1 /* 2 * Copyright (c) 2000, 2013, 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/gcTraceTime.hpp" 32 #include "gc_implementation/shared/vmGCOperations.hpp" 33 #include "gc_interface/collectedHeap.inline.hpp" 34 #include "memory/filemap.hpp" 35 #include "memory/gcLocker.inline.hpp" 36 #include "memory/genCollectedHeap.hpp" 37 #include "memory/genOopClosures.inline.hpp" 38 #include "memory/generation.inline.hpp" 39 #include "memory/generationSpec.hpp" 40 #include "memory/resourceArea.hpp" 41 #include "memory/sharedHeap.hpp" 42 #include "memory/space.hpp" 43 #include "oops/oop.inline.hpp" 44 #include "oops/oop.inline2.hpp" 45 #include "runtime/biasedLocking.hpp" 46 #include "runtime/fprofiler.hpp" 47 #include "runtime/handles.hpp" 48 #include "runtime/handles.inline.hpp" 49 #include "runtime/java.hpp" 50 #include "runtime/vmThread.hpp" 51 #include "services/memoryService.hpp" 52 #include "utilities/vmError.hpp" 53 #include "utilities/workgroup.hpp" 54 #include "utilities/macros.hpp" 55 #if INCLUDE_ALL_GCS 56 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp" 57 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp" 58 #endif // INCLUDE_ALL_GCS 59 60 GenCollectedHeap* GenCollectedHeap::_gch; 61 NOT_PRODUCT(size_t GenCollectedHeap::_skip_header_HeapWords = 0;) 62 63 // The set of potentially parallel tasks in strong root scanning. 64 enum GCH_process_strong_roots_tasks { 65 // We probably want to parallelize both of these internally, but for now... 66 GCH_PS_younger_gens, 67 // Leave this one last. 68 GCH_PS_NumElements 69 }; 70 71 GenCollectedHeap::GenCollectedHeap(GenCollectorPolicy *policy) : 72 SharedHeap(policy), 73 _gen_policy(policy), 74 _gen_process_strong_tasks(new SubTasksDone(GCH_PS_NumElements)), 75 _full_collections_completed(0) 76 { 77 if (_gen_process_strong_tasks == NULL || 78 !_gen_process_strong_tasks->valid()) { 79 vm_exit_during_initialization("Failed necessary allocation."); 80 } 81 assert(policy != NULL, "Sanity check"); 82 } 83 84 jint GenCollectedHeap::initialize() { 85 CollectedHeap::pre_initialize(); 86 87 int i; 88 _n_gens = gen_policy()->number_of_generations(); 89 90 // While there are no constraints in the GC code that HeapWordSize 91 // be any particular value, there are multiple other areas in the 92 // system which believe this to be true (e.g. oop->object_size in some 93 // cases incorrectly returns the size in wordSize units rather than 94 // HeapWordSize). 95 guarantee(HeapWordSize == wordSize, "HeapWordSize must equal wordSize"); 96 97 // The heap must be at least as aligned as generations. 98 size_t alignment = Generation::GenGrain; 99 100 _gen_specs = gen_policy()->generations(); 101 102 // Make sure the sizes are all aligned. 103 for (i = 0; i < _n_gens; i++) { 104 _gen_specs[i]->align(alignment); 105 } 106 107 // Allocate space for the heap. 108 109 char* heap_address; 110 size_t total_reserved = 0; 111 int n_covered_regions = 0; 112 ReservedSpace heap_rs(0); 113 114 heap_address = allocate(alignment, &total_reserved, 115 &n_covered_regions, &heap_rs); 116 117 if (!heap_rs.is_reserved()) { 118 vm_shutdown_during_initialization( 119 "Could not reserve enough space for object heap"); 120 return JNI_ENOMEM; 121 } 122 123 _reserved = MemRegion((HeapWord*)heap_rs.base(), 124 (HeapWord*)(heap_rs.base() + heap_rs.size())); 125 126 // It is important to do this in a way such that concurrent readers can't 127 // temporarily think somethings in the heap. (Seen this happen in asserts.) 128 _reserved.set_word_size(0); 129 _reserved.set_start((HeapWord*)heap_rs.base()); 130 size_t actual_heap_size = heap_rs.size(); 131 _reserved.set_end((HeapWord*)(heap_rs.base() + actual_heap_size)); 132 133 _rem_set = collector_policy()->create_rem_set(_reserved, n_covered_regions); 134 set_barrier_set(rem_set()->bs()); 135 136 _gch = this; 137 138 for (i = 0; i < _n_gens; i++) { 139 ReservedSpace this_rs = heap_rs.first_part(_gen_specs[i]->max_size(), false, false); 140 _gens[i] = _gen_specs[i]->init(this_rs, i, rem_set()); 141 heap_rs = heap_rs.last_part(_gen_specs[i]->max_size()); 142 } 143 clear_incremental_collection_failed(); 144 145 #if INCLUDE_ALL_GCS 146 // If we are running CMS, create the collector responsible 147 // for collecting the CMS generations. 148 if (collector_policy()->is_concurrent_mark_sweep_policy()) { 149 bool success = create_cms_collector(); 150 if (!success) return JNI_ENOMEM; 151 } 152 #endif // INCLUDE_ALL_GCS 153 154 return JNI_OK; 155 } 156 157 158 char* GenCollectedHeap::allocate(size_t alignment, 159 size_t* _total_reserved, 160 int* _n_covered_regions, 161 ReservedSpace* heap_rs){ 162 const char overflow_msg[] = "The size of the object heap + VM data exceeds " 163 "the maximum representable size"; 164 165 // Now figure out the total size. 166 size_t total_reserved = 0; 167 int n_covered_regions = 0; 168 const size_t pageSize = UseLargePages ? 