Mon, 13 Oct 2014 16:09:57 -0700
8061651: Interface to the Lookup Index Cache to improve URLClassPath search time
Summary: Implemented the interface in sun.misc.URLClassPath and corresponding JVM_XXX APIs
Reviewed-by: mchung, acorn, jiangli, dholmes
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 */
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 // public collection interfaces
709 void GenCollectedHeap::collect(GCCause::Cause cause) {
710 if (should_do_concurrent_full_gc(cause)) {
711 #if INCLUDE_ALL_GCS
712 // mostly concurrent full collection
713 collect_mostly_concurrent(cause);
714 #else // INCLUDE_ALL_GCS
715 ShouldNotReachHere();
716 #endif // INCLUDE_ALL_GCS
717 } else if (cause == GCCause::_wb_young_gc) {
718 // minor collection for WhiteBox API
719 collect(cause, 0);
720 } else {
721 #ifdef ASSERT
722 if (cause == GCCause::_scavenge_alot) {
723 // minor collection only
724 collect(cause, 0);
725 } else {
726 // Stop-the-world full collection
727 collect(cause, n_gens() - 1);
728 }
729 #else
730 // Stop-the-world full collection
731 collect(cause, n_gens() - 1);
732 #endif
733 }
734 }
736 void GenCollectedHeap::collect(GCCause::Cause cause, int max_level) {
737 // The caller doesn't have the Heap_lock
738 assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");
739 MutexLocker ml(Heap_lock);
740 collect_locked(cause, max_level);
741 }
743 void GenCollectedHeap::collect_locked(GCCause::Cause cause) {
744 // The caller has the Heap_lock
745 assert(Heap_lock->owned_by_self(), "this thread should own the Heap_lock");
746 collect_locked(cause, n_gens() - 1);
747 }
749 // this is the private collection interface
750 // The Heap_lock is expected to be held on entry.
752 void GenCollectedHeap::collect_locked(GCCause::Cause cause, int max_level) {
753 // Read the GC count while holding the Heap_lock
754 unsigned int gc_count_before = total_collections();
755 unsigned int full_gc_count_before = total_full_collections();
756 {
757 MutexUnlocker mu(Heap_lock); // give up heap lock, execute gets it back
758 VM_GenCollectFull op(gc_count_before, full_gc_count_before,
759 cause, max_level);
760 VMThread::execute(&op);
761 }
762 }
764 #if INCLUDE_ALL_GCS
765 bool GenCollectedHeap::create_cms_collector() {
767 assert(((_gens[1]->kind() == Generation::ConcurrentMarkSweep) ||
768 (_gens[1]->kind() == Generation::ASConcurrentMarkSweep)),
769 "Unexpected generation kinds");
770 // Skip two header words in the block content verification
771 NOT_PRODUCT(_skip_header_HeapWords = CMSCollector::skip_header_HeapWords();)
772 CMSCollector* collector = new CMSCollector(
773 (ConcurrentMarkSweepGeneration*)_gens[1],
774 _rem_set->as_CardTableRS(),
775 (ConcurrentMarkSweepPolicy*) collector_policy());
777 if (collector == NULL || !collector->completed_initialization()) {
778 if (collector) {
779 delete collector; // Be nice in embedded situation
780 }
781 vm_shutdown_during_initialization("Could not create CMS collector");
782 return false;
783 }
784 return true; // success
785 }
787 void GenCollectedHeap::collect_mostly_concurrent(GCCause::Cause cause) {
788 assert(!Heap_lock->owned_by_self(), "Should not own Heap_lock");
790 MutexLocker ml(Heap_lock);
791 // Read the GC counts while holding the Heap_lock
792 unsigned int full_gc_count_before = total_full_collections();
793 unsigned int gc_count_before = total_collections();
794 {
795 MutexUnlocker mu(Heap_lock);
796 VM_GenCollectFullConcurrent op(gc_count_before, full_gc_count_before, cause);
797 VMThread::execute(&op);
798 }
799 }
800 #endif // INCLUDE_ALL_GCS
802 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs) {
803 do_full_collection(clear_all_soft_refs, _n_gens - 1);
804 }
806 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs,
807 int max_level) {
808 int local_max_level;
809 if (!incremental_collection_will_fail(false /* don't consult_young */) &&
810 gc_cause() == GCCause::_gc_locker) {
811 local_max_level = 0;
812 } else {
813 local_max_level = max_level;
814 }
816 do_collection(true /* full */,
817 clear_all_soft_refs /* clear_all_soft_refs */,
818 0 /* size */,
819 false /* is_tlab */,
820 local_max_level /* max_level */);
821 // Hack XXX FIX ME !!!
