1 /*
2 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * 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 GenCollectedHeap* gch = GenCollectedHeap::heap();
33 #ifdef ASSERT
34 if (gch->collector_policy()->should_clear_all_soft_refs()) {
35 assert(clear_all_softrefs, "Policy should have been checked earlier");
36 }
37 #endif
38
39 // hook up weak ref data so it can be used during Mark-Sweep
40 assert(ref_processor() == NULL, "no stomping");
41 assert(rp != NULL, "should be non-NULL");
42 _ref_processor = rp;
43 rp->setup_policy(clear_all_softrefs);
44
45 TraceTime t1("Full GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);
46
47 // When collecting the permanent generation methodOops may be moving,
48 // so we either have to flush all bcp data or convert it into bci.
49 CodeCache::gc_prologue();
50 Threads::gc_prologue();
51
52 // Increment the invocation count for the permanent generation, since it is
53 // implicitly collected whenever we do a full mark sweep collection.
54 gch->perm_gen()->stat_record()->invocations++;
55
56 // Capture heap size before collection for printing.
57 size_t gch_prev_used = gch->used();
58
59 // Some of the card table updates below assume that the perm gen is
60 // also being collected.
61 assert(level == gch->n_gens() - 1,
62 "All generations are being collected, ergo perm gen too.");
63
64 // Capture used regions for each generation that will be
65 // subject to collection, so that card table adjustments can
66 // be made intelligently (see clear / invalidate further below).
67 gch->save_used_regions(level, true /* perm */);
68
69 allocate_stacks();
70
71 mark_sweep_phase1(level, clear_all_softrefs);
72
73 mark_sweep_phase2();
74
75 // Don't add any more derived pointers during phase3
76 COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
77 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
78
79 mark_sweep_phase3(level);
80
81 VALIDATE_MARK_SWEEP_ONLY(
82 if (ValidateMarkSweep) {
83 guarantee(_root_refs_stack->length() == 0, "should be empty by now");
84 }
85 )
86
87 mark_sweep_phase4();
88
89 VALIDATE_MARK_SWEEP_ONLY(
90 if (ValidateMarkSweep) {
91 guarantee(_live_oops->length() == _live_oops_moved_to->length(),
92 "should be the same size");
93 }
94 )
95
96 restore_marks();
97
98 // Set saved marks for allocation profiler (and other things? -- dld)
99 // (Should this be in general part?)
100 gch->save_marks();
101
102 deallocate_stacks();
103
104 // If compaction completely evacuated all generations younger than this
105 // one, then we can clear the card table. Otherwise, we must invalidate
106 // it (consider all cards dirty). In the future, we might consider doing
107 // compaction within generations only, and doing card-table sliding.
108 bool all_empty = true;
109 for (int i = 0; all_empty && i < level; i++) {
110 Generation* g = gch->get_gen(i);
111 all_empty = all_empty && gch->get_gen(i)->used() == 0;
112 }
113 GenRemSet* rs = gch->rem_set();
114 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
115 if (all_empty) {
116 // We've evacuated all generations below us.
117 Generation* g = gch->get_gen(level);
118 rs->clear_into_younger(g, true /* perm */);
119 } else {
120 // Invalidate the cards corresponding to the currently used
121 // region and clear those corresponding to the evacuated region
122 // of all generations just collected (i.e. level and younger).
123 rs->invalidate_or_clear(gch->get_gen(level),
124 true /* younger */,
125 true /* perm */);
126 }
127
128 Threads::gc_epilogue();
129 CodeCache::gc_epilogue();
130
131 if (PrintGC && !PrintGCDetails) {
132 gch->print_heap_change(gch_prev_used);
133 }
134
135 // refs processing: clean slate
136 _ref_processor = NULL;
137
138 // Update heap occupancy information which is used as
139 // input to soft ref clearing policy at the next gc.
140 Universe::update_heap_info_at_gc();
141
142 // Update time of last gc for all generations we collected
143 // (which curently is all the generations in the heap).
