1 /*
   2  * Copyright (c) 2001, 2019, 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 "aot/aotLoader.hpp"
  27 #include "classfile/classLoaderDataGraph.hpp"
  28 #include "classfile/stringTable.hpp"
  29 #include "classfile/symbolTable.hpp"
  30 #include "classfile/systemDictionary.hpp"
  31 #include "code/codeCache.hpp"
  32 #include "gc/parallel/parallelScavengeHeap.hpp"
  33 #include "gc/parallel/psAdaptiveSizePolicy.hpp"
  34 #include "gc/parallel/psMarkSweep.hpp"
  35 #include "gc/parallel/psMarkSweepDecorator.hpp"
  36 #include "gc/parallel/psOldGen.hpp"
  37 #include "gc/parallel/psScavenge.hpp"
  38 #include "gc/parallel/psYoungGen.hpp"
  39 #include "gc/serial/markSweep.hpp"
  40 #include "gc/shared/gcCause.hpp"
  41 #include "gc/shared/gcHeapSummary.hpp"
  42 #include "gc/shared/gcId.hpp"
  43 #include "gc/shared/gcLocker.hpp"
  44 #include "gc/shared/gcTimer.hpp"
  45 #include "gc/shared/gcTrace.hpp"
  46 #include "gc/shared/gcTraceTime.inline.hpp"
  47 #include "gc/shared/isGCActiveMark.hpp"
  48 #include "gc/shared/referencePolicy.hpp"
  49 #include "gc/shared/referenceProcessor.hpp"
  50 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
  51 #include "gc/shared/spaceDecorator.hpp"
  52 #include "gc/shared/weakProcessor.hpp"
  53 #include "logging/log.hpp"
  54 #include "oops/oop.inline.hpp"
  55 #include "runtime/biasedLocking.hpp"
  56 #include "runtime/flags/flagSetting.hpp"
  57 #include "runtime/handles.inline.hpp"
  58 #include "runtime/safepoint.hpp"
  59 #include "runtime/vmThread.hpp"
  60 #include "services/management.hpp"
  61 #include "services/memoryService.hpp"
  62 #include "utilities/align.hpp"
  63 #include "utilities/events.hpp"
  64 #include "utilities/stack.inline.hpp"
  65 #if INCLUDE_JVMCI
  66 #include "jvmci/jvmci.hpp"
  67 #endif
  68 
  69 elapsedTimer        PSMarkSweep::_accumulated_time;
  70 jlong               PSMarkSweep::_time_of_last_gc   = 0;
  71 CollectorCounters*  PSMarkSweep::_counters = NULL;
  72 
  73 SpanSubjectToDiscoveryClosure PSMarkSweep::_span_based_discoverer;
  74 
  75 void PSMarkSweep::initialize() {
  76   _span_based_discoverer.set_span(ParallelScavengeHeap::heap()->reserved_region());
  77   set_ref_processor(new ReferenceProcessor(&_span_based_discoverer));     // a vanilla ref proc
  78   _counters = new CollectorCounters("Serial full collection pauses", 1);
  79   MarkSweep::initialize();
  80 }
  81 
  82 // This method contains all heap specific policy for invoking mark sweep.
  83 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact
  84 // the heap. It will do nothing further. If we need to bail out for policy
  85 // reasons, scavenge before full gc, or any other specialized behavior, it
  86 // needs to be added here.
  87 //
  88 // Note that this method should only be called from the vm_thread while
  89 // at a safepoint!
  90 //
  91 // Note that the all_soft_refs_clear flag in the collector policy
  92 // may be true because this method can be called without intervening
  93 // activity.  For example when the heap space is tight and full measure
  94 // are being taken to free space.
  95 
  96 void PSMarkSweep::invoke(bool maximum_heap_compaction) {
  97   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
  98   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
  99   assert(!ParallelScavengeHeap::heap()->is_gc_active(), "not reentrant");
 100 
 101   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 102   GCCause::Cause gc_cause = heap->gc_cause();
 103   PSAdaptiveSizePolicy* policy = heap->size_policy();
 104   IsGCActiveMark mark;
 105 
 106   if (ScavengeBeforeFullGC) {
 107     PSScavenge::invoke_no_policy();
 108   }
 109 
 110   const bool clear_all_soft_refs =
 111     heap->soft_ref_policy()->should_clear_all_soft_refs();
 112 
 113   uint count = maximum_heap_compaction ? 1 : MarkSweepAlwaysCompactCount;
 114   UIntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);
 115   PSMarkSweep::invoke_no_policy(clear_all_soft_refs || maximum_heap_compaction);
 116 }
 117 
 118 // This method contains no policy. You should probably
 119 // be calling invoke() instead.