822 // A scavenge may not have been attempted, or may have
823 // been attempted and failed, because the old gen was too full
824 if (local_max_level == 0 && gc_cause() == GCCause::_gc_locker &&
825 incremental_collection_will_fail(false /* don't consult_young */)) {
826 if (PrintGCDetails) {
827 gclog_or_tty->print_cr("GC locker: Trying a full collection "
828 "because scavenge failed");
829 }
830 // This time allow the old gen to be collected as well
831 do_collection(true /* full */,
832 clear_all_soft_refs /* clear_all_soft_refs */,
833 0 /* size */,
834 false /* is_tlab */,
835 n_gens() - 1 /* max_level */);
836 }
837 }
839 bool GenCollectedHeap::is_in_young(oop p) {
840 bool result = ((HeapWord*)p) < _gens[_n_gens - 1]->reserved().start();
841 assert(result == _gens[0]->is_in_reserved(p),
842 err_msg("incorrect test - result=%d, p=" PTR_FORMAT, result, p2i((void*)p)));
843 return result;
844 }
846 // Returns "TRUE" iff "p" points into the committed areas of the heap.
847 bool GenCollectedHeap::is_in(const void* p) const {
848 #ifndef ASSERT
849 guarantee(VerifyBeforeGC ||
850 VerifyDuringGC ||
851 VerifyBeforeExit ||
852 VerifyDuringStartup ||
853 PrintAssembly ||
854 tty->count() != 0 || // already printing
855 VerifyAfterGC ||
856 VMError::fatal_error_in_progress(), "too expensive");
858 #endif
859 // This might be sped up with a cache of the last generation that
860 // answered yes.
861 for (int i = 0; i < _n_gens; i++) {
862 if (_gens[i]->is_in(p)) return true;
863 }
864 // Otherwise...
865 return false;
866 }
868 #ifdef ASSERT
869 // Don't implement this by using is_in_young(). This method is used
870 // in some cases to check that is_in_young() is correct.
871 bool GenCollectedHeap::is_in_partial_collection(const void* p) {
872 assert(is_in_reserved(p) || p == NULL,
873 "Does not work if address is non-null and outside of the heap");
874 return p < _gens[_n_gens - 2]->reserved().end() && p != NULL;
875 }
876 #endif
878 void GenCollectedHeap::oop_iterate(ExtendedOopClosure* cl) {
879 for (int i = 0; i < _n_gens; i++) {
880 _gens[i]->oop_iterate(cl);
881 }
882 }
884 void GenCollectedHeap::object_iterate(ObjectClosure* cl) {
885 for (int i = 0; i < _n_gens; i++) {
886 _gens[i]->object_iterate(cl);
887 }
888 }
890 void GenCollectedHeap::safe_object_iterate(ObjectClosure* cl) {
891 for (int i = 0; i < _n_gens; i++) {
892 _gens[i]->safe_object_iterate(cl);
893 }
894 }
896 Space* GenCollectedHeap::space_containing(const void* addr) const {
897 for (int i = 0; i < _n_gens; i++) {
898 Space* res = _gens[i]->space_containing(addr);
899 if (res != NULL) return res;
900 }
901 // Otherwise...
