1 /*
   2  * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "aot/aotLoader.hpp"
  27 #include "classfile/stringTable.hpp"
  28 #include "classfile/symbolTable.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "gc/parallel/parallelScavengeHeap.hpp"
  32 #include "gc/parallel/psAdaptiveSizePolicy.hpp"
  33 #include "gc/parallel/psMarkSweep.hpp"
  34 #include "gc/parallel/psMarkSweepDecorator.hpp"
  35 #include "gc/parallel/psOldGen.hpp"
  36 #include "gc/parallel/psScavenge.hpp"
  37 #include "gc/parallel/psYoungGen.hpp"
  38 #include "gc/serial/markSweep.hpp"
  39 #include "gc/shared/gcCause.hpp"
  40 #include "gc/shared/gcHeapSummary.hpp"
  41 #include "gc/shared/gcId.hpp"
  42 #include "gc/shared/gcLocker.hpp"
  43 #include "gc/shared/gcTimer.hpp"
  44 #include "gc/shared/gcTrace.hpp"
  45 #include "gc/shared/gcTraceTime.inline.hpp"
  46 #include "gc/shared/isGCActiveMark.hpp"
  47 #include "gc/shared/referencePolicy.hpp"
  48 #include "gc/shared/referenceProcessor.hpp"
  49 #include "gc/shared/spaceDecorator.hpp"
  50 #include "gc/shared/weakProcessor.hpp"
  51 #include "logging/log.hpp"
  52 #include "oops/oop.inline.hpp"
  53 #include "runtime/biasedLocking.hpp"
  54 #include "runtime/flags/flagSetting.hpp"
  55 #include "runtime/handles.inline.hpp"
  56 #include "runtime/safepoint.hpp"
  57 #include "runtime/vmThread.hpp"
  58 #include "services/management.hpp"
  59 #include "services/memoryService.hpp"
  60 #include "utilities/align.hpp"
  61 #include "utilities/events.hpp"
  62 #include "utilities/stack.inline.hpp"
  63 
  64 elapsedTimer        PSMarkSweep::_accumulated_time;
  65 jlong               PSMarkSweep::_time_of_last_gc   = 0;
  66 CollectorCounters*  PSMarkSweep::_counters = NULL;
  67 
  68 SpanSubjectToDiscoveryClosure PSMarkSweep::_span_discoverer;
  69 
  70 void PSMarkSweep::initialize() {
  71   _span_discoverer.set_span(ParallelScavengeHeap::heap()->reserved_region());
  72   set_ref_processor(new ReferenceProcessor(&_span_discoverer));     // a vanilla ref proc
  73   _counters = new CollectorCounters("PSMarkSweep", 1);
  74 }
  75 
  76 // This method contains all heap specific policy for invoking mark sweep.
  77 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact
  78 // the heap. It will do nothing further. If we need to bail out for policy
  79 // reasons, scavenge before full gc, or any other specialized behavior, it
  80 // needs to be added here.
  81 //
  82 // Note that this method should only be called from the vm_thread while
  83 // at a safepoint!
  84 //
  85 // Note that the all_soft_refs_clear flag in the collector policy
  86 // may be true because this method can be called without intervening
  87 // activity.  For example when the heap space is tight and full measure
  88 // are being taken to free space.
  89 
  90 void PSMarkSweep::invoke(bool maximum_heap_compaction) {
  91   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
  92   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
  93   assert(!ParallelScavengeHeap::heap()->is_gc_active(), "not reentrant");
  94 
  95   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
  96   GCCause::Cause gc_cause = heap->gc_cause();
  97   PSAdaptiveSizePolicy* policy = heap->size_policy();
  98   IsGCActiveMark mark;
  99 
 100   if (ScavengeBeforeFullGC) {
 101     PSScavenge::invoke_no_policy();
 102   }
 103 
 104   const bool clear_all_soft_refs =
 105     heap->soft_ref_policy()->should_clear_all_soft_refs();
 106 
 107   uint count = maximum_heap_compaction ? 1 : MarkSweepAlwaysCompactCount;
 108   UIntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);
 109   PSMarkSweep::invoke_no_policy(clear_all_soft_refs || maximum_heap_compaction);
 110 }
 111 
 112 // This method contains no policy. You should probably
 113 // be calling invoke() instead.
