1 /*
2 * Copyright (c) 2001, 2012, 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 "precompiled.hpp"
26 #include "classfile/javaClasses.hpp"
27 #include "classfile/symbolTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "classfile/vmSymbols.hpp"
30 #include "code/codeCache.hpp"
31 #include "code/icBuffer.hpp"
32 #include "gc_implementation/g1/g1Log.hpp"
33 #include "gc_implementation/g1/g1MarkSweep.hpp"
34 #include "gc_implementation/shared/gcHeapSummary.hpp"
35 #include "gc_implementation/shared/gcTimer.hpp"
36 #include "gc_implementation/shared/gcTrace.hpp"
37 #include "gc_implementation/shared/gcTraceTime.hpp"
38 #include "memory/gcLocker.hpp"
39 #include "memory/genCollectedHeap.hpp"
40 #include "memory/modRefBarrierSet.hpp"
41 #include "memory/referencePolicy.hpp"
42 #include "memory/space.hpp"
43 #include "oops/instanceRefKlass.hpp"
44 #include "oops/oop.inline.hpp"
45 #include "prims/jvmtiExport.hpp"
46 #include "runtime/aprofiler.hpp"
47 #include "runtime/biasedLocking.hpp"
48 #include "runtime/fprofiler.hpp"
49 #include "runtime/synchronizer.hpp"
50 #include "runtime/thread.hpp"
51 #include "runtime/vmThread.hpp"
52 #include "utilities/copy.hpp"
53 #include "utilities/events.hpp"
54
55 class HeapRegion;
56
57 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
58 bool clear_all_softrefs) {
59 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
60
61 SharedHeap* sh = SharedHeap::heap();
62 #ifdef ASSERT
63 if (sh->collector_policy()->should_clear_all_soft_refs()) {
64 assert(clear_all_softrefs, "Policy should have been checked earler");
65 }
66 #endif
67 // hook up weak ref data so it can be used during Mark-Sweep
68 assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
69 assert(rp != NULL, "should be non-NULL");
70 assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Precondition");
71
72 GenMarkSweep::_ref_processor = rp;
73 rp->setup_policy(clear_all_softrefs);
74
75 // When collecting the permanent generation methodOops may be moving,
76 // so we either have to flush all bcp data or convert it into bci.
77 CodeCache::gc_prologue();
78 Threads::gc_prologue();
79
80 // Increment the invocation count for the permanent generation, since it is
81 // implicitly collected whenever we do a full mark sweep collection.
82 sh->perm_gen()->stat_record()->invocations++;
83
84 bool marked_for_unloading = false;
85
86 allocate_stacks();
87
88 // We should save the marks of the currently locked biased monitors.
89 // The marking doesn't preserve the marks of biased objects.
90 BiasedLocking::preserve_marks();
91
92 mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
93
94 mark_sweep_phase2();
95
96 // Don't add any more derived pointers during phase3
97 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
98
99 mark_sweep_phase3();
100
101 mark_sweep_phase4();
102
103 GenMarkSweep::restore_marks();
104 BiasedLocking::restore_marks();
105 GenMarkSweep::deallocate_stacks();
106
107 // We must invalidate the perm-gen rs, so that it gets rebuilt.
108 GenRemSet* rs = sh->rem_set();
109 rs->invalidate(sh->perm_gen()->used_region(), true /*whole_heap*/);
110
111 // "free at last gc" is calculated from these.
112 // CHF: cheating for now!!!
113 // Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
114 // Universe::set_heap_used_at_last_gc(Universe::heap()->used());
115
116 Threads::gc_epilogue();
117 CodeCache::gc_epilogue();
118 JvmtiExport::gc_epilogue();
119
120 // refs processing: clean slate
121 GenMarkSweep::_ref_processor = NULL;
122 }
123
124
125 void G1MarkSweep::allocate_stacks() {
126 GenMarkSweep::_preserved_count_max = 0;
127 GenMarkSweep::_preserved_marks = NULL;
128 GenMarkSweep::_preserved_count = 0;
129 }
130
131 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
132 bool clear_all_softrefs) {
133 // Recursively traverse all live objects and mark them
134 GCTraceTime tm("phase 1", G1Log::fine() && Verbose, true, gc_timer());
135 GenMarkSweep::trace(" 1");
136
137 SharedHeap* sh = SharedHeap::heap();
138
139 sh->process_strong_roots(true, // activeate StrongRootsScope
140 true, // Collecting permanent generation.