902 assert(false, "Could not find containing space");
903 return NULL;
904 }
907 HeapWord* GenCollectedHeap::block_start(const void* addr) const {
908 assert(is_in_reserved(addr), "block_start of address outside of heap");
909 for (int i = 0; i < _n_gens; i++) {
910 if (_gens[i]->is_in_reserved(addr)) {
911 assert(_gens[i]->is_in(addr),
912 "addr should be in allocated part of generation");
913 return _gens[i]->block_start(addr);
914 }
915 }
916 assert(false, "Some generation should contain the address");
917 return NULL;
918 }
920 size_t GenCollectedHeap::block_size(const HeapWord* addr) const {
921 assert(is_in_reserved(addr), "block_size of address outside of heap");
922 for (int i = 0; i < _n_gens; i++) {
923 if (_gens[i]->is_in_reserved(addr)) {
924 assert(_gens[i]->is_in(addr),
925 "addr should be in allocated part of generation");
926 return _gens[i]->block_size(addr);
927 }
928 }
929 assert(false, "Some generation should contain the address");
930 return 0;
931 }
933 bool GenCollectedHeap::block_is_obj(const HeapWord* addr) const {
934 assert(is_in_reserved(addr), "block_is_obj of address outside of heap");
935 assert(block_start(addr) == addr, "addr must be a block start");
936 for (int i = 0; i < _n_gens; i++) {
937 if (_gens[i]->is_in_reserved(addr)) {
938 return _gens[i]->block_is_obj(addr);
939 }
940 }
941 assert(false, "Some generation should contain the address");
942 return false;
943 }
945 bool GenCollectedHeap::supports_tlab_allocation() const {
946 for (int i = 0; i < _n_gens; i += 1) {
947 if (_gens[i]->supports_tlab_allocation()) {
948 return true;
949 }
950 }
951 return false;
952 }
954 size_t GenCollectedHeap::tlab_capacity(Thread* thr) const {
955 size_t result = 0;
956 for (int i = 0; i < _n_gens; i += 1) {
957 if (_gens[i]->supports_tlab_allocation()) {
958 result += _gens[i]->tlab_capacity();
959 }
960 }
961 return result;
962 }
964 size_t GenCollectedHeap::tlab_used(Thread* thr) const {
965 size_t result = 0;
966 for (int i = 0; i < _n_gens; i += 1) {
967 if (_gens[i]->supports_tlab_allocation()) {
968 result += _gens[i]->tlab_used();
969 }
970 }
971 return result;
972 }
974 size_t GenCollectedHeap::unsafe_max_tlab_alloc(Thread* thr) const {
975 size_t result = 0;
976 for (int i = 0; i < _n_gens; i += 1) {
977 if (_gens[i]->supports_tlab_allocation()) {
978 result += _gens[i]->unsafe_max_tlab_alloc();
979 }
980 }
981 return result;
982 }
984 HeapWord* GenCollectedHeap::allocate_new_tlab(size_t size) {
985 bool gc_overhead_limit_was_exceeded;
986 return collector_policy()->mem_allocate_work(size /* size */,
987 true /* is_tlab */,
988 &gc_overhead_limit_was_exceeded);
989 }
991 // Requires "*prev_ptr" to be non-NULL. Deletes and a block of minimal size
992 // from the list headed by "*prev_ptr".
993 static ScratchBlock *removeSmallestScratch(ScratchBlock **prev_ptr) {
994 bool first = true;
995 size_t min_size = 0; // "first" makes this conceptually infinite.