169 os::large_page_size() : os::vm_page_size(); 170 171 for (int i = 0; i < _n_gens; i++) { 172 total_reserved += _gen_specs[i]->max_size(); 173 if (total_reserved < _gen_specs[i]->max_size()) { 174 vm_exit_during_initialization(overflow_msg); 175 } 176 n_covered_regions += _gen_specs[i]->n_covered_regions(); 177 } 178 assert(total_reserved % pageSize == 0, 179 err_msg("Gen size; total_reserved=" SIZE_FORMAT ", pageSize=" 180 SIZE_FORMAT, total_reserved, pageSize)); 181 182 // Needed until the cardtable is fixed to have the right number 183 // of covered regions. 184 n_covered_regions += 2; 185 186 if (UseLargePages) { 187 assert(total_reserved != 0, "total_reserved cannot be 0"); 188 total_reserved = round_to(total_reserved, os::large_page_size()); 189 if (total_reserved < os::large_page_size()) { 190 vm_exit_during_initialization(overflow_msg); 191 } 192 } 193 194 *_total_reserved = total_reserved; 195 *_n_covered_regions = n_covered_regions; 196 *heap_rs = Universe::reserve_heap(total_reserved, alignment); 197 return heap_rs->base(); 198 } 199 200 201 void GenCollectedHeap::post_initialize() { 202 SharedHeap::post_initialize(); 203 TwoGenerationCollectorPolicy *policy = 204 (TwoGenerationCollectorPolicy *)collector_policy(); 205 guarantee(policy->is_two_generation_policy(), "Illegal policy type"); 206 DefNewGeneration* def_new_gen = (DefNewGeneration*) get_gen(0); 207 assert(def_new_gen->kind() == Generation::DefNew || 208 def_new_gen->kind() == Generation::ParNew || 209 def_new_gen->kind() == Generation::ASParNew, 210 "Wrong generation kind"); 211 212 Generation* old_gen = get_gen(1); 213 assert(old_gen->kind() == Generation::ConcurrentMarkSweep || 214 old_gen->kind() == Generation::ASConcurrentMarkSweep || 215 old_gen->kind() == Generation::MarkSweepCompact, 216 "Wrong generation kind"); 217 218 policy->initialize_size_policy(def_new_gen->eden()->capacity(), 219 old_gen->capacity(), 220 def_new_gen->from()->capacity()); 221 policy->initialize_gc_policy_counters(); 222 } 223 224 void GenCollectedHeap::ref_processing_init() { 225 SharedHeap::ref_processing_init(); 226 for (int i = 0; i < _n_gens; i++) { 227 _gens[i]->ref_processor_init(); 228 } 229 } 230 231 size_t GenCollectedHeap::capacity() const { 232 size_t res = 0; 233 for (int i = 0; i < _n_gens; i++) { 234 res += _gens[i]->capacity(); 235 } 236 return res; 237 } 238 239 size_t GenCollectedHeap::used() const { 240 size_t res = 0; 241 for (int i = 0; i < _n_gens; i++) { 242 res += _gens[i]->used(); 243 } 244 return res; 245 } 246 247 // Save the "used_region" for generations level and lower. 248 void GenCollectedHeap::save_used_regions(int level) { 249 assert(level < _n_gens, "Illegal level parameter"); 250 for (int i = level; i >= 0; i--) { 251 _gens[i]->save_used_region(); 252 } 253 } 254 255 size_t GenCollectedHeap::max_capacity() const { 256 size_t res = 0; 257 for (int i = 0; i < _n_gens; i++) { 258 res += _gens[i]->max_capacity(); 259 } 260 return res; 261 } 262 263 // Update the _full_collections_completed counter 264 // at the end of a stop-world full GC. 265 unsigned int GenCollectedHeap::update_full_collections_completed() { 266 MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag); 267 assert(_full_collections_completed <= _total_full_collections, 268 "Can't complete more collections than were started"); 269 _full_collections_completed = _total_full_collections; 270 ml.notify_all(); 271 return _full_collections_completed; 272 } 273 274 // Update the _full_collections_completed counter, as appropriate, 275 // at the end of a concurrent GC cycle. Note the conditional update 276 // below to allow this method to be called by a concurrent collector 277 // without synchronizing in any manner with the VM thread (which 278 // may already have initiated a STW full collection "concurrently"). 279 unsigned int GenCollectedHeap::update_full_collections_completed(unsigned int count) { 280 MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag); 281 assert((_full_collections_completed <= _total_full_collections) && 282 (count <= _total_full_collections), 283 "Can't complete more collections than were started"); 284 if (count > _full_collections_completed) { 285 _full_collections_completed = count; 286 ml.notify_all(); 287 } 288 return _full_collections_completed; 289 } 290 291 292 #ifndef PRODUCT 293 // Override of memory state checking method in CollectedHeap: 294 // Some collectors (CMS for example) can't have badHeapWordVal written 295 // in the first two words of an object. (For instance , in the case of 296 // CMS these words hold state used to synchronize between certain 297 // (concurrent) GC steps and direct allocating mutators.) 298 // The skip_header_HeapWords() method below, allows us to skip 299 // over the requisite number of HeapWord's. Note that (for 300 // generational collectors) this means that those many words are 301 // skipped in each object, irrespective of the generation in which 302 // that object lives. The resultant loss of precision seems to be 303 // harmless and the pain of avoiding that imprecision appears somewhat 304 // higher than we are prepared to pay for such rudimentary debugging 305 // support. 306 void GenCollectedHeap::check_for_non_bad_heap_word_value(HeapWord* addr, 307 size_t size) { 308 if (CheckMemoryInitialization && ZapUnusedHeapArea) { 309 // We are asked to check a size in HeapWords, 310 // but the memory is mangled in juint words. 