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/_referenceProcessor.cpp.incl"
27
28 // List of discovered references.
29 class DiscoveredList {
30 public:
31 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
32 oop head() const {
33 return UseCompressedOops ? oopDesc::decode_heap_oop_not_null(_compressed_head) :
34 _oop_head;
35 }
36 HeapWord* adr_head() {
37 return UseCompressedOops ? (HeapWord*)&_compressed_head :
38 (HeapWord*)&_oop_head;
39 }
40 void set_head(oop o) {
41 if (UseCompressedOops) {
42 // Must compress the head ptr.
43 _compressed_head = oopDesc::encode_heap_oop_not_null(o);
44 } else {
45 _oop_head = o;
46 }
47 }
48 bool empty() const { return head() == ReferenceProcessor::sentinel_ref(); }
49 size_t length() { return _len; }
50 void set_length(size_t len) { _len = len; }
51 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
52 void dec_length(size_t dec) { _len -= dec; }
53 private:
54 // Set value depending on UseCompressedOops. This could be a template class
55 // but then we have to fix all the instantiations and declarations that use this class.
56 oop _oop_head;
57 narrowOop _compressed_head;
58 size_t _len;
59 };
60
61 oop ReferenceProcessor::_sentinelRef = NULL;
62
63 const int subclasses_of_ref = REF_PHANTOM - REF_OTHER;
64
65 void referenceProcessor_init() {
66 ReferenceProcessor::init_statics();
67 }
68
69 void ReferenceProcessor::init_statics() {
70 assert(_sentinelRef == NULL, "should be initialized precisely once");
71 EXCEPTION_MARK;
72 _sentinelRef = instanceKlass::cast(
73 SystemDictionary::reference_klass())->
74 allocate_permanent_instance(THREAD);
75
76 // Initialize the master soft ref clock.
77 java_lang_ref_SoftReference::set_clock(os::javaTimeMillis());
78
79 if (HAS_PENDING_EXCEPTION) {
80 Handle ex(THREAD, PENDING_EXCEPTION);
81 vm_exit_during_initialization(ex);
82 }
83 assert(_sentinelRef != NULL && _sentinelRef->is_oop(),
84 "Just constructed it!");
85 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
86 RefDiscoveryPolicy == ReferentBasedDiscovery,
87 "Unrecongnized RefDiscoveryPolicy");
88 }
89
90 ReferenceProcessor*
91 ReferenceProcessor::create_ref_processor(MemRegion span,
92 bool atomic_discovery,
93 bool mt_discovery,
94 BoolObjectClosure* is_alive_non_header,
95 int parallel_gc_threads,
96 bool mt_processing,
97 bool dl_needs_barrier) {
98 int mt_degree = 1;
99 if (parallel_gc_threads > 1) {
100 mt_degree = parallel_gc_threads;
101 }
102 ReferenceProcessor* rp =
103 new ReferenceProcessor(span, atomic_discovery,
104 mt_discovery, mt_degree,
105 mt_processing && (parallel_gc_threads > 0),
106 dl_needs_barrier);
107 if (rp == NULL) {
108 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
109 }
110 rp->set_is_alive_non_header(is_alive_non_header);
111 return rp;
112 }
113
114 ReferenceProcessor::ReferenceProcessor(MemRegion span,
115 bool atomic_discovery,
116 bool mt_discovery,
117 int mt_degree,
118 bool mt_processing,
119 bool discovered_list_needs_barrier) :
120 _discovering_refs(false),
121 _enqueuing_is_done(false),
122 _is_alive_non_header(NULL),
123 _discovered_list_needs_barrier(discovered_list_needs_barrier),
124 _bs(NULL),
125 _processing_is_mt(mt_processing),
126 _next_id(0)
127 {
128 _span = span;
129 _discovery_is_atomic = atomic_discovery;
130 _discovery_is_mt = mt_discovery;
131 _num_q = mt_degree;
132 _discoveredSoftRefs = NEW_C_HEAP_ARRAY(DiscoveredList, _num_q * subclasses_of_ref);
133 if (_discoveredSoftRefs == NULL) {
134 vm_exit_during_initialization("Could not allocated RefProc Array");
135 }
136 _discoveredWeakRefs = &_discoveredSoftRefs[_num_q];
137 _discoveredFinalRefs = &_discoveredWeakRefs[_num_q];
138 _discoveredPhantomRefs = &_discoveredFinalRefs[_num_q];
139 assert(sentinel_ref() != NULL, "_sentinelRef is NULL");
140 // Initialized all entries to _sentinelRef
141 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
142 _discoveredSoftRefs[i].set_head(sentinel_ref());
143 _discoveredSoftRefs[i].set_length(0);
144 }
145 // If we do barreirs, cache a copy of the barrier set.
146 if (discovered_list_needs_barrier) {
147 _bs = Universe::heap()->barrier_set();
148 }
149 }
150
151 #ifndef PRODUCT
152 void ReferenceProcessor::verify_no_references_recorded() {
153 guarantee(!_discovering_refs, "Discovering refs?");
154 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
155 guarantee(_discoveredSoftRefs[i].empty(),
156 "Found non-empty discovered list");
157 }
158 }
159 #endif
160
161 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
162 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
163 if (UseCompressedOops) {
164 f->do_oop((narrowOop*)_discoveredSoftRefs[i].adr_head());
165 } else {
166 f->do_oop((oop*)_discoveredSoftRefs[i].adr_head());
167 }
168 }
169 }
170
171 void ReferenceProcessor::oops_do(OopClosure* f) {
172 f->do_oop(adr_sentinel_ref());
173 }
174
175 void ReferenceProcessor::update_soft_ref_master_clock() {
176 // Update (advance) the soft ref master clock field. This must be done
177 // after processing the soft ref list.
