lock());
6532 // relinquish the free_list_lock and bitMaplock()
6533 _bit_map->lock()->unlock();
6534 _freelistLock->unlock();
6535 ConcurrentMarkSweepThread::desynchronize(true);
6536 ConcurrentMarkSweepThread::acknowledge_yield_request();
6537 _collector->stopTimer();
6538 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6539 if (PrintCMSStatistics != 0) {
6540 _collector->incrementYields();
6541 }
6542 _collector->icms_wait();
6543
6544 // See the comment in coordinator_yield()
6545 for (unsigned i = 0;
6546 i < CMSYieldSleepCount &&
6547 ConcurrentMarkSweepThread::should_yield() &&
6548 !CMSCollector::foregroundGCIsActive();
6549 ++i) {
6550 os::sleep(Thread::current(), 1, false);
6551 ConcurrentMarkSweepThread::acknowledge_yield_request();
6552 }
6553
6554 ConcurrentMarkSweepThread::synchronize(true);
6555 _freelistLock->lock_without_safepoint_check();
6556 _bit_map->lock()->lock_without_safepoint_check();
6557 _collector->startTimer();
6558 }
6559
6560 ///////////////////////////////////////////////////////////
6561 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6562 // MarkRefsIntoAndScanClosure
6563 ///////////////////////////////////////////////////////////
6564 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6565 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6566 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6567 _span(span),
6568 _bit_map(bit_map),
6569 _work_queue(work_queue),
6570 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6571 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6572 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6573 revisit_stack)
6574 {
6575 _ref_processor = rp;
6576 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6577 }
6578
6579 // This closure is used to mark refs into the CMS generation at the
6580 // second (final) checkpoint, and to scan and transitively follow
6581 // the unmarked oops. The marks are made in the marking bit map and
6582 // the work_queue is used for keeping the (newly) grey objects during
6583 // the scan phase whence they are also available for stealing by parallel
6584 // threads. Since the marking bit map is shared, updates are
6585 // synchronized (via CAS).
6586 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6587 if (obj != NULL) {
6588 // Ignore mark word because this could be an already marked oop
6589 // that may be chained at the end of the overflow list.
6590 assert(obj->is_oop(true), "expected an oop");
6591 HeapWord* addr = (HeapWord*)obj;
6592 if (_span.contains(addr) &&
6593 !_bit_map->isMarked(addr)) {
6594 // mark bit map (object will become grey):
6595 // It is possible for several threads to be
6596 // trying to "claim" this object concurrently;
6597 // the unique thread that succeeds in marking the
6598 // object first will do the subsequent push on
6599 // to the work queue (or overflow list).
6600 if (_bit_map->par_mark(addr)) {
6601 // push on work_queue (which may not be empty), and trim the
6602 // queue to an appropriate length by applying this closure to
6603 // the oops in the oops popped from the stack (i.e. blacken the
6604 // grey objects)
6605 bool res = _work_queue->push(obj);
6606 assert(res, "Low water mark should be less than capacity?");
6607 trim_queue(_low_water_mark);
6608 } // Else, another thread claimed the object
6609 }
6610 }
6611 }
6612
6613 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6614 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6615
6616 // This closure is used to rescan the marked objects on the dirty cards
6617 // in the mod union table and the card table proper.
6618 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6619 oop p, MemRegion mr) {
6620
6621 size_t size = 0;
6622 HeapWord* addr = (HeapWord*)p;
6623 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6624 assert(_span.contains(addr), "we are scanning the CMS generation");
6625 // check if it's time to yield
6626 if (do_yield_check()) {
6627 // We yielded for some foreground stop-world work,
6628 // and we have been asked to abort this ongoing preclean cycle.
6629 return 0;
6630 }
6631 if (_bitMap->isMarked(addr)) {
6632 // it's marked; is it potentially uninitialized?
6633 if (p->klass_or_null() != NULL) {
6634 if (CMSPermGenPrecleaningEnabled && !p->is_parsable()) {
6635 // Signal precleaning to redirty the card since
6636 // the klass pointer is already installed.
6637 assert(size == 0, "Initial value");
6638 } else {
6639 assert(p->is_parsable(), "must be parsable.");
6640 // an initialized object; ignore mark word in verification below
6641 // since we are running concurrent with mutators
6642 assert(p->is_oop(true), "should be an oop");
6643 if (p->is_objArray()) {
6644 // objArrays are precisely marked; restrict scanning
6645 // to dirty cards only.
6646 size = CompactibleFreeListSpace::adjustObjectSize(
6647 p->oop_iterate(_scanningClosure, mr));
6648 } else {
6649 // A non-array may have been imprecisely marked; we need
6650 // to scan object in its entirety.
6651 size = CompactibleFreeListSpace::adjustObjectSize(
6652 p->oop_iterate(_scanningClosure));
6653 }
6654 #ifdef DEBUG
6655 size_t direct_size =
6656 CompactibleFreeListSpace::adjustObjectSize(p->size());
6657 assert(size == direct_size, "Inconsistency in size");
6658 assert(size >= 3, "Necessary for Printezis marks to work");
6659 if (!_bitMap->isMarked(addr+1)) {
6660 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6661 } else {
6662 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6663 assert(_bitMap->isMarked(addr+size-1),
6664 "inconsistent Printezis mark");
6665 }
6666 #endif // DEBUG
6667 }
6668 } else {
6669 // an unitialized object
6670 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6671 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6672 size = pointer_delta(nextOneAddr + 1, addr);
6673 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6674 "alignment problem");
6675 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6676 // will dirty the card when the klass pointer is installed in the
6677 // object (signalling the completion of initialization).
6678 }
6679 } else {
6680 // Either a not yet marked object or an uninitialized object
6681 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6682 // An uninitialized object, skip to the next card, since
6683 // we may not be able to read its P-bits yet.
6684 assert(size == 0, "Initial value");
6685 } else {
6686 // An object not (yet) reached by marking: we merely need to
6687 // compute its size so as to go look at the next block.
6688 assert(p->is_oop(true), "should be an oop");
6689 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6690 }
6691 }
6692 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6693 return size;
6694 }
6695
6696 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6697 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6698 "CMS thread should hold CMS token");
6699 assert_lock_strong(_freelistLock);
6700 assert_lock_strong(_bitMap->lock());
6701 // relinquish the free_list_lock and bitMaplock()
6702 _bitMap->lock()->unlock();
6703 _freelistLock->unlock();
6704 ConcurrentMarkSweepThread::desynchronize(true);
6705 ConcurrentMarkSweepThread::acknowledge_yield_request();
6706 _collector->stopTimer();
6707 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6708 if (PrintCMSStatistics != 0) {
6709 _collector->incrementYields();
6710 }
6711 _collector->icms_wait();
6712
6713 // See the comment in coordinator_yield()
6714 for (unsigned i = 0; i < CMSYieldSleepCount &&
6715 ConcurrentMarkSweepThread::should_yield() &&
6716 !CMSCollector::foregroundGCIsActive(); ++i) {
6717 os::sleep(Thread::current(), 1, false);
6718 ConcurrentMarkSweepThread::acknowledge_yield_request();
6719 }
6720
6721 ConcurrentMarkSweepThread::synchronize(true);
6722 _freelistLock->lock_without_safepoint_check();
6723 _bitMap->lock()->lock_without_safepoint_check();
6724 _collector->startTimer();
6725 }
6726
6727
6728 //////////////////////////////////////////////////////////////////
6729 // SurvivorSpacePrecleanClosure
6730 //////////////////////////////////////////////////////////////////
6731 // This (single-threaded) closure is used to preclean the oops in
6732 // the survivor spaces.
6733 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6734
6735 HeapWord* addr = (HeapWord*)p;
6736 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6737 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6738 assert(p->klass_or_null() != NULL, "object should be initializd");
6739 assert(p->is_parsable(), "must be parsable.");
6740 // an initialized object; ignore mark word in verification below
6741 // since we are running concurrent with mutators
6742 assert(p->is_oop(true), "should be an oop");
6743 // Note that we do not yield while we iterate over
6744 // the interior oops of p, pushing the relevant ones
6745 // on our marking stack.
6746 size_t size = p->oop_iterate(_scanning_closure);
6747 do_yield_check();
6748 // Observe that below, we do not abandon the preclean
6749 // phase as soon as we should; rather we empty the
6750 // marking stack before returning. This is to satisfy
6751 // some existing assertions. In general, it may be a
6752 // good idea to abort immediately and complete the marking
6753 // from the grey objects at a later time.
6754 while (!_mark_stack->isEmpty()) {
6755 oop new_oop = _mark_stack->pop();
6756 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6757 assert(new_oop->is_parsable(), "Found unparsable oop");
6758 assert(_bit_map->isMarked((HeapWord*)new_oop),
6759 "only grey objects on this stack");
6760 // iterate over the oops in this oop, marking and pushing
6761 // the ones in CMS heap (i.e. in _span).
6762 new_oop->oop_iterate(_scanning_closure);
6763 // check if it's time to yield
6764 do_yield_check();
6765 }
6766 unsigned int after_count =
6767 GenCollectedHeap::heap()->total_collections();
6768 bool abort = (_before_count != after_count) ||
6769 _collector->should_abort_preclean();
6770 return abort ? 0 : size;
6771 }
6772
6773 void SurvivorSpacePrecleanClosure::do_yield_work() {
6774 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6775 "CMS thread should hold CMS token");
6776 assert_lock_strong(_bit_map->lock());
6777 // Relinquish the bit map lock
6778 _bit_map->lock()->unlock();
6779 ConcurrentMarkSweepThread::desynchronize(true);
6780 ConcurrentMarkSweepThread::acknowledge_yield_request();
6781 _collector->stopTimer();
6782 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6783 if (PrintCMSStatistics != 0) {
6784 _collector->incrementYields();
6785 }
6786 _collector->icms_wait();
6787
6788 // See the comment in coordinator_yield()
6789 for (unsigned i = 0; i < CMSYieldSleepCount &&
6790 ConcurrentMarkSweepThread::should_yield() &&
6791 !CMSCollector::foregroundGCIsActive(); ++i) {
6792 os::sleep(Thread::current(), 1, false);
6793 ConcurrentMarkSweepThread::acknowledge_yield_request();
6794 }
6795
6796 ConcurrentMarkSweepThread::synchronize(true);
6797 _bit_map->lock()->lock_without_safepoint_check();
6798 _collector->startTimer();
6799 }
6800
6801 // This closure is used to rescan the marked objects on the dirty cards
6802 // in the mod union table and the card table proper. In the parallel
6803 // case, although the bitMap is shared, we do a single read so the
6804 // isMarked() query is "safe".
6805 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6806 // Ignore mark word because we are running concurrent with mutators
6807 assert(p->is_oop_or_null(true), "expected an oop or null");
6808 HeapWord* addr = (HeapWord*)p;
6809 assert(_span.contains(addr), "we are scanning the CMS generation");
6810 bool is_obj_array = false;
6811 #ifdef DEBUG
6812 if (!_parallel) {
6813 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6814 assert(_collector->overflow_list_is_empty(),
6815 "overflow list should be empty");
6816
6817 }
6818 #endif // DEBUG
6819 if (_bit_map->isMarked(addr)) {
6820 // Obj arrays are precisely marked, non-arrays are not;
6821 // so we scan objArrays precisely and non-arrays in their
6822 // entirety.