311 juint* start = (juint*) (addr + skip_header_HeapWords()); 312 juint* end = (juint*) (addr + size); 313 for (juint* slot = start; slot < end; slot += 1) { 314 assert(*slot == badHeapWordVal, 315 "Found non badHeapWordValue in pre-allocation check"); 316 } 317 } 318 } 319 #endif 320 321 HeapWord* GenCollectedHeap::attempt_allocation(size_t size, 322 bool is_tlab, 323 bool first_only) { 324 HeapWord* res; 325 for (int i = 0; i < _n_gens; i++) { 326 if (_gens[i]->should_allocate(size, is_tlab)) { 327 res = _gens[i]->allocate(size, is_tlab); 328 if (res != NULL) return res; 329 else if (first_only) break; 330 } 331 } 332 // Otherwise... 333 return NULL; 334 } 335 336 HeapWord* GenCollectedHeap::mem_allocate(size_t size, 337 bool* gc_overhead_limit_was_exceeded) { 338 return collector_policy()->mem_allocate_work(size, 339 false /* is_tlab */, 340 gc_overhead_limit_was_exceeded); 341 } 342 343 bool GenCollectedHeap::must_clear_all_soft_refs() { 344 return _gc_cause == GCCause::_last_ditch_collection; 345 } 346 347 bool GenCollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) { 348 return UseConcMarkSweepGC && 349 ((cause == GCCause::_gc_locker && GCLockerInvokesConcurrent) || 350 (cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent)); 351 } 352 353 void GenCollectedHeap::do_collection(bool full, 354 bool clear_all_soft_refs, 355 size_t size, 356 bool is_tlab, 357 int max_level) { 358 bool prepared_for_verification = false; 359 ResourceMark rm; 360 DEBUG_ONLY(Thread* my_thread = Thread::current();) 361 362 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint"); 363 assert(my_thread->is_VM_thread() || 364 my_thread->is_ConcurrentGC_thread(), 365 "incorrect thread type capability"); 366 assert(Heap_lock->is_locked(), 367 "the requesting thread should have the Heap_lock"); 368 guarantee(!is_gc_active(), "collection is not reentrant"); 369 assert(max_level < n_gens(), "sanity check"); 370 371 if (GC_locker::check_active_before_gc()) { 372 return; // GC is disabled (e.g. JNI GetXXXCritical operation) 373 } 374 375 const bool do_clear_all_soft_refs = clear_all_soft_refs || 376 collector_policy()->should_clear_all_soft_refs(); 377 378 ClearedAllSoftRefs casr(do_clear_all_soft_refs, collector_policy()); 379 380 const size_t metadata_prev_used = MetaspaceAux::allocated_used_bytes(); 381 382 print_heap_before_gc(); 383 384 { 385 FlagSetting fl(_is_gc_active, true); 386 387 bool complete = full && (max_level == (n_gens()-1)); 388 const char* gc_cause_prefix = complete ? "Full GC" : "GC"; 389 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps); 390 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); 391 GCTraceTime t(GCCauseString(gc_cause_prefix, gc_cause()), PrintGCDetails, false, NULL); 392 393 gc_prologue(complete); 394 increment_total_collections(complete); 395 396 size_t gch_prev_used = used(); 397 398 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 } 409 410 bool must_restore_marks_for_biased_locking = false; 411 412 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 GCTraceTime t1(_gens[i]->short_name(), PrintGCDetails, false, NULL); 425 TraceCollectorStats tcs(_gens[i]->counters()); 426 TraceMemoryManagerStats tmms(_gens[i]->kind(),gc_cause()); 427 428 size_t prev_used = _gens[i]->used(); 429 _gens[i]->stat_record()->invocations++; 430 _gens[i]->stat_record()->accumulated_time.start(); 431 432 // Must be done anew before each collection because 433 // a previous collection will do mangling and will 434 // change top of some spaces. 435 record_gen_tops_before_GC(); 436 437 if (PrintGC && Verbose) { 438 gclog_or_tty->print("level=%d invoke=%d size=" SIZE_FORMAT, 439 i, 440 _gens[i]->stat_record()->invocations, 441 size*HeapWordSize); 442 } 443 444 if (VerifyBeforeGC && i >= VerifyGCLevel && 445 total_collections() >= VerifyGCStartAt) { 446 HandleMark hm; // Discard invalid handles created during verification 447 if (!prepared_for_verification) { 448 prepare_for_verify(); 449 prepared_for_verification = true; 450 } 451 Universe::verify(" VerifyBeforeGC:"); 452 } 453 COMPILER2_PRESENT(DerivedPointerTable::clear()); 454 455 if (!must_restore_marks_for_biased_locking && 456 _gens[i]->performs_in_place_marking()) { 457 // We perform this mark word preservation work lazily 458 // because it's only at this point that we know whether we 459 // absolutely have to do it; we want to avoid doing it for 460 // scavenge-only collections where it's unnecessary 461 must_restore_marks_for_biased_locking = true; 462 BiasedLocking::preserve_marks(); 463 } 464 465 // Do collection work 466 { 467 // Note on ref discovery: For what appear to be historical reasons, 468 // GCH enables and disabled (by enqueing) refs discovery. 