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 "memory/universe.hpp"
  54 #include "logging/log.hpp"
  55 #include "oops/oop.inline.hpp"
  56 #include "runtime/biasedLocking.hpp"
  57 #include "runtime/flags/flagSetting.hpp"
  58 #include "runtime/handles.inline.hpp"
  59 #include "runtime/safepoint.hpp"
  60 #include "runtime/vmThread.hpp"
  61 #include "services/management.hpp"
  62 #include "services/memoryService.hpp"
  63 #include "utilities/align.hpp"
  64 #include "utilities/events.hpp"
  65 #include "utilities/stack.inline.hpp"
  66 #if INCLUDE_JVMCI
  67 #include "jvmci/jvmci.hpp"
  68 #endif
  69 
  70 elapsedTimer        PSMarkSweep::_accumulated_time;
  71 jlong               PSMarkSweep::_time_of_last_gc   = 0;
  72 CollectorCounters*  PSMarkSweep::_counters = NULL;
  73 
  74 SpanSubjectToDiscoveryClosure PSMarkSweep::_span_based_discoverer;
  75 
  76 void PSMarkSweep::initialize() {
  77   _span_based_discoverer.set_span(ParallelScavengeHeap::heap()->reserved_region());
  78   set_ref_processor(new ReferenceProcessor(&_span_based_discoverer));     // a vanilla ref proc
  79   _counters = new CollectorCounters("Serial full collection pauses", 1);
  80   MarkSweep::initialize();
  81 }
  82 
  83 // This method contains all heap specific policy for invoking mark sweep.
  84 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact
  85 // the heap. It will do nothing further. If we need to bail out for policy
  86 // reasons, scavenge before full gc, or any other specialized behavior, it
  87 // needs to be added here.
  88 //
  89 // Note that this method should only be called from the vm_thread while
  90 // at a safepoint!
  91 //
  92 // Note that the all_soft_refs_clear flag in the soft ref policy
  93 // may be true because this method can be called without intervening
  94 // activity.  For example when the heap space is tight and full measure
  95 // are being taken to free space.
  96 
  97 void PSMarkSweep::invoke(bool maximum_heap_compaction) {
  98   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
  99   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
 100   assert(!ParallelScavengeHeap::heap()->is_gc_active(), "not reentrant");
 101 
 102   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 103   GCCause::Cause gc_cause = heap->gc_cause();
 104   PSAdaptiveSizePolicy* policy = heap->size_policy();
 105   IsGCActiveMark mark;
 106 
 107   if (ScavengeBeforeFullGC) {
 108     PSScavenge::invoke_no_policy();
 109   }
 110 
 111   const bool clear_all_soft_refs =
 112     heap->soft_ref_policy()->should_clear_all_soft_refs();
 113 
 114   uint count = maximum_heap_compaction ? 1 : MarkSweepAlwaysCompactCount;
 115   UIntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);
 116   PSMarkSweep::invoke_no_policy(clear_all_soft_refs || maximum_heap_compaction);
 117 }
 118 
 119 // This method contains no policy. You should probably
 120 // be calling invoke() instead.
 121 bool PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
 122   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 123   assert(ref_processor() != NULL, "Sanity");
 124 
 125   if (GCLocker::check_active_before_gc()) {
 126     return false;
 127   }
 128 
 129   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 130   GCCause::Cause gc_cause = heap->gc_cause();
 131 
 132   GCIdMark gc_id_mark;
 133   _gc_timer->register_gc_start();
 134   _gc_tracer->report_gc_start(gc_cause, _gc_timer->gc_start());
 135 
 136   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 137 
 138   // The scope of casr should end after code that can change
 139   // SoftRefolicy::_should_clear_all_soft_refs.
 140   ClearedAllSoftRefs casr(clear_all_softrefs, heap->soft_ref_policy());
 141 
 142   PSYoungGen* young_gen = heap->young_gen();
 143   PSOldGen* old_gen = heap->old_gen();
 144 
 145   // Increment the invocation count
 146   heap->increment_total_collections(true /* full */);
 147 
 148   // Save information needed to minimize mangling
 149   heap->record_gen_tops_before_GC();
 150 
 151   // We need to track unique mark sweep invocations as well.
