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).
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/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
60
61 GenCollectedHeap* GenCollectedHeap::_gch;
62 NOT_PRODUCT(size_t GenCollectedHeap::_skip_header_HeapWords = 0;)
63
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 };
71
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 }
84
85 jint GenCollectedHeap::initialize() {
86 CollectedHeap::pre_initialize();
87
88 int i;
89 _n_gens = gen_policy()->number_of_generations();
90
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");
97
98 // The heap must be at least as aligned as generations.
99 size_t gen_alignment = Generation::GenGrain;
100
101 _gen_specs = gen_policy()->generations();
102
103 // Make sure the sizes are all aligned.
104 for (i = 0; i < _n_gens; i++) {
105 _gen_specs[i]->align(gen_alignment);
106 }
107
108 // Allocate space for the heap.
109
110 char* heap_address;
111 size_t total_reserved = 0;
112 int n_covered_regions = 0;
113 ReservedSpace heap_rs;
114
115 size_t heap_alignment = collector_policy()->heap_alignment();
116
117 heap_address = allocate(heap_alignment, &total_reserved,
118 &n_covered_regions, &heap_rs);
119
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 }
125
126 initialize_reserved_region((HeapWord*)heap_rs.base(), (HeapWord*)(heap_rs.base() + heap_rs.size()));
127
128 _rem_set = collector_policy()->create_rem_set(reserved_region(), n_covered_regions);
129 set_barrier_set(rem_set()->bs());
130
131 _gch = this;
132
133 for (i = 0; i < _n_gens; i++) {
134 ReservedSpace this_rs = heap_rs.first_part(_gen_specs[i]->max_size(), false, false);
135 _gens[i] = _gen_specs[i]->init(this_rs, i, rem_set());
136 heap_rs = heap_rs.last_part(_gen_specs[i]->max_size());
137 }
138 clear_incremental_collection_failed();
139
140 #if INCLUDE_ALL_GCS
141 // If we are running CMS, create the collector responsible
142 // for collecting the CMS generations.
143 if (collector_policy()->is_concurrent_mark_sweep_policy()) {
144 bool success = create_cms_collector();
145 if (!success) return JNI_ENOMEM;
146 }
147 #endif // INCLUDE_ALL_GCS
148
149 return JNI_OK;
150 }
151
152
153 char* GenCollectedHeap::allocate(size_t alignment,
154 size_t* _total_reserved,
155 int* _n_covered_regions,
156 ReservedSpace* heap_rs){
157 const char overflow_msg[] = "The size of the object heap + VM data exceeds "
158 "the maximum representable size";
159
160 // Now figure out the total size.
161 size_t total_reserved = 0;
162 int n_covered_regions = 0;
163 const size_t pageSize = UseLargePages ?
164 os::large_page_size() : os::vm_page_size();
165
166 assert(alignment % pageSize == 0, "Must be");
167
168 for (int i = 0; i < _n_gens; i++) {
169 total_reserved += _gen_specs[i]->max_size();
170 if (total_reserved < _gen_specs[i]->max_size()) {
171 vm_exit_during_initialization(overflow_msg);
172 }
173 n_covered_regions += _gen_specs[i]->n_covered_regions();
174 }
175 assert(total_reserved % alignment == 0,
176 err_msg("Gen size; total_reserved=" SIZE_FORMAT ", alignment="
177 SIZE_FORMAT, total_reserved, alignment));
178
179 // Needed until the cardtable is fixed to have the right number
180 // of covered regions.
181 n_covered_regions += 2;
182
183 *_total_reserved = total_reserved;
184 *_n_covered_regions = n_covered_regions;
185
186 *heap_rs = Universe::reserve_heap(total_reserved, alignment);
187 return heap_rs->base();
188 }
189
190
191 void GenCollectedHeap::post_initialize() {
192 SharedHeap::post_initialize();
193 GenCollectorPolicy *policy = (GenCollectorPolicy *)collector_policy();
194 guarantee(policy->is_generation_policy(), "Illegal policy type");
195 DefNewGeneration* def_new_gen = (DefNewGeneration*) get_gen(0);
196 assert(def_new_gen->kind() == Generation::DefNew ||
197 def_new_gen->kind() == Generation::ParNew,
198 "Wrong generation kind");
199
200 Generation* old_gen = get_gen(1);
201 assert(old_gen->kind() == Generation::ConcurrentMarkSweep ||
202 old_gen->kind() == Generation::MarkSweepCompact,
203 "Wrong generation kind");
204
205 policy->initialize_size_policy(def_new_gen->eden()->capacity(),
206 old_gen->capacity(),
207 def_new_gen->from()->capacity());
208 policy->initialize_gc_policy_counters();
209 }
210
211 void GenCollectedHeap::ref_processing_init() {
212 SharedHeap::ref_processing_init();
213 for (int i = 0; i < _n_gens; i++) {
214 _gens[i]->ref_processor_init();
215 }
216 }
217
218 size_t GenCollectedHeap::capacity() const {
219 size_t res = 0;
220 for (int i = 0; i < _n_gens; i++) {
221 res += _gens[i]->capacity();
222 }
223 return res;
224 }
225
226 size_t GenCollectedHeap::used() const {
227 size_t res = 0;
228 for (int i = 0; i < _n_gens; i++) {
229 res += _gens[i]->used();
230 }
231 return res;
232 }
233
234 // Save the "used_region" for generations level and lower.
235 void GenCollectedHeap::save_used_regions(int level) {
236 assert(level < _n_gens, "Illegal level parameter");
237 for (int i = level; i >= 0; i--) {
238 _gens[i]->save_used_region();
239 }
240 }
241
242 size_t GenCollectedHeap::max_capacity() const {
243 size_t res = 0;
244 for (int i = 0; i < _n_gens; i++) {
245 res += _gens[i]->max_capacity();
246 }
247 return res;
248 }
249
250 // Update the _full_collections_completed counter
251 // at the end of a stop-world full GC.
