1 /*
   2  * Copyright (c) 2001, 2019, 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/classLoaderDataGraph.hpp"
  28 #include "classfile/stringTable.hpp"
  29 #include "classfile/symbolTable.hpp"
  30 #include "classfile/systemDictionary.hpp"
  31 #include "code/codeCache.hpp"
  32 #include "gc/parallel/parallelScavengeHeap.hpp"
  33 #include "gc/parallel/psAdaptiveSizePolicy.hpp"
  34 #include "gc/parallel/psMarkSweep.hpp"
  35 #include "gc/parallel/psMarkSweepDecorator.hpp"
  36 #include "gc/parallel/psOldGen.hpp"
  37 #include "gc/parallel/psScavenge.hpp"
  38 #include "gc/parallel/psYoungGen.hpp"
  39 #include "gc/serial/markSweep.hpp"
  40 #include "gc/shared/gcCause.hpp"
  41 #include "gc/shared/gcHeapSummary.hpp"
  42 #include "gc/shared/gcId.hpp"
  43 #include "gc/shared/gcLocker.hpp"
  44 #include "gc/shared/gcTimer.hpp"
  45 #include "gc/shared/gcTrace.hpp"
  46 #include "gc/shared/gcTraceTime.inline.hpp"
  47 #include "gc/shared/isGCActiveMark.hpp"
  48 #include "gc/shared/referencePolicy.hpp"
  49 #include "gc/shared/referenceProcessor.hpp"
  50 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
  51 #include "gc/shared/spaceDecorator.hpp"
  52 #include "gc/shared/weakProcessor.hpp"
  53 #include "logging/log.hpp"
  54 #include "oops/oop.inline.hpp"
  55 #include "runtime/biasedLocking.hpp"
  56 #include "runtime/flags/flagSetting.hpp"
  57 #include "runtime/handles.inline.hpp"
  58 #include "runtime/safepoint.hpp"
  59 #include "runtime/vmThread.hpp"
  60 #include "services/management.hpp"
  61 #include "services/memoryService.hpp"
  62 #include "utilities/align.hpp"
  63 #include "utilities/events.hpp"
  64 #include "utilities/stack.inline.hpp"
  65 
  66 elapsedTimer        PSMarkSweep::_accumulated_time;
  67 jlong               PSMarkSweep::_time_of_last_gc   = 0;
  68 CollectorCounters*  PSMarkSweep::_counters = NULL;
  69 
  70 SpanSubjectToDiscoveryClosure PSMarkSweep::_span_based_discoverer;
  71 
  72 void PSMarkSweep::initialize() {
  73   _span_based_discoverer.set_span(ParallelScavengeHeap::heap()->reserved_region());
  74   set_ref_processor(new ReferenceProcessor(&_span_based_discoverer));     // a vanilla ref proc
  75   _counters = new CollectorCounters("Serial full collection pauses", 1);
  76   MarkSweep::initialize();
  77 }
  78 
  79 // This method contains all heap specific policy for invoking mark sweep.
  80 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact
  81 // the heap. It will do nothing further. If we need to bail out for policy
  82 // reasons, scavenge before full gc, or any other specialized behavior, it
  83 // needs to be added here.
  84 //
  85 // Note that this method should only be called from the vm_thread while
  86 // at a safepoint!
  87 //
  88 // Note that the all_soft_refs_clear flag in the collector policy
  89 // may be true because this method can be called without intervening
  90 // activity.  For example when the heap space is tight and full measure
  91 // are being taken to free space.
  92 
  93 void PSMarkSweep::invoke(bool maximum_heap_compaction) {
  94   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
  95   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
  96   assert(!ParallelScavengeHeap::heap()->is_gc_active(), "not reentrant");
  97 
  98   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
  99   GCCause::Cause gc_cause = heap->gc_cause();
 100   PSAdaptiveSizePolicy* policy = heap->size_policy();
 101   IsGCActiveMark mark;
 102 
 103   if (ScavengeBeforeFullGC) {
 104     PSScavenge::invoke_no_policy();
 105   }
 106 
 107   const bool clear_all_soft_refs =
 108     heap->soft_ref_policy()->should_clear_all_soft_refs();
 109 
 110   uint count = maximum_heap_compaction ? 1 : MarkSweepAlwaysCompactCount;
 111   UIntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);
 112   PSMarkSweep::invoke_no_policy(clear_all_soft_refs || maximum_heap_compaction);
 113 }
 114 
 115 // This method contains no policy. You should probably
 116 // be calling invoke() instead.
