1 /* 2 * Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "classfile/symbolTable.hpp" 27 #include "classfile/systemDictionary.hpp" 28 #include "classfile/vmSymbols.hpp" 29 #include "code/icBuffer.hpp" 30 #include "gc_implementation/shared/collectorCounters.hpp" 31 #include "gc_implementation/shared/gcTrace.hpp" 32 #include "gc_implementation/shared/gcTraceTime.hpp" 33 #include "gc_implementation/shared/vmGCOperations.hpp" 34 #include "gc_interface/collectedHeap.inline.hpp" 35 #include "memory/filemap.hpp" 36 #include "memory/gcLocker.inline.hpp" 37 #include "memory/genCollectedHeap.hpp" 38 #include "memory/genOopClosures.inline.hpp" 39 #include "memory/generation.inline.hpp" 40 #include "memory/generationSpec.hpp" 41 #include "memory/resourceArea.hpp" 42 #include "memory/sharedHeap.hpp" 43 #include "memory/space.hpp" 44 #include "oops/oop.inline.hpp" 45 #include "oops/oop.inline2.hpp" 46 #include "runtime/biasedLocking.hpp" 47 #include "runtime/fprofiler.hpp" 48 #include "runtime/handles.hpp" 49 #include "runtime/handles.inline.hpp" 50 #include "runtime/java.hpp" 51 #include "runtime/vmThread.hpp" 52 #include "services/memoryService.hpp" 53 #include "utilities/vmError.hpp" 54 #include "utilities/workgroup.hpp" 55 #include "utilities/macros.hpp" 56 #if INCLUDE_ALL_GCS 57 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp" 58 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp" 59 #endif // INCLUDE_ALL_GCS 60 61 GenCollectedHeap* GenCollectedHeap::_gch; 62 NOT_PRODUCT(size_t GenCollectedHeap::_skip_header_HeapWords = 0;) 63 64 // The set of potentially parallel tasks in root scanning. 65 enum GCH_strong_roots_tasks { 66 // We probably want to parallelize both of these internally, but for now... 67 GCH_PS_younger_gens, 68 // Leave this one last. 69 GCH_PS_NumElements 70 }; 71 72 GenCollectedHeap::GenCollectedHeap(GenCollectorPolicy *policy) : 73 SharedHeap(policy), 74 _gen_policy(policy), 75 _gen_process_roots_tasks(new SubTasksDone(GCH_PS_NumElements)), 76 _full_collections_completed(0) 77 { 78 if (_gen_process_roots_tasks == NULL || 79 !_gen_process_roots_tasks->valid()) { 80 vm_exit_during_initialization("Failed necessary allocation."); 81 } 82 assert(policy != NULL, "Sanity check"); 83 } 84 85 jint GenCollectedHeap::initialize() { 86 CollectedHeap::pre_initialize(); 87 88 int i; 89 _n_gens = gen_policy()->number_of_generations(); 90 91 // While there are no constraints in the GC code that HeapWordSize 92 // be any particular value, there are multiple other areas in the 93 // system which believe this to be true (e.g. oop->object_size in some 94 // cases incorrectly returns the size in wordSize units rather than 95 // HeapWordSize). 96 guarantee(HeapWordSize == wordSize, "HeapWordSize must equal wordSize"); 97 98 // The heap must be at least as aligned as generations. 99 size_t gen_alignment = Generation::GenGrain; 100 101 _gen_specs = gen_policy()->generations(); 102 103 // Make sure the sizes are all aligned. 104 for (i = 0; i < _n_gens; i++) { 105 _gen_specs[i]->align(gen_alignment); 106 } 107 108 // Allocate space for the heap. 109 110 char* heap_address; 111 size_t total_reserved = 0; 112 int n_covered_regions = 0; 113 ReservedSpace heap_rs; 114 115 size_t heap_alignment = collector_policy()->heap_alignment(); 116 117 heap_address = allocate(heap_alignment, &total_reserved, 118 &n_covered_regions, &heap_rs); 119 120 if (!heap_rs.is_reserved()) { 121 vm_shutdown_during_initialization( 122 "Could not reserve enough space for object heap"); 123 return JNI_ENOMEM; 124 } 125 126 initialize_reserved_region((HeapWord*)heap_rs.base(), (HeapWord*)(heap_rs.base() + heap_rs.size())); 127 128 _rem_set = collector_policy()->create_rem_set(reserved_region(), n_covered_regions); 129 set_barrier_set(rem_set()->bs()); 130 131 _gch = this; 132 133 ReservedSpace young_rs = heap_rs.first_part(_gen_specs[0]->max_size(), false, false); 134 _young_gen = _gen_specs[0]->init(young_rs, 0, rem_set()); 135 heap_rs = heap_rs.last_part(_gen_specs[0]->max_size()); 136 137 ReservedSpace old_rs = heap_rs.first_part(_gen_specs[1]->max_size(), false, false); 138 _old_gen = _gen_specs[1]->init(old_rs, 1, rem_set()); 139 heap_rs = heap_rs.last_part(_gen_specs[1]->max_size()); 140 clear_incremental_collection_failed(); 141 142 #if INCLUDE_ALL_GCS 143 // If we are running CMS, create the collector responsible 144 // for collecting the CMS generations. 145 if (collector_policy()->is_concurrent_mark_sweep_policy()) { 146 bool success = create_cms_collector(); 147 if (!success) return JNI_ENOMEM; 148 } 149 #endif // INCLUDE_ALL_GCS 150 151 return JNI_OK; 152 } 153 154 char* GenCollectedHeap::allocate(size_t alignment, 155 size_t* _total_reserved, 156 int* _n_covered_regions, 157 ReservedSpace* heap_rs){ 158 const char overflow_msg[] = "The size of the object heap + VM data exceeds " 159 "the maximum representable size"; 160 161 // Now figure out the total size. 162 size_t total_reserved = 0; 163 int n_covered_regions = 0; 164 const size_t pageSize = UseLargePages ? 