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/_genMarkSweep.cpp.incl"
27
28 void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,
29 bool clear_all_softrefs) {
30 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
31
32 // hook up weak ref data so it can be used during Mark-Sweep
33 assert(ref_processor() == NULL, "no stomping");
34 _ref_processor = rp;
35 assert(rp != NULL, "should be non-NULL");
36
37 TraceTime t1("Full GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);
38
39 // When collecting the permanent generation methodOops may be moving,
40 // so we either have to flush all bcp data or convert it into bci.
41 CodeCache::gc_prologue();
42 Threads::gc_prologue();
43
44 // Increment the invocation count for the permanent generation, since it is
45 // implicitly collected whenever we do a full mark sweep collection.
46 GenCollectedHeap* gch = GenCollectedHeap::heap();
47 gch->perm_gen()->stat_record()->invocations++;
48
49 // Capture heap size before collection for printing.
50 size_t gch_prev_used = gch->used();
51
52 // Some of the card table updates below assume that the perm gen is
53 // also being collected.
54 assert(level == gch->n_gens() - 1,
55 "All generations are being collected, ergo perm gen too.");
56
57 // Capture used regions for each generation that will be
58 // subject to collection, so that card table adjustments can
59 // be made intelligently (see clear / invalidate further below).
60 gch->save_used_regions(level, true /* perm */);
61
62 allocate_stacks();
63
64 mark_sweep_phase1(level, clear_all_softrefs);
65
66 mark_sweep_phase2();
67
68 // Don't add any more derived pointers during phase3
69 COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
70 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
71
72 mark_sweep_phase3(level);
73
74 VALIDATE_MARK_SWEEP_ONLY(
75 if (ValidateMarkSweep) {
76 guarantee(_root_refs_stack->length() == 0, "should be empty by now");
77 }
78 )
79
80 mark_sweep_phase4();
81
82 VALIDATE_MARK_SWEEP_ONLY(
83 if (ValidateMarkSweep) {
84 guarantee(_live_oops->length() == _live_oops_moved_to->length(),
85 "should be the same size");
86 }
87 )
88
89 restore_marks();
90
91 // Set saved marks for allocation profiler (and other things? -- dld)
92 // (Should this be in general part?)
93 gch->save_marks();
94
95 deallocate_stacks();
96
97 // If compaction completely evacuated all generations younger than this
98 // one, then we can clear the card table. Otherwise, we must invalidate
99 // it (consider all cards dirty). In the future, we might consider doing
100 // compaction within generations only, and doing card-table sliding.
101 bool all_empty = true;
102 for (int i = 0; all_empty && i < level; i++) {
103 Generation* g = gch->get_gen(i);
104 all_empty = all_empty && gch->get_gen(i)->used() == 0;
105 }
106 GenRemSet* rs = gch->rem_set();
107 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
108 if (all_empty) {
109 // We've evacuated all generations below us.
110 Generation* g = gch->get_gen(level);
111 rs->clear_into_younger(g, true /* perm */);
112 } else {
113 // Invalidate the cards corresponding to the currently used
114 // region and clear those corresponding to the evacuated region
115 // of all generations just collected (i.e. level and younger).
116 rs->invalidate_or_clear(gch->get_gen(level),
117 true /* younger */,
118 true /* perm */);
119 }
120
121 Threads::gc_epilogue();
122 CodeCache::gc_epilogue();
123
124 if (PrintGC && !PrintGCDetails) {
125 gch->print_heap_change(gch_prev_used);
126 }
127
128 // refs processing: clean slate
129 _ref_processor = NULL;
130
131 // Update heap occupancy information which is used as
132 // input to soft ref clearing policy at the next gc.
133 Universe::update_heap_info_at_gc();
134
135 // Update time of last gc for all generations we collected
136 // (which curently is all the generations in the heap).
137 gch->update_time_of_last_gc(os::javaTimeMillis());
138 }
139
140 void GenMarkSweep::allocate_stacks() {
141 GenCollectedHeap* gch = GenCollectedHeap::heap();
142 // Scratch request on behalf of oldest generation; will do no
143 // allocation.
144 ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);
145
146 // $$$ To cut a corner, we'll only use the first scratch block, and then
147 // revert to malloc.