252 unsigned int GenCollectedHeap::update_full_collections_completed() {
253 MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
254 assert(_full_collections_completed <= _total_full_collections,
255 "Can't complete more collections than were started");
256 _full_collections_completed = _total_full_collections;
257 ml.notify_all();
258 return _full_collections_completed;
259 }
260
261 // Update the _full_collections_completed counter, as appropriate,
262 // at the end of a concurrent GC cycle. Note the conditional update
263 // below to allow this method to be called by a concurrent collector
264 // without synchronizing in any manner with the VM thread (which
265 // may already have initiated a STW full collection "concurrently").
266 unsigned int GenCollectedHeap::update_full_collections_completed(unsigned int count) {
267 MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
268 assert((_full_collections_completed <= _total_full_collections) &&
269 (count <= _total_full_collections),
270 "Can't complete more collections than were started");
271 if (count > _full_collections_completed) {
272 _full_collections_completed = count;
273 ml.notify_all();
274 }
275 return _full_collections_completed;
276 }
277
278
279 #ifndef PRODUCT
280 // Override of memory state checking method in CollectedHeap:
281 // Some collectors (CMS for example) can't have badHeapWordVal written
282 // in the first two words of an object. (For instance , in the case of
283 // CMS these words hold state used to synchronize between certain
284 // (concurrent) GC steps and direct allocating mutators.)
285 // The skip_header_HeapWords() method below, allows us to skip
286 // over the requisite number of HeapWord's. Note that (for
287 // generational collectors) this means that those many words are
288 // skipped in each object, irrespective of the generation in which
289 // that object lives. The resultant loss of precision seems to be
290 // harmless and the pain of avoiding that imprecision appears somewhat
291 // higher than we are prepared to pay for such rudimentary debugging
292 // support.
293 void GenCollectedHeap::check_for_non_bad_heap_word_value(HeapWord* addr,
294 size_t size) {
295 if (CheckMemoryInitialization && ZapUnusedHeapArea) {
296 // We are asked to check a size in HeapWords,
297 // but the memory is mangled in juint words.
298 juint* start = (juint*) (addr + skip_header_HeapWords());
299 juint* end = (juint*) (addr + size);
300 for (juint* slot = start; slot < end; slot += 1) {
301 assert(*slot == badHeapWordVal,
302 "Found non badHeapWordValue in pre-allocation check");
303 }
304 }
305 }
306 #endif
307
308 HeapWord* GenCollectedHeap::attempt_allocation(size_t size,
309 bool is_tlab,
310 bool first_only) {
311 HeapWord* res;
312 for (int i = 0; i < _n_gens; i++) {
313 if (_gens[i]->should_allocate(size, is_tlab)) {
314 res = _gens[i]->allocate(size, is_tlab);
315 if (res != NULL) return res;
316 else if (first_only) break;
317 }
318 }
319 // Otherwise...
320 return NULL;
321 }
322
323 HeapWord* GenCollectedHeap::mem_allocate(size_t size,
324 bool* gc_overhead_limit_was_exceeded) {
325 return collector_policy()->mem_allocate_work(size,
326 false /* is_tlab */,
327 gc_overhead_limit_was_exceeded);
328 }
329
330 bool GenCollectedHeap::must_clear_all_soft_refs() {
331 return _gc_cause == GCCause::_last_ditch_collection;
332 }
333
334 bool GenCollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) {
335 return UseConcMarkSweepGC &&
336 ((cause == GCCause::_gc_locker && GCLockerInvokesConcurrent) ||
337 (cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent));
338 }
339
340 void GenCollectedHeap::do_collection(bool full,
341 bool clear_all_soft_refs,
342 size_t size,
343 bool is_tlab,
344 int max_level) {
345 bool prepared_for_verification = false;
346 ResourceMark rm;
347 DEBUG_ONLY(Thread* my_thread = Thread::current();)
348
349 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
350 assert(my_thread->is_VM_thread() ||
351 my_thread->is_ConcurrentGC_thread(),
352 "incorrect thread type capability");
353 assert(Heap_lock->is_locked(),
354 "the requesting thread should have the Heap_lock");
355 guarantee(!is_gc_active(), "collection is not reentrant");
356 assert(max_level < n_gens(), "sanity check");
357
358 if (GC_locker::check_active_before_gc()) {
359 return; // GC is disabled (e.g. JNI GetXXXCritical operation)
360 }
361
362 const bool do_clear_all_soft_refs = clear_all_soft_refs ||
363 collector_policy()->should_clear_all_soft_refs();
364
365 ClearedAllSoftRefs casr(do_clear_all_soft_refs, collector_policy());
366
367 const size_t metadata_prev_used = MetaspaceAux::used_bytes();
368
369 print_heap_before_gc();
370
371 {
372 FlagSetting fl(_is_gc_active, true);
373
374 bool complete = full && (max_level == (n_gens()-1));
375 const char* gc_cause_prefix = complete ? "Full GC" : "GC";
376 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
377 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
378 // The PrintGCDetails logging starts before we have incremented the GC id. We will do that later
379 // so we can assume here that the next GC id is what we want.
380 GCTraceTime t(GCCauseString(gc_cause_prefix, gc_cause()), PrintGCDetails, false, NULL, GCId::peek());
381
382 gc_prologue(complete);
383 increment_total_collections(complete);
384
385 size_t gch_prev_used = used();
386
387 int starting_level = 0;
388 if (full) {
389 // Search for the oldest generation which will collect all younger
390 // generations, and start collection loop there.