 152   _total_invocations++;
 153 
 154   heap->print_heap_before_gc();
 155   heap->trace_heap_before_gc(_gc_tracer);
 156 
 157   // Fill in TLABs
 158   heap->ensure_parsability(true);  // retire TLABs
 159 
 160   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
 161     HandleMark hm;  // Discard invalid handles created during verification
 162     Universe::verify("Before GC");
 163   }
 164 
 165   // Verify object start arrays
 166   if (VerifyObjectStartArray &&
 167       VerifyBeforeGC) {
 168     old_gen->verify_object_start_array();
 169   }
 170 
 171   // Filled in below to track the state of the young gen after the collection.
 172   bool eden_empty;
 173   bool survivors_empty;
 174   bool young_gen_empty;
 175 
 176   {
 177     HandleMark hm;
 178 
 179     GCTraceCPUTime tcpu;
 180     GCTraceTime(Info, gc) t("Pause Full", NULL, gc_cause, true);
 181 
 182     heap->pre_full_gc_dump(_gc_timer);
 183 
 184     TraceCollectorStats tcs(counters());
 185     TraceMemoryManagerStats tms(heap->old_gc_manager(),gc_cause);
 186 
 187     if (log_is_enabled(Debug, gc, heap, exit)) {
 188       accumulated_time()->start();
 189     }
 190 
 191     // Let the size policy know we're starting
 192     size_policy->major_collection_begin();
 193 
 194     BiasedLocking::preserve_marks();
 195 
 196     // Capture metadata size before collection for sizing.
 197     size_t metadata_prev_used = MetaspaceUtils::used_bytes();
 198 
 199     size_t old_gen_prev_used = old_gen->used_in_bytes();
 200     size_t young_gen_prev_used = young_gen->used_in_bytes();
 201 
 202     allocate_stacks();
 203 
 204 #if COMPILER2_OR_JVMCI
 205     DerivedPointerTable::clear();
 206 #endif
 207 
 208     ref_processor()->enable_discovery();
 209     ref_processor()->setup_policy(clear_all_softrefs);
 210 
 211     mark_sweep_phase1(clear_all_softrefs);
 212 
 213     mark_sweep_phase2();
 214 
 215 #if COMPILER2_OR_JVMCI
 216     // Don't add any more derived pointers during phase3
 217     assert(DerivedPointerTable::is_active(), "Sanity");
 218     DerivedPointerTable::set_active(false);
 219 #endif
 220 
 221     mark_sweep_phase3();
 222 
 223     mark_sweep_phase4();
 224 
 225     restore_marks();
 226 
 227     deallocate_stacks();
 228 
 229     if (ZapUnusedHeapArea) {
 230       // Do a complete mangle (top to end) because the usage for
 231       // scratch does not maintain a top pointer.
 232       young_gen->to_space()->mangle_unused_area_complete();
 233     }
 234 
 235     eden_empty = young_gen->eden_space()->is_empty();
 236     if (!eden_empty) {
 237       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
 238     }
 239 
 240     // Update heap occupancy information which is used as
 241     // input to soft ref clearing policy at the next gc.
 242     Universe::update_heap_info_at_gc();
 243 
 244     survivors_empty = young_gen->from_space()->is_empty() &&
 245                       young_gen->to_space()->is_empty();
 246     young_gen_empty = eden_empty && survivors_empty;
 247 
 248     PSCardTable* card_table = heap->card_table();
 249     MemRegion old_mr = heap->old_gen()->reserved();
 250     if (young_gen_empty) {
 251       card_table->clear(MemRegion(old_mr.start(), old_mr.end()));
 252     } else {
 253       card_table->invalidate(MemRegion(old_mr.start(), old_mr.end()));
 254     }
 255 
 256     // Delete metaspaces for unloaded class loaders and clean up loader_data graph
 257     ClassLoaderDataGraph::purge();
 258     MetaspaceUtils::verify_metrics();
 259 
 260     BiasedLocking::restore_marks();
 261     heap->prune_scavengable_nmethods();
 262     JvmtiExport::gc_epilogue();
 263 
 264 #if COMPILER2_OR_JVMCI
 265     DerivedPointerTable::update_pointers();
 266 #endif
 267 
 268     assert(!ref_processor()->discovery_enabled(), "Should have been disabled earlier");
 269 
 270     // Update time of last GC
 271     reset_millis_since_last_gc();
 272 
 273     // Let the size policy know we're done
 274     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
 275 
 276     if (UseAdaptiveSizePolicy) {
 277 
 278      log_debug(gc, ergo)("AdaptiveSizeStart: collection: %d ", heap->total_collections());
 279      log_trace(gc, ergo)("old_gen_capacity: " SIZE_FORMAT " young_gen_capacity: " SIZE_FORMAT,
 280                          old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
 281 
 282       // Don't check if the size_policy is ready here.  Let
 283       // the size_policy check that internally.
