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 /*
2 * Copyright (c) 2000, 2014, 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).
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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.
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23 */
25 #include "precompiled.hpp"
26 #include "classfile/symbolTable.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "classfile/vmSymbols.hpp"
29 #include "code/icBuffer.hpp"
30 #include "gc_implementation/shared/collectorCounters.hpp"
31 #include "gc_implementation/shared/gcTrace.hpp"
32 #include "gc_implementation/shared/gcTraceTime.hpp"
33 #include "gc_implementation/shared/vmGCOperations.hpp"
34 #include "gc_interface/collectedHeap.inline.hpp"
35 #include "memory/filemap.hpp"
36 #include "memory/gcLocker.inline.hpp"
37 #include "memory/genCollectedHeap.hpp"
38 #include "memory/genOopClosures.inline.hpp"
39 #include "memory/generation.inline.hpp"
40 #include "memory/generationSpec.hpp"
41 #include "memory/resourceArea.hpp"
42 #include "memory/sharedHeap.hpp"
43 #include "memory/space.hpp"
44 #include "oops/oop.inline.hpp"
45 #include "oops/oop.inline2.hpp"
46 #include "runtime/biasedLocking.hpp"
47 #include "runtime/fprofiler.hpp"
48 #include "runtime/handles.hpp"
49 #include "runtime/handles.inline.hpp"
50 #include "runtime/java.hpp"
51 #include "runtime/vmThread.hpp"
52 #include "services/memoryService.hpp"
53 #include "utilities/vmError.hpp"
54 #include "utilities/workgroup.hpp"
55 #include "utilities/macros.hpp"
56 #if INCLUDE_ALL_GCS
57 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
58 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
59 #endif // INCLUDE_ALL_GCS
61 GenCollectedHeap* GenCollectedHeap::_gch;
62 NOT_PRODUCT(size_t GenCollectedHeap::_skip_header_HeapWords = 0;)
64 // The set of potentially parallel tasks in root scanning.
65 enum GCH_strong_roots_tasks {
66 // We probably want to parallelize both of these internally, but for now...
67 GCH_PS_younger_gens,
68 // Leave this one last.
69 GCH_PS_NumElements
70 };
72 GenCollectedHeap::GenCollectedHeap(GenCollectorPolicy *policy) :
73 SharedHeap(policy),
74 _gen_policy(policy),
75 _gen_process_roots_tasks(new SubTasksDone(GCH_PS_NumElements)),
76 _full_collections_completed(0)
77 {
78 if (_gen_process_roots_tasks == NULL ||
79 !_gen_process_roots_tasks->valid()) {
80 vm_exit_during_initialization("Failed necessary allocation.");
81 }
82 assert(policy != NULL, "Sanity check");
83 }
85 jint GenCollectedHeap::initialize() {
86 CollectedHeap::pre_initialize();
88 int i;
89 _n_gens = gen_policy()->number_of_generations();
91 // While there are no constraints in the GC code that HeapWordSize
92 // be any particular value, there are multiple other areas in the
93 // system which believe this to be true (e.g. oop->object_size in some
94 // cases incorrectly returns the size in wordSize units rather than
95 // HeapWordSize).
96 guarantee(HeapWordSize == wordSize, "HeapWordSize must equal wordSize");
98 // The heap must be at least as aligned as generations.
99 size_t gen_alignment = Generation::GenGrain;
101 _gen_specs = gen_policy()->generations();
103 // Make sure the sizes are all aligned.
104 for (i = 0; i < _n_gens; i++) {
105 _gen_specs[i]->align(gen_alignment);
106 }
108 // Allocate space for the heap.
110 char* heap_address;
111 size_t total_reserved = 0;
112 int n_covered_regions = 0;
113 ReservedSpace heap_rs;
115 size_t heap_alignment = collector_policy()->heap_alignment();
117 heap_address = allocate(heap_alignment, &total_reserved,
118 &n_covered_regions, &heap_rs);
120 if (!heap_rs.is_reserved()) {
121 vm_shutdown_during_initialization(
122 "Could not reserve enough space for object heap");
123 return JNI_ENOMEM;
124 }
126 _reserved = MemRegion((HeapWord*)heap_rs.base(),
127 (HeapWord*)(heap_rs.base() + heap_rs.size()));
129 // It is important to do this in a way such that concurrent readers can't
130 // temporarily think somethings in the heap. (Seen this happen in asserts.)
131 _reserved.set_word_size(0);
132 _reserved.set_start((HeapWord*)heap_rs.base());
133 size_t actual_heap_size = heap_rs.size();
134 _reserved.set_end((HeapWord*)(heap_rs.base() + actual_heap_size));
136 _rem_set = collector_policy()->create_rem_set(_reserved, n_covered_regions);
137 set_barrier_set(rem_set()->bs());
139 _gch = this;
141 for (i = 0; i < _n_gens; i++) {
142 ReservedSpace this_rs = heap_rs.first_part(_gen_specs[i]->max_size(), false, false);
143 _gens[i] = _gen_specs[i]->init(this_rs, i, rem_set());
144 heap_rs = heap_rs.last_part(_gen_specs[i]->max_size());
145 }
146 clear_incremental_collection_failed();
148 #if INCLUDE_ALL_GCS
149 // If we are running CMS, create the collector responsible
150 // for collecting the CMS generations.
151 if (collector_policy()->is_concurrent_mark_sweep_policy()) {
152 bool success = create_cms_collector();
153 if (!success) return JNI_ENOMEM;
154 }
155 #endif // INCLUDE_ALL_GCS
157 return JNI_OK;
158 }
161 char* GenCollectedHeap::allocate(size_t alignment,
162 size_t* _total_reserved,
163 int* _n_covered_regions,
164 ReservedSpace* heap_rs){
165 const char overflow_msg[] = "The size of the object heap + VM data exceeds "
166 "the maximum representable size";
168 // Now figure out the total size.
169 size_t total_reserved = 0;
170 int n_covered_regions = 0;
171 const size_t pageSize = UseLargePages ?