6823 if (p->is_objArray()) {
6824 is_obj_array = true;
6825 if (_parallel) {
6826 p->oop_iterate(_par_scan_closure, mr);
6827 } else {
6828 p->oop_iterate(_scan_closure, mr);
6829 }
6830 } else {
6831 if (_parallel) {
6832 p->oop_iterate(_par_scan_closure);
6833 } else {
6834 p->oop_iterate(_scan_closure);
6835 }
6836 }
6837 }
6838 #ifdef DEBUG
6839 if (!_parallel) {
6840 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6841 assert(_collector->overflow_list_is_empty(),
6842 "overflow list should be empty");
6843
6844 }
6845 #endif // DEBUG
6846 return is_obj_array;
6847 }
6848
6849 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6850 MemRegion span,
6851 CMSBitMap* bitMap, CMSMarkStack* markStack,
6852 CMSMarkStack* revisitStack,
6853 bool should_yield, bool verifying):
6854 _collector(collector),
6855 _span(span),
6856 _bitMap(bitMap),
6857 _mut(&collector->_modUnionTable),
6858 _markStack(markStack),
6859 _revisitStack(revisitStack),
6860 _yield(should_yield),
6861 _skipBits(0)
6862 {
6863 assert(_markStack->isEmpty(), "stack should be empty");
6864 _finger = _bitMap->startWord();
6865 _threshold = _finger;
6866 assert(_collector->_restart_addr == NULL, "Sanity check");
6867 assert(_span.contains(_finger), "Out of bounds _finger?");
6868 DEBUG_ONLY(_verifying = verifying;)
6869 }
6870
6871 void MarkFromRootsClosure::reset(HeapWord* addr) {
6872 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6873 assert(_span.contains(addr), "Out of bounds _finger?");
6874 _finger = addr;
6875 _threshold = (HeapWord*)round_to(
6876 (intptr_t)_finger, CardTableModRefBS::card_size);
6877 }
6878
6879 // Should revisit to see if this should be restructured for
6880 // greater efficiency.
6881 bool MarkFromRootsClosure::do_bit(size_t offset) {
6882 if (_skipBits > 0) {
6883 _skipBits--;
6884 return true;
6885 }
6886 // convert offset into a HeapWord*
6887 HeapWord* addr = _bitMap->startWord() + offset;
6888 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6889 "address out of range");
6890 assert(_bitMap->isMarked(addr), "tautology");
6891 if (_bitMap->isMarked(addr+1)) {
6892 // this is an allocated but not yet initialized object
6893 assert(_skipBits == 0, "tautology");
6894 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6895 oop p = oop(addr);
6896 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6897 DEBUG_ONLY(if (!_verifying) {)
6898 // We re-dirty the cards on which this object lies and increase
6899 // the _threshold so that we'll come back to scan this object
6900 // during the preclean or remark phase. (CMSCleanOnEnter)
6901 if (CMSCleanOnEnter) {
6902 size_t sz = _collector->block_size_using_printezis_bits(addr);
6903 HeapWord* end_card_addr = (HeapWord*)round_to(
6904 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6905 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6906 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6907 // Bump _threshold to end_card_addr; note that
6908 // _threshold cannot possibly exceed end_card_addr, anyhow.
6909 // This prevents future clearing of the card as the scan proceeds
6910 // to the right.
6911 assert(_threshold <= end_card_addr,
6912 "Because we are just scanning into this object");
6913 if (_threshold < end_card_addr) {
6914 _threshold = end_card_addr;
6915 }
6916 if (p->klass_or_null() != NULL) {
6917 // Redirty the range of cards...
6918 _mut->mark_range(redirty_range);
6919 } // ...else the setting of klass will dirty the card anyway.
6920 }
6921 DEBUG_ONLY(})
6922 return true;
6923 }
6924 }
6925 scanOopsInOop(addr);
6926 return true;
6927 }
6928
6929 // We take a break if we've been at this for a while,
6930 // so as to avoid monopolizing the locks involved.
6931 void MarkFromRootsClosure::do_yield_work() {
6932 // First give up the locks, then yield, then re-lock
6933 // We should probably use a constructor/destructor idiom to
6934 // do this unlock/lock or modify the MutexUnlocker class to
6935 // serve our purpose. XXX
6936 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6937 "CMS thread should hold CMS token");
6938 assert_lock_strong(_bitMap->lock());
6939 _bitMap->lock()->unlock();
6940 ConcurrentMarkSweepThread::desynchronize(true);
6941 ConcurrentMarkSweepThread::acknowledge_yield_request();
6942 _collector->stopTimer();
6943 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6944 if (PrintCMSStatistics != 0) {
6945 _collector->incrementYields();
6946 }
6947 _collector->icms_wait();
6948
6949 // See the comment in coordinator_yield()
6950 for (unsigned i = 0; i < CMSYieldSleepCount &&
6951 ConcurrentMarkSweepThread::should_yield() &&
6952 !CMSCollector::foregroundGCIsActive(); ++i) {
6953 os::sleep(Thread::current(), 1, false);
6954 ConcurrentMarkSweepThread::acknowledge_yield_request();
6955 }
6956
6957 ConcurrentMarkSweepThread::synchronize(true);
6958 _bitMap->lock()->lock_without_safepoint_check();
6959 _collector->startTimer();
6960 }
6961
6962 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6963 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6964 assert(_markStack->isEmpty(),
6965 "should drain stack to limit stack usage");
6966 // convert ptr to an oop preparatory to scanning
6967 oop obj = oop(ptr);
6968 // Ignore mark word in verification below, since we
6969 // may be running concurrent with mutators.
6970 assert(obj->is_oop(true), "should be an oop");
6971 assert(_finger <= ptr, "_finger runneth ahead");
6972 // advance the finger to right end of this object
6973 _finger = ptr + obj->size();
6974 assert(_finger > ptr, "we just incremented it above");
6975 // On large heaps, it may take us some time to get through
6976 // the marking phase (especially if running iCMS). During
6977 // this time it's possible that a lot of mutations have
6978 // accumulated in the card table and the mod union table --
6979 // these mutation records are redundant until we have
6980 // actually traced into the corresponding card.
6981 // Here, we check whether advancing the finger would make
6982 // us cross into a new card, and if so clear corresponding
6983 // cards in the MUT (preclean them in the card-table in the
6984 // future).
6985
6986 DEBUG_ONLY(if (!_verifying) {)
6987 // The clean-on-enter optimization is disabled by default,
6988 // until we fix 6178663.
6989 if (CMSCleanOnEnter && (_finger > _threshold)) {
6990 // [_threshold, _finger) represents the interval
6991 // of cards to be cleared in MUT (or precleaned in card table).
6992 // The set of cards to be cleared is all those that overlap
6993 // with the interval [_threshold, _finger); note that
6994 // _threshold is always kept card-aligned but _finger isn't
6995 // always card-aligned.
6996 HeapWord* old_threshold = _threshold;
6997 assert(old_threshold == (HeapWord*)round_to(
6998 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6999 "_threshold should always be card-aligned");
7000 _threshold = (HeapWord*)round_to(
7001 (intptr_t)_finger, CardTableModRefBS::card_size);
7002 MemRegion mr(old_threshold, _threshold);
7003 assert(!mr.is_empty(), "Control point invariant");
7004 assert(_span.contains(mr), "Should clear within span");
7005 // XXX When _finger crosses from old gen into perm gen
7006 // we may be doing unnecessary cleaning; do better in the
7007 // future by detecting that condition and clearing fewer
7008 // MUT/CT entries.
7009 _mut->clear_range(mr);
7010 }
7011 DEBUG_ONLY(})
7012
7013 // Note: the finger doesn't advance while we drain
7014 // the stack below.
7015 PushOrMarkClosure pushOrMarkClosure(_collector,
7016 _span, _bitMap, _markStack,
7017 _revisitStack,
7018 _finger, this);
7019 bool res = _markStack->push(obj);
7020 assert(res, "Empty non-zero size stack should have space for single push");
7021 while (!_markStack->isEmpty()) {
7022 oop new_oop = _markStack->pop();
7023 // Skip verifying header mark word below because we are
7024 // running concurrent with mutators.
7025 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7026 // now scan this oop's oops
7027 new_oop->oop_iterate(&pushOrMarkClosure);
7028 do_yield_check();
7029 }
7030 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7031 }
7032
7033 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7034 CMSCollector* collector, MemRegion span,
7035 CMSBitMap* bit_map,
7036 OopTaskQueue* work_queue,
7037 CMSMarkStack* overflow_stack,
7038 CMSMarkStack* revisit_stack,
7039 bool should_yield):
7040 _collector(collector),
7041 _whole_span(collector->_span),
7042 _span(span),
7043 _bit_map(bit_map),
7044 _mut(&collector->_modUnionTable),
7045 _work_queue(work_queue),
7046 _overflow_stack(overflow_stack),
7047 _revisit_stack(revisit_stack),
7048 _yield(should_yield),
7049 _skip_bits(0),
7050 _task(task)
7051 {
7052 assert(_work_queue->size() == 0, "work_queue should be empty");
7053 _finger = span.start();
7054 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7055 assert(_span.contains(_finger), "Out of bounds _finger?");
7056 }
7057
7058 // Should revisit to see if this should be restructured for
7059 // greater efficiency.
7060 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7061 if (_skip_bits > 0) {
7062 _skip_bits--;
7063 return true;
7064 }
7065 // convert offset into a HeapWord*
7066 HeapWord* addr = _bit_map->startWord() + offset;
7067 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7068 "address out of range");
7069 assert(_bit_map->isMarked(addr), "tautology");
7070 if (_bit_map->isMarked(addr+1)) {
7071 // this is an allocated object that might not yet be initialized
7072 assert(_skip_bits == 0, "tautology");
7073 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7074 oop p = oop(addr);
7075 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7076 // in the case of Clean-on-Enter optimization, redirty card
7077 // and avoid clearing card by increasing the threshold.
7078 return true;
7079 }
7080 }
7081 scan_oops_in_oop(addr);
7082 return true;
7083 }
7084
7085 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7086 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7087 // Should we assert that our work queue is empty or
7088 // below some drain limit?
7089 assert(_work_queue->size() == 0,
7090 "should drain stack to limit stack usage");
7091 // convert ptr to an oop preparatory to scanning
7092 oop obj = oop(ptr);
7093 // Ignore mark word in verification below, since we
7094 // may be running concurrent with mutators.
7095 assert(obj->is_oop(true), "should be an oop");
7096 assert(_finger <= ptr, "_finger runneth ahead");
7097 // advance the finger to right end of this object
7098 _finger = ptr + obj->size();
7099 assert(_finger > ptr, "we just incremented it above");
7100 // On large heaps, it may take us some time to get through
7101 // the marking phase (especially if running iCMS). During
7102 // this time it's possible that a lot of mutations have
7103 // accumulated in the card table and the mod union table --
7104 // these mutation records are redundant until we have
7105 // actually traced into the corresponding card.
7106 // Here, we check whether advancing the finger would make
7107 // us cross into a new card, and if so clear corresponding
7108 // cards in the MUT (preclean them in the card-table in the
7109 // future).
