Thu, 22 Sep 2011 10:57:37 -0700
6484982: G1: process references during evacuation pauses
Summary: G1 now uses two reference processors - one is used by concurrent marking and the other is used by STW GCs (both full and incremental evacuation pauses). In an evacuation pause, the reference processor is embedded into the closures used to scan objects. Doing so causes causes reference objects to be 'discovered' by the reference processor. At the end of the evacuation pause, these discovered reference objects are processed - preserving (and copying) referent objects (and their reachable graphs) as appropriate.
Reviewed-by: ysr, jwilhelm, brutisso, stefank, tonyp
1 /*
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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/g1MarkSweep.hpp"
33 #include "memory/gcLocker.hpp"
34 #include "memory/genCollectedHeap.hpp"
35 #include "memory/modRefBarrierSet.hpp"
36 #include "memory/referencePolicy.hpp"
37 #include "memory/space.hpp"
38 #include "oops/instanceRefKlass.hpp"
39 #include "oops/oop.inline.hpp"
40 #include "prims/jvmtiExport.hpp"
41 #include "runtime/aprofiler.hpp"
42 #include "runtime/biasedLocking.hpp"
43 #include "runtime/fprofiler.hpp"
44 #include "runtime/synchronizer.hpp"
45 #include "runtime/thread.hpp"
46 #include "runtime/vmThread.hpp"
47 #include "utilities/copy.hpp"
48 #include "utilities/events.hpp"
50 class HeapRegion;
52 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
53 bool clear_all_softrefs) {
54 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
56 SharedHeap* sh = SharedHeap::heap();
57 #ifdef ASSERT
58 if (sh->collector_policy()->should_clear_all_soft_refs()) {
59 assert(clear_all_softrefs, "Policy should have been checked earler");
60 }
61 #endif
62 // hook up weak ref data so it can be used during Mark-Sweep
63 assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
64 assert(rp != NULL, "should be non-NULL");
65 assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Precondition");
67 GenMarkSweep::_ref_processor = rp;
68 rp->setup_policy(clear_all_softrefs);
70 // When collecting the permanent generation methodOops may be moving,
71 // so we either have to flush all bcp data or convert it into bci.
72 CodeCache::gc_prologue();
73 Threads::gc_prologue();
75 // Increment the invocation count for the permanent generation, since it is
76 // implicitly collected whenever we do a full mark sweep collection.
77 sh->perm_gen()->stat_record()->invocations++;
79 bool marked_for_unloading = false;
81 allocate_stacks();
83 // We should save the marks of the currently locked biased monitors.
84 // The marking doesn't preserve the marks of biased objects.
85 BiasedLocking::preserve_marks();
87 mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
89 mark_sweep_phase2();
91 // Don't add any more derived pointers during phase3
92 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
94 mark_sweep_phase3();
96 mark_sweep_phase4();
98 GenMarkSweep::restore_marks();
99 BiasedLocking::restore_marks();
100 GenMarkSweep::deallocate_stacks();
102 // We must invalidate the perm-gen rs, so that it gets rebuilt.
103 GenRemSet* rs = sh->rem_set();
104 rs->invalidate(sh->perm_gen()->used_region(), true /*whole_heap*/);
106 // "free at last gc" is calculated from these.
107 // CHF: cheating for now!!!
108 // Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
109 // Universe::set_heap_used_at_last_gc(Universe::heap()->used());
111 Threads::gc_epilogue();
112 CodeCache::gc_epilogue();
113 JvmtiExport::gc_epilogue();
115 // refs processing: clean slate
116 GenMarkSweep::_ref_processor = NULL;
117 }
120 void G1MarkSweep::allocate_stacks() {
121 GenMarkSweep::_preserved_count_max = 0;
122 GenMarkSweep::_preserved_marks = NULL;
123 GenMarkSweep::_preserved_count = 0;
124 }
126 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
127 bool clear_all_softrefs) {
128 // Recursively traverse all live objects and mark them
129 EventMark m("1 mark object");
130 TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
131 GenMarkSweep::trace(" 1");
133 SharedHeap* sh = SharedHeap::heap();
135 sh->process_strong_roots(true, // activeate StrongRootsScope
136 true, // Collecting permanent generation.
