Wed, 03 Mar 2010 14:48:26 -0800
4396719: Mark Sweep stack overflow on deeply nested Object arrays
Summary: Use an explicit stack for object arrays and process them in chunks.
Reviewed-by: iveresov, apetrusenko
1 /*
2 * Copyright 2001-2009 Sun Microsystems, Inc. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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25 #include "incls/_precompiled.incl"
26 #include "incls/_g1MarkSweep.cpp.incl"
28 class HeapRegion;
30 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
31 bool clear_all_softrefs) {
32 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
34 // hook up weak ref data so it can be used during Mark-Sweep
35 assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
36 assert(rp != NULL, "should be non-NULL");
37 GenMarkSweep::_ref_processor = rp;
38 rp->setup_policy(clear_all_softrefs);
40 // When collecting the permanent generation methodOops may be moving,
41 // so we either have to flush all bcp data or convert it into bci.
42 CodeCache::gc_prologue();
43 Threads::gc_prologue();
45 // Increment the invocation count for the permanent generation, since it is
46 // implicitly collected whenever we do a full mark sweep collection.
47 SharedHeap* sh = SharedHeap::heap();
48 sh->perm_gen()->stat_record()->invocations++;
50 bool marked_for_unloading = false;
52 allocate_stacks();
54 // We should save the marks of the currently locked biased monitors.
55 // The marking doesn't preserve the marks of biased objects.
56 BiasedLocking::preserve_marks();
58 mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
60 if (VerifyDuringGC) {
61 G1CollectedHeap* g1h = G1CollectedHeap::heap();
62 g1h->checkConcurrentMark();
63 }
65 mark_sweep_phase2();
67 // Don't add any more derived pointers during phase3
68 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
70 mark_sweep_phase3();
72 mark_sweep_phase4();
74 GenMarkSweep::restore_marks();
75 BiasedLocking::restore_marks();
76 GenMarkSweep::deallocate_stacks();
78 // We must invalidate the perm-gen rs, so that it gets rebuilt.
79 GenRemSet* rs = sh->rem_set();
80 rs->invalidate(sh->perm_gen()->used_region(), true /*whole_heap*/);
82 // "free at last gc" is calculated from these.
83 // CHF: cheating for now!!!
84 // Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
85 // Universe::set_heap_used_at_last_gc(Universe::heap()->used());
87 Threads::gc_epilogue();
88 CodeCache::gc_epilogue();
90 // refs processing: clean slate
91 GenMarkSweep::_ref_processor = NULL;
92 }
95 void G1MarkSweep::allocate_stacks() {
96 GenMarkSweep::_preserved_count_max = 0;
97 GenMarkSweep::_preserved_marks = NULL;
98 GenMarkSweep::_preserved_count = 0;
99 GenMarkSweep::_preserved_mark_stack = NULL;
100 GenMarkSweep::_preserved_oop_stack = NULL;
102 GenMarkSweep::_marking_stack =
103 new (ResourceObj::C_HEAP) GrowableArray<oop>(4000, true);
104 GenMarkSweep::_objarray_stack =
105 new (ResourceObj::C_HEAP) GrowableArray<ObjArrayTask>(50, true);
107 int size = SystemDictionary::number_of_classes() * 2;
108 GenMarkSweep::_revisit_klass_stack =
109 new (ResourceObj::C_HEAP) GrowableArray<Klass*>(size, true);
110 // (#klass/k)^2 for k ~ 10 appears a better fit, but this will have to do
111 // for now until we have a chance to work out a more optimal setting.
112 GenMarkSweep::_revisit_mdo_stack =
113 new (ResourceObj::C_HEAP) GrowableArray<DataLayout*>(size*2, true);
115 }
117 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
118 bool clear_all_softrefs) {
119 // Recursively traverse all live objects and mark them
120 EventMark m("1 mark object");
121 TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
122 GenMarkSweep::trace(" 1");
124 SharedHeap* sh = SharedHeap::heap();
126 sh->process_strong_roots(true, // activeate StrongRootsScope
127 true, // Collecting permanent generation.