 117 bool PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
 118   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 119   assert(ref_processor() != NULL, "Sanity");
 120 
 121   if (GCLocker::check_active_before_gc()) {
 122     return false;
 123   }
 124 
 125   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 126   GCCause::Cause gc_cause = heap->gc_cause();
 127 
 128   GCIdMark gc_id_mark;
 129   _gc_timer->register_gc_start();
 130   _gc_tracer->report_gc_start(gc_cause, _gc_timer->gc_start());
 131 
 132   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 133 
 134   // The scope of casr should end after code that can change
 135   // CollectorPolicy::_should_clear_all_soft_refs.
 136   ClearedAllSoftRefs casr(clear_all_softrefs, heap->soft_ref_policy());
 137 
 138   PSYoungGen* young_gen = heap->young_gen();
 139   PSOldGen* old_gen = heap->old_gen();
 140 
 141   // Increment the invocation count
 142   heap->increment_total_collections(true /* full */);
 143 
 144   // Save information needed to minimize mangling
 145   heap->record_gen_tops_before_GC();
 146 
 147   // We need to track unique mark sweep invocations as well.
 148   _total_invocations++;
 149 
 150   heap->print_heap_before_gc();
 151   heap->trace_heap_before_gc(_gc_tracer);
 152 
 153   // Fill in TLABs
 154   heap->ensure_parsability(true);  // retire TLABs
 155 
 156   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
 157     HandleMark hm;  // Discard invalid handles created during verification
 158     Universe::verify("Before GC");
 159   }
 160 
 161   // Verify object start arrays
 162   if (VerifyObjectStartArray &&
 163       VerifyBeforeGC) {
 164     old_gen->verify_object_start_array();
 165   }
 166 
 167   // Filled in below to track the state of the young gen after the collection.
 168   bool eden_empty;
 169   bool survivors_empty;
 170   bool young_gen_empty;
 171 
 172   {
 173     HandleMark hm;
 174 
 175     GCTraceCPUTime tcpu;
 176     GCTraceTime(Info, gc) t("Pause Full", NULL, gc_cause, true);
 177 
 178     heap->pre_full_gc_dump(_gc_timer);
 179 
 180     TraceCollectorStats tcs(counters());
 181     TraceMemoryManagerStats tms(heap->old_gc_manager(),gc_cause);
 182 
 183     if (log_is_enabled(Debug, gc, heap, exit)) {
 184       accumulated_time()->start();
 185     }
 186 
 187     // Let the size policy know we're starting
 188     size_policy->major_collection_begin();
 189 
 190     CodeCache::gc_prologue();
 191     BiasedLocking::preserve_marks();
 192 
 193     // Capture metadata size before collection for sizing.
 194     size_t metadata_prev_used = MetaspaceUtils::used_bytes();
 195 
 196     size_t old_gen_prev_used = old_gen->used_in_bytes();
 197     size_t young_gen_prev_used = young_gen->used_in_bytes();
 198 
 199     allocate_stacks();
 200 
 201 #if COMPILER2_OR_JVMCI
 202     DerivedPointerTable::clear();
 203 #endif
 204 
 205     ref_processor()->enable_discovery();
 206     ref_processor()->setup_policy(clear_all_softrefs);
 207 
 208     mark_sweep_phase1(clear_all_softrefs);
 209 
 210     mark_sweep_phase2();
 211 
 212 #if COMPILER2_OR_JVMCI
 213     // Don't add any more derived pointers during phase3
 214     assert(DerivedPointerTable::is_active(), "Sanity");
 215     DerivedPointerTable::set_active(false);
 216 #endif
 217 
 218     mark_sweep_phase3();
 219 
 220     mark_sweep_phase4();
 221 
 222     restore_marks();
 223 
 224     deallocate_stacks();
 225 
 226     if (ZapUnusedHeapArea) {
 227       // Do a complete mangle (top to end) because the usage for
 228       // scratch does not maintain a top pointer.
 229       young_gen->to_space()->mangle_unused_area_complete();
 230     }
 231 
 232     eden_empty = young_gen->eden_space()->is_empty();
 233     if (!eden_empty) {
 234       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
 235     }
 236 
 237     // Update heap occupancy information which is used as
 238     // input to soft ref clearing policy at the next gc.
