1 /*
   2  * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/symbolTable.hpp"
  27 #include "classfile/systemDictionary.hpp"
  28 #include "code/codeCache.hpp"
  29 #include "gc_implementation/parallelScavenge/parallelScavengeHeap.hpp"
  30 #include "gc_implementation/parallelScavenge/psAdaptiveSizePolicy.hpp"
  31 #include "gc_implementation/parallelScavenge/psMarkSweep.hpp"
  32 #include "gc_implementation/parallelScavenge/psMarkSweepDecorator.hpp"
  33 #include "gc_implementation/parallelScavenge/psOldGen.hpp"
  34 #include "gc_implementation/parallelScavenge/psScavenge.hpp"
  35 #include "gc_implementation/parallelScavenge/psYoungGen.hpp"
  36 #include "gc_implementation/shared/gcHeapSummary.hpp"
  37 #include "gc_implementation/shared/gcTimer.hpp"
  38 #include "gc_implementation/shared/gcTrace.hpp"
  39 #include "gc_implementation/shared/gcTraceTime.hpp"
  40 #include "gc_implementation/shared/isGCActiveMark.hpp"
  41 #include "gc_implementation/shared/markSweep.hpp"
  42 #include "gc_implementation/shared/spaceDecorator.hpp"
  43 #include "gc_interface/gcCause.hpp"
  44 #include "memory/gcLocker.inline.hpp"
  45 #include "memory/referencePolicy.hpp"
  46 #include "memory/referenceProcessor.hpp"
  47 #include "oops/oop.inline.hpp"
  48 #include "runtime/biasedLocking.hpp"
  49 #include "runtime/fprofiler.hpp"
  50 #include "runtime/safepoint.hpp"
  51 #include "runtime/vmThread.hpp"
  52 #include "services/management.hpp"
  53 #include "services/memoryService.hpp"
  54 #include "utilities/events.hpp"
  55 #include "utilities/stack.inline.hpp"
  56 
  57 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
  58 
  59 elapsedTimer        PSMarkSweep::_accumulated_time;
  60 jlong               PSMarkSweep::_time_of_last_gc   = 0;
  61 CollectorCounters*  PSMarkSweep::_counters = NULL;
  62 
  63 void PSMarkSweep::initialize() {
  64   MemRegion mr = Universe::heap()->reserved_region();
  65   _ref_processor = new ReferenceProcessor(mr);     // a vanilla ref proc
  66   _counters = new CollectorCounters("PSMarkSweep", 1);
  67 }
  68 
  69 // This method contains all heap specific policy for invoking mark sweep.
  70 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact
  71 // the heap. It will do nothing further. If we need to bail out for policy
  72 // reasons, scavenge before full gc, or any other specialized behavior, it
  73 // needs to be added here.
  74 //
  75 // Note that this method should only be called from the vm_thread while
  76 // at a safepoint!
  77 //
  78 // Note that the all_soft_refs_clear flag in the collector policy
  79 // may be true because this method can be called without intervening
  80 // activity.  For example when the heap space is tight and full measure
  81 // are being taken to free space.
  82 
  83 void PSMarkSweep::invoke(bool maximum_heap_compaction) {
  84   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
  85   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
  86   assert(!Universe::heap()->is_gc_active(), "not reentrant");
  87 
  88   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
  89   GCCause::Cause gc_cause = heap->gc_cause();
  90   PSAdaptiveSizePolicy* policy = heap->size_policy();
  91   IsGCActiveMark mark;
  92 
  93   if (ScavengeBeforeFullGC) {
  94     PSScavenge::invoke_no_policy();
  95   }
  96 
  97   const bool clear_all_soft_refs =
  98     heap->collector_policy()->should_clear_all_soft_refs();
  99 
 100   uint count = maximum_heap_compaction ? 1 : MarkSweepAlwaysCompactCount;
 101   UIntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);
 102   PSMarkSweep::invoke_no_policy(clear_all_soft_refs || maximum_heap_compaction);
 103 }
 104 
 105 // This method contains no policy. You should probably
 106 // be calling invoke() instead.
 107 bool PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
 108   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 109   assert(ref_processor() != NULL, "Sanity");
 110 
 111   if (GC_locker::check_active_before_gc()) {
 112     return false;
 113   }
 114 
 115   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 116   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 117   GCCause::Cause gc_cause = heap->gc_cause();
 118 
 119   _gc_timer->register_gc_start();
 120   _gc_tracer->report_gc_start(gc_cause, _gc_timer->gc_start());
 121 
 122   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 123 
 124   // The scope of casr should end after code that can change
 125   // CollectorPolicy::_should_clear_all_soft_refs.