178 jlong now = os::javaTimeMillis();
179 jlong clock = java_lang_ref_SoftReference::clock();
180 NOT_PRODUCT(
181 if (now < clock) {
182 warning("time warp: %d to %d", clock, now);
183 }
184 )
185 // In product mode, protect ourselves from system time being adjusted
186 // externally and going backward; see note in the implementation of
187 // GenCollectedHeap::time_since_last_gc() for the right way to fix
188 // this uniformly throughout the VM; see bug-id 4741166. XXX
189 if (now > clock) {
190 java_lang_ref_SoftReference::set_clock(now);
191 }
192 // Else leave clock stalled at its old value until time progresses
193 // past clock value.
194 }
195
196 void ReferenceProcessor::process_discovered_references(
197 ReferencePolicy* policy,
198 BoolObjectClosure* is_alive,
199 OopClosure* keep_alive,
200 VoidClosure* complete_gc,
201 AbstractRefProcTaskExecutor* task_executor) {
202 NOT_PRODUCT(verify_ok_to_handle_reflists());
203
204 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
205 // Stop treating discovered references specially.
206 disable_discovery();
207
208 bool trace_time = PrintGCDetails && PrintReferenceGC;
209 // Soft references
210 {
211 TraceTime tt("SoftReference", trace_time, false, gclog_or_tty);
212 process_discovered_reflist(_discoveredSoftRefs, policy, true,
213 is_alive, keep_alive, complete_gc, task_executor);
214 }
215
216 update_soft_ref_master_clock();
217
218 // Weak references
219 {
220 TraceTime tt("WeakReference", trace_time, false, gclog_or_tty);
221 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
222 is_alive, keep_alive, complete_gc, task_executor);
223 }
224
225 // Final references
226 {
227 TraceTime tt("FinalReference", trace_time, false, gclog_or_tty);
228 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
229 is_alive, keep_alive, complete_gc, task_executor);
230 }
231
232 // Phantom references
233 {
234 TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty);
235 process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
236 is_alive, keep_alive, complete_gc, task_executor);
237 }
238
239 // Weak global JNI references. It would make more sense (semantically) to
240 // traverse these simultaneously with the regular weak references above, but
241 // that is not how the JDK1.2 specification is. See #4126360. Native code can
242 // thus use JNI weak references to circumvent the phantom references and
243 // resurrect a "post-mortem" object.
244 {
245 TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty);
246 if (task_executor != NULL) {
247 task_executor->set_single_threaded_mode();
248 }
249 process_phaseJNI(is_alive, keep_alive, complete_gc);
250 }
251 }
252
253 #ifndef PRODUCT
254 // Calculate the number of jni handles.
255 uint ReferenceProcessor::count_jni_refs() {
256 class AlwaysAliveClosure: public BoolObjectClosure {
257 public:
258 virtual bool do_object_b(oop obj) { return true; }
259 virtual void do_object(oop obj) { assert(false, "Don't call"); }
260 };
261
262 class CountHandleClosure: public OopClosure {
263 private:
264 int _count;
265 public:
266 CountHandleClosure(): _count(0) {}
267 void do_oop(oop* unused) { _count++; }
268 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
269 int count() { return _count; }
270 };
271 CountHandleClosure global_handle_count;
272 AlwaysAliveClosure always_alive;
273 JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
274 return global_handle_count.count();
275 }
276 #endif
277
278 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
279 OopClosure* keep_alive,
280 VoidClosure* complete_gc) {
281 #ifndef PRODUCT
282 if (PrintGCDetails && PrintReferenceGC) {
283 unsigned int count = count_jni_refs();
284 gclog_or_tty->print(", %u refs", count);
285 }
286 #endif
287 JNIHandles::weak_oops_do(is_alive, keep_alive);
288 // Finally remember to keep sentinel around
289 keep_alive->do_oop(adr_sentinel_ref());
290 complete_gc->do_void();
291 }
292
293
294 template <class T>
295 static bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
296 AbstractRefProcTaskExecutor* task_executor) {
297
298 // Remember old value of pending references list
299 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
300 T old_pending_list_value = *pending_list_addr;
301
302 // Enqueue references that are not made active again, and
303 // clear the decks for the next collection (cycle).
304 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
305 // Do the oop-check on pending_list_addr missed in
306 // enqueue_discovered_reflist. We should probably
307 // do a raw oop_check so that future such idempotent
308 // oop_stores relying on the oop-check side-effect
309 // may be elided automatically and safely without
310 // affecting correctness.
311 oop_store(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr));
312
313 // Stop treating discovered references specially.
314 ref->disable_discovery();
315
316 // Return true if new pending references were added
317 return old_pending_list_value != *pending_list_addr;
318 }
319
320 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
321 NOT_PRODUCT(verify_ok_to_handle_reflists());
322 if (UseCompressedOops) {
323 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
324 } else {
325 return enqueue_discovered_ref_helper<oop>(this, task_executor);
326 }
327 }
328
329 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
330 HeapWord* pending_list_addr) {
331 // Given a list of refs linked through the "discovered" field
332 // (java.lang.ref.Reference.discovered) chain them through the
333 // "next" field (java.lang.ref.Reference.next) and prepend
334 // to the pending list.
335 if (TraceReferenceGC && PrintGCDetails) {
336 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
337 INTPTR_FORMAT, (address)refs_list.head());
338 }
339 oop obj = refs_list.head();
340 // Walk down the list, copying the discovered field into
341 // the next field and clearing it (except for the last
342 // non-sentinel object which is treated specially to avoid
343 // confusion with an active reference).