 284       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
 285           AdaptiveSizePolicy::should_update_promo_stats(gc_cause)) {
 286         // Swap the survivor spaces if from_space is empty. The
 287         // resize_young_gen() called below is normally used after
 288         // a successful young GC and swapping of survivor spaces;
 289         // otherwise, it will fail to resize the young gen with
 290         // the current implementation.
 291         if (young_gen->from_space()->is_empty()) {
 292           young_gen->from_space()->clear(SpaceDecorator::Mangle);
 293           young_gen->swap_spaces();
 294         }
 295 
 296         // Calculate optimal free space amounts
 297         assert(young_gen->max_size() >
 298           young_gen->from_space()->capacity_in_bytes() +
 299           young_gen->to_space()->capacity_in_bytes(),
 300           "Sizes of space in young gen are out of bounds");
 301 
 302         size_t young_live = young_gen->used_in_bytes();
 303         size_t eden_live = young_gen->eden_space()->used_in_bytes();
 304         size_t old_live = old_gen->used_in_bytes();
 305         size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
 306         size_t max_old_gen_size = old_gen->max_gen_size();
 307         size_t max_eden_size = young_gen->max_size() -
 308           young_gen->from_space()->capacity_in_bytes() -
 309           young_gen->to_space()->capacity_in_bytes();
 310 
 311         // Used for diagnostics
 312         size_policy->clear_generation_free_space_flags();
 313 
 314         size_policy->compute_generations_free_space(young_live,
 315                                                     eden_live,
 316                                                     old_live,
 317                                                     cur_eden,
 318                                                     max_old_gen_size,
 319                                                     max_eden_size,
 320                                                     true /* full gc*/);
 321 
 322         size_policy->check_gc_overhead_limit(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(gc, ergo, heap)(" 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::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     //ScavengableNMethods::scavengable_nmethods_do(CodeBlobToOopClosure(mark_and_push_closure()));
 531     AOT_ONLY(AOTLoader::oops_do(mark_and_push_closure());)
 532     JVMCI_ONLY(JVMCI::oops_do(mark_and_push_closure());)
 533   }
 534 
 535   // Flush marking stack.
 536   follow_stack();
 537 
 538   // Process reference objects found during marking
 539   {
 540     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer);
 541 
 542     ref_processor()->setup_policy(clear_all_softrefs);
 543     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues());
 544     const ReferenceProcessorStats& stats =
 545       ref_processor()->process_discovered_references(
 546         is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL, &pt);
 547     gc_tracer()->report_gc_reference_stats(stats);
 548     pt.print_all_references();
 549   }
 550 
 551   // This is the point where the entire marking should have completed.
 552   assert(_marking_stack.is_empty(), "Marking should have completed");
 553 
 554   {
 555     GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer);
 556     WeakProcessor::weak_oops_do(is_alive_closure(), &do_nothing_cl);
 557   }
 558 
 559   {
 560     GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer);
 561 
 562     // Unload classes and purge the SystemDictionary.
 563     bool purged_class = SystemDictionary::do_unloading(_gc_timer);
 564 
 565     // Unload nmethods.
 566     CodeCache::do_unloading(is_alive_closure(), purged_class);
 567 
 568     // Prune dead klasses from subklass/sibling/implementor lists.
 569     Klass::clean_weak_klass_links(purged_class);
 570 
 571     // Clean JVMCI metadata handles.