144 gch->update_time_of_last_gc(os::javaTimeMillis());
145 }
146
147 void GenMarkSweep::allocate_stacks() {
148 GenCollectedHeap* gch = GenCollectedHeap::heap();
149 // Scratch request on behalf of oldest generation; will do no
150 // allocation.
151 ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);
152
153 // $$$ To cut a corner, we'll only use the first scratch block, and then
154 // revert to malloc.
155 if (scratch != NULL) {
156 _preserved_count_max =
157 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
158 } else {
159 _preserved_count_max = 0;
160 }
161
162 _preserved_marks = (PreservedMark*)scratch;
163 _preserved_count = 0;
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 if (!UseG1GC) {
194 GenCollectedHeap* gch = GenCollectedHeap::heap();
195 gch->release_scratch();
196 }
197
198 _preserved_mark_stack.clear(true);
199 _preserved_oop_stack.clear(true);
200 _marking_stack.clear();
201 _objarray_stack.clear(true);
202 _revisit_klass_stack.clear(true);
203 _revisit_mdo_stack.clear(true);
204
205 #ifdef VALIDATE_MARK_SWEEP
206 if (ValidateMarkSweep) {
207 delete _root_refs_stack;
208 delete _other_refs_stack;
209 delete _adjusted_pointers;
210 delete _live_oops;
211 delete _live_oops_size;
212 delete _live_oops_moved_to;
213 _live_oops_index = 0;
214 _live_oops_index_at_perm = 0;
215 }
216 #endif
217 }
218
219 void GenMarkSweep::mark_sweep_phase1(int level,
220 bool clear_all_softrefs) {
221 // Recursively traverse all live objects and mark them
222 EventMark m("1 mark object");
223 TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
224 trace(" 1");
225
226 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));
227
228 GenCollectedHeap* gch = GenCollectedHeap::heap();
229
230 // Because follow_root_closure is created statically, cannot
231 // use OopsInGenClosure constructor which takes a generation,
232 // as the Universe has not been created when the static constructors
233 // are run.
234 follow_root_closure.set_orig_generation(gch->get_gen(level));
235
236 gch->gen_process_strong_roots(level,
237 false, // Younger gens are not roots.
238 true, // activate StrongRootsScope
239 true, // Collecting permanent generation.
240 SharedHeap::SO_SystemClasses,
241 &follow_root_closure,
242 true, // walk code active on stacks
243 &follow_root_closure);
244
245 // Process reference objects found during marking
246 {
247 ref_processor()->setup_policy(clear_all_softrefs);
248 ref_processor()->process_discovered_references(
249 &is_alive, &keep_alive, &follow_stack_closure, NULL);
250 }
251
252 // Follow system dictionary roots and unload classes
253 bool purged_class = SystemDictionary::do_unloading(&is_alive);
254
255 // Follow code cache roots
256 CodeCache::do_unloading(&is_alive, &keep_alive, purged_class);
257 follow_stack(); // Flush marking stack
258
259 // Update subklass/sibling/implementor links of live klasses
260 follow_weak_klass_links();
261 assert(_marking_stack.is_empty(), "just drained");
262
263 // Visit memoized MDO's and clear any unmarked weak refs
264 follow_mdo_weak_refs();
265 assert(_marking_stack.is_empty(), "just drained");
266
267 // Visit symbol and interned string tables and delete unmarked oops
268 SymbolTable::unlink(&is_alive);
269 StringTable::unlink(&is_alive);
270
271 assert(_marking_stack.is_empty(), "stack should be empty by now");
272 }
273
274
275 void GenMarkSweep::mark_sweep_phase2() {
276 // Now all live objects are marked, compute the new object addresses.
277
278 // It is imperative that we traverse perm_gen LAST. If dead space is
279 // allowed a range of dead object may get overwritten by a dead int
280 // array. If perm_gen is not traversed last a klassOop may get
281 // overwritten. This is fine since it is dead, but if the class has dead
282 // instances we have to skip them, and in order to find their size we
283 // need the klassOop!