391 for (int i = max_level; i >= 0; i--) {
392 if (_gens[i]->full_collects_younger_generations()) {
393 starting_level = i;
394 break;
395 }
396 }
397 }
398
399 bool must_restore_marks_for_biased_locking = false;
400
401 int max_level_collected = starting_level;
402 for (int i = starting_level; i <= max_level; i++) {
403 if (_gens[i]->should_collect(full, size, is_tlab)) {
404 if (i == n_gens() - 1) { // a major collection is to happen
405 if (!complete) {
406 // The full_collections increment was missed above.
407 increment_total_full_collections();
408 }
409 pre_full_gc_dump(NULL); // do any pre full gc dumps
410 }
411 // Timer for individual generations. Last argument is false: no CR
412 // FIXME: We should try to start the timing earlier to cover more of the GC pause
413 // The PrintGCDetails logging starts before we have incremented the GC id. We will do that later
414 // so we can assume here that the next GC id is what we want.
415 GCTraceTime t1(_gens[i]->short_name(), PrintGCDetails, false, NULL, GCId::peek());
416 TraceCollectorStats tcs(_gens[i]->counters());
417 TraceMemoryManagerStats tmms(_gens[i]->kind(),gc_cause());
418
419 size_t prev_used = _gens[i]->used();
420 _gens[i]->stat_record()->invocations++;
421 _gens[i]->stat_record()->accumulated_time.start();
422
423 // Must be done anew before each collection because
424 // a previous collection will do mangling and will
425 // change top of some spaces.
426 record_gen_tops_before_GC();
427
428 if (PrintGC && Verbose) {
429 gclog_or_tty->print("level=%d invoke=%d size=" SIZE_FORMAT,
430 i,
431 _gens[i]->stat_record()->invocations,
432 size*HeapWordSize);
433 }
434
435 if (VerifyBeforeGC && i >= VerifyGCLevel &&
436 total_collections() >= VerifyGCStartAt) {
437 HandleMark hm; // Discard invalid handles created during verification
438 if (!prepared_for_verification) {
439 prepare_for_verify();
440 prepared_for_verification = true;
441 }
442 Universe::verify(" VerifyBeforeGC:");
443 }
444 COMPILER2_PRESENT(DerivedPointerTable::clear());
445
446 if (!must_restore_marks_for_biased_locking &&
447 _gens[i]->performs_in_place_marking()) {
448 // We perform this mark word preservation work lazily
449 // because it's only at this point that we know whether we
450 // absolutely have to do it; we want to avoid doing it for
451 // scavenge-only collections where it's unnecessary
452 must_restore_marks_for_biased_locking = true;
453 BiasedLocking::preserve_marks();
454 }
455
456 // Do collection work
457 {
458 // Note on ref discovery: For what appear to be historical reasons,
459 // GCH enables and disabled (by enqueing) refs discovery.
460 // In the future this should be moved into the generation's
461 // collect method so that ref discovery and enqueueing concerns
462 // are local to a generation. The collect method could return
463 // an appropriate indication in the case that notification on
464 // the ref lock was needed. This will make the treatment of
465 // weak refs more uniform (and indeed remove such concerns
466 // from GCH). XXX
467
468 HandleMark hm; // Discard invalid handles created during gc
469 save_marks(); // save marks for all gens
470 // We want to discover references, but not process them yet.
471 // This mode is disabled in process_discovered_references if the
472 // generation does some collection work, or in
473 // enqueue_discovered_references if the generation returns
474 // without doing any work.
475 ReferenceProcessor* rp = _gens[i]->ref_processor();
476 // If the discovery of ("weak") refs in this generation is
477 // atomic wrt other collectors in this configuration, we
478 // are guaranteed to have empty discovered ref lists.
479 if (rp->discovery_is_atomic()) {
480 rp->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/);
481 rp->setup_policy(do_clear_all_soft_refs);
482 } else {
483 // collect() below will enable discovery as appropriate
484 }
485 _gens[i]->collect(full, do_clear_all_soft_refs, size, is_tlab);
486 if (!rp->enqueuing_is_done()) {
487 rp->enqueue_discovered_references();
488 } else {
489 rp->set_enqueuing_is_done(false);
490 }
491 rp->verify_no_references_recorded();
492 }
493 max_level_collected = i;
494
495 // Determine if allocation request was met.
496 if (size > 0) {
497 if (!is_tlab || _gens[i]->supports_tlab_allocation()) {
498 if (size*HeapWordSize <= _gens[i]->unsafe_max_alloc_nogc()) {
499 size = 0;
500 }
501 }
502 }
503
504 COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
505
506 _gens[i]->stat_record()->accumulated_time.stop();
507
508 update_gc_stats(i, full);
509
510 if (VerifyAfterGC && i >= VerifyGCLevel &&
511 total_collections() >= VerifyGCStartAt) {
512 HandleMark hm; // Discard invalid handles created during verification
513 Universe::verify(" VerifyAfterGC:");
514 }
515
516 if (PrintGCDetails) {
517 gclog_or_tty->print(":");
518 _gens[i]->print_heap_change(prev_used);
519 }
520 }
521 }
522
523 // Update "complete" boolean wrt what actually transpired --
524 // for instance, a promotion failure could have led to
525 // a whole heap collection.
526 complete = complete || (max_level_collected == n_gens() - 1);
527
528 if (complete) { // We did a "major" collection
529 // FIXME: See comment at pre_full_gc_dump call
530 post_full_gc_dump(NULL); // do any post full gc dumps
531 }
532
533 if (PrintGCDetails) {
534 print_heap_change(gch_prev_used);
535
536 // Print metaspace info for full GC with PrintGCDetails flag.
537 if (complete) {
538 MetaspaceAux::print_metaspace_change(metadata_prev_used);
539 }
540 }
541
542 for (int j = max_level_collected; j >= 0; j -= 1) {
543 // Adjust generation sizes.
