1 /*
   2  * Copyright (c) 2001, 2018, 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/stringTable.hpp"
  28 #include "classfile/symbolTable.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "gc/parallel/parallelScavengeHeap.hpp"
  32 #include "gc/parallel/psAdaptiveSizePolicy.hpp"
  33 #include "gc/parallel/psMarkSweep.hpp"
  34 #include "gc/parallel/psMarkSweepDecorator.hpp"
  35 #include "gc/parallel/psOldGen.hpp"
  36 #include "gc/parallel/psScavenge.hpp"
  37 #include "gc/parallel/psYoungGen.hpp"
  38 #include "gc/serial/markSweep.hpp"
  39 #include "gc/shared/gcCause.hpp"
  40 #include "gc/shared/gcHeapSummary.hpp"
  41 #include "gc/shared/gcId.hpp"
  42 #include "gc/shared/gcLocker.hpp"
  43 #include "gc/shared/gcTimer.hpp"
  44 #include "gc/shared/gcTrace.hpp"
  45 #include "gc/shared/gcTraceTime.inline.hpp"
  46 #include "gc/shared/isGCActiveMark.hpp"
  47 #include "gc/shared/referencePolicy.hpp"
  48 #include "gc/shared/referenceProcessor.hpp"
  49 #include "gc/shared/spaceDecorator.hpp"
  50 #include "gc/shared/weakProcessor.hpp"
  51 #include "logging/log.hpp"
  52 #include "oops/oop.inline.hpp"
  53 #include "runtime/biasedLocking.hpp"
  54 #include "runtime/flags/flagSetting.hpp"
  55 #include "runtime/handles.inline.hpp"
  56 #include "runtime/safepoint.hpp"
  57 #include "runtime/vmThread.hpp"
  58 #include "services/management.hpp"
  59 #include "services/memoryService.hpp"
  60 #include "utilities/align.hpp"
  61 #include "utilities/events.hpp"
  62 #include "utilities/stack.inline.hpp"
  63 
  64 elapsedTimer        PSMarkSweep::_accumulated_time;
  65 jlong               PSMarkSweep::_time_of_last_gc   = 0;
  66 CollectorCounters*  PSMarkSweep::_counters = NULL;
  67 
  68 SpanSubjectToDiscoveryClosure PSMarkSweep::_span_based_discoverer;
  69 
  70 void PSMarkSweep::initialize() {
  71   _span_based_discoverer.set_span(ParallelScavengeHeap::heap()->reserved_region());
  72   set_ref_processor(new ReferenceProcessor(&_span_based_discoverer));     // a vanilla ref proc
  73   _counters = new CollectorCounters("PSMarkSweep", 1);
  74   MarkSweep::initialize();
  75 }
  76 
  77 // This method contains all heap specific policy for invoking mark sweep.
  78 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact
  79 // the heap. It will do nothing further. If we need to bail out for policy
  80 // reasons, scavenge before full gc, or any other specialized behavior, it
  81 // needs to be added here.
  82 //
  83 // Note that this method should only be called from the vm_thread while
  84 // at a safepoint!
  85 //
  86 // Note that the all_soft_refs_clear flag in the collector policy
  87 // may be true because this method can be called without intervening
  88 // activity.  For example when the heap space is tight and full measure
  89 // are being taken to free space.
  90 
  91 void PSMarkSweep::invoke(bool maximum_heap_compaction) {
  92   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
  93   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
  94   assert(!ParallelScavengeHeap::heap()->is_gc_active(), "not reentrant");
  95 
  96   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
  97   GCCause::Cause gc_cause = heap->gc_cause();
  98   PSAdaptiveSizePolicy* policy = heap->size_policy();
  99   IsGCActiveMark mark;
 100 
 101   if (ScavengeBeforeFullGC) {
 102     PSScavenge::invoke_no_policy();
 103   }
 104 
 105   const bool clear_all_soft_refs =
 106     heap->soft_ref_policy()->should_clear_all_soft_refs();
 107 
 108   uint count = maximum_heap_compaction ? 1 : MarkSweepAlwaysCompactCount;
 109   UIntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);
 110   PSMarkSweep::invoke_no_policy(clear_all_soft_refs || maximum_heap_compaction);
 111 }
 112 
 113 // This method contains no policy. You should probably
 114 // be calling invoke() instead.