 239     Universe::update_heap_info_at_gc();
 240 
 241     survivors_empty = young_gen->from_space()->is_empty() &&
 242                       young_gen->to_space()->is_empty();
 243     young_gen_empty = eden_empty && survivors_empty;
 244 
 245     PSCardTable* card_table = heap->card_table();
 246     MemRegion old_mr = heap->old_gen()->reserved();
 247     if (young_gen_empty) {
 248       card_table->clear(MemRegion(old_mr.start(), old_mr.end()));
 249     } else {
 250       card_table->invalidate(MemRegion(old_mr.start(), old_mr.end()));
 251     }
 252 
 253     // Delete metaspaces for unloaded class loaders and clean up loader_data graph
 254     ClassLoaderDataGraph::purge();
 255     MetaspaceUtils::verify_metrics();
 256 
 257     BiasedLocking::restore_marks();
 258     CodeCache::gc_epilogue();
 259     JvmtiExport::gc_epilogue();
 260 
 261 #if COMPILER2_OR_JVMCI
 262     DerivedPointerTable::update_pointers();
 263 #endif
 264 
 265     assert(!ref_processor()->discovery_enabled(), "Should have been disabled earlier");
 266 
 267     // Update time of last GC
 268     reset_millis_since_last_gc();
 269 
 270     // Let the size policy know we're done
 271     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
 272 
 273     if (UseAdaptiveSizePolicy) {
 274 
 275      log_debug(gc, ergo)("AdaptiveSizeStart: collection: %d ", heap->total_collections());
 276      log_trace(gc, ergo)("old_gen_capacity: " SIZE_FORMAT " young_gen_capacity: " SIZE_FORMAT,
 277                          old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
 278 
 279       // Don't check if the size_policy is ready here.  Let
 280       // the size_policy check that internally.
 281       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
 282           AdaptiveSizePolicy::should_update_promo_stats(gc_cause)) {
 283         // Swap the survivor spaces if from_space is empty. The
 284         // resize_young_gen() called below is normally used after
 285         // a successful young GC and swapping of survivor spaces;
 286         // otherwise, it will fail to resize the young gen with
 287         // the current implementation.
 288         if (young_gen->from_space()->is_empty()) {
 289           young_gen->from_space()->clear(SpaceDecorator::Mangle);
 290           young_gen->swap_spaces();
 291         }
 292 
 293         // Calculate optimal free space amounts
 294         assert(young_gen->max_size() >
 295           young_gen->from_space()->capacity_in_bytes() +
 296           young_gen->to_space()->capacity_in_bytes(),
 297           "Sizes of space in young gen are out of bounds");
 298 
 299         size_t young_live = young_gen->used_in_bytes();
 300         size_t eden_live = young_gen->eden_space()->used_in_bytes();
 301         size_t old_live = old_gen->used_in_bytes();
 302         size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
 303         size_t max_old_gen_size = old_gen->max_gen_size();
 304         size_t max_eden_size = young_gen->max_size() -
 305           young_gen->from_space()->capacity_in_bytes() -
 306           young_gen->to_space()->capacity_in_bytes();
 307 
 308         // Used for diagnostics
 309         size_policy->clear_generation_free_space_flags();
 310 
 311         size_policy->compute_generations_free_space(young_live,
 312                                                     eden_live,
 313                                                     old_live,
 314                                                     cur_eden,
 315                                                     max_old_gen_size,
 316                                                     max_eden_size,
 317                                                     true /* full gc*/);
 318 
 319         size_policy->check_gc_overhead_limit(young_live,
 320                                              eden_live,
 321                                              max_old_gen_size,
 322                                              max_eden_size,
 323                                              true /* full gc*/,
 324                                              gc_cause,
 325                                              heap->soft_ref_policy());
 326 
 327         size_policy->decay_supplemental_growth(true /* full gc*/);
 328 
 329         heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
 330 
 331         heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
 332                                size_policy->calculated_survivor_size_in_bytes());
 333       }