137 SharedHeap::SO_SystemClasses,
138 &GenMarkSweep::follow_root_closure,
139 &GenMarkSweep::follow_code_root_closure,
140 &GenMarkSweep::follow_root_closure);
142 // Process reference objects found during marking
143 ReferenceProcessor* rp = GenMarkSweep::ref_processor();
144 assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Sanity");
146 rp->setup_policy(clear_all_softrefs);
147 rp->process_discovered_references(&GenMarkSweep::is_alive,
148 &GenMarkSweep::keep_alive,
149 &GenMarkSweep::follow_stack_closure,
150 NULL);
152 // Follow system dictionary roots and unload classes
153 bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
154 assert(GenMarkSweep::_marking_stack.is_empty(),
155 "stack should be empty by now");
157 // Follow code cache roots (has to be done after system dictionary,
158 // assumes all live klasses are marked)
159 CodeCache::do_unloading(&GenMarkSweep::is_alive,
160 &GenMarkSweep::keep_alive,
161 purged_class);
162 GenMarkSweep::follow_stack();
164 // Update subklass/sibling/implementor links of live klasses
165 GenMarkSweep::follow_weak_klass_links();
166 assert(GenMarkSweep::_marking_stack.is_empty(),
167 "stack should be empty by now");
169 // Visit memoized MDO's and clear any unmarked weak refs
170 GenMarkSweep::follow_mdo_weak_refs();
171 assert(GenMarkSweep::_marking_stack.is_empty(), "just drained");
173 // Visit interned string tables and delete unmarked oops
174 StringTable::unlink(&GenMarkSweep::is_alive);
175 // Clean up unreferenced symbols in symbol table.
176 SymbolTable::unlink();
178 assert(GenMarkSweep::_marking_stack.is_empty(),
179 "stack should be empty by now");
181 if (VerifyDuringGC) {
182 HandleMark hm; // handle scope
183 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
184 gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying ");
185 Universe::heap()->prepare_for_verify();
186 // Note: we can verify only the heap here. When an object is
187 // marked, the previous value of the mark word (including
188 // identity hash values, ages, etc) is preserved, and the mark
189 // word is set to markOop::marked_value - effectively removing
190 // any hash values from the mark word. These hash values are
191 // used when verifying the dictionaries and so removing them
192 // from the mark word can make verification of the dictionaries
193 // fail. At the end of the GC, the orginal mark word values
194 // (including hash values) are restored to the appropriate
195 // objects.
196 Universe::heap()->verify(/* allow dirty */ true,
197 /* silent */ false,
198 /* option */ VerifyOption_G1UseMarkWord);
200 G1CollectedHeap* g1h = G1CollectedHeap::heap();
201 gclog_or_tty->print_cr("]");
202 }
203 }
205 class G1PrepareCompactClosure: public HeapRegionClosure {
206 G1CollectedHeap* _g1h;
207 ModRefBarrierSet* _mrbs;
208 CompactPoint _cp;
209 HumongousRegionSet _humongous_proxy_set;
211 void free_humongous_region(HeapRegion* hr) {
212 HeapWord* end = hr->end();
213 size_t dummy_pre_used;
214 FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");
216 assert(hr->startsHumongous(),
217 "Only the start of a humongous region should be freed.");
218 _g1h->free_humongous_region(hr, &dummy_pre_used, &dummy_free_list,
219 &_humongous_proxy_set, false /* par */);
220 hr->prepare_for_compaction(&_cp);
221 // Also clear the part of the card table that will be unused after
222 // compaction.
223 _mrbs->clear(MemRegion(hr->compaction_top(), end));
224 dummy_free_list.remove_all();
225 }
227 public:
228 G1PrepareCompactClosure(CompactibleSpace* cs)
229 : _g1h(G1CollectedHeap::heap()),
230 _mrbs(G1CollectedHeap::heap()->mr_bs()),
231 _cp(NULL, cs, cs->initialize_threshold()),
232 _humongous_proxy_set("G1MarkSweep Humongous Proxy Set") { }
234 void update_sets() {
235 // We'll recalculate total used bytes and recreate the free list
236 // at the end of the GC, so no point in updating those values here.
237 _g1h->update_sets_after_freeing_regions(0, /* pre_used */
238 NULL, /* free_list */
239 &_humongous_proxy_set,
240 false /* par */);
241 }
243 bool doHeapRegion(HeapRegion* hr) {
244 if (hr->isHumongous()) {
245 if (hr->startsHumongous()) {
246 oop obj = oop(hr->bottom());
247 if (obj->is_gc_marked()) {
248 obj->forward_to(obj);
249 } else {
250 free_humongous_region(hr);
251 }
252 } else {
253 assert(hr->continuesHumongous(), "Invalid humongous.");
254 }
255 } else {
256 hr->prepare_for_compaction(&_cp);
257 // Also clear the part of the card table that will be unused after
258 // compaction.
259 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
260 }
261 return false;
262 }
263 };
265 // Finds the first HeapRegion.
266 class FindFirstRegionClosure: public HeapRegionClosure {
267 HeapRegion* _a_region;
268 public:
269 FindFirstRegionClosure() : _a_region(NULL) {}
270 bool doHeapRegion(HeapRegion* r) {
271 _a_region = r;
272 return true;
273 }
274 HeapRegion* result() { return _a_region; }
275 };
277 void G1MarkSweep::mark_sweep_phase2() {
278 // Now all live objects are marked, compute the new object addresses.