544 _gens[j]->compute_new_size();
545 }
546
547 if (complete) {
548 // Delete metaspaces for unloaded class loaders and clean up loader_data graph
549 ClassLoaderDataGraph::purge();
550 MetaspaceAux::verify_metrics();
551 // Resize the metaspace capacity after full collections
552 MetaspaceGC::compute_new_size();
553 update_full_collections_completed();
554 }
555
556 // Track memory usage and detect low memory after GC finishes
557 MemoryService::track_memory_usage();
558
559 gc_epilogue(complete);
560
561 if (must_restore_marks_for_biased_locking) {
562 BiasedLocking::restore_marks();
563 }
564 }
565
566 print_heap_after_gc();
567
568 #ifdef TRACESPINNING
569 ParallelTaskTerminator::print_termination_counts();
570 #endif
571 }
572
573 HeapWord* GenCollectedHeap::satisfy_failed_allocation(size_t size, bool is_tlab) {
574 return collector_policy()->satisfy_failed_allocation(size, is_tlab);
575 }
576
577 void GenCollectedHeap::set_par_threads(uint t) {
578 SharedHeap::set_par_threads(t);
579 _gen_process_roots_tasks->set_n_threads(t);
580 }
581
582 void GenCollectedHeap::
583 gen_process_roots(int level,
584 bool younger_gens_as_roots,
585 bool activate_scope,
586 SharedHeap::ScanningOption so,
587 OopsInGenClosure* not_older_gens,
588 OopsInGenClosure* weak_roots,
589 OopsInGenClosure* older_gens,
590 CLDClosure* cld_closure,
591 CLDClosure* weak_cld_closure,
592 CodeBlobClosure* code_closure) {
593
594 // General roots.
595 SharedHeap::process_roots(activate_scope, so,
596 not_older_gens, weak_roots,
597 cld_closure, weak_cld_closure,
598 code_closure);
599
600 if (younger_gens_as_roots) {
601 if (!_gen_process_roots_tasks->is_task_claimed(GCH_PS_younger_gens)) {
602 for (int i = 0; i < level; i++) {
603 not_older_gens->set_generation(_gens[i]);
604 _gens[i]->oop_iterate(not_older_gens);
605 }
606 not_older_gens->reset_generation();
607 }
608 }
609 // When collection is parallel, all threads get to cooperate to do
610 // older-gen scanning.
611 for (int i = level+1; i < _n_gens; i++) {
612 older_gens->set_generation(_gens[i]);
613 rem_set()->younger_refs_iterate(_gens[i], older_gens);
614 older_gens->reset_generation();
615 }
616
617 _gen_process_roots_tasks->all_tasks_completed();
618 }
619
620 void GenCollectedHeap::
621 gen_process_roots(int level,
622 bool younger_gens_as_roots,
623 bool activate_scope,
624 SharedHeap::ScanningOption so,
625 bool only_strong_roots,
626 OopsInGenClosure* not_older_gens,
627 OopsInGenClosure* older_gens,
628 CLDClosure* cld_closure) {
629
630 const bool is_adjust_phase = !only_strong_roots && !younger_gens_as_roots;
631
632 bool is_moving_collection = false;
633 if (level == 0 || is_adjust_phase) {
634 // young collections are always moving
635 is_moving_collection = true;
636 }
637
638 MarkingCodeBlobClosure mark_code_closure(not_older_gens, is_moving_collection);
639 CodeBlobClosure* code_closure = &mark_code_closure;
640
641 gen_process_roots(level,
642 younger_gens_as_roots,
643 activate_scope, so,
644 not_older_gens, only_strong_roots ? NULL : not_older_gens,
645 older_gens,
646 cld_closure, only_strong_roots ? NULL : cld_closure,
647 code_closure);
648
649 }
650
651 void GenCollectedHeap::gen_process_weak_roots(OopClosure* root_closure) {
652 SharedHeap::process_weak_roots(root_closure);
653 // "Local" "weak" refs
654 for (int i = 0; i < _n_gens; i++) {
655 _gens[i]->ref_processor()->weak_oops_do(root_closure);
656 }
657 }
658
659 #define GCH_SINCE_SAVE_MARKS_ITERATE_DEFN(OopClosureType, nv_suffix) \
660 void GenCollectedHeap:: \
661 oop_since_save_marks_iterate(int level, \
662 OopClosureType* cur, \
663 OopClosureType* older) { \
664 _gens[level]->oop_since_save_marks_iterate##nv_suffix(cur); \
665 for (int i = level+1; i < n_gens(); i++) { \
666 _gens[i]->oop_since_save_marks_iterate##nv_suffix(older); \
667 } \
668 }
669
670 ALL_SINCE_SAVE_MARKS_CLOSURES(GCH_SINCE_SAVE_MARKS_ITERATE_DEFN)
671
672 #undef GCH_SINCE_SAVE_MARKS_ITERATE_DEFN
673
674 bool GenCollectedHeap::no_allocs_since_save_marks(int level) {
675 for (int i = level; i < _n_gens; i++) {
676 if (!_gens[i]->no_allocs_since_save_marks()) return false;
677 }
678 return true;
679 }
680
681 bool GenCollectedHeap::supports_inline_contig_alloc() const {
682 return _gens[0]->supports_inline_contig_alloc();
683 }
684
685 HeapWord** GenCollectedHeap::top_addr() const {
686 return _gens[0]->top_addr();
687 }
688
689 HeapWord** GenCollectedHeap::end_addr() const {
690 return _gens[0]->end_addr();
691 }
692
693 // public collection interfaces
694
695 void GenCollectedHeap::collect(GCCause::Cause cause) {
696 if (should_do_concurrent_full_gc(cause)) {
697 #if INCLUDE_ALL_GCS
698 // mostly concurrent full collection
699 collect_mostly_concurrent(cause);
700 #else // INCLUDE_ALL_GCS
701 ShouldNotReachHere();
702 #endif // INCLUDE_ALL_GCS
703 } else if (cause == GCCause::_wb_young_gc) {
704 // minor collection for WhiteBox API
705 collect(cause, 0);
706 } else {
707 #ifdef ASSERT
708 if (cause == GCCause::_scavenge_alot) {
709 // minor collection only
710 collect(cause, 0);
711 } else {
712 // Stop-the-world full collection
713 collect(cause, n_gens() - 1);
714 }
715 #else
716 // Stop-the-world full collection
717 collect(cause, n_gens() - 1);
718 #endif
719 }
720 }
721
722 void GenCollectedHeap::collect(GCCause::Cause cause, int max_level) {
723 // The caller doesn't have the Heap_lock
724 assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");
725 MutexLocker ml(Heap_lock);
726 collect_locked(cause, max_level);
727 }
728
729 void GenCollectedHeap::collect_locked(GCCause::Cause cause) {
730 // The caller has the Heap_lock
731 assert(Heap_lock->owned_by_self(), "this thread should own the Heap_lock");
732 collect_locked(cause, n_gens() - 1);
733 }
734
735 // this is the private collection interface
736 // The Heap_lock is expected to be held on entry.