172 os::large_page_size() : os::vm_page_size();
174 assert(alignment % pageSize == 0, "Must be");
176 for (int i = 0; i < _n_gens; i++) {
177 total_reserved += _gen_specs[i]->max_size();
178 if (total_reserved < _gen_specs[i]->max_size()) {
179 vm_exit_during_initialization(overflow_msg);
180 }
181 n_covered_regions += _gen_specs[i]->n_covered_regions();
182 }
183 assert(total_reserved % alignment == 0,
184 err_msg("Gen size; total_reserved=" SIZE_FORMAT ", alignment="
185 SIZE_FORMAT, total_reserved, alignment));
187 // Needed until the cardtable is fixed to have the right number
188 // of covered regions.
189 n_covered_regions += 2;
191 *_total_reserved = total_reserved;
192 *_n_covered_regions = n_covered_regions;
194 *heap_rs = Universe::reserve_heap(total_reserved, alignment);
195 return heap_rs->base();
196 }
199 void GenCollectedHeap::post_initialize() {
200 SharedHeap::post_initialize();
201 TwoGenerationCollectorPolicy *policy =
202 (TwoGenerationCollectorPolicy *)collector_policy();
203 guarantee(policy->is_two_generation_policy(), "Illegal policy type");
204 DefNewGeneration* def_new_gen = (DefNewGeneration*) get_gen(0);
205 assert(def_new_gen->kind() == Generation::DefNew ||
206 def_new_gen->kind() == Generation::ParNew ||
207 def_new_gen->kind() == Generation::ASParNew,
208 "Wrong generation kind");
210 Generation* old_gen = get_gen(1);
211 assert(old_gen->kind() == Generation::ConcurrentMarkSweep ||
212 old_gen->kind() == Generation::ASConcurrentMarkSweep ||
213 old_gen->kind() == Generation::MarkSweepCompact,
214 "Wrong generation kind");
216 policy->initialize_size_policy(def_new_gen->eden()->capacity(),
217 old_gen->capacity(),
218 def_new_gen->from()->capacity());
219 policy->initialize_gc_policy_counters();
220 }
222 void GenCollectedHeap::ref_processing_init() {
223 SharedHeap::ref_processing_init();
224 for (int i = 0; i < _n_gens; i++) {
225 _gens[i]->ref_processor_init();
226 }
227 }
229 size_t GenCollectedHeap::capacity() const {
230 size_t res = 0;
231 for (int i = 0; i < _n_gens; i++) {
232 res += _gens[i]->capacity();
233 }
234 return res;
235 }
237 size_t GenCollectedHeap::used() const {
238 size_t res = 0;
239 for (int i = 0; i < _n_gens; i++) {
240 res += _gens[i]->used();
241 }
242 return res;
243 }
245 // Save the "used_region" for generations level and lower.
246 void GenCollectedHeap::save_used_regions(int level) {
247 assert(level < _n_gens, "Illegal level parameter");
248 for (int i = level; i >= 0; i--) {
249 _gens[i]->save_used_region();
250 }
251 }
253 size_t GenCollectedHeap::max_capacity() const {
254 size_t res = 0;
255 for (int i = 0; i < _n_gens; i++) {
256 res += _gens[i]->max_capacity();
257 }
258 return res;
259 }
261 // Update the _full_collections_completed counter
262 // at the end of a stop-world full GC.
263 unsigned int GenCollectedHeap::update_full_collections_completed() {
264 MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
265 assert(_full_collections_completed <= _total_full_collections,
266 "Can't complete more collections than were started");
267 _full_collections_completed = _total_full_collections;
268 ml.notify_all();
269 return _full_collections_completed;
270 }
272 // Update the _full_collections_completed counter, as appropriate,
273 // at the end of a concurrent GC cycle. Note the conditional update
274 // below to allow this method to be called by a concurrent collector
275 // without synchronizing in any manner with the VM thread (which
276 // may already have initiated a STW full collection "concurrently").
277 unsigned int GenCollectedHeap::update_full_collections_completed(unsigned int count) {
278 MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
279 assert((_full_collections_completed <= _total_full_collections) &&
280 (count <= _total_full_collections),
281 "Can't complete more collections than were started");
282 if (count > _full_collections_completed) {
283 _full_collections_completed = count;
284 ml.notify_all();
285 }
286 return _full_collections_completed;
287 }
290 #ifndef PRODUCT
291 // Override of memory state checking method in CollectedHeap:
292 // Some collectors (CMS for example) can't have badHeapWordVal written
293 // in the first two words of an object. (For instance , in the case of
294 // CMS these words hold state used to synchronize between certain
295 // (concurrent) GC steps and direct allocating mutators.)
296 // The skip_header_HeapWords() method below, allows us to skip
297 // over the requisite number of HeapWord's. Note that (for
298 // generational collectors) this means that those many words are
299 // skipped in each object, irrespective of the generation in which
300 // that object lives. The resultant loss of precision seems to be
301 // harmless and the pain of avoiding that imprecision appears somewhat
302 // higher than we are prepared to pay for such rudimentary debugging
303 // support.
304 void GenCollectedHeap::check_for_non_bad_heap_word_value(HeapWord* addr,
305 size_t size) {
306 if (CheckMemoryInitialization && ZapUnusedHeapArea) {
307 // We are asked to check a size in HeapWords,
308 // but the memory is mangled in juint words.
309 juint* start = (juint*) (addr + skip_header_HeapWords());
310 juint* end = (juint*) (addr + size);
311 for (juint* slot = start; slot < end; slot += 1) {
312 assert(*slot == badHeapWordVal,
313 "Found non badHeapWordValue in pre-allocation check");
314 }
315 }
316 }
317 #endif
319 HeapWord* GenCollectedHeap::attempt_allocation(size_t size,
320 bool is_tlab,
321 bool first_only) {
322 HeapWord* res;
323 for (int i = 0; i < _n_gens; i++) {
324 if (_gens[i]->should_allocate(size, is_tlab)) {
325 res = _gens[i]->allocate(size, is_tlab);
326 if (res != NULL) return res;
327 else if (first_only) break;
328 }
329 }
330 // Otherwise...