128 SharedHeap::SO_SystemClasses,
129 &GenMarkSweep::follow_root_closure,
130 &GenMarkSweep::follow_code_root_closure,
131 &GenMarkSweep::follow_root_closure);
133 // Process reference objects found during marking
134 ReferenceProcessor* rp = GenMarkSweep::ref_processor();
135 rp->setup_policy(clear_all_softrefs);
136 rp->process_discovered_references(&GenMarkSweep::is_alive,
137 &GenMarkSweep::keep_alive,
138 &GenMarkSweep::follow_stack_closure,
139 NULL);
141 // Follow system dictionary roots and unload classes
142 bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
143 assert(GenMarkSweep::_marking_stack->is_empty(),
144 "stack should be empty by now");
146 // Follow code cache roots (has to be done after system dictionary,
147 // assumes all live klasses are marked)
148 CodeCache::do_unloading(&GenMarkSweep::is_alive,
149 &GenMarkSweep::keep_alive,
150 purged_class);
151 GenMarkSweep::follow_stack();
153 // Update subklass/sibling/implementor links of live klasses
154 GenMarkSweep::follow_weak_klass_links();
155 assert(GenMarkSweep::_marking_stack->is_empty(),
156 "stack should be empty by now");
158 // Visit memoized MDO's and clear any unmarked weak refs
159 GenMarkSweep::follow_mdo_weak_refs();
160 assert(GenMarkSweep::_marking_stack->is_empty(), "just drained");
163 // Visit symbol and interned string tables and delete unmarked oops
164 SymbolTable::unlink(&GenMarkSweep::is_alive);
165 StringTable::unlink(&GenMarkSweep::is_alive);
167 assert(GenMarkSweep::_marking_stack->is_empty(),
168 "stack should be empty by now");
169 }
171 class G1PrepareCompactClosure: public HeapRegionClosure {
172 ModRefBarrierSet* _mrbs;
173 CompactPoint _cp;
175 void free_humongous_region(HeapRegion* hr) {
176 HeapWord* bot = hr->bottom();
177 HeapWord* end = hr->end();
178 assert(hr->startsHumongous(),
179 "Only the start of a humongous region should be freed.");
180 G1CollectedHeap::heap()->free_region(hr);
181 hr->prepare_for_compaction(&_cp);
182 // Also clear the part of the card table that will be unused after
183 // compaction.
184 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
185 }
187 public:
188 G1PrepareCompactClosure(CompactibleSpace* cs) :
189 _cp(NULL, cs, cs->initialize_threshold()),
190 _mrbs(G1CollectedHeap::heap()->mr_bs())
191 {}
192 bool doHeapRegion(HeapRegion* hr) {
193 if (hr->isHumongous()) {
194 if (hr->startsHumongous()) {
195 oop obj = oop(hr->bottom());
196 if (obj->is_gc_marked()) {
197 obj->forward_to(obj);
198 } else {
199 free_humongous_region(hr);
200 }
201 } else {
202 assert(hr->continuesHumongous(), "Invalid humongous.");
203 }
204 } else {
205 hr->prepare_for_compaction(&_cp);
206 // Also clear the part of the card table that will be unused after
207 // compaction.
208 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
209 }
210 return false;
211 }
212 };
214 // Finds the first HeapRegion.
215 class FindFirstRegionClosure: public HeapRegionClosure {
216 HeapRegion* _a_region;
217 public:
218 FindFirstRegionClosure() : _a_region(NULL) {}
219 bool doHeapRegion(HeapRegion* r) {
220 _a_region = r;
221 return true;
222 }
223 HeapRegion* result() { return _a_region; }
224 };
226 void G1MarkSweep::mark_sweep_phase2() {
227 // Now all live objects are marked, compute the new object addresses.
229 // It is imperative that we traverse perm_gen LAST. If dead space is
230 // allowed a range of dead object may get overwritten by a dead int
231 // array. If perm_gen is not traversed last a klassOop may get
232 // overwritten. This is fine since it is dead, but if the class has dead
233 // instances we have to skip them, and in order to find their size we
234 // need the klassOop!
235 //
236 // It is not required that we traverse spaces in the same order in
237 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
238 // tracking expects us to do so. See comment under phase4.
