Mon, 07 Jul 2014 10:12:40 +0200
8049421: G1 Class Unloading after completing a concurrent mark cycle
Reviewed-by: tschatzl, ehelin, brutisso, coleenp, roland, iveresov
Contributed-by: stefan.karlsson@oracle.com, mikael.gerdin@oracle.com
1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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/g1Log.hpp"
33 #include "gc_implementation/g1/g1MarkSweep.hpp"
34 #include "gc_implementation/g1/g1StringDedup.hpp"
35 #include "gc_implementation/shared/gcHeapSummary.hpp"
36 #include "gc_implementation/shared/gcTimer.hpp"
37 #include "gc_implementation/shared/gcTrace.hpp"
38 #include "gc_implementation/shared/gcTraceTime.hpp"
39 #include "memory/gcLocker.hpp"
40 #include "memory/genCollectedHeap.hpp"
41 #include "memory/modRefBarrierSet.hpp"
42 #include "memory/referencePolicy.hpp"
43 #include "memory/space.hpp"
44 #include "oops/instanceRefKlass.hpp"
45 #include "oops/oop.inline.hpp"
46 #include "prims/jvmtiExport.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"
55 class HeapRegion;
57 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
58 bool clear_all_softrefs) {
59 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
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");
72 GenMarkSweep::_ref_processor = rp;
73 rp->setup_policy(clear_all_softrefs);
75 // When collecting the permanent generation Method*s 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();
80 bool marked_for_unloading = false;
82 allocate_stacks();
84 // We should save the marks of the currently locked biased monitors.
85 // The marking doesn't preserve the marks of biased objects.
86 BiasedLocking::preserve_marks();
88 mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
90 mark_sweep_phase2();
92 // Don't add any more derived pointers during phase3
93 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
95 mark_sweep_phase3();
97 mark_sweep_phase4();
99 GenMarkSweep::restore_marks();
100 BiasedLocking::restore_marks();
101 GenMarkSweep::deallocate_stacks();
103 // "free at last gc" is calculated from these.
104 // CHF: cheating for now!!!
105 // Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
106 // Universe::set_heap_used_at_last_gc(Universe::heap()->used());
108 Threads::gc_epilogue();
109 CodeCache::gc_epilogue();
110 JvmtiExport::gc_epilogue();
112 // refs processing: clean slate
113 GenMarkSweep::_ref_processor = NULL;
114 }
117 void G1MarkSweep::allocate_stacks() {
118 GenMarkSweep::_preserved_count_max = 0;
119 GenMarkSweep::_preserved_marks = NULL;
120 GenMarkSweep::_preserved_count = 0;
121 }
123 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
124 bool clear_all_softrefs) {
125 // Recursively traverse all live objects and mark them
126 GCTraceTime tm("phase 1", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
127 GenMarkSweep::trace(" 1");
129 SharedHeap* sh = SharedHeap::heap();
131 // Need cleared claim bits for the roots processing
132 ClassLoaderDataGraph::clear_claimed_marks();
134 MarkingCodeBlobClosure follow_code_closure(&GenMarkSweep::follow_root_closure, !CodeBlobToOopClosure::FixRelocations);
135 sh->process_strong_roots(true, // activate StrongRootsScope
136 SharedHeap::SO_None,
137 &GenMarkSweep::follow_root_closure,
138 &GenMarkSweep::follow_cld_closure,
139 &follow_code_closure);
141 // Process reference objects found during marking
142 ReferenceProcessor* rp = GenMarkSweep::ref_processor();
143 assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Sanity");
145 rp->setup_policy(clear_all_softrefs);
146 const ReferenceProcessorStats& stats =
147 rp->process_discovered_references(&GenMarkSweep::is_alive,
148 &GenMarkSweep::keep_alive,
149 &GenMarkSweep::follow_stack_closure,
150 NULL,
151 gc_timer(),
152 gc_tracer()->gc_id());
153 gc_tracer()->report_gc_reference_stats(stats);
156 // This is the point where the entire marking should have completed.
