1 /*
   2  * Copyright (c) 2001, 2013, 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 elapsedTimer        PSMarkSweep::_accumulated_time;
  58 jlong               PSMarkSweep::_time_of_last_gc   = 0;
  59 CollectorCounters*  PSMarkSweep::_counters = NULL;
  60 
  61 void PSMarkSweep::initialize() {
  62   MemRegion mr = Universe::heap()->reserved_region();
  63   _ref_processor = new ReferenceProcessor(mr);     // a vanilla ref proc
  64   _counters = new CollectorCounters("PSMarkSweep", 1);
  65 }
  66 
  67 // This method contains all heap specific policy for invoking mark sweep.
  68 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact
  69 // the heap. It will do nothing further. If we need to bail out for policy
  70 // reasons, scavenge before full gc, or any other specialized behavior, it
  71 // needs to be added here.
  72 //
  73 // Note that this method should only be called from the vm_thread while
  74 // at a safepoint!
  75 //
  76 // Note that the all_soft_refs_clear flag in the collector policy
  77 // may be true because this method can be called without intervening
  78 // activity.  For example when the heap space is tight and full measure
  79 // are being taken to free space.
  80 
  81 void PSMarkSweep::invoke(bool maximum_heap_compaction) {
  82   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
  83   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
  84   assert(!Universe::heap()->is_gc_active(), "not reentrant");
  85 
  86   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
  87   GCCause::Cause gc_cause = heap->gc_cause();
  88   PSAdaptiveSizePolicy* policy = heap->size_policy();
  89   IsGCActiveMark mark;
  90 
  91   if (ScavengeBeforeFullGC) {
  92     PSScavenge::invoke_no_policy();
  93   }
  94 
  95   const bool clear_all_soft_refs =
  96     heap->collector_policy()->should_clear_all_soft_refs();
  97 
  98   uint count = maximum_heap_compaction ? 1 : MarkSweepAlwaysCompactCount;
  99   UIntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);
 100   PSMarkSweep::invoke_no_policy(clear_all_soft_refs || maximum_heap_compaction);
 101 }
 102 
 103 // This method contains no policy. You should probably
 104 // be calling invoke() instead.
 105 bool PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
 106   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 107   assert(ref_processor() != NULL, "Sanity");
 108 
 109   if (GC_locker::check_active_before_gc()) {
 110     return false;
 111   }
 112 
 113   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 114   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 115   GCCause::Cause gc_cause = heap->gc_cause();
 116 
 117   _gc_timer->register_gc_start(os::elapsed_counter());
 118   _gc_tracer->report_gc_start(gc_cause, _gc_timer->gc_start());
 119 
 120   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 121 
 122   // The scope of casr should end after code that can change
 123   // CollectorPolicy::_should_clear_all_soft_refs.
 124   ClearedAllSoftRefs casr(clear_all_softrefs, heap->collector_policy());
 125 
 126   PSYoungGen* young_gen = heap->young_gen();
 127   PSOldGen* old_gen = heap->old_gen();
 128 
 129   // Increment the invocation count
 130   heap->increment_total_collections(true /* full */);
 131 
 132   // Save information needed to minimize mangling
 133   heap->record_gen_tops_before_GC();
 134 
 135   // We need to track unique mark sweep invocations as well.
 136   _total_invocations++;
 137 
 138   AdaptiveSizePolicyOutput(size_policy, heap->total_collections());
 139 
 140   heap->print_heap_before_gc();
 141   heap->trace_heap_before_gc(_gc_tracer);
 142 
 143   // Fill in TLABs
 144   heap->accumulate_statistics_all_tlabs();
 145   heap->ensure_parsability(true);  // retire TLABs
 146 
 147   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
 148     HandleMark hm;  // Discard invalid handles created during verification
 149     Universe::verify(" VerifyBeforeGC:");
 150   }
 151 
 152   // Verify object start arrays
 153   if (VerifyObjectStartArray &&
 154       VerifyBeforeGC) {
 155     old_gen->verify_object_start_array();
 156   }
 157 
 158   heap->pre_full_gc_dump(_gc_timer);
 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     gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
 169     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
 170     GCTraceTime t1(GCCauseString("Full GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
 171     TraceCollectorStats tcs(counters());
 172     TraceMemoryManagerStats tms(true /* Full GC */,gc_cause);
 173 
 174     if (TraceGen1Time) accumulated_time()->start();
 175 
 176     // Let the size policy know we're starting
 177     size_policy->major_collection_begin();
 178 
 179     CodeCache::gc_prologue();
 180     Threads::gc_prologue();
 181     BiasedLocking::preserve_marks();
 182 
 183     // Capture heap size before collection for printing.