7110
7111 // The clean-on-enter optimization is disabled by default,
7112 // until we fix 6178663.
7113 if (CMSCleanOnEnter && (_finger > _threshold)) {
7114 // [_threshold, _finger) represents the interval
7115 // of cards to be cleared in MUT (or precleaned in card table).
7116 // The set of cards to be cleared is all those that overlap
7117 // with the interval [_threshold, _finger); note that
7118 // _threshold is always kept card-aligned but _finger isn't
7119 // always card-aligned.
7120 HeapWord* old_threshold = _threshold;
7121 assert(old_threshold == (HeapWord*)round_to(
7122 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7123 "_threshold should always be card-aligned");
7124 _threshold = (HeapWord*)round_to(
7125 (intptr_t)_finger, CardTableModRefBS::card_size);
7126 MemRegion mr(old_threshold, _threshold);
7127 assert(!mr.is_empty(), "Control point invariant");
7128 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7129 // XXX When _finger crosses from old gen into perm gen
7130 // we may be doing unnecessary cleaning; do better in the
7131 // future by detecting that condition and clearing fewer
7132 // MUT/CT entries.
7133 _mut->clear_range(mr);
7134 }
7135
7136 // Note: the local finger doesn't advance while we drain
7137 // the stack below, but the global finger sure can and will.
7138 HeapWord** gfa = _task->global_finger_addr();
7139 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7140 _span, _bit_map,
7141 _work_queue,
7142 _overflow_stack,
7143 _revisit_stack,
7144 _finger,
7145 gfa, this);
7146 bool res = _work_queue->push(obj); // overflow could occur here
7147 assert(res, "Will hold once we use workqueues");
7148 while (true) {
7149 oop new_oop;
7150 if (!_work_queue->pop_local(new_oop)) {
7151 // We emptied our work_queue; check if there's stuff that can
7152 // be gotten from the overflow stack.
7153 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7154 _overflow_stack, _work_queue)) {
7155 do_yield_check();
7156 continue;
7157 } else { // done
7158 break;
7159 }
7160 }
7161 // Skip verifying header mark word below because we are
7162 // running concurrent with mutators.
7163 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7164 // now scan this oop's oops
7165 new_oop->oop_iterate(&pushOrMarkClosure);
7166 do_yield_check();
7167 }
7168 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7169 }
7170
7171 // Yield in response to a request from VM Thread or
7172 // from mutators.
7173 void Par_MarkFromRootsClosure::do_yield_work() {
7174 assert(_task != NULL, "sanity");
7175 _task->yield();
7176 }
7177
7178 // A variant of the above used for verifying CMS marking work.
7179 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7180 MemRegion span,
7181 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7182 CMSMarkStack* mark_stack):
7183 _collector(collector),
7184 _span(span),
7185 _verification_bm(verification_bm),
7186 _cms_bm(cms_bm),
7187 _mark_stack(mark_stack),
7188 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7189 mark_stack)
7190 {
7191 assert(_mark_stack->isEmpty(), "stack should be empty");
7192 _finger = _verification_bm->startWord();
7193 assert(_collector->_restart_addr == NULL, "Sanity check");
7194 assert(_span.contains(_finger), "Out of bounds _finger?");
7195 }
7196
7197 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7198 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7199 assert(_span.contains(addr), "Out of bounds _finger?");
7200 _finger = addr;
7201 }
7202
7203 // Should revisit to see if this should be restructured for
7204 // greater efficiency.
7205 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7206 // convert offset into a HeapWord*
7207 HeapWord* addr = _verification_bm->startWord() + offset;
7208 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7209 "address out of range");
7210 assert(_verification_bm->isMarked(addr), "tautology");
7211 assert(_cms_bm->isMarked(addr), "tautology");
7212
7213 assert(_mark_stack->isEmpty(),
7214 "should drain stack to limit stack usage");
7215 // convert addr to an oop preparatory to scanning
7216 oop obj = oop(addr);
7217 assert(obj->is_oop(), "should be an oop");
7218 assert(_finger <= addr, "_finger runneth ahead");
7219 // advance the finger to right end of this object
7220 _finger = addr + obj->size();
7221 assert(_finger > addr, "we just incremented it above");
7222 // Note: the finger doesn't advance while we drain
7223 // the stack below.
7224 bool res = _mark_stack->push(obj);
7225 assert(res, "Empty non-zero size stack should have space for single push");
7226 while (!_mark_stack->isEmpty()) {
7227 oop new_oop = _mark_stack->pop();
7228 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7229 // now scan this oop's oops
7230 new_oop->oop_iterate(&_pam_verify_closure);
7231 }
7232 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7233 return true;
7234 }
7235
7236 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7237 CMSCollector* collector, MemRegion span,
7238 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7239 CMSMarkStack* mark_stack):
7240 OopClosure(collector->ref_processor()),
7241 _collector(collector),
7242 _span(span),
7243 _verification_bm(verification_bm),
7244 _cms_bm(cms_bm),
7245 _mark_stack(mark_stack)
7246 { }
7247
7248 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7249 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7250
7251 // Upon stack overflow, we discard (part of) the stack,
7252 // remembering the least address amongst those discarded
7253 // in CMSCollector's _restart_address.
7254 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7255 // Remember the least grey address discarded
7256 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7257 _collector->lower_restart_addr(ra);
7258 _mark_stack->reset(); // discard stack contents
7259 _mark_stack->expand(); // expand the stack if possible
7260 }
7261
7262 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7263 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7264 HeapWord* addr = (HeapWord*)obj;
7265 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7266 // Oop lies in _span and isn't yet grey or black
7267 _verification_bm->mark(addr); // now grey
7268 if (!_cms_bm->isMarked(addr)) {
7269 oop(addr)->print();
7270 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7271 addr);
7272 fatal("... aborting");
7273 }
7274
7275 if (!_mark_stack->push(obj)) { // stack overflow
7276 if (PrintCMSStatistics != 0) {
7277 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7278 SIZE_FORMAT, _mark_stack->capacity());
7279 }
7280 assert(_mark_stack->isFull(), "Else push should have succeeded");
7281 handle_stack_overflow(addr);
7282 }
7283 // anything including and to the right of _finger
7284 // will be scanned as we iterate over the remainder of the
7285 // bit map
7286 }
7287 }
7288
7289 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7290 MemRegion span,
7291 CMSBitMap* bitMap, CMSMarkStack* markStack,
7292 CMSMarkStack* revisitStack,
7293 HeapWord* finger, MarkFromRootsClosure* parent) :
7294 OopClosure(collector->ref_processor()),
7295 _collector(collector),
7296 _span(span),
7297 _bitMap(bitMap),
7298 _markStack(markStack),
7299 _revisitStack(revisitStack),
7300 _finger(finger),
7301 _parent(parent),
7302 _should_remember_klasses(collector->should_unload_classes())
7303 { }
7304
7305 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7306 MemRegion span,
7307 CMSBitMap* bit_map,
7308 OopTaskQueue* work_queue,
7309 CMSMarkStack* overflow_stack,
7310 CMSMarkStack* revisit_stack,
7311 HeapWord* finger,
7312 HeapWord** global_finger_addr,
7313 Par_MarkFromRootsClosure* parent) :
7314 OopClosure(collector->ref_processor()),
7315 _collector(collector),
7316 _whole_span(collector->_span),
7317 _span(span),
7318 _bit_map(bit_map),
7319 _work_queue(work_queue),
7320 _overflow_stack(overflow_stack),
7321 _revisit_stack(revisit_stack),
7322 _finger(finger),
7323 _global_finger_addr(global_finger_addr),
7324 _parent(parent),
7325 _should_remember_klasses(collector->should_unload_classes())
7326 { }
7327
7328 // Assumes thread-safe access by callers, who are
7329 // responsible for mutual exclusion.
7330 void CMSCollector::lower_restart_addr(HeapWord* low) {
7331 assert(_span.contains(low), "Out of bounds addr");
7332 if (_restart_addr == NULL) {
7333 _restart_addr = low;
7334 } else {
7335 _restart_addr = MIN2(_restart_addr, low);
7336 }
7337 }
7338
7339 // Upon stack overflow, we discard (part of) the stack,
7340 // remembering the least address amongst those discarded
7341 // in CMSCollector's _restart_address.
7342 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7343 // Remember the least grey address discarded
7344 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7345 _collector->lower_restart_addr(ra);
7346 _markStack->reset(); // discard stack contents
7347 _markStack->expand(); // expand the stack if possible
7348 }
7349
7350 // Upon stack overflow, we discard (part of) the stack,
7351 // remembering the least address amongst those discarded
7352 // in CMSCollector's _restart_address.
7353 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7354 // We need to do this under a mutex to prevent other
7355 // workers from interfering with the work done below.
7356 MutexLockerEx ml(_overflow_stack->par_lock(),
7357 Mutex::_no_safepoint_check_flag);
7358 // Remember the least grey address discarded
7359 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7360 _collector->lower_restart_addr(ra);
7361 _overflow_stack->reset(); // discard stack contents
7362 _overflow_stack->expand(); // expand the stack if possible
7363 }
7364
7365 void PushOrMarkClosure::do_oop(oop obj) {
7366 // Ignore mark word because we are running concurrent with mutators.
7367 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7368 HeapWord* addr = (HeapWord*)obj;
7369 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7370 // Oop lies in _span and isn't yet grey or black
7371 _bitMap->mark(addr); // now grey
7372 if (addr < _finger) {
7373 // the bit map iteration has already either passed, or
7374 // sampled, this bit in the bit map; we'll need to
7375 // use the marking stack to scan this oop's oops.
7376 bool simulate_overflow = false;
7377 NOT_PRODUCT(
7378 if (CMSMarkStackOverflowALot &&
7379 _collector->simulate_overflow()) {
7380 // simulate a stack overflow
7381 simulate_overflow = true;
7382 }
7383 )
7384 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7385 if (PrintCMSStatistics != 0) {
7386 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7387 SIZE_FORMAT, _markStack->capacity());
7388 }
7389 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7390 handle_stack_overflow(addr);
7391 }
7392 }
7393 // anything including and to the right of _finger
7394 // will be scanned as we iterate over the remainder of the
7395 // bit map
7396 do_yield_check();
7397 }
7398 }
7399
7400 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7401 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7402
7403 void Par_PushOrMarkClosure::do_oop(oop obj) {
7404 // Ignore mark word because we are running concurrent with mutators.
7405 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7406 HeapWord* addr = (HeapWord*)obj;
7407 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7408 // Oop lies in _span and isn't yet grey or black
7409 // We read the global_finger (volatile read) strictly after marking oop
7410 bool res = _bit_map->par_mark(addr); // now grey
7411 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7412 // Should we push this marked oop on our stack?
7413 // -- if someone else marked it, nothing to do
7414 // -- if target oop is above global finger nothing to do
7415 // -- if target oop is in chunk and above local finger
7416 // then nothing to do
7417 // -- else push on work queue
7418 if ( !res // someone else marked it, they will deal with it
7419 || (addr >= *gfa) // will be scanned in a later task
7420 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7421 return;
7422 }
7423 // the bit map iteration has already either passed, or
7424 // sampled, this bit in the bit map; we'll need to
7425 // use the marking stack to scan this oop's oops.