157 assert(GenMarkSweep::_marking_stack.is_empty(), "Marking should have completed");
159 // Unload classes and purge the SystemDictionary.
160 bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
162 // Unload nmethods.
163 CodeCache::do_unloading(&GenMarkSweep::is_alive, purged_class);
165 // Prune dead klasses from subklass/sibling/implementor lists.
166 Klass::clean_weak_klass_links(&GenMarkSweep::is_alive);
168 // Delete entries for dead interned string and clean up unreferenced symbols in symbol table.
169 G1CollectedHeap::heap()->unlink_string_and_symbol_table(&GenMarkSweep::is_alive);
171 if (VerifyDuringGC) {
172 HandleMark hm; // handle scope
173 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
174 Universe::heap()->prepare_for_verify();
175 // Note: we can verify only the heap here. When an object is
176 // marked, the previous value of the mark word (including
177 // identity hash values, ages, etc) is preserved, and the mark
178 // word is set to markOop::marked_value - effectively removing
179 // any hash values from the mark word. These hash values are
180 // used when verifying the dictionaries and so removing them
181 // from the mark word can make verification of the dictionaries
182 // fail. At the end of the GC, the orginal mark word values
183 // (including hash values) are restored to the appropriate
184 // objects.
185 if (!VerifySilently) {
186 gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying ");
187 }
188 Universe::heap()->verify(VerifySilently, VerifyOption_G1UseMarkWord);
189 if (!VerifySilently) {
190 gclog_or_tty->print_cr("]");
191 }
192 }
194 gc_tracer()->report_object_count_after_gc(&GenMarkSweep::is_alive);
195 }
197 class G1PrepareCompactClosure: public HeapRegionClosure {
198 G1CollectedHeap* _g1h;
199 ModRefBarrierSet* _mrbs;
200 CompactPoint _cp;
201 HeapRegionSetCount _humongous_regions_removed;
203 void free_humongous_region(HeapRegion* hr) {
204 HeapWord* end = hr->end();
205 FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");
207 assert(hr->startsHumongous(),
208 "Only the start of a humongous region should be freed.");
210 hr->set_containing_set(NULL);
211 _humongous_regions_removed.increment(1u, hr->capacity());
213 _g1h->free_humongous_region(hr, &dummy_free_list, false /* par */);
214 hr->prepare_for_compaction(&_cp);
215 // Also clear the part of the card table that will be unused after
216 // compaction.
217 _mrbs->clear(MemRegion(hr->compaction_top(), end));
218 dummy_free_list.remove_all();
219 }
221 public:
222 G1PrepareCompactClosure(CompactibleSpace* cs)
223 : _g1h(G1CollectedHeap::heap()),
224 _mrbs(_g1h->g1_barrier_set()),
225 _cp(NULL, cs, cs->initialize_threshold()),
226 _humongous_regions_removed() { }
228 void update_sets() {
229 // We'll recalculate total used bytes and recreate the free list
230 // at the end of the GC, so no point in updating those values here.
231 HeapRegionSetCount empty_set;
232 _g1h->remove_from_old_sets(empty_set, _humongous_regions_removed);
233 }
235 bool doHeapRegion(HeapRegion* hr) {
236 if (hr->isHumongous()) {
237 if (hr->startsHumongous()) {
238 oop obj = oop(hr->bottom());
239 if (obj->is_gc_marked()) {
240 obj->forward_to(obj);
241 } else {
242 free_humongous_region(hr);
243 }
244 } else {
245 assert(hr->continuesHumongous(), "Invalid humongous.");
246 }
247 } else {
248 hr->prepare_for_compaction(&_cp);
249 // Also clear the part of the card table that will be unused after
250 // compaction.
251 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
252 }
253 return false;
254 }
255 };
257 void G1MarkSweep::mark_sweep_phase2() {
258 // Now all live objects are marked, compute the new object addresses.