 184     size_t prev_used = heap->used();
 185 
 186     // Capture metadata size before collection for sizing.
 187     size_t metadata_prev_used = MetaspaceAux::allocated_used_bytes();
 188 
 189     // For PrintGCDetails
 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     COMPILER2_PRESENT(DerivedPointerTable::clear());
 196 
 197     ref_processor()->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/);
 198     ref_processor()->setup_policy(clear_all_softrefs);
 199 
 200     mark_sweep_phase1(clear_all_softrefs);
 201 
 202     mark_sweep_phase2();
 203 
 204     // Don't add any more derived pointers during phase3
 205     COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
 206     COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
 207 
 208     mark_sweep_phase3();
 209 
 210     mark_sweep_phase4();
 211 
 212     restore_marks();
 213 
 214     deallocate_stacks();
 215 
 216     if (ZapUnusedHeapArea) {
 217       // Do a complete mangle (top to end) because the usage for
 218       // scratch does not maintain a top pointer.
 219       young_gen->to_space()->mangle_unused_area_complete();
 220     }
 221 
 222     eden_empty = young_gen->eden_space()->is_empty();
 223     if (!eden_empty) {
 224       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
 225     }
 226 
 227     // Update heap occupancy information which is used as
 228     // input to soft ref clearing policy at the next gc.
 229     Universe::update_heap_info_at_gc();
 230 
 231     survivors_empty = young_gen->from_space()->is_empty() &&
 232                       young_gen->to_space()->is_empty();
 233     young_gen_empty = eden_empty && survivors_empty;
 234 
 235     BarrierSet* bs = heap->barrier_set();
 236     if (bs->is_a(BarrierSet::ModRef)) {
 237       ModRefBarrierSet* modBS = (ModRefBarrierSet*)bs;
 238       MemRegion old_mr = heap->old_gen()->reserved();
 239       if (young_gen_empty) {
 240         modBS->clear(MemRegion(old_mr.start(), old_mr.end()));
 241       } else {
 242         modBS->invalidate(MemRegion(old_mr.start(), old_mr.end()));
 243       }
 244     }
 245 
 246     // Delete metaspaces for unloaded class loaders and clean up loader_data graph
 247     ClassLoaderDataGraph::purge();
 248     MetaspaceAux::verify_metrics();
 249 
 250     BiasedLocking::restore_marks();
 251     Threads::gc_epilogue();
 252     CodeCache::gc_epilogue();
 253     JvmtiExport::gc_epilogue();
 254 
 255     COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
 256 
 257     ref_processor()->enqueue_discovered_references(NULL);
 258 
 259     // Update time of last GC
 260     reset_millis_since_last_gc();
 261 
 262     // Let the size policy know we're done
 263     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
 264 
 265     if (UseAdaptiveSizePolicy) {
 266 
 267       if (PrintAdaptiveSizePolicy) {
 268         gclog_or_tty->print("AdaptiveSizeStart: ");
 269         gclog_or_tty->stamp();
 270         gclog_or_tty->print_cr(" collection: %d ",
 271                        heap->total_collections());
 272         if (Verbose) {
 273           gclog_or_tty->print("old_gen_capacity: %d young_gen_capacity: %d",
 274             old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
 275         }
 276       }
 277 
 278       // Don't check if the size_policy is ready here.  Let
 279       // the size_policy check that internally.