165 os::large_page_size() : os::vm_page_size(); 166 167 assert(alignment % pageSize == 0, "Must be"); 168 169 for (int i = 0; i < _n_gens; i++) { 170 total_reserved += _gen_specs[i]->max_size(); 171 if (total_reserved < _gen_specs[i]->max_size()) { 172 vm_exit_during_initialization(overflow_msg); 173 } 174 n_covered_regions += _gen_specs[i]->n_covered_regions(); 175 } 176 assert(total_reserved % alignment == 0, 177 err_msg("Gen size; total_reserved=" SIZE_FORMAT ", alignment=" 178 SIZE_FORMAT, total_reserved, alignment)); 179 180 // Needed until the cardtable is fixed to have the right number 181 // of covered regions. 182 n_covered_regions += 2; 183 184 *_total_reserved = total_reserved; 185 *_n_covered_regions = n_covered_regions; 186 187 *heap_rs = Universe::reserve_heap(total_reserved, alignment); 188 return heap_rs->base(); 189 } 190 191 void GenCollectedHeap::post_initialize() { 192 SharedHeap::post_initialize(); 193 GenCollectorPolicy *policy = (GenCollectorPolicy *)collector_policy(); 194 guarantee(policy->is_generation_policy(), "Illegal policy type"); 195 DefNewGeneration* def_new_gen = (DefNewGeneration*) get_gen(0); 196 assert(def_new_gen->kind() == Generation::DefNew || 197 def_new_gen->kind() == Generation::ParNew, 198 "Wrong generation kind"); 199 200 Generation* old_gen = get_gen(1); 201 assert(old_gen->kind() == Generation::ConcurrentMarkSweep || 202 old_gen->kind() == Generation::MarkSweepCompact, 203 "Wrong generation kind"); 204 205 policy->initialize_size_policy(def_new_gen->eden()->capacity(), 206 old_gen->capacity(), 207 def_new_gen->from()->capacity()); 208 policy->initialize_gc_policy_counters(); 209 } 210 211 void GenCollectedHeap::ref_processing_init() { 212 SharedHeap::ref_processing_init(); 213 _young_gen->ref_processor_init(); 214 _old_gen->ref_processor_init(); 215 } 216 217 size_t GenCollectedHeap::capacity() const { 218 return _young_gen->capacity() + _old_gen->capacity(); 219 } 220 221 size_t GenCollectedHeap::used() const { 222 return _young_gen->used() + _old_gen->used(); 223 } 224 225 // Save the "used_region" for generations level and lower. 226 void GenCollectedHeap::save_used_regions(int level) { 227 assert(level < _n_gens, "Illegal level parameter"); 228 if (level == 1) { 229 _old_gen->save_used_region(); 230 } 231 _young_gen->save_used_region(); 232 } 233 234 size_t GenCollectedHeap::max_capacity() const { 235 return _young_gen->max_capacity() + _old_gen->max_capacity(); 236 } 237 238 // Update the _full_collections_completed counter 239 // at the end of a stop-world full GC. 240 unsigned int GenCollectedHeap::update_full_collections_completed() { 241 MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag); 242 assert(_full_collections_completed <= _total_full_collections, 243 "Can't complete more collections than were started"); 244 _full_collections_completed = _total_full_collections; 245 ml.notify_all(); 246 return _full_collections_completed; 247 } 248 249 // Update the _full_collections_completed counter, as appropriate, 250 // at the end of a concurrent GC cycle. Note the conditional update 251 // below to allow this method to be called by a concurrent collector 252 // without synchronizing in any manner with the VM thread (which 253 // may already have initiated a STW full collection "concurrently"). 254 unsigned int GenCollectedHeap::update_full_collections_completed(unsigned int count) { 255 MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag); 256 assert((_full_collections_completed <= _total_full_collections) && 257 (count <= _total_full_collections), 258 "Can't complete more collections than were started"); 259 if (count > _full_collections_completed) { 260 _full_collections_completed = count; 261 ml.notify_all(); 262 } 263 return _full_collections_completed; 264 } 265 266 267 #ifndef PRODUCT 268 // Override of memory state checking method in CollectedHeap: 269 // Some collectors (CMS for example) can't have badHeapWordVal written 270 // in the first two words of an object. (For instance , in the case of 271 // CMS these words hold state used to synchronize between certain 272 // (concurrent) GC steps and direct allocating mutators.) 273 // The skip_header_HeapWords() method below, allows us to skip 274 // over the requisite number of HeapWord's. Note that (for 275 // generational collectors) this means that those many words are 276 // skipped in each object, irrespective of the generation in which 277 // that object lives. The resultant loss of precision seems to be 278 // harmless and the pain of avoiding that imprecision appears somewhat 279 // higher than we are prepared to pay for such rudimentary debugging 280 // support. 281 void GenCollectedHeap::check_for_non_bad_heap_word_value(HeapWord* addr, 282 size_t size) { 283 if (CheckMemoryInitialization && ZapUnusedHeapArea) { 284 // We are asked to check a size in HeapWords, 285 // but the memory is mangled in juint words. 