 114 bool PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
 115   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 116   assert(ref_processor() != NULL, "Sanity");
 117 
 118   if (GCLocker::check_active_before_gc()) {
 119     return false;
 120   }
 121 
 122   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 123   GCCause::Cause gc_cause = heap->gc_cause();
 124 
 125   GCIdMark gc_id_mark;
 126   _gc_timer->register_gc_start();
 127   _gc_tracer->report_gc_start(gc_cause, _gc_timer->gc_start());
 128 
 129   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 130 
 131   // The scope of casr should end after code that can change
 132   // CollectorPolicy::_should_clear_all_soft_refs.
 133   ClearedAllSoftRefs casr(clear_all_softrefs, heap->soft_ref_policy());
 134 
 135   PSYoungGen* young_gen = heap->young_gen();
 136   PSOldGen* old_gen = heap->old_gen();
 137 
 138   // Increment the invocation count
 139   heap->increment_total_collections(true /* full */);
 140 
 141   // Save information needed to minimize mangling
 142   heap->record_gen_tops_before_GC();
 143 
 144   // We need to track unique mark sweep invocations as well.
 145   _total_invocations++;
 146 
 147   heap->print_heap_before_gc();
 148   heap->trace_heap_before_gc(_gc_tracer);
 149 
 150   // Fill in TLABs
 151   heap->accumulate_statistics_all_tlabs();
 152   heap->ensure_parsability(true);  // retire TLABs
 153 
 154   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
 155     HandleMark hm;  // Discard invalid handles created during verification
 156     Universe::verify("Before GC");
 157   }
 158 
 159   // Verify object start arrays
 160   if (VerifyObjectStartArray &&
 161       VerifyBeforeGC) {
 162     old_gen->verify_object_start_array();
 163   }
 164 
 165   // Filled in below to track the state of the young gen after the collection.
 166   bool eden_empty;
 167   bool survivors_empty;
 168   bool young_gen_empty;
 169 
 170   {
 171     HandleMark hm;
 172 
 173     GCTraceCPUTime tcpu;
 174     GCTraceTime(Info, gc) t("Pause Full", NULL, gc_cause, true);
 175 
 176     heap->pre_full_gc_dump(_gc_timer);
 177 
 178     TraceCollectorStats tcs(counters());
 179     TraceMemoryManagerStats tms(heap->old_gc_manager(),gc_cause);
 180 
 181     if (log_is_enabled(Debug, gc, heap, exit)) {
 182       accumulated_time()->start();
 183     }
 184 
 185     // Let the size policy know we're starting
 186     size_policy->major_collection_begin();
 187 
 188     CodeCache::gc_prologue();
 189     BiasedLocking::preserve_marks();
 190 
 191     // Capture metadata size before collection for sizing.
 192     size_t metadata_prev_used = MetaspaceUtils::used_bytes();
 193 
 194     size_t old_gen_prev_used = old_gen->used_in_bytes();
 195     size_t young_gen_prev_used = young_gen->used_in_bytes();
 196 
 197     allocate_stacks();
 198 
 199 #if COMPILER2_OR_JVMCI
 200     DerivedPointerTable::clear();
 201 #endif
 202 
 203     ref_processor()->enable_discovery();
 204     ref_processor()->setup_policy(clear_all_softrefs);
 205 
 206     mark_sweep_phase1(clear_all_softrefs);
 207 
 208     mark_sweep_phase2();
 209 
 210 #if COMPILER2_OR_JVMCI
 211     // Don't add any more derived pointers during phase3
 212     assert(DerivedPointerTable::is_active(), "Sanity");
 213     DerivedPointerTable::set_active(false);
 214 #endif
 215 
 216     mark_sweep_phase3();
 217 
 218     mark_sweep_phase4();
 219 
 220     restore_marks();
 221 
 222     deallocate_stacks();
 223 
 224     if (ZapUnusedHeapArea) {
 225       // Do a complete mangle (top to end) because the usage for
 226       // scratch does not maintain a top pointer.
 227       young_gen->to_space()->mangle_unused_area_complete();
 228     }
 229 
 230     eden_empty = young_gen->eden_space()->is_empty();
 231     if (!eden_empty) {
 232       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
 233     }
 234 
 235     // Update heap occupancy information which is used as
 236     // input to soft ref clearing policy at the next gc.