 280       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
 281           ((gc_cause != GCCause::_java_lang_system_gc) ||
 282             UseAdaptiveSizePolicyWithSystemGC)) {
 283         // Swap the survivor spaces if from_space is empty
 284         if (UseAdaptiveSizePolicyResizeYoungGenAtMajorCollection &&
 285             young_gen->from_space()->is_empty()) {
 286           young_gen->from_space()->clear(SpaceDecorator::Mangle);
 287           young_gen->swap_spaces();
 288         }
 289 
 290         // Calculate optimal free space amounts
 291         assert(young_gen->max_size() >
 292           young_gen->from_space()->capacity_in_bytes() +
 293           young_gen->to_space()->capacity_in_bytes(),
 294           "Sizes of space in young gen are out-of-bounds");
 295 
 296         size_t young_live = young_gen->used_in_bytes();
 297         size_t eden_live = young_gen->eden_space()->used_in_bytes();
 298         size_t old_live = old_gen->used_in_bytes();
 299         size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
 300         size_t max_old_gen_size = old_gen->max_gen_size();
 301         size_t max_eden_size = young_gen->max_size() -
 302           young_gen->from_space()->capacity_in_bytes() -
 303           young_gen->to_space()->capacity_in_bytes();
 304 
 305         // Used for diagnostics
 306         size_policy->clear_generation_free_space_flags();
 307 
 308         size_policy->compute_generations_free_space(young_live,
 309                                                     eden_live,
 310                                                     old_live,
 311                                                     cur_eden,
 312                                                     max_old_gen_size,
 313                                                     max_eden_size,
 314                                                     true /* full gc*/);
 315 
 316         size_policy->check_gc_overhead_limit(young_live,
 317                                              eden_live,
 318                                              max_old_gen_size,
 319                                              max_eden_size,
 320                                              true /* full gc*/,
 321                                              gc_cause,
 322                                              heap->collector_policy());
 323 
 324         size_policy->decay_supplemental_growth(true /* full gc*/);
 325 
 326         heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
 327 
 328         if (UseAdaptiveSizePolicyResizeYoungGenAtMajorCollection) {
 329           heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
 330                                  size_policy->calculated_survivor_size_in_bytes());
 331         }
 332       }
 333       if (PrintAdaptiveSizePolicy) {
 334         gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",
 335                        heap->total_collections());
 336       }
 337     }
 338 
 339     if (UsePerfData) {
 340       heap->gc_policy_counters()->update_counters();
 341       heap->gc_policy_counters()->update_old_capacity(
 342         old_gen->capacity_in_bytes());
 343       heap->gc_policy_counters()->update_young_capacity(
 344         young_gen->capacity_in_bytes());
 345     }
 346 
 347     heap->resize_all_tlabs();
 348 
 349     // We collected the heap, recalculate the metaspace capacity
 350     MetaspaceGC::compute_new_size();
 351 
 352     if (TraceGen1Time) accumulated_time()->stop();
 353 
 354     if (PrintGC) {
 355       if (PrintGCDetails) {
 356         // Don't print a GC timestamp here.  This is after the GC so
 357         // would be confusing.
 358         young_gen->print_used_change(young_gen_prev_used);
 359         old_gen->print_used_change(old_gen_prev_used);
 360       }
 361       heap->print_heap_change(prev_used);
 362       if (PrintGCDetails) {
 363         MetaspaceAux::print_metaspace_change(metadata_prev_used);
 364       }
 365     }
 366 
 367     // Track memory usage and detect low memory
 368     MemoryService::track_memory_usage();
 369     heap->update_counters();
 370   }
 371 
 372   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
 373     HandleMark hm;  // Discard invalid handles created during verification
 374     Universe::verify(" VerifyAfterGC:");
 375   }
 376 
 377   // Re-verify object start arrays
 378   if (VerifyObjectStartArray &&
 379       VerifyAfterGC) {
 380     old_gen->verify_object_start_array();
 381   }
 382 
 383   if (ZapUnusedHeapArea) {
 384     old_gen->object_space()->check_mangled_unused_area_complete();
 385   }
 386 
 387   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 388 
 389   heap->print_heap_after_gc();
 390   heap->trace_heap_after_gc(_gc_tracer);
 391 
 392   heap->post_full_gc_dump(_gc_timer);
 393 
 394 #ifdef TRACESPINNING
 395   ParallelTaskTerminator::print_termination_counts();
 396 #endif
 397 
 398   _gc_timer->register_gc_end(os::elapsed_counter());
 399 
 400   _gc_tracer->report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
 401 
 402   return true;
 403 }
 404 
 405 bool PSMarkSweep::absorb_live_data_from_eden(PSAdaptiveSizePolicy* size_policy,
 406                                              PSYoungGen* young_gen,
 407                                              PSOldGen* old_gen) {
 408   MutableSpace* const eden_space = young_gen->eden_space();
 409   assert(!eden_space->is_empty(), "eden must be non-empty");
 410   assert(young_gen->virtual_space()->alignment() ==
 411          old_gen->virtual_space()->alignment(), "alignments do not match");
 412 
 413   if (!(UseAdaptiveSizePolicy && UseAdaptiveGCBoundary)) {
 414     return false;
 415   }
 416 
 417   // Both generations must be completely committed.