286 juint* start = (juint*) (addr + skip_header_HeapWords()); 287 juint* end = (juint*) (addr + size); 288 for (juint* slot = start; slot < end; slot += 1) { 289 assert(*slot == badHeapWordVal, 290 "Found non badHeapWordValue in pre-allocation check"); 291 } 292 } 293 } 294 #endif 295 296 HeapWord* GenCollectedHeap::attempt_allocation(size_t size, 297 bool is_tlab, 298 bool first_only) { 299 HeapWord* res = NULL; 300 301 if (_young_gen->should_allocate(size, is_tlab)) { 302 res = _young_gen->allocate(size, is_tlab); 303 if (res != NULL || first_only) { 304 return res; 305 } 306 } 307 308 if (_old_gen->should_allocate(size, is_tlab)) { 309 res = _old_gen->allocate(size, is_tlab); 310 } 311 312 return res; 313 } 314 315 HeapWord* GenCollectedHeap::mem_allocate(size_t size, 316 bool* gc_overhead_limit_was_exceeded) { 317 return collector_policy()->mem_allocate_work(size, 318 false /* is_tlab */, 319 gc_overhead_limit_was_exceeded); 320 } 321 322 bool GenCollectedHeap::must_clear_all_soft_refs() { 323 return _gc_cause == GCCause::_last_ditch_collection; 324 } 325 326 bool GenCollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) { 327 return UseConcMarkSweepGC && 328 ((cause == GCCause::_gc_locker && GCLockerInvokesConcurrent) || 329 (cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent)); 330 } 331 332 void GenCollectedHeap::collect_generation(Generation* gen, bool full, size_t size, 333 bool is_tlab, bool run_verification, bool clear_soft_refs) { 334 // Timer for individual generations. Last argument is false: no CR 335 // FIXME: We should try to start the timing earlier to cover more of the GC pause 336 // The PrintGCDetails logging starts before we have incremented the GC id. We will do that later 337 // so we can assume here that the next GC id is what we want. 338 GCTraceTime t1(gen->short_name(), PrintGCDetails, false, NULL, GCId::peek()); 339 TraceCollectorStats tcs(gen->counters()); 340 TraceMemoryManagerStats tmms(gen->kind(),gc_cause()); 341 342 size_t prev_used = gen->used(); 343 gen->stat_record()->invocations++; 344 gen->stat_record()->accumulated_time.start(); 345 346 // Must be done anew before each collection because 347 // a previous collection will do mangling and will 348 // change top of some spaces. 349 record_gen_tops_before_GC(); 350 351 if (PrintGC && Verbose) { 352 gclog_or_tty->print("level=%d invoke=%d size=" SIZE_FORMAT, 353 gen->level(), 354 gen->stat_record()->invocations, 355 size * HeapWordSize); 356 } 357 358 if (run_verification && VerifyBeforeGC) { 359 HandleMark hm; // Discard invalid handles created during verification 360 Universe::verify(" VerifyBeforeGC:"); 361 } 362 COMPILER2_PRESENT(DerivedPointerTable::clear()); 363 364 // Do collection work 365 { 366 // Note on ref discovery: For what appear to be historical reasons, 367 // GCH enables and disabled (by enqueing) refs discovery. 368 // In the future this should be moved into the generation's 369 // collect method so that ref discovery and enqueueing concerns 370 // are local to a generation. The collect method could return 371 // an appropriate indication in the case that notification on 372 // the ref lock was needed. This will make the treatment of 373 // weak refs more uniform (and indeed remove such concerns 374 // from GCH). XXX 375 376 HandleMark hm; // Discard invalid handles created during gc 377 save_marks(); // save marks for all gens 378 // We want to discover references, but not process them yet. 379 // This mode is disabled in process_discovered_references if the 380 // generation does some collection work, or in 381 // enqueue_discovered_references if the generation returns 382 // without doing any work. 383 ReferenceProcessor* rp = gen->ref_processor(); 384 // If the discovery of ("weak") refs in this generation is 385 // atomic wrt other collectors in this configuration, we 386 // are guaranteed to have empty discovered ref lists. 387 if (rp->discovery_is_atomic()) { 388 rp->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/); 389 rp->setup_policy(clear_soft_refs); 390 } else { 391 // collect() below will enable discovery as appropriate 392 } 393 gen->collect(full, clear_soft_refs, size, is_tlab); 394 if (!rp->enqueuing_is_done()) { 395 rp->enqueue_discovered_references(); 396 } else { 397 rp->set_enqueuing_is_done(false); 398 } 399 rp->verify_no_references_recorded(); 400 } 401 402 // Determine if allocation request was met. 403 if (size > 0) { 404 if (!is_tlab || gen->supports_tlab_allocation()) { 405 if (size * HeapWordSize <= gen->unsafe_max_alloc_nogc()) { 406 size = 0; 407 } 408 } 409 } 410 411 COMPILER2_PRESENT(DerivedPointerTable::update_pointers()); 412 413 gen->stat_record()->accumulated_time.stop(); 414 415 update_gc_stats(gen->level(), full); 416 417 if (run_verification && VerifyAfterGC) { 418 HandleMark hm; // Discard invalid handles created during verification 419 Universe::verify(" VerifyAfterGC:"); 420 } 421 422 if (PrintGCDetails) { 423 gclog_or_tty->print(":"); 424 gen->print_heap_change(prev_used); 425 } 426 } 427 428 void GenCollectedHeap::do_collection(bool full, 429 bool clear_all_soft_refs, 430 size_t size, 431 bool is_tlab, 432 int max_level) { 433 ResourceMark rm; 434 DEBUG_ONLY(Thread* my_thread = Thread::current();) 435 436 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint"); 437 assert(my_thread->is_VM_thread() || 438 my_thread->is_ConcurrentGC_thread(), 439 "incorrect thread type capability"); 440 assert(Heap_lock->is_locked(), 441 "the requesting thread should have the Heap_lock"); 442 guarantee(!is_gc_active(), "collection is not reentrant"); 443 assert(max_level < n_gens(), "sanity check"); 444 445 if (GC_locker::check_active_before_gc()) { 446 return; // GC is disabled (e.g. JNI GetXXXCritical operation) 447 } 448 449 const bool do_clear_all_soft_refs = clear_all_soft_refs || 450 collector_policy()->should_clear_all_soft_refs(); 451 452 ClearedAllSoftRefs casr(do_clear_all_soft_refs, collector_policy()); 