331 return NULL;
332 }
334 HeapWord* GenCollectedHeap::mem_allocate(size_t size,
335 bool* gc_overhead_limit_was_exceeded) {
336 return collector_policy()->mem_allocate_work(size,
337 false /* is_tlab */,
338 gc_overhead_limit_was_exceeded);
339 }
341 bool GenCollectedHeap::must_clear_all_soft_refs() {
342 return _gc_cause == GCCause::_last_ditch_collection;
343 }
345 bool GenCollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) {
346 return UseConcMarkSweepGC &&
347 ((cause == GCCause::_gc_locker && GCLockerInvokesConcurrent) ||
348 (cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent));
349 }
351 void GenCollectedHeap::do_collection(bool full,
352 bool clear_all_soft_refs,
353 size_t size,
354 bool is_tlab,
355 int max_level) {
356 bool prepared_for_verification = false;
357 ResourceMark rm;
358 DEBUG_ONLY(Thread* my_thread = Thread::current();)
360 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
361 assert(my_thread->is_VM_thread() ||
362 my_thread->is_ConcurrentGC_thread(),
363 "incorrect thread type capability");
364 assert(Heap_lock->is_locked(),
365 "the requesting thread should have the Heap_lock");
366 guarantee(!is_gc_active(), "collection is not reentrant");
367 assert(max_level < n_gens(), "sanity check");
369 if (GC_locker::check_active_before_gc()) {
370 return; // GC is disabled (e.g. JNI GetXXXCritical operation)
371 }
373 const bool do_clear_all_soft_refs = clear_all_soft_refs ||
374 collector_policy()->should_clear_all_soft_refs();
376 ClearedAllSoftRefs casr(do_clear_all_soft_refs, collector_policy());
378 const size_t metadata_prev_used = MetaspaceAux::used_bytes();
380 print_heap_before_gc();
382 {
383 FlagSetting fl(_is_gc_active, true);
385 bool complete = full && (max_level == (n_gens()-1));
386 const char* gc_cause_prefix = complete ? "Full GC" : "GC";
387 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
388 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
389 // The PrintGCDetails logging starts before we have incremented the GC id. We will do that later
390 // so we can assume here that the next GC id is what we want.
391 GCTraceTime t(GCCauseString(gc_cause_prefix, gc_cause()), PrintGCDetails, false, NULL, GCId::peek());
393 gc_prologue(complete);
394 increment_total_collections(complete);
396 size_t gch_prev_used = used();
398 int starting_level = 0;
399 if (full) {
400 // Search for the oldest generation which will collect all younger
401 // generations, and start collection loop there.
402 for (int i = max_level; i >= 0; i--) {
403 if (_gens[i]->full_collects_younger_generations()) {
404 starting_level = i;
405 break;
406 }
407 }
408 }
410 bool must_restore_marks_for_biased_locking = false;
412 int max_level_collected = starting_level;
413 for (int i = starting_level; i <= max_level; i++) {
414 if (_gens[i]->should_collect(full, size, is_tlab)) {
415 if (i == n_gens() - 1) { // a major collection is to happen
416 if (!complete) {
417 // The full_collections increment was missed above.
418 increment_total_full_collections();
419 }
420 pre_full_gc_dump(NULL); // do any pre full gc dumps
421 }
422 // Timer for individual generations. Last argument is false: no CR
423 // FIXME: We should try to start the timing earlier to cover more of the GC pause
424 // The PrintGCDetails logging starts before we have incremented the GC id. We will do that later
425 // so we can assume here that the next GC id is what we want.
426 GCTraceTime t1(_gens[i]->short_name(), PrintGCDetails, false, NULL, GCId::peek());
427 TraceCollectorStats tcs(_gens[i]->counters());
428 TraceMemoryManagerStats tmms(_gens[i]->kind(),gc_cause());
430 size_t prev_used = _gens[i]->used();
431 _gens[i]->stat_record()->invocations++;
432 _gens[i]->stat_record()->accumulated_time.start();
434 // Must be done anew before each collection because
435 // a previous collection will do mangling and will
436 // change top of some spaces.
437 record_gen_tops_before_GC();
439 if (PrintGC && Verbose) {
440 gclog_or_tty->print("level=%d invoke=%d size=" SIZE_FORMAT,
441 i,
442 _gens[i]->stat_record()->invocations,
443 size*HeapWordSize);
444 }
446 if (VerifyBeforeGC && i >= VerifyGCLevel &&
447 total_collections() >= VerifyGCStartAt) {
448 HandleMark hm; // Discard invalid handles created during verification
449 if (!prepared_for_verification) {
450 prepare_for_verify();
451 prepared_for_verification = true;
452 }
453 Universe::verify(" VerifyBeforeGC:");
454 }
455 COMPILER2_PRESENT(DerivedPointerTable::clear());
457 if (!must_restore_marks_for_biased_locking &&
458 _gens[i]->performs_in_place_marking()) {
459 // We perform this mark word preservation work lazily
460 // because it's only at this point that we know whether we
461 // absolutely have to do it; we want to avoid doing it for
462 // scavenge-only collections where it's unnecessary
463 must_restore_marks_for_biased_locking = true;
464 BiasedLocking::preserve_marks();
465 }
467 // Do collection work
468 {
469 // Note on ref discovery: For what appear to be historical reasons,
470 // GCH enables and disabled (by enqueing) refs discovery.
471 // In the future this should be moved into the generation's
472 // collect method so that ref discovery and enqueueing concerns
473 // are local to a generation. The collect method could return
474 // an appropriate indication in the case that notification on
475 // the ref lock was needed. This will make the treatment of
476 // weak refs more uniform (and indeed remove such concerns
477 // from GCH). XXX
479 HandleMark hm; // Discard invalid handles created during gc
480 save_marks(); // save marks for all gens
481 // We want to discover references, but not process them yet.
482 // This mode is disabled in process_discovered_references if the
483 // generation does some collection work, or in
484 // enqueue_discovered_references if the generation returns
485 // without doing any work.
486 ReferenceProcessor* rp = _gens[i]->ref_processor();
487 // If the discovery of ("weak") refs in this generation is
488 // atomic wrt other collectors in this configuration, we
489 // are guaranteed to have empty discovered ref lists.