 418   if (young_gen->virtual_space()->uncommitted_size() != 0) {
 419     return false;
 420   }
 421   if (old_gen->virtual_space()->uncommitted_size() != 0) {
 422     return false;
 423   }
 424 
 425   // Figure out how much to take from eden.  Include the average amount promoted
 426   // in the total; otherwise the next young gen GC will simply bail out to a
 427   // full GC.
 428   const size_t alignment = old_gen->virtual_space()->alignment();
 429   const size_t eden_used = eden_space->used_in_bytes();
 430   const size_t promoted = (size_t)size_policy->avg_promoted()->padded_average();
 431   const size_t absorb_size = align_size_up(eden_used + promoted, alignment);
 432   const size_t eden_capacity = eden_space->capacity_in_bytes();
 433 
 434   if (absorb_size >= eden_capacity) {
 435     return false; // Must leave some space in eden.
 436   }
 437 
 438   const size_t new_young_size = young_gen->capacity_in_bytes() - absorb_size;
 439   if (new_young_size < young_gen->min_gen_size()) {
 440     return false; // Respect young gen minimum size.
 441   }
 442 
 443   if (TraceAdaptiveGCBoundary && Verbose) {
 444     gclog_or_tty->print(" absorbing " SIZE_FORMAT "K:  "
 445                         "eden " SIZE_FORMAT "K->" SIZE_FORMAT "K "
 446                         "from " SIZE_FORMAT "K, to " SIZE_FORMAT "K "
 447                         "young_gen " SIZE_FORMAT "K->" SIZE_FORMAT "K ",
 448                         absorb_size / K,
 449                         eden_capacity / K, (eden_capacity - absorb_size) / K,
 450                         young_gen->from_space()->used_in_bytes() / K,
 451                         young_gen->to_space()->used_in_bytes() / K,
 452                         young_gen->capacity_in_bytes() / K, new_young_size / K);
 453   }
 454 
 455   // Fill the unused part of the old gen.
 456   MutableSpace* const old_space = old_gen->object_space();
 457   HeapWord* const unused_start = old_space->top();
 458   size_t const unused_words = pointer_delta(old_space->end(), unused_start);
 459 
 460   if (unused_words > 0) {
 461     if (unused_words < CollectedHeap::min_fill_size()) {
 462       return false;  // If the old gen cannot be filled, must give up.
 463     }
 464     CollectedHeap::fill_with_objects(unused_start, unused_words);
 465   }
 466 
 467   // Take the live data from eden and set both top and end in the old gen to
 468   // eden top.  (Need to set end because reset_after_change() mangles the region
 469   // from end to virtual_space->high() in debug builds).
 470   HeapWord* const new_top = eden_space->top();
 471   old_gen->virtual_space()->expand_into(young_gen->virtual_space(),
 472                                         absorb_size);
 473   young_gen->reset_after_change();
 474   old_space->set_top(new_top);
 475   old_space->set_end(new_top);
 476   old_gen->reset_after_change();
 477 
 478   // Update the object start array for the filler object and the data from eden.
 479   ObjectStartArray* const start_array = old_gen->start_array();
 480   for (HeapWord* p = unused_start; p < new_top; p += oop(p)->size()) {
 481     start_array->allocate_block(p);
 482   }
 483 
 484   // Could update the promoted average here, but it is not typically updated at
 485   // full GCs and the value to use is unclear.  Something like
 486   //
 487   // cur_promoted_avg + absorb_size / number_of_scavenges_since_last_full_gc.