 237     Universe::update_heap_info_at_gc();
 238 
 239     survivors_empty = young_gen->from_space()->is_empty() &&
 240                       young_gen->to_space()->is_empty();
 241     young_gen_empty = eden_empty && survivors_empty;
 242 
 243     PSCardTable* card_table = heap->card_table();
 244     MemRegion old_mr = heap->old_gen()->reserved();
 245     if (young_gen_empty) {
 246       card_table->clear(MemRegion(old_mr.start(), old_mr.end()));
 247     } else {
 248       card_table->invalidate(MemRegion(old_mr.start(), old_mr.end()));
 249     }
 250 
 251     // Delete metaspaces for unloaded class loaders and clean up loader_data graph
 252     ClassLoaderDataGraph::purge();
 253     MetaspaceUtils::verify_metrics();
 254 
 255     BiasedLocking::restore_marks();
 256     CodeCache::gc_epilogue();
 257     JvmtiExport::gc_epilogue();
 258 
 259 #if COMPILER2_OR_JVMCI
 260     DerivedPointerTable::update_pointers();
 261 #endif
 262 
 263     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->num_q());
 264 
 265     ref_processor()->enqueue_discovered_references(NULL, &pt);
 266 
 267     pt.print_enqueue_phase();
 268 
 269     // Update time of last GC
 270     reset_millis_since_last_gc();
 271 
 272     // Let the size policy know we're done
 273     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
 274 
 275     if (UseAdaptiveSizePolicy) {
 276 
 277      log_debug(gc, ergo)("AdaptiveSizeStart: collection: %d ", heap->total_collections());
 278      log_trace(gc, ergo)("old_gen_capacity: " SIZE_FORMAT " young_gen_capacity: " SIZE_FORMAT,
 279                          old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
 280 
 281       // Don't check if the size_policy is ready here.  Let
 282       // the size_policy check that internally.
 283       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
 284           AdaptiveSizePolicy::should_update_promo_stats(gc_cause)) {
 285         // Swap the survivor spaces if from_space is empty. The
 286         // resize_young_gen() called below is normally used after
 287         // a successful young GC and swapping of survivor spaces;
 288         // otherwise, it will fail to resize the young gen with
 289         // the current implementation.
 290         if (young_gen->from_space()->is_empty()) {
 291           young_gen->from_space()->clear(SpaceDecorator::Mangle);
 292           young_gen->swap_spaces();
 293         }
 294 
 295         // Calculate optimal free space amounts
 296         assert(young_gen->max_size() >
 297           young_gen->from_space()->capacity_in_bytes() +
 298           young_gen->to_space()->capacity_in_bytes(),
 299           "Sizes of space in young gen are out-of-bounds");
 300 
 301         size_t young_live = young_gen->used_in_bytes();
 302         size_t eden_live = young_gen->eden_space()->used_in_bytes();
 303         size_t old_live = old_gen->used_in_bytes();
 304         size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
 305         size_t max_old_gen_size = old_gen->max_gen_size();
 306         size_t max_eden_size = young_gen->max_size() -
 307           young_gen->from_space()->capacity_in_bytes() -
 308           young_gen->to_space()->capacity_in_bytes();
 309 
 310         // Used for diagnostics
 311         size_policy->clear_generation_free_space_flags();
 312 
 313         size_policy->compute_generations_free_space(young_live,
 314                                                     eden_live,
 315                                                     old_live,
 316                                                     cur_eden,
 317                                                     max_old_gen_size,
 318                                                     max_eden_size,
 319                                                     true /* full gc*/);
 320 
 321         size_policy->check_gc_overhead_limit(young_live,
 322                                              eden_live,
 323                                              max_old_gen_size,
 324                                              max_eden_size,
 325                                              true /* full gc*/,
 326                                              gc_cause,
 327                                              heap->soft_ref_policy());
 328 
 329         size_policy->decay_supplemental_growth(true /* full gc*/);
 330 
 331         heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
 332 
 333         heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