469 // In the future this should be moved into the generation's 470 // collect method so that ref discovery and enqueueing concerns 471 // are local to a generation. The collect method could return 472 // an appropriate indication in the case that notification on 473 // the ref lock was needed. This will make the treatment of 474 // weak refs more uniform (and indeed remove such concerns 475 // from GCH). XXX 476 477 HandleMark hm; // Discard invalid handles created during gc 478 save_marks(); // save marks for all gens 479 // We want to discover references, but not process them yet. 480 // This mode is disabled in process_discovered_references if the 481 // generation does some collection work, or in 482 // enqueue_discovered_references if the generation returns 483 // without doing any work. 484 ReferenceProcessor* rp = _gens[i]->ref_processor(); 485 // If the discovery of ("weak") refs in this generation is 486 // atomic wrt other collectors in this configuration, we 487 // are guaranteed to have empty discovered ref lists. 488 if (rp->discovery_is_atomic()) { 489 rp->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/); 490 rp->setup_policy(do_clear_all_soft_refs); 491 } else { 492 // collect() below will enable discovery as appropriate 493 } 494 _gens[i]->collect(full, do_clear_all_soft_refs, size, is_tlab); 495 if (!rp->enqueuing_is_done()) { 496 rp->enqueue_discovered_references(); 497 } else { 498 rp->set_enqueuing_is_done(false); 499 } 500 rp->verify_no_references_recorded(); 501 } 502 max_level_collected = i; 503 504 // Determine if allocation request was met. 505 if (size > 0) { 506 if (!is_tlab || _gens[i]->supports_tlab_allocation()) { 507 if (size*HeapWordSize <= _gens[i]->unsafe_max_alloc_nogc()) { 508 size = 0; 509 } 510 } 511 } 512 513 COMPILER2_PRESENT(DerivedPointerTable::update_pointers()); 514 515 _gens[i]->stat_record()->accumulated_time.stop(); 516 517 update_gc_stats(i, full); 518 519 if (VerifyAfterGC && i >= VerifyGCLevel && 520 total_collections() >= VerifyGCStartAt) { 521 HandleMark hm; // Discard invalid handles created during verification 522 Universe::verify(" VerifyAfterGC:"); 523 } 524 525 if (PrintGCDetails) { 526 gclog_or_tty->print(":"); 527 _gens[i]->print_heap_change(prev_used); 528 } 529 } 530 } 531 532 // Update "complete" boolean wrt what actually transpired -- 533 // for instance, a promotion failure could have led to 534 // a whole heap collection. 535 complete = complete || (max_level_collected == n_gens() - 1); 536 537 if (complete) { // We did a "major" collection 538 // FIXME: See comment at pre_full_gc_dump call 539 post_full_gc_dump(NULL); // do any post full gc dumps 540 } 541 542 if (PrintGCDetails) { 543 print_heap_change(gch_prev_used); 544 545 // Print metaspace info for full GC with PrintGCDetails flag. 546 if (complete) { 547 MetaspaceAux::print_metaspace_change(metadata_prev_used); 548 } 549 } 550 551 for (int j = max_level_collected; j >= 0; j -= 1) { 552 // Adjust generation sizes. 553 _gens[j]->compute_new_size(); 554 } 555 556 if (complete) { 557 // Delete metaspaces for unloaded class loaders and clean up loader_data graph 558 ClassLoaderDataGraph::purge(); 559 MetaspaceAux::verify_metrics(); 560 // Resize the metaspace capacity after full collections 561 MetaspaceGC::compute_new_size(); 562 update_full_collections_completed(); 563 } 564 565 // Track memory usage and detect low memory after GC finishes 566 MemoryService::track_memory_usage(); 567 568 gc_epilogue(complete); 569 570 if (must_restore_marks_for_biased_locking) { 571 BiasedLocking::restore_marks(); 572 } 573 } 574 575 AdaptiveSizePolicy* sp = gen_policy()->size_policy(); 576 AdaptiveSizePolicyOutput(sp, total_collections()); 577 578 print_heap_after_gc(); 579 580 #ifdef TRACESPINNING 581 ParallelTaskTerminator::print_termination_counts(); 582 #endif 583 } 584 585 HeapWord* GenCollectedHeap::satisfy_failed_allocation(size_t size, bool is_tlab) { 586 return collector_policy()->satisfy_failed_allocation(size, is_tlab); 587 } 588 589 void GenCollectedHeap::set_par_threads(uint t) { 590 SharedHeap::set_par_threads(t); 591 _gen_process_strong_tasks->set_n_threads(t); 592 } 593 594 void GenCollectedHeap:: 595 gen_process_strong_roots(int level, 596 bool younger_gens_as_roots, 597 bool activate_scope, 598 bool is_scavenging, 599 SharedHeap::ScanningOption so, 600 OopsInGenClosure* not_older_gens, 601 bool do_code_roots, 602 OopsInGenClosure* older_gens, 603 KlassClosure* klass_closure) { 604 // General strong roots. 605 606 if (!do_code_roots) { 607 SharedHeap::process_strong_roots(activate_scope, is_scavenging, so, 608 not_older_gens, NULL, klass_closure); 609 } else { 610 bool do_code_marking = (activate_scope || nmethod::oops_do_marking_is_active()); 611 CodeBlobToOopClosure code_roots(not_older_gens, /*do_marking=*/ do_code_marking); 612 SharedHeap::process_strong_roots(activate_scope, is_scavenging, so, 613 not_older_gens, &code_roots, klass_closure); 614 } 615 616 if (younger_gens_as_roots) { 617 if (!_gen_process_strong_tasks->is_task_claimed(GCH_PS_younger_gens)) { 618 for (int i = 0; i < level; i++) { 619 not_older_gens->set_generation(_gens[i]); 620 _gens[i]->oop_iterate(not_older_gens); 621 } 622 not_older_gens->reset_generation(); 623 } 624 } 625 // When collection is parallel, all threads get to cooperate to do 626 // older-gen scanning. 