 488 
 489   size_policy->set_bytes_absorbed_from_eden(absorb_size);
 490   return true;
 491 }
 492 
 493 void PSMarkSweep::allocate_stacks() {
 494   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 495   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 496 
 497   PSYoungGen* young_gen = heap->young_gen();
 498 
 499   MutableSpace* to_space = young_gen->to_space();
 500   _preserved_marks = (PreservedMark*)to_space->top();
 501   _preserved_count = 0;
 502 
 503   // We want to calculate the size in bytes first.
 504   _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));
 505   // Now divide by the size of a PreservedMark
 506   _preserved_count_max /= sizeof(PreservedMark);
 507 }
 508 
 509 
 510 void PSMarkSweep::deallocate_stacks() {
 511   _preserved_mark_stack.clear(true);
 512   _preserved_oop_stack.clear(true);
 513   _marking_stack.clear();
 514   _objarray_stack.clear(true);
 515 }
 516 
 517 void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 518   // Recursively traverse all live objects and mark them
 519   GCTraceTime tm("phase 1", PrintGCDetails && Verbose, true, _gc_timer);
 520   trace(" 1");
 521 
 522   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 523   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 524 
 525   // Need to clear claim bits before the tracing starts.
 526   ClassLoaderDataGraph::clear_claimed_marks();
 527 
 528   // General strong roots.
 529   {
 530     ParallelScavengeHeap::ParStrongRootsScope psrs;
 531     Universe::oops_do(mark_and_push_closure());
 532     JNIHandles::oops_do(mark_and_push_closure());   // Global (strong) JNI handles
 533     CLDToOopClosure mark_and_push_from_cld(mark_and_push_closure());
 534     CodeBlobToOopClosure each_active_code_blob(mark_and_push_closure(), /*do_marking=*/ true);
 535     Threads::oops_do(mark_and_push_closure(), &mark_and_push_from_cld, &each_active_code_blob);
 536     ObjectSynchronizer::oops_do(mark_and_push_closure());
 537     FlatProfiler::oops_do(mark_and_push_closure());
 538     Management::oops_do(mark_and_push_closure());
 539     JvmtiExport::oops_do(mark_and_push_closure());
 540     SystemDictionary::always_strong_oops_do(mark_and_push_closure());
 541     ClassLoaderDataGraph::always_strong_oops_do(mark_and_push_closure(), follow_klass_closure(), true);
 542     // Do not treat nmethods as strong roots for mark/sweep, since we can unload them.
 543     //CodeCache::scavenge_root_nmethods_do(CodeBlobToOopClosure(mark_and_push_closure()));
 544   }
 545 
 546   // Flush marking stack.
 547   follow_stack();
 548 
 549   // Process reference objects found during marking
 550   {
 551     ref_processor()->setup_policy(clear_all_softrefs);
 552     const ReferenceProcessorStats& stats =
 553       ref_processor()->process_discovered_references(
 554         is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL, _gc_timer);
 555     gc_tracer()->report_gc_reference_stats(stats);
 556   }
 557 
 558   // This is the point where the entire marking should have completed.
 559   assert(_marking_stack.is_empty(), "Marking should have completed");
 560 
 561   // Unload classes and purge the SystemDictionary.
 562   bool purged_class = SystemDictionary::do_unloading(is_alive_closure());
 563 
 564   // Unload nmethods.
 565   CodeCache::do_unloading(is_alive_closure(), purged_class);
 566 
 567   // Prune dead klasses from subklass/sibling/implementor lists.
 568   Klass::clean_weak_klass_links(is_alive_closure());
 569 
 570   // Delete entries for dead interned strings.
 571   StringTable::unlink(is_alive_closure());
 572 
 573   // Clean up unreferenced symbols in symbol table.
 574   SymbolTable::unlink();
 575   _gc_tracer->report_object_count_after_gc(is_alive_closure());
 576 }
 577 
 578 
 579 void PSMarkSweep::mark_sweep_phase2() {
 580   GCTraceTime tm("phase 2", PrintGCDetails && Verbose, true, _gc_timer);
 581   trace("2");
 582 
 583   // Now all live objects are marked, compute the new object addresses.