490 if (rp->discovery_is_atomic()) {
491 rp->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/);
492 rp->setup_policy(do_clear_all_soft_refs);
493 } else {
494 // collect() below will enable discovery as appropriate
495 }
496 _gens[i]->collect(full, do_clear_all_soft_refs, size, is_tlab);
497 if (!rp->enqueuing_is_done()) {
498 rp->enqueue_discovered_references();
499 } else {
500 rp->set_enqueuing_is_done(false);
501 }
502 rp->verify_no_references_recorded();
503 }
504 max_level_collected = i;
506 // Determine if allocation request was met.
507 if (size > 0) {
508 if (!is_tlab || _gens[i]->supports_tlab_allocation()) {
509 if (size*HeapWordSize <= _gens[i]->unsafe_max_alloc_nogc()) {
510 size = 0;
511 }
512 }
513 }
515 COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
517 _gens[i]->stat_record()->accumulated_time.stop();
519 update_gc_stats(i, full);
521 if (VerifyAfterGC && i >= VerifyGCLevel &&
522 total_collections() >= VerifyGCStartAt) {
523 HandleMark hm; // Discard invalid handles created during verification
524 Universe::verify(" VerifyAfterGC:");
525 }
527 if (PrintGCDetails) {
528 gclog_or_tty->print(":");
529 _gens[i]->print_heap_change(prev_used);
530 }
531 }
532 }
534 // Update "complete" boolean wrt what actually transpired --
535 // for instance, a promotion failure could have led to
536 // a whole heap collection.
537 complete = complete || (max_level_collected == n_gens() - 1);
539 if (complete) { // We did a "major" collection
540 // FIXME: See comment at pre_full_gc_dump call
541 post_full_gc_dump(NULL); // do any post full gc dumps
542 }
544 if (PrintGCDetails) {
545 print_heap_change(gch_prev_used);
547 // Print metaspace info for full GC with PrintGCDetails flag.
548 if (complete) {
549 MetaspaceAux::print_metaspace_change(metadata_prev_used);
550 }
551 }
553 for (int j = max_level_collected; j >= 0; j -= 1) {
554 // Adjust generation sizes.
555 _gens[j]->compute_new_size();
556 }
558 if (complete) {
559 // Delete metaspaces for unloaded class loaders and clean up loader_data graph
560 ClassLoaderDataGraph::purge();
561 MetaspaceAux::verify_metrics();
562 // Resize the metaspace capacity after full collections
563 MetaspaceGC::compute_new_size();
564 update_full_collections_completed();
565 }
567 // Track memory usage and detect low memory after GC finishes
568 MemoryService::track_memory_usage();
570 gc_epilogue(complete);
572 if (must_restore_marks_for_biased_locking) {
573 BiasedLocking::restore_marks();
574 }
575 }
577 AdaptiveSizePolicy* sp = gen_policy()->size_policy();
578 AdaptiveSizePolicyOutput(sp, total_collections());
580 print_heap_after_gc();
582 #ifdef TRACESPINNING
583 ParallelTaskTerminator::print_termination_counts();
584 #endif
585 }
587 HeapWord* GenCollectedHeap::satisfy_failed_allocation(size_t size, bool is_tlab) {
588 return collector_policy()->satisfy_failed_allocation(size, is_tlab);
589 }
591 void GenCollectedHeap::set_par_threads(uint t) {
592 SharedHeap::set_par_threads(t);
593 _gen_process_roots_tasks->set_n_threads(t);
594 }
596 void GenCollectedHeap::
597 gen_process_roots(int level,
598 bool younger_gens_as_roots,
599 bool activate_scope,
600 SharedHeap::ScanningOption so,
601 OopsInGenClosure* not_older_gens,
602 OopsInGenClosure* weak_roots,
603 OopsInGenClosure* older_gens,
604 CLDClosure* cld_closure,
605 CLDClosure* weak_cld_closure,
606 CodeBlobClosure* code_closure) {
608 // General roots.
609 SharedHeap::process_roots(activate_scope, so,
610 not_older_gens, weak_roots,
611 cld_closure, weak_cld_closure,
612 code_closure);
614 if (younger_gens_as_roots) {
615 if (!_gen_process_roots_tasks->is_task_claimed(GCH_PS_younger_gens)) {
616 for (int i = 0; i < level; i++) {
617 not_older_gens->set_generation(_gens[i]);
618 _gens[i]->oop_iterate(not_older_gens);
619 }
620 not_older_gens->reset_generation();
621 }
622 }
623 // When collection is parallel, all threads get to cooperate to do
624 // older-gen scanning.