737
738 void GenCollectedHeap::collect_locked(GCCause::Cause cause, int max_level) {
739 // Read the GC count while holding the Heap_lock
740 unsigned int gc_count_before = total_collections();
741 unsigned int full_gc_count_before = total_full_collections();
742 {
743 MutexUnlocker mu(Heap_lock); // give up heap lock, execute gets it back
744 VM_GenCollectFull op(gc_count_before, full_gc_count_before,
745 cause, max_level);
746 VMThread::execute(&op);
747 }
748 }
749
750 #if INCLUDE_ALL_GCS
751 bool GenCollectedHeap::create_cms_collector() {
752
753 assert(_gens[1]->kind() == Generation::ConcurrentMarkSweep,
754 "Unexpected generation kinds");
755 // Skip two header words in the block content verification
756 NOT_PRODUCT(_skip_header_HeapWords = CMSCollector::skip_header_HeapWords();)
757 CMSCollector* collector = new CMSCollector(
758 (ConcurrentMarkSweepGeneration*)_gens[1],
759 _rem_set->as_CardTableRS(),
760 (ConcurrentMarkSweepPolicy*) collector_policy());
761
762 if (collector == NULL || !collector->completed_initialization()) {
763 if (collector) {
764 delete collector; // Be nice in embedded situation
765 }
766 vm_shutdown_during_initialization("Could not create CMS collector");
767 return false;
768 }
769 return true; // success
770 }
771
772 void GenCollectedHeap::collect_mostly_concurrent(GCCause::Cause cause) {
773 assert(!Heap_lock->owned_by_self(), "Should not own Heap_lock");
774
775 MutexLocker ml(Heap_lock);
776 // Read the GC counts while holding the Heap_lock
777 unsigned int full_gc_count_before = total_full_collections();
778 unsigned int gc_count_before = total_collections();
779 {
780 MutexUnlocker mu(Heap_lock);
781 VM_GenCollectFullConcurrent op(gc_count_before, full_gc_count_before, cause);
782 VMThread::execute(&op);
783 }
784 }
785 #endif // INCLUDE_ALL_GCS
786
787 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs) {
788 do_full_collection(clear_all_soft_refs, _n_gens - 1);
789 }
790
791 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs,
792 int max_level) {
793 int local_max_level;
794 if (!incremental_collection_will_fail(false /* don't consult_young */) &&
795 gc_cause() == GCCause::_gc_locker) {
796 local_max_level = 0;
797 } else {
798 local_max_level = max_level;
799 }
800
801 do_collection(true /* full */,
802 clear_all_soft_refs /* clear_all_soft_refs */,
803 0 /* size */,
804 false /* is_tlab */,
805 local_max_level /* max_level */);
806 // Hack XXX FIX ME !!!
807 // A scavenge may not have been attempted, or may have
808 // been attempted and failed, because the old gen was too full
809 if (local_max_level == 0 && gc_cause() == GCCause::_gc_locker &&
810 incremental_collection_will_fail(false /* don't consult_young */)) {
811 if (PrintGCDetails) {
812 gclog_or_tty->print_cr("GC locker: Trying a full collection "
813 "because scavenge failed");
814 }
815 // This time allow the old gen to be collected as well
816 do_collection(true /* full */,
817 clear_all_soft_refs /* clear_all_soft_refs */,
818 0 /* size */,
819 false /* is_tlab */,
820 n_gens() - 1 /* max_level */);
821 }
822 }
823
824 bool GenCollectedHeap::is_in_young(oop p) {
825 bool result = ((HeapWord*)p) < _gens[_n_gens - 1]->reserved().start();
826 assert(result == _gens[0]->is_in_reserved(p),
827 err_msg("incorrect test - result=%d, p=" INTPTR_FORMAT, result, p2i((void*)p)));
828 return result;
829 }
830
831 // Returns "TRUE" iff "p" points into the committed areas of the heap.
832 bool GenCollectedHeap::is_in(const void* p) const {
833 #ifndef ASSERT
834 guarantee(VerifyBeforeGC ||
835 VerifyDuringGC ||
836 VerifyBeforeExit ||
837 VerifyDuringStartup ||
838 PrintAssembly ||
839 tty->count() != 0 || // already printing
840 VerifyAfterGC ||
841 VMError::fatal_error_in_progress(), "too expensive");
842
843 #endif
844 // This might be sped up with a cache of the last generation that
845 // answered yes.
