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/generationSizer.hpp"
  30 #include "gc_implementation/parallelScavenge/parallelScavengeHeap.hpp"
  31 #include "gc_implementation/parallelScavenge/psAdaptiveSizePolicy.hpp"
  32 #include "gc_implementation/parallelScavenge/psMarkSweep.hpp"
  33 #include "gc_implementation/parallelScavenge/psMarkSweepDecorator.hpp"
  34 #include "gc_implementation/parallelScavenge/psOldGen.hpp"
  35 #include "gc_implementation/parallelScavenge/psScavenge.hpp"
  36 #include "gc_implementation/parallelScavenge/psYoungGen.hpp"
  37 #include "gc_implementation/shared/isGCActiveMark.hpp"
  38 #include "gc_implementation/shared/markSweep.hpp"
  39 #include "gc_implementation/shared/spaceDecorator.hpp"
  40 #include "gc_interface/gcCause.hpp"
  41 #include "memory/gcLocker.inline.hpp"
  42 #include "memory/referencePolicy.hpp"
  43 #include "memory/referenceProcessor.hpp"
  44 #include "oops/oop.inline.hpp"
  45 #include "runtime/biasedLocking.hpp"
  46 #include "runtime/fprofiler.hpp"
  47 #include "runtime/safepoint.hpp"
  48 #include "runtime/vmThread.hpp"
  49 #include "services/management.hpp"
  50 #include "services/memoryService.hpp"
  51 #include "utilities/events.hpp"
  52 #include "utilities/stack.inline.hpp"
  53 
  54 elapsedTimer        PSMarkSweep::_accumulated_time;
  55 jlong               PSMarkSweep::_time_of_last_gc   = 0;
  56 CollectorCounters*  PSMarkSweep::_counters = NULL;
  57 
  58 void PSMarkSweep::initialize() {
  59   MemRegion mr = Universe::heap()->reserved_region();
  60   _ref_processor = new ReferenceProcessor(mr);     // a vanilla ref proc
  61   _counters = new CollectorCounters("PSMarkSweep", 1);
  62 }
  63 
  64 // This method contains all heap specific policy for invoking mark sweep.
  65 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact
  66 // the heap. It will do nothing further. If we need to bail out for policy
  67 // reasons, scavenge before full gc, or any other specialized behavior, it
  68 // needs to be added here.
  69 //
  70 // Note that this method should only be called from the vm_thread while
  71 // at a safepoint!
  72 //
  73 // Note that the all_soft_refs_clear flag in the collector policy
  74 // may be true because this method can be called without intervening
  75 // activity.  For example when the heap space is tight and full measure
  76 // are being taken to free space.
  77 
  78 void PSMarkSweep::invoke(bool maximum_heap_compaction) {
  79   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
  80   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
  81   assert(!Universe::heap()->is_gc_active(), "not reentrant");
  82 
  83   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
  84   GCCause::Cause gc_cause = heap->gc_cause();
  85   PSAdaptiveSizePolicy* policy = heap->size_policy();
  86   IsGCActiveMark mark;
  87 
  88   if (ScavengeBeforeFullGC) {
  89     PSScavenge::invoke_no_policy();
  90   }
  91 
  92   const bool clear_all_soft_refs =
  93     heap->collector_policy()->should_clear_all_soft_refs();
  94 
  95   uint count = maximum_heap_compaction ? 1 : MarkSweepAlwaysCompactCount;
  96   UIntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);
  97   PSMarkSweep::invoke_no_policy(clear_all_soft_refs || maximum_heap_compaction);
  98 }
  99 
 100 // This method contains no policy. You should probably
 101 // be calling invoke() instead.
 102 bool PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
 103   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 104   assert(ref_processor() != NULL, "Sanity");
 105 
 106   if (GC_locker::check_active_before_gc()) {
 107     return false;
 108   }
 109 
 110   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 111   GCCause::Cause gc_cause = heap->gc_cause();
 112   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 113   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 114 
 115   // The scope of casr should end after code that can change
 116   // CollectorPolicy::_should_clear_all_soft_refs.
 117   ClearedAllSoftRefs casr(clear_all_softrefs, heap->collector_policy());
 118 
 119   PSYoungGen* young_gen = heap->young_gen();
 120   PSOldGen* old_gen = heap->old_gen();
 121 
 122   // Increment the invocation count
 123   heap->increment_total_collections(true /* full */);
 124 
 125   // Save information needed to minimize mangling
 126   heap->record_gen_tops_before_GC();
 127 
 128   // We need to track unique mark sweep invocations as well.