344 while (obj != sentinel_ref()) {
345 assert(obj->is_instanceRef(), "should be reference object");
346 oop next = java_lang_ref_Reference::discovered(obj);
347 if (TraceReferenceGC && PrintGCDetails) {
348 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next " INTPTR_FORMAT,
349 obj, next);
350 }
351 assert(java_lang_ref_Reference::next(obj) == NULL,
352 "The reference should not be enqueued");
353 if (next == sentinel_ref()) { // obj is last
354 // Swap refs_list into pendling_list_addr and
355 // set obj's next to what we read from pending_list_addr.
356 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
357 // Need oop_check on pending_list_addr above;
358 // see special oop-check code at the end of
359 // enqueue_discovered_reflists() further below.
360 if (old == NULL) {
361 // obj should be made to point to itself, since
362 // pending list was empty.
363 java_lang_ref_Reference::set_next(obj, obj);
364 } else {
365 java_lang_ref_Reference::set_next(obj, old);
366 }
367 } else {
368 java_lang_ref_Reference::set_next(obj, next);
369 }
370 java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
371 obj = next;
372 }
373 }
374
375 // Parallel enqueue task
376 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
377 public:
378 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
379 DiscoveredList discovered_refs[],
380 HeapWord* pending_list_addr,
381 oop sentinel_ref,
382 int n_queues)
383 : EnqueueTask(ref_processor, discovered_refs,
384 pending_list_addr, sentinel_ref, n_queues)
385 { }
386
387 virtual void work(unsigned int work_id) {
388 assert(work_id < (unsigned int)_ref_processor.num_q(), "Index out-of-bounds");
389 // Simplest first cut: static partitioning.
390 int index = work_id;
391 for (int j = 0; j < subclasses_of_ref; j++, index += _n_queues) {
392 _ref_processor.enqueue_discovered_reflist(
393 _refs_lists[index], _pending_list_addr);
394 _refs_lists[index].set_head(_sentinel_ref);
395 _refs_lists[index].set_length(0);
396 }
397 }
398 };
399
400 // Enqueue references that are not made active again
401 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
402 AbstractRefProcTaskExecutor* task_executor) {
403 if (_processing_is_mt && task_executor != NULL) {
404 // Parallel code
405 RefProcEnqueueTask tsk(*this, _discoveredSoftRefs,
406 pending_list_addr, sentinel_ref(), _num_q);
407 task_executor->execute(tsk);
408 } else {
409 // Serial code: call the parent class's implementation
410 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
411 enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr);
412 _discoveredSoftRefs[i].set_head(sentinel_ref());
413 _discoveredSoftRefs[i].set_length(0);
414 }
415 }
416 }
417
418 // Iterator for the list of discovered references.
419 class DiscoveredListIterator {
420 public:
421 inline DiscoveredListIterator(DiscoveredList& refs_list,
422 OopClosure* keep_alive,
423 BoolObjectClosure* is_alive);
424
425 // End Of List.
426 inline bool has_next() const { return _next != ReferenceProcessor::sentinel_ref(); }
427
428 // Get oop to the Reference object.
429 inline oop obj() const { return _ref; }
430
431 // Get oop to the referent object.
432 inline oop referent() const { return _referent; }
433
434 // Returns true if referent is alive.
435 inline bool is_referent_alive() const;
436
437 // Loads data for the current reference.
438 // The "allow_null_referent" argument tells us to allow for the possibility
439 // of a NULL referent in the discovered Reference object. This typically
440 // happens in the case of concurrent collectors that may have done the
441 // discovery concurrently, or interleaved, with mutator execution.
442 inline void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
443
444 // Move to the next discovered reference.
445 inline void next();
446
447 // Remove the current reference from the list
448 inline void remove();
449
450 // Make the Reference object active again.
451 inline void make_active() { java_lang_ref_Reference::set_next(_ref, NULL); }
452
453 // Make the referent alive.
454 inline void make_referent_alive() {
455 if (UseCompressedOops) {
456 _keep_alive->do_oop((narrowOop*)_referent_addr);
457 } else {
458 _keep_alive->do_oop((oop*)_referent_addr);
459 }
460 }
461
462 // Update the discovered field.
463 inline void update_discovered() {
464 // First _prev_next ref actually points into DiscoveredList (gross).
465 if (UseCompressedOops) {
466 _keep_alive->do_oop((narrowOop*)_prev_next);
467 } else {
468 _keep_alive->do_oop((oop*)_prev_next);
469 }
470 }
471
472 // NULL out referent pointer.
473 inline void clear_referent() { oop_store_raw(_referent_addr, NULL); }
474
475 // Statistics
476 NOT_PRODUCT(
477 inline size_t processed() const { return _processed; }
478 inline size_t removed() const { return _removed; }
479 )
480
481 inline void move_to_next();
482
483 private:
484 DiscoveredList& _refs_list;
485 HeapWord* _prev_next;
486 oop _ref;
487 HeapWord* _discovered_addr;
488 oop _next;
489 HeapWord* _referent_addr;
490 oop _referent;
491 OopClosure* _keep_alive;
492 BoolObjectClosure* _is_alive;
493 DEBUG_ONLY(
494 oop _first_seen; // cyclic linked list check
495 )
496 NOT_PRODUCT(
497 size_t _processed;
498 size_t _removed;
499 )
500 };
501
502 inline DiscoveredListIterator::DiscoveredListIterator(DiscoveredList& refs_list,
503 OopClosure* keep_alive,
504 BoolObjectClosure* is_alive)
505 : _refs_list(refs_list),
506 _prev_next(refs_list.adr_head()),
507 _ref(refs_list.head()),
508 #ifdef ASSERT
509 _first_seen(refs_list.head()),
510 #endif
511 #ifndef PRODUCT
512 _processed(0),
513 _removed(0),
514 #endif
515 _next(refs_list.head()),
516 _keep_alive(keep_alive),
517 _is_alive(is_alive)
518 { }
519
520 inline bool DiscoveredListIterator::is_referent_alive() const {
521 return _is_alive->do_object_b(_referent);
522 }
523
524 inline void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
525 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
526 oop discovered = java_lang_ref_Reference::discovered(_ref);
527 assert(_discovered_addr && discovered->is_oop_or_null(),
528 "discovered field is bad");
529 _next = discovered;
530 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
531 _referent = java_lang_ref_Reference::referent(_ref);
532 assert(Universe::heap()->is_in_reserved_or_null(_referent),
533 "Wrong oop found in java.lang.Reference object");
534 assert(allow_null_referent ?