 334       log_debug(gc, ergo)("AdaptiveSizeStop: collection: %d ", heap->total_collections());
 335     }
 336 
 337     if (UsePerfData) {
 338       heap->gc_policy_counters()->update_counters();
 339       heap->gc_policy_counters()->update_old_capacity(
 340         old_gen->capacity_in_bytes());
 341       heap->gc_policy_counters()->update_young_capacity(
 342         young_gen->capacity_in_bytes());
 343     }
 344 
 345     heap->resize_all_tlabs();
 346 
 347     // We collected the heap, recalculate the metaspace capacity
 348     MetaspaceGC::compute_new_size();
 349 
 350     if (log_is_enabled(Debug, gc, heap, exit)) {
 351       accumulated_time()->stop();
 352     }
 353 
 354     young_gen->print_used_change(young_gen_prev_used);
 355     old_gen->print_used_change(old_gen_prev_used);
 356     MetaspaceUtils::print_metaspace_change(metadata_prev_used);
 357 
 358     // Track memory usage and detect low memory
 359     MemoryService::track_memory_usage();
 360     heap->update_counters();
 361 
 362     heap->post_full_gc_dump(_gc_timer);
 363   }
 364 
 365   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
 366     HandleMark hm;  // Discard invalid handles created during verification
 367     Universe::verify("After GC");
 368   }
 369 
 370   // Re-verify object start arrays
 371   if (VerifyObjectStartArray &&
 372       VerifyAfterGC) {
 373     old_gen->verify_object_start_array();
 374   }
 375 
 376   if (ZapUnusedHeapArea) {
 377     old_gen->object_space()->check_mangled_unused_area_complete();
 378   }
 379 
 380   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 381 
 382   heap->print_heap_after_gc();
 383   heap->trace_heap_after_gc(_gc_tracer);
 384 
 385 #ifdef TRACESPINNING
 386   ParallelTaskTerminator::print_termination_counts();
 387 #endif
 388 
 389   AdaptiveSizePolicyOutput::print(size_policy, heap->total_collections());
 390 
 391   _gc_timer->register_gc_end();
 392 
 393   _gc_tracer->report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
 394 
 395   return true;
 396 }
 397 
 398 bool PSMarkSweep::absorb_live_data_from_eden(PSAdaptiveSizePolicy* size_policy,
 399                                              PSYoungGen* young_gen,
 400                                              PSOldGen* old_gen) {
 401   MutableSpace* const eden_space = young_gen->eden_space();
 402   assert(!eden_space->is_empty(), "eden must be non-empty");
 403   assert(young_gen->virtual_space()->alignment() ==
 404          old_gen->virtual_space()->alignment(), "alignments do not match");
 405 
 406   if (!(UseAdaptiveSizePolicy && UseAdaptiveGCBoundary)) {
 407     return false;
 408   }
 409 
 410   // Both generations must be completely committed.
 411   if (young_gen->virtual_space()->uncommitted_size() != 0) {
 412     return false;
 413   }
 414   if (old_gen->virtual_space()->uncommitted_size() != 0) {
 415     return false;
 416   }
 417 
 418   // Figure out how much to take from eden.  Include the average amount promoted
 419   // in the total; otherwise the next young gen GC will simply bail out to a
 420   // full GC.
 421   const size_t alignment = old_gen->virtual_space()->alignment();
 422   const size_t eden_used = eden_space->used_in_bytes();
 423   const size_t promoted = (size_t)size_policy->avg_promoted()->padded_average();
 424   const size_t absorb_size = align_up(eden_used + promoted, alignment);
 425   const size_t eden_capacity = eden_space->capacity_in_bytes();
 426 
 427   if (absorb_size >= eden_capacity) {
 428     return false; // Must leave some space in eden.
 429   }
 430 
 431   const size_t new_young_size = young_gen->capacity_in_bytes() - absorb_size;
 432   if (new_young_size < young_gen->min_gen_size()) {
 433     return false; // Respect young gen minimum size.
 434   }
 435 
 436   log_trace(gc, ergo, heap)(" absorbing " SIZE_FORMAT "K:  "
 437                             "eden " SIZE_FORMAT "K->" SIZE_FORMAT "K "
 438                             "from " SIZE_FORMAT "K, to " SIZE_FORMAT "K "
 439                             "young_gen " SIZE_FORMAT "K->" SIZE_FORMAT "K ",
 440                             absorb_size / K,
 441                             eden_capacity / K, (eden_capacity - absorb_size) / K,
 442                             young_gen->from_space()->used_in_bytes() / K,
 443                             young_gen->to_space()->used_in_bytes() / K,
 444                             young_gen->capacity_in_bytes() / K, new_young_size / K);
 445 
 446   // Fill the unused part of the old gen.