 115 bool PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
 116   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 117   assert(ref_processor() != NULL, "Sanity");
 118 
 119   if (GCLocker::check_active_before_gc()) {
 120     return false;
 121   }
 122 
 123   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 124   GCCause::Cause gc_cause = heap->gc_cause();
 125 
 126   GCIdMark gc_id_mark;
 127   _gc_timer->register_gc_start();
 128   _gc_tracer->report_gc_start(gc_cause, _gc_timer->gc_start());
 129 
 130   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 131 
 132   // The scope of casr should end after code that can change
 133   // CollectorPolicy::_should_clear_all_soft_refs.
 134   ClearedAllSoftRefs casr(clear_all_softrefs, heap->soft_ref_policy());
 135 
 136   PSYoungGen* young_gen = heap->young_gen();
 137   PSOldGen* old_gen = heap->old_gen();
 138 
 139   // Increment the invocation count
 140   heap->increment_total_collections(true /* full */);
 141 
 142   // Save information needed to minimize mangling
 143   heap->record_gen_tops_before_GC();
 144 
 145   // We need to track unique mark sweep invocations as well.
 146   _total_invocations++;
 147 
 148   heap->print_heap_before_gc();
 149   heap->trace_heap_before_gc(_gc_tracer);
 150 
 151   // Fill in TLABs
 152   heap->accumulate_statistics_all_tlabs();
 153   heap->ensure_parsability(true);  // retire TLABs
 154 
 155   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
 156     HandleMark hm;  // Discard invalid handles created during verification
 157     Universe::verify("Before GC");
 158   }
 159 
 160   // Verify object start arrays
 161   if (VerifyObjectStartArray &&
 162       VerifyBeforeGC) {
 163     old_gen->verify_object_start_array();
 164   }
 165 
 166   // Filled in below to track the state of the young gen after the collection.
 167   bool eden_empty;
 168   bool survivors_empty;
 169   bool young_gen_empty;
 170 
 171   {
 172     HandleMark hm;
 173 
 174     GCTraceCPUTime tcpu;
 175     GCTraceTime(Info, gc) t("Pause Full", NULL, gc_cause, true);
 176 
 177     heap->pre_full_gc_dump(_gc_timer);
 178 
 179     TraceCollectorStats tcs(counters());
 180     TraceMemoryManagerStats tms(heap->old_gc_manager(),gc_cause);
 181 
 182     if (log_is_enabled(Debug, gc, heap, exit)) {
 183       accumulated_time()->start();
 184     }
 185 
 186     // Let the size policy know we're starting
 187     size_policy->major_collection_begin();
 188 
 189     CodeCache::gc_prologue();
 190     BiasedLocking::preserve_marks();
 191 
 192     // Capture metadata size before collection for sizing.
 193     size_t metadata_prev_used = MetaspaceUtils::used_bytes();
 194 
 195     size_t old_gen_prev_used = old_gen->used_in_bytes();
 196     size_t young_gen_prev_used = young_gen->used_in_bytes();
 197 
 198     allocate_stacks();
 199 
 200 #if COMPILER2_OR_JVMCI
 201     DerivedPointerTable::clear();
 202 #endif
 203 
 204     ref_processor()->enable_discovery();
 205     ref_processor()->setup_policy(clear_all_softrefs);
 206 
 207     mark_sweep_phase1(clear_all_softrefs);
 208 
 209     mark_sweep_phase2();
 210 
 211 #if COMPILER2_OR_JVMCI
 212     // Don't add any more derived pointers during phase3
 213     assert(DerivedPointerTable::is_active(), "Sanity");
 214     DerivedPointerTable::set_active(false);
 215 #endif
 216 
 217     mark_sweep_phase3();
 218 
 219     mark_sweep_phase4();
 220 
 221     restore_marks();
 222 
 223     deallocate_stacks();
 224 
 225     if (ZapUnusedHeapArea) {
 226       // Do a complete mangle (top to end) because the usage for
 227       // scratch does not maintain a top pointer.
 228       young_gen->to_space()->mangle_unused_area_complete();
 229     }
 230 
 231     eden_empty = young_gen->eden_space()->is_empty();
 232     if (!eden_empty) {
 233       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
 234     }
 235 
 236     // Update heap occupancy information which is used as
 237     // input to soft ref clearing policy at the next gc.