 120 bool PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
 121   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 122   assert(ref_processor() != NULL, "Sanity");
 123 
 124   if (GCLocker::check_active_before_gc()) {
 125     return false;
 126   }
 127 
 128   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 129   GCCause::Cause gc_cause = heap->gc_cause();
 130 
 131   GCIdMark gc_id_mark;
 132   _gc_timer->register_gc_start();
 133   _gc_tracer->report_gc_start(gc_cause, _gc_timer->gc_start());
 134 
 135   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 136 
 137   // The scope of casr should end after code that can change
 138   // CollectorPolicy::_should_clear_all_soft_refs.
 139   ClearedAllSoftRefs casr(clear_all_softrefs, heap->soft_ref_policy());
 140 
 141   PSYoungGen* young_gen = heap->young_gen();
 142   PSOldGen* old_gen = heap->old_gen();
 143 
 144   // Increment the invocation count
 145   heap->increment_total_collections(true /* full */);
 146 
 147   // Save information needed to minimize mangling
 148   heap->record_gen_tops_before_GC();
 149 
 150   // We need to track unique mark sweep invocations as well.
 151   _total_invocations++;
 152 
 153   heap->print_heap_before_gc();
 154   heap->trace_heap_before_gc(_gc_tracer);
 155 
 156   // Fill in TLABs
 157   heap->ensure_parsability(true);  // retire TLABs
 158 
 159   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
 160     HandleMark hm;  // Discard invalid handles created during verification
 161     Universe::verify("Before GC");
 162   }
 163 
 164   // Verify object start arrays
 165   if (VerifyObjectStartArray &&
 166       VerifyBeforeGC) {
 167     old_gen->verify_object_start_array();
 168   }
 169 
 170   // Filled in below to track the state of the young gen after the collection.
 171   bool eden_empty;
 172   bool survivors_empty;
 173   bool young_gen_empty;
 174 
 175   {
 176     HandleMark hm;
 177 
 178     GCTraceCPUTime tcpu;
 179     GCTraceTime(Info, gc) t("Pause Full", NULL, gc_cause, true);
 180 
 181     heap->pre_full_gc_dump(_gc_timer);
 182 
 183     TraceCollectorStats tcs(counters());
 184     TraceMemoryManagerStats tms(heap->old_gc_manager(),gc_cause);
 185 
 186     if (log_is_enabled(Debug, gc, heap, exit)) {
 187       accumulated_time()->start();
 188     }
 189 
 190     // Let the size policy know we're starting
 191     size_policy->major_collection_begin();
 192 
 193     BiasedLocking::preserve_marks();
 194 
 195     // Capture metadata size before collection for sizing.
 196     size_t metadata_prev_used = MetaspaceUtils::used_bytes();
 197 
 198     size_t old_gen_prev_used = old_gen->used_in_bytes();
 199     size_t young_gen_prev_used = young_gen->used_in_bytes();
 200 
 201     allocate_stacks();
 202 
 203 #if COMPILER2_OR_JVMCI
 204     DerivedPointerTable::clear();
 205 #endif
 206 
 207     ref_processor()->enable_discovery();
 208     ref_processor()->setup_policy(clear_all_softrefs);
 209 
 210     mark_sweep_phase1(clear_all_softrefs);
 211 
 212     mark_sweep_phase2();
 213 
 214 #if COMPILER2_OR_JVMCI
 215     // Don't add any more derived pointers during phase3
 216     assert(DerivedPointerTable::is_active(), "Sanity");
 217     DerivedPointerTable::set_active(false);
 218 #endif
 219 
 220     mark_sweep_phase3();
 221 
 222     mark_sweep_phase4();
 223 
 224     restore_marks();
 225 
 226     deallocate_stacks();
 227 
 228     if (ZapUnusedHeapArea) {
 229       // Do a complete mangle (top to end) because the usage for
 230       // scratch does not maintain a top pointer.
 231       young_gen->to_space()->mangle_unused_area_complete();
 232     }
 233 
 234     eden_empty = young_gen->eden_space()->is_empty();
 235     if (!eden_empty) {
 236       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
 237     }
 238 
 239     // Update heap occupancy information which is used as
 240     // input to soft ref clearing policy at the next gc.