 334                                size_policy->calculated_survivor_size_in_bytes());
 335       }
 336       log_debug(gc, ergo)("AdaptiveSizeStop: collection: %d ", heap->total_collections());
 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 (log_is_enabled(Debug, gc, heap, exit)) {
 353       accumulated_time()->stop();
 354     }
 355 
 356     young_gen->print_used_change(young_gen_prev_used);
 357     old_gen->print_used_change(old_gen_prev_used);
 358     MetaspaceUtils::print_metaspace_change(metadata_prev_used);
 359 
 360     // Track memory usage and detect low memory
 361     MemoryService::track_memory_usage();
 362     heap->update_counters();
 363 
 364     heap->post_full_gc_dump(_gc_timer);
 365   }
 366 
 367   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
 368     HandleMark hm;  // Discard invalid handles created during verification
 369     Universe::verify("After GC");
 370   }
 371 
 372   // Re-verify object start arrays
 373   if (VerifyObjectStartArray &&
 374       VerifyAfterGC) {
 375     old_gen->verify_object_start_array();
 376   }
 377 
 378   if (ZapUnusedHeapArea) {
 379     old_gen->object_space()->check_mangled_unused_area_complete();
 380   }
 381 
 382   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 383 
 384   heap->print_heap_after_gc();
 385   heap->trace_heap_after_gc(_gc_tracer);
 386 
 387 #ifdef TRACESPINNING
 388   ParallelTaskTerminator::print_termination_counts();
 389 #endif
 390 
 391   AdaptiveSizePolicyOutput::print(size_policy, heap->total_collections());
 392 
 393   _gc_timer->register_gc_end();
 394 
 395   _gc_tracer->report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
 396 
 397   return true;
 398 }
 399 
 400 bool PSMarkSweep::absorb_live_data_from_eden(PSAdaptiveSizePolicy* size_policy,
 401                                              PSYoungGen* young_gen,
 402                                              PSOldGen* old_gen) {
 403   MutableSpace* const eden_space = young_gen->eden_space();
 404   assert(!eden_space->is_empty(), "eden must be non-empty");
 405   assert(young_gen->virtual_space()->alignment() ==
 406          old_gen->virtual_space()->alignment(), "alignments do not match");
 407 
 408   if (!(UseAdaptiveSizePolicy && UseAdaptiveGCBoundary)) {
 409     return false;
 410   }
 411 
 412   // Both generations must be completely committed.
 413   if (young_gen->virtual_space()->uncommitted_size() != 0) {
 414     return false;
 415   }
 416   if (old_gen->virtual_space()->uncommitted_size() != 0) {
 417     return false;
 418   }
 419 
 420   // Figure out how much to take from eden.  Include the average amount promoted
 421   // in the total; otherwise the next young gen GC will simply bail out to a
 422   // full GC.
 423   const size_t alignment = old_gen->virtual_space()->alignment();
 424   const size_t eden_used = eden_space->used_in_bytes();
 425   const size_t promoted = (size_t)size_policy->avg_promoted()->padded_average();
 426   const size_t absorb_size = align_up(eden_used + promoted, alignment);
 427   const size_t eden_capacity = eden_space->capacity_in_bytes();
 428 
 429   if (absorb_size >= eden_capacity) {
 430     return false; // Must leave some space in eden.
 431   }
 432 
 433   const size_t new_young_size = young_gen->capacity_in_bytes() - absorb_size;
 434   if (new_young_size < young_gen->min_gen_size()) {
 435     return false; // Respect young gen minimum size.
 436   }
 437 
 438   log_trace(heap, ergo)(" absorbing " SIZE_FORMAT "K:  "
 439                         "eden " SIZE_FORMAT "K->" SIZE_FORMAT "K "
 440                         "from " SIZE_FORMAT "K, to " SIZE_FORMAT "K "
 441                         "young_gen " SIZE_FORMAT "K->" SIZE_FORMAT "K ",
 442                         absorb_size / K,
 443                         eden_capacity / K, (eden_capacity - absorb_size) / K,
 444                         young_gen->from_space()->used_in_bytes() / K,
 445                         young_gen->to_space()->used_in_bytes() / K,
 446                         young_gen->capacity_in_bytes() / K, new_young_size / K);
 447 
 448   // Fill the unused part of the old gen.
 449   MutableSpace* const old_space = old_gen->object_space();
 450   HeapWord* const unused_start = old_space->top();
 451   size_t const unused_words = pointer_delta(old_space->end(), unused_start);
 452 
 453   if (unused_words > 0) {
 454     if (unused_words < CollectedHeap::min_fill_size()) {
 455       return false;  // If the old gen cannot be filled, must give up.