996 ScratchBlock **smallest_ptr, *smallest;
997 ScratchBlock *cur = *prev_ptr;
998 while (cur) {
999 assert(*prev_ptr == cur, "just checking");
1000 if (first || cur->num_words < min_size) {
1001 smallest_ptr = prev_ptr;
1002 smallest = cur;
1003 min_size = smallest->num_words;
1004 first = false;
1005 }
1006 prev_ptr = &cur->next;
1007 cur = cur->next;
1008 }
1009 smallest = *smallest_ptr;
1010 *smallest_ptr = smallest->next;
1011 return smallest;
1012 }
1014 // Sort the scratch block list headed by res into decreasing size order,
1015 // and set "res" to the result.
1016 static void sort_scratch_list(ScratchBlock*& list) {
1017 ScratchBlock* sorted = NULL;
1018 ScratchBlock* unsorted = list;
1019 while (unsorted) {
1020 ScratchBlock *smallest = removeSmallestScratch(&unsorted);
1021 smallest->next = sorted;
1022 sorted = smallest;
1023 }
1024 list = sorted;
1025 }
1027 ScratchBlock* GenCollectedHeap::gather_scratch(Generation* requestor,
1028 size_t max_alloc_words) {
1029 ScratchBlock* res = NULL;
1030 for (int i = 0; i < _n_gens; i++) {
1031 _gens[i]->contribute_scratch(res, requestor, max_alloc_words);
1032 }
1033 sort_scratch_list(res);
1034 return res;
1035 }
1037 void GenCollectedHeap::release_scratch() {
1038 for (int i = 0; i < _n_gens; i++) {
1039 _gens[i]->reset_scratch();
1040 }
1041 }
1043 class GenPrepareForVerifyClosure: public GenCollectedHeap::GenClosure {
1044 void do_generation(Generation* gen) {
1045 gen->prepare_for_verify();
1046 }
1047 };
1049 void GenCollectedHeap::prepare_for_verify() {
1050 ensure_parsability(false); // no need to retire TLABs
1051 GenPrepareForVerifyClosure blk;
1052 generation_iterate(&blk, false);
1053 }
1056 void GenCollectedHeap::generation_iterate(GenClosure* cl,
1057 bool old_to_young) {
1058 if (old_to_young) {
1059 for (int i = _n_gens-1; i >= 0; i--) {
1060 cl->do_generation(_gens[i]);
1061 }
1062 } else {
1063 for (int i = 0; i < _n_gens; i++) {
1064 cl->do_generation(_gens[i]);
1065 }
1066 }
1067 }
1069 void GenCollectedHeap::space_iterate(SpaceClosure* cl) {
1070 for (int i = 0; i < _n_gens; i++) {
1071 _gens[i]->space_iterate(cl, true);
1072 }
1073 }
1075 bool GenCollectedHeap::is_maximal_no_gc() const {
1076 for (int i = 0; i < _n_gens; i++) {
1077 if (!_gens[i]->is_maximal_no_gc()) {
1078 return false;
1079 }
1080 }
1081 return true;
1082 }
1084 void GenCollectedHeap::save_marks() {
1085 for (int i = 0; i < _n_gens; i++) {
1086 _gens[i]->save_marks();
1087 }
1088 }
1090 GenCollectedHeap* GenCollectedHeap::heap() {
1091 assert(_gch != NULL, "Uninitialized access to GenCollectedHeap::heap()");
1092 assert(_gch->kind() == CollectedHeap::GenCollectedHeap, "not a generational heap");
1093 return _gch;
1094 }
1097 void GenCollectedHeap::prepare_for_compaction() {
1098 guarantee(_n_gens = 2, "Wrong number of generations");
1099 Generation* old_gen = _gens[1];
1100 // Start by compacting into same gen.