846 for (int i = 0; i < _n_gens; i++) {
847 if (_gens[i]->is_in(p)) return true;
848 }
849 // Otherwise...
850 return false;
851 }
852
853 #ifdef ASSERT
854 // Don't implement this by using is_in_young(). This method is used
855 // in some cases to check that is_in_young() is correct.
856 bool GenCollectedHeap::is_in_partial_collection(const void* p) {
857 assert(is_in_reserved(p) || p == NULL,
858 "Does not work if address is non-null and outside of the heap");
859 return p < _gens[_n_gens - 2]->reserved().end() && p != NULL;
860 }
861 #endif
862
863 void GenCollectedHeap::oop_iterate(ExtendedOopClosure* cl) {
864 for (int i = 0; i < _n_gens; i++) {
865 _gens[i]->oop_iterate(cl);
866 }
867 }
868
869 void GenCollectedHeap::object_iterate(ObjectClosure* cl) {
870 for (int i = 0; i < _n_gens; i++) {
871 _gens[i]->object_iterate(cl);
872 }
873 }
874
875 void GenCollectedHeap::safe_object_iterate(ObjectClosure* cl) {
876 for (int i = 0; i < _n_gens; i++) {
877 _gens[i]->safe_object_iterate(cl);
878 }
879 }
880
881 Space* GenCollectedHeap::space_containing(const void* addr) const {
882 for (int i = 0; i < _n_gens; i++) {
883 Space* res = _gens[i]->space_containing(addr);
884 if (res != NULL) return res;
885 }
886 // Otherwise...
887 assert(false, "Could not find containing space");
888 return NULL;
889 }
890
891
892 HeapWord* GenCollectedHeap::block_start(const void* addr) const {
893 assert(is_in_reserved(addr), "block_start of address outside of heap");
894 for (int i = 0; i < _n_gens; i++) {
895 if (_gens[i]->is_in_reserved(addr)) {
896 assert(_gens[i]->is_in(addr),
897 "addr should be in allocated part of generation");
898 return _gens[i]->block_start(addr);
899 }
900 }
901 assert(false, "Some generation should contain the address");
902 return NULL;
903 }
904
905 size_t GenCollectedHeap::block_size(const HeapWord* addr) const {
906 assert(is_in_reserved(addr), "block_size of address outside of heap");
907 for (int i = 0; i < _n_gens; i++) {
908 if (_gens[i]->is_in_reserved(addr)) {
909 assert(_gens[i]->is_in(addr),
910 "addr should be in allocated part of generation");
911 return _gens[i]->block_size(addr);
912 }
913 }
914 assert(false, "Some generation should contain the address");
915 return 0;
916 }
917
918 bool GenCollectedHeap::block_is_obj(const HeapWord* addr) const {
919 assert(is_in_reserved(addr), "block_is_obj of address outside of heap");
920 assert(block_start(addr) == addr, "addr must be a block start");
921 for (int i = 0; i < _n_gens; i++) {
922 if (_gens[i]->is_in_reserved(addr)) {
923 return _gens[i]->block_is_obj(addr);
924 }
925 }
926 assert(false, "Some generation should contain the address");
927 return false;
928 }
929
930 bool GenCollectedHeap::supports_tlab_allocation() const {
931 for (int i = 0; i < _n_gens; i += 1) {
932 if (_gens[i]->supports_tlab_allocation()) {
933 return true;
934 }
935 }
936 return false;
937 }
938
939 size_t GenCollectedHeap::tlab_capacity(Thread* thr) const {
940 size_t result = 0;
941 for (int i = 0; i < _n_gens; i += 1) {
942 if (_gens[i]->supports_tlab_allocation()) {
943 result += _gens[i]->tlab_capacity();
944 }
945 }
946 return result;
947 }
948
949 size_t GenCollectedHeap::tlab_used(Thread* thr) const {
950 size_t result = 0;
951 for (int i = 0; i < _n_gens; i += 1) {
952 if (_gens[i]->supports_tlab_allocation()) {
953 result += _gens[i]->tlab_used();
954 }
955 }
956 return result;
957 }
958
959 size_t GenCollectedHeap::unsafe_max_tlab_alloc(Thread* thr) const {
960 size_t result = 0;
961 for (int i = 0; i < _n_gens; i += 1) {
962 if (_gens[i]->supports_tlab_allocation()) {
963 result += _gens[i]->unsafe_max_tlab_alloc();
964 }
965 }
966 return result;
967 }
968
969 HeapWord* GenCollectedHeap::allocate_new_tlab(size_t size) {
970 bool gc_overhead_limit_was_exceeded;
971 return collector_policy()->mem_allocate_work(size /* size */,
972 true /* is_tlab */,
973 &gc_overhead_limit_was_exceeded);
974 }
975
976 // Requires "*prev_ptr" to be non-NULL. Deletes and a block of minimal size
977 // from the list headed by "*prev_ptr".
978 static ScratchBlock *removeSmallestScratch(ScratchBlock **prev_ptr) {
979 bool first = true;
980 size_t min_size = 0; // "first" makes this conceptually infinite.
981 ScratchBlock **smallest_ptr, *smallest;
982 ScratchBlock *cur = *prev_ptr;
983 while (cur) {
984 assert(*prev_ptr == cur, "just checking");
985 if (first || cur->num_words < min_size) {
986 smallest_ptr = prev_ptr;
987 smallest = cur;
988 min_size = smallest->num_words;
989 first = false;
990 }
991 prev_ptr = &cur->next;
992 cur = cur->next;
993 }
994 smallest = *smallest_ptr;
995 *smallest_ptr = smallest->next;
996 return smallest;
997 }
998
999 // Sort the scratch block list headed by res into decreasing size order,
1000 // and set "res" to the result.