453 454 const size_t metadata_prev_used = MetaspaceAux::used_bytes(); 455 456 print_heap_before_gc(); 457 458 { 459 FlagSetting fl(_is_gc_active, true); 460 461 bool complete = full && (max_level == (n_gens()-1)); 462 const char* gc_cause_prefix = complete ? "Full GC" : "GC"; 463 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps); 464 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); 465 // The PrintGCDetails logging starts before we have incremented the GC id. We will do that later 466 // so we can assume here that the next GC id is what we want. 467 GCTraceTime t(GCCauseString(gc_cause_prefix, gc_cause()), PrintGCDetails, false, NULL, GCId::peek()); 468 469 gc_prologue(complete); 470 increment_total_collections(complete); 471 472 size_t gch_prev_used = used(); 473 bool must_restore_marks_for_biased_locking = false; 474 bool run_verification = total_collections() >= VerifyGCStartAt; 475 476 if (_young_gen->performs_in_place_marking() || 477 _old_gen->performs_in_place_marking()) { 478 // We want to avoid doing this for 479 // scavenge-only collections where it's unnecessary. 480 must_restore_marks_for_biased_locking = true; 481 BiasedLocking::preserve_marks(); 482 } 483 484 bool prepared_for_verification = false; 485 int max_level_collected = 0; 486 if (!(full && _old_gen->full_collects_younger_generations()) && 487 _young_gen->should_collect(full, size, is_tlab)) { 488 if (run_verification && VerifyGCLevel <= 0 && VerifyBeforeGC) { 489 prepare_for_verify(); 490 prepared_for_verification = true; 491 } 492 collect_generation(_young_gen, full, size, is_tlab, run_verification && VerifyGCLevel <= 0, do_clear_all_soft_refs); 493 } 494 if (max_level == 1 && _old_gen->should_collect(full, size, is_tlab)) { 495 if (!complete) { 496 // The full_collections increment was missed above. 497 increment_total_full_collections(); 498 } 499 pre_full_gc_dump(NULL); // do any pre full gc dumps 500 if (run_verification && VerifyGCLevel <= 1 && VerifyBeforeGC) { 501 if (!prepared_for_verification) { 502 prepare_for_verify(); 503 } 504 } 505 collect_generation(_old_gen, full, size, is_tlab, run_verification && VerifyGCLevel <= 1, do_clear_all_soft_refs); 506 max_level_collected = 1; 507 } 508 509 // Update "complete" boolean wrt what actually transpired -- 510 // for instance, a promotion failure could have led to 511 // a whole heap collection. 512 complete = complete || (max_level_collected == n_gens() - 1); 513 514 if (complete) { // We did a "major" collection 515 // FIXME: See comment at pre_full_gc_dump call 516 post_full_gc_dump(NULL); // do any post full gc dumps 517 } 518 519 if (PrintGCDetails) { 520 print_heap_change(gch_prev_used); 521 522 // Print metaspace info for full GC with PrintGCDetails flag. 523 if (complete) { 524 MetaspaceAux::print_metaspace_change(metadata_prev_used); 525 } 526 } 527 528 // Adjust generation sizes. 529 if (max_level_collected == 1) { 530 _old_gen->compute_new_size(); 531 } 532 _young_gen->compute_new_size(); 533 534 if (complete) { 535 // Delete metaspaces for unloaded class loaders and clean up loader_data graph 536 ClassLoaderDataGraph::purge(); 537 MetaspaceAux::verify_metrics(); 538 // Resize the metaspace capacity after full collections 539 MetaspaceGC::compute_new_size(); 540 update_full_collections_completed(); 541 } 542 543 // Track memory usage and detect low memory after GC finishes 544 MemoryService::track_memory_usage(); 545 546 gc_epilogue(complete); 547 548 if (must_restore_marks_for_biased_locking) { 549 BiasedLocking::restore_marks(); 550 } 551 } 552 553 print_heap_after_gc(); 554 555 #ifdef TRACESPINNING 556 ParallelTaskTerminator::print_termination_counts(); 557 #endif 558 } 559 560 HeapWord* GenCollectedHeap::satisfy_failed_allocation(size_t size, bool is_tlab) { 561 return collector_policy()->satisfy_failed_allocation(size, is_tlab); 562 } 563 564 void GenCollectedHeap::set_par_threads(uint t) { 565 SharedHeap::set_par_threads(t); 566 _gen_process_roots_tasks->set_n_threads(t); 567 } 568 569 void GenCollectedHeap:: 570 gen_process_roots(int level, 571 bool younger_gens_as_roots, 572 bool activate_scope, 573 SharedHeap::ScanningOption so, 574 OopsInGenClosure* not_older_gens, 575 OopsInGenClosure* weak_roots, 576 OopsInGenClosure* older_gens, 577 CLDClosure* cld_closure, 578 CLDClosure* weak_cld_closure, 579 CodeBlobClosure* code_closure) { 580 581 // General roots. 582 SharedHeap::process_roots(activate_scope, so, 583 not_older_gens, weak_roots, 584 cld_closure, weak_cld_closure, 585 code_closure); 586 587 if (younger_gens_as_roots) { 588 if (!_gen_process_roots_tasks->is_task_claimed(GCH_PS_younger_gens)) { 589 if (level == 1) { 590 not_older_gens->set_generation(_young_gen); 591 _young_gen->oop_iterate(not_older_gens); 592 } 593 not_older_gens->reset_generation(); 594 } 595 } 596 // When collection is parallel, all threads get to cooperate to do 597 // older-gen scanning. 