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