7426 bool simulate_overflow = false;
7427 NOT_PRODUCT(
7428 if (CMSMarkStackOverflowALot &&
7429 _collector->simulate_overflow()) {
7430 // simulate a stack overflow
7431 simulate_overflow = true;
7432 }
7433 )
7434 if (simulate_overflow ||
7435 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7436 // stack overflow
7437 if (PrintCMSStatistics != 0) {
7438 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7439 SIZE_FORMAT, _overflow_stack->capacity());
7440 }
7441 // We cannot assert that the overflow stack is full because
7442 // it may have been emptied since.
7443 assert(simulate_overflow ||
7444 _work_queue->size() == _work_queue->max_elems(),
7445 "Else push should have succeeded");
7446 handle_stack_overflow(addr);
7447 }
7448 do_yield_check();
7449 }
7450 }
7451
7452 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7453 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7454
7455 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7456 MemRegion span,
7457 ReferenceProcessor* rp,
7458 CMSBitMap* bit_map,
7459 CMSBitMap* mod_union_table,
7460 CMSMarkStack* mark_stack,
7461 CMSMarkStack* revisit_stack,
7462 bool concurrent_precleaning):
7463 OopClosure(rp),
7464 _collector(collector),
7465 _span(span),
7466 _bit_map(bit_map),
7467 _mod_union_table(mod_union_table),
7468 _mark_stack(mark_stack),
7469 _revisit_stack(revisit_stack),
7470 _concurrent_precleaning(concurrent_precleaning),
7471 _should_remember_klasses(collector->should_unload_classes())
7472 {
7473 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7474 }
7475
7476 // Grey object rescan during pre-cleaning and second checkpoint phases --
7477 // the non-parallel version (the parallel version appears further below.)
7478 void PushAndMarkClosure::do_oop(oop obj) {
7479 // Ignore mark word verification. If during concurrent precleaning,
7480 // the object monitor may be locked. If during the checkpoint
7481 // phases, the object may already have been reached by a different
7482 // path and may be at the end of the global overflow list (so
7483 // the mark word may be NULL).
7484 assert(obj->is_oop_or_null(true /* ignore mark word */),
7485 "expected an oop or NULL");
7486 HeapWord* addr = (HeapWord*)obj;
7487 // Check if oop points into the CMS generation
7488 // and is not marked
7489 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7490 // a white object ...
7491 _bit_map->mark(addr); // ... now grey
7492 // push on the marking stack (grey set)
7493 bool simulate_overflow = false;
7494 NOT_PRODUCT(
7495 if (CMSMarkStackOverflowALot &&
7496 _collector->simulate_overflow()) {
7497 // simulate a stack overflow
7498 simulate_overflow = true;
7499 }
7500 )
7501 if (simulate_overflow || !_mark_stack->push(obj)) {
7502 if (_concurrent_precleaning) {
7503 // During precleaning we can just dirty the appropriate card(s)
7504 // in the mod union table, thus ensuring that the object remains
7505 // in the grey set and continue. In the case of object arrays
7506 // we need to dirty all of the cards that the object spans,
7507 // since the rescan of object arrays will be limited to the
7508 // dirty cards.
7509 // Note that no one can be intefering with us in this action
7510 // of dirtying the mod union table, so no locking or atomics
7511 // are required.
7512 if (obj->is_objArray()) {
7513 size_t sz = obj->size();
7514 HeapWord* end_card_addr = (HeapWord*)round_to(
7515 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7516 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7517 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7518 _mod_union_table->mark_range(redirty_range);
7519 } else {
7520 _mod_union_table->mark(addr);
7521 }
7522 _collector->_ser_pmc_preclean_ovflw++;
7523 } else {
7524 // During the remark phase, we need to remember this oop
7525 // in the overflow list.
7526 _collector->push_on_overflow_list(obj);
7527 _collector->_ser_pmc_remark_ovflw++;
7528 }
7529 }
7530 }
7531 }
7532
7533 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7534 MemRegion span,
7535 ReferenceProcessor* rp,
7536 CMSBitMap* bit_map,
7537 OopTaskQueue* work_queue,
7538 CMSMarkStack* revisit_stack):
7539 OopClosure(rp),
7540 _collector(collector),
7541 _span(span),
7542 _bit_map(bit_map),
7543 _work_queue(work_queue),
7544 _revisit_stack(revisit_stack),
7545 _should_remember_klasses(collector->should_unload_classes())
7546 {
7547 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7548 }
7549
7550 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7551 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7552
7553 // Grey object rescan during second checkpoint phase --
7554 // the parallel version.
7555 void Par_PushAndMarkClosure::do_oop(oop obj) {
7556 // In the assert below, we ignore the mark word because
7557 // this oop may point to an already visited object that is
7558 // on the overflow stack (in which case the mark word has
7559 // been hijacked for chaining into the overflow stack --
7560 // if this is the last object in the overflow stack then
7561 // its mark word will be NULL). Because this object may
7562 // have been subsequently popped off the global overflow
7563 // stack, and the mark word possibly restored to the prototypical
7564 // value, by the time we get to examined this failing assert in
7565 // the debugger, is_oop_or_null(false) may subsequently start
7566 // to hold.
7567 assert(obj->is_oop_or_null(true),
7568 "expected an oop or NULL");
7569 HeapWord* addr = (HeapWord*)obj;
7570 // Check if oop points into the CMS generation
7571 // and is not marked
7572 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7573 // a white object ...
7574 // If we manage to "claim" the object, by being the
7575 // first thread to mark it, then we push it on our
7576 // marking stack
7577 if (_bit_map->par_mark(addr)) { // ... now grey
7578 // push on work queue (grey set)
7579 bool simulate_overflow = false;
7580 NOT_PRODUCT(
7581 if (CMSMarkStackOverflowALot &&
7582 _collector->par_simulate_overflow()) {
7583 // simulate a stack overflow
7584 simulate_overflow = true;
7585 }
7586 )
7587 if (simulate_overflow || !_work_queue->push(obj)) {
7588 _collector->par_push_on_overflow_list(obj);
7589 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7590 }
7591 } // Else, some other thread got there first
7592 }
7593 }
7594
7595 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7596 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7597
7598 void PushAndMarkClosure::remember_klass(Klass* k) {
7599 if (!_revisit_stack->push(oop(k))) {
7600 fatal("Revisit stack overflowed in PushAndMarkClosure");
7601 }
7602 }
7603
7604 void Par_PushAndMarkClosure::remember_klass(Klass* k) {
7605 if (!_revisit_stack->par_push(oop(k))) {
7606 fatal("Revist stack overflowed in Par_PushAndMarkClosure");
7607 }
7608 }
7609
7610 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7611 Mutex* bml = _collector->bitMapLock();
7612 assert_lock_strong(bml);
7613 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7614 "CMS thread should hold CMS token");
7615
7616 bml->unlock();
7617 ConcurrentMarkSweepThread::desynchronize(true);
7618
7619 ConcurrentMarkSweepThread::acknowledge_yield_request();
7620
7621 _collector->stopTimer();
7622 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7623 if (PrintCMSStatistics != 0) {
7624 _collector->incrementYields();
7625 }
7626 _collector->icms_wait();
7627
7628 // See the comment in coordinator_yield()
7629 for (unsigned i = 0; i < CMSYieldSleepCount &&
7630 ConcurrentMarkSweepThread::should_yield() &&
7631 !CMSCollector::foregroundGCIsActive(); ++i) {
7632 os::sleep(Thread::current(), 1, false);
7633 ConcurrentMarkSweepThread::acknowledge_yield_request();
7634 }
7635
7636 ConcurrentMarkSweepThread::synchronize(true);
7637 bml->lock();
7638
7639 _collector->startTimer();
7640 }
7641
7642 bool CMSPrecleanRefsYieldClosure::should_return() {
7643 if (ConcurrentMarkSweepThread::should_yield()) {
7644 do_yield_work();
7645 }
7646 return _collector->foregroundGCIsActive();
7647 }
7648
7649 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7650 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7651 "mr should be aligned to start at a card boundary");
7652 // We'd like to assert:
7653 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7654 // "mr should be a range of cards");
7655 // However, that would be too strong in one case -- the last
7656 // partition ends at _unallocated_block which, in general, can be
7657 // an arbitrary boundary, not necessarily card aligned.
7658 if (PrintCMSStatistics != 0) {
7659 _num_dirty_cards +=
7660 mr.word_size()/CardTableModRefBS::card_size_in_words;
7661 }
7662 _space->object_iterate_mem(mr, &_scan_cl);
7663 }
7664
7665 SweepClosure::SweepClosure(CMSCollector* collector,
7666 ConcurrentMarkSweepGeneration* g,
7667 CMSBitMap* bitMap, bool should_yield) :
7668 _collector(collector),
7669 _g(g),
7670 _sp(g->cmsSpace()),
7671 _limit(_sp->sweep_limit()),
7672 _freelistLock(_sp->freelistLock()),
7673 _bitMap(bitMap),
7674 _yield(should_yield),
7675 _inFreeRange(false), // No free range at beginning of sweep
7676 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7677 _lastFreeRangeCoalesced(false),
7678 _freeFinger(g->used_region().start())
7679 {
7680 NOT_PRODUCT(
7681 _numObjectsFreed = 0;
7682 _numWordsFreed = 0;
7683 _numObjectsLive = 0;
7684 _numWordsLive = 0;
7685 _numObjectsAlreadyFree = 0;
7686 _numWordsAlreadyFree = 0;
7687 _last_fc = NULL;
7688
7689 _sp->initializeIndexedFreeListArrayReturnedBytes();
7690 _sp->dictionary()->initializeDictReturnedBytes();
7691 )
7692 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7693 "sweep _limit out of bounds");
7694 if (CMSTraceSweeper) {
7695 gclog_or_tty->print("\n====================\nStarting new sweep\n");
7696 }
7697 }
7698
7699 // We need this destructor to reclaim any space at the end
7700 // of the space, which do_blk below may not have added back to
7701 // the free lists. [basically dealing with the "fringe effect"]
7702 SweepClosure::~SweepClosure() {
7703 assert_lock_strong(_freelistLock);
7704 // this should be treated as the end of a free run if any
7705 // The current free range should be returned to the free lists
7706 // as one coalesced chunk.