598 if (level == 0) { 599 older_gens->set_generation(_old_gen); 600 rem_set()->younger_refs_iterate(_old_gen, older_gens); 601 older_gens->reset_generation(); 602 } 603 604 _gen_process_roots_tasks->all_tasks_completed(); 605 } 606 607 void GenCollectedHeap:: 608 gen_process_roots(int level, 609 bool younger_gens_as_roots, 610 bool activate_scope, 611 SharedHeap::ScanningOption so, 612 bool only_strong_roots, 613 OopsInGenClosure* not_older_gens, 614 OopsInGenClosure* older_gens, 615 CLDClosure* cld_closure) { 616 617 const bool is_adjust_phase = !only_strong_roots && !younger_gens_as_roots; 618 619 bool is_moving_collection = false; 620 if (level == 0 || is_adjust_phase) { 621 // young collections are always moving 622 is_moving_collection = true; 623 } 624 625 MarkingCodeBlobClosure mark_code_closure(not_older_gens, is_moving_collection); 626 CodeBlobClosure* code_closure = &mark_code_closure; 627 628 gen_process_roots(level, 629 younger_gens_as_roots, 630 activate_scope, so, 631 not_older_gens, only_strong_roots ? NULL : not_older_gens, 632 older_gens, 633 cld_closure, only_strong_roots ? NULL : cld_closure, 634 code_closure); 635 636 } 637 638 void GenCollectedHeap::gen_process_weak_roots(OopClosure* root_closure) { 639 SharedHeap::process_weak_roots(root_closure); 640 // "Local" "weak" refs 641 _young_gen->ref_processor()->weak_oops_do(root_closure); 642 _old_gen->ref_processor()->weak_oops_do(root_closure); 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 if (level == 0) { \ 651 _young_gen->oop_since_save_marks_iterate##nv_suffix(cur); \ 652 _old_gen->oop_since_save_marks_iterate##nv_suffix(older); \ 653 } else { \ 654 _old_gen->oop_since_save_marks_iterate##nv_suffix(cur); \ 655 } \ 656 } 657 658 ALL_SINCE_SAVE_MARKS_CLOSURES(GCH_SINCE_SAVE_MARKS_ITERATE_DEFN) 659 660 #undef GCH_SINCE_SAVE_MARKS_ITERATE_DEFN 661 662 bool GenCollectedHeap::no_allocs_since_save_marks(int level) { 663 if (level == 0) { 664 if (!_young_gen->no_allocs_since_save_marks()) return false; 665 } 666 if (!_old_gen->no_allocs_since_save_marks()) return false; 667 return true; 668 } 669 670 bool GenCollectedHeap::supports_inline_contig_alloc() const { 671 return _young_gen->supports_inline_contig_alloc(); 672 } 673 674 HeapWord** GenCollectedHeap::top_addr() const { 675 return _young_gen->top_addr(); 676 } 677 678 HeapWord** GenCollectedHeap::end_addr() const { 679 return _young_gen->end_addr(); 680 } 681 682 // public collection interfaces 683 684 void GenCollectedHeap::collect(GCCause::Cause cause) { 685 if (should_do_concurrent_full_gc(cause)) { 686 #if INCLUDE_ALL_GCS 687 // mostly concurrent full collection 688 collect_mostly_concurrent(cause); 689 #else // INCLUDE_ALL_GCS 690 ShouldNotReachHere(); 691 #endif // INCLUDE_ALL_GCS 692 } else if (cause == GCCause::_wb_young_gc) { 693 // minor collection for WhiteBox API 694 collect(cause, 0); 695 } else { 696 #ifdef ASSERT 697 if (cause == GCCause::_scavenge_alot) { 698 // minor collection only 699 collect(cause, 0); 700 } else { 701 // Stop-the-world full collection 702 collect(cause, n_gens() - 1); 703 } 704 #else 705 // Stop-the-world full collection 706 collect(cause, n_gens() - 1); 707 #endif 708 } 709 } 710 711 void GenCollectedHeap::collect(GCCause::Cause cause, int max_level) { 712 // The caller doesn't have the Heap_lock 713 assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock"); 714 MutexLocker ml(Heap_lock); 715 collect_locked(cause, max_level); 716 } 717 718 void GenCollectedHeap::collect_locked(GCCause::Cause cause) { 719 // The caller has the Heap_lock 720 assert(Heap_lock->owned_by_self(), "this thread should own the Heap_lock"); 721 collect_locked(cause, n_gens() - 1); 722 } 723 724 // this is the private collection interface 725 // The Heap_lock is expected to be held on entry. 726 727 void GenCollectedHeap::collect_locked(GCCause::Cause cause, int max_level) { 728 // Read the GC count while holding the Heap_lock 729 unsigned int gc_count_before = total_collections(); 730 unsigned int full_gc_count_before = total_full_collections(); 731 { 732 MutexUnlocker mu(Heap_lock); // give up heap lock, execute gets it back 733 VM_GenCollectFull op(gc_count_before, full_gc_count_before, 734 cause, max_level); 735 VMThread::execute(&op); 736 } 737 } 738 739 #if INCLUDE_ALL_GCS 740 bool GenCollectedHeap::create_cms_collector() { 741 742 assert(_old_gen->kind() == Generation::ConcurrentMarkSweep, 743 "Unexpected generation kinds"); 744 // Skip two header words in the block content verification 745 NOT_PRODUCT(_skip_header_HeapWords = CMSCollector::skip_header_HeapWords();) 746 CMSCollector* collector = new CMSCollector( 747 (ConcurrentMarkSweepGeneration*)_old_gen, 748 _rem_set->as_CardTableRS(), 749 (ConcurrentMarkSweepPolicy*) collector_policy()); 750 751 if (collector == NULL || !collector->completed_initialization()) { 752 if (collector) { 753 delete collector; // Be nice in embedded situation 754 } 755 vm_shutdown_during_initialization("Could not create CMS collector"); 756 return false; 757 } 758 return true; // success 759 } 760 761 void GenCollectedHeap::collect_mostly_concurrent(GCCause::Cause cause) { 762 assert(!Heap_lock->owned_by_self(), "Should not own Heap_lock"); 763 764 MutexLocker ml(Heap_lock); 765 // Read the GC counts while holding the Heap_lock 766 unsigned int full_gc_count_before = total_full_collections(); 767 unsigned int gc_count_before = total_collections(); 768 { 769 MutexUnlocker mu(Heap_lock); 770 VM_GenCollectFullConcurrent op(gc_count_before, full_gc_count_before, cause); 771 VMThread::execute(&op); 772 } 773 } 774 #endif // INCLUDE_ALL_GCS 775 776 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs) { 777 do_full_collection(clear_all_soft_refs, _n_gens - 1); 778 } 779 780 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs, 781 int max_level) { 782 int local_max_level; 783 if (!incremental_collection_will_fail(false /* don't consult_young */) && 784 gc_cause() == GCCause::_gc_locker) { 785 local_max_level = 0; 786 } else { 787 local_max_level = max_level; 788 } 789 790 do_collection(true /* full */, 791 clear_all_soft_refs /* clear_all_soft_refs */, 792 0 /* size */, 793 false /* is_tlab */, 794 local_max_level /* max_level */); 795 // Hack XXX FIX ME !!! 