240 G1CollectedHeap* g1h = G1CollectedHeap::heap();
241 Generation* pg = g1h->perm_gen();
243 EventMark m("2 compute new addresses");
244 TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
245 GenMarkSweep::trace("2");
247 FindFirstRegionClosure cl;
248 g1h->heap_region_iterate(&cl);
249 HeapRegion *r = cl.result();
250 CompactibleSpace* sp = r;
251 if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) {
252 sp = r->next_compaction_space();
253 }
255 G1PrepareCompactClosure blk(sp);
256 g1h->heap_region_iterate(&blk);
258 CompactPoint perm_cp(pg, NULL, NULL);
259 pg->prepare_for_compaction(&perm_cp);
260 }
262 class G1AdjustPointersClosure: public HeapRegionClosure {
263 public:
264 bool doHeapRegion(HeapRegion* r) {
265 if (r->isHumongous()) {
266 if (r->startsHumongous()) {
267 // We must adjust the pointers on the single H object.
268 oop obj = oop(r->bottom());
269 debug_only(GenMarkSweep::track_interior_pointers(obj));
270 // point all the oops to the new location
271 obj->adjust_pointers();
272 debug_only(GenMarkSweep::check_interior_pointers());
273 }
274 } else {
275 // This really ought to be "as_CompactibleSpace"...
276 r->adjust_pointers();
277 }
278 return false;
279 }
280 };
282 void G1MarkSweep::mark_sweep_phase3() {
283 G1CollectedHeap* g1h = G1CollectedHeap::heap();
284 Generation* pg = g1h->perm_gen();
286 // Adjust the pointers to reflect the new locations
287 EventMark m("3 adjust pointers");
288 TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
289 GenMarkSweep::trace("3");
291 SharedHeap* sh = SharedHeap::heap();
293 sh->process_strong_roots(true, // activate StrongRootsScope
294 true, // Collecting permanent generation.
295 SharedHeap::SO_AllClasses,
296 &GenMarkSweep::adjust_root_pointer_closure,
297 NULL, // do not touch code cache here
298 &GenMarkSweep::adjust_pointer_closure);
300 g1h->ref_processor()->weak_oops_do(&GenMarkSweep::adjust_root_pointer_closure);
302 // Now adjust pointers in remaining weak roots. (All of which should
303 // have been cleared if they pointed to non-surviving objects.)
304 g1h->g1_process_weak_roots(&GenMarkSweep::adjust_root_pointer_closure,
305 &GenMarkSweep::adjust_pointer_closure);
307 GenMarkSweep::adjust_marks();
309 G1AdjustPointersClosure blk;
310 g1h->heap_region_iterate(&blk);
311 pg->adjust_pointers();
312 }
314 class G1SpaceCompactClosure: public HeapRegionClosure {
315 public:
316 G1SpaceCompactClosure() {}
318 bool doHeapRegion(HeapRegion* hr) {
319 if (hr->isHumongous()) {
320 if (hr->startsHumongous()) {
321 oop obj = oop(hr->bottom());
322 if (obj->is_gc_marked()) {
323 obj->init_mark();
324 } else {
325 assert(hr->is_empty(), "Should have been cleared in phase 2.");
326 }
327 hr->reset_during_compaction();
328 }
329 } else {
330 hr->compact();
331 }
332 return false;
333 }
334 };
336 void G1MarkSweep::mark_sweep_phase4() {
337 // All pointers are now adjusted, move objects accordingly
339 // It is imperative that we traverse perm_gen first in phase4. All
340 // classes must be allocated earlier than their instances, and traversing
341 // perm_gen first makes sure that all klassOops have moved to their new
342 // location before any instance does a dispatch through it's klass!
344 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
345 // in the same order in phase2, phase3 and phase4. We don't quite do that
346 // here (perm_gen first rather than last), so we tell the validate code
347 // to use a higher index (saved from phase2) when verifying perm_gen.
348 G1CollectedHeap* g1h = G1CollectedHeap::heap();
349 Generation* pg = g1h->perm_gen();
351 EventMark m("4 compact heap");
352 TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
353 GenMarkSweep::trace("4");
355 pg->compact();
357 G1SpaceCompactClosure blk;
358 g1h->heap_region_iterate(&blk);
360 }
362 // Local Variables: ***
363 // c-indentation-style: gnu ***
364 // End: ***