 238     Universe::update_heap_info_at_gc();
 239 
 240     survivors_empty = young_gen->from_space()->is_empty() &&
 241                       young_gen->to_space()->is_empty();
 242     young_gen_empty = eden_empty && survivors_empty;
 243 
 244     PSCardTable* card_table = heap->card_table();
 245     MemRegion old_mr = heap->old_gen()->reserved();
 246     if (young_gen_empty) {
 247       card_table->clear(MemRegion(old_mr.start(), old_mr.end()));
 248     } else {
 249       card_table->invalidate(MemRegion(old_mr.start(), old_mr.end()));
 250     }
 251 
 252     // Delete metaspaces for unloaded class loaders and clean up loader_data graph
 253     ClassLoaderDataGraph::purge();
 254     MetaspaceUtils::verify_metrics();
 255 
 256     BiasedLocking::restore_marks();
 257     CodeCache::gc_epilogue();
 258     JvmtiExport::gc_epilogue();
 259 
 260 #if COMPILER2_OR_JVMCI
 261     DerivedPointerTable::update_pointers();
 262 #endif
 263 
 264     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->num_queues());
 265 
 266     ref_processor()->enqueue_discovered_references(NULL, &pt);
 267 
 268     pt.print_enqueue_phase();
 269 
 270     // Update time of last GC
 271     reset_millis_since_last_gc();
 272 
 273     // Let the size policy know we're done
 274     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
 275 
 276     if (UseAdaptiveSizePolicy) {
 277 
 278      log_debug(gc, ergo)("AdaptiveSizeStart: collection: %d ", heap->total_collections());
 279      log_trace(gc, ergo)("old_gen_capacity: " SIZE_FORMAT " young_gen_capacity: " SIZE_FORMAT,
 280                          old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
 281 
 282       // Don't check if the size_policy is ready here.  Let
 283       // the size_policy check that internally.
 284       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
 285           AdaptiveSizePolicy::should_update_promo_stats(gc_cause)) {
 286         // Swap the survivor spaces if from_space is empty. The
 287         // resize_young_gen() called below is normally used after
 288         // a successful young GC and swapping of survivor spaces;
 289         // otherwise, it will fail to resize the young gen with
 290         // the current implementation.
 291         if (young_gen->from_space()->is_empty()) {
 292           young_gen->from_space()->clear(SpaceDecorator::Mangle);
 293           young_gen->swap_spaces();
 294         }
 295 
 296         // Calculate optimal free space amounts
 297         assert(young_gen->max_size() >
 298           young_gen->from_space()->capacity_in_bytes() +
 299           young_gen->to_space()->capacity_in_bytes(),
 300           "Sizes of space in young gen are out-of-bounds");
 301 
 302         size_t young_live = young_gen->used_in_bytes();
 303         size_t eden_live = young_gen->eden_space()->used_in_bytes();
 304         size_t old_live = old_gen->used_in_bytes();
 305         size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
 306         size_t max_old_gen_size = old_gen->max_gen_size();
 307         size_t max_eden_size = young_gen->max_size() -
 308           young_gen->from_space()->capacity_in_bytes() -
 309           young_gen->to_space()->capacity_in_bytes();
 310 
 311         // Used for diagnostics
 312         size_policy->clear_generation_free_space_flags();
 313 
 314         size_policy->compute_generations_free_space(young_live,
 315                                                     eden_live,
 316                                                     old_live,
 317                                                     cur_eden,
 318                                                     max_old_gen_size,
 319                                                     max_eden_size,
 320                                                     true /* full gc*/);
 321 
 322         size_policy->check_gc_overhead_limit(young_live,
 323                                              eden_live,
 324                                              max_old_gen_size,
 325                                              max_eden_size,
 326                                              true /* full gc*/,
 327                                              gc_cause,
 328                                              heap->soft_ref_policy());
 329 
 330         size_policy->decay_supplemental_growth(true /* full gc*/);
 331 
 332         heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
 333 
 334         heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
 335                                size_policy->calculated_survivor_size_in_bytes());
 336       }
 337       log_debug(gc, ergo)("AdaptiveSizeStop: collection: %d ", heap->total_collections());
 338     }
 339 