796 // A scavenge may not have been attempted, or may have 797 // been attempted and failed, because the old gen was too full 798 if (local_max_level == 0 && gc_cause() == GCCause::_gc_locker && 799 incremental_collection_will_fail(false /* don't consult_young */)) { 800 if (PrintGCDetails) { 801 gclog_or_tty->print_cr("GC locker: Trying a full collection " 802 "because scavenge failed"); 803 } 804 // This time allow the old gen to be collected as well 805 do_collection(true /* full */, 806 clear_all_soft_refs /* clear_all_soft_refs */, 807 0 /* size */, 808 false /* is_tlab */, 809 n_gens() - 1 /* max_level */); 810 } 811 } 812 813 bool GenCollectedHeap::is_in_young(oop p) { 814 bool result = ((HeapWord*)p) < _old_gen->reserved().start(); 815 assert(result == _young_gen->is_in_reserved(p), 816 err_msg("incorrect test - result=%d, p=" INTPTR_FORMAT, result, p2i((void*)p))); 817 return result; 818 } 819 820 // Returns "TRUE" iff "p" points into the committed areas of the heap. 821 bool GenCollectedHeap::is_in(const void* p) const { 822 #ifndef ASSERT 823 guarantee(VerifyBeforeGC || 824 VerifyDuringGC || 825 VerifyBeforeExit || 826 VerifyDuringStartup || 827 PrintAssembly || 828 tty->count() != 0 || // already printing 829 VerifyAfterGC || 830 VMError::fatal_error_in_progress(), "too expensive"); 831 832 #endif 833 // This might be sped up with a cache of the last generation that 834 // answered yes. 835 if (_young_gen->is_in(p) || _old_gen->is_in(p)) { 836 return true; 837 } 838 // Otherwise... 839 return false; 840 } 841 842 #ifdef ASSERT 843 // Don't implement this by using is_in_young(). This method is used 844 // in some cases to check that is_in_young() is correct. 845 bool GenCollectedHeap::is_in_partial_collection(const void* p) { 846 assert(is_in_reserved(p) || p == NULL, 847 "Does not work if address is non-null and outside of the heap"); 848 return p < _young_gen->reserved().end() && p != NULL; 849 } 850 #endif 851 852 void GenCollectedHeap::oop_iterate(ExtendedOopClosure* cl) { 853 _young_gen->oop_iterate(cl); 854 _old_gen->oop_iterate(cl); 855 } 856 857 void GenCollectedHeap::object_iterate(ObjectClosure* cl) { 858 _young_gen->object_iterate(cl); 859 _old_gen->object_iterate(cl); 860 } 861 862 void GenCollectedHeap::safe_object_iterate(ObjectClosure* cl) { 863 _young_gen->safe_object_iterate(cl); 864 _old_gen->safe_object_iterate(cl); 865 } 866 867 Space* GenCollectedHeap::space_containing(const void* addr) const { 868 Space* res = _young_gen->space_containing(addr); 869 if (res != NULL) { 870 return res; 871 } 872 res = _old_gen->space_containing(addr); 873 assert(res != NULL, "Could not find containing space"); 874 return res; 875 } 876 877 HeapWord* GenCollectedHeap::block_start(const void* addr) const { 878 assert(is_in_reserved(addr), "block_start of address outside of heap"); 879 if (_young_gen->is_in_reserved(addr)) { 880 assert(_young_gen->is_in(addr), "addr should be in allocated part of generation"); 881 return _young_gen->block_start(addr); 882 } 883 884 assert(_old_gen->is_in_reserved(addr), "Some generation should contain the address"); 885 assert(_old_gen->is_in(addr), "addr should be in allocated part of generation"); 886 return _old_gen->block_start(addr); 887 } 888 889 size_t GenCollectedHeap::block_size(const HeapWord* addr) const { 890 assert(is_in_reserved(addr), "block_size of address outside of heap"); 891 if (_young_gen->is_in_reserved(addr)) { 892 assert(_young_gen->is_in(addr), "addr should be in allocated part of generation"); 893 return _young_gen->block_size(addr); 894 } 895 896 assert(_old_gen->is_in_reserved(addr), "Some generation should contain the address"); 897 assert(_old_gen->is_in(addr), "addr should be in allocated part of generation"); 898 return _old_gen->block_size(addr); 899 } 900 901 bool GenCollectedHeap::block_is_obj(const HeapWord* addr) const { 902 assert(is_in_reserved(addr), "block_is_obj of address outside of heap"); 903 assert(block_start(addr) == addr, "addr must be a block start"); 904 if (_young_gen->is_in_reserved(addr)) { 905 return _young_gen->block_is_obj(addr); 906 } 907 908 assert(_old_gen->is_in_reserved(addr), "Some generation should contain the address"); 909 return _old_gen->block_is_obj(addr); 910 } 911 912 bool GenCollectedHeap::supports_tlab_allocation() const { 913 assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!"); 914 return _young_gen->supports_tlab_allocation(); 915 } 916 917 size_t GenCollectedHeap::tlab_capacity(Thread* thr) const { 918 assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!"); 919 if (_young_gen->supports_tlab_allocation()) { 920 return _young_gen->tlab_capacity(); 921 } 922 return 0; 923 } 924 925 size_t GenCollectedHeap::tlab_used(Thread* thr) const { 926 assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!"); 927 if (_young_gen->supports_tlab_allocation()) { 928 return _young_gen->tlab_used(); 929 } 930 return 0; 931 } 932 933 size_t GenCollectedHeap::unsafe_max_tlab_alloc(Thread* thr) const { 934 assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!"); 935 if (_young_gen->supports_tlab_allocation()) { 936 return _young_gen->unsafe_max_tlab_alloc(); 937 } 938 return 0; 939 } 940 941 HeapWord* GenCollectedHeap::allocate_new_tlab(size_t size) { 942 bool gc_overhead_limit_was_exceeded; 943 return collector_policy()->mem_allocate_work(size /* size */, 944 true /* is_tlab */, 945 &gc_overhead_limit_was_exceeded); 946 } 947 948 // Requires "*prev_ptr" to be non-NULL. Deletes and a block of minimal size 949 // from the list headed by "*prev_ptr". 950 static ScratchBlock *removeSmallestScratch(ScratchBlock **prev_ptr) { 951 bool first = true; 952 size_t min_size = 0; // "first" makes this conceptually infinite. 953 ScratchBlock **smallest_ptr, *smallest; 954 ScratchBlock *cur = *prev_ptr; 955 while (cur) { 956 assert(*prev_ptr == cur, "just checking"); 957 if (first || cur->num_words < min_size) { 958 smallest_ptr = prev_ptr; 959 smallest = cur; 960 min_size = smallest->num_words; 961 first = false; 962 } 963 prev_ptr = &cur->next; 964 cur = cur->next; 965 } 966 smallest = *smallest_ptr; 967 *smallest_ptr = smallest->next; 968 return smallest; 969 } 970 971 // Sort the scratch block list headed by res into decreasing size order, 972 // and set "res" to the result. 973 static void sort_scratch_list(ScratchBlock*& list) { 974 ScratchBlock* sorted = NULL; 975 ScratchBlock* unsorted = list; 976 while (unsorted) { 977 ScratchBlock *smallest = removeSmallestScratch(&unsorted); 978 smallest->next = sorted; 979 sorted = smallest; 980 } 981 list = sorted; 982 } 983 984 ScratchBlock* GenCollectedHeap::gather_scratch(Generation* requestor, 985 size_t max_alloc_words) { 986 ScratchBlock* res = NULL; 987 _young_gen->contribute_scratch(res, requestor, max_alloc_words); 988 _old_gen->contribute_scratch(res, requestor, max_alloc_words); 989 sort_scratch_list(res); 990 return res; 991 } 992 993 void GenCollectedHeap::release_scratch() { 994 _young_gen->reset_scratch(); 995 _old_gen->reset_scratch(); 996 } 997 998 class GenPrepareForVerifyClosure: public GenCollectedHeap::GenClosure { 999 void do_generation(Generation* gen) { 1000 gen->prepare_for_verify(); 1001 } 1002 }; 1003 1004 void GenCollectedHeap::prepare_for_verify() { 1005 ensure_parsability(false); // no need to retire TLABs 1006 GenPrepareForVerifyClosure blk; 1007 generation_iterate(&blk, false); 1008 } 1009 1010 void GenCollectedHeap::generation_iterate(GenClosure* cl, 1011 bool old_to_young) { 1012 if (old_to_young) { 1013 cl->do_generation(_old_gen); 1014 cl->do_generation(_young_gen); 1015 } else { 1016 cl->do_generation(_young_gen); 1017 cl->do_generation(_old_gen); 1018 } 1019 } 1020 1021 void GenCollectedHeap::space_iterate(SpaceClosure* cl) { 1022 _young_gen->space_iterate(cl, true); 1023 _old_gen->space_iterate(cl, true); 1024 } 1025 1026 bool GenCollectedHeap::is_maximal_no_gc() const { 1027 return _young_gen->is_maximal_no_gc() && _old_gen->is_maximal_no_gc(); 1028 } 1029 1030 void GenCollectedHeap::save_marks() { 1031 _young_gen->save_marks(); 1032 _old_gen->save_marks(); 1033 } 1034 1035 GenCollectedHeap* GenCollectedHeap::heap() { 1036 assert(_gch != NULL, "Uninitialized access to GenCollectedHeap::heap()"); 1037 assert(_gch->kind() == CollectedHeap::GenCollectedHeap, "not a generational heap"); 1038 return _gch; 1039 } 1040 1041 1042 void GenCollectedHeap::prepare_for_compaction() { 1043 guarantee(_n_gens = 2, "Wrong number of generations"); 1044 Generation* old_gen = _old_gen; 1045 // Start by compacting into same gen. 1046 CompactPoint cp(old_gen); 1047 old_gen->prepare_for_compaction(&cp); 1048 Generation* young_gen = _young_gen; 1049 young_gen->prepare_for_compaction(&cp); 1050 } 1051 1052 GCStats* GenCollectedHeap::gc_stats(int level) const { 1053 if (level == 0) { 1054 return _young_gen->gc_stats(); 1055 } else { 1056 return _old_gen->gc_stats(); 1057 } 1058 } 1059 1060 void GenCollectedHeap::verify(bool silent, VerifyOption option /* ignored */) { 1061 if (!silent) { 1062 gclog_or_tty->print("%s", _old_gen->name()); 1063 gclog_or_tty->print(" "); 1064 } 1065 _old_gen->verify(); 1066 1067 if (!silent) { 1068 gclog_or_tty->print("%s", _young_gen->name()); 1069 gclog_or_tty->print(" "); 1070 } 1071 _young_gen->verify(); 1072 1073 if (!silent) { 1074 gclog_or_tty->print("remset "); 1075 } 1076 rem_set()->verify(); 1077 } 1078 1079 void GenCollectedHeap::print_on(outputStream* st) const { 1080 _young_gen->print_on(st); 1081 _old_gen->print_on(st); 1082 MetaspaceAux::print_on(st); 1083 } 1084 1085 void GenCollectedHeap::gc_threads_do(ThreadClosure* tc) const { 1086 if (workers() != NULL) { 1087 workers()->threads_do(tc); 1088 } 1089 #if INCLUDE_ALL_GCS 1090 if (UseConcMarkSweepGC) { 1091 ConcurrentMarkSweepThread::threads_do(tc); 1092 } 1093 #endif // INCLUDE_ALL_GCS 1094 } 1095 1096 void GenCollectedHeap::print_gc_threads_on(outputStream* st) const { 1097 #if INCLUDE_ALL_GCS 1098 if (UseParNewGC) { 1099 workers()->print_worker_threads_on(st); 1100 } 1101 if (UseConcMarkSweepGC) { 