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