625 for (int i = level+1; i < _n_gens; i++) {
626 older_gens->set_generation(_gens[i]);
627 rem_set()->younger_refs_iterate(_gens[i], older_gens);
628 older_gens->reset_generation();
629 }
631 _gen_process_roots_tasks->all_tasks_completed();
632 }
634 void GenCollectedHeap::
635 gen_process_roots(int level,
636 bool younger_gens_as_roots,
637 bool activate_scope,
638 SharedHeap::ScanningOption so,
639 bool only_strong_roots,
640 OopsInGenClosure* not_older_gens,
641 OopsInGenClosure* older_gens,
642 CLDClosure* cld_closure) {
644 const bool is_adjust_phase = !only_strong_roots && !younger_gens_as_roots;
646 bool is_moving_collection = false;
647 if (level == 0 || is_adjust_phase) {
648 // young collections are always moving
649 is_moving_collection = true;
650 }
652 MarkingCodeBlobClosure mark_code_closure(not_older_gens, is_moving_collection);
653 CodeBlobClosure* code_closure = &mark_code_closure;
655 gen_process_roots(level,
656 younger_gens_as_roots,
657 activate_scope, so,
658 not_older_gens, only_strong_roots ? NULL : not_older_gens,
659 older_gens,
660 cld_closure, only_strong_roots ? NULL : cld_closure,
661 code_closure);
663 }
665 void GenCollectedHeap::gen_process_weak_roots(OopClosure* root_closure) {
666 SharedHeap::process_weak_roots(root_closure);
667 // "Local" "weak" refs
668 for (int i = 0; i < _n_gens; i++) {
669 _gens[i]->ref_processor()->weak_oops_do(root_closure);
670 }
671 }
673 #define GCH_SINCE_SAVE_MARKS_ITERATE_DEFN(OopClosureType, nv_suffix) \
674 void GenCollectedHeap:: \
675 oop_since_save_marks_iterate(int level, \
676 OopClosureType* cur, \
677 OopClosureType* older) { \
678 _gens[level]->oop_since_save_marks_iterate##nv_suffix(cur); \
679 for (int i = level+1; i < n_gens(); i++) { \
680 _gens[i]->oop_since_save_marks_iterate##nv_suffix(older); \
681 } \
682 }
684 ALL_SINCE_SAVE_MARKS_CLOSURES(GCH_SINCE_SAVE_MARKS_ITERATE_DEFN)
686 #undef GCH_SINCE_SAVE_MARKS_ITERATE_DEFN
688 bool GenCollectedHeap::no_allocs_since_save_marks(int level) {
689 for (int i = level; i < _n_gens; i++) {
690 if (!_gens[i]->no_allocs_since_save_marks()) return false;
691 }
692 return true;
693 }
695 bool GenCollectedHeap::supports_inline_contig_alloc() const {
696 return _gens[0]->supports_inline_contig_alloc();
697 }
699 HeapWord** GenCollectedHeap::top_addr() const {
700 return _gens[0]->top_addr();
701 }
703 HeapWord** GenCollectedHeap::end_addr() const {
704 return _gens[0]->end_addr();
705 }
707 size_t GenCollectedHeap::unsafe_max_alloc() {
708 return _gens[0]->unsafe_max_alloc_nogc();
709 }
711 // public collection interfaces
713 void GenCollectedHeap::collect(GCCause::Cause cause) {
714 if (should_do_concurrent_full_gc(cause)) {
715 #if INCLUDE_ALL_GCS
716 // mostly concurrent full collection
717 collect_mostly_concurrent(cause);
718 #else // INCLUDE_ALL_GCS
719 ShouldNotReachHere();
720 #endif // INCLUDE_ALL_GCS
721 } else {
722 #ifdef ASSERT
723 if (cause == GCCause::_scavenge_alot) {
724 // minor collection only
725 collect(cause, 0);
726 } else {
727 // Stop-the-world full collection
728 collect(cause, n_gens() - 1);
729 }
730 #else
731 // Stop-the-world full collection
732 collect(cause, n_gens() - 1);
733 #endif
734 }
735 }
737 void GenCollectedHeap::collect(GCCause::Cause cause, int max_level) {
738 // The caller doesn't have the Heap_lock
739 assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");
740 MutexLocker ml(Heap_lock);
741 collect_locked(cause, max_level);
742 }
744 void GenCollectedHeap::collect_locked(GCCause::Cause cause) {
745 // The caller has the Heap_lock
746 assert(Heap_lock->owned_by_self(), "this thread should own the Heap_lock");
747 collect_locked(cause, n_gens() - 1);
748 }
750 // this is the private collection interface
751 // The Heap_lock is expected to be held on entry.
753 void GenCollectedHeap::collect_locked(GCCause::Cause cause, int max_level) {
754 // Read the GC count while holding the Heap_lock
755 unsigned int gc_count_before = total_collections();
756 unsigned int full_gc_count_before = total_full_collections();
757 {
758 MutexUnlocker mu(Heap_lock); // give up heap lock, execute gets it back
759 VM_GenCollectFull op(gc_count_before, full_gc_count_before,
760 cause, max_level);
761 VMThread::execute(&op);
762 }
763 }
765 #if INCLUDE_ALL_GCS
766 bool GenCollectedHeap::create_cms_collector() {
768 assert(((_gens[1]->kind() == Generation::ConcurrentMarkSweep) ||
769 (_gens[1]->kind() == Generation::ASConcurrentMarkSweep)),
770 "Unexpected generation kinds");
771 // Skip two header words in the block content verification
772 NOT_PRODUCT(_skip_header_HeapWords = CMSCollector::skip_header_HeapWords();)
773 CMSCollector* collector = new CMSCollector(
774 (ConcurrentMarkSweepGeneration*)_gens[1],
775 _rem_set->as_CardTableRS(),
776 (ConcurrentMarkSweepPolicy*) collector_policy());
778 if (collector == NULL || !collector->completed_initialization()) {
779 if (collector) {
780 delete collector; // Be nice in embedded situation
781 }
782 vm_shutdown_during_initialization("Could not create CMS collector");
783 return false;
784 }
785 return true; // success
786 }
788 void GenCollectedHeap::collect_mostly_concurrent(GCCause::Cause cause) {
789 assert(!Heap_lock->owned_by_self(), "Should not own Heap_lock");
791 MutexLocker ml(Heap_lock);
792 // Read the GC counts while holding the Heap_lock
793 unsigned int full_gc_count_before = total_full_collections();
794 unsigned int gc_count_before = total_collections();
795 {
796 MutexUnlocker mu(Heap_lock);
797 VM_GenCollectFullConcurrent op(gc_count_before, full_gc_count_before, cause);
798 VMThread::execute(&op);
799 }
800 }
801 #endif // INCLUDE_ALL_GCS
803 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs) {
804 do_full_collection(clear_all_soft_refs, _n_gens - 1);
805 }
807 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs,
808 int max_level) {
809 int local_max_level;
810 if (!incremental_collection_will_fail(false /* don't consult_young */) &&
811 gc_cause() == GCCause::_gc_locker) {
812 local_max_level = 0;
813 } else {
814 local_max_level = max_level;
815 }
817 do_collection(true /* full */,
818 clear_all_soft_refs /* clear_all_soft_refs */,
819 0 /* size */,
820 false /* is_tlab */,
821 local_max_level /* max_level */);
822 // Hack XXX FIX ME !!!