 129   _total_invocations++;
 130 
 131   AdaptiveSizePolicyOutput(size_policy, heap->total_collections());
 132 
 133   heap->print_heap_before_gc();
 134 
 135   // Fill in TLABs
 136   heap->accumulate_statistics_all_tlabs();
 137   heap->ensure_parsability(true);  // retire TLABs
 138 
 139   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
 140     HandleMark hm;  // Discard invalid handles created during verification
 141     Universe::verify(" VerifyBeforeGC:");
 142   }
 143 
 144   // Verify object start arrays
 145   if (VerifyObjectStartArray &&
 146       VerifyBeforeGC) {
 147     old_gen->verify_object_start_array();
 148   }
 149 
 150   heap->pre_full_gc_dump();
 151 
 152   // Filled in below to track the state of the young gen after the collection.
 153   bool eden_empty;
 154   bool survivors_empty;
 155   bool young_gen_empty;
 156 
 157   {
 158     HandleMark hm;
 159 
 160     gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
 161     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
 162     TraceTime t1(GCCauseString("Full GC", gc_cause), PrintGC, !PrintGCDetails, gclog_or_tty);
 163     TraceCollectorStats tcs(counters());
 164     TraceMemoryManagerStats tms(true /* Full GC */,gc_cause);
 165 
 166     if (TraceGen1Time) accumulated_time()->start();
 167 
 168     // Let the size policy know we're starting
 169     size_policy->major_collection_begin();
 170 
 171     CodeCache::gc_prologue();
 172     Threads::gc_prologue();
 173     BiasedLocking::preserve_marks();
 174 
 175     // Capture heap size before collection for printing.
 176     size_t prev_used = heap->used();
 177 
 178     // Capture metadata size before collection for sizing.
 179     size_t metadata_prev_used = MetaspaceAux::allocated_used_bytes();
 180 
 181     // For PrintGCDetails
 182     size_t old_gen_prev_used = old_gen->used_in_bytes();
 183     size_t young_gen_prev_used = young_gen->used_in_bytes();
 184 
 185     allocate_stacks();
 186 
 187     COMPILER2_PRESENT(DerivedPointerTable::clear());
 188 
 189     ref_processor()->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/);
 190     ref_processor()->setup_policy(clear_all_softrefs);
 191 
 192     mark_sweep_phase1(clear_all_softrefs);
 193 
 194     mark_sweep_phase2();
 195 
 196     // Don't add any more derived pointers during phase3
 197     COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
 198     COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
 199 
 200     mark_sweep_phase3();
 201 
 202     mark_sweep_phase4();
 203 
 204     restore_marks();
 205 
 206     deallocate_stacks();
 207 
 208     if (ZapUnusedHeapArea) {
 209       // Do a complete mangle (top to end) because the usage for
 210       // scratch does not maintain a top pointer.
 211       young_gen->to_space()->mangle_unused_area_complete();
 212     }
 213 
 214     eden_empty = young_gen->eden_space()->is_empty();
 215     if (!eden_empty) {
 216       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
 217     }
 218 
 219     // Update heap occupancy information which is used as
 220     // input to soft ref clearing policy at the next gc.
 221     Universe::update_heap_info_at_gc();
 222 
 223     survivors_empty = young_gen->from_space()->is_empty() &&
 224                       young_gen->to_space()->is_empty();
 225     young_gen_empty = eden_empty && survivors_empty;
 226 
 227     BarrierSet* bs = heap->barrier_set();
 228     if (bs->is_a(BarrierSet::ModRef)) {
 229       ModRefBarrierSet* modBS = (ModRefBarrierSet*)bs;
 230       MemRegion old_mr = heap->old_gen()->reserved();
 231       if (young_gen_empty) {
 232         modBS->clear(MemRegion(old_mr.start(), old_mr.end()));
 233       } else {
 234         modBS->invalidate(MemRegion(old_mr.start(), old_mr.end()));
 235       }
 236     }
 237 
 238     // Delete metaspaces for unloaded class loaders and clean up loader_data graph
 239     ClassLoaderDataGraph::purge();
 240     MetaspaceAux::verify_metrics();
 241 
 242     BiasedLocking::restore_marks();
 243     Threads::gc_epilogue();
 244     CodeCache::gc_epilogue();
 245     JvmtiExport::gc_epilogue();
 246 
 247     COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
 248 
 249     ref_processor()->enqueue_discovered_references(NULL);
 250 
 251     // Update time of last GC
 252     reset_millis_since_last_gc();
 253 
 254     // Let the size policy know we're done
 255     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
 256 
 257     if (UseAdaptiveSizePolicy) {
 258 
 259       if (PrintAdaptiveSizePolicy) {
 260         gclog_or_tty->print("AdaptiveSizeStart: ");
 261         gclog_or_tty->stamp();
 262         gclog_or_tty->print_cr(" collection: %d ",
 263                        heap->total_collections());
 264         if (Verbose) {
 265           gclog_or_tty->print("old_gen_capacity: %d young_gen_capacity: %d",
 266             old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
 267         }
 268       }
 269 
 270       // Don't check if the size_policy is ready here.  Let
 271       // the size_policy check that internally.