 241     Universe::update_heap_info_at_gc();
 242 
 243     survivors_empty = young_gen->from_space()->is_empty() &&
 244                       young_gen->to_space()->is_empty();
 245     young_gen_empty = eden_empty && survivors_empty;
 246 
 247     PSCardTable* card_table = heap->card_table();
 248     MemRegion old_mr = heap->old_gen()->reserved();
 249     if (young_gen_empty) {
 250       card_table->clear(MemRegion(old_mr.start(), old_mr.end()));
 251     } else {
 252       card_table->invalidate(MemRegion(old_mr.start(), old_mr.end()));
 253     }
 254 
 255     // Delete metaspaces for unloaded class loaders and clean up loader_data graph
 256     ClassLoaderDataGraph::purge();
 257     MetaspaceUtils::verify_metrics();
 258 
 259     BiasedLocking::restore_marks();
 260     heap->prune_scavengable_nmethods();
 261     JvmtiExport::gc_epilogue();
 262 
 263 #if COMPILER2_OR_JVMCI
 264     DerivedPointerTable::update_pointers();
 265 #endif
 266 
 267     assert(!ref_processor()->discovery_enabled(), "Should have been disabled earlier");
 268 
 269     // Update time of last GC
 270     reset_millis_since_last_gc();
 271 
 272     // Let the size policy know we're done
 273     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
 274 
 275     if (UseAdaptiveSizePolicy) {
 276 
 277      log_debug(gc, ergo)("AdaptiveSizeStart: collection: %d ", heap->total_collections());
 278      log_trace(gc, ergo)("old_gen_capacity: " SIZE_FORMAT " young_gen_capacity: " SIZE_FORMAT,
 279                          old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
 280 
 281       // Don't check if the size_policy is ready here.  Let
 282       // the size_policy check that internally.
 283       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
 284           AdaptiveSizePolicy::should_update_promo_stats(gc_cause)) {
 285         // Swap the survivor spaces if from_space is empty. The
 286         // resize_young_gen() called below is normally used after
 287         // a successful young GC and swapping of survivor spaces;
 288         // otherwise, it will fail to resize the young gen with
 289         // the current implementation.
 290         if (young_gen->from_space()->is_empty()) {
 291           young_gen->from_space()->clear(SpaceDecorator::Mangle);
 292           young_gen->swap_spaces();
 293         }
 294 
 295         // Calculate optimal free space amounts
 296         assert(young_gen->max_size() >
 297           young_gen->from_space()->capacity_in_bytes() +
 298           young_gen->to_space()->capacity_in_bytes(),
 299           "Sizes of space in young gen are out of bounds");
 300 
 301         size_t young_live = young_gen->used_in_bytes();
 302         size_t eden_live = young_gen->eden_space()->used_in_bytes();
 303         size_t old_live = old_gen->used_in_bytes();
 304         size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
 305         size_t max_old_gen_size = old_gen->max_gen_size();
 306         size_t max_eden_size = young_gen->max_size() -
 307           young_gen->from_space()->capacity_in_bytes() -
 308           young_gen->to_space()->capacity_in_bytes();
 309 
 310         // Used for diagnostics
 311         size_policy->clear_generation_free_space_flags();
 312 
 313         size_policy->compute_generations_free_space(young_live,
 314                                                     eden_live,
 315                                                     old_live,
 316                                                     cur_eden,
 317                                                     max_old_gen_size,
 318                                                     max_eden_size,
 319                                                     true /* full gc*/);
 320 
 321         size_policy->check_gc_overhead_limit(eden_live,
 322                                              max_old_gen_size,
 323                                              max_eden_size,
 324                                              true /* full gc*/,
 325                                              gc_cause,
 326                                              heap->soft_ref_policy());
 327 
 328         size_policy->decay_supplemental_growth(true /* full gc*/);
 329 
 330         heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
 331 
 332         heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
 333                                size_policy->calculated_survivor_size_in_bytes());
 334       }
 335       log_debug(gc, ergo)("AdaptiveSizeStop: collection: %d ", heap->total_collections());
 336     }
 337 
 338     if (UsePerfData) {
 339       heap->gc_policy_counters()->update_counters();