535 _referent->is_oop_or_null()
536 : _referent->is_oop(),
537 "bad referent");
538 }
539
540 inline void DiscoveredListIterator::next() {
541 _prev_next = _discovered_addr;
542 move_to_next();
543 }
544
545 inline void DiscoveredListIterator::remove() {
546 assert(_ref->is_oop(), "Dropping a bad reference");
547 oop_store_raw(_discovered_addr, NULL);
548 // First _prev_next ref actually points into DiscoveredList (gross).
549 if (UseCompressedOops) {
550 // Remove Reference object from list.
551 oopDesc::encode_store_heap_oop_not_null((narrowOop*)_prev_next, _next);
552 } else {
553 // Remove Reference object from list.
554 oopDesc::store_heap_oop((oop*)_prev_next, _next);
555 }
556 NOT_PRODUCT(_removed++);
557 _refs_list.dec_length(1);
558 }
559
560 inline void DiscoveredListIterator::move_to_next() {
561 _ref = _next;
562 assert(_ref != _first_seen, "cyclic ref_list found");
563 NOT_PRODUCT(_processed++);
564 }
565
566 // NOTE: process_phase*() are largely similar, and at a high level
567 // merely iterate over the extant list applying a predicate to
568 // each of its elements and possibly removing that element from the
569 // list and applying some further closures to that element.
570 // We should consider the possibility of replacing these
571 // process_phase*() methods by abstracting them into
572 // a single general iterator invocation that receives appropriate
573 // closures that accomplish this work.
574
575 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
576 // referents are not alive, but that should be kept alive for policy reasons.
577 // Keep alive the transitive closure of all such referents.
578 void
579 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
580 ReferencePolicy* policy,
581 BoolObjectClosure* is_alive,
582 OopClosure* keep_alive,
583 VoidClosure* complete_gc) {
584 assert(policy != NULL, "Must have a non-NULL policy");
585 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
586 // Decide which softly reachable refs should be kept alive.
587 while (iter.has_next()) {
588 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
589 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
590 if (referent_is_dead && !policy->should_clear_reference(iter.obj())) {
591 if (TraceReferenceGC) {
592 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
593 iter.obj(), iter.obj()->blueprint()->internal_name());
594 }
595 // Remove Reference object from list
596 iter.remove();
597 // Make the Reference object active again
598 iter.make_active();
599 // keep the referent around
600 iter.make_referent_alive();
601 iter.move_to_next();
602 } else {
603 iter.next();
604 }
605 }
606 // Close the reachable set
607 complete_gc->do_void();
608 NOT_PRODUCT(
609 if (PrintGCDetails && TraceReferenceGC) {
610 gclog_or_tty->print(" Dropped %d dead Refs out of %d "
611 "discovered Refs by policy ", iter.removed(), iter.processed());
612 }
613 )
614 }
615
616 // Traverse the list and remove any Refs that are not active, or
617 // whose referents are either alive or NULL.
618 void
619 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
620 BoolObjectClosure* is_alive,
621 OopClosure* keep_alive) {
622 assert(discovery_is_atomic(), "Error");
623 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
624 while (iter.has_next()) {
625 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
626 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
627 assert(next == NULL, "Should not discover inactive Reference");
628 if (iter.is_referent_alive()) {
629 if (TraceReferenceGC) {
630 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
631 iter.obj(), iter.obj()->blueprint()->internal_name());
632 }
633 // The referent is reachable after all.
634 // Remove Reference object from list.
635 iter.remove();
636 // Update the referent pointer as necessary: Note that this
637 // should not entail any recursive marking because the
638 // referent must already have been traversed.
639 iter.make_referent_alive();
640 iter.move_to_next();
641 } else {
642 iter.next();
643 }
644 }
645 NOT_PRODUCT(
646 if (PrintGCDetails && TraceReferenceGC) {
647 gclog_or_tty->print(" Dropped %d active Refs out of %d "
648 "Refs in discovered list ", iter.removed(), iter.processed());
649 }
650 )
651 }
652
653 void
654 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
655 BoolObjectClosure* is_alive,
656 OopClosure* keep_alive,
657 VoidClosure* complete_gc) {
658 assert(!discovery_is_atomic(), "Error");
659 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
660 while (iter.has_next()) {
661 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
662 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
663 oop next = java_lang_ref_Reference::next(iter.obj());
664 if ((iter.referent() == NULL || iter.is_referent_alive() ||
665 next != NULL)) {
666 assert(next->is_oop_or_null(), "bad next field");
667 // Remove Reference object from list
668 iter.remove();
669 // Trace the cohorts
670 iter.make_referent_alive();
671 if (UseCompressedOops) {
672 keep_alive->do_oop((narrowOop*)next_addr);
673 } else {
674 keep_alive->do_oop((oop*)next_addr);
675 }
676 iter.move_to_next();
677 } else {
678 iter.next();
679 }
680 }
681 // Now close the newly reachable set
682 complete_gc->do_void();
683 NOT_PRODUCT(
684 if (PrintGCDetails && TraceReferenceGC) {
685 gclog_or_tty->print(" Dropped %d active Refs out of %d "
686 "Refs in discovered list ", iter.removed(), iter.processed());
687 }
688 )
689 }
690
691 // Traverse the list and process the referents, by either
692 // clearing them or keeping them (and their reachable
693 // closure) alive.
