rev 47223 : [mq]: heapz8

   1 /*
   2  * Copyright (c) 2001, 2017, 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.
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  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.inline.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 "logging/log.hpp"
  51 #include "oops/oop.inline.hpp"
  52 #include "runtime/biasedLocking.hpp"

  53 #include "runtime/safepoint.hpp"
  54 #include "runtime/vmThread.hpp"
  55 #include "services/management.hpp"
  56 #include "services/memoryService.hpp"
  57 #include "utilities/align.hpp"
  58 #include "utilities/events.hpp"
  59 #include "utilities/stack.inline.hpp"
  60 
  61 elapsedTimer        PSMarkSweep::_accumulated_time;
  62 jlong               PSMarkSweep::_time_of_last_gc   = 0;
  63 CollectorCounters*  PSMarkSweep::_counters = NULL;
  64 
  65 void PSMarkSweep::initialize() {
  66   MemRegion mr = ParallelScavengeHeap::heap()->reserved_region();
  67   set_ref_processor(new ReferenceProcessor(mr));     // a vanilla ref proc
  68   _counters = new CollectorCounters("PSMarkSweep", 1);
  69 }
  70 
  71 // This method contains all heap specific policy for invoking mark sweep.
  72 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact
  73 // the heap. It will do nothing further. If we need to bail out for policy
  74 // reasons, scavenge before full gc, or any other specialized behavior, it
  75 // needs to be added here.
  76 //
  77 // Note that this method should only be called from the vm_thread while
  78 // at a safepoint!
  79 //
  80 // Note that the all_soft_refs_clear flag in the collector policy
  81 // may be true because this method can be called without intervening
  82 // activity.  For example when the heap space is tight and full measure
  83 // are being taken to free space.
  84 
  85 void PSMarkSweep::invoke(bool maximum_heap_compaction) {
  86   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
  87   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
  88   assert(!ParallelScavengeHeap::heap()->is_gc_active(), "not reentrant");
  89 
  90   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
  91   GCCause::Cause gc_cause = heap->gc_cause();
  92   PSAdaptiveSizePolicy* policy = heap->size_policy();
  93   IsGCActiveMark mark;
  94 
  95   if (ScavengeBeforeFullGC) {
  96     PSScavenge::invoke_no_policy();
  97   }
  98 
  99   const bool clear_all_soft_refs =
 100     heap->collector_policy()->should_clear_all_soft_refs();
 101 
 102   uint count = maximum_heap_compaction ? 1 : MarkSweepAlwaysCompactCount;
 103   UIntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);
 104   PSMarkSweep::invoke_no_policy(clear_all_soft_refs || maximum_heap_compaction);
 105 }
 106 
 107 // This method contains no policy. You should probably
 108 // be calling invoke() instead.
 109 bool PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
 110   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 111   assert(ref_processor() != NULL, "Sanity");
 112 
 113   if (GCLocker::check_active_before_gc()) {
 114     return false;
 115   }
 116 
 117   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 118   GCCause::Cause gc_cause = heap->gc_cause();
 119 
 120   GCIdMark gc_id_mark;
 121   _gc_timer->register_gc_start();
 122   _gc_tracer->report_gc_start(gc_cause, _gc_timer->gc_start());
 123 
 124   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 125 
 126   // The scope of casr should end after code that can change
 127   // CollectorPolicy::_should_clear_all_soft_refs.
 128   ClearedAllSoftRefs casr(clear_all_softrefs, heap->collector_policy());
 129 
 130   PSYoungGen* young_gen = heap->young_gen();
 131   PSOldGen* old_gen = heap->old_gen();
 132 
 133   // Increment the invocation count
 134   heap->increment_total_collections(true /* full */);
 135 
 136   // Save information needed to minimize mangling
 137   heap->record_gen_tops_before_GC();
 138 
 139   // We need to track unique mark sweep invocations as well.