823 // A scavenge may not have been attempted, or may have
824 // been attempted and failed, because the old gen was too full
825 if (local_max_level == 0 && gc_cause() == GCCause::_gc_locker &&
826 incremental_collection_will_fail(false /* don't consult_young */)) {
827 if (PrintGCDetails) {
828 gclog_or_tty->print_cr("GC locker: Trying a full collection "
829 "because scavenge failed");
830 }
831 // This time allow the old gen to be collected as well
832 do_collection(true /* full */,
833 clear_all_soft_refs /* clear_all_soft_refs */,
834 0 /* size */,
835 false /* is_tlab */,
836 n_gens() - 1 /* max_level */);
837 }
838 }
840 bool GenCollectedHeap::is_in_young(oop p) {
841 bool result = ((HeapWord*)p) < _gens[_n_gens - 1]->reserved().start();
842 assert(result == _gens[0]->is_in_reserved(p),
843 err_msg("incorrect test - result=%d, p=" PTR_FORMAT, result, p2i((void*)p)));
844 return result;
845 }
847 // Returns "TRUE" iff "p" points into the committed areas of the heap.
848 bool GenCollectedHeap::is_in(const void* p) const {
849 #ifndef ASSERT
850 guarantee(VerifyBeforeGC ||
851 VerifyDuringGC ||
852 VerifyBeforeExit ||
853 VerifyDuringStartup ||
854 PrintAssembly ||
855 tty->count() != 0 || // already printing
856 VerifyAfterGC ||
857 VMError::fatal_error_in_progress(), "too expensive");
859 #endif
860 // This might be sped up with a cache of the last generation that
861 // answered yes.
862 for (int i = 0; i < _n_gens; i++) {
863 if (_gens[i]->is_in(p)) return true;
864 }
865 // Otherwise...
866 return false;
867 }
869 #ifdef ASSERT
870 // Don't implement this by using is_in_young(). This method is used
871 // in some cases to check that is_in_young() is correct.
872 bool GenCollectedHeap::is_in_partial_collection(const void* p) {
873 assert(is_in_reserved(p) || p == NULL,
874 "Does not work if address is non-null and outside of the heap");
875 return p < _gens[_n_gens - 2]->reserved().end() && p != NULL;
876 }
877 #endif
879 void GenCollectedHeap::oop_iterate(ExtendedOopClosure* cl) {
880 for (int i = 0; i < _n_gens; i++) {
881 _gens[i]->oop_iterate(cl);
882 }
883 }
885 void GenCollectedHeap::object_iterate(ObjectClosure* cl) {
886 for (int i = 0; i < _n_gens; i++) {
887 _gens[i]->object_iterate(cl);
888 }
889 }
891 void GenCollectedHeap::safe_object_iterate(ObjectClosure* cl) {
892 for (int i = 0; i < _n_gens; i++) {
893 _gens[i]->safe_object_iterate(cl);
894 }
895 }
897 Space* GenCollectedHeap::space_containing(const void* addr) const {
898 for (int i = 0; i < _n_gens; i++) {
899 Space* res = _gens[i]->space_containing(addr);
900 if (res != NULL) return res;
901 }
902 // Otherwise...
903 assert(false, "Could not find containing space");
904 return NULL;
905 }
908 HeapWord* GenCollectedHeap::block_start(const void* addr) const {
909 assert(is_in_reserved(addr), "block_start of address outside of heap");
910 for (int i = 0; i < _n_gens; i++) {
911 if (_gens[i]->is_in_reserved(addr)) {
912 assert(_gens[i]->is_in(addr),
913 "addr should be in allocated part of generation");
914 return _gens[i]->block_start(addr);
915 }
916 }
917 assert(false, "Some generation should contain the address");
918 return NULL;
919 }
921 size_t GenCollectedHeap::block_size(const HeapWord* addr) const {
922 assert(is_in_reserved(addr), "block_size of address outside of heap");
923 for (int i = 0; i < _n_gens; i++) {
924 if (_gens[i]->is_in_reserved(addr)) {
925 assert(_gens[i]->is_in(addr),
926 "addr should be in allocated part of generation");
927 return _gens[i]->block_size(addr);
928 }
929 }
930 assert(false, "Some generation should contain the address");
931 return 0;
932 }
934 bool GenCollectedHeap::block_is_obj(const HeapWord* addr) const {
935 assert(is_in_reserved(addr), "block_is_obj of address outside of heap");
936 assert(block_start(addr) == addr, "addr must be a block start");
937 for (int i = 0; i < _n_gens; i++) {
938 if (_gens[i]->is_in_reserved(addr)) {
939 return _gens[i]->block_is_obj(addr);
940 }
941 }
942 assert(false, "Some generation should contain the address");
943 return false;
944 }
946 bool GenCollectedHeap::supports_tlab_allocation() const {
947 for (int i = 0; i < _n_gens; i += 1) {
948 if (_gens[i]->supports_tlab_allocation()) {
949 return true;
950 }
951 }
952 return false;
953 }
955 size_t GenCollectedHeap::tlab_capacity(Thread* thr) const {
956 size_t result = 0;
957 for (int i = 0; i < _n_gens; i += 1) {
958 if (_gens[i]->supports_tlab_allocation()) {
959 result += _gens[i]->tlab_capacity();
960 }
961 }
962 return result;
963 }
965 size_t GenCollectedHeap::tlab_used(Thread* thr) const {
966 size_t result = 0;
967 for (int i = 0; i < _n_gens; i += 1) {
968 if (_gens[i]->supports_tlab_allocation()) {
969 result += _gens[i]->tlab_used();
970 }
971 }
972 return result;
973 }
975 size_t GenCollectedHeap::unsafe_max_tlab_alloc(Thread* thr) const {
976 size_t result = 0;
977 for (int i = 0; i < _n_gens; i += 1) {
978 if (_gens[i]->supports_tlab_allocation()) {
979 result += _gens[i]->unsafe_max_tlab_alloc();
980 }
981 }
982 return result;
983 }
985 HeapWord* GenCollectedHeap::allocate_new_tlab(size_t size) {
986 bool gc_overhead_limit_was_exceeded;
987 return collector_policy()->mem_allocate_work(size /* size */,
988 true /* is_tlab */,
989 &gc_overhead_limit_was_exceeded);
990 }
992 // Requires "*prev_ptr" to be non-NULL. Deletes and a block of minimal size
993 // from the list headed by "*prev_ptr".