 340       heap->gc_policy_counters()->update_old_capacity(
 341         old_gen->capacity_in_bytes());
 342       heap->gc_policy_counters()->update_young_capacity(
 343         young_gen->capacity_in_bytes());
 344     }
 345 
 346     heap->resize_all_tlabs();
 347 
 348     // We collected the heap, recalculate the metaspace capacity
 349     MetaspaceGC::compute_new_size();
 350 
 351     if (log_is_enabled(Debug, gc, heap, exit)) {
 352       accumulated_time()->stop();
 353     }
 354 
 355     young_gen->print_used_change(young_gen_prev_used);
 356     old_gen->print_used_change(old_gen_prev_used);
 357     MetaspaceUtils::print_metaspace_change(metadata_prev_used);
 358 
 359     // Track memory usage and detect low memory
 360     MemoryService::track_memory_usage();
 361     heap->update_counters();
 362 
 363     heap->post_full_gc_dump(_gc_timer);
 364   }
 365 
 366   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
 367     HandleMark hm;  // Discard invalid handles created during verification
 368     Universe::verify("After GC");
 369   }
 370 
 371   // Re-verify object start arrays
 372   if (VerifyObjectStartArray &&
 373       VerifyAfterGC) {
 374     old_gen->verify_object_start_array();
 375   }
 376 
 377   if (ZapUnusedHeapArea) {
 378     old_gen->object_space()->check_mangled_unused_area_complete();
 379   }
 380 
 381   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 382 
 383   heap->print_heap_after_gc();
 384   heap->trace_heap_after_gc(_gc_tracer);
 385 
 386 #ifdef TRACESPINNING
 387   ParallelTaskTerminator::print_termination_counts();
 388 #endif
 389 
 390   AdaptiveSizePolicyOutput::print(size_policy, heap->total_collections());
 391 
 392   _gc_timer->register_gc_end();
 393 
 394   _gc_tracer->report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
 395 
 396   return true;
 397 }
 398 
 399 bool PSMarkSweep::absorb_live_data_from_eden(PSAdaptiveSizePolicy* size_policy,
 400                                              PSYoungGen* young_gen,
 401                                              PSOldGen* old_gen) {
 402   MutableSpace* const eden_space = young_gen->eden_space();
 403   assert(!eden_space->is_empty(), "eden must be non-empty");
 404   assert(young_gen->virtual_space()->alignment() ==
 405          old_gen->virtual_space()->alignment(), "alignments do not match");
 406 
 407   if (!(UseAdaptiveSizePolicy && UseAdaptiveGCBoundary)) {
 408     return false;
 409   }
 410 
 411   // Both generations must be completely committed.
 412   if (young_gen->virtual_space()->uncommitted_size() != 0) {
 413     return false;
 414   }
 415   if (old_gen->virtual_space()->uncommitted_size() != 0) {
 416     return false;
 417   }
 418 
 419   // Figure out how much to take from eden.  Include the average amount promoted
 420   // in the total; otherwise the next young gen GC will simply bail out to a
 421   // full GC.
 422   const size_t alignment = old_gen->virtual_space()->alignment();
 423   const size_t eden_used = eden_space->used_in_bytes();
 424   const size_t promoted = (size_t)size_policy->avg_promoted()->padded_average();
 425   const size_t absorb_size = align_up(eden_used + promoted, alignment);
 426   const size_t eden_capacity = eden_space->capacity_in_bytes();
 427 
 428   if (absorb_size >= eden_capacity) {
 429     return false; // Must leave some space in eden.
 430   }
 431 
 432   const size_t new_young_size = young_gen->capacity_in_bytes() - absorb_size;
 433   if (new_young_size < young_gen->min_gen_size()) {
 434     return false; // Respect young gen minimum size.
 435   }
 436 
 437   log_trace(gc, ergo, heap)(" absorbing " SIZE_FORMAT "K:  "
 438                             "eden " SIZE_FORMAT "K->" SIZE_FORMAT "K "
 439                             "from " SIZE_FORMAT "K, to " SIZE_FORMAT "K "
 440                             "young_gen " SIZE_FORMAT "K->" SIZE_FORMAT "K ",
 441                             absorb_size / K,
 442                             eden_capacity / K, (eden_capacity - absorb_size) / K,
 443                             young_gen->from_space()->used_in_bytes() / K,
 444                             young_gen->to_space()->used_in_bytes() / K,
 445                             young_gen->capacity_in_bytes() / K, new_young_size / K);
 446 
 447   // Fill the unused part of the old gen.
 448   MutableSpace* const old_space = old_gen->object_space();
 449   HeapWord* const unused_start = old_space->top();
 450   size_t const unused_words = pointer_delta(old_space->end(), unused_start);
 451 
 452   if (unused_words > 0) {
 453     if (unused_words < CollectedHeap::min_fill_size()) {
 454       return false;  // If the old gen cannot be filled, must give up.