280 // It is imperative that we traverse perm_gen LAST. If dead space is
281 // allowed a range of dead object may get overwritten by a dead int
282 // array. If perm_gen is not traversed last a klassOop may get
283 // overwritten. This is fine since it is dead, but if the class has dead
284 // instances we have to skip them, and in order to find their size we
285 // need the klassOop!
286 //
287 // It is not required that we traverse spaces in the same order in
288 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
289 // tracking expects us to do so. See comment under phase4.
291 G1CollectedHeap* g1h = G1CollectedHeap::heap();
292 Generation* pg = g1h->perm_gen();
294 EventMark m("2 compute new addresses");
295 TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
296 GenMarkSweep::trace("2");
298 FindFirstRegionClosure cl;
299 g1h->heap_region_iterate(&cl);
300 HeapRegion *r = cl.result();
301 CompactibleSpace* sp = r;
302 if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) {
303 sp = r->next_compaction_space();
304 }
306 G1PrepareCompactClosure blk(sp);
307 g1h->heap_region_iterate(&blk);
308 blk.update_sets();
310 CompactPoint perm_cp(pg, NULL, NULL);
311 pg->prepare_for_compaction(&perm_cp);
312 }
314 class G1AdjustPointersClosure: public HeapRegionClosure {
315 public:
316 bool doHeapRegion(HeapRegion* r) {
317 if (r->isHumongous()) {
318 if (r->startsHumongous()) {
319 // We must adjust the pointers on the single H object.
320 oop obj = oop(r->bottom());
321 debug_only(GenMarkSweep::track_interior_pointers(obj));
322 // point all the oops to the new location
323 obj->adjust_pointers();
324 debug_only(GenMarkSweep::check_interior_pointers());
325 }
326 } else {
327 // This really ought to be "as_CompactibleSpace"...
328 r->adjust_pointers();
329 }
330 return false;
331 }
332 };
334 void G1MarkSweep::mark_sweep_phase3() {
335 G1CollectedHeap* g1h = G1CollectedHeap::heap();
336 Generation* pg = g1h->perm_gen();
338 // Adjust the pointers to reflect the new locations
339 EventMark m("3 adjust pointers");
340 TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
341 GenMarkSweep::trace("3");
343 SharedHeap* sh = SharedHeap::heap();
345 sh->process_strong_roots(true, // activate StrongRootsScope
346 true, // Collecting permanent generation.
347 SharedHeap::SO_AllClasses,
348 &GenMarkSweep::adjust_root_pointer_closure,
349 NULL, // do not touch code cache here
350 &GenMarkSweep::adjust_pointer_closure);
352 assert(GenMarkSweep::ref_processor() == g1h->ref_processor_stw(), "Sanity");
353 g1h->ref_processor_stw()->weak_oops_do(&GenMarkSweep::adjust_root_pointer_closure);
355 // Now adjust pointers in remaining weak roots. (All of which should
356 // have been cleared if they pointed to non-surviving objects.)
357 g1h->g1_process_weak_roots(&GenMarkSweep::adjust_root_pointer_closure,
358 &GenMarkSweep::adjust_pointer_closure);
360 GenMarkSweep::adjust_marks();
362 G1AdjustPointersClosure blk;
363 g1h->heap_region_iterate(&blk);
364 pg->adjust_pointers();
365 }
367 class G1SpaceCompactClosure: public HeapRegionClosure {
368 public:
369 G1SpaceCompactClosure() {}
371 bool doHeapRegion(HeapRegion* hr) {
372 if (hr->isHumongous()) {
373 if (hr->startsHumongous()) {
374 oop obj = oop(hr->bottom());
375 if (obj->is_gc_marked()) {
376 obj->init_mark();
377 } else {
378 assert(hr->is_empty(), "Should have been cleared in phase 2.");
379 }
380 hr->reset_during_compaction();
381 }
382 } else {
383 hr->compact();
384 }
385 return false;
386 }
387 };
389 void G1MarkSweep::mark_sweep_phase4() {
390 // All pointers are now adjusted, move objects accordingly
392 // It is imperative that we traverse perm_gen first in phase4. All
393 // classes must be allocated earlier than their instances, and traversing
394 // perm_gen first makes sure that all klassOops have moved to their new
395 // location before any instance does a dispatch through it's klass!
397 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
398 // in the same order in phase2, phase3 and phase4. We don't quite do that
399 // here (perm_gen first rather than last), so we tell the validate code
400 // to use a higher index (saved from phase2) when verifying perm_gen.
401 G1CollectedHeap* g1h = G1CollectedHeap::heap();
402 Generation* pg = g1h->perm_gen();
404 EventMark m("4 compact heap");
405 TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
406 GenMarkSweep::trace("4");
408 pg->compact();
410 G1SpaceCompactClosure blk;
411 g1h->heap_region_iterate(&blk);
413 }
415 // Local Variables: ***
416 // c-indentation-style: gnu ***
417 // End: ***