627 for (int i = level+1; i < _n_gens; i++) { 628 older_gens->set_generation(_gens[i]); 629 rem_set()->younger_refs_iterate(_gens[i], older_gens); 630 older_gens->reset_generation(); 631 } 632 633 _gen_process_strong_tasks->all_tasks_completed(); 634 } 635 636 void GenCollectedHeap::gen_process_weak_roots(OopClosure* root_closure, 637 CodeBlobClosure* code_roots) { 638 SharedHeap::process_weak_roots(root_closure, code_roots); 639 // "Local" "weak" refs 640 for (int i = 0; i < _n_gens; i++) { 641 _gens[i]->ref_processor()->weak_oops_do(root_closure); 642 } 643 } 644 645 #define GCH_SINCE_SAVE_MARKS_ITERATE_DEFN(OopClosureType, nv_suffix) \ 646 void GenCollectedHeap:: \ 647 oop_since_save_marks_iterate(int level, \ 648 OopClosureType* cur, \ 649 OopClosureType* older) { \ 650 _gens[level]->oop_since_save_marks_iterate##nv_suffix(cur); \ 651 for (int i = level+1; i < n_gens(); i++) { \ 652 _gens[i]->oop_since_save_marks_iterate##nv_suffix(older); \ 653 } \ 654 } 655 656 ALL_SINCE_SAVE_MARKS_CLOSURES(GCH_SINCE_SAVE_MARKS_ITERATE_DEFN) 657 658 #undef GCH_SINCE_SAVE_MARKS_ITERATE_DEFN 659 660 bool GenCollectedHeap::no_allocs_since_save_marks(int level) { 661 for (int i = level; i < _n_gens; i++) { 662 if (!_gens[i]->no_allocs_since_save_marks()) return false; 663 } 664 return true; 665 } 666 667 bool GenCollectedHeap::supports_inline_contig_alloc() const { 668 return _gens[0]->supports_inline_contig_alloc(); 669 } 670 671 HeapWord** GenCollectedHeap::top_addr() const { 672 return _gens[0]->top_addr(); 673 } 674 675 HeapWord** GenCollectedHeap::end_addr() const { 676 return _gens[0]->end_addr(); 677 } 678 679 size_t GenCollectedHeap::unsafe_max_alloc() { 680 return _gens[0]->unsafe_max_alloc_nogc(); 681 } 682 683 // public collection interfaces 684 685 void GenCollectedHeap::collect(GCCause::Cause cause) { 686 if (should_do_concurrent_full_gc(cause)) { 687 #if INCLUDE_ALL_GCS 688 // mostly concurrent full collection 689 collect_mostly_concurrent(cause); 690 #else // INCLUDE_ALL_GCS 691 ShouldNotReachHere(); 692 #endif // INCLUDE_ALL_GCS 693 } else { 694 #ifdef ASSERT 695 if (cause == GCCause::_scavenge_alot) { 696 // minor collection only 697 collect(cause, 0); 698 } else { 699 // Stop-the-world full collection 700 collect(cause, n_gens() - 1); 701 } 702 #else 703 // Stop-the-world full collection 704 collect(cause, n_gens() - 1); 705 #endif 706 } 707 } 708 709 void GenCollectedHeap::collect(GCCause::Cause cause, int max_level) { 710 // The caller doesn't have the Heap_lock 711 assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock"); 712 MutexLocker ml(Heap_lock); 713 collect_locked(cause, max_level); 714 } 715 716 void GenCollectedHeap::collect_locked(GCCause::Cause cause) { 717 // The caller has the Heap_lock 718 assert(Heap_lock->owned_by_self(), "this thread should own the Heap_lock"); 719 collect_locked(cause, n_gens() - 1); 720 } 721 722 // this is the private collection interface 723 // The Heap_lock is expected to be held on entry. 724 725 void GenCollectedHeap::collect_locked(GCCause::Cause cause, int max_level) { 726 // Read the GC count while holding the Heap_lock 727 unsigned int gc_count_before = total_collections(); 728 unsigned int full_gc_count_before = total_full_collections(); 729 { 730 MutexUnlocker mu(Heap_lock); // give up heap lock, execute gets it back 731 VM_GenCollectFull op(gc_count_before, full_gc_count_before, 732 cause, max_level); 733 VMThread::execute(&op); 734 } 735 } 736 737 #if INCLUDE_ALL_GCS 738 bool GenCollectedHeap::create_cms_collector() { 739 740 assert(((_gens[1]->kind() == Generation::ConcurrentMarkSweep) || 741 (_gens[1]->kind() == Generation::ASConcurrentMarkSweep)), 742 "Unexpected generation kinds"); 743 // Skip two header words in the block content verification 744 NOT_PRODUCT(_skip_header_HeapWords = CMSCollector::skip_header_HeapWords();) 745 CMSCollector* collector = new CMSCollector( 746 (ConcurrentMarkSweepGeneration*)_gens[1], 747 _rem_set->as_CardTableRS(), 748 (ConcurrentMarkSweepPolicy*) collector_policy()); 749 750 if (collector == NULL || !collector->completed_initialization()) { 751 if (collector) { 752 delete collector; // Be nice in embedded situation 753 } 754 vm_shutdown_during_initialization("Could not create CMS collector"); 755 return false; 756 } 757 return true; // success 758 } 759 760 void GenCollectedHeap::collect_mostly_concurrent(GCCause::Cause cause) { 761 assert(!Heap_lock->owned_by_self(), "Should not own Heap_lock"); 762 763 MutexLocker ml(Heap_lock); 764 // Read the GC counts while holding the Heap_lock 765 unsigned int full_gc_count_before = total_full_collections(); 766 unsigned int gc_count_before = total_collections(); 767 { 768 MutexUnlocker mu(Heap_lock); 769 VM_GenCollectFullConcurrent op(gc_count_before, full_gc_count_before, cause); 770 VMThread::execute(&op); 771 } 772 } 773 #endif // INCLUDE_ALL_GCS 774 775 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs) { 776 do_full_collection(clear_all_soft_refs, _n_gens - 1); 777 } 778 779 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs, 780 int max_level) { 781 int local_max_level; 782 if (!incremental_collection_will_fail(false /* don't consult_young */) && 783 gc_cause() == GCCause::_gc_locker) { 784 local_max_level = 0; 785 } else { 786 local_max_level = max_level; 787 } 788 789 do_collection(true /* full */, 790 clear_all_soft_refs /* clear_all_soft_refs */, 791 0 /* size */, 792 false /* is_tlab */, 793 local_max_level /* max_level */); 794 // Hack XXX FIX ME !!! 