 272       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
 273           ((gc_cause != GCCause::_java_lang_system_gc) ||
 274             UseAdaptiveSizePolicyWithSystemGC)) {
 275         // Calculate optimal free space amounts
 276         assert(young_gen->max_size() >
 277           young_gen->from_space()->capacity_in_bytes() +
 278           young_gen->to_space()->capacity_in_bytes(),
 279           "Sizes of space in young gen are out-of-bounds");
 280 
 281         size_t young_live = young_gen->used_in_bytes();
 282         size_t eden_live = young_gen->eden_space()->used_in_bytes();
 283         size_t old_live = old_gen->used_in_bytes();
 284         size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
 285         size_t max_old_gen_size = old_gen->max_gen_size();
 286         size_t max_eden_size = young_gen->max_size() -
 287           young_gen->from_space()->capacity_in_bytes() -
 288           young_gen->to_space()->capacity_in_bytes();
 289 
 290         // Used for diagnostics
 291         size_policy->clear_generation_free_space_flags();
 292 
 293         size_policy->compute_generations_free_space(young_live,
 294                                                     eden_live,
 295                                                     old_live,
 296                                                     cur_eden,
 297                                                     max_old_gen_size,
 298                                                     max_eden_size,
 299                                                     true /* full gc*/);
 300 
 301         size_policy->check_gc_overhead_limit(young_live,
 302                                              eden_live,
 303                                              max_old_gen_size,
 304                                              max_eden_size,
 305                                              true /* full gc*/,
 306                                              gc_cause,
 307                                              heap->collector_policy());
 308 
 309         size_policy->decay_supplemental_growth(true /* full gc*/);
 310 
 311         heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
 312 
 313         // Don't resize the young generation at an major collection.  A
 314         // desired young generation size may have been calculated but
 315         // resizing the young generation complicates the code because the
 316         // resizing of the old generation may have moved the boundary
 317         // between the young generation and the old generation.  Let the
 318         // young generation resizing happen at the minor collections.
 319       }
 320       if (PrintAdaptiveSizePolicy) {
 321         gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",
 322                        heap->total_collections());
 323       }
 324     }
 325 
 326     if (UsePerfData) {
 327       heap->gc_policy_counters()->update_counters();
 328       heap->gc_policy_counters()->update_old_capacity(
 329         old_gen->capacity_in_bytes());
 330       heap->gc_policy_counters()->update_young_capacity(
 331         young_gen->capacity_in_bytes());
 332     }
 333 
 334     heap->resize_all_tlabs();
 335 
 336     // We collected the heap, recalculate the metaspace capacity
 337     MetaspaceGC::compute_new_size();
 338 
 339     if (TraceGen1Time) accumulated_time()->stop();
 340 
 341     if (PrintGC) {
 342       if (PrintGCDetails) {
 343         // Don't print a GC timestamp here.  This is after the GC so
 344         // would be confusing.