 126   ClearedAllSoftRefs casr(clear_all_softrefs, heap->collector_policy());
 127 
 128   PSYoungGen* young_gen = heap->young_gen();
 129   PSOldGen* old_gen = heap->old_gen();
 130 
 131   // Increment the invocation count
 132   heap->increment_total_collections(true /* full */);
 133 
 134   // Save information needed to minimize mangling
 135   heap->record_gen_tops_before_GC();
 136 
 137   // We need to track unique mark sweep invocations as well.
 138   _total_invocations++;
 139 
 140   AdaptiveSizePolicyOutput(size_policy, heap->total_collections());
 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(" VerifyBeforeGC:");
 152   }
 153 
 154   // Verify object start arrays
 155   if (VerifyObjectStartArray &&
 156       VerifyBeforeGC) {
 157     old_gen->verify_object_start_array();
 158   }
 159 
 160   heap->pre_full_gc_dump(_gc_timer);
 161 
 162   // Filled in below to track the state of the young gen after the collection.
 163   bool eden_empty;
 164   bool survivors_empty;
 165   bool young_gen_empty;
 166 
 167   {
 168     HandleMark hm;
 169 
 170     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
 171     GCTraceTime t1(GCCauseString("Full GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer->gc_id());
 172     TraceCollectorStats tcs(counters());
 173     TraceMemoryManagerStats tms(true /* Full GC */,gc_cause);
 174 
 175     if (TraceGen1Time) accumulated_time()->start();
 176 
 177     // Let the size policy know we're starting
 178     size_policy->major_collection_begin();
 179 
 180     CodeCache::gc_prologue();
 181     Threads::gc_prologue();
 182     BiasedLocking::preserve_marks();
 183 
 184     // Capture heap size before collection for printing.
 185     size_t prev_used = heap->used();
 186 
 187     // Capture metadata size before collection for sizing.
 188     size_t metadata_prev_used = MetaspaceAux::used_bytes();
 189 
 190     // For PrintGCDetails
 191     size_t old_gen_prev_used = old_gen->used_in_bytes();
 192     size_t young_gen_prev_used = young_gen->used_in_bytes();
 193 
 194     allocate_stacks();
 195 
 196     COMPILER2_PRESENT(DerivedPointerTable::clear());
 197 
 198     ref_processor()->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/);
 199     ref_processor()->setup_policy(clear_all_softrefs);
 200 
 201     mark_sweep_phase1(clear_all_softrefs);
 202 
 203     mark_sweep_phase2();
 204 
 205     // Don't add any more derived pointers during phase3
 206     COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
 207     COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
 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     BarrierSet* bs = heap->barrier_set();
 237     if (bs->is_a(BarrierSet::ModRef)) {
 238       ModRefBarrierSet* modBS = (ModRefBarrierSet*)bs;
 239       MemRegion old_mr = heap->old_gen()->reserved();
 240       if (young_gen_empty) {
 241         modBS->clear(MemRegion(old_mr.start(), old_mr.end()));
 242       } else {
 243         modBS->invalidate(MemRegion(old_mr.start(), old_mr.end()));
 244       }
 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     Threads::gc_epilogue();
 253     CodeCache::gc_epilogue();
 254     JvmtiExport::gc_epilogue();
 255 
 256     COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
 257 
 258     ref_processor()->enqueue_discovered_references(NULL);
 259 
 260     // Update time of last GC
 261     reset_millis_since_last_gc();
 262 
 263     // Let the size policy know we're done
 264     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
 265 
 266     if (UseAdaptiveSizePolicy) {
 267 
 268       if (PrintAdaptiveSizePolicy) {
 269         gclog_or_tty->print("AdaptiveSizeStart: ");
 270         gclog_or_tty->stamp();
 271         gclog_or_tty->print_cr(" collection: %d ",
 272                        heap->total_collections());
 273         if (Verbose) {
 274           gclog_or_tty->print("old_gen_capacity: %d young_gen_capacity: %d",
 275             old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
 276         }
 277       }
 278 
 279       // Don't check if the size_policy is ready here.  Let
 280       // the size_policy check that internally.