694 void
695 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
696 bool clear_referent,
697 BoolObjectClosure* is_alive,
698 OopClosure* keep_alive,
699 VoidClosure* complete_gc) {
700 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
701 while (iter.has_next()) {
702 iter.update_discovered();
703 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
704 if (clear_referent) {
705 // NULL out referent pointer
706 iter.clear_referent();
707 } else {
708 // keep the referent around
709 iter.make_referent_alive();
710 }
711 if (TraceReferenceGC) {
712 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
713 clear_referent ? "cleared " : "",
714 iter.obj(), iter.obj()->blueprint()->internal_name());
715 }
716 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
717 // If discovery is concurrent, we may have objects with null referents,
718 // being those that were concurrently cleared after they were discovered
719 // (and not subsequently precleaned).
720 assert( (discovery_is_atomic() && iter.referent()->is_oop())
721 || (!discovery_is_atomic() && iter.referent()->is_oop_or_null(UseConcMarkSweepGC)),
722 "Adding a bad referent");
723 iter.next();
724 }
725 // Remember to keep sentinel pointer around
726 iter.update_discovered();
727 // Close the reachable set
728 complete_gc->do_void();
729 }
730
731 void
732 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) {
733 oop obj = refs_list.head();
734 while (obj != sentinel_ref()) {
735 oop discovered = java_lang_ref_Reference::discovered(obj);
736 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
737 obj = discovered;
738 }
739 refs_list.set_head(sentinel_ref());
740 refs_list.set_length(0);
741 }
742
743 void ReferenceProcessor::abandon_partial_discovery() {
744 // loop over the lists
745 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
746 if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) {
747 gclog_or_tty->print_cr(
748 "\nAbandoning %s discovered list",
749 list_name(i));
750 }
751 abandon_partial_discovered_list(_discoveredSoftRefs[i]);
752 }
753 }
754
755 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
756 public:
757 RefProcPhase1Task(ReferenceProcessor& ref_processor,
758 DiscoveredList refs_lists[],
759 ReferencePolicy* policy,
760 bool marks_oops_alive)
761 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
762 _policy(policy)
763 { }
764 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
765 OopClosure& keep_alive,
766 VoidClosure& complete_gc)
767 {
768 _ref_processor.process_phase1(_refs_lists[i], _policy,
769 &is_alive, &keep_alive, &complete_gc);
770 }
771 private:
772 ReferencePolicy* _policy;
773 };
774
775 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
776 public:
777 RefProcPhase2Task(ReferenceProcessor& ref_processor,
778 DiscoveredList refs_lists[],
779 bool marks_oops_alive)
780 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
781 { }
782 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
783 OopClosure& keep_alive,
784 VoidClosure& complete_gc)
785 {
786 _ref_processor.process_phase2(_refs_lists[i],
787 &is_alive, &keep_alive, &complete_gc);
788 }
789 };
790
791 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
792 public:
793 RefProcPhase3Task(ReferenceProcessor& ref_processor,
794 DiscoveredList refs_lists[],
795 bool clear_referent,
796 bool marks_oops_alive)
797 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
798 _clear_referent(clear_referent)
799 { }
800 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
801 OopClosure& keep_alive,
802 VoidClosure& complete_gc)
803 {
804 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
805 &is_alive, &keep_alive, &complete_gc);
806 }
807 private:
808 bool _clear_referent;
809 };
810
811 // Balances reference queues.
812 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
813 {
814 // calculate total length
815 size_t total_refs = 0;
816 for (int i = 0; i < _num_q; ++i) {
817 total_refs += ref_lists[i].length();
818 }
819 size_t avg_refs = total_refs / _num_q + 1;
820 int to_idx = 0;
821 for (int from_idx = 0; from_idx < _num_q; from_idx++) {
822 while (ref_lists[from_idx].length() > avg_refs) {
823 assert(to_idx < _num_q, "Sanity Check!");
824 if (ref_lists[to_idx].length() < avg_refs) {
825 // move superfluous refs
826 size_t refs_to_move =
827 MIN2(ref_lists[from_idx].length() - avg_refs,
828 avg_refs - ref_lists[to_idx].length());
829 oop move_head = ref_lists[from_idx].head();
830 oop move_tail = move_head;
831 oop new_head = move_head;
832 // find an element to split the list on
833 for (size_t j = 0; j < refs_to_move; ++j) {
834 move_tail = new_head;
835 new_head = java_lang_ref_Reference::discovered(new_head);
836 }
837 java_lang_ref_Reference::set_discovered(move_tail, ref_lists[to_idx].head());
838 ref_lists[to_idx].set_head(move_head);
839 ref_lists[to_idx].inc_length(refs_to_move);
840 ref_lists[from_idx].set_head(new_head);
841 ref_lists[from_idx].dec_length(refs_to_move);
842 } else {
843 ++to_idx;
844 }
845 }
846 }
847 }
848
849 void
850 ReferenceProcessor::process_discovered_reflist(
851 DiscoveredList refs_lists[],
852 ReferencePolicy* policy,
853 bool clear_referent,
854 BoolObjectClosure* is_alive,
855 OopClosure* keep_alive,
856 VoidClosure* complete_gc,
857 AbstractRefProcTaskExecutor* task_executor)
858 {
859 bool mt = task_executor != NULL && _processing_is_mt;
860 if (mt && ParallelRefProcBalancingEnabled) {
861 balance_queues(refs_lists);
862 }
863 if (PrintReferenceGC && PrintGCDetails) {
864 size_t total = 0;
865 for (int i = 0; i < _num_q; ++i) {
866 total += refs_lists[i].length();
867 }
868 gclog_or_tty->print(", %u refs", total);
869 }
870
871 // Phase 1 (soft refs only):
872 // . Traverse the list and remove any SoftReferences whose
873 // referents are not alive, but that should be kept alive for
874 // policy reasons. Keep alive the transitive closure of all
875 // such referents.