1101 CompactPoint cp(old_gen);
1102 old_gen->prepare_for_compaction(&cp);
1103 Generation* young_gen = _gens[0];
1104 young_gen->prepare_for_compaction(&cp);
1105 }
1107 GCStats* GenCollectedHeap::gc_stats(int level) const {
1108 return _gens[level]->gc_stats();
1109 }
1111 void GenCollectedHeap::verify(bool silent, VerifyOption option /* ignored */) {
1112 for (int i = _n_gens-1; i >= 0; i--) {
1113 Generation* g = _gens[i];
1114 if (!silent) {
1115 gclog_or_tty->print("%s", g->name());
1116 gclog_or_tty->print(" ");
1117 }
1118 g->verify();
1119 }
1120 if (!silent) {
1121 gclog_or_tty->print("remset ");
1122 }
1123 rem_set()->verify();
1124 }
1126 void GenCollectedHeap::print_on(outputStream* st) const {
1127 for (int i = 0; i < _n_gens; i++) {
1128 _gens[i]->print_on(st);
1129 }
1130 MetaspaceAux::print_on(st);
1131 }
1133 void GenCollectedHeap::gc_threads_do(ThreadClosure* tc) const {
1134 if (workers() != NULL) {
1135 workers()->threads_do(tc);
1136 }
1137 #if INCLUDE_ALL_GCS
1138 if (UseConcMarkSweepGC) {
1139 ConcurrentMarkSweepThread::threads_do(tc);
1140 }
1141 #endif // INCLUDE_ALL_GCS
1142 }
1144 void GenCollectedHeap::print_gc_threads_on(outputStream* st) const {
1145 #if INCLUDE_ALL_GCS
1146 if (UseParNewGC) {
1147 workers()->print_worker_threads_on(st);
1148 }
1149 if (UseConcMarkSweepGC) {
1150 ConcurrentMarkSweepThread::print_all_on(st);
1151 }
1152 #endif // INCLUDE_ALL_GCS
1153 }
1155 void GenCollectedHeap::print_on_error(outputStream* st) const {
1156 this->CollectedHeap::print_on_error(st);
1158 #if INCLUDE_ALL_GCS
1159 if (UseConcMarkSweepGC) {
1160 st->cr();
1161 CMSCollector::print_on_error(st);
1162 }
1163 #endif // INCLUDE_ALL_GCS
1164 }
1166 void GenCollectedHeap::print_tracing_info() const {
1167 if (TraceGen0Time) {
1168 get_gen(0)->print_summary_info();
1169 }
1170 if (TraceGen1Time) {
1171 get_gen(1)->print_summary_info();
1172 }
1173 }
1175 void GenCollectedHeap::print_heap_change(size_t prev_used) const {
1176 if (PrintGCDetails && Verbose) {
1177 gclog_or_tty->print(" " SIZE_FORMAT
1178 "->" SIZE_FORMAT
1179 "(" SIZE_FORMAT ")",
1180 prev_used, used(), capacity());
1181 } else {
1182 gclog_or_tty->print(" " SIZE_FORMAT "K"
1183 "->" SIZE_FORMAT "K"
1184 "(" SIZE_FORMAT "K)",
1185 prev_used / K, used() / K, capacity() / K);
1186 }
1187 }
1189 class GenGCPrologueClosure: public GenCollectedHeap::GenClosure {
1190 private:
1191 bool _full;
1192 public:
1193 void do_generation(Generation* gen) {
1194 gen->gc_prologue(_full);
1195 }
1196 GenGCPrologueClosure(bool full) : _full(full) {};
1197 };
1199 void GenCollectedHeap::gc_prologue(bool full) {
1200 assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
1202 always_do_update_barrier = false;
1203 // Fill TLAB's and such
1204 CollectedHeap::accumulate_statistics_all_tlabs();
1205 ensure_parsability(true); // retire TLABs
1207 // Walk generations
1208 GenGCPrologueClosure blk(full);
1209 generation_iterate(&blk, false); // not old-to-young.