 584 
 585   // It is not required that we traverse spaces in the same order in
 586   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 587   // tracking expects us to do so. See comment under phase4.
 588 
 589   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 590   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 591 
 592   PSOldGen* old_gen = heap->old_gen();
 593 
 594   // Begin compacting into the old gen
 595   PSMarkSweepDecorator::set_destination_decorator_tenured();
 596 
 597   // This will also compact the young gen spaces.
 598   old_gen->precompact();
 599 }
 600 
 601 // This should be moved to the shared markSweep code!
 602 class PSAlwaysTrueClosure: public BoolObjectClosure {
 603 public:
 604   bool do_object_b(oop p) { return true; }
 605 };
 606 static PSAlwaysTrueClosure always_true;
 607 
 608 void PSMarkSweep::mark_sweep_phase3() {
 609   // Adjust the pointers to reflect the new locations
 610   GCTraceTime tm("phase 3", PrintGCDetails && Verbose, true, _gc_timer);
 611   trace("3");
 612 
 613   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 614   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 615 
 616   PSYoungGen* young_gen = heap->young_gen();
 617   PSOldGen* old_gen = heap->old_gen();
 618 
 619   // Need to clear claim bits before the tracing starts.
 620   ClassLoaderDataGraph::clear_claimed_marks();
 621 
 622   // General strong roots.
 623   Universe::oops_do(adjust_pointer_closure());
 624   JNIHandles::oops_do(adjust_pointer_closure());   // Global (strong) JNI handles
 625   CLDToOopClosure adjust_from_cld(adjust_pointer_closure());
 626   Threads::oops_do(adjust_pointer_closure(), &adjust_from_cld, NULL);
 627   ObjectSynchronizer::oops_do(adjust_pointer_closure());
 628   FlatProfiler::oops_do(adjust_pointer_closure());
 629   Management::oops_do(adjust_pointer_closure());
 630   JvmtiExport::oops_do(adjust_pointer_closure());
 631   // SO_AllClasses
 632   SystemDictionary::oops_do(adjust_pointer_closure());
 633   ClassLoaderDataGraph::oops_do(adjust_pointer_closure(), adjust_klass_closure(), true);
 634 
 635   // Now adjust pointers in remaining weak roots.  (All of which should
 636   // have been cleared if they pointed to non-surviving objects.)
 637   // Global (weak) JNI handles
 638   JNIHandles::weak_oops_do(&always_true, adjust_pointer_closure());
 639 
 640   CodeCache::oops_do(adjust_pointer_closure());
 641   StringTable::oops_do(adjust_pointer_closure());
 642   ref_processor()->weak_oops_do(adjust_pointer_closure());
 643   PSScavenge::reference_processor()->weak_oops_do(adjust_pointer_closure());
 644 
 645   adjust_marks();
 646 
 647   young_gen->adjust_pointers();
 648   old_gen->adjust_pointers();
 649 }
 650 
 651 void PSMarkSweep::mark_sweep_phase4() {
 652   EventMark m("4 compact heap");
 653   GCTraceTime tm("phase 4", PrintGCDetails && Verbose, true, _gc_timer);
 654   trace("4");
 655 
 656   // All pointers are now adjusted, move objects accordingly
 657 
 658   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 659   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 660 
 661   PSYoungGen* young_gen = heap->young_gen();
 662   PSOldGen* old_gen = heap->old_gen();
 663 
 664   old_gen->compact();
 665   young_gen->compact();
 666 }
 667 
 668 jlong PSMarkSweep::millis_since_last_gc() {
 669   // We need a monotonically non-deccreasing time in ms but
 670   // os::javaTimeMillis() does not guarantee monotonicity.
 671   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 672   jlong ret_val = now - _time_of_last_gc;
 673   // XXX See note in genCollectedHeap::millis_since_last_gc().
 674   if (ret_val < 0) {
 675     NOT_PRODUCT(warning("time warp: "INT64_FORMAT, ret_val);)
 676     return 0;
 677   }
 678   return ret_val;
 679 }
 680 
 681 void PSMarkSweep::reset_millis_since_last_gc() {
 682   // We need a monotonically non-deccreasing time in ms but
 683   // os::javaTimeMillis() does not guarantee monotonicity.
 684   _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 685 }