1001 static void sort_scratch_list(ScratchBlock*& list) {
1002 ScratchBlock* sorted = NULL;
1003 ScratchBlock* unsorted = list;
1004 while (unsorted) {
1005 ScratchBlock *smallest = removeSmallestScratch(&unsorted);
1006 smallest->next = sorted;
1007 sorted = smallest;
1008 }
1009 list = sorted;
1010 }
1011
1012 ScratchBlock* GenCollectedHeap::gather_scratch(Generation* requestor,
1013 size_t max_alloc_words) {
1014 ScratchBlock* res = NULL;
1015 for (int i = 0; i < _n_gens; i++) {
1016 _gens[i]->contribute_scratch(res, requestor, max_alloc_words);
1017 }
1018 sort_scratch_list(res);
1019 return res;
1020 }
1021
1022 void GenCollectedHeap::release_scratch() {
1023 for (int i = 0; i < _n_gens; i++) {
1024 _gens[i]->reset_scratch();
1025 }
1026 }
1027
1028 class GenPrepareForVerifyClosure: public GenCollectedHeap::GenClosure {
1029 void do_generation(Generation* gen) {
1030 gen->prepare_for_verify();
1031 }
1032 };
1033
1034 void GenCollectedHeap::prepare_for_verify() {
1035 ensure_parsability(false); // no need to retire TLABs
1036 GenPrepareForVerifyClosure blk;
1037 generation_iterate(&blk, false);
1038 }
1039
1040
1041 void GenCollectedHeap::generation_iterate(GenClosure* cl,
1042 bool old_to_young) {
1043 if (old_to_young) {
1044 for (int i = _n_gens-1; i >= 0; i--) {
1045 cl->do_generation(_gens[i]);
1046 }
1047 } else {
1048 for (int i = 0; i < _n_gens; i++) {
1049 cl->do_generation(_gens[i]);
1050 }
1051 }
1052 }
1053
1054 void GenCollectedHeap::space_iterate(SpaceClosure* cl) {
1055 for (int i = 0; i < _n_gens; i++) {
1056 _gens[i]->space_iterate(cl, true);
1057 }
1058 }
1059
1060 bool GenCollectedHeap::is_maximal_no_gc() const {
1061 for (int i = 0; i < _n_gens; i++) {
1062 if (!_gens[i]->is_maximal_no_gc()) {
1063 return false;
1064 }
1065 }
1066 return true;
1067 }
1068
1069 void GenCollectedHeap::save_marks() {
1070 for (int i = 0; i < _n_gens; i++) {
1071 _gens[i]->save_marks();
1072 }
1073 }
1074
1075 GenCollectedHeap* GenCollectedHeap::heap() {
1076 assert(_gch != NULL, "Uninitialized access to GenCollectedHeap::heap()");
1077 assert(_gch->kind() == CollectedHeap::GenCollectedHeap, "not a generational heap");
1078 return _gch;
1079 }
1080
1081
1082 void GenCollectedHeap::prepare_for_compaction() {
1083 guarantee(_n_gens = 2, "Wrong number of generations");
1084 Generation* old_gen = _gens[1];
1085 // Start by compacting into same gen.
1086 CompactPoint cp(old_gen);
1087 old_gen->prepare_for_compaction(&cp);
1088 Generation* young_gen = _gens[0];
1089 young_gen->prepare_for_compaction(&cp);
1090 }
1091
1092 GCStats* GenCollectedHeap::gc_stats(int level) const {
1093 return _gens[level]->gc_stats();
1094 }
1095
1096 void GenCollectedHeap::verify(bool silent, VerifyOption option /* ignored */) {
1097 for (int i = _n_gens-1; i >= 0; i--) {
1098 Generation* g = _gens[i];
1099 if (!silent) {
1100 gclog_or_tty->print("%s", g->name());
1101 gclog_or_tty->print(" ");
1102 }
1103 g->verify();
1104 }
1105 if (!silent) {
1106 gclog_or_tty->print("remset ");
1107 }
1108 rem_set()->verify();
1109 }
1110
1111 void GenCollectedHeap::print_on(outputStream* st) const {
1112 for (int i = 0; i < _n_gens; i++) {
1113 _gens[i]->print_on(st);
1114 }
1115 MetaspaceAux::print_on(st);
1116 }
1117
1118 void GenCollectedHeap::gc_threads_do(ThreadClosure* tc) const {
1119 if (workers() != NULL) {
1120 workers()->threads_do(tc);
1121 }
1122 #if INCLUDE_ALL_GCS
1123 if (UseConcMarkSweepGC) {
1124 ConcurrentMarkSweepThread::threads_do(tc);
1125 }
1126 #endif // INCLUDE_ALL_GCS
1127 }
1128
1129 void GenCollectedHeap::print_gc_threads_on(outputStream* st) const {
1130 #if INCLUDE_ALL_GCS
1131 if (UseParNewGC) {
1132 workers()->print_worker_threads_on(st);
1133 }
1134 if (UseConcMarkSweepGC) {
1135 ConcurrentMarkSweepThread::print_all_on(st);
1136 }
1137 #endif // INCLUDE_ALL_GCS
1138 }
1139
1140 void GenCollectedHeap::print_on_error(outputStream* st) const {
1141 this->CollectedHeap::print_on_error(st);
1142
1143 #if INCLUDE_ALL_GCS
1144 if (UseConcMarkSweepGC) {
1145 st->cr();
1146 CMSCollector::print_on_error(st);
1147 }
1148 #endif // INCLUDE_ALL_GCS
1149 }
1150
1151 void GenCollectedHeap::print_tracing_info() const {
1152 if (TraceYoungGenTime) {
1153 get_gen(0)->print_summary_info();
1154 }
1155 if (TraceOldGenTime) {
1156 get_gen(1)->print_summary_info();
1157 }
1158 }
1159
1160 void GenCollectedHeap::print_heap_change(size_t prev_used) const {
1161 if (PrintGCDetails && Verbose) {
1162 gclog_or_tty->print(" " SIZE_FORMAT
1163 "->" SIZE_FORMAT
1164 "(" SIZE_FORMAT ")",
1165 prev_used, used(), capacity());
1166 } else {
1167 gclog_or_tty->print(" " SIZE_FORMAT "K"
1168 "->" SIZE_FORMAT "K"
1169 "(" SIZE_FORMAT "K)",
1170 prev_used / K, used() / K, capacity() / K);
1171 }
1172 }
1173
1174 class GenGCPrologueClosure: public GenCollectedHeap::GenClosure {
1175 private:
1176 bool _full;
1177 public:
1178 void do_generation(Generation* gen) {
1179 gen->gc_prologue(_full);
1180 }
1181 GenGCPrologueClosure(bool full) : _full(full) {};
1182 };
1183
1184 void GenCollectedHeap::gc_prologue(bool full) {
1185 assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
1186
1187 always_do_update_barrier = false;
1188 // Fill TLAB's and such
1189 CollectedHeap::accumulate_statistics_all_tlabs();
1190 ensure_parsability(true); // retire TLABs
1191
1192 // Walk generations
1193 GenGCPrologueClosure blk(full);
1194 generation_iterate(&blk, false); // not old-to-young.