 340     if (UsePerfData) {
 341       heap->gc_policy_counters()->update_counters();
 342       heap->gc_policy_counters()->update_old_capacity(
 343         old_gen->capacity_in_bytes());
 344       heap->gc_policy_counters()->update_young_capacity(
 345         young_gen->capacity_in_bytes());
 346     }
 347 
 348     heap->resize_all_tlabs();
 349 
 350     // We collected the heap, recalculate the metaspace capacity
 351     MetaspaceGC::compute_new_size();
 352 
 353     if (log_is_enabled(Debug, gc, heap, exit)) {
 354       accumulated_time()->stop();
 355     }
 356 
 357     young_gen->print_used_change(young_gen_prev_used);
 358     old_gen->print_used_change(old_gen_prev_used);
 359     MetaspaceUtils::print_metaspace_change(metadata_prev_used);
 360 
 361     // Track memory usage and detect low memory
 362     MemoryService::track_memory_usage();
 363     heap->update_counters();
 364 
 365     heap->post_full_gc_dump(_gc_timer);
 366   }
 367 
 368   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
 369     HandleMark hm;  // Discard invalid handles created during verification
 370     Universe::verify("After GC");
 371   }
 372 
 373   // Re-verify object start arrays
 374   if (VerifyObjectStartArray &&
 375       VerifyAfterGC) {
 376     old_gen->verify_object_start_array();
 377   }
 378 
 379   if (ZapUnusedHeapArea) {
 380     old_gen->object_space()->check_mangled_unused_area_complete();
 381   }
 382 
 383   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 384 
 385   heap->print_heap_after_gc();
 386   heap->trace_heap_after_gc(_gc_tracer);
 387 
 388 #ifdef TRACESPINNING
 389   ParallelTaskTerminator::print_termination_counts();
 390 #endif
 391 
 392   AdaptiveSizePolicyOutput::print(size_policy, heap->total_collections());
 393 
 394   _gc_timer->register_gc_end();
 395 
 396   _gc_tracer->report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
 397 
 398   return true;
 399 }
 400 
 401 bool PSMarkSweep::absorb_live_data_from_eden(PSAdaptiveSizePolicy* size_policy,
 402                                              PSYoungGen* young_gen,
 403                                              PSOldGen* old_gen) {
 404   MutableSpace* const eden_space = young_gen->eden_space();
 405   assert(!eden_space->is_empty(), "eden must be non-empty");
 406   assert(young_gen->virtual_space()->alignment() ==
 407          old_gen->virtual_space()->alignment(), "alignments do not match");
 408 
 409   if (!(UseAdaptiveSizePolicy && UseAdaptiveGCBoundary)) {
 410     return false;
 411   }
 412 
 413   // Both generations must be completely committed.
 414   if (young_gen->virtual_space()->uncommitted_size() != 0) {
 415     return false;
 416   }
 417   if (old_gen->virtual_space()->uncommitted_size() != 0) {
 418     return false;
 419   }
 420 
 421   // Figure out how much to take from eden.  Include the average amount promoted
 422   // in the total; otherwise the next young gen GC will simply bail out to a
 423   // full GC.
 424   const size_t alignment = old_gen->virtual_space()->alignment();
 425   const size_t eden_used = eden_space->used_in_bytes();
 426   const size_t promoted = (size_t)size_policy->avg_promoted()->padded_average();
 427   const size_t absorb_size = align_up(eden_used + promoted, alignment);
 428   const size_t eden_capacity = eden_space->capacity_in_bytes();
 429 
 430   if (absorb_size >= eden_capacity) {
 431     return false; // Must leave some space in eden.
 432   }
 433 
 434   const size_t new_young_size = young_gen->capacity_in_bytes() - absorb_size;
 435   if (new_young_size < young_gen->min_gen_size()) {
 436     return false; // Respect young gen minimum size.
 437   }
 438 
 439   log_trace(heap, ergo)(" absorbing " SIZE_FORMAT "K:  "
 440                         "eden " SIZE_FORMAT "K->" SIZE_FORMAT "K "
 441                         "from " SIZE_FORMAT "K, to " SIZE_FORMAT "K "
 442                         "young_gen " SIZE_FORMAT "K->" SIZE_FORMAT "K ",
 443                         absorb_size / K,
 444                         eden_capacity / K, (eden_capacity - absorb_size) / K,
 445                         young_gen->from_space()->used_in_bytes() / K,
 446                         young_gen->to_space()->used_in_bytes() / K,
 447                         young_gen->capacity_in_bytes() / K, new_young_size / K);
 448 
 449   // Fill the unused part of the old gen.
 450   MutableSpace* const old_space = old_gen->object_space();
 451   HeapWord* const unused_start = old_space->top();
 452   size_t const unused_words = pointer_delta(old_space->end(), unused_start);
 453 
 454   if (unused_words > 0) {
 455     if (unused_words < CollectedHeap::min_fill_size()) {
 456       return false;  // If the old gen cannot be filled, must give up.