 345         young_gen->print_used_change(young_gen_prev_used);
 346         old_gen->print_used_change(old_gen_prev_used);
 347       }
 348       heap->print_heap_change(prev_used);
 349       if (PrintGCDetails) {
 350         MetaspaceAux::print_metaspace_change(metadata_prev_used);
 351       }
 352     }
 353 
 354     // Track memory usage and detect low memory
 355     MemoryService::track_memory_usage();
 356     heap->update_counters();
 357   }
 358 
 359   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
 360     HandleMark hm;  // Discard invalid handles created during verification
 361     Universe::verify(" VerifyAfterGC:");
 362   }
 363 
 364   // Re-verify object start arrays
 365   if (VerifyObjectStartArray &&
 366       VerifyAfterGC) {
 367     old_gen->verify_object_start_array();
 368   }
 369 
 370   if (ZapUnusedHeapArea) {
 371     old_gen->object_space()->check_mangled_unused_area_complete();
 372   }
 373 
 374   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 375 
 376   heap->print_heap_after_gc();
 377 
 378   heap->post_full_gc_dump();
 379 
 380 #ifdef TRACESPINNING
 381   ParallelTaskTerminator::print_termination_counts();
 382 #endif
 383 
 384   return true;
 385 }
 386 
 387 bool PSMarkSweep::absorb_live_data_from_eden(PSAdaptiveSizePolicy* size_policy,
 388                                              PSYoungGen* young_gen,
 389                                              PSOldGen* old_gen) {
 390   MutableSpace* const eden_space = young_gen->eden_space();
 391   assert(!eden_space->is_empty(), "eden must be non-empty");
 392   assert(young_gen->virtual_space()->alignment() ==
 393          old_gen->virtual_space()->alignment(), "alignments do not match");
 394 
 395   if (!(UseAdaptiveSizePolicy && UseAdaptiveGCBoundary)) {
 396     return false;
 397   }
 398 
 399   // Both generations must be completely committed.
 400   if (young_gen->virtual_space()->uncommitted_size() != 0) {
 401     return false;
 402   }
 403   if (old_gen->virtual_space()->uncommitted_size() != 0) {
 404     return false;
 405   }
 406 
 407   // Figure out how much to take from eden.  Include the average amount promoted
 408   // in the total; otherwise the next young gen GC will simply bail out to a
 409   // full GC.
 410   const size_t alignment = old_gen->virtual_space()->alignment();
 411   const size_t eden_used = eden_space->used_in_bytes();
 412   const size_t promoted = (size_t)size_policy->avg_promoted()->padded_average();
 413   const size_t absorb_size = align_size_up(eden_used + promoted, alignment);
 414   const size_t eden_capacity = eden_space->capacity_in_bytes();
 415 
 416   if (absorb_size >= eden_capacity) {
 417     return false; // Must leave some space in eden.
 418   }
 419 
 420   const size_t new_young_size = young_gen->capacity_in_bytes() - absorb_size;
 421   if (new_young_size < young_gen->min_gen_size()) {
 422     return false; // Respect young gen minimum size.
 423   }
 424 
 425   if (TraceAdaptiveGCBoundary && Verbose) {
 426     gclog_or_tty->print(" absorbing " SIZE_FORMAT "K:  "
 427                         "eden " SIZE_FORMAT "K->" SIZE_FORMAT "K "
 428                         "from " SIZE_FORMAT "K, to " SIZE_FORMAT "K "
 429                         "young_gen " SIZE_FORMAT "K->" SIZE_FORMAT "K ",
 430                         absorb_size / K,
 431                         eden_capacity / K, (eden_capacity - absorb_size) / K,
 432                         young_gen->from_space()->used_in_bytes() / K,
 433                         young_gen->to_space()->used_in_bytes() / K,
 434                         young_gen->capacity_in_bytes() / K, new_young_size / K);
 435   }
 436 
 437   // Fill the unused part of the old gen.
 438   MutableSpace* const old_space = old_gen->object_space();
 439   HeapWord* const unused_start = old_space->top();
 440   size_t const unused_words = pointer_delta(old_space->end(), unused_start);
 441 
 442   if (unused_words > 0) {
 443     if (unused_words < CollectedHeap::min_fill_size()) {
 444       return false;  // If the old gen cannot be filled, must give up.
 445     }
 446     CollectedHeap::fill_with_objects(unused_start, unused_words);
 447   }
 448 
 449   // Take the live data from eden and set both top and end in the old gen to
 450   // eden top.  (Need to set end because reset_after_change() mangles the region
 451   // from end to virtual_space->high() in debug builds).
 452   HeapWord* const new_top = eden_space->top();
 453   old_gen->virtual_space()->expand_into(young_gen->virtual_space(),
 454                                         absorb_size);
 455   young_gen->reset_after_change();
 456   old_space->set_top(new_top);
 457   old_space->set_end(new_top);
 458   old_gen->reset_after_change();
 459 
 460   // Update the object start array for the filler object and the data from eden.