260 // It is not required that we traverse spaces in the same order in
261 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
262 // tracking expects us to do so. See comment under phase4.
264 G1CollectedHeap* g1h = G1CollectedHeap::heap();
266 GCTraceTime tm("phase 2", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
267 GenMarkSweep::trace("2");
269 // find the first region
270 HeapRegion* r = g1h->region_at(0);
271 CompactibleSpace* sp = r;
272 if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) {
273 sp = r->next_compaction_space();
274 }
276 G1PrepareCompactClosure blk(sp);
277 g1h->heap_region_iterate(&blk);
278 blk.update_sets();
279 }
281 class G1AdjustPointersClosure: public HeapRegionClosure {
282 public:
283 bool doHeapRegion(HeapRegion* r) {
284 if (r->isHumongous()) {
285 if (r->startsHumongous()) {
286 // We must adjust the pointers on the single H object.
287 oop obj = oop(r->bottom());
288 // point all the oops to the new location
289 obj->adjust_pointers();
290 }
291 } else {
292 // This really ought to be "as_CompactibleSpace"...
293 r->adjust_pointers();
294 }
295 return false;
296 }
297 };
299 void G1MarkSweep::mark_sweep_phase3() {
300 G1CollectedHeap* g1h = G1CollectedHeap::heap();
302 // Adjust the pointers to reflect the new locations
303 GCTraceTime tm("phase 3", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
304 GenMarkSweep::trace("3");
306 SharedHeap* sh = SharedHeap::heap();
308 // Need cleared claim bits for the roots processing
309 ClassLoaderDataGraph::clear_claimed_marks();
311 CodeBlobToOopClosure adjust_code_closure(&GenMarkSweep::adjust_pointer_closure, CodeBlobToOopClosure::FixRelocations);
312 sh->process_all_roots(true, // activate StrongRootsScope
313 SharedHeap::SO_AllCodeCache,
314 &GenMarkSweep::adjust_pointer_closure,
315 &GenMarkSweep::adjust_cld_closure,
316 &adjust_code_closure);
318 assert(GenMarkSweep::ref_processor() == g1h->ref_processor_stw(), "Sanity");
319 g1h->ref_processor_stw()->weak_oops_do(&GenMarkSweep::adjust_pointer_closure);
321 // Now adjust pointers in remaining weak roots. (All of which should
322 // have been cleared if they pointed to non-surviving objects.)
323 sh->process_weak_roots(&GenMarkSweep::adjust_pointer_closure);
325 if (G1StringDedup::is_enabled()) {
326 G1StringDedup::oops_do(&GenMarkSweep::adjust_pointer_closure);
327 }
329 GenMarkSweep::adjust_marks();
331 G1AdjustPointersClosure blk;
332 g1h->heap_region_iterate(&blk);
333 }
335 class G1SpaceCompactClosure: public HeapRegionClosure {
336 public:
337 G1SpaceCompactClosure() {}
339 bool doHeapRegion(HeapRegion* hr) {
340 if (hr->isHumongous()) {
341 if (hr->startsHumongous()) {
342 oop obj = oop(hr->bottom());
343 if (obj->is_gc_marked()) {
344 obj->init_mark();
345 } else {
346 assert(hr->is_empty(), "Should have been cleared in phase 2.");
347 }
348 hr->reset_during_compaction();
349 }
350 } else {
351 hr->compact();
352 }
353 return false;
354 }
355 };
357 void G1MarkSweep::mark_sweep_phase4() {
358 // All pointers are now adjusted, move objects accordingly
360 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
361 // in the same order in phase2, phase3 and phase4. We don't quite do that
362 // here (code and comment not fixed for perm removal), so we tell the validate code
363 // to use a higher index (saved from phase2) when verifying perm_gen.
364 G1CollectedHeap* g1h = G1CollectedHeap::heap();
366 GCTraceTime tm("phase 4", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
367 GenMarkSweep::trace("4");
369 G1SpaceCompactClosure blk;
370 g1h->heap_region_iterate(&blk);
372 }