 281       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
 282           ((gc_cause != GCCause::_java_lang_system_gc) ||
 283             UseAdaptiveSizePolicyWithSystemGC)) {
 284         // Calculate optimal free space amounts
 285         assert(young_gen->max_size() >
 286           young_gen->from_space()->capacity_in_bytes() +
 287           young_gen->to_space()->capacity_in_bytes(),
 288           "Sizes of space in young gen are out-of-bounds");
 289 
 290         size_t young_live = young_gen->used_in_bytes();
 291         size_t eden_live = young_gen->eden_space()->used_in_bytes();
 292         size_t old_live = old_gen->used_in_bytes();
 293         size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
 294         size_t max_old_gen_size = old_gen->max_gen_size();
 295         size_t max_eden_size = young_gen->max_size() -
 296           young_gen->from_space()->capacity_in_bytes() -
 297           young_gen->to_space()->capacity_in_bytes();
 298 
 299         // Used for diagnostics
 300         size_policy->clear_generation_free_space_flags();
 301 
 302         size_policy->compute_generations_free_space(young_live,
 303                                                     eden_live,
 304                                                     old_live,
 305                                                     cur_eden,
 306                                                     max_old_gen_size,
 307                                                     max_eden_size,
 308                                                     true /* full gc*/);
 309 
 310         size_policy->check_gc_overhead_limit(young_live,
 311                                              eden_live,
 312                                              max_old_gen_size,
 313                                              max_eden_size,
 314                                              true /* full gc*/,
 315                                              gc_cause,
 316                                              heap->collector_policy());
 317 
 318         size_policy->decay_supplemental_growth(true /* full gc*/);
 319 
 320         heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
 321 
 322         // Don't resize the young generation at an major collection.  A
 323         // desired young generation size may have been calculated but
 324         // resizing the young generation complicates the code because the
 325         // resizing of the old generation may have moved the boundary
 326         // between the young generation and the old generation.  Let the
 327         // young generation resizing happen at the minor collections.
 328       }
 329       if (PrintAdaptiveSizePolicy) {
 330         gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",
 331                        heap->total_collections());
 332       }
 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 (TraceGen1Time) accumulated_time()->stop();
 349 
 350     if (PrintGC) {
 351       if (PrintGCDetails) {
 352         // Don't print a GC timestamp here.  This is after the GC so
 353         // would be confusing.
 354         young_gen->print_used_change(young_gen_prev_used);
 355         old_gen->print_used_change(old_gen_prev_used);
 356       }
 357       heap->print_heap_change(prev_used);
 358       if (PrintGCDetails) {
 359         MetaspaceAux::print_metaspace_change(metadata_prev_used);
 360       }
 361     }
 362 
 363     // Track memory usage and detect low memory
 364     MemoryService::track_memory_usage();
 365     heap->update_counters();
 366   }
 367 
 368   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
 369     HandleMark hm;  // Discard invalid handles created during verification
 370     Universe::verify(" VerifyAfterGC:");
 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   heap->post_full_gc_dump(_gc_timer);
 389 
 390 #ifdef TRACESPINNING
 391   ParallelTaskTerminator::print_termination_counts();
 392 #endif
 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_size_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   if (TraceAdaptiveGCBoundary && Verbose) {
 440     gclog_or_tty->print(" absorbing " SIZE_FORMAT "K:  "
 441                         "eden " SIZE_FORMAT "K->" SIZE_FORMAT "K "
 442                         "from " SIZE_FORMAT "K, to " SIZE_FORMAT "K "
 443                         "young_gen " SIZE_FORMAT "K->" SIZE_FORMAT "K ",
 444                         absorb_size / K,
 445                         eden_capacity / K, (eden_capacity - absorb_size) / K,
 446                         young_gen->from_space()->used_in_bytes() / K,
 447                         young_gen->to_space()->used_in_bytes() / K,
 448                         young_gen->capacity_in_bytes() / K, new_young_size / K);
 449   }
 450 
 451   // Fill the unused part of the old gen.
 452   MutableSpace* const old_space = old_gen->object_space();
 453   HeapWord* const unused_start = old_space->top();
 454   size_t const unused_words = pointer_delta(old_space->end(), unused_start);
 455 
 456   if (unused_words > 0) {
 457     if (unused_words < CollectedHeap::min_fill_size()) {
 458       return false;  // If the old gen cannot be filled, must give up.