 140   _total_invocations++;
 141 
 142   heap->print_heap_before_gc();
 143   heap->trace_heap_before_gc(_gc_tracer);
 144 
 145   // Fill in TLABs
 146   heap->accumulate_statistics_all_tlabs();
 147   heap->ensure_parsability(true);  // retire TLABs
 148 
 149   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
 150     HandleMark hm;  // Discard invalid handles created during verification
 151     Universe::verify("Before GC");
 152   }
 153 
 154   // Verify object start arrays
 155   if (VerifyObjectStartArray &&
 156       VerifyBeforeGC) {
 157     old_gen->verify_object_start_array();
 158   }
 159 
 160   // Filled in below to track the state of the young gen after the collection.
 161   bool eden_empty;
 162   bool survivors_empty;
 163   bool young_gen_empty;
 164 
 165   {
 166     HandleMark hm;
 167 
 168     GCTraceCPUTime tcpu;
 169     GCTraceTime(Info, gc) t("Pause Full", NULL, gc_cause, true);
 170 
 171     heap->pre_full_gc_dump(_gc_timer);
 172 
 173     TraceCollectorStats tcs(counters());
 174     TraceMemoryManagerStats tms(true /* Full GC */,gc_cause);
 175 
 176     if (TraceOldGenTime) accumulated_time()->start();
 177 
 178     // Let the size policy know we're starting
 179     size_policy->major_collection_begin();
 180 
 181     CodeCache::gc_prologue();
 182     BiasedLocking::preserve_marks();
 183 
 184     // Capture metadata size before collection for sizing.
 185     size_t metadata_prev_used = MetaspaceAux::used_bytes();
 186 
 187     size_t old_gen_prev_used = old_gen->used_in_bytes();
 188     size_t young_gen_prev_used = young_gen->used_in_bytes();
 189 
 190     allocate_stacks();
 191 
 192 #if defined(COMPILER2) || INCLUDE_JVMCI
 193     DerivedPointerTable::clear();
 194 #endif
 195 
 196     ref_processor()->enable_discovery();
 197     ref_processor()->setup_policy(clear_all_softrefs);
 198 
 199     mark_sweep_phase1(clear_all_softrefs);
 200 
 201     mark_sweep_phase2();
 202 
 203 #if defined(COMPILER2) || INCLUDE_JVMCI
 204     // Don't add any more derived pointers during phase3
 205     assert(DerivedPointerTable::is_active(), "Sanity");
 206     DerivedPointerTable::set_active(false);
 207 #endif
 208 
 209     mark_sweep_phase3();
 210 
 211     mark_sweep_phase4();
 212 
 213     restore_marks();
 214 
 215     deallocate_stacks();
 216 
 217     if (ZapUnusedHeapArea) {
 218       // Do a complete mangle (top to end) because the usage for
 219       // scratch does not maintain a top pointer.
 220       young_gen->to_space()->mangle_unused_area_complete();
 221     }
 222 
 223     eden_empty = young_gen->eden_space()->is_empty();
 224     if (!eden_empty) {
 225       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
 226     }
 227 
 228     // Update heap occupancy information which is used as
 229     // input to soft ref clearing policy at the next gc.
 230     Universe::update_heap_info_at_gc();
 231 
 232     survivors_empty = young_gen->from_space()->is_empty() &&
 233                       young_gen->to_space()->is_empty();
 234     young_gen_empty = eden_empty && survivors_empty;
 235 
 236     ModRefBarrierSet* modBS = barrier_set_cast<ModRefBarrierSet>(heap->barrier_set());
 237     MemRegion old_mr = heap->old_gen()->reserved();
 238     if (young_gen_empty) {
 239       modBS->clear(MemRegion(old_mr.start(), old_mr.end()));
 240     } else {
 241       modBS->invalidate(MemRegion(old_mr.start(), old_mr.end()));
 242     }
 243 
 244     // Delete metaspaces for unloaded class loaders and clean up loader_data graph
 245     ClassLoaderDataGraph::purge();
 246     MetaspaceAux::verify_metrics();
 247 
 248     BiasedLocking::restore_marks();
 249     CodeCache::gc_epilogue();
 250     JvmtiExport::gc_epilogue();
 251 
 252 #if defined(COMPILER2) || INCLUDE_JVMCI
 253     DerivedPointerTable::update_pointers();
 254 #endif
 255 
 256     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->num_q());
 257 
 258     ref_processor()->enqueue_discovered_references(NULL, &pt);
 259 
 260     pt.print_enqueue_phase();
 261 
 262     // Update time of last GC
 263     reset_millis_since_last_gc();
 264 
 265     // Let the size policy know we're done
 266     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
 267 
 268     if (UseAdaptiveSizePolicy) {
 269 
 270      log_debug(gc, ergo)("AdaptiveSizeStart: collection: %d ", heap->total_collections());
 271      log_trace(gc, ergo)("old_gen_capacity: " SIZE_FORMAT " young_gen_capacity: " SIZE_FORMAT,
 272                          old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
 273 
 274       // Don't check if the size_policy is ready here.  Let
 275       // the size_policy check that internally.