 461   ObjectStartArray* const start_array = old_gen->start_array();
 462   for (HeapWord* p = unused_start; p < new_top; p += oop(p)->size()) {
 463     start_array->allocate_block(p);
 464   }
 465 
 466   // Could update the promoted average here, but it is not typically updated at
 467   // full GCs and the value to use is unclear.  Something like
 468   //
 469   // cur_promoted_avg + absorb_size / number_of_scavenges_since_last_full_gc.
 470 
 471   size_policy->set_bytes_absorbed_from_eden(absorb_size);
 472   return true;
 473 }
 474 
 475 void PSMarkSweep::allocate_stacks() {
 476   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 477   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 478 
 479   PSYoungGen* young_gen = heap->young_gen();
 480 
 481   MutableSpace* to_space = young_gen->to_space();
 482   _preserved_marks = (PreservedMark*)to_space->top();
 483   _preserved_count = 0;
 484 
 485   // We want to calculate the size in bytes first.
 486   _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));
 487   // Now divide by the size of a PreservedMark
 488   _preserved_count_max /= sizeof(PreservedMark);
 489 }
 490 
 491 
 492 void PSMarkSweep::deallocate_stacks() {
 493   _preserved_mark_stack.clear(true);
 494   _preserved_oop_stack.clear(true);
 495   _marking_stack.clear();
 496   _objarray_stack.clear(true);
 497 }
 498 
 499 void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 500   // Recursively traverse all live objects and mark them
 501   TraceTime tm("phase 1", PrintGCDetails && Verbose, true, gclog_or_tty);
 502   trace(" 1");
 503 
 504   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 505   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 506 
 507   // Need to clear claim bits before the tracing starts.
 508   ClassLoaderDataGraph::clear_claimed_marks();
 509 
 510   // General strong roots.
 511   {
 512     ParallelScavengeHeap::ParStrongRootsScope psrs;
 513     Universe::oops_do(mark_and_push_closure());
 514     JNIHandles::oops_do(mark_and_push_closure());   // Global (strong) JNI handles
 515     CLDToOopClosure mark_and_push_from_cld(mark_and_push_closure());
 516     CodeBlobToOopClosure each_active_code_blob(mark_and_push_closure(), /*do_marking=*/ true);
 517     Threads::oops_do(mark_and_push_closure(), &mark_and_push_from_cld, &each_active_code_blob);
 518     ObjectSynchronizer::oops_do(mark_and_push_closure());
 519     FlatProfiler::oops_do(mark_and_push_closure());
 520     Management::oops_do(mark_and_push_closure());
 521     JvmtiExport::oops_do(mark_and_push_closure());
 522     SystemDictionary::always_strong_oops_do(mark_and_push_closure());
 523     ClassLoaderDataGraph::always_strong_oops_do(mark_and_push_closure(), follow_klass_closure(), true);
 524     // Do not treat nmethods as strong roots for mark/sweep, since we can unload them.
 525     //CodeCache::scavenge_root_nmethods_do(CodeBlobToOopClosure(mark_and_push_closure()));
 526   }
 527 
 528   // Flush marking stack.
 529   follow_stack();
 530 
 531   // Process reference objects found during marking
 532   {
 533     ref_processor()->setup_policy(clear_all_softrefs);
 534     ref_processor()->process_discovered_references(
 535       is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL);
 536   }
 537 
 538   // This is the point where the entire marking should have completed.
 539   assert(_marking_stack.is_empty(), "Marking should have completed");
 540 
 541   // Unload classes and purge the SystemDictionary.
 542   bool purged_class = SystemDictionary::do_unloading(is_alive_closure());
 543 
 544   // Unload nmethods.
 545   CodeCache::do_unloading(is_alive_closure(), purged_class);
 546 
 547   // Prune dead klasses from subklass/sibling/implementor lists.
 548   Klass::clean_weak_klass_links(is_alive_closure());
 549 
 550   // Delete entries for dead interned strings.
 551   StringTable::unlink(is_alive_closure());
 552 
 553   // Clean up unreferenced symbols in symbol table.
 554   SymbolTable::unlink();
 555 }
 556 
 557 
 558 void PSMarkSweep::mark_sweep_phase2() {
 559   TraceTime tm("phase 2", PrintGCDetails && Verbose, true, gclog_or_tty);
 560   trace("2");
 561 
 562   // Now all live objects are marked, compute the new object addresses.