284 //
285 // It is not required that we traverse spaces in the same order in
286 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
287 // tracking expects us to do so. See comment under phase4.
288
289 GenCollectedHeap* gch = GenCollectedHeap::heap();
290 Generation* pg = gch->perm_gen();
291
292 EventMark m("2 compute new addresses");
293 TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
294 trace("2");
295
296 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));
297
298 gch->prepare_for_compaction();
299
300 VALIDATE_MARK_SWEEP_ONLY(_live_oops_index_at_perm = _live_oops_index);
301 CompactPoint perm_cp(pg, NULL, NULL);
302 pg->prepare_for_compaction(&perm_cp);
303 }
304
305 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
306 public:
307 void do_generation(Generation* gen) {
308 gen->adjust_pointers();
309 }
310 };
311
312 void GenMarkSweep::mark_sweep_phase3(int level) {
313 GenCollectedHeap* gch = GenCollectedHeap::heap();
314 Generation* pg = gch->perm_gen();
315
316 // Adjust the pointers to reflect the new locations
317 EventMark m("3 adjust pointers");
318 TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
319 trace("3");
320
321 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));
322
323 // Needs to be done before the system dictionary is adjusted.
324 pg->pre_adjust_pointers();
325
326 // Because the two closures below are created statically, cannot
327 // use OopsInGenClosure constructor which takes a generation,
328 // as the Universe has not been created when the static constructors
329 // are run.
330 adjust_root_pointer_closure.set_orig_generation(gch->get_gen(level));
331 adjust_pointer_closure.set_orig_generation(gch->get_gen(level));
332
333 gch->gen_process_strong_roots(level,
334 false, // Younger gens are not roots.
335 true, // activate StrongRootsScope
336 true, // Collecting permanent generation.
337 SharedHeap::SO_AllClasses,
338 &adjust_root_pointer_closure,
339 false, // do not walk code
340 &adjust_root_pointer_closure);
341
342 // Now adjust pointers in remaining weak roots. (All of which should
343 // have been cleared if they pointed to non-surviving objects.)
344 CodeBlobToOopClosure adjust_code_pointer_closure(&adjust_pointer_closure,
345 /*do_marking=*/ false);
346 gch->gen_process_weak_roots(&adjust_root_pointer_closure,
347 &adjust_code_pointer_closure,
348 &adjust_pointer_closure);
349
350 adjust_marks();
351 GenAdjustPointersClosure blk;
352 gch->generation_iterate(&blk, true);
353 pg->adjust_pointers();
354 }
355
356 class GenCompactClosure: public GenCollectedHeap::GenClosure {
357 public:
358 void do_generation(Generation* gen) {
359 gen->compact();
360 }
361 };
362
363 void GenMarkSweep::mark_sweep_phase4() {
364 // All pointers are now adjusted, move objects accordingly
365
366 // It is imperative that we traverse perm_gen first in phase4. All
367 // classes must be allocated earlier than their instances, and traversing
368 // perm_gen first makes sure that all klassOops have moved to their new
369 // location before any instance does a dispatch through it's klass!
370
371 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
372 // in the same order in phase2, phase3 and phase4. We don't quite do that
373 // here (perm_gen first rather than last), so we tell the validate code
374 // to use a higher index (saved from phase2) when verifying perm_gen.
375 GenCollectedHeap* gch = GenCollectedHeap::heap();
376 Generation* pg = gch->perm_gen();
377
378 EventMark m("4 compact heap");
379 TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
380 trace("4");
381
382 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(true));
383
384 pg->compact();
385
386 VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));
387
388 GenCompactClosure blk;
389 gch->generation_iterate(&blk, true);
390
391 VALIDATE_MARK_SWEEP_ONLY(compaction_complete());
392
393 pg->post_compact(); // Shared spaces verification.
394 }