876 if (policy != NULL) {
877 if (mt) {
878 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
879 task_executor->execute(phase1);
880 } else {
881 for (int i = 0; i < _num_q; i++) {
882 process_phase1(refs_lists[i], policy,
883 is_alive, keep_alive, complete_gc);
884 }
885 }
886 } else { // policy == NULL
887 assert(refs_lists != _discoveredSoftRefs,
888 "Policy must be specified for soft references.");
889 }
890
891 // Phase 2:
892 // . Traverse the list and remove any refs whose referents are alive.
893 if (mt) {
894 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
895 task_executor->execute(phase2);
896 } else {
897 for (int i = 0; i < _num_q; i++) {
898 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
899 }
900 }
901
902 // Phase 3:
903 // . Traverse the list and process referents as appropriate.
904 if (mt) {
905 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
906 task_executor->execute(phase3);
907 } else {
908 for (int i = 0; i < _num_q; i++) {
909 process_phase3(refs_lists[i], clear_referent,
910 is_alive, keep_alive, complete_gc);
911 }
912 }
913 }
914
915 void ReferenceProcessor::clean_up_discovered_references() {
916 // loop over the lists
917 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
918 if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) {
919 gclog_or_tty->print_cr(
920 "\nScrubbing %s discovered list of Null referents",
921 list_name(i));
922 }
923 clean_up_discovered_reflist(_discoveredSoftRefs[i]);
924 }
925 }
926
927 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) {
928 assert(!discovery_is_atomic(), "Else why call this method?");
929 DiscoveredListIterator iter(refs_list, NULL, NULL);
930 while (iter.has_next()) {
931 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
932 oop next = java_lang_ref_Reference::next(iter.obj());
933 assert(next->is_oop_or_null(), "bad next field");
934 // If referent has been cleared or Reference is not active,
935 // drop it.
936 if (iter.referent() == NULL || next != NULL) {
937 debug_only(
938 if (PrintGCDetails && TraceReferenceGC) {
939 gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: "
940 INTPTR_FORMAT " with next field: " INTPTR_FORMAT
941 " and referent: " INTPTR_FORMAT,
942 iter.obj(), next, iter.referent());
943 }
944 )
945 // Remove Reference object from list
946 iter.remove();
947 iter.move_to_next();
948 } else {
949 iter.next();
950 }
951 }
952 NOT_PRODUCT(
953 if (PrintGCDetails && TraceReferenceGC) {
954 gclog_or_tty->print(
955 " Removed %d Refs with NULL referents out of %d discovered Refs",
956 iter.removed(), iter.processed());
957 }
958 )
959 }
960
961 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
962 int id = 0;
963 // Determine the queue index to use for this object.
964 if (_discovery_is_mt) {
965 // During a multi-threaded discovery phase,
966 // each thread saves to its "own" list.
967 Thread* thr = Thread::current();
968 assert(thr->is_GC_task_thread(),
969 "Dubious cast from Thread* to WorkerThread*?");
970 id = ((WorkerThread*)thr)->id();
971 } else {
972 // single-threaded discovery, we save in round-robin
973 // fashion to each of the lists.
974 if (_processing_is_mt) {
975 id = next_id();
976 }
977 }
978 assert(0 <= id && id < _num_q, "Id is out-of-bounds (call Freud?)");
979
980 // Get the discovered queue to which we will add
981 DiscoveredList* list = NULL;
982 switch (rt) {
983 case REF_OTHER:
984 // Unknown reference type, no special treatment
985 break;
986 case REF_SOFT:
987 list = &_discoveredSoftRefs[id];
988 break;
989 case REF_WEAK:
990 list = &_discoveredWeakRefs[id];
991 break;
992 case REF_FINAL:
993 list = &_discoveredFinalRefs[id];
994 break;
995 case REF_PHANTOM:
996 list = &_discoveredPhantomRefs[id];
997 break;
998 case REF_NONE:
999 // we should not reach here if we are an instanceRefKlass
1000 default:
1001 ShouldNotReachHere();
1002 }
1003 return list;
1004 }
1005
1006 inline void
1007 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
1008 oop obj,
1009 HeapWord* discovered_addr) {
1010 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
1011 // First we must make sure this object is only enqueued once. CAS in a non null
1012 // discovered_addr.
1013 oop current_head = refs_list.head();
1014
1015 // Note: In the case of G1, this pre-barrier is strictly
1016 // not necessary because the only case we are interested in
1017 // here is when *discovered_addr is NULL, so this will expand to
1018 // nothing. As a result, I am just manually eliding this out for G1.
1019 if (_discovered_list_needs_barrier && !UseG1GC) {
1020 _bs->write_ref_field_pre((void*)discovered_addr, current_head); guarantee(false, "Needs to be fixed: YSR");
1021 }
1022 oop retest = oopDesc::atomic_compare_exchange_oop(current_head, discovered_addr,
1023 NULL);
1024 if (retest == NULL) {
1025 // This thread just won the right to enqueue the object.
1026 // We have separate lists for enqueueing so no synchronization
1027 // is necessary.
1028 refs_list.set_head(obj);
1029 refs_list.inc_length(1);
1030 if (_discovered_list_needs_barrier) {
1031 _bs->write_ref_field((void*)discovered_addr, current_head); guarantee(false, "Needs to be fixed: YSR");
1032 }
1033
1034 } else {
1035 // If retest was non NULL, another thread beat us to it:
1036 // The reference has already been discovered...