 276       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
 277           AdaptiveSizePolicy::should_update_promo_stats(gc_cause)) {
 278         // Swap the survivor spaces if from_space is empty. The
 279         // resize_young_gen() called below is normally used after
 280         // a successful young GC and swapping of survivor spaces;
 281         // otherwise, it will fail to resize the young gen with
 282         // the current implementation.
 283         if (young_gen->from_space()->is_empty()) {
 284           young_gen->from_space()->clear(SpaceDecorator::Mangle);
 285           young_gen->swap_spaces();
 286         }
 287 
 288         // Calculate optimal free space amounts
 289         assert(young_gen->max_size() >
 290           young_gen->from_space()->capacity_in_bytes() +
 291           young_gen->to_space()->capacity_in_bytes(),
 292           "Sizes of space in young gen are out-of-bounds");
 293 
 294         size_t young_live = young_gen->used_in_bytes();
 295         size_t eden_live = young_gen->eden_space()->used_in_bytes();
 296         size_t old_live = old_gen->used_in_bytes();
 297         size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
 298         size_t max_old_gen_size = old_gen->max_gen_size();
 299         size_t max_eden_size = young_gen->max_size() -
 300           young_gen->from_space()->capacity_in_bytes() -
 301           young_gen->to_space()->capacity_in_bytes();
 302 
 303         // Used for diagnostics
 304         size_policy->clear_generation_free_space_flags();
 305 
 306         size_policy->compute_generations_free_space(young_live,
 307                                                     eden_live,
 308                                                     old_live,
 309                                                     cur_eden,
 310                                                     max_old_gen_size,
 311                                                     max_eden_size,
 312                                                     true /* full gc*/);
 313 
 314         size_policy->check_gc_overhead_limit(young_live,
 315                                              eden_live,
 316                                              max_old_gen_size,
 317                                              max_eden_size,
 318                                              true /* full gc*/,
 319                                              gc_cause,
 320                                              heap->collector_policy());
 321 
 322         size_policy->decay_supplemental_growth(true /* full gc*/);
 323 
 324         heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
 325 
 326         heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
 327                                size_policy->calculated_survivor_size_in_bytes());
 328       }
 329       log_debug(gc, ergo)("AdaptiveSizeStop: collection: %d ", heap->total_collections());
 330     }
 331 
 332     if (UsePerfData) {
 333       heap->gc_policy_counters()->update_counters();
 334       heap->gc_policy_counters()->update_old_capacity(
 335         old_gen->capacity_in_bytes());
 336       heap->gc_policy_counters()->update_young_capacity(
 337         young_gen->capacity_in_bytes());
 338     }
 339 
 340     heap->resize_all_tlabs();
 341 
 342     // We collected the heap, recalculate the metaspace capacity
 343     MetaspaceGC::compute_new_size();
 344 
 345     if (TraceOldGenTime) accumulated_time()->stop();
 346 
 347     young_gen->print_used_change(young_gen_prev_used);
 348     old_gen->print_used_change(old_gen_prev_used);
 349     MetaspaceAux::print_metaspace_change(metadata_prev_used);
 350 
 351     // Track memory usage and detect low memory
 352     MemoryService::track_memory_usage();
 353     heap->update_counters();
 354 
 355     heap->post_full_gc_dump(_gc_timer);
 356   }
 357 
 358   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
 359     HandleMark hm;  // Discard invalid handles created during verification