 572     JVMCI_ONLY(JVMCI::do_unloading(purged_class));
 573   }
 574 
 575   _gc_tracer->report_object_count_after_gc(is_alive_closure());
 576 }
 577 
 578 
 579 void PSMarkSweep::mark_sweep_phase2() {
 580   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
 581 
 582   // Now all live objects are marked, compute the new object addresses.
 583 
 584   // It is not required that we traverse spaces in the same order in
 585   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 586   // tracking expects us to do so. See comment under phase4.
 587 
 588   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 589   PSOldGen* old_gen = heap->old_gen();
 590 
 591   // Begin compacting into the old gen
 592   PSMarkSweepDecorator::set_destination_decorator_tenured();
 593 
 594   // This will also compact the young gen spaces.
 595   old_gen->precompact();
 596 }
 597 
 598 void PSMarkSweep::mark_sweep_phase3() {
 599   // Adjust the pointers to reflect the new locations
 600   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", _gc_timer);
 601 
 602   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 603   PSYoungGen* young_gen = heap->young_gen();
 604   PSOldGen* old_gen = heap->old_gen();
 605 
 606   // Need to clear claim bits before the tracing starts.
 607   ClassLoaderDataGraph::clear_claimed_marks();
 608 
 609   // General strong roots.
 610   Universe::oops_do(adjust_pointer_closure());
 611   JNIHandles::oops_do(adjust_pointer_closure());   // Global (strong) JNI handles
 612   Threads::oops_do(adjust_pointer_closure(), NULL);
 613   ObjectSynchronizer::oops_do(adjust_pointer_closure());
 614   Management::oops_do(adjust_pointer_closure());
 615   JvmtiExport::oops_do(adjust_pointer_closure());
 616   SystemDictionary::oops_do(adjust_pointer_closure());
 617   ClassLoaderDataGraph::cld_do(adjust_cld_closure());
 618 
 619   // Now adjust pointers in remaining weak roots.  (All of which should
 620   // have been cleared if they pointed to non-surviving objects.)
 621   // Global (weak) JNI handles
 622   WeakProcessor::oops_do(adjust_pointer_closure());
 623 
 624   CodeBlobToOopClosure adjust_from_blobs(adjust_pointer_closure(), CodeBlobToOopClosure::FixRelocations);
 625   CodeCache::blobs_do(&adjust_from_blobs);
 626   AOT_ONLY(AOTLoader::oops_do(adjust_pointer_closure());)
 627 
 628   JVMCI_ONLY(JVMCI::oops_do(adjust_pointer_closure());)
 629 
 630   ref_processor()->weak_oops_do(adjust_pointer_closure());
 631   PSScavenge::reference_processor()->weak_oops_do(adjust_pointer_closure());
 632 
 633   adjust_marks();
 634 
 635   young_gen->adjust_pointers();
 636   old_gen->adjust_pointers();
 637 }
 638 
 639 void PSMarkSweep::mark_sweep_phase4() {
 640   EventMark m("4 compact heap");
 641   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
 642 
 643   // All pointers are now adjusted, move objects accordingly
 644 
 645   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 646   PSYoungGen* young_gen = heap->young_gen();
 647   PSOldGen* old_gen = heap->old_gen();
 648 
 649   old_gen->compact();
 650   young_gen->compact();
 651 }
 652 
 653 jlong PSMarkSweep::millis_since_last_gc() {
 654   // We need a monotonically non-decreasing time in ms but
 655   // os::javaTimeMillis() does not guarantee monotonicity.
 656   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 657   jlong ret_val = now - _time_of_last_gc;
 658   // XXX See note in genCollectedHeap::millis_since_last_gc().
 659   if (ret_val < 0) {
 660     NOT_PRODUCT(log_warning(gc)("time warp: " JLONG_FORMAT, ret_val);)
 661     return 0;
 662   }
 663   return ret_val;
 664 }
 665 
 666 void PSMarkSweep::reset_millis_since_last_gc() {
 667   // We need a monotonically non-decreasing time in ms but
 668   // os::javaTimeMillis() does not guarantee monotonicity.
 669   _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 670 }