 455     }
 456     CollectedHeap::fill_with_objects(unused_start, unused_words);
 457   }
 458 
 459   // Take the live data from eden and set both top and end in the old gen to
 460   // eden top.  (Need to set end because reset_after_change() mangles the region
 461   // from end to virtual_space->high() in debug builds).
 462   HeapWord* const new_top = eden_space->top();
 463   old_gen->virtual_space()->expand_into(young_gen->virtual_space(),
 464                                         absorb_size);
 465   young_gen->reset_after_change();
 466   old_space->set_top(new_top);
 467   old_space->set_end(new_top);
 468   old_gen->reset_after_change();
 469 
 470   // Update the object start array for the filler object and the data from eden.
 471   ObjectStartArray* const start_array = old_gen->start_array();
 472   for (HeapWord* p = unused_start; p < new_top; p += oop(p)->size()) {
 473     start_array->allocate_block(p);
 474   }
 475 
 476   // Could update the promoted average here, but it is not typically updated at
 477   // full GCs and the value to use is unclear.  Something like
 478   //
 479   // cur_promoted_avg + absorb_size / number_of_scavenges_since_last_full_gc.
 480 
 481   size_policy->set_bytes_absorbed_from_eden(absorb_size);
 482   return true;
 483 }
 484 
 485 void PSMarkSweep::allocate_stacks() {
 486   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 487   PSYoungGen* young_gen = heap->young_gen();
 488 
 489   MutableSpace* to_space = young_gen->to_space();
 490   _preserved_marks = (PreservedMark*)to_space->top();
 491   _preserved_count = 0;
 492 
 493   // We want to calculate the size in bytes first.
 494   _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));
 495   // Now divide by the size of a PreservedMark
 496   _preserved_count_max /= sizeof(PreservedMark);
 497 }
 498 
 499 
 500 void PSMarkSweep::deallocate_stacks() {
 501   _preserved_mark_stack.clear(true);
 502   _preserved_oop_stack.clear(true);
 503   _marking_stack.clear();
 504   _objarray_stack.clear(true);
 505 }
 506 
 507 void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 508   // Recursively traverse all live objects and mark them
 509   GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
 510 
 511   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 512 
 513   // Need to clear claim bits before the tracing starts.
 514   ClassLoaderDataGraph::clear_claimed_marks();
 515 
 516   // General strong roots.
 517   {
 518     ParallelScavengeHeap::ParStrongRootsScope psrs;
 519     Universe::oops_do(mark_and_push_closure());
 520     JNIHandles::oops_do(mark_and_push_closure());   // Global (strong) JNI handles
 521     MarkingCodeBlobClosure each_active_code_blob(mark_and_push_closure(), !CodeBlobToOopClosure::FixRelocations);
 522     Threads::oops_do(mark_and_push_closure(), &each_active_code_blob);
 523     ObjectSynchronizer::oops_do(mark_and_push_closure());
 524     Management::oops_do(mark_and_push_closure());
 525     JvmtiExport::oops_do(mark_and_push_closure());
 526     SystemDictionary::oops_do(mark_and_push_closure());
 527     ClassLoaderDataGraph::always_strong_cld_do(follow_cld_closure());
 528     // Do not treat nmethods as strong roots for mark/sweep, since we can unload them.
 529     //ScavengableNMethods::scavengable_nmethods_do(CodeBlobToOopClosure(mark_and_push_closure()));
 530     AOTLoader::oops_do(mark_and_push_closure());
 531   }
 532 
 533   // Flush marking stack.
 534   follow_stack();
 535 
 536   // Process reference objects found during marking
 537   {
 538     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer);
 539 
 540     ref_processor()->setup_policy(clear_all_softrefs);
 541     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues());
 542     const ReferenceProcessorStats& stats =
 543       ref_processor()->process_discovered_references(
 544         is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL, &pt);
 545     gc_tracer()->report_gc_reference_stats(stats);
 546     pt.print_all_references();
 547   }
 548 
 549   // This is the point where the entire marking should have completed.
 550   assert(_marking_stack.is_empty(), "Marking should have completed");
 551 
 552   {
 553     GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer);
 554     WeakProcessor::weak_oops_do(is_alive_closure(), &do_nothing_cl);
 555   }
 556 
 557   {
 558     GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer);
 559 
 560     // Unload classes and purge the SystemDictionary.