7707 if (inFreeRange()) {
7708 flushCurFreeChunk(freeFinger(),
7709 pointer_delta(_limit, freeFinger()));
7710 assert(freeFinger() < _limit, "the finger pointeth off base");
7711 if (CMSTraceSweeper) {
7712 gclog_or_tty->print("destructor:");
7713 gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") "
7714 "[coalesced:"SIZE_FORMAT"]\n",
7715 freeFinger(), pointer_delta(_limit, freeFinger()),
7716 lastFreeRangeCoalesced());
7717 }
7718 }
7719 NOT_PRODUCT(
7720 if (Verbose && PrintGC) {
7721 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, "
7722 SIZE_FORMAT " bytes",
7723 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7724 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7725 SIZE_FORMAT" bytes "
7726 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7727 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7728 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7729 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) *
7730 sizeof(HeapWord);
7731 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7732
7733 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7734 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7735 size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes();
7736 size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes;
7737 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes);
7738 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7739 indexListReturnedBytes);
7740 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7741 dictReturnedBytes);
7742 }
7743 }
7744 )
7745 // Now, in debug mode, just null out the sweep_limit
7746 NOT_PRODUCT(_sp->clear_sweep_limit();)
7747 if (CMSTraceSweeper) {
7748 gclog_or_tty->print("end of sweep\n================\n");
7749 }
7750 }
7751
7752 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7753 bool freeRangeInFreeLists) {
7754 if (CMSTraceSweeper) {
7755 gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n",
7756 freeFinger, _sp->block_size(freeFinger),
7757 freeRangeInFreeLists);
7758 }
7759 assert(!inFreeRange(), "Trampling existing free range");
7760 set_inFreeRange(true);
7761 set_lastFreeRangeCoalesced(false);
7762
7763 set_freeFinger(freeFinger);
7764 set_freeRangeInFreeLists(freeRangeInFreeLists);
7765 if (CMSTestInFreeList) {
7766 if (freeRangeInFreeLists) {
7767 FreeChunk* fc = (FreeChunk*) freeFinger;
7768 assert(fc->isFree(), "A chunk on the free list should be free.");
7769 assert(fc->size() > 0, "Free range should have a size");
7770 assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists");
7771 }
7772 }
7773 }
7774
7775 // Note that the sweeper runs concurrently with mutators. Thus,
7776 // it is possible for direct allocation in this generation to happen
7777 // in the middle of the sweep. Note that the sweeper also coalesces
7778 // contiguous free blocks. Thus, unless the sweeper and the allocator
7779 // synchronize appropriately freshly allocated blocks may get swept up.
7780 // This is accomplished by the sweeper locking the free lists while
7781 // it is sweeping. Thus blocks that are determined to be free are
7782 // indeed free. There is however one additional complication:
7783 // blocks that have been allocated since the final checkpoint and
7784 // mark, will not have been marked and so would be treated as
7785 // unreachable and swept up. To prevent this, the allocator marks
7786 // the bit map when allocating during the sweep phase. This leads,
7787 // however, to a further complication -- objects may have been allocated
7788 // but not yet initialized -- in the sense that the header isn't yet
7789 // installed. The sweeper can not then determine the size of the block
7790 // in order to skip over it. To deal with this case, we use a technique
7791 // (due to Printezis) to encode such uninitialized block sizes in the
7792 // bit map. Since the bit map uses a bit per every HeapWord, but the
7793 // CMS generation has a minimum object size of 3 HeapWords, it follows
7794 // that "normal marks" won't be adjacent in the bit map (there will
7795 // always be at least two 0 bits between successive 1 bits). We make use
7796 // of these "unused" bits to represent uninitialized blocks -- the bit
7797 // corresponding to the start of the uninitialized object and the next
7798 // bit are both set. Finally, a 1 bit marks the end of the object that
7799 // started with the two consecutive 1 bits to indicate its potentially
7800 // uninitialized state.
7801
7802 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7803 FreeChunk* fc = (FreeChunk*)addr;
7804 size_t res;
7805
7806 // check if we are done sweepinrg
7807 if (addr == _limit) { // we have swept up to the limit, do nothing more
7808 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7809 "sweep _limit out of bounds");
7810 // help the closure application finish
7811 return pointer_delta(_sp->end(), _limit);
7812 }
7813 assert(addr <= _limit, "sweep invariant");
7814
7815 // check if we should yield
7816 do_yield_check(addr);
7817 if (fc->isFree()) {
7818 // Chunk that is already free
7819 res = fc->size();
7820 doAlreadyFreeChunk(fc);
7821 debug_only(_sp->verifyFreeLists());
7822 assert(res == fc->size(), "Don't expect the size to change");
7823 NOT_PRODUCT(
7824 _numObjectsAlreadyFree++;
7825 _numWordsAlreadyFree += res;
7826 )
7827 NOT_PRODUCT(_last_fc = fc;)
7828 } else if (!_bitMap->isMarked(addr)) {
7829 // Chunk is fresh garbage
7830 res = doGarbageChunk(fc);
7831 debug_only(_sp->verifyFreeLists());
7832 NOT_PRODUCT(
7833 _numObjectsFreed++;
7834 _numWordsFreed += res;
7835 )
7836 } else {
7837 // Chunk that is alive.
7838 res = doLiveChunk(fc);
7839 debug_only(_sp->verifyFreeLists());
7840 NOT_PRODUCT(
7841 _numObjectsLive++;
7842 _numWordsLive += res;
7843 )
7844 }
7845 return res;
7846 }
7847
7848 // For the smart allocation, record following
7849 // split deaths - a free chunk is removed from its free list because
7850 // it is being split into two or more chunks.
7851 // split birth - a free chunk is being added to its free list because
7852 // a larger free chunk has been split and resulted in this free chunk.
7853 // coal death - a free chunk is being removed from its free list because
7854 // it is being coalesced into a large free chunk.
7855 // coal birth - a free chunk is being added to its free list because
7856 // it was created when two or more free chunks where coalesced into
7857 // this free chunk.
7858 //
7859 // These statistics are used to determine the desired number of free
7860 // chunks of a given size. The desired number is chosen to be relative
7861 // to the end of a CMS sweep. The desired number at the end of a sweep
7862 // is the
7863 // count-at-end-of-previous-sweep (an amount that was enough)
7864 // - count-at-beginning-of-current-sweep (the excess)
7865 // + split-births (gains in this size during interval)
7866 // - split-deaths (demands on this size during interval)
7867 // where the interval is from the end of one sweep to the end of the
7868 // next.
7869 //
7870 // When sweeping the sweeper maintains an accumulated chunk which is
7871 // the chunk that is made up of chunks that have been coalesced. That
7872 // will be termed the left-hand chunk. A new chunk of garbage that
7873 // is being considered for coalescing will be referred to as the
7874 // right-hand chunk.
7875 //
7876 // When making a decision on whether to coalesce a right-hand chunk with
7877 // the current left-hand chunk, the current count vs. the desired count
7878 // of the left-hand chunk is considered. Also if the right-hand chunk
7879 // is near the large chunk at the end of the heap (see
7880 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7881 // left-hand chunk is coalesced.
7882 //
7883 // When making a decision about whether to split a chunk, the desired count
7884 // vs. the current count of the candidate to be split is also considered.
7885 // If the candidate is underpopulated (currently fewer chunks than desired)
7886 // a chunk of an overpopulated (currently more chunks than desired) size may
7887 // be chosen. The "hint" associated with a free list, if non-null, points
7888 // to a free list which may be overpopulated.
7889 //
7890
7891 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) {
7892 size_t size = fc->size();
7893 // Chunks that cannot be coalesced are not in the
7894 // free lists.
7895 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7896 assert(_sp->verifyChunkInFreeLists(fc),
7897 "free chunk should be in free lists");
7898 }
7899 // a chunk that is already free, should not have been
7900 // marked in the bit map
7901 HeapWord* addr = (HeapWord*) fc;
7902 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7903 // Verify that the bit map has no bits marked between
7904 // addr and purported end of this block.
7905 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7906
7907 // Some chunks cannot be coalesced in under any circumstances.
7908 // See the definition of cantCoalesce().
7909 if (!fc->cantCoalesce()) {
7910 // This chunk can potentially be coalesced.
7911 if (_sp->adaptive_freelists()) {
7912 // All the work is done in
7913 doPostIsFreeOrGarbageChunk(fc, size);
7914 } else { // Not adaptive free lists
7915 // this is a free chunk that can potentially be coalesced by the sweeper;
7916 if (!inFreeRange()) {
7917 // if the next chunk is a free block that can't be coalesced
7918 // it doesn't make sense to remove this chunk from the free lists
7919 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7920 assert((HeapWord*)nextChunk <= _limit, "sweep invariant");
7921 if ((HeapWord*)nextChunk < _limit && // there's a next chunk...
7922 nextChunk->isFree() && // which is free...
7923 nextChunk->cantCoalesce()) { // ... but cant be coalesced
7924 // nothing to do
7925 } else {
7926 // Potentially the start of a new free range:
7927 // Don't eagerly remove it from the free lists.
7928 // No need to remove it if it will just be put
7929 // back again. (Also from a pragmatic point of view
7930 // if it is a free block in a region that is beyond
7931 // any allocated blocks, an assertion will fail)
7932 // Remember the start of a free run.
7933 initialize_free_range(addr, true);
7934 // end - can coalesce with next chunk
7935 }
7936 } else {
7937 // the midst of a free range, we are coalescing
7938 debug_only(record_free_block_coalesced(fc);)
7939 if (CMSTraceSweeper) {
7940 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
7941 }
7942 // remove it from the free lists
7943 _sp->removeFreeChunkFromFreeLists(fc);
7944 set_lastFreeRangeCoalesced(true);
7945 // If the chunk is being coalesced and the current free range is
7946 // in the free lists, remove the current free range so that it
7947 // will be returned to the free lists in its entirety - all
7948 // the coalesced pieces included.
7949 if (freeRangeInFreeLists()) {
7950 FreeChunk* ffc = (FreeChunk*) freeFinger();
7951 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7952 "Size of free range is inconsistent with chunk size.");
7953 if (CMSTestInFreeList) {
7954 assert(_sp->verifyChunkInFreeLists(ffc),
7955 "free range is not in free lists");
7956 }
7957 _sp->removeFreeChunkFromFreeLists(ffc);
7958 set_freeRangeInFreeLists(false);
7959 }
7960 }
7961 }
7962 } else {
7963 // Code path common to both original and adaptive free lists.
7964
7965 // cant coalesce with previous block; this should be treated
7966 // as the end of a free run if any
7967 if (inFreeRange()) {
7968 // we kicked some butt; time to pick up the garbage
7969 assert(freeFinger() < addr, "the finger pointeth off base");
7970 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
7971 }
7972 // else, nothing to do, just continue
7973 }
7974 }
7975
7976 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) {
7977 // This is a chunk of garbage. It is not in any free list.
7978 // Add it to a free list or let it possibly be coalesced into
7979 // a larger chunk.
7980 HeapWord* addr = (HeapWord*) fc;
7981 size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7982
7983 if (_sp->adaptive_freelists()) {
7984 // Verify that the bit map has no bits marked between
7985 // addr and purported end of just dead object.
7986 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7987
7988 doPostIsFreeOrGarbageChunk(fc, size);
7989 } else {
7990 if (!inFreeRange()) {
7991 // start of a new free range
7992 assert(size > 0, "A free range should have a size");
7993 initialize_free_range(addr, false);
7994
7995 } else {
7996 // this will be swept up when we hit the end of the
7997 // free range
7998 if (CMSTraceSweeper) {
7999 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8000 }
8001 // If the chunk is being coalesced and the current free range is
8002 // in the free lists, remove the current free range so that it
8003 // will be returned to the free lists in its entirety - all
8004 // the coalesced pieces included.