1037 if (TraceReferenceGC) {
1038 gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)",
1039 obj, obj->blueprint()->internal_name());
1040 }
1041 }
1042 }
1043
1044 // We mention two of several possible choices here:
1045 // #0: if the reference object is not in the "originating generation"
1046 // (or part of the heap being collected, indicated by our "span"
1047 // we don't treat it specially (i.e. we scan it as we would
1048 // a normal oop, treating its references as strong references).
1049 // This means that references can't be enqueued unless their
1050 // referent is also in the same span. This is the simplest,
1051 // most "local" and most conservative approach, albeit one
1052 // that may cause weak references to be enqueued least promptly.
1053 // We call this choice the "ReferenceBasedDiscovery" policy.
1054 // #1: the reference object may be in any generation (span), but if
1055 // the referent is in the generation (span) being currently collected
1056 // then we can discover the reference object, provided
1057 // the object has not already been discovered by
1058 // a different concurrently running collector (as may be the
1059 // case, for instance, if the reference object is in CMS and
1060 // the referent in DefNewGeneration), and provided the processing
1061 // of this reference object by the current collector will
1062 // appear atomic to every other collector in the system.
1063 // (Thus, for instance, a concurrent collector may not
1064 // discover references in other generations even if the
1065 // referent is in its own generation). This policy may,
1066 // in certain cases, enqueue references somewhat sooner than
1067 // might Policy #0 above, but at marginally increased cost
1068 // and complexity in processing these references.
1069 // We call this choice the "RefeferentBasedDiscovery" policy.
1070 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
1071 // We enqueue references only if we are discovering refs
1072 // (rather than processing discovered refs).
1073 if (!_discovering_refs || !RegisterReferences) {
1074 return false;
1075 }
1076 // We only enqueue active references.
1077 oop next = java_lang_ref_Reference::next(obj);
1078 if (next != NULL) {
1079 return false;
1080 }
1081
1082 HeapWord* obj_addr = (HeapWord*)obj;
1083 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1084 !_span.contains(obj_addr)) {
1085 // Reference is not in the originating generation;
1086 // don't treat it specially (i.e. we want to scan it as a normal
1087 // object with strong references).
1088 return false;
1089 }
1090
1091 // We only enqueue references whose referents are not (yet) strongly
1092 // reachable.
1093 if (is_alive_non_header() != NULL) {
1094 oop referent = java_lang_ref_Reference::referent(obj);
1095 // We'd like to assert the following:
1096 // assert(referent != NULL, "Refs with null referents already filtered");
1097 // However, since this code may be executed concurrently with
1098 // mutators, which can clear() the referent, it is not
1099 // guaranteed that the referent is non-NULL.
1100 if (is_alive_non_header()->do_object_b(referent)) {
1101 return false; // referent is reachable
1102 }
1103 }
1104
1105 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
1106 const oop discovered = java_lang_ref_Reference::discovered(obj);
1107 assert(discovered->is_oop_or_null(), "bad discovered field");
1108 if (discovered != NULL) {
1109 // The reference has already been discovered...
1110 if (TraceReferenceGC) {
1111 gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)",
1112 obj, obj->blueprint()->internal_name());
1113 }
1114 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1115 // assumes that an object is not processed twice;
1116 // if it's been already discovered it must be on another
1117 // generation's discovered list; so we won't discover it.
1118 return false;
1119 } else {
1120 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1121 "Unrecognized policy");
1122 // Check assumption that an object is not potentially
1123 // discovered twice except by concurrent collectors that potentially
1124 // trace the same Reference object twice.
1125 assert(UseConcMarkSweepGC,
1126 "Only possible with an incremental-update concurrent collector");
1127 return true;
1128 }
1129 }
1130
1131 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1132 oop referent = java_lang_ref_Reference::referent(obj);
1133 assert(referent->is_oop(), "bad referent");
1134 // enqueue if and only if either:
1135 // reference is in our span or
1136 // we are an atomic collector and referent is in our span
1137 if (_span.contains(obj_addr) ||
1138 (discovery_is_atomic() && _span.contains(referent))) {
1139 // should_enqueue = true;
1140 } else {
1141 return false;
1142 }
1143 } else {
1144 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1145 _span.contains(obj_addr), "code inconsistency");
1146 }
1147
1148 // Get the right type of discovered queue head.
1149 DiscoveredList* list = get_discovered_list(rt);
1150 if (list == NULL) {
1151 return false; // nothing special needs to be done
1152 }
1153
1154 if (_discovery_is_mt) {
1155 add_to_discovered_list_mt(*list, obj, discovered_addr);
1156 } else {
1157 // If "_discovered_list_needs_barrier", we do write barriers when
1158 // updating the discovered reference list. Otherwise, we do a raw store
1159 // here: the field will be visited later when processing the discovered
1160 // references.
1161 oop current_head = list->head();
1162 // As in the case further above, since we are over-writing a NULL
1163 // pre-value, we can safely elide the pre-barrier here for the case of G1.
1164 assert(discovered == NULL, "control point invariant");
1165 if (_discovered_list_needs_barrier && !UseG1GC) { // safe to elide for G1
1166 _bs->write_ref_field_pre((oop*)discovered_addr, current_head);
1167 }
1168 oop_store_raw(discovered_addr, current_head);
1169 if (_discovered_list_needs_barrier) {
1170 _bs->write_ref_field((oop*)discovered_addr, current_head);
1171 }
1172 list->set_head(obj);
1173 list->inc_length(1);
1174 }
1175
1176 // In the MT discovery case, it is currently possible to see
1177 // the following message multiple times if several threads
1178 // discover a reference about the same time. Only one will
1179 // however have actually added it to the disocvered queue.
1180 // One could let add_to_discovered_list_mt() return an
1181 // indication for success in queueing (by 1 thread) or
1182 // failure (by all other threads), but I decided the extra
1183 // code was not worth the effort for something that is
1184 // only used for debugging support.