141 SharedHeap::SO_SystemClasses,
142 &GenMarkSweep::follow_root_closure,
143 &GenMarkSweep::follow_code_root_closure,
144 &GenMarkSweep::follow_root_closure);
145
146 // Process reference objects found during marking
147 ReferenceProcessor* rp = GenMarkSweep::ref_processor();
148 assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Sanity");
149
150 rp->setup_policy(clear_all_softrefs);
151 const ReferenceProcessorStats& stats =
152 rp->process_discovered_references(&GenMarkSweep::is_alive,
153 &GenMarkSweep::keep_alive,
154 &GenMarkSweep::follow_stack_closure,
155 NULL,
156 gc_timer());
157 gc_tracer()->report_gc_reference_stats(stats);
158
159 // Follow system dictionary roots and unload classes
160 bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
161 assert(GenMarkSweep::_marking_stack.is_empty(),
162 "stack should be empty by now");
163
164 // Follow code cache roots (has to be done after system dictionary,
165 // assumes all live klasses are marked)
166 CodeCache::do_unloading(&GenMarkSweep::is_alive,
167 &GenMarkSweep::keep_alive,
168 purged_class);
169 GenMarkSweep::follow_stack();
170
171 // Update subklass/sibling/implementor links of live klasses
172 GenMarkSweep::follow_weak_klass_links();
173 assert(GenMarkSweep::_marking_stack.is_empty(),
174 "stack should be empty by now");
175
176 // Visit memoized MDO's and clear any unmarked weak refs
177 GenMarkSweep::follow_mdo_weak_refs();
178 assert(GenMarkSweep::_marking_stack.is_empty(), "just drained");
179
180 // Visit interned string tables and delete unmarked oops
181 StringTable::unlink(&GenMarkSweep::is_alive);
182 // Clean up unreferenced symbols in symbol table.
183 SymbolTable::unlink();
184
185 assert(GenMarkSweep::_marking_stack.is_empty(),
186 "stack should be empty by now");
187
188 if (VerifyDuringGC) {
189 HandleMark hm; // handle scope
190 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
191 gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying ");
192 Universe::heap()->prepare_for_verify();
193 // Note: we can verify only the heap here. When an object is
194 // marked, the previous value of the mark word (including
195 // identity hash values, ages, etc) is preserved, and the mark
196 // word is set to markOop::marked_value - effectively removing
197 // any hash values from the mark word. These hash values are
198 // used when verifying the dictionaries and so removing them
199 // from the mark word can make verification of the dictionaries
200 // fail. At the end of the GC, the orginal mark word values
201 // (including hash values) are restored to the appropriate
202 // objects.
203 Universe::heap()->verify(/* silent */ false,
204 /* option */ VerifyOption_G1UseMarkWord);
205
206 G1CollectedHeap* g1h = G1CollectedHeap::heap();
207 gclog_or_tty->print_cr("]");
208 }
209 }
210
211 class G1PrepareCompactClosure: public HeapRegionClosure {
212 G1CollectedHeap* _g1h;
213 ModRefBarrierSet* _mrbs;
214 CompactPoint _cp;
215 HumongousRegionSet _humongous_proxy_set;
216
217 void free_humongous_region(HeapRegion* hr) {
218 HeapWord* end = hr->end();
219 size_t dummy_pre_used;
220 FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");
221
222 assert(hr->startsHumongous(),
223 "Only the start of a humongous region should be freed.");
224 _g1h->free_humongous_region(hr, &dummy_pre_used, &dummy_free_list,
225 &_humongous_proxy_set, false /* par */);
226 hr->prepare_for_compaction(&_cp);
227 // Also clear the part of the card table that will be unused after
228 // compaction.
229 _mrbs->clear(MemRegion(hr->compaction_top(), end));
230 dummy_free_list.remove_all();
231 }
232
233 public:
234 G1PrepareCompactClosure(CompactibleSpace* cs)
235 : _g1h(G1CollectedHeap::heap()),
236 _mrbs(G1CollectedHeap::heap()->mr_bs()),
237 _cp(NULL, cs, cs->initialize_threshold()),
238 _humongous_proxy_set("G1MarkSweep Humongous Proxy Set") { }
239
240 void update_sets() {
241 // We'll recalculate total used bytes and recreate the free list
242 // at the end of the GC, so no point in updating those values here.
243 _g1h->update_sets_after_freeing_regions(0, /* pre_used */
244 NULL, /* free_list */
245 NULL, /* old_proxy_set */
246 &_humongous_proxy_set,
247 false /* par */);
248 }
249
250 bool doHeapRegion(HeapRegion* hr) {
251 if (hr->isHumongous()) {
252 if (hr->startsHumongous()) {
253 oop obj = oop(hr->bottom());
254 if (obj->is_gc_marked()) {
255 obj->forward_to(obj);
256 } else {
257 free_humongous_region(hr);
258 }
259 } else {
260 assert(hr->continuesHumongous(), "Invalid humongous.");
261 }
262 } else {
263 hr->prepare_for_compaction(&_cp);
264 // Also clear the part of the card table that will be unused after
265 // compaction.
266 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
267 }
268 return false;
269 }
270 };
271
272 void G1MarkSweep::mark_sweep_phase2() {
273 // Now all live objects are marked, compute the new object addresses.