8005 if (freeRangeInFreeLists()) {
8006 FreeChunk* ffc = (FreeChunk*)freeFinger();
8007 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8008 "Size of free range is inconsistent with chunk size.");
8009 if (CMSTestInFreeList) {
8010 assert(_sp->verifyChunkInFreeLists(ffc),
8011 "free range is not in free lists");
8012 }
8013 _sp->removeFreeChunkFromFreeLists(ffc);
8014 set_freeRangeInFreeLists(false);
8015 }
8016 set_lastFreeRangeCoalesced(true);
8017 }
8018 // this will be swept up when we hit the end of the free range
8019
8020 // Verify that the bit map has no bits marked between
8021 // addr and purported end of just dead object.
8022 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8023 }
8024 return size;
8025 }
8026
8027 size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
8028 HeapWord* addr = (HeapWord*) fc;
8029 // The sweeper has just found a live object. Return any accumulated
8030 // left hand chunk to the free lists.
8031 if (inFreeRange()) {
8032 if (_sp->adaptive_freelists()) {
8033 flushCurFreeChunk(freeFinger(),
8034 pointer_delta(addr, freeFinger()));
8035 } else { // not adaptive freelists
8036 set_inFreeRange(false);
8037 // Add the free range back to the free list if it is not already
8038 // there.
8039 if (!freeRangeInFreeLists()) {
8040 assert(freeFinger() < addr, "the finger pointeth off base");
8041 if (CMSTraceSweeper) {
8042 gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) "
8043 "[coalesced:%d]\n",
8044 freeFinger(), pointer_delta(addr, freeFinger()),
8045 lastFreeRangeCoalesced());
8046 }
8047 _sp->addChunkAndRepairOffsetTable(freeFinger(),
8048 pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced());
8049 }
8050 }
8051 }
8052
8053 // Common code path for original and adaptive free lists.
8054
8055 // this object is live: we'd normally expect this to be
8056 // an oop, and like to assert the following:
8057 // assert(oop(addr)->is_oop(), "live block should be an oop");
8058 // However, as we commented above, this may be an object whose
8059 // header hasn't yet been initialized.
8060 size_t size;
8061 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8062 if (_bitMap->isMarked(addr + 1)) {
8063 // Determine the size from the bit map, rather than trying to
8064 // compute it from the object header.
8065 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8066 size = pointer_delta(nextOneAddr + 1, addr);
8067 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8068 "alignment problem");
8069
8070 #ifdef DEBUG
8071 if (oop(addr)->klass_or_null() != NULL &&
8072 ( !_collector->should_unload_classes()
8073 || oop(addr)->is_parsable())) {
8074 // Ignore mark word because we are running concurrent with mutators
8075 assert(oop(addr)->is_oop(true), "live block should be an oop");
8076 assert(size ==
8077 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8078 "P-mark and computed size do not agree");
8079 }
8080 #endif
8081
8082 } else {
8083 // This should be an initialized object that's alive.
8084 assert(oop(addr)->klass_or_null() != NULL &&
8085 (!_collector->should_unload_classes()
8086 || oop(addr)->is_parsable()),
8087 "Should be an initialized object");
8088 // Ignore mark word because we are running concurrent with mutators
8089 assert(oop(addr)->is_oop(true), "live block should be an oop");
8090 // Verify that the bit map has no bits marked between
8091 // addr and purported end of this block.
8092 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8093 assert(size >= 3, "Necessary for Printezis marks to work");
8094 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8095 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8096 }
8097 return size;
8098 }
8099
8100 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc,
8101 size_t chunkSize) {
8102 // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation
8103 // scheme.
8104 bool fcInFreeLists = fc->isFree();
8105 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8106 assert((HeapWord*)fc <= _limit, "sweep invariant");
8107 if (CMSTestInFreeList && fcInFreeLists) {
8108 assert(_sp->verifyChunkInFreeLists(fc),
8109 "free chunk is not in free lists");
8110 }
8111
8112
8113 if (CMSTraceSweeper) {
8114 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8115 }
8116
8117 HeapWord* addr = (HeapWord*) fc;
8118
8119 bool coalesce;
8120 size_t left = pointer_delta(addr, freeFinger());
8121 size_t right = chunkSize;
8122 switch (FLSCoalescePolicy) {
8123 // numeric value forms a coalition aggressiveness metric
8124 case 0: { // never coalesce
8125 coalesce = false;
8126 break;
8127 }
8128 case 1: { // coalesce if left & right chunks on overpopulated lists
8129 coalesce = _sp->coalOverPopulated(left) &&
8130 _sp->coalOverPopulated(right);
8131 break;
8132 }
8133 case 2: { // coalesce if left chunk on overpopulated list (default)
8134 coalesce = _sp->coalOverPopulated(left);
8135 break;
8136 }
8137 case 3: { // coalesce if left OR right chunk on overpopulated list
8138 coalesce = _sp->coalOverPopulated(left) ||
8139 _sp->coalOverPopulated(right);
8140 break;
8141 }
8142 case 4: { // always coalesce
8143 coalesce = true;
8144 break;
8145 }
8146 default:
8147 ShouldNotReachHere();
8148 }
8149
8150 // Should the current free range be coalesced?
8151 // If the chunk is in a free range and either we decided to coalesce above
8152 // or the chunk is near the large block at the end of the heap
8153 // (isNearLargestChunk() returns true), then coalesce this chunk.
8154 bool doCoalesce = inFreeRange() &&
8155 (coalesce || _g->isNearLargestChunk((HeapWord*)fc));
8156 if (doCoalesce) {
8157 // Coalesce the current free range on the left with the new
8158 // chunk on the right. If either is on a free list,
8159 // it must be removed from the list and stashed in the closure.
8160 if (freeRangeInFreeLists()) {
8161 FreeChunk* ffc = (FreeChunk*)freeFinger();
8162 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8163 "Size of free range is inconsistent with chunk size.");
8164 if (CMSTestInFreeList) {
8165 assert(_sp->verifyChunkInFreeLists(ffc),
8166 "Chunk is not in free lists");
8167 }
8168 _sp->coalDeath(ffc->size());
8169 _sp->removeFreeChunkFromFreeLists(ffc);
8170 set_freeRangeInFreeLists(false);
8171 }
8172 if (fcInFreeLists) {
8173 _sp->coalDeath(chunkSize);
8174 assert(fc->size() == chunkSize,
8175 "The chunk has the wrong size or is not in the free lists");
8176 _sp->removeFreeChunkFromFreeLists(fc);
8177 }
8178 set_lastFreeRangeCoalesced(true);
8179 } else { // not in a free range and/or should not coalesce
8180 // Return the current free range and start a new one.
8181 if (inFreeRange()) {
8182 // In a free range but cannot coalesce with the right hand chunk.
8183 // Put the current free range into the free lists.
8184 flushCurFreeChunk(freeFinger(),
8185 pointer_delta(addr, freeFinger()));
8186 }
8187 // Set up for new free range. Pass along whether the right hand
8188 // chunk is in the free lists.
8189 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8190 }
8191 }
8192 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) {
8193 assert(inFreeRange(), "Should only be called if currently in a free range.");
8194 assert(size > 0,
8195 "A zero sized chunk cannot be added to the free lists.");
8196 if (!freeRangeInFreeLists()) {
8197 if(CMSTestInFreeList) {
8198 FreeChunk* fc = (FreeChunk*) chunk;
8199 fc->setSize(size);
8200 assert(!_sp->verifyChunkInFreeLists(fc),
8201 "chunk should not be in free lists yet");
8202 }
8203 if (CMSTraceSweeper) {
8204 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8205 chunk, size);
8206 }
8207 // A new free range is going to be starting. The current
8208 // free range has not been added to the free lists yet or
8209 // was removed so add it back.
8210 // If the current free range was coalesced, then the death
8211 // of the free range was recorded. Record a birth now.
8212 if (lastFreeRangeCoalesced()) {
8213 _sp->coalBirth(size);
8214 }
8215 _sp->addChunkAndRepairOffsetTable(chunk, size,
8216 lastFreeRangeCoalesced());
8217 }
8218 set_inFreeRange(false);
8219 set_freeRangeInFreeLists(false);
8220 }
8221
8222 // We take a break if we've been at this for a while,
8223 // so as to avoid monopolizing the locks involved.
8224 void SweepClosure::do_yield_work(HeapWord* addr) {
8225 // Return current free chunk being used for coalescing (if any)
8226 // to the appropriate freelist. After yielding, the next
8227 // free block encountered will start a coalescing range of
8228 // free blocks. If the next free block is adjacent to the
8229 // chunk just flushed, they will need to wait for the next
8230 // sweep to be coalesced.
8231 if (inFreeRange()) {
8232 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8233 }
8234
8235 // First give up the locks, then yield, then re-lock.
8236 // We should probably use a constructor/destructor idiom to
8237 // do this unlock/lock or modify the MutexUnlocker class to
8238 // serve our purpose. XXX
8239 assert_lock_strong(_bitMap->lock());
8240 assert_lock_strong(_freelistLock);
8241 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8242 "CMS thread should hold CMS token");
8243 _bitMap->lock()->unlock();
8244 _freelistLock->unlock();
8245 ConcurrentMarkSweepThread::desynchronize(true);
8246 ConcurrentMarkSweepThread::acknowledge_yield_request();
8247 _collector->stopTimer();
8248 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8249 if (PrintCMSStatistics != 0) {
8250 _collector->incrementYields();
8251 }
8252 _collector->icms_wait();
8253
8254 // See the comment in coordinator_yield()
8255 for (unsigned i = 0; i < CMSYieldSleepCount &&
8256 ConcurrentMarkSweepThread::should_yield() &&
8257 !CMSCollector::foregroundGCIsActive(); ++i) {
8258 os::sleep(Thread::current(), 1, false);
8259 ConcurrentMarkSweepThread::acknowledge_yield_request();
8260 }
8261
8262 ConcurrentMarkSweepThread::synchronize(true);
8263 _freelistLock->lock();
8264 _bitMap->lock()->lock_without_safepoint_check();
8265 _collector->startTimer();
8266 }
8267
8268 #ifndef PRODUCT
8269 // This is actually very useful in a product build if it can
8270 // be called from the debugger. Compile it into the product
8271 // as needed.
8272 bool debug_verifyChunkInFreeLists(FreeChunk* fc) {
8273 return debug_cms_space->verifyChunkInFreeLists(fc);
8274 }
8275
8276 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const {
8277 if (CMSTraceSweeper) {
8278 gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size());
8279 }
8280 }
8281 #endif
8282
8283 // CMSIsAliveClosure
8284 bool CMSIsAliveClosure::do_object_b(oop obj) {
8285 HeapWord* addr = (HeapWord*)obj;
8286 return addr != NULL &&
8287 (!_span.contains(addr) || _bit_map->isMarked(addr));
8288 }
8289
8290 // CMSKeepAliveClosure: the serial version
8291 void CMSKeepAliveClosure::do_oop(oop obj) {
8292 HeapWord* addr = (HeapWord*)obj;
8293 if (_span.contains(addr) &&
8294 !_bit_map->isMarked(addr)) {
8295 _bit_map->mark(addr);
8296 bool simulate_overflow = false;
8297 NOT_PRODUCT(
8298 if (CMSMarkStackOverflowALot &&
8299 _collector->simulate_overflow()) {
8300 // simulate a stack overflow
8301 simulate_overflow = true;
8302 }
8303 )
8304 if (simulate_overflow || !_mark_stack->push(obj)) {
8305 _collector->push_on_overflow_list(obj);
8306 _collector->_ser_kac_ovflw++;
8307 }
8308 }
8309 }
8310
8311 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8312 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8313
8314 // CMSParKeepAliveClosure: a parallel version of the above.