148 if (scratch != NULL) {
149 _preserved_count_max =
150 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
151 } else {
152 _preserved_count_max = 0;
153 }
154
155 _preserved_marks = (PreservedMark*)scratch;
156 _preserved_count = 0;
157 _preserved_mark_stack = NULL;
158 _preserved_oop_stack = NULL;
159
160 _marking_stack = new (ResourceObj::C_HEAP) GrowableArray<oop>(4000, true);
161
162 int size = SystemDictionary::number_of_classes() * 2;
163 _revisit_klass_stack = new (ResourceObj::C_HEAP) GrowableArray<Klass*>(size, true);
164
165 #ifdef VALIDATE_MARK_SWEEP
166 if (ValidateMarkSweep) {
167 _root_refs_stack = new (ResourceObj::C_HEAP) GrowableArray<void*>(100, true);
168 _other_refs_stack = new (ResourceObj::C_HEAP) GrowableArray<void*>(100, true);
169 _adjusted_pointers = new (ResourceObj::C_HEAP) GrowableArray<void*>(100, true);
170 _live_oops = new (ResourceObj::C_HEAP) GrowableArray<oop>(100, true);
171 _live_oops_moved_to = new (ResourceObj::C_HEAP) GrowableArray<oop>(100, true);
172 _live_oops_size = new (ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
173 }
174 if (RecordMarkSweepCompaction) {
175 if (_cur_gc_live_oops == NULL) {
176 _cur_gc_live_oops = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
177 _cur_gc_live_oops_moved_to = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
178 _cur_gc_live_oops_size = new(ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
179 _last_gc_live_oops = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
180 _last_gc_live_oops_moved_to = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
181 _last_gc_live_oops_size = new(ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
182 } else {
183 _cur_gc_live_oops->clear();
184 _cur_gc_live_oops_moved_to->clear();
185 _cur_gc_live_oops_size->clear();
186 }
187 }
188 #endif
189 }
190
191
192 void GenMarkSweep::deallocate_stacks() {
193
194 if (!UseG1GC) {
195 GenCollectedHeap* gch = GenCollectedHeap::heap();
196 gch->release_scratch();
197 }
198
199 if (_preserved_oop_stack) {
200 delete _preserved_mark_stack;
201 _preserved_mark_stack = NULL;
202 delete _preserved_oop_stack;
203 _preserved_oop_stack = NULL;
204 }
205
206 delete _marking_stack;
207 delete _revisit_klass_stack;
208
209 #ifdef VALIDATE_MARK_SWEEP
210 if (ValidateMarkSweep) {
211 delete _root_refs_stack;
212 delete _other_refs_stack;
213 delete _adjusted_pointers;
214 delete _live_oops;
215 delete _live_oops_size;
216 delete _live_oops_moved_to;
217 _live_oops_index = 0;
218 _live_oops_index_at_perm = 0;
219 }
220 #endif
221 }
222
223 void GenMarkSweep::mark_sweep_phase1(int level,
224 bool clear_all_softrefs) {
225 // Recursively traverse all live objects and mark them
226 EventMark m("1 mark object");
227 TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
228 trace(" 1");
229
230 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));
231
232 GenCollectedHeap* gch = GenCollectedHeap::heap();
233
234 // Because follow_root_closure is created statically, cannot
235 // use OopsInGenClosure constructor which takes a generation,
236 // as the Universe has not been created when the static constructors
237 // are run.
238 follow_root_closure.set_orig_generation(gch->get_gen(level));
239
240 gch->gen_process_strong_roots(level,
241 false, // Younger gens are not roots.
242 true, // Collecting permanent generation.
243 SharedHeap::SO_SystemClasses,
244 &follow_root_closure, &follow_root_closure);
245
246 // Process reference objects found during marking
247 {
248 ReferencePolicy *soft_ref_policy;
249 if (clear_all_softrefs) {
250 soft_ref_policy = new AlwaysClearPolicy();
251 } else {
252 #ifdef COMPILER2
253 soft_ref_policy = new LRUMaxHeapPolicy();
254 #else
255 soft_ref_policy = new LRUCurrentHeapPolicy();
256 #endif // COMPILER2
257 }
258 assert(soft_ref_policy != NULL,"No soft reference policy");
259 ref_processor()->process_discovered_references(
260 soft_ref_policy, &is_alive, &keep_alive,
261 &follow_stack_closure, NULL);
262 }
263
264 // Follow system dictionary roots and unload classes
265 bool purged_class = SystemDictionary::do_unloading(&is_alive);
266
267 // Follow code cache roots
268 CodeCache::do_unloading(&is_alive, &keep_alive, purged_class);
269 follow_stack(); // Flush marking stack
270
271 // Update subklass/sibling/implementor links of live klasses
272 follow_weak_klass_links();
273 assert(_marking_stack->is_empty(), "just drained");
274
275 // Visit symbol and interned string tables and delete unmarked oops
276 SymbolTable::unlink(&is_alive);
277 StringTable::unlink(&is_alive);
278
279 assert(_marking_stack->is_empty(), "stack should be empty by now");
280 }
281
282
283 void GenMarkSweep::mark_sweep_phase2() {
284 // Now all live objects are marked, compute the new object addresses.