1195 };
1196
1197 class GenGCEpilogueClosure: public GenCollectedHeap::GenClosure {
1198 private:
1199 bool _full;
1200 public:
1201 void do_generation(Generation* gen) {
1202 gen->gc_epilogue(_full);
1203 }
1204 GenGCEpilogueClosure(bool full) : _full(full) {};
1205 };
1206
1207 void GenCollectedHeap::gc_epilogue(bool full) {
1208 #ifdef COMPILER2
1209 assert(DerivedPointerTable::is_empty(), "derived pointer present");
1210 size_t actual_gap = pointer_delta((HeapWord*) (max_uintx-3), *(end_addr()));
1211 guarantee(actual_gap > (size_t)FastAllocateSizeLimit, "inline allocation wraps");
1212 #endif /* COMPILER2 */
1213
1214 resize_all_tlabs();
1215
1216 GenGCEpilogueClosure blk(full);
1217 generation_iterate(&blk, false); // not old-to-young.
1218
1219 if (!CleanChunkPoolAsync) {
1220 Chunk::clean_chunk_pool();
1221 }
1222
1223 MetaspaceCounters::update_performance_counters();
1224 CompressedClassSpaceCounters::update_performance_counters();
1225
1226 always_do_update_barrier = UseConcMarkSweepGC;
1227 };
1228
1229 #ifndef PRODUCT
1230 class GenGCSaveTopsBeforeGCClosure: public GenCollectedHeap::GenClosure {
1231 private:
1232 public:
1233 void do_generation(Generation* gen) {
1234 gen->record_spaces_top();
1235 }
1236 };
1237
1238 void GenCollectedHeap::record_gen_tops_before_GC() {
1239 if (ZapUnusedHeapArea) {
1240 GenGCSaveTopsBeforeGCClosure blk;
1241 generation_iterate(&blk, false); // not old-to-young.
1242 }
1243 }
1244 #endif // not PRODUCT
1245
1246 class GenEnsureParsabilityClosure: public GenCollectedHeap::GenClosure {
1247 public:
1248 void do_generation(Generation* gen) {
1249 gen->ensure_parsability();
1250 }
1251 };
1252
1253 void GenCollectedHeap::ensure_parsability(bool retire_tlabs) {
1254 CollectedHeap::ensure_parsability(retire_tlabs);
1255 GenEnsureParsabilityClosure ep_cl;
1256 generation_iterate(&ep_cl, false);
1257 }
1258
1259 oop GenCollectedHeap::handle_failed_promotion(Generation* old_gen,
1260 oop obj,
1261 size_t obj_size) {
1262 guarantee(old_gen->level() == 1, "We only get here with an old generation");
1263 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1264 HeapWord* result = NULL;
1265
1266 result = old_gen->expand_and_allocate(obj_size, false);
1267
1268 if (result != NULL) {
1269 Copy::aligned_disjoint_words((HeapWord*)obj, result, obj_size);
1270 }
1271 return oop(result);
1272 }
1273
1274 class GenTimeOfLastGCClosure: public GenCollectedHeap::GenClosure {
1275 jlong _time; // in ms
1276 jlong _now; // in ms
1277
1278 public:
1279 GenTimeOfLastGCClosure(jlong now) : _time(now), _now(now) { }
1280
1281 jlong time() { return _time; }
1282
1283 void do_generation(Generation* gen) {
1284 _time = MIN2(_time, gen->time_of_last_gc(_now));
1285 }
1286 };
1287
1288 jlong GenCollectedHeap::millis_since_last_gc() {
1289 // We need a monotonically non-decreasing time in ms but
1290 // os::javaTimeMillis() does not guarantee monotonicity.
1291 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1292 GenTimeOfLastGCClosure tolgc_cl(now);
1293 // iterate over generations getting the oldest
1294 // time that a generation was collected
1295 generation_iterate(&tolgc_cl, false);
1296
1297 // javaTimeNanos() is guaranteed to be monotonically non-decreasing
1298 // provided the underlying platform provides such a time source
1299 // (and it is bug free). So we still have to guard against getting
1300 // back a time later than 'now'.
1301 jlong retVal = now - tolgc_cl.time();
1302 if (retVal < 0) {
1303 NOT_PRODUCT(warning("time warp: "INT64_FORMAT, (int64_t) retVal);)
1304 return 0;
1305 }
1306 return retVal;
1307 }