8315 // The work queues are private to each closure (thread),
8316 // but (may be) available for stealing by other threads.
8317 void CMSParKeepAliveClosure::do_oop(oop obj) {
8318 HeapWord* addr = (HeapWord*)obj;
8319 if (_span.contains(addr) &&
8320 !_bit_map->isMarked(addr)) {
8321 // In general, during recursive tracing, several threads
8322 // may be concurrently getting here; the first one to
8323 // "tag" it, claims it.
8324 if (_bit_map->par_mark(addr)) {
8325 bool res = _work_queue->push(obj);
8326 assert(res, "Low water mark should be much less than capacity");
8327 // Do a recursive trim in the hope that this will keep
8328 // stack usage lower, but leave some oops for potential stealers
8329 trim_queue(_low_water_mark);
8330 } // Else, another thread got there first
8331 }
8332 }
8333
8334 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8335 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8336
8337 void CMSParKeepAliveClosure::trim_queue(uint max) {
8338 while (_work_queue->size() > max) {
8339 oop new_oop;
8340 if (_work_queue->pop_local(new_oop)) {
8341 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8342 assert(_bit_map->isMarked((HeapWord*)new_oop),
8343 "no white objects on this stack!");
8344 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8345 // iterate over the oops in this oop, marking and pushing
8346 // the ones in CMS heap (i.e. in _span).
8347 new_oop->oop_iterate(&_mark_and_push);
8348 }
8349 }
8350 }
8351
8352 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8353 HeapWord* addr = (HeapWord*)obj;
8354 if (_span.contains(addr) &&
8355 !_bit_map->isMarked(addr)) {
8356 if (_bit_map->par_mark(addr)) {
8357 bool simulate_overflow = false;
8358 NOT_PRODUCT(
8359 if (CMSMarkStackOverflowALot &&
8360 _collector->par_simulate_overflow()) {
8361 // simulate a stack overflow
8362 simulate_overflow = true;
8363 }
8364 )
8365 if (simulate_overflow || !_work_queue->push(obj)) {
8366 _collector->par_push_on_overflow_list(obj);
8367 _collector->_par_kac_ovflw++;
8368 }
8369 } // Else another thread got there already
8370 }
8371 }
8372
8373 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8374 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8375
8376 //////////////////////////////////////////////////////////////////
8377 // CMSExpansionCause /////////////////////////////
8378 //////////////////////////////////////////////////////////////////
8379 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8380 switch (cause) {
8381 case _no_expansion:
8382 return "No expansion";
8383 case _satisfy_free_ratio:
8384 return "Free ratio";
8385 case _satisfy_promotion:
8386 return "Satisfy promotion";
8387 case _satisfy_allocation:
8388 return "allocation";
8389 case _allocate_par_lab:
8390 return "Par LAB";
8391 case _allocate_par_spooling_space:
8392 return "Par Spooling Space";
8393 case _adaptive_size_policy:
8394 return "Ergonomics";
8395 default:
8396 return "unknown";
8397 }
8398 }
8399
8400 void CMSDrainMarkingStackClosure::do_void() {
8401 // the max number to take from overflow list at a time
8402 const size_t num = _mark_stack->capacity()/4;
8403 while (!_mark_stack->isEmpty() ||
8404 // if stack is empty, check the overflow list
8405 _collector->take_from_overflow_list(num, _mark_stack)) {
8406 oop obj = _mark_stack->pop();
8407 HeapWord* addr = (HeapWord*)obj;
8408 assert(_span.contains(addr), "Should be within span");
8409 assert(_bit_map->isMarked(addr), "Should be marked");
8410 assert(obj->is_oop(), "Should be an oop");
8411 obj->oop_iterate(_keep_alive);
8412 }
8413 }
8414
8415 void CMSParDrainMarkingStackClosure::do_void() {
8416 // drain queue
8417 trim_queue(0);
8418 }
8419
8420 // Trim our work_queue so its length is below max at return
8421 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8422 while (_work_queue->size() > max) {
8423 oop new_oop;
8424 if (_work_queue->pop_local(new_oop)) {
8425 assert(new_oop->is_oop(), "Expected an oop");
8426 assert(_bit_map->isMarked((HeapWord*)new_oop),
8427 "no white objects on this stack!");
8428 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8429 // iterate over the oops in this oop, marking and pushing
8430 // the ones in CMS heap (i.e. in _span).
8431 new_oop->oop_iterate(&_mark_and_push);
8432 }
8433 }
8434 }
8435
8436 ////////////////////////////////////////////////////////////////////
8437 // Support for Marking Stack Overflow list handling and related code
8438 ////////////////////////////////////////////////////////////////////
8439 // Much of the following code is similar in shape and spirit to the
8440 // code used in ParNewGC. We should try and share that code
8441 // as much as possible in the future.
8442
8443 #ifndef PRODUCT
8444 // Debugging support for CMSStackOverflowALot
8445
8446 // It's OK to call this multi-threaded; the worst thing
8447 // that can happen is that we'll get a bunch of closely
8448 // spaced simulated oveflows, but that's OK, in fact
8449 // probably good as it would exercise the overflow code
8450 // under contention.
8451 bool CMSCollector::simulate_overflow() {
8452 if (_overflow_counter-- <= 0) { // just being defensive
8453 _overflow_counter = CMSMarkStackOverflowInterval;
8454 return true;
8455 } else {
8456 return false;
8457 }
8458 }
8459
8460 bool CMSCollector::par_simulate_overflow() {
8461 return simulate_overflow();
8462 }
8463 #endif
8464
8465 // Single-threaded
8466 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8467 assert(stack->isEmpty(), "Expected precondition");
8468 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8469 size_t i = num;
8470 oop cur = _overflow_list;
8471 const markOop proto = markOopDesc::prototype();
8472 NOT_PRODUCT(size_t n = 0;)
8473 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8474 next = oop(cur->mark());
8475 cur->set_mark(proto); // until proven otherwise
8476 assert(cur->is_oop(), "Should be an oop");
8477 bool res = stack->push(cur);
8478 assert(res, "Bit off more than can chew?");
8479 NOT_PRODUCT(n++;)
8480 }
8481 _overflow_list = cur;
8482 #ifndef PRODUCT
8483 assert(_num_par_pushes >= n, "Too many pops?");
8484 _num_par_pushes -=n;
8485 #endif
8486 return !stack->isEmpty();
8487 }
8488
8489 // Multi-threaded; use CAS to break off a prefix
8490 bool CMSCollector::par_take_from_overflow_list(size_t num,
8491 OopTaskQueue* work_q) {
8492 assert(work_q->size() == 0, "That's the current policy");
8493 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8494 if (_overflow_list == NULL) {
8495 return false;
8496 }
8497 // Grab the entire list; we'll put back a suffix
8498 oop prefix = (oop)Atomic::xchg_ptr(NULL, &_overflow_list);
8499 if (prefix == NULL) { // someone grabbed it before we did ...
8500 // ... we could spin for a short while, but for now we don't
8501 return false;
8502 }
8503 size_t i = num;
8504 oop cur = prefix;
8505 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8506 if (cur->mark() != NULL) {
8507 oop suffix_head = cur->mark(); // suffix will be put back on global list
8508 cur->set_mark(NULL); // break off suffix
8509 // Find tail of suffix so we can prepend suffix to global list
8510 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8511 oop suffix_tail = cur;
8512 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8513 "Tautology");
8514 oop observed_overflow_list = _overflow_list;
8515 do {
8516 cur = observed_overflow_list;
8517 suffix_tail->set_mark(markOop(cur));
8518 observed_overflow_list =
8519 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur);
8520 } while (cur != observed_overflow_list);
8521 }
8522
8523 // Push the prefix elements on work_q
8524 assert(prefix != NULL, "control point invariant");
8525 const markOop proto = markOopDesc::prototype();
8526 oop next;
8527 NOT_PRODUCT(size_t n = 0;)
8528 for (cur = prefix; cur != NULL; cur = next) {
8529 next = oop(cur->mark());
8530 cur->set_mark(proto); // until proven otherwise
8531 assert(cur->is_oop(), "Should be an oop");
8532 bool res = work_q->push(cur);
8533 assert(res, "Bit off more than we can chew?");
8534 NOT_PRODUCT(n++;)
8535 }
8536 #ifndef PRODUCT
8537 assert(_num_par_pushes >= n, "Too many pops?");
8538 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8539 #endif
8540 return true;
8541 }
8542
8543 // Single-threaded
8544 void CMSCollector::push_on_overflow_list(oop p) {
8545 NOT_PRODUCT(_num_par_pushes++;)
8546 assert(p->is_oop(), "Not an oop");
8547 preserve_mark_if_necessary(p);
8548 p->set_mark((markOop)_overflow_list);
8549 _overflow_list = p;
8550 }
8551
8552 // Multi-threaded; use CAS to prepend to overflow list
8553 void CMSCollector::par_push_on_overflow_list(oop p) {
8554 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8555 assert(p->is_oop(), "Not an oop");
8556 par_preserve_mark_if_necessary(p);
8557 oop observed_overflow_list = _overflow_list;
8558 oop cur_overflow_list;
8559 do {
8560 cur_overflow_list = observed_overflow_list;
8561 p->set_mark(markOop(cur_overflow_list));
8562 observed_overflow_list =
8563 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8564 } while (cur_overflow_list != observed_overflow_list);
8565 }
8566
8567 // Single threaded
8568 // General Note on GrowableArray: pushes may silently fail
8569 // because we are (temporarily) out of C-heap for expanding
8570 // the stack. The problem is quite ubiquitous and affects
8571 // a lot of code in the JVM. The prudent thing for GrowableArray
8572 // to do (for now) is to exit with an error. However, that may
8573 // be too draconian in some cases because the caller may be
8574 // able to recover without much harm. For suych cases, we
8575 // should probably introduce a "soft_push" method which returns
8576 // an indication of success or failure with the assumption that
8577 // the caller may be able to recover from a failure; code in
8578 // the VM can then be changed, incrementally, to deal with such
8579 // failures where possible, thus, incrementally hardening the VM
8580 // in such low resource situations.
8581 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8582 int PreserveMarkStackSize = 128;
8583
8584 if (_preserved_oop_stack == NULL) {
8585 assert(_preserved_mark_stack == NULL,
8586 "bijection with preserved_oop_stack");
8587 // Allocate the stacks
8588 _preserved_oop_stack = new (ResourceObj::C_HEAP)
8589 GrowableArray<oop>(PreserveMarkStackSize, true);
8590 _preserved_mark_stack = new (ResourceObj::C_HEAP)
8591 GrowableArray<markOop>(PreserveMarkStackSize, true);
8592 if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) {
8593 vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */,
8594 "Preserved Mark/Oop Stack for CMS (C-heap)");
8595 }
8596 }
8597 _preserved_oop_stack->push(p);
8598 _preserved_mark_stack->push(m);
8599 assert(m == p->mark(), "Mark word changed");
8600 assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(),
8601 "bijection");
8602 }
8603
8604 // Single threaded
8605 void CMSCollector::preserve_mark_if_necessary(oop p) {
8606 markOop m = p->mark();
8607 if (m->must_be_preserved(p)) {
8608 preserve_mark_work(p, m);
8609 }
8610 }
8611
8612 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8613 markOop m = p->mark();
8614 if (m->must_be_preserved(p)) {
8615 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8616 // Even though we read the mark word without holding
8617 // the lock, we are assured that it will not change
8618 // because we "own" this oop, so no other thread can
8619 // be trying to push it on the overflow list; see
8620 // the assertion in preserve_mark_work() that checks
8621 // that m == p->mark().