 457     }
 458     CollectedHeap::fill_with_objects(unused_start, unused_words);
 459   }
 460 
 461   // Take the live data from eden and set both top and end in the old gen to
 462   // eden top.  (Need to set end because reset_after_change() mangles the region
 463   // from end to virtual_space->high() in debug builds).
 464   HeapWord* const new_top = eden_space->top();
 465   old_gen->virtual_space()->expand_into(young_gen->virtual_space(),
 466                                         absorb_size);
 467   young_gen->reset_after_change();
 468   old_space->set_top(new_top);
 469   old_space->set_end(new_top);
 470   old_gen->reset_after_change();
 471 
 472   // Update the object start array for the filler object and the data from eden.
 473   ObjectStartArray* const start_array = old_gen->start_array();
 474   for (HeapWord* p = unused_start; p < new_top; p += oop(p)->size()) {
 475     start_array->allocate_block(p);
 476   }
 477 
 478   // Could update the promoted average here, but it is not typically updated at
 479   // full GCs and the value to use is unclear.  Something like
 480   //
 481   // cur_promoted_avg + absorb_size / number_of_scavenges_since_last_full_gc.
 482 
 483   size_policy->set_bytes_absorbed_from_eden(absorb_size);
 484   return true;
 485 }
 486 
 487 void PSMarkSweep::allocate_stacks() {
 488   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 489   PSYoungGen* young_gen = heap->young_gen();
 490 
 491   MutableSpace* to_space = young_gen->to_space();
 492   _preserved_marks = (PreservedMark*)to_space->top();
 493   _preserved_count = 0;
 494 
 495   // We want to calculate the size in bytes first.
 496   _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));
 497   // Now divide by the size of a PreservedMark
 498   _preserved_count_max /= sizeof(PreservedMark);
 499 }
 500 
 501 
 502 void PSMarkSweep::deallocate_stacks() {
 503   _preserved_mark_stack.clear(true);
 504   _preserved_oop_stack.clear(true);
 505   _marking_stack.clear();
 506   _objarray_stack.clear(true);
 507 }
 508 
 509 void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 510   // Recursively traverse all live objects and mark them
 511   GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
 512 
 513   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 514 
 515   // Need to clear claim bits before the tracing starts.
 516   ClassLoaderDataGraph::clear_claimed_marks();
 517 
 518   // General strong roots.
 519   {
 520     ParallelScavengeHeap::ParStrongRootsScope psrs;
 521     Universe::oops_do(mark_and_push_closure());
 522     JNIHandles::oops_do(mark_and_push_closure());   // Global (strong) JNI handles
 523     MarkingCodeBlobClosure each_active_code_blob(mark_and_push_closure(), !CodeBlobToOopClosure::FixRelocations);
 524     Threads::oops_do(mark_and_push_closure(), &each_active_code_blob);
 525     ObjectSynchronizer::oops_do(mark_and_push_closure());
 526     Management::oops_do(mark_and_push_closure());
 527     JvmtiExport::oops_do(mark_and_push_closure());
 528     SystemDictionary::always_strong_oops_do(mark_and_push_closure());
 529     ClassLoaderDataGraph::always_strong_cld_do(follow_cld_closure());
 530     // Do not treat nmethods as strong roots for mark/sweep, since we can unload them.
 531     //CodeCache::scavenge_root_nmethods_do(CodeBlobToOopClosure(mark_and_push_closure()));
 532     AOTLoader::oops_do(mark_and_push_closure());
 533   }
 534 
 535   // Flush marking stack.
 536   follow_stack();
 537 
 538   // Process reference objects found during marking
 539   {
 540     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer);
 541 
 542     ref_processor()->setup_policy(clear_all_softrefs);
 543     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->num_queues());
 544     const ReferenceProcessorStats& stats =
 545       ref_processor()->process_discovered_references(
 546         is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL, &pt);
 547     gc_tracer()->report_gc_reference_stats(stats);
 548     pt.print_all_references();
 549   }
 550 
 551   // This is the point where the entire marking should have completed.
 552   assert(_marking_stack.is_empty(), "Marking should have completed");
 553 
 554   {
 555     GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer);
 556     WeakProcessor::weak_oops_do(is_alive_closure(), &do_nothing_cl);
 557   }
 558 
 559   {
 560     GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer);
 561 
 562     // Unload classes and purge the SystemDictionary.
 563     bool purged_class = SystemDictionary::do_unloading(is_alive_closure(), _gc_timer);
 564 
 565     // Unload nmethods.