 360     Universe::verify("After GC");
 361   }
 362 
 363   // Re-verify object start arrays
 364   if (VerifyObjectStartArray &&
 365       VerifyAfterGC) {
 366     old_gen->verify_object_start_array();
 367   }
 368 
 369   if (ZapUnusedHeapArea) {
 370     old_gen->object_space()->check_mangled_unused_area_complete();
 371   }
 372 
 373   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 374 
 375   heap->print_heap_after_gc();
 376   heap->trace_heap_after_gc(_gc_tracer);
 377 
 378 #ifdef TRACESPINNING
 379   ParallelTaskTerminator::print_termination_counts();
 380 #endif
 381 
 382   AdaptiveSizePolicyOutput::print(size_policy, heap->total_collections());
 383 
 384   _gc_timer->register_gc_end();
 385 
 386   _gc_tracer->report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
 387 
 388   return true;
 389 }
 390 
 391 bool PSMarkSweep::absorb_live_data_from_eden(PSAdaptiveSizePolicy* size_policy,
 392                                              PSYoungGen* young_gen,
 393                                              PSOldGen* old_gen) {
 394   MutableSpace* const eden_space = young_gen->eden_space();
 395   assert(!eden_space->is_empty(), "eden must be non-empty");
 396   assert(young_gen->virtual_space()->alignment() ==
 397          old_gen->virtual_space()->alignment(), "alignments do not match");
 398 
 399   if (!(UseAdaptiveSizePolicy && UseAdaptiveGCBoundary)) {
 400     return false;
 401   }
 402 
 403   // Both generations must be completely committed.
 404   if (young_gen->virtual_space()->uncommitted_size() != 0) {
 405     return false;
 406   }
 407   if (old_gen->virtual_space()->uncommitted_size() != 0) {
 408     return false;
 409   }
 410 
 411   // Figure out how much to take from eden.  Include the average amount promoted
 412   // in the total; otherwise the next young gen GC will simply bail out to a
 413   // full GC.
 414   const size_t alignment = old_gen->virtual_space()->alignment();
 415   const size_t eden_used = eden_space->used_in_bytes();
 416   const size_t promoted = (size_t)size_policy->avg_promoted()->padded_average();
 417   const size_t absorb_size = align_up(eden_used + promoted, alignment);
 418   const size_t eden_capacity = eden_space->capacity_in_bytes();
 419 
 420   if (absorb_size >= eden_capacity) {
 421     return false; // Must leave some space in eden.
 422   }
 423 
 424   const size_t new_young_size = young_gen->capacity_in_bytes() - absorb_size;
 425   if (new_young_size < young_gen->min_gen_size()) {
 426     return false; // Respect young gen minimum size.
 427   }
 428 
 429   log_trace(heap, ergo)(" absorbing " SIZE_FORMAT "K:  "
 430                         "eden " SIZE_FORMAT "K->" SIZE_FORMAT "K "
 431                         "from " SIZE_FORMAT "K, to " SIZE_FORMAT "K "
 432                         "young_gen " SIZE_FORMAT "K->" SIZE_FORMAT "K ",
 433                         absorb_size / K,
 434                         eden_capacity / K, (eden_capacity - absorb_size) / K,
 435                         young_gen->from_space()->used_in_bytes() / K,
 436                         young_gen->to_space()->used_in_bytes() / K,
 437                         young_gen->capacity_in_bytes() / K, new_young_size / K);
 438 
 439   // Fill the unused part of the old gen.
 440   MutableSpace* const old_space = old_gen->object_space();
 441   HeapWord* const unused_start = old_space->top();
 442   size_t const unused_words = pointer_delta(old_space->end(), unused_start);
 443 
 444   if (unused_words > 0) {
 445     if (unused_words < CollectedHeap::min_fill_size()) {
 446       return false;  // If the old gen cannot be filled, must give up.
 447     }
 448     CollectedHeap::fill_with_objects(unused_start, unused_words);
 449   }
 450 
 451   // Take the live data from eden and set both top and end in the old gen to
 452   // eden top.  (Need to set end because reset_after_change() mangles the region
 453   // from end to virtual_space->high() in debug builds).