795 // A scavenge may not have been attempted, or may have 796 // been attempted and failed, because the old gen was too full 797 if (local_max_level == 0 && gc_cause() == GCCause::_gc_locker && 798 incremental_collection_will_fail(false /* don't consult_young */)) { 799 if (PrintGCDetails) { 800 gclog_or_tty->print_cr("GC locker: Trying a full collection " 801 "because scavenge failed"); 802 } 803 // This time allow the old gen to be collected as well 804 do_collection(true /* full */, 805 clear_all_soft_refs /* clear_all_soft_refs */, 806 0 /* size */, 807 false /* is_tlab */, 808 n_gens() - 1 /* max_level */); 809 } 810 } 811 812 bool GenCollectedHeap::is_in_young(oop p) { 813 bool result = ((HeapWord*)p) < _gens[_n_gens - 1]->reserved().start(); 814 assert(result == _gens[0]->is_in_reserved(p), 815 err_msg("incorrect test - result=%d, p=" PTR_FORMAT, result, (void*)p)); 816 return result; 817 } 818 819 // Returns "TRUE" iff "p" points into the committed areas of the heap. 820 bool GenCollectedHeap::is_in(const void* p) const { 821 #ifndef ASSERT 822 guarantee(VerifyBeforeGC || 823 VerifyDuringGC || 824 VerifyBeforeExit || 825 VerifyDuringStartup || 826 PrintAssembly || 827 tty->count() != 0 || // already printing 828 VerifyAfterGC || 829 VMError::fatal_error_in_progress(), "too expensive"); 830 831 #endif 832 // This might be sped up with a cache of the last generation that 833 // answered yes. 834 for (int i = 0; i < _n_gens; i++) { 835 if (_gens[i]->is_in(p)) return true; 836 } 837 // Otherwise... 838 return false; 839 } 840 841 #ifdef ASSERT 842 // Don't implement this by using is_in_young(). This method is used 843 // in some cases to check that is_in_young() is correct. 844 bool GenCollectedHeap::is_in_partial_collection(const void* p) { 845 assert(is_in_reserved(p) || p == NULL, 846 "Does not work if address is non-null and outside of the heap"); 847 return p < _gens[_n_gens - 2]->reserved().end() && p != NULL; 848 } 849 #endif 850 851 void GenCollectedHeap::oop_iterate(ExtendedOopClosure* cl) { 852 for (int i = 0; i < _n_gens; i++) { 853 _gens[i]->oop_iterate(cl); 854 } 855 } 856 857 void GenCollectedHeap::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) { 858 for (int i = 0; i < _n_gens; i++) { 859 _gens[i]->oop_iterate(mr, cl); 860 } 861 } 862 863 void GenCollectedHeap::object_iterate(ObjectClosure* cl) { 864 for (int i = 0; i < _n_gens; i++) { 865 _gens[i]->object_iterate(cl); 866 } 867 } 868 869 void GenCollectedHeap::safe_object_iterate(ObjectClosure* cl) { 870 for (int i = 0; i < _n_gens; i++) { 871 _gens[i]->safe_object_iterate(cl); 872 } 873 } 874 875 Space* GenCollectedHeap::space_containing(const void* addr) const { 876 for (int i = 0; i < _n_gens; i++) { 877 Space* res = _gens[i]->space_containing(addr); 878 if (res != NULL) return res; 879 } 880 // Otherwise... 881 assert(false, "Could not find containing space"); 882 return NULL; 883 } 884 885 886 HeapWord* GenCollectedHeap::block_start(const void* addr) const { 887 assert(is_in_reserved(addr), "block_start of address outside of heap"); 888 for (int i = 0; i < _n_gens; i++) { 889 if (_gens[i]->is_in_reserved(addr)) { 890 assert(_gens[i]->is_in(addr), 891 "addr should be in allocated part of generation"); 892 return _gens[i]->block_start(addr); 893 } 894 } 895 assert(false, "Some generation should contain the address"); 896 return NULL; 897 } 898 899 size_t GenCollectedHeap::block_size(const HeapWord* addr) const { 900 assert(is_in_reserved(addr), "block_size of address outside of heap"); 901 for (int i = 0; i < _n_gens; i++) { 902 if (_gens[i]->is_in_reserved(addr)) { 903 assert(_gens[i]->is_in(addr), 904 "addr should be in allocated part of generation"); 905 return _gens[i]->block_size(addr); 906 } 907 } 908 assert(false, "Some generation should contain the address"); 909 return 0; 910 } 911 912 bool GenCollectedHeap::block_is_obj(const HeapWord* addr) const { 913 assert(is_in_reserved(addr), "block_is_obj of address outside of heap"); 914 assert(block_start(addr) == addr, "addr must be a block start"); 915 for (int i = 0; i < _n_gens; i++) { 916 if (_gens[i]->is_in_reserved(addr)) { 917 return _gens[i]->block_is_obj(addr); 918 } 919 } 920 assert(false, "Some generation should contain the address"); 921 return false; 922 } 923 924 bool GenCollectedHeap::supports_tlab_allocation() const { 925 for (int i = 0; i < _n_gens; i += 1) { 926 if (_gens[i]->supports_tlab_allocation()) { 927 return true; 928 } 929 } 930 return false; 931 } 932 933 size_t GenCollectedHeap::tlab_capacity(Thread* thr) const { 934 size_t result = 0; 935 for (int i = 0; i < _n_gens; i += 1) { 936 if (_gens[i]->supports_tlab_allocation()) { 937 result += _gens[i]->tlab_capacity(); 938 } 939 } 940 return result; 941 } 942 943 size_t GenCollectedHeap::unsafe_max_tlab_alloc(Thread* thr) const { 944 size_t result = 0; 945 for (int i = 0; i < _n_gens; i += 1) { 946 if (_gens[i]->supports_tlab_allocation()) { 947 result += _gens[i]->unsafe_max_tlab_alloc(); 948 } 949 } 950 return result; 951 } 952 953 HeapWord* GenCollectedHeap::allocate_new_tlab(size_t size) { 954 bool gc_overhead_limit_was_exceeded; 955 return collector_policy()->mem_allocate_work(size /* size */, 956 true /* is_tlab */, 957 &gc_overhead_limit_was_exceeded); 958 } 959 960 // Requires "*prev_ptr" to be non-NULL. Deletes and a block of minimal size 961 // from the list headed by "*prev_ptr". 