1102 ConcurrentMarkSweepThread::print_all_on(st); 1103 } 1104 #endif // INCLUDE_ALL_GCS 1105 } 1106 1107 void GenCollectedHeap::print_on_error(outputStream* st) const { 1108 this->CollectedHeap::print_on_error(st); 1109 1110 #if INCLUDE_ALL_GCS 1111 if (UseConcMarkSweepGC) { 1112 st->cr(); 1113 CMSCollector::print_on_error(st); 1114 } 1115 #endif // INCLUDE_ALL_GCS 1116 } 1117 1118 void GenCollectedHeap::print_tracing_info() const { 1119 if (TraceYoungGenTime) { 1120 get_gen(0)->print_summary_info(); 1121 } 1122 if (TraceOldGenTime) { 1123 get_gen(1)->print_summary_info(); 1124 } 1125 } 1126 1127 void GenCollectedHeap::print_heap_change(size_t prev_used) const { 1128 if (PrintGCDetails && Verbose) { 1129 gclog_or_tty->print(" " SIZE_FORMAT 1130 "->" SIZE_FORMAT 1131 "(" SIZE_FORMAT ")", 1132 prev_used, used(), capacity()); 1133 } else { 1134 gclog_or_tty->print(" " SIZE_FORMAT "K" 1135 "->" SIZE_FORMAT "K" 1136 "(" SIZE_FORMAT "K)", 1137 prev_used / K, used() / K, capacity() / K); 1138 } 1139 } 1140 1141 class GenGCPrologueClosure: public GenCollectedHeap::GenClosure { 1142 private: 1143 bool _full; 1144 public: 1145 void do_generation(Generation* gen) { 1146 gen->gc_prologue(_full); 1147 } 1148 GenGCPrologueClosure(bool full) : _full(full) {}; 1149 }; 1150 1151 void GenCollectedHeap::gc_prologue(bool full) { 1152 assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer"); 1153 1154 always_do_update_barrier = false; 1155 // Fill TLAB's and such 1156 CollectedHeap::accumulate_statistics_all_tlabs(); 1157 ensure_parsability(true); // retire TLABs 1158 1159 // Walk generations 1160 GenGCPrologueClosure blk(full); 1161 generation_iterate(&blk, false); // not old-to-young. 1162 }; 1163 1164 class GenGCEpilogueClosure: public GenCollectedHeap::GenClosure { 1165 private: 1166 bool _full; 1167 public: 1168 void do_generation(Generation* gen) { 1169 gen->gc_epilogue(_full); 1170 } 1171 GenGCEpilogueClosure(bool full) : _full(full) {}; 1172 }; 1173 1174 void GenCollectedHeap::gc_epilogue(bool full) { 1175 #ifdef COMPILER2 1176 assert(DerivedPointerTable::is_empty(), "derived pointer present"); 1177 size_t actual_gap = pointer_delta((HeapWord*) (max_uintx-3), *(end_addr())); 1178 guarantee(actual_gap > (size_t)FastAllocateSizeLimit, "inline allocation wraps"); 1179 #endif /* COMPILER2 */ 1180 1181 resize_all_tlabs(); 1182 1183 GenGCEpilogueClosure blk(full); 1184 generation_iterate(&blk, false); // not old-to-young. 1185 1186 if (!CleanChunkPoolAsync) { 1187 Chunk::clean_chunk_pool(); 1188 } 1189 1190 MetaspaceCounters::update_performance_counters(); 1191 CompressedClassSpaceCounters::update_performance_counters(); 1192 1193 always_do_update_barrier = UseConcMarkSweepGC; 1194 }; 1195 1196 #ifndef PRODUCT 1197 class GenGCSaveTopsBeforeGCClosure: public GenCollectedHeap::GenClosure { 1198 private: 1199 public: 1200 void do_generation(Generation* gen) { 1201 gen->record_spaces_top(); 1202 } 1203 }; 1204 1205 void GenCollectedHeap::record_gen_tops_before_GC() { 1206 if (ZapUnusedHeapArea) { 1207 GenGCSaveTopsBeforeGCClosure blk; 1208 generation_iterate(&blk, false); // not old-to-young. 1209 } 1210 } 1211 #endif // not PRODUCT 1212 1213 class GenEnsureParsabilityClosure: public GenCollectedHeap::GenClosure { 1214 public: 1215 void do_generation(Generation* gen) { 1216 gen->ensure_parsability(); 1217 } 1218 }; 1219 1220 void GenCollectedHeap::ensure_parsability(bool retire_tlabs) { 1221 CollectedHeap::ensure_parsability(retire_tlabs); 1222 GenEnsureParsabilityClosure ep_cl; 1223 generation_iterate(&ep_cl, false); 1224 } 1225 1226 oop GenCollectedHeap::handle_failed_promotion(Generation* old_gen, 1227 oop obj, 1228 size_t obj_size) { 1229 guarantee(old_gen->level() == 1, "We only get here with an old generation"); 1230 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in"); 1231 HeapWord* result = NULL; 1232 1233 result = old_gen->expand_and_allocate(obj_size, false); 1234 1235 if (result != NULL) { 1236 Copy::aligned_disjoint_words((HeapWord*)obj, result, obj_size); 1237 } 1238 return oop(result); 1239 } 1240 1241 class GenTimeOfLastGCClosure: public GenCollectedHeap::GenClosure { 1242 jlong _time; // in ms 1243 jlong _now; // in ms 1244 1245 public: 1246 GenTimeOfLastGCClosure(jlong now) : _time(now), _now(now) { } 1247 1248 jlong time() { return _time; } 1249 1250 void do_generation(Generation* gen) { 1251 _time = MIN2(_time, gen->time_of_last_gc(_now)); 1252 } 1253 }; 1254 1255 jlong GenCollectedHeap::millis_since_last_gc() { 1256 // We need a monotonically non-decreasing time in ms but 1257 // os::javaTimeMillis() does not guarantee monotonicity. 1258 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 1259 GenTimeOfLastGCClosure tolgc_cl(now); 1260 // iterate over generations getting the oldest 1261 // time that a generation was collected 1262 generation_iterate(&tolgc_cl, false); 1263 1264 // javaTimeNanos() is guaranteed to be monotonically non-decreasing 1265 // provided the underlying platform provides such a time source 1266 // (and it is bug free). So we still have to guard against getting 1267 // back a time later than 'now'. 1268 jlong retVal = now - tolgc_cl.time(); 1269 if (retVal < 0) { 1270 NOT_PRODUCT(warning("time warp: "INT64_FORMAT, (int64_t) retVal);) 1271 return 0; 1272 } 1273 return retVal; 1274 }