 454   HeapWord* const new_top = eden_space->top();
 455   old_gen->virtual_space()->expand_into(young_gen->virtual_space(),
 456                                         absorb_size);
 457   young_gen->reset_after_change();
 458   old_space->set_top(new_top);
 459   old_space->set_end(new_top);
 460   old_gen->reset_after_change();
 461 
 462   // Update the object start array for the filler object and the data from eden.
 463   ObjectStartArray* const start_array = old_gen->start_array();
 464   for (HeapWord* p = unused_start; p < new_top; p += oop(p)->size()) {
 465     start_array->allocate_block(p);
 466   }
 467 
 468   // Could update the promoted average here, but it is not typically updated at
 469   // full GCs and the value to use is unclear.  Something like
 470   //
 471   // cur_promoted_avg + absorb_size / number_of_scavenges_since_last_full_gc.
 472 
 473   size_policy->set_bytes_absorbed_from_eden(absorb_size);
 474   return true;
 475 }
 476 
 477 void PSMarkSweep::allocate_stacks() {
 478   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 479   PSYoungGen* young_gen = heap->young_gen();
 480 
 481   MutableSpace* to_space = young_gen->to_space();
 482   _preserved_marks = (PreservedMark*)to_space->top();
 483   _preserved_count = 0;
 484 
 485   // We want to calculate the size in bytes first.
 486   _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));
 487   // Now divide by the size of a PreservedMark
 488   _preserved_count_max /= sizeof(PreservedMark);
 489 }
 490 
 491 
 492 void PSMarkSweep::deallocate_stacks() {
 493   _preserved_mark_stack.clear(true);
 494   _preserved_oop_stack.clear(true);
 495   _marking_stack.clear();
 496   _objarray_stack.clear(true);
 497 }
 498 
 499 void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 500   // Recursively traverse all live objects and mark them
 501   GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
 502 
 503   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 504 
 505   // Need to clear claim bits before the tracing starts.
 506   ClassLoaderDataGraph::clear_claimed_marks();
 507 
 508   // General strong roots.
 509   {
 510     ParallelScavengeHeap::ParStrongRootsScope psrs;
 511     Universe::oops_do(mark_and_push_closure());
 512     JNIHandles::oops_do(mark_and_push_closure());   // Global (strong) JNI handles
 513     MarkingCodeBlobClosure each_active_code_blob(mark_and_push_closure(), !CodeBlobToOopClosure::FixRelocations);
 514     Threads::oops_do(mark_and_push_closure(), &each_active_code_blob);
 515     ObjectSynchronizer::oops_do(mark_and_push_closure());
 516     Management::oops_do(mark_and_push_closure());
 517     JvmtiExport::oops_do(mark_and_push_closure());
 518     SystemDictionary::always_strong_oops_do(mark_and_push_closure());
 519     ClassLoaderDataGraph::always_strong_cld_do(follow_cld_closure());
 520     // Do not treat nmethods as strong roots for mark/sweep, since we can unload them.
 521     //CodeCache::scavenge_root_nmethods_do(CodeBlobToOopClosure(mark_and_push_closure()));
 522     AOTLoader::oops_do(mark_and_push_closure());
 523   }
 524 
 525   // Flush marking stack.
 526   follow_stack();
 527 
 528   // Process reference objects found during marking
 529   {
 530     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer);
 531 
 532     ref_processor()->setup_policy(clear_all_softrefs);
 533     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->num_q());
 534     const ReferenceProcessorStats& stats =
 535       ref_processor()->process_discovered_references(
 536         is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL, &pt);
 537     gc_tracer()->report_gc_reference_stats(stats);
 538     pt.print_all_references();
 539   }
 540 
 541   // This is the point where the entire marking should have completed.
 542   assert(_marking_stack.is_empty(), "Marking should have completed");
 543 
 544   {
 545     GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer);
 546 
 547     // Unload classes and purge the SystemDictionary.
 548     bool purged_class = SystemDictionary::do_unloading(is_alive_closure(), _gc_timer);
 549 
 550     // Unload nmethods.
 551     CodeCache::do_unloading(is_alive_closure(), purged_class);
 552 
 553     // Prune dead klasses from subklass/sibling/implementor lists.
 554     Klass::clean_weak_klass_links(is_alive_closure());
 555   }
 556 
 557   {
 558     GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer);
 559     // Delete entries for dead interned strings.