 456     }
 457     CollectedHeap::fill_with_objects(unused_start, unused_words);
 458   }
 459 
 460   // Take the live data from eden and set both top and end in the old gen to
 461   // eden top.  (Need to set end because reset_after_change() mangles the region
 462   // from end to virtual_space->high() in debug builds).
 463   HeapWord* const new_top = eden_space->top();
 464   old_gen->virtual_space()->expand_into(young_gen->virtual_space(),
 465                                         absorb_size);
 466   young_gen->reset_after_change();
 467   old_space->set_top(new_top);
 468   old_space->set_end(new_top);
 469   old_gen->reset_after_change();
 470 
 471   // Update the object start array for the filler object and the data from eden.
 472   ObjectStartArray* const start_array = old_gen->start_array();
 473   for (HeapWord* p = unused_start; p < new_top; p += oop(p)->size()) {
 474     start_array->allocate_block(p);
 475   }
 476 
 477   // Could update the promoted average here, but it is not typically updated at
 478   // full GCs and the value to use is unclear.  Something like
 479   //
 480   // cur_promoted_avg + absorb_size / number_of_scavenges_since_last_full_gc.
 481 
 482   size_policy->set_bytes_absorbed_from_eden(absorb_size);
 483   return true;
 484 }
 485 
 486 void PSMarkSweep::allocate_stacks() {
 487   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 488   PSYoungGen* young_gen = heap->young_gen();
 489 
 490   MutableSpace* to_space = young_gen->to_space();
 491   _preserved_marks = (PreservedMark*)to_space->top();
 492   _preserved_count = 0;
 493 
 494   // We want to calculate the size in bytes first.
 495   _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));
 496   // Now divide by the size of a PreservedMark
 497   _preserved_count_max /= sizeof(PreservedMark);
 498 }
 499 
 500 
 501 void PSMarkSweep::deallocate_stacks() {
 502   _preserved_mark_stack.clear(true);
 503   _preserved_oop_stack.clear(true);
 504   _marking_stack.clear();
 505   _objarray_stack.clear(true);
 506 }
 507 
 508 void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 509   // Recursively traverse all live objects and mark them
 510   GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
 511 
 512   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 513 
 514   // Need to clear claim bits before the tracing starts.
 515   ClassLoaderDataGraph::clear_claimed_marks();
 516 
 517   // General strong roots.
 518   {
 519     ParallelScavengeHeap::ParStrongRootsScope psrs;
 520     Universe::oops_do(mark_and_push_closure());
 521     JNIHandles::oops_do(mark_and_push_closure());   // Global (strong) JNI handles
 522     MarkingCodeBlobClosure each_active_code_blob(mark_and_push_closure(), !CodeBlobToOopClosure::FixRelocations);
 523     Threads::oops_do(mark_and_push_closure(), &each_active_code_blob);
 524     ObjectSynchronizer::oops_do(mark_and_push_closure());
 525     Management::oops_do(mark_and_push_closure());
 526     JvmtiExport::oops_do(mark_and_push_closure());
 527     SystemDictionary::always_strong_oops_do(mark_and_push_closure());
 528     ClassLoaderDataGraph::always_strong_cld_do(follow_cld_closure());
 529     // Do not treat nmethods as strong roots for mark/sweep, since we can unload them.
 530     //CodeCache::scavenge_root_nmethods_do(CodeBlobToOopClosure(mark_and_push_closure()));
 531     AOTLoader::oops_do(mark_and_push_closure());
 532   }
 533 
 534   // Flush marking stack.
 535   follow_stack();
 536 
 537   // Process reference objects found during marking
 538   {
 539     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer);
 540 
 541     ref_processor()->setup_policy(clear_all_softrefs);
 542     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->num_q());
 543     const ReferenceProcessorStats& stats =
 544       ref_processor()->process_discovered_references(
 545         is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL, &pt);
 546     gc_tracer()->report_gc_reference_stats(stats);
 547     pt.print_all_references();
 548   }
 549 
 550   // This is the point where the entire marking should have completed.
 551   assert(_marking_stack.is_empty(), "Marking should have completed");
 552 
 553   {
 554     GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer);
 555     WeakProcessor::weak_oops_do(is_alive_closure(), &do_nothing_cl);
 556   }
 557 
 558   {
 559     GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer);
 560 
 561     // Unload classes and purge the SystemDictionary.