285
286 // It is imperative that we traverse perm_gen LAST. If dead space is
287 // allowed a range of dead object may get overwritten by a dead int
288 // array. If perm_gen is not traversed last a klassOop may get
289 // overwritten. This is fine since it is dead, but if the class has dead
290 // instances we have to skip them, and in order to find their size we
291 // need the klassOop!
292 //
293 // It is not required that we traverse spaces in the same order in
294 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
295 // tracking expects us to do so. See comment under phase4.
296
297 GenCollectedHeap* gch = GenCollectedHeap::heap();
298 Generation* pg = gch->perm_gen();
299
300 EventMark m("2 compute new addresses");
301 TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
302 trace("2");
303
304 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));
305
306 gch->prepare_for_compaction();
307
308 VALIDATE_MARK_SWEEP_ONLY(_live_oops_index_at_perm = _live_oops_index);
309 CompactPoint perm_cp(pg, NULL, NULL);
310 pg->prepare_for_compaction(&perm_cp);
311 }
312
313 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
314 public:
315 void do_generation(Generation* gen) {
316 gen->adjust_pointers();
317 }
318 };
319
320 void GenMarkSweep::mark_sweep_phase3(int level) {
321 GenCollectedHeap* gch = GenCollectedHeap::heap();
322 Generation* pg = gch->perm_gen();
323
324 // Adjust the pointers to reflect the new locations
325 EventMark m("3 adjust pointers");
326 TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
327 trace("3");
328
329 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));
330
331 // Needs to be done before the system dictionary is adjusted.
332 pg->pre_adjust_pointers();
333
334 // Because the two closures below are created statically, cannot
335 // use OopsInGenClosure constructor which takes a generation,
336 // as the Universe has not been created when the static constructors
337 // are run.
338 adjust_root_pointer_closure.set_orig_generation(gch->get_gen(level));
339 adjust_pointer_closure.set_orig_generation(gch->get_gen(level));
340
341 gch->gen_process_strong_roots(level,
342 false, // Younger gens are not roots.
343 true, // Collecting permanent generation.
344 SharedHeap::SO_AllClasses,
345 &adjust_root_pointer_closure,
346 &adjust_root_pointer_closure);
347
348 // Now adjust pointers in remaining weak roots. (All of which should
349 // have been cleared if they pointed to non-surviving objects.)
350 gch->gen_process_weak_roots(&adjust_root_pointer_closure,
351 &adjust_pointer_closure);
352
353 adjust_marks();
354 GenAdjustPointersClosure blk;
355 gch->generation_iterate(&blk, true);
356 pg->adjust_pointers();
357 }
358
359 class GenCompactClosure: public GenCollectedHeap::GenClosure {
360 public:
361 void do_generation(Generation* gen) {
362 gen->compact();
363 }
364 };
365
366 void GenMarkSweep::mark_sweep_phase4() {
367 // All pointers are now adjusted, move objects accordingly
368
369 // It is imperative that we traverse perm_gen first in phase4. All
370 // classes must be allocated earlier than their instances, and traversing
371 // perm_gen first makes sure that all klassOops have moved to their new
372 // location before any instance does a dispatch through it's klass!
373
374 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
375 // in the same order in phase2, phase3 and phase4. We don't quite do that
376 // here (perm_gen first rather than last), so we tell the validate code
377 // to use a higher index (saved from phase2) when verifying perm_gen.
378 GenCollectedHeap* gch = GenCollectedHeap::heap();
379 Generation* pg = gch->perm_gen();
380
381 EventMark m("4 compact heap");
382 TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
383 trace("4");
384
385 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(true));
386
387 pg->compact();
388
389 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));
390
391 GenCompactClosure blk;
392 gch->generation_iterate(&blk, true);
393
394 VALIDATE_MARK_SWEEP_ONLY(compaction_complete());
395
396 pg->post_compact(); // Shared spaces verification.
397 }