 459     }
 460     CollectedHeap::fill_with_objects(unused_start, unused_words);
 461   }
 462 
 463   // Take the live data from eden and set both top and end in the old gen to
 464   // eden top.  (Need to set end because reset_after_change() mangles the region
 465   // from end to virtual_space->high() in debug builds).
 466   HeapWord* const new_top = eden_space->top();
 467   old_gen->virtual_space()->expand_into(young_gen->virtual_space(),
 468                                         absorb_size);
 469   young_gen->reset_after_change();
 470   old_space->set_top(new_top);
 471   old_space->set_end(new_top);
 472   old_gen->reset_after_change();
 473 
 474   // Update the object start array for the filler object and the data from eden.
 475   ObjectStartArray* const start_array = old_gen->start_array();
 476   for (HeapWord* p = unused_start; p < new_top; p += oop(p)->size()) {
 477     start_array->allocate_block(p);
 478   }
 479 
 480   // Could update the promoted average here, but it is not typically updated at
 481   // full GCs and the value to use is unclear.  Something like
 482   //
 483   // cur_promoted_avg + absorb_size / number_of_scavenges_since_last_full_gc.
 484 
 485   size_policy->set_bytes_absorbed_from_eden(absorb_size);
 486   return true;
 487 }
 488 
 489 void PSMarkSweep::allocate_stacks() {
 490   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 491   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 492 
 493   PSYoungGen* young_gen = heap->young_gen();
 494 
 495   MutableSpace* to_space = young_gen->to_space();
 496   _preserved_marks = (PreservedMark*)to_space->top();
 497   _preserved_count = 0;
 498 
 499   // We want to calculate the size in bytes first.
 500   _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));
 501   // Now divide by the size of a PreservedMark
 502   _preserved_count_max /= sizeof(PreservedMark);
 503 }
 504 
 505 
 506 void PSMarkSweep::deallocate_stacks() {
 507   _preserved_mark_stack.clear(true);
 508   _preserved_oop_stack.clear(true);
 509   _marking_stack.clear();
 510   _objarray_stack.clear(true);
 511 }
 512 
 513 void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 514   // Recursively traverse all live objects and mark them
 515   GCTraceTime tm("phase 1", PrintGCDetails && Verbose, true, _gc_timer, _gc_tracer->gc_id());
 516   trace(" 1");
 517 
 518   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 519   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 520 
 521   // Need to clear claim bits before the tracing starts.
 522   ClassLoaderDataGraph::clear_claimed_marks();
 523 
 524   // General strong roots.
 525   {
 526     ParallelScavengeHeap::ParStrongRootsScope psrs;
 527     Universe::oops_do(mark_and_push_closure());
 528     JNIHandles::oops_do(mark_and_push_closure());   // Global (strong) JNI handles
 529     CLDToOopClosure mark_and_push_from_cld(mark_and_push_closure());
 530     MarkingCodeBlobClosure each_active_code_blob(mark_and_push_closure(), !CodeBlobToOopClosure::FixRelocations);
 531     Threads::oops_do(mark_and_push_closure(), &mark_and_push_from_cld, &each_active_code_blob);
 532     ObjectSynchronizer::oops_do(mark_and_push_closure());
 533     FlatProfiler::oops_do(mark_and_push_closure());
 534     Management::oops_do(mark_and_push_closure());
 535     JvmtiExport::oops_do(mark_and_push_closure());
 536     SystemDictionary::always_strong_oops_do(mark_and_push_closure());
 537     ClassLoaderDataGraph::always_strong_cld_do(follow_cld_closure());
 538     // Do not treat nmethods as strong roots for mark/sweep, since we can unload them.
 539     //CodeCache::scavenge_root_nmethods_do(CodeBlobToOopClosure(mark_and_push_closure()));
 540   }
 541 
 542   // Flush marking stack.
 543   follow_stack();
 544 
 545   // Process reference objects found during marking
 546   {
 547     ref_processor()->setup_policy(clear_all_softrefs);
 548     const ReferenceProcessorStats& stats =
 549       ref_processor()->process_discovered_references(
 550         is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL, _gc_timer, _gc_tracer->gc_id());
 551     gc_tracer()->report_gc_reference_stats(stats);
 552   }
 553 
 554   // This is the point where the entire marking should have completed.