 561     bool purged_class = SystemDictionary::do_unloading(_gc_timer);
 562 
 563     // Unload nmethods.
 564     CodeCache::do_unloading(is_alive_closure(), purged_class);
 565 
 566     // Prune dead klasses from subklass/sibling/implementor lists.
 567     Klass::clean_weak_klass_links(purged_class);
 568 
 569     // Clean JVMCI metadata handles.
 570     JVMCI_ONLY(JVMCI::do_unloading(is_alive_closure(), purged_class));
 571   }
 572 
 573   _gc_tracer->report_object_count_after_gc(is_alive_closure());
 574 }
 575 
 576 
 577 void PSMarkSweep::mark_sweep_phase2() {
 578   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
 579 
 580   // Now all live objects are marked, compute the new object addresses.
 581 
 582   // It is not required that we traverse spaces in the same order in
 583   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 584   // tracking expects us to do so. See comment under phase4.
 585 
 586   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 587   PSOldGen* old_gen = heap->old_gen();
 588 
 589   // Begin compacting into the old gen
 590   PSMarkSweepDecorator::set_destination_decorator_tenured();
 591 
 592   // This will also compact the young gen spaces.
 593   old_gen->precompact();
 594 }
 595 
 596 void PSMarkSweep::mark_sweep_phase3() {
 597   // Adjust the pointers to reflect the new locations
 598   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", _gc_timer);
 599 
 600   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 601   PSYoungGen* young_gen = heap->young_gen();
 602   PSOldGen* old_gen = heap->old_gen();
 603 
 604   // Need to clear claim bits before the tracing starts.
 605   ClassLoaderDataGraph::clear_claimed_marks();
 606 
 607   // General strong roots.
 608   Universe::oops_do(adjust_pointer_closure());
 609   JNIHandles::oops_do(adjust_pointer_closure());   // Global (strong) JNI handles
 610   Threads::oops_do(adjust_pointer_closure(), NULL);
 611   ObjectSynchronizer::oops_do(adjust_pointer_closure());
 612   Management::oops_do(adjust_pointer_closure());
 613   JvmtiExport::oops_do(adjust_pointer_closure());
 614   SystemDictionary::oops_do(adjust_pointer_closure());
 615   ClassLoaderDataGraph::cld_do(adjust_cld_closure());
 616 
 617   // Now adjust pointers in remaining weak roots.  (All of which should
 618   // have been cleared if they pointed to non-surviving objects.)
 619   // Global (weak) JNI handles
 620   WeakProcessor::oops_do(adjust_pointer_closure());
 621 
 622   CodeBlobToOopClosure adjust_from_blobs(adjust_pointer_closure(), CodeBlobToOopClosure::FixRelocations);
 623   CodeCache::blobs_do(&adjust_from_blobs);
 624   AOTLoader::oops_do(adjust_pointer_closure());
 625   ref_processor()->weak_oops_do(adjust_pointer_closure());
 626   PSScavenge::reference_processor()->weak_oops_do(adjust_pointer_closure());
 627 
 628   adjust_marks();
 629 
 630   young_gen->adjust_pointers();
 631   old_gen->adjust_pointers();
 632 }
 633 
 634 void PSMarkSweep::mark_sweep_phase4() {
 635   EventMark m("4 compact heap");
 636   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
 637 
 638   // All pointers are now adjusted, move objects accordingly
 639 
 640   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 641   PSYoungGen* young_gen = heap->young_gen();
 642   PSOldGen* old_gen = heap->old_gen();
 643 
 644   old_gen->compact();
 645   young_gen->compact();
 646 }
 647 
 648 jlong PSMarkSweep::millis_since_last_gc() {
 649   // We need a monotonically non-decreasing time in ms but
 650   // os::javaTimeMillis() does not guarantee monotonicity.
 651   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 652   jlong ret_val = now - _time_of_last_gc;
 653   // XXX See note in genCollectedHeap::millis_since_last_gc().
 654   if (ret_val < 0) {
 655     NOT_PRODUCT(log_warning(gc)("time warp: " JLONG_FORMAT, ret_val);)
 656     return 0;
 657   }
 658   return ret_val;
 659 }
 660 
 661 void PSMarkSweep::reset_millis_since_last_gc() {
 662   // We need a monotonically non-decreasing time in ms but
 663   // os::javaTimeMillis() does not guarantee monotonicity.
 664   _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 665 }