274
275 // It is imperative that we traverse perm_gen LAST. If dead space is
276 // allowed a range of dead object may get overwritten by a dead int
277 // array. If perm_gen is not traversed last a klassOop may get
278 // overwritten. This is fine since it is dead, but if the class has dead
279 // instances we have to skip them, and in order to find their size we
280 // need the klassOop!
281 //
282 // It is not required that we traverse spaces in the same order in
283 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
284 // tracking expects us to do so. See comment under phase4.
285
286 G1CollectedHeap* g1h = G1CollectedHeap::heap();
287 Generation* pg = g1h->perm_gen();
288
289 GCTraceTime tm("phase 2", G1Log::fine() && Verbose, true, gc_timer());
290 GenMarkSweep::trace("2");
291
292 // find the first region
293 HeapRegion* r = g1h->region_at(0);
294 CompactibleSpace* sp = r;
295 if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) {
296 sp = r->next_compaction_space();
297 }
298
299 G1PrepareCompactClosure blk(sp);
300 g1h->heap_region_iterate(&blk);
301 blk.update_sets();
302
303 CompactPoint perm_cp(pg, NULL, NULL);
304 pg->prepare_for_compaction(&perm_cp);
305 }
306
307 class G1AdjustPointersClosure: public HeapRegionClosure {
308 public:
309 bool doHeapRegion(HeapRegion* r) {
310 if (r->isHumongous()) {
311 if (r->startsHumongous()) {
312 // We must adjust the pointers on the single H object.
313 oop obj = oop(r->bottom());
314 debug_only(GenMarkSweep::track_interior_pointers(obj));
315 // point all the oops to the new location
316 obj->adjust_pointers();
317 debug_only(GenMarkSweep::check_interior_pointers());
318 }
319 } else {
320 // This really ought to be "as_CompactibleSpace"...
321 r->adjust_pointers();
322 }
323 return false;
324 }
325 };
326
327 void G1MarkSweep::mark_sweep_phase3() {
328 G1CollectedHeap* g1h = G1CollectedHeap::heap();
329 Generation* pg = g1h->perm_gen();
330
331 // Adjust the pointers to reflect the new locations
332 GCTraceTime tm("phase 3", G1Log::fine() && Verbose, true, gc_timer());
333 GenMarkSweep::trace("3");
334
335 SharedHeap* sh = SharedHeap::heap();
336
337 sh->process_strong_roots(true, // activate StrongRootsScope
338 true, // Collecting permanent generation.
339 SharedHeap::SO_AllClasses,
340 &GenMarkSweep::adjust_root_pointer_closure,
341 NULL, // do not touch code cache here
342 &GenMarkSweep::adjust_pointer_closure);
343
344 assert(GenMarkSweep::ref_processor() == g1h->ref_processor_stw(), "Sanity");
345 g1h->ref_processor_stw()->weak_oops_do(&GenMarkSweep::adjust_root_pointer_closure);
346
347 // Now adjust pointers in remaining weak roots. (All of which should
348 // have been cleared if they pointed to non-surviving objects.)
349 g1h->g1_process_weak_roots(&GenMarkSweep::adjust_root_pointer_closure,
350 &GenMarkSweep::adjust_pointer_closure);
351
352 GenMarkSweep::adjust_marks();
353
354 G1AdjustPointersClosure blk;
355 g1h->heap_region_iterate(&blk);
356 pg->adjust_pointers();
357 }
358
359 class G1SpaceCompactClosure: public HeapRegionClosure {
360 public:
361 G1SpaceCompactClosure() {}
362
363 bool doHeapRegion(HeapRegion* hr) {
364 if (hr->isHumongous()) {
365 if (hr->startsHumongous()) {
366 oop obj = oop(hr->bottom());
367 if (obj->is_gc_marked()) {
368 obj->init_mark();
369 } else {
370 assert(hr->is_empty(), "Should have been cleared in phase 2.");
371 }
372 hr->reset_during_compaction();
373 }
374 } else {
375 hr->compact();
376 }
377 return false;
378 }
379 };
380
381 void G1MarkSweep::mark_sweep_phase4() {
382 // All pointers are now adjusted, move objects accordingly
383
384 // It is imperative that we traverse perm_gen first in phase4. All
385 // classes must be allocated earlier than their instances, and traversing
386 // perm_gen first makes sure that all klassOops have moved to their new
387 // location before any instance does a dispatch through it's klass!
388
389 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
390 // in the same order in phase2, phase3 and phase4. We don't quite do that
391 // here (perm_gen first rather than last), so we tell the validate code
392 // to use a higher index (saved from phase2) when verifying perm_gen.
393 G1CollectedHeap* g1h = G1CollectedHeap::heap();
394 Generation* pg = g1h->perm_gen();
395
396 GCTraceTime tm("phase 4", G1Log::fine() && Verbose, true, gc_timer());
397 GenMarkSweep::trace("4");
398
399 pg->compact();
400
401 G1SpaceCompactClosure blk;
402 g1h->heap_region_iterate(&blk);
403
404 }