 555   assert(_marking_stack.is_empty(), "Marking should have completed");
 556 
 557   // Unload classes and purge the SystemDictionary.
 558   bool purged_class = SystemDictionary::do_unloading(is_alive_closure());
 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   // Delete entries for dead interned strings.
 567   StringTable::unlink(is_alive_closure());
 568 
 569   // Clean up unreferenced symbols in symbol table.
 570   SymbolTable::unlink();
 571   _gc_tracer->report_object_count_after_gc(is_alive_closure());
 572 }
 573 
 574 
 575 void PSMarkSweep::mark_sweep_phase2() {
 576   GCTraceTime tm("phase 2", PrintGCDetails && Verbose, true, _gc_timer, _gc_tracer->gc_id());
 577   trace("2");
 578 
 579   // Now all live objects are marked, compute the new object addresses.
 580 
 581   // It is not required that we traverse spaces in the same order in
 582   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 583   // tracking expects us to do so. See comment under phase4.
 584 
 585   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 586   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 587 
 588   PSOldGen* old_gen = heap->old_gen();
 589 
 590   // Begin compacting into the old gen
 591   PSMarkSweepDecorator::set_destination_decorator_tenured();
 592 
 593   // This will also compact the young gen spaces.
 594   old_gen->precompact();
 595 }
 596 
 597 void PSMarkSweep::mark_sweep_phase3() {
 598   // Adjust the pointers to reflect the new locations
 599   GCTraceTime tm("phase 3", PrintGCDetails && Verbose, true, _gc_timer, _gc_tracer->gc_id());
 600   trace("3");
 601 
 602   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 603   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 604 
 605   PSYoungGen* young_gen = heap->young_gen();
 606   PSOldGen* old_gen = heap->old_gen();
 607 
 608   // Need to clear claim bits before the tracing starts.
 609   ClassLoaderDataGraph::clear_claimed_marks();
 610 
 611   // General strong roots.
 612   Universe::oops_do(adjust_pointer_closure());
 613   JNIHandles::oops_do(adjust_pointer_closure());   // Global (strong) JNI handles
 614   CLDToOopClosure adjust_from_cld(adjust_pointer_closure());
 615   Threads::oops_do(adjust_pointer_closure(), &adjust_from_cld, NULL);
 616   ObjectSynchronizer::oops_do(adjust_pointer_closure());
 617   FlatProfiler::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   JNIHandles::weak_oops_do(adjust_pointer_closure());
 627 
 628   CodeBlobToOopClosure adjust_from_blobs(adjust_pointer_closure(), CodeBlobToOopClosure::FixRelocations);
 629   CodeCache::blobs_do(&adjust_from_blobs);
 630   StringTable::oops_do(adjust_pointer_closure());
 631   ref_processor()->weak_oops_do(adjust_pointer_closure());
 632   PSScavenge::reference_processor()->weak_oops_do(adjust_pointer_closure());
 633 
 634   adjust_marks();
 635 
 636   young_gen->adjust_pointers();
 637   old_gen->adjust_pointers();
 638 }
 639 
 640 void PSMarkSweep::mark_sweep_phase4() {
 641   EventMark m("4 compact heap");
 642   GCTraceTime tm("phase 4", PrintGCDetails && Verbose, true, _gc_timer, _gc_tracer->gc_id());
 643   trace("4");
 644 
 645   // All pointers are now adjusted, move objects accordingly
 646 
 647   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 648   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 649 
 650   PSYoungGen* young_gen = heap->young_gen();
 651   PSOldGen* old_gen = heap->old_gen();
 652 
 653   old_gen->compact();
 654   young_gen->compact();
 655 }
 656 
 657 jlong PSMarkSweep::millis_since_last_gc() {
 658   // We need a monotonically non-deccreasing time in ms but
 659   // os::javaTimeMillis() does not guarantee monotonicity.
 660   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 661   jlong ret_val = now - _time_of_last_gc;
 662   // XXX See note in genCollectedHeap::millis_since_last_gc().
 663   if (ret_val < 0) {
 664     NOT_PRODUCT(warning("time warp: "INT64_FORMAT, ret_val);)
 665     return 0;
 666   }
 667   return ret_val;
 668 }
 669 
 670 void PSMarkSweep::reset_millis_since_last_gc() {
 671   // We need a monotonically non-deccreasing time in ms but
 672   // os::javaTimeMillis() does not guarantee monotonicity.
 673   _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 674 }