1210 };
1212 class GenGCEpilogueClosure: public GenCollectedHeap::GenClosure {
1213 private:
1214 bool _full;
1215 public:
1216 void do_generation(Generation* gen) {
1217 gen->gc_epilogue(_full);
1218 }
1219 GenGCEpilogueClosure(bool full) : _full(full) {};
1220 };
1222 void GenCollectedHeap::gc_epilogue(bool full) {
1223 #ifdef COMPILER2
1224 assert(DerivedPointerTable::is_empty(), "derived pointer present");
1225 size_t actual_gap = pointer_delta((HeapWord*) (max_uintx-3), *(end_addr()));
1226 guarantee(actual_gap > (size_t)FastAllocateSizeLimit, "inline allocation wraps");
1227 #endif /* COMPILER2 */
1229 resize_all_tlabs();
1231 GenGCEpilogueClosure blk(full);
1232 generation_iterate(&blk, false); // not old-to-young.
1234 if (!CleanChunkPoolAsync) {
1235 Chunk::clean_chunk_pool();
1236 }
1238 MetaspaceCounters::update_performance_counters();
1239 CompressedClassSpaceCounters::update_performance_counters();
1241 always_do_update_barrier = UseConcMarkSweepGC;
1242 };
1244 #ifndef PRODUCT
1245 class GenGCSaveTopsBeforeGCClosure: public GenCollectedHeap::GenClosure {
1246 private:
1247 public:
1248 void do_generation(Generation* gen) {
1249 gen->record_spaces_top();
1250 }
1251 };
1253 void GenCollectedHeap::record_gen_tops_before_GC() {
1254 if (ZapUnusedHeapArea) {
1255 GenGCSaveTopsBeforeGCClosure blk;
1256 generation_iterate(&blk, false); // not old-to-young.
1257 }
1258 }
1259 #endif // not PRODUCT
1261 class GenEnsureParsabilityClosure: public GenCollectedHeap::GenClosure {
1262 public:
1263 void do_generation(Generation* gen) {
1264 gen->ensure_parsability();
1265 }
1266 };
1268 void GenCollectedHeap::ensure_parsability(bool retire_tlabs) {
1269 CollectedHeap::ensure_parsability(retire_tlabs);
1270 GenEnsureParsabilityClosure ep_cl;
1271 generation_iterate(&ep_cl, false);
1272 }
1274 oop GenCollectedHeap::handle_failed_promotion(Generation* old_gen,
1275 oop obj,
1276 size_t obj_size) {
1277 guarantee(old_gen->level() == 1, "We only get here with an old generation");
1278 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1279 HeapWord* result = NULL;
1281 result = old_gen->expand_and_allocate(obj_size, false);
1283 if (result != NULL) {
1284 Copy::aligned_disjoint_words((HeapWord*)obj, result, obj_size);
1285 }
1286 return oop(result);
1287 }
1289 class GenTimeOfLastGCClosure: public GenCollectedHeap::GenClosure {
1290 jlong _time; // in ms
1291 jlong _now; // in ms
1293 public:
1294 GenTimeOfLastGCClosure(jlong now) : _time(now), _now(now) { }
1296 jlong time() { return _time; }
1298 void do_generation(Generation* gen) {
1299 _time = MIN2(_time, gen->time_of_last_gc(_now));
1300 }
1301 };
1303 jlong GenCollectedHeap::millis_since_last_gc() {
1304 // We need a monotonically non-deccreasing time in ms but
1305 // os::javaTimeMillis() does not guarantee monotonicity.
1306 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1307 GenTimeOfLastGCClosure tolgc_cl(now);
1308 // iterate over generations getting the oldest
1309 // time that a generation was collected
1310 generation_iterate(&tolgc_cl, false);
1312 // javaTimeNanos() is guaranteed to be monotonically non-decreasing
1313 // provided the underlying platform provides such a time source
1314 // (and it is bug free). So we still have to guard against getting
1315 // back a time later than 'now'.
1316 jlong retVal = now - tolgc_cl.time();
1317 if (retVal < 0) {
1318 NOT_PRODUCT(warning("time warp: "INT64_FORMAT, (int64_t) retVal);)
1319 return 0;
1320 }
1321 return retVal;
1322 }