994 static ScratchBlock *removeSmallestScratch(ScratchBlock **prev_ptr) {
995 bool first = true;
996 size_t min_size = 0; // "first" makes this conceptually infinite.
997 ScratchBlock **smallest_ptr, *smallest;
998 ScratchBlock *cur = *prev_ptr;
999 while (cur) {
1000 assert(*prev_ptr == cur, "just checking");
1001 if (first || cur->num_words < min_size) {
1002 smallest_ptr = prev_ptr;
1003 smallest = cur;
1004 min_size = smallest->num_words;
1005 first = false;
1006 }
1007 prev_ptr = &cur->next;
1008 cur = cur->next;
1009 }
1010 smallest = *smallest_ptr;
1011 *smallest_ptr = smallest->next;
1012 return smallest;
1013 }
1015 // Sort the scratch block list headed by res into decreasing size order,
1016 // and set "res" to the result.
1017 static void sort_scratch_list(ScratchBlock*& list) {
1018 ScratchBlock* sorted = NULL;
1019 ScratchBlock* unsorted = list;
1020 while (unsorted) {
1021 ScratchBlock *smallest = removeSmallestScratch(&unsorted);
1022 smallest->next = sorted;
1023 sorted = smallest;
1024 }
1025 list = sorted;
1026 }
1028 ScratchBlock* GenCollectedHeap::gather_scratch(Generation* requestor,
1029 size_t max_alloc_words) {
1030 ScratchBlock* res = NULL;
1031 for (int i = 0; i < _n_gens; i++) {
1032 _gens[i]->contribute_scratch(res, requestor, max_alloc_words);
1033 }
1034 sort_scratch_list(res);
1035 return res;
1036 }
1038 void GenCollectedHeap::release_scratch() {
1039 for (int i = 0; i < _n_gens; i++) {
1040 _gens[i]->reset_scratch();
1041 }
1042 }
1044 class GenPrepareForVerifyClosure: public GenCollectedHeap::GenClosure {
1045 void do_generation(Generation* gen) {
1046 gen->prepare_for_verify();
1047 }
1048 };
1050 void GenCollectedHeap::prepare_for_verify() {
1051 ensure_parsability(false); // no need to retire TLABs
1052 GenPrepareForVerifyClosure blk;
1053 generation_iterate(&blk, false);
1054 }
1057 void GenCollectedHeap::generation_iterate(GenClosure* cl,
1058 bool old_to_young) {
1059 if (old_to_young) {
1060 for (int i = _n_gens-1; i >= 0; i--) {
1061 cl->do_generation(_gens[i]);
1062 }
1063 } else {
1064 for (int i = 0; i < _n_gens; i++) {
1065 cl->do_generation(_gens[i]);
1066 }
1067 }
1068 }
1070 void GenCollectedHeap::space_iterate(SpaceClosure* cl) {
1071 for (int i = 0; i < _n_gens; i++) {
1072 _gens[i]->space_iterate(cl, true);
1073 }
1074 }
1076 bool GenCollectedHeap::is_maximal_no_gc() const {
1077 for (int i = 0; i < _n_gens; i++) {
1078 if (!_gens[i]->is_maximal_no_gc()) {
1079 return false;
1080 }
1081 }
1082 return true;
1083 }
1085 void GenCollectedHeap::save_marks() {
1086 for (int i = 0; i < _n_gens; i++) {
1087 _gens[i]->save_marks();
1088 }
1089 }
1091 GenCollectedHeap* GenCollectedHeap::heap() {
1092 assert(_gch != NULL, "Uninitialized access to GenCollectedHeap::heap()");
1093 assert(_gch->kind() == CollectedHeap::GenCollectedHeap, "not a generational heap");
1094 return _gch;
1095 }
1098 void GenCollectedHeap::prepare_for_compaction() {
1099 guarantee(_n_gens = 2, "Wrong number of generations");
1100 Generation* old_gen = _gens[1];
1101 // Start by compacting into same gen.
1102 CompactPoint cp(old_gen, NULL, NULL);
1103 old_gen->prepare_for_compaction(&cp);
1104 Generation* young_gen = _gens[0];
1105 young_gen->prepare_for_compaction(&cp);
1106 }
1108 GCStats* GenCollectedHeap::gc_stats(int level) const {
1109 return _gens[level]->gc_stats();
1110 }
1112 void GenCollectedHeap::verify(bool silent, VerifyOption option /* ignored */) {
1113 for (int i = _n_gens-1; i >= 0; i--) {
1114 Generation* g = _gens[i];
1115 if (!silent) {
1116 gclog_or_tty->print("%s", g->name());
1117 gclog_or_tty->print(" ");
1118 }
1119 g->verify();
1120 }
1121 if (!silent) {
1122 gclog_or_tty->print("remset ");
1123 }
1124 rem_set()->verify();
1125 }
1127 void GenCollectedHeap::print_on(outputStream* st) const {
1128 for (int i = 0; i < _n_gens; i++) {
1129 _gens[i]->print_on(st);
1130 }
1131 MetaspaceAux::print_on(st);
1132 }
1134 void GenCollectedHeap::gc_threads_do(ThreadClosure* tc) const {
1135 if (workers() != NULL) {
1136 workers()->threads_do(tc);
1137 }
1138 #if INCLUDE_ALL_GCS
1139 if (UseConcMarkSweepGC) {
1140 ConcurrentMarkSweepThread::threads_do(tc);
1141 }
1142 #endif // INCLUDE_ALL_GCS
1143 }
1145 void GenCollectedHeap::print_gc_threads_on(outputStream* st) const {
1146 #if INCLUDE_ALL_GCS
1147 if (UseParNewGC) {
1148 workers()->print_worker_threads_on(st);
1149 }
1150 if (UseConcMarkSweepGC) {
1151 ConcurrentMarkSweepThread::print_all_on(st);
1152 }
1153 #endif // INCLUDE_ALL_GCS
1154 }
1156 void GenCollectedHeap::print_on_error(outputStream* st) const {
1157 this->CollectedHeap::print_on_error(st);
1159 #if INCLUDE_ALL_GCS
1160 if (UseConcMarkSweepGC) {
1161 st->cr();
1162 CMSCollector::print_on_error(st);
1163 }
1164 #endif // INCLUDE_ALL_GCS
1165 }