 566     CodeCache::do_unloading(is_alive_closure(), purged_class);
 567 
 568     // Prune dead klasses from subklass/sibling/implementor lists.
 569     Klass::clean_weak_klass_links(purged_class);
 570   }
 571 
 572   {
 573     GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer);
 574     // Delete entries for dead interned strings.
 575     StringTable::unlink(is_alive_closure());
 576   }
 577 
 578   {
 579     GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer);
 580     // Clean up unreferenced symbols in symbol table.
 581     SymbolTable::unlink();
 582   }
 583 
 584   _gc_tracer->report_object_count_after_gc(is_alive_closure());
 585 }
 586 
 587 
 588 void PSMarkSweep::mark_sweep_phase2() {
 589   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
 590 
 591   // Now all live objects are marked, compute the new object addresses.
 592 
 593   // It is not required that we traverse spaces in the same order in
 594   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 595   // tracking expects us to do so. See comment under phase4.
 596 
 597   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 598   PSOldGen* old_gen = heap->old_gen();
 599 
 600   // Begin compacting into the old gen
 601   PSMarkSweepDecorator::set_destination_decorator_tenured();
 602 
 603   // This will also compact the young gen spaces.
 604   old_gen->precompact();
 605 }
 606 
 607 void PSMarkSweep::mark_sweep_phase3() {
 608   // Adjust the pointers to reflect the new locations
 609   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", _gc_timer);
 610 
 611   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 612   PSYoungGen* young_gen = heap->young_gen();
 613   PSOldGen* old_gen = heap->old_gen();
 614 
 615   // Need to clear claim bits before the tracing starts.
 616   ClassLoaderDataGraph::clear_claimed_marks();
 617 
 618   // General strong roots.
 619   Universe::oops_do(adjust_pointer_closure());
 620   JNIHandles::oops_do(adjust_pointer_closure());   // Global (strong) JNI handles
 621   Threads::oops_do(adjust_pointer_closure(), NULL);
 622   ObjectSynchronizer::oops_do(adjust_pointer_closure());
 623   Management::oops_do(adjust_pointer_closure());
 624   JvmtiExport::oops_do(adjust_pointer_closure());
 625   SystemDictionary::oops_do(adjust_pointer_closure());
 626   ClassLoaderDataGraph::cld_do(adjust_cld_closure());
 627 
 628   // Now adjust pointers in remaining weak roots.  (All of which should
 629   // have been cleared if they pointed to non-surviving objects.)
 630   // Global (weak) JNI handles
 631   WeakProcessor::oops_do(adjust_pointer_closure());
 632 
 633   CodeBlobToOopClosure adjust_from_blobs(adjust_pointer_closure(), CodeBlobToOopClosure::FixRelocations);
 634   CodeCache::blobs_do(&adjust_from_blobs);
 635   AOTLoader::oops_do(adjust_pointer_closure());
 636   StringTable::oops_do(adjust_pointer_closure());
 637   ref_processor()->weak_oops_do(adjust_pointer_closure());
 638   PSScavenge::reference_processor()->weak_oops_do(adjust_pointer_closure());
 639 
 640   adjust_marks();
 641 
 642   young_gen->adjust_pointers();
 643   old_gen->adjust_pointers();
 644 }
 645 
 646 void PSMarkSweep::mark_sweep_phase4() {
 647   EventMark m("4 compact heap");
 648   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
 649 
 650   // All pointers are now adjusted, move objects accordingly
 651 
 652   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 653   PSYoungGen* young_gen = heap->young_gen();
 654   PSOldGen* old_gen = heap->old_gen();
 655 
 656   old_gen->compact();
 657   young_gen->compact();
 658 }
 659 
 660 jlong PSMarkSweep::millis_since_last_gc() {
 661   // We need a monotonically non-decreasing time in ms but
 662   // os::javaTimeMillis() does not guarantee monotonicity.
 663   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 664   jlong ret_val = now - _time_of_last_gc;
 665   // XXX See note in genCollectedHeap::millis_since_last_gc().
 666   if (ret_val < 0) {
 667     NOT_PRODUCT(log_warning(gc)("time warp: " JLONG_FORMAT, ret_val);)
 668     return 0;
 669   }
 670   return ret_val;
 671 }
 672 
 673 void PSMarkSweep::reset_millis_since_last_gc() {
 674   // We need a monotonically non-decreasing time in ms but
 675   // os::javaTimeMillis() does not guarantee monotonicity.
 676   _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 677 }