 560     StringTable::unlink(is_alive_closure());
 561   }
 562 
 563   {
 564     GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer);
 565     // Clean up unreferenced symbols in symbol table.
 566     SymbolTable::unlink();
 567   }
 568 
 569   _gc_tracer->report_object_count_after_gc(is_alive_closure());
 570 }
 571 
 572 
 573 void PSMarkSweep::mark_sweep_phase2() {
 574   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
 575 
 576   // Now all live objects are marked, compute the new object addresses.
 577 
 578   // It is not required that we traverse spaces in the same order in
 579   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 580   // tracking expects us to do so. See comment under phase4.
 581 
 582   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 583   PSOldGen* old_gen = heap->old_gen();
 584 
 585   // Begin compacting into the old gen
 586   PSMarkSweepDecorator::set_destination_decorator_tenured();
 587 
 588   // This will also compact the young gen spaces.
 589   old_gen->precompact();
 590 }
 591 
 592 void PSMarkSweep::mark_sweep_phase3() {
 593   // Adjust the pointers to reflect the new locations
 594   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", _gc_timer);
 595 
 596   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 597   PSYoungGen* young_gen = heap->young_gen();
 598   PSOldGen* old_gen = heap->old_gen();
 599 
 600   // Need to clear claim bits before the tracing starts.
 601   ClassLoaderDataGraph::clear_claimed_marks();
 602 
 603   // General strong roots.
 604   Universe::oops_do(adjust_pointer_closure());
 605   JNIHandles::oops_do(adjust_pointer_closure());   // Global (strong) JNI handles
 606   Threads::oops_do(adjust_pointer_closure(), NULL);
 607   ObjectSynchronizer::oops_do(adjust_pointer_closure());
 608   Management::oops_do(adjust_pointer_closure());
 609   JvmtiExport::oops_do(adjust_pointer_closure());
 610   SystemDictionary::oops_do(adjust_pointer_closure());
 611   ClassLoaderDataGraph::cld_do(adjust_cld_closure());
 612 
 613   // Now adjust pointers in remaining weak roots.  (All of which should
 614   // have been cleared if they pointed to non-surviving objects.)
 615   // Global (weak) JNI handles
 616   JNIHandles::weak_oops_do(adjust_pointer_closure());

 617 
 618   CodeBlobToOopClosure adjust_from_blobs(adjust_pointer_closure(), CodeBlobToOopClosure::FixRelocations);
 619   CodeCache::blobs_do(&adjust_from_blobs);
 620   AOTLoader::oops_do(adjust_pointer_closure());
 621   StringTable::oops_do(adjust_pointer_closure());
 622   ref_processor()->weak_oops_do(adjust_pointer_closure());
 623   PSScavenge::reference_processor()->weak_oops_do(adjust_pointer_closure());
 624 
 625   adjust_marks();
 626 
 627   young_gen->adjust_pointers();
 628   old_gen->adjust_pointers();
 629 }
 630 
 631 void PSMarkSweep::mark_sweep_phase4() {
 632   EventMark m("4 compact heap");
 633   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
 634 
 635   // All pointers are now adjusted, move objects accordingly
 636 
 637   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 638   PSYoungGen* young_gen = heap->young_gen();
 639   PSOldGen* old_gen = heap->old_gen();
 640 
 641   old_gen->compact();
 642   young_gen->compact();
 643 }
 644 
 645 jlong PSMarkSweep::millis_since_last_gc() {
 646   // We need a monotonically non-decreasing time in ms but
 647   // os::javaTimeMillis() does not guarantee monotonicity.
 648   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 649   jlong ret_val = now - _time_of_last_gc;
 650   // XXX See note in genCollectedHeap::millis_since_last_gc().
 651   if (ret_val < 0) {
 652     NOT_PRODUCT(log_warning(gc)("time warp: " JLONG_FORMAT, ret_val);)
 653     return 0;
 654   }
 655   return ret_val;
 656 }
 657 
 658 void PSMarkSweep::reset_millis_since_last_gc() {
 659   // We need a monotonically non-decreasing time in ms but
 660   // os::javaTimeMillis() does not guarantee monotonicity.
 661   _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 662 }
--- EOF ---