1167 void GenCollectedHeap::print_tracing_info() const {
1168 if (TraceGen0Time) {
1169 get_gen(0)->print_summary_info();
1170 }
1171 if (TraceGen1Time) {
1172 get_gen(1)->print_summary_info();
1173 }
1174 }
1176 void GenCollectedHeap::print_heap_change(size_t prev_used) const {
1177 if (PrintGCDetails && Verbose) {
1178 gclog_or_tty->print(" " SIZE_FORMAT
1179 "->" SIZE_FORMAT
1180 "(" SIZE_FORMAT ")",
1181 prev_used, used(), capacity());
1182 } else {
1183 gclog_or_tty->print(" " SIZE_FORMAT "K"
1184 "->" SIZE_FORMAT "K"
1185 "(" SIZE_FORMAT "K)",
1186 prev_used / K, used() / K, capacity() / K);
1187 }
1188 }
1190 class GenGCPrologueClosure: public GenCollectedHeap::GenClosure {
1191 private:
1192 bool _full;
1193 public:
1194 void do_generation(Generation* gen) {
1195 gen->gc_prologue(_full);
1196 }
1197 GenGCPrologueClosure(bool full) : _full(full) {};
1198 };
1200 void GenCollectedHeap::gc_prologue(bool full) {
1201 assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
1203 always_do_update_barrier = false;
1204 // Fill TLAB's and such
1205 CollectedHeap::accumulate_statistics_all_tlabs();
1206 ensure_parsability(true); // retire TLABs
1208 // Walk generations
1209 GenGCPrologueClosure blk(full);
1210 generation_iterate(&blk, false); // not old-to-young.
1211 };
1213 class GenGCEpilogueClosure: public GenCollectedHeap::GenClosure {
1214 private:
1215 bool _full;
1216 public:
1217 void do_generation(Generation* gen) {
1218 gen->gc_epilogue(_full);
1219 }
1220 GenGCEpilogueClosure(bool full) : _full(full) {};
1221 };
1223 void GenCollectedHeap::gc_epilogue(bool full) {
1224 #ifdef COMPILER2
1225 assert(DerivedPointerTable::is_empty(), "derived pointer present");
1226 size_t actual_gap = pointer_delta((HeapWord*) (max_uintx-3), *(end_addr()));
1227 guarantee(actual_gap > (size_t)FastAllocateSizeLimit, "inline allocation wraps");
1228 #endif /* COMPILER2 */
1230 resize_all_tlabs();
1232 GenGCEpilogueClosure blk(full);
1233 generation_iterate(&blk, false); // not old-to-young.
1235 if (!CleanChunkPoolAsync) {
1236 Chunk::clean_chunk_pool();
1237 }
1239 MetaspaceCounters::update_performance_counters();
1240 CompressedClassSpaceCounters::update_performance_counters();
1242 always_do_update_barrier = UseConcMarkSweepGC;
1243 };
1245 #ifndef PRODUCT
1246 class GenGCSaveTopsBeforeGCClosure: public GenCollectedHeap::GenClosure {
1247 private:
1248 public:
1249 void do_generation(Generation* gen) {
1250 gen->record_spaces_top();
1251 }
1252 };
1254 void GenCollectedHeap::record_gen_tops_before_GC() {
1255 if (ZapUnusedHeapArea) {
1256 GenGCSaveTopsBeforeGCClosure blk;
1257 generation_iterate(&blk, false); // not old-to-young.
1258 }
1259 }
1260 #endif // not PRODUCT
1262 class GenEnsureParsabilityClosure: public GenCollectedHeap::GenClosure {
1263 public:
1264 void do_generation(Generation* gen) {
1265 gen->ensure_parsability();
1266 }
1267 };
1269 void GenCollectedHeap::ensure_parsability(bool retire_tlabs) {
1270 CollectedHeap::ensure_parsability(retire_tlabs);
1271 GenEnsureParsabilityClosure ep_cl;
1272 generation_iterate(&ep_cl, false);
1273 }
1275 oop GenCollectedHeap::handle_failed_promotion(Generation* old_gen,
1276 oop obj,
1277 size_t obj_size) {
1278 guarantee(old_gen->level() == 1, "We only get here with an old generation");
1279 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1280 HeapWord* result = NULL;
1282 result = old_gen->expand_and_allocate(obj_size, false);
1284 if (result != NULL) {
1285 Copy::aligned_disjoint_words((HeapWord*)obj, result, obj_size);
1286 }
1287 return oop(result);
1288 }
1290 class GenTimeOfLastGCClosure: public GenCollectedHeap::GenClosure {
1291 jlong _time; // in ms
1292 jlong _now; // in ms
1294 public:
1295 GenTimeOfLastGCClosure(jlong now) : _time(now), _now(now) { }
1297 jlong time() { return _time; }
1299 void do_generation(Generation* gen) {
1300 _time = MIN2(_time, gen->time_of_last_gc(_now));
1301 }
1302 };
1304 jlong GenCollectedHeap::millis_since_last_gc() {
1305 // We need a monotonically non-deccreasing time in ms but
1306 // os::javaTimeMillis() does not guarantee monotonicity.
1307 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1308 GenTimeOfLastGCClosure tolgc_cl(now);
1309 // iterate over generations getting the oldest
1310 // time that a generation was collected
1311 generation_iterate(&tolgc_cl, false);
1313 // javaTimeNanos() is guaranteed to be monotonically non-decreasing
1314 // provided the underlying platform provides such a time source
1315 // (and it is bug free). So we still have to guard against getting
1316 // back a time later than 'now'.
1317 jlong retVal = now - tolgc_cl.time();
1318 if (retVal < 0) {
1319 NOT_PRODUCT(warning("time warp: "INT64_FORMAT, (int64_t) retVal);)
1320 return 0;
1321 }
1322 return retVal;
1323 }