 447   MutableSpace* const old_space = old_gen->object_space();
 448   HeapWord* const unused_start = old_space->top();
 449   size_t const unused_words = pointer_delta(old_space->end(), unused_start);
 450 
 451   if (unused_words > 0) {
 452     if (unused_words < CollectedHeap::min_fill_size()) {
 453       return false;  // If the old gen cannot be filled, must give up.
 454     }
 455     CollectedHeap::fill_with_objects(unused_start, unused_words);
 456   }
 457 
 458   // Take the live data from eden and set both top and end in the old gen to
 459   // eden top.  (Need to set end because reset_after_change() mangles the region
 460   // from end to virtual_space->high() in debug builds).
 461   HeapWord* const new_top = eden_space->top();
 462   old_gen->virtual_space()->expand_into(young_gen->virtual_space(),
 463                                         absorb_size);
 464   young_gen->reset_after_change();
 465   old_space->set_top(new_top);
 466   old_space->set_end(new_top);
 467   old_gen->reset_after_change();
 468 
 469   // Update the object start array for the filler object and the data from eden.
 470   ObjectStartArray* const start_array = old_gen->start_array();
 471   for (HeapWord* p = unused_start; p < new_top; p += oop(p)->size()) {
 472     start_array->allocate_block(p);
 473   }
 474 
 475   // Could update the promoted average here, but it is not typically updated at
 476   // full GCs and the value to use is unclear.  Something like
 477   //
 478   // cur_promoted_avg + absorb_size / number_of_scavenges_since_last_full_gc.
 479 
 480   size_policy->set_bytes_absorbed_from_eden(absorb_size);
 481   return true;
 482 }
 483 
 484 void PSMarkSweep::allocate_stacks() {
 485   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 486   PSYoungGen* young_gen = heap->young_gen();
 487 
 488   MutableSpace* to_space = young_gen->to_space();
 489   _preserved_marks = (PreservedMark*)to_space->top();
 490   _preserved_count = 0;
 491 
 492   // We want to calculate the size in bytes first.
 493   _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));
 494   // Now divide by the size of a PreservedMark
 495   _preserved_count_max /= sizeof(PreservedMark);
 496 }
 497 
 498 
 499 void PSMarkSweep::deallocate_stacks() {
 500   _preserved_mark_stack.clear(true);
 501   _preserved_oop_stack.clear(true);
 502   _marking_stack.clear();
 503   _objarray_stack.clear(true);
 504 }
 505 
 506 void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 507   // Recursively traverse all live objects and mark them
 508   GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
 509 
 510   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 511 
 512   // Need to clear claim bits before the tracing starts.
 513   ClassLoaderDataGraph::clear_claimed_marks();
 514 
 515   // General strong roots.
 516   {
 517     ParallelScavengeHeap::ParStrongRootsScope psrs;
 518     Universe::oops_do(mark_and_push_closure());
 519     JNIHandles::oops_do(mark_and_push_closure());   // Global (strong) JNI handles
 520     MarkingCodeBlobClosure each_active_code_blob(mark_and_push_closure(), !CodeBlobToOopClosure::FixRelocations);
 521     Threads::oops_do(mark_and_push_closure(), &each_active_code_blob);
 522     ObjectSynchronizer::oops_do(mark_and_push_closure());
 523     Management::oops_do(mark_and_push_closure());
 524     JvmtiExport::oops_do(mark_and_push_closure());
 525     SystemDictionary::oops_do(mark_and_push_closure());
 526     ClassLoaderDataGraph::always_strong_cld_do(follow_cld_closure());
 527     // Do not treat nmethods as strong roots for mark/sweep, since we can unload them.
 528     //CodeCache::scavenge_root_nmethods_do(CodeBlobToOopClosure(mark_and_push_closure()));
 529     AOTLoader::oops_do(mark_and_push_closure());
 530   }
 531 
 532   // Flush marking stack.
 533   follow_stack();
 534 
 535   // Process reference objects found during marking
 536   {
 537     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer);
 538 
 539     ref_processor()->setup_policy(clear_all_softrefs);
 540     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues());
 541     const ReferenceProcessorStats& stats =
 542       ref_processor()->process_discovered_references(
 543         is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL, &pt);
 544     gc_tracer()->report_gc_reference_stats(stats);
 545     pt.print_all_references();
 546   }
 547 
 548   // This is the point where the entire marking should have completed.