 563 
 564   // It is not required that we traverse spaces in the same order in
 565   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 566   // tracking expects us to do so. See comment under phase4.
 567 
 568   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 569   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 570 
 571   PSOldGen* old_gen = heap->old_gen();
 572 
 573   // Begin compacting into the old gen
 574   PSMarkSweepDecorator::set_destination_decorator_tenured();
 575 
 576   // This will also compact the young gen spaces.
 577   old_gen->precompact();
 578 }
 579 
 580 // This should be moved to the shared markSweep code!
 581 class PSAlwaysTrueClosure: public BoolObjectClosure {
 582 public:
 583   bool do_object_b(oop p) { return true; }
 584 };
 585 static PSAlwaysTrueClosure always_true;
 586 
 587 void PSMarkSweep::mark_sweep_phase3() {
 588   // Adjust the pointers to reflect the new locations
 589   TraceTime tm("phase 3", PrintGCDetails && Verbose, true, gclog_or_tty);
 590   trace("3");
 591 
 592   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 593   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 594 
 595   PSYoungGen* young_gen = heap->young_gen();
 596   PSOldGen* old_gen = heap->old_gen();
 597 
 598   // Need to clear claim bits before the tracing starts.
 599   ClassLoaderDataGraph::clear_claimed_marks();
 600 
 601   // General strong roots.
 602   Universe::oops_do(adjust_pointer_closure());
 603   JNIHandles::oops_do(adjust_pointer_closure());   // Global (strong) JNI handles
 604   CLDToOopClosure adjust_from_cld(adjust_pointer_closure());
 605   Threads::oops_do(adjust_pointer_closure(), &adjust_from_cld, NULL);
 606   ObjectSynchronizer::oops_do(adjust_pointer_closure());
 607   FlatProfiler::oops_do(adjust_pointer_closure());
 608   Management::oops_do(adjust_pointer_closure());
 609   JvmtiExport::oops_do(adjust_pointer_closure());
 610   // SO_AllClasses
 611   SystemDictionary::oops_do(adjust_pointer_closure());
 612   ClassLoaderDataGraph::oops_do(adjust_pointer_closure(), adjust_klass_closure(), true);
 613 
 614   // Now adjust pointers in remaining weak roots.  (All of which should
 615   // have been cleared if they pointed to non-surviving objects.)
 616   // Global (weak) JNI handles
 617   JNIHandles::weak_oops_do(&always_true, adjust_pointer_closure());
 618 
 619   CodeCache::oops_do(adjust_pointer_closure());
 620   StringTable::oops_do(adjust_pointer_closure());
 621   ref_processor()->weak_oops_do(adjust_pointer_closure());
 622   PSScavenge::reference_processor()->weak_oops_do(adjust_pointer_closure());
 623 
 624   adjust_marks();
 625 
 626   young_gen->adjust_pointers();
 627   old_gen->adjust_pointers();
 628 }
 629 
 630 void PSMarkSweep::mark_sweep_phase4() {
 631   EventMark m("4 compact heap");
 632   TraceTime tm("phase 4", PrintGCDetails && Verbose, true, gclog_or_tty);
 633   trace("4");
 634 
 635   // All pointers are now adjusted, move objects accordingly
 636 
 637   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 638   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 639 
 640   PSYoungGen* young_gen = heap->young_gen();
 641   PSOldGen* old_gen = heap->old_gen();
 642 
 643   old_gen->compact();
 644   young_gen->compact();
 645 }
 646 
 647 jlong PSMarkSweep::millis_since_last_gc() {
 648   // We need a monotonically non-deccreasing time in ms but
 649   // os::javaTimeMillis() does not guarantee monotonicity.
 650   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 651   jlong ret_val = now - _time_of_last_gc;
 652   // XXX See note in genCollectedHeap::millis_since_last_gc().
 653   if (ret_val < 0) {
 654     NOT_PRODUCT(warning("time warp: "INT64_FORMAT, ret_val);)
 655     return 0;
 656   }
 657   return ret_val;
 658 }
 659 
 660 void PSMarkSweep::reset_millis_since_last_gc() {
 661   // We need a monotonically non-deccreasing time in ms but
 662   // os::javaTimeMillis() does not guarantee monotonicity.
 663   _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 664 }