962 static ScratchBlock *removeSmallestScratch(ScratchBlock **prev_ptr) { 963 bool first = true; 964 size_t min_size = 0; // "first" makes this conceptually infinite. 965 ScratchBlock **smallest_ptr, *smallest; 966 ScratchBlock *cur = *prev_ptr; 967 while (cur) { 968 assert(*prev_ptr == cur, "just checking"); 969 if (first || cur->num_words < min_size) { 970 smallest_ptr = prev_ptr; 971 smallest = cur; 972 min_size = smallest->num_words; 973 first = false; 974 } 975 prev_ptr = &cur->next; 976 cur = cur->next; 977 } 978 smallest = *smallest_ptr; 979 *smallest_ptr = smallest->next; 980 return smallest; 981 } 982 983 // Sort the scratch block list headed by res into decreasing size order, 984 // and set "res" to the result. 985 static void sort_scratch_list(ScratchBlock*& list) { 986 ScratchBlock* sorted = NULL; 987 ScratchBlock* unsorted = list; 988 while (unsorted) { 989 ScratchBlock *smallest = removeSmallestScratch(&unsorted); 990 smallest->next = sorted; 991 sorted = smallest; 992 } 993 list = sorted; 994 } 995 996 ScratchBlock* GenCollectedHeap::gather_scratch(Generation* requestor, 997 size_t max_alloc_words) { 998 ScratchBlock* res = NULL; 999 for (int i = 0; i < _n_gens; i++) { 1000 _gens[i]->contribute_scratch(res, requestor, max_alloc_words); 1001 } 1002 sort_scratch_list(res); 1003 return res; 1004 } 1005 1006 void GenCollectedHeap::release_scratch() { 1007 for (int i = 0; i < _n_gens; i++) { 1008 _gens[i]->reset_scratch(); 1009 } 1010 } 1011 1012 class GenPrepareForVerifyClosure: public GenCollectedHeap::GenClosure { 1013 void do_generation(Generation* gen) { 1014 gen->prepare_for_verify(); 1015 } 1016 }; 1017 1018 void GenCollectedHeap::prepare_for_verify() { 1019 ensure_parsability(false); // no need to retire TLABs 1020 GenPrepareForVerifyClosure blk; 1021 generation_iterate(&blk, false); 1022 } 1023 1024 1025 void GenCollectedHeap::generation_iterate(GenClosure* cl, 1026 bool old_to_young) { 1027 if (old_to_young) { 1028 for (int i = _n_gens-1; i >= 0; i--) { 1029 cl->do_generation(_gens[i]); 1030 } 1031 } else { 1032 for (int i = 0; i < _n_gens; i++) { 1033 cl->do_generation(_gens[i]); 1034 } 1035 } 1036 } 1037 1038 void GenCollectedHeap::space_iterate(SpaceClosure* cl) { 1039 for (int i = 0; i < _n_gens; i++) { 1040 _gens[i]->space_iterate(cl, true); 1041 } 1042 } 1043 1044 bool GenCollectedHeap::is_maximal_no_gc() const { 1045 for (int i = 0; i < _n_gens; i++) { 1046 if (!_gens[i]->is_maximal_no_gc()) { 1047 return false; 1048 } 1049 } 1050 return true; 1051 } 1052 1053 void GenCollectedHeap::save_marks() { 1054 for (int i = 0; i < _n_gens; i++) { 1055 _gens[i]->save_marks(); 1056 } 1057 } 1058 1059 void GenCollectedHeap::compute_new_generation_sizes(int collectedGen) { 1060 for (int i = 0; i <= collectedGen; i++) { 1061 _gens[i]->compute_new_size(); 1062 } 1063 } 1064 1065 GenCollectedHeap* GenCollectedHeap::heap() { 1066 assert(_gch != NULL, "Uninitialized access to GenCollectedHeap::heap()"); 1067 assert(_gch->kind() == CollectedHeap::GenCollectedHeap, "not a generational heap"); 1068 return _gch; 1069 } 1070 1071 1072 void GenCollectedHeap::prepare_for_compaction() { 1073 guarantee(_n_gens = 2, "Wrong number of generations"); 1074 Generation* old_gen = _gens[1]; 1075 // Start by compacting into same gen. 1076 CompactPoint cp(old_gen, NULL, NULL); 1077 old_gen->prepare_for_compaction(&cp); 1078 Generation* young_gen = _gens[0]; 1079 young_gen->prepare_for_compaction(&cp); 1080 } 1081 1082 GCStats* GenCollectedHeap::gc_stats(int level) const { 1083 return _gens[level]->gc_stats(); 1084 } 1085 1086 void GenCollectedHeap::verify(bool silent, VerifyOption option /* ignored */) { 1087 for (int i = _n_gens-1; i >= 0; i--) { 1088 Generation* g = _gens[i]; 1089 if (!silent) { 1090 gclog_or_tty->print(g->name()); 1091 gclog_or_tty->print(" "); 1092 } 1093 g->verify(); 1094 } 1095 if (!silent) { 1096 gclog_or_tty->print("remset "); 1097 } 1098 rem_set()->verify(); 1099 } 1100 1101 void GenCollectedHeap::print_on(outputStream* st) const { 1102 for (int i = 0; i < _n_gens; i++) { 1103 _gens[i]->print_on(st); 1104 } 1105 MetaspaceAux::print_on(st); 1106 } 1107 1108 void GenCollectedHeap::gc_threads_do(ThreadClosure* tc) const { 1109 if (workers() != NULL) { 1110 workers()->threads_do(tc); 1111 } 1112 #if INCLUDE_ALL_GCS 1113 if (UseConcMarkSweepGC) { 1114 ConcurrentMarkSweepThread::threads_do(tc); 1115 } 1116 #endif // INCLUDE_ALL_GCS 1117 } 1118 1119 void GenCollectedHeap::print_gc_threads_on(outputStream* st) const { 1120 #if INCLUDE_ALL_GCS 1121 if (UseParNewGC) { 1122 workers()->print_worker_threads_on(st); 1123 } 1124 if (UseConcMarkSweepGC) { 1125 ConcurrentMarkSweepThread::print_all_on(st); 1126 } 1127 #endif // INCLUDE_ALL_GCS 1128 } 1129 1130 void