 562     bool purged_class = SystemDictionary::do_unloading(is_alive_closure(), _gc_timer);
 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();
 569   }
 570 
 571   {
 572     GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer);
 573     // Delete entries for dead interned strings.
 574     StringTable::unlink(is_alive_closure());
 575   }
 576 
 577   {
 578     GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer);
 579     // Clean up unreferenced symbols in symbol table.
 580     SymbolTable::unlink();
 581   }
 582 
 583   _gc_tracer->report_object_count_after_gc(is_alive_closure());
 584 }
 585 
 586 
 587 void PSMarkSweep::mark_sweep_phase2() {
 588   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
 589 
 590   // Now all live objects are marked, compute the new object addresses.
 591 
 592   // It is not required that we traverse spaces in the same order in
 593   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 594   // tracking expects us to do so. See comment under phase4.
 595 
 596   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 597   PSOldGen* old_gen = heap->old_gen();
 598 
 599   // Begin compacting into the old gen
 600   PSMarkSweepDecorator::set_destination_decorator_tenured();
 601 
 602   // This will also compact the young gen spaces.
 603   old_gen->precompact();
 604 }
 605 
 606 void PSMarkSweep::mark_sweep_phase3() {
 607   // Adjust the pointers to reflect the new locations
 608   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", _gc_timer);
 609 
 610   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 611   PSYoungGen* young_gen = heap->young_gen();
 612   PSOldGen* old_gen = heap->old_gen();
 613 
 614   // Need to clear claim bits before the tracing starts.
 615   ClassLoaderDataGraph::clear_claimed_marks();
 616 
 617   // General strong roots.
 618   Universe::oops_do(adjust_pointer_closure());
 619   JNIHandles::oops_do(adjust_pointer_closure());   // Global (strong) JNI handles
 620   Threads::oops_do(adjust_pointer_closure(), NULL);
 621   ObjectSynchronizer::oops_do(adjust_pointer_closure());
 622   Management::oops_do(adjust_pointer_closure());
 623   JvmtiExport::oops_do(adjust_pointer_closure());
 624   SystemDictionary::oops_do(adjust_pointer_closure());
 625   ClassLoaderDataGraph::cld_do(adjust_cld_closure());
 626 
 627   // Now adjust pointers in remaining weak roots.  (All of which should
 628   // have been cleared if they pointed to non-surviving objects.)
 629   // Global (weak) JNI handles
 630   WeakProcessor::oops_do(adjust_pointer_closure());
 631 
 632   CodeBlobToOopClosure adjust_from_blobs(adjust_pointer_closure(), CodeBlobToOopClosure::FixRelocations);
 633   CodeCache::blobs_do(&adjust_from_blobs);
 634   AOTLoader::oops_do(adjust_pointer_closure());
 635   StringTable::oops_do(adjust_pointer_closure());
 636   ref_processor()->weak_oops_do(adjust_pointer_closure());
 637   PSScavenge::reference_processor()->weak_oops_do(adjust_pointer_closure());
 638 
 639   adjust_marks();
 640 
 641   young_gen->adjust_pointers();
 642   old_gen->adjust_pointers();
 643 }
 644 
 645 void PSMarkSweep::mark_sweep_phase4() {
 646   EventMark m("4 compact heap");
 647   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
 648 
 649   // All pointers are now adjusted, move objects accordingly
 650 
 651   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 652   PSYoungGen* young_gen = heap->young_gen();
 653   PSOldGen* old_gen = heap->old_gen();
 654 
 655   old_gen->compact();
 656   young_gen->compact();
 657 }
 658 
 659 jlong PSMarkSweep::millis_since_last_gc() {
 660   // We need a monotonically non-decreasing time in ms but
 661   // os::javaTimeMillis() does not guarantee monotonicity.
 662   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 663   jlong ret_val = now - _time_of_last_gc;
 664   // XXX See note in genCollectedHeap::millis_since_last_gc().
 665   if (ret_val < 0) {
 666     NOT_PRODUCT(log_warning(gc)("time warp: " JLONG_FORMAT, ret_val);)
 667     return 0;
 668   }
 669   return ret_val;
 670 }
 671 
 672 void PSMarkSweep::reset_millis_since_last_gc() {
 673   // We need a monotonically non-decreasing time in ms but
 674   // os::javaTimeMillis() does not guarantee monotonicity.
 675   _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 676 }