8622 preserve_mark_work(p, m);
8623 }
8624 }
8625
8626 // We should be able to do this multi-threaded,
8627 // a chunk of stack being a task (this is
8628 // correct because each oop only ever appears
8629 // once in the overflow list. However, it's
8630 // not very easy to completely overlap this with
8631 // other operations, so will generally not be done
8632 // until all work's been completed. Because we
8633 // expect the preserved oop stack (set) to be small,
8634 // it's probably fine to do this single-threaded.
8635 // We can explore cleverer concurrent/overlapped/parallel
8636 // processing of preserved marks if we feel the
8637 // need for this in the future. Stack overflow should
8638 // be so rare in practice and, when it happens, its
8639 // effect on performance so great that this will
8640 // likely just be in the noise anyway.
8641 void CMSCollector::restore_preserved_marks_if_any() {
8642 if (_preserved_oop_stack == NULL) {
8643 assert(_preserved_mark_stack == NULL,
8644 "bijection with preserved_oop_stack");
8645 return;
8646 }
8647
8648 assert(SafepointSynchronize::is_at_safepoint(),
8649 "world should be stopped");
8650 assert(Thread::current()->is_ConcurrentGC_thread() ||
8651 Thread::current()->is_VM_thread(),
8652 "should be single-threaded");
8653
8654 int length = _preserved_oop_stack->length();
8655 assert(_preserved_mark_stack->length() == length, "bijection");
8656 for (int i = 0; i < length; i++) {
8657 oop p = _preserved_oop_stack->at(i);
8658 assert(p->is_oop(), "Should be an oop");
8659 assert(_span.contains(p), "oop should be in _span");
8660 assert(p->mark() == markOopDesc::prototype(),
8661 "Set when taken from overflow list");
8662 markOop m = _preserved_mark_stack->at(i);
8663 p->set_mark(m);
8664 }
8665 _preserved_mark_stack->clear();
8666 _preserved_oop_stack->clear();
8667 assert(_preserved_mark_stack->is_empty() &&
8668 _preserved_oop_stack->is_empty(),
8669 "stacks were cleared above");
8670 }
8671
8672 #ifndef PRODUCT
8673 bool CMSCollector::no_preserved_marks() const {
8674 return ( ( _preserved_mark_stack == NULL
8675 && _preserved_oop_stack == NULL)
8676 || ( _preserved_mark_stack->is_empty()
8677 && _preserved_oop_stack->is_empty()));
8678 }
8679 #endif
8680
8681 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
8682 {
8683 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8684 CMSAdaptiveSizePolicy* size_policy =
8685 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
8686 assert(size_policy->is_gc_cms_adaptive_size_policy(),
8687 "Wrong type for size policy");
8688 return size_policy;
8689 }
8690
8691 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
8692 size_t desired_promo_size) {
8693 if (cur_promo_size < desired_promo_size) {
8694 size_t expand_bytes = desired_promo_size - cur_promo_size;
8695 if (PrintAdaptiveSizePolicy && Verbose) {
8696 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8697 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
8698 expand_bytes);
8699 }
8700 expand(expand_bytes,
8701 MinHeapDeltaBytes,
8702 CMSExpansionCause::_adaptive_size_policy);
8703 } else if (desired_promo_size < cur_promo_size) {
8704 size_t shrink_bytes = cur_promo_size - desired_promo_size;
8705 if (PrintAdaptiveSizePolicy && Verbose) {
8706 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8707 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
8708 shrink_bytes);
8709 }
8710 shrink(shrink_bytes);
8711 }
8712 }
8713
8714 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
8715 GenCollectedHeap* gch = GenCollectedHeap::heap();
8716 CMSGCAdaptivePolicyCounters* counters =
8717 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
8718 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
8719 "Wrong kind of counters");
8720 return counters;
8721 }
8722
8723
8724 void ASConcurrentMarkSweepGeneration::update_counters() {
8725 if (UsePerfData) {
8726 _space_counters->update_all();
8727 _gen_counters->update_all();
8728 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8729 GenCollectedHeap* gch = GenCollectedHeap::heap();
8730 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8731 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8732 "Wrong gc statistics type");
8733 counters->update_counters(gc_stats_l);
8734 }
8735 }
8736
8737 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
8738 if (UsePerfData) {
8739 _space_counters->update_used(used);
8740 _space_counters->update_capacity();
8741 _gen_counters->update_all();
8742
8743 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8744 GenCollectedHeap* gch = GenCollectedHeap::heap();
8745 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8746 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8747 "Wrong gc statistics type");
8748 counters->update_counters(gc_stats_l);
8749 }
8750 }
8751
8752 // The desired expansion delta is computed so that:
8753 // . desired free percentage or greater is used
8754 void ASConcurrentMarkSweepGeneration::compute_new_size() {
8755 assert_locked_or_safepoint(Heap_lock);
8756
8757 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8758
8759 // If incremental collection failed, we just want to expand
8760 // to the limit.
8761 if (incremental_collection_failed()) {
8762 clear_incremental_collection_failed();
8763 grow_to_reserved();
8764 return;
8765 }
8766
8767 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
8768
8769 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
8770 "Wrong type of heap");
8771 int prev_level = level() - 1;
8772 assert(prev_level >= 0, "The cms generation is the lowest generation");
8773 Generation* prev_gen = gch->get_gen(prev_level);
8774 assert(prev_gen->kind() == Generation::ASParNew,
8775 "Wrong type of young generation");
8776 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
8777 size_t cur_eden = younger_gen->eden()->capacity();
8778 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
8779 size_t cur_promo = free();
8780 size_policy->compute_tenured_generation_free_space(cur_promo,
8781 max_available(),
8782 cur_eden);
8783 resize(cur_promo, size_policy->promo_size());
8784
8785 // Record the new size of the space in the cms generation
8786 // that is available for promotions. This is temporary.
8787 // It should be the desired promo size.
8788 size_policy->avg_cms_promo()->sample(free());
8789 size_policy->avg_old_live()->sample(used());
8790
8791 if (UsePerfData) {
8792 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8793 counters->update_cms_capacity_counter(capacity());
8794 }
8795 }
8796
8797 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
8798 assert_locked_or_safepoint(Heap_lock);
8799 assert_lock_strong(freelistLock());
8800 HeapWord* old_end = _cmsSpace->end();
8801 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
8802 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
8803 FreeChunk* chunk_at_end = find_chunk_at_end();
8804 if (chunk_at_end == NULL) {
8805 // No room to shrink
8806 if (PrintGCDetails && Verbose) {
8807 gclog_or_tty->print_cr("No room to shrink: old_end "
8808 PTR_FORMAT " unallocated_start " PTR_FORMAT
8809 " chunk_at_end " PTR_FORMAT,
8810 old_end, unallocated_start, chunk_at_end);
8811 }
8812 return;
8813 } else {
8814
8815 // Find the chunk at the end of the space and determine
8816 // how much it can be shrunk.
8817 size_t shrinkable_size_in_bytes = chunk_at_end->size();
8818 size_t aligned_shrinkable_size_in_bytes =
8819 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
8820 assert(unallocated_start <= chunk_at_end->end(),
8821 "Inconsistent chunk at end of space");
8822 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
8823 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
8824
8825 // Shrink the underlying space
8826 _virtual_space.shrink_by(bytes);
8827 if (PrintGCDetails && Verbose) {
8828 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
8829 " desired_bytes " SIZE_FORMAT
8830 " shrinkable_size_in_bytes " SIZE_FORMAT
8831 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
8832 " bytes " SIZE_FORMAT,
8833 desired_bytes, shrinkable_size_in_bytes,
8834 aligned_shrinkable_size_in_bytes, bytes);
8835 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
8836 " unallocated_start " SIZE_FORMAT,
8837 old_end, unallocated_start);
8838 }
8839
8840 // If the space did shrink (shrinking is not guaranteed),
8841 // shrink the chunk at the end by the appropriate amount.
8842 if (((HeapWord*)_virtual_space.high()) < old_end) {
8843 size_t new_word_size =
8844 heap_word_size(_virtual_space.committed_size());
8845
8846 // Have to remove the chunk from the dictionary because it is changing
8847 // size and might be someplace elsewhere in the dictionary.
8848
8849 // Get the chunk at end, shrink it, and put it
8850 // back.
8851 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
8852 size_t word_size_change = word_size_before - new_word_size;
8853 size_t chunk_at_end_old_size = chunk_at_end->size();
8854 assert(chunk_at_end_old_size >= word_size_change,
8855 "Shrink is too large");
8856 chunk_at_end->setSize(chunk_at_end_old_size -
8857 word_size_change);
8858 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
8859 word_size_change);
8860
8861 _cmsSpace->returnChunkToDictionary(chunk_at_end);
8862
8863 MemRegion mr(_cmsSpace->bottom(), new_word_size);
8864 _bts->resize(new_word_size); // resize the block offset shared array
8865 Universe::heap()->barrier_set()->resize_covered_region(mr);
8866 _cmsSpace->assert_locked();
8867 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
8868
8869 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
8870
8871 // update the space and generation capacity counters
8872 if (UsePerfData) {
8873 _space_counters->update_capacity();
8874 _gen_counters->update_all();
8875 }
8876
8877 if (Verbose && PrintGCDetails) {
8878 size_t new_mem_size = _virtual_space.committed_size();
8879 size_t old_mem_size = new_mem_size + bytes;
8880 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
8881 name(), old_mem_size/K, bytes/K, new_mem_size/K);
8882 }
8883 }
8884
8885 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
8886 "Inconsistency at end of space");
8887 assert(chunk_at_end->end() == _cmsSpace->end(),
8888 "Shrinking is inconsistent");
8889 return;
8890 }
8891 }
8892
8893 // Transfer some number of overflown objects to usual marking
8894 // stack. Return true if some objects were transferred.
8895 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8896 size_t num = MIN2((size_t)_mark_stack->capacity()/4,
8897 (size_t)ParGCDesiredObjsFromOverflowList);
8898
8899 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8900 assert(_collector->overflow_list_is_empty() || res,
8901 "If list is not empty, we should have taken something");
8902 assert(!res || !_mark_stack->isEmpty(),
8903 "If we took something, it should now be on our stack");
8904 return res;
8905 }
8906
8907 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8908 size_t res = _sp->block_size_no_stall(addr, _collector);
8909 assert(res != 0, "Should always be able to compute a size");
8910 if (_sp->block_is_obj(addr)) {
8911 if (_live_bit_map->isMarked(addr)) {
8912 // It can't have been dead in a previous cycle
8913 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8914 } else {
8915 _dead_bit_map->mark(addr); // mark the dead object
8916 }
8917 }
8918 return res;
8919 }