1185 if (TraceReferenceGC) {
1186 oop referent = java_lang_ref_Reference::referent(obj);
1187 if (PrintGCDetails) {
1188 gclog_or_tty->print_cr("Enqueued reference (" INTPTR_FORMAT ": %s)",
1189 obj, obj->blueprint()->internal_name());
1190 }
1191 assert(referent->is_oop(), "Enqueued a bad referent");
1192 }
1193 assert(obj->is_oop(), "Enqueued a bad reference");
1194 return true;
1195 }
1196
1197 // Preclean the discovered references by removing those
1198 // whose referents are alive, and by marking from those that
1199 // are not active. These lists can be handled here
1200 // in any order and, indeed, concurrently.
1201 void ReferenceProcessor::preclean_discovered_references(
1202 BoolObjectClosure* is_alive,
1203 OopClosure* keep_alive,
1204 VoidClosure* complete_gc,
1205 YieldClosure* yield) {
1206
1207 NOT_PRODUCT(verify_ok_to_handle_reflists());
1208
1209 // Soft references
1210 {
1211 TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
1212 false, gclog_or_tty);
1213 for (int i = 0; i < _num_q; i++) {
1214 if (yield->should_return()) {
1215 return;
1216 }
1217 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1218 keep_alive, complete_gc, yield);
1219 }
1220 }
1221
1222 // Weak references
1223 {
1224 TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
1225 false, gclog_or_tty);
1226 for (int i = 0; i < _num_q; i++) {
1227 if (yield->should_return()) {
1228 return;
1229 }
1230 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1231 keep_alive, complete_gc, yield);
1232 }
1233 }
1234
1235 // Final references
1236 {
1237 TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
1238 false, gclog_or_tty);
1239 for (int i = 0; i < _num_q; i++) {
1240 if (yield->should_return()) {
1241 return;
1242 }
1243 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1244 keep_alive, complete_gc, yield);
1245 }
1246 }
1247
1248 // Phantom references
1249 {
1250 TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
1251 false, gclog_or_tty);
1252 for (int i = 0; i < _num_q; i++) {
1253 if (yield->should_return()) {
1254 return;
1255 }
1256 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1257 keep_alive, complete_gc, yield);
1258 }
1259 }
1260 }
1261
1262 // Walk the given discovered ref list, and remove all reference objects
1263 // whose referents are still alive, whose referents are NULL or which
1264 // are not active (have a non-NULL next field). NOTE: When we are
1265 // thus precleaning the ref lists (which happens single-threaded today),
1266 // we do not disable refs discovery to honour the correct semantics of
1267 // java.lang.Reference. As a result, we need to be careful below
1268 // that ref removal steps interleave safely with ref discovery steps
1269 // (in this thread).
1270 void
1271 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1272 BoolObjectClosure* is_alive,
1273 OopClosure* keep_alive,
1274 VoidClosure* complete_gc,
1275 YieldClosure* yield) {
1276 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1277 while (iter.has_next()) {
1278 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1279 oop obj = iter.obj();
1280 oop next = java_lang_ref_Reference::next(obj);
1281 if (iter.referent() == NULL || iter.is_referent_alive() ||
1282 next != NULL) {
1283 // The referent has been cleared, or is alive, or the Reference is not
1284 // active; we need to trace and mark its cohort.
1285 if (TraceReferenceGC) {
1286 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1287 iter.obj(), iter.obj()->blueprint()->internal_name());
1288 }
1289 // Remove Reference object from list
1290 iter.remove();
1291 // Keep alive its cohort.
1292 iter.make_referent_alive();
1293 if (UseCompressedOops) {
1294 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1295 keep_alive->do_oop(next_addr);
1296 } else {
1297 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1298 keep_alive->do_oop(next_addr);
1299 }
1300 iter.move_to_next();
1301 } else {
1302 iter.next();
1303 }
1304 }
1305 // Close the reachable set
1306 complete_gc->do_void();
1307
1308 NOT_PRODUCT(
1309 if (PrintGCDetails && PrintReferenceGC) {
1310 gclog_or_tty->print(" Dropped %d Refs out of %d "
1311 "Refs in discovered list ", iter.removed(), iter.processed());
1312 }
1313 )
1314 }
1315
1316 const char* ReferenceProcessor::list_name(int i) {
1317 assert(i >= 0 && i <= _num_q * subclasses_of_ref, "Out of bounds index");
1318 int j = i / _num_q;
1319 switch (j) {
1320 case 0: return "SoftRef";
1321 case 1: return "WeakRef";
1322 case 2: return "FinalRef";
1323 case 3: return "PhantomRef";
1324 }
1325 ShouldNotReachHere();
1326 return NULL;
1327 }
1328
1329 #ifndef PRODUCT
1330 void ReferenceProcessor::verify_ok_to_handle_reflists() {
1331 // empty for now
1332 }
1333 #endif
1334
1335 void ReferenceProcessor::verify() {
1336 guarantee(sentinel_ref() != NULL && sentinel_ref()->is_oop(), "Lost _sentinelRef");
1337 }
1338
1339 #ifndef PRODUCT
1340 void ReferenceProcessor::clear_discovered_references() {
1341 guarantee(!_discovering_refs, "Discovering refs?");
1342 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
1343 oop obj = _discoveredSoftRefs[i].head();
1344 while (obj != sentinel_ref()) {
1345 oop next = java_lang_ref_Reference::discovered(obj);
1346 java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
1347 obj = next;
1348 }
1349 _discoveredSoftRefs[i].set_head(sentinel_ref());
1350 _discoveredSoftRefs[i].set_length(0);
1351 }
1352 }
1353 #endif // PRODUCT