 549   assert(_marking_stack.is_empty(), "Marking should have completed");
 550 
 551   {
 552     GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer);
 553     WeakProcessor::weak_oops_do(is_alive_closure(), &do_nothing_cl);
 554   }
 555 
 556   {
 557     GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer);
 558 
 559     // Unload classes and purge the SystemDictionary.
 560     bool purged_class = SystemDictionary::do_unloading(_gc_timer);
 561 
 562     // Unload nmethods.
 563     CodeCache::do_unloading(is_alive_closure(), purged_class);
 564 
 565     // Prune dead klasses from subklass/sibling/implementor lists.
 566     Klass::clean_weak_klass_links(purged_class);
 567   }
 568 
 569   {
 570     GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer);
 571     // Delete entries for dead interned strings.
 572     StringTable::unlink(is_alive_closure());
 573   }
 574 
 575   {
 576     GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer);
 577     // Clean up unreferenced symbols in symbol table.
 578     SymbolTable::unlink();
 579   }
 580 
 581   _gc_tracer->report_object_count_after_gc(is_alive_closure());
 582 }
 583 
 584 
 585 void PSMarkSweep::mark_sweep_phase2() {
 586   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
 587 
 588   // Now all live objects are marked, compute the new object addresses.
 589 
 590   // It is not required that we traverse spaces in the same order in
 591   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 592   // tracking expects us to do so. See comment under phase4.
 593 
 594   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 595   PSOldGen* old_gen = heap->old_gen();
 596 
 597   // Begin compacting into the old gen
 598   PSMarkSweepDecorator::set_destination_decorator_tenured();
 599 
 600   // This will also compact the young gen spaces.
 601   old_gen->precompact();
 602 }
 603 
 604 void PSMarkSweep::mark_sweep_phase3() {
 605   // Adjust the pointers to reflect the new locations
 606   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", _gc_timer);
 607 
 608   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 609   PSYoungGen* young_gen = heap->young_gen();
 610   PSOldGen* old_gen = heap->old_gen();
 611 
 612   // Need to clear claim bits before the tracing starts.
 613   ClassLoaderDataGraph::clear_claimed_marks();
 614 
 615   // General strong roots.
 616   Universe::oops_do(adjust_pointer_closure());
 617   JNIHandles::oops_do(adjust_pointer_closure());   // Global (strong) JNI handles
 618   Threads::oops_do(adjust_pointer_closure(), NULL);
 619   ObjectSynchronizer::oops_do(adjust_pointer_closure());
 620   Management::oops_do(adjust_pointer_closure());
 621   JvmtiExport::oops_do(adjust_pointer_closure());
 622   SystemDictionary::oops_do(adjust_pointer_closure());
 623   ClassLoaderDataGraph::cld_do(adjust_cld_closure());
 624 
 625   // Now adjust pointers in remaining weak roots.  (All of which should
 626   // have been cleared if they pointed to non-surviving objects.)
 627   // Global (weak) JNI handles
 628   WeakProcessor::oops_do(adjust_pointer_closure());
 629 
 630   CodeBlobToOopClosure adjust_from_blobs(adjust_pointer_closure(), CodeBlobToOopClosure::FixRelocations);
 631   CodeCache::blobs_do(&adjust_from_blobs);
 632   AOTLoader::oops_do(adjust_pointer_closure());
 633   StringTable::oops_do(adjust_pointer_closure());
 634   ref_processor()->weak_oops_do(adjust_pointer_closure());
 635   PSScavenge::reference_processor()->weak_oops_do(adjust_pointer_closure());
 636 
 637   adjust_marks();
 638 
 639   young_gen->adjust_pointers();
 640   old_gen->adjust_pointers();
 641 }
 642 
 643 void PSMarkSweep::mark_sweep_phase4() {
 644   EventMark m("4 compact heap");
 645   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
 646 
 647   // All pointers are now adjusted, move objects accordingly
 648 
 649   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 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-decreasing 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(log_warning(gc)("time warp: " JLONG_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-decreasing time in ms but
 672   // os::javaTimeMillis() does not guarantee monotonicity.
 673   _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 674 }