GenCollectedHeap::print_on_error(outputStream* st) const { 1131 this->CollectedHeap::print_on_error(st); 1132 1133 #if INCLUDE_ALL_GCS 1134 if (UseConcMarkSweepGC) { 1135 st->cr(); 1136 CMSCollector::print_on_error(st); 1137 } 1138 #endif // INCLUDE_ALL_GCS 1139 } 1140 1141 void GenCollectedHeap::print_tracing_info() const { 1142 if (TraceGen0Time) { 1143 get_gen(0)->print_summary_info(); 1144 } 1145 if (TraceGen1Time) { 1146 get_gen(1)->print_summary_info(); 1147 } 1148 } 1149 1150 void GenCollectedHeap::print_heap_change(size_t prev_used) const { 1151 if (PrintGCDetails && Verbose) { 1152 gclog_or_tty->print(" " SIZE_FORMAT 1153 "->" SIZE_FORMAT 1154 "(" SIZE_FORMAT ")", 1155 prev_used, used(), capacity()); 1156 } else { 1157 gclog_or_tty->print(" " SIZE_FORMAT "K" 1158 "->" SIZE_FORMAT "K" 1159 "(" SIZE_FORMAT "K)", 1160 prev_used / K, used() / K, capacity() / K); 1161 } 1162 } 1163 1164 class GenGCPrologueClosure: public GenCollectedHeap::GenClosure { 1165 private: 1166 bool _full; 1167 public: 1168 void do_generation(Generation* gen) { 1169 gen->gc_prologue(_full); 1170 } 1171 GenGCPrologueClosure(bool full) : _full(full) {}; 1172 }; 1173 1174 void GenCollectedHeap::gc_prologue(bool full) { 1175 assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer"); 1176 1177 always_do_update_barrier = false; 1178 // Fill TLAB's and such 1179 CollectedHeap::accumulate_statistics_all_tlabs(); 1180 ensure_parsability(true); // retire TLABs 1181 1182 // Walk generations 1183 GenGCPrologueClosure blk(full); 1184 generation_iterate(&blk, false); // not old-to-young. 1185 }; 1186 1187 class GenGCEpilogueClosure: public GenCollectedHeap::GenClosure { 1188 private: 1189 bool _full; 1190 public: 1191 void do_generation(Generation* gen) { 1192 gen->gc_epilogue(_full); 1193 } 1194 GenGCEpilogueClosure(bool full) : _full(full) {}; 1195 }; 1196 1197 void GenCollectedHeap::gc_epilogue(bool full) { 1198 #ifdef COMPILER2 1199 assert(DerivedPointerTable::is_empty(), "derived pointer present"); 1200 size_t actual_gap = pointer_delta((HeapWord*) (max_uintx-3), *(end_addr())); 1201 guarantee(actual_gap > (size_t)FastAllocateSizeLimit, "inline allocation wraps"); 1202 #endif /* COMPILER2 */ 1203 1204 resize_all_tlabs(); 1205 1206 GenGCEpilogueClosure blk(full); 1207 generation_iterate(&blk, false); // not old-to-young. 1208 1209 if (!CleanChunkPoolAsync) { 1210 Chunk::clean_chunk_pool(); 1211 } 1212 1213 MetaspaceCounters::update_performance_counters(); 1214 CompressedClassSpaceCounters::update_performance_counters(); 1215 1216 always_do_update_barrier = UseConcMarkSweepGC; 1217 }; 1218 1219 #ifndef PRODUCT 1220 class GenGCSaveTopsBeforeGCClosure: public GenCollectedHeap::GenClosure { 1221 private: 1222 public: 1223 void do_generation(Generation* gen) { 1224 gen->record_spaces_top(); 1225 } 1226 }; 1227 1228 void GenCollectedHeap::record_gen_tops_before_GC() { 1229 if (ZapUnusedHeapArea) { 1230 GenGCSaveTopsBeforeGCClosure blk; 1231 generation_iterate(&blk, false); // not old-to-young. 1232 } 1233 } 1234 #endif // not PRODUCT 1235 1236 class GenEnsureParsabilityClosure: public GenCollectedHeap::GenClosure { 1237 public: 1238 void do_generation(Generation* gen) { 1239 gen->ensure_parsability(); 1240 } 1241 }; 1242 1243 void GenCollectedHeap::ensure_parsability(bool retire_tlabs) { 1244 CollectedHeap::ensure_parsability(retire_tlabs); 1245 GenEnsureParsabilityClosure ep_cl; 1246 generation_iterate(&ep_cl, false); 1247 } 1248 1249 oop GenCollectedHeap::handle_failed_promotion(Generation* old_gen, 1250 oop obj, 1251 size_t obj_size) { 1252 guarantee(old_gen->level() == 1, "We only get here with an old generation"); 1253 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in"); 1254 HeapWord* result = NULL; 1255 1256 result = old_gen->expand_and_allocate(obj_size, false); 1257 1258 if (result != NULL) { 1259 Copy::aligned_disjoint_words((HeapWord*)obj, result, obj_size); 1260 } 1261 return oop(result); 1262 } 1263 1264 class GenTimeOfLastGCClosure: public GenCollectedHeap::GenClosure { 1265 jlong _time; // in ms 1266 jlong _now; // in ms 1267 1268 public: 1269 GenTimeOfLastGCClosure(jlong now) : _time(now), _now(now) { } 1270 1271 jlong time() { return _time; } 1272 1273 void do_generation(Generation* gen) { 1274 _time = MIN2(_time, gen->time_of_last_gc(_now)); 1275 } 1276 }; 1277 1278 jlong GenCollectedHeap::millis_since_last_gc() { 1279 // We need a monotonically non-deccreasing time in ms but 1280 // os::javaTimeMillis() does not guarantee monotonicity. 1281 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 1282 GenTimeOfLastGCClosure tolgc_cl(now); 1283 // iterate over generations getting the oldest 1284 // time that a generation was collected 1285 generation_iterate(&tolgc_cl, false); 1286 1287 // javaTimeNanos() is guaranteed to be monotonically non-decreasing 1288 // provided the underlying platform provides such a time source 1289 // (and it is bug free). So we still have to guard against getting 1290 // back a time later than 'now'. 1291 jlong retVal = now - tolgc_cl.time(); 1292 if (retVal < 0) { 1293 NOT_PRODUCT(warning("time warp: "INT64_FORMAT, retVal);) 1294 return 0; 1295 } 1296 return retVal; 1297 }