1 /*
   2  * Copyright (c) 2001, 2010, 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/psPermGen.hpp"
  36 #include "gc_implementation/parallelScavenge/psScavenge.hpp"
  37 #include "gc_implementation/parallelScavenge/psYoungGen.hpp"
  38 #include "gc_implementation/shared/isGCActiveMark.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 unsigned int        PSMarkSweep::_total_invocations = 0;
  56 jlong               PSMarkSweep::_time_of_last_gc   = 0;
  57 CollectorCounters*  PSMarkSweep::_counters = NULL;
  58 
  59 void PSMarkSweep::initialize() {
  60   MemRegion mr = Universe::heap()->reserved_region();
  61   _ref_processor = new ReferenceProcessor(mr);     // a vanilla ref proc
  62   _counters = new CollectorCounters("PSMarkSweep", 1);
  63 }
  64 
  65 // This method contains all heap specific policy for invoking mark sweep.
  66 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact
  67 // the heap. It will do nothing further. If we need to bail out for policy
  68 // reasons, scavenge before full gc, or any other specialized behavior, it
  69 // needs to be added here.
  70 //
  71 // Note that this method should only be called from the vm_thread while
  72 // at a safepoint!
  73 //
  74 // Note that the all_soft_refs_clear flag in the collector policy
  75 // may be true because this method can be called without intervening
  76 // activity.  For example when the heap space is tight and full measure
  77 // are being taken to free space.
  78 
  79 void PSMarkSweep::invoke(bool maximum_heap_compaction) {
  80   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
  81   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
  82   assert(!Universe::heap()->is_gc_active(), "not reentrant");
  83 
  84   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
  85   GCCause::Cause gc_cause = heap->gc_cause();
  86   PSAdaptiveSizePolicy* policy = heap->size_policy();
  87   IsGCActiveMark mark;
  88 
  89   if (ScavengeBeforeFullGC) {
  90     PSScavenge::invoke_no_policy();
  91   }
  92 
  93   const bool clear_all_soft_refs =
  94     heap->collector_policy()->should_clear_all_soft_refs();
  95 
  96   int count = (maximum_heap_compaction)?1:MarkSweepAlwaysCompactCount;
  97   IntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);
  98   PSMarkSweep::invoke_no_policy(clear_all_soft_refs || maximum_heap_compaction);
  99 }
 100 
 101 // This method contains no policy. You should probably
 102 // be calling invoke() instead.
 103 void PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
 104   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 105   assert(ref_processor() != NULL, "Sanity");
 106 
 107   if (GC_locker::check_active_before_gc()) {
 108     return;
 109   }
 110 
 111   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 112   GCCause::Cause gc_cause = heap->gc_cause();
 113   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 114   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 115 
 116   // The scope of casr should end after code that can change
 117   // CollectorPolicy::_should_clear_all_soft_refs.
 118   ClearedAllSoftRefs casr(clear_all_softrefs, heap->collector_policy());
 119 
 120   PSYoungGen* young_gen = heap->young_gen();
 121   PSOldGen* old_gen = heap->old_gen();
 122   PSPermGen* perm_gen = heap->perm_gen();
 123 
 124   // Increment the invocation count
 125   heap->increment_total_collections(true /* full */);
 126 
 127   // Save information needed to minimize mangling
 128   heap->record_gen_tops_before_GC();
 129 
 130   // We need to track unique mark sweep invocations as well.
 131   _total_invocations++;
 132 
 133   AdaptiveSizePolicyOutput(size_policy, heap->total_collections());
 134 
 135   if (PrintHeapAtGC) {
 136     Universe::print_heap_before_gc();
 137   }
 138 
 139   // Fill in TLABs
 140   heap->accumulate_statistics_all_tlabs();
 141   heap->ensure_parsability(true);  // retire TLABs
 142 
 143   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
 144     HandleMark hm;  // Discard invalid handles created during verification
 145     gclog_or_tty->print(" VerifyBeforeGC:");
 146     Universe::verify(true);
 147   }
 148 
 149   // Verify object start arrays
 150   if (VerifyObjectStartArray &&
 151       VerifyBeforeGC) {
 152     old_gen->verify_object_start_array();
 153     perm_gen->verify_object_start_array();
 154   }
 155 
 156   heap->pre_full_gc_dump();
 157 
 158   // Filled in below to track the state of the young gen after the collection.
 159   bool eden_empty;
 160   bool survivors_empty;
 161   bool young_gen_empty;
 162 
 163   {
 164     HandleMark hm;
 165     const bool is_system_gc = gc_cause == GCCause::_java_lang_system_gc;
 166     // This is useful for debugging but don't change the output the
 167     // the customer sees.
 168     const char* gc_cause_str = "Full GC";
 169     if (is_system_gc && PrintGCDetails) {
 170       gc_cause_str = "Full GC (System)";
 171     }
 172     gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
 173     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
 174     TraceTime t1(gc_cause_str, PrintGC, !PrintGCDetails, gclog_or_tty);
 175     TraceCollectorStats tcs(counters());
 176     TraceMemoryManagerStats tms(true /* Full GC */);
 177 
 178     if (TraceGen1Time) accumulated_time()->start();
 179 
 180     // Let the size policy know we're starting
 181     size_policy->major_collection_begin();
 182 
 183     // When collecting the permanent generation methodOops may be moving,
 184     // so we either have to flush all bcp data or convert it into bci.
 185     CodeCache::gc_prologue();
 186     Threads::gc_prologue();
 187     BiasedLocking::preserve_marks();
 188 
 189     // Capture heap size before collection for printing.
 190     size_t prev_used = heap->used();
 191 
 192     // Capture perm gen size before collection for sizing.
 193     size_t perm_gen_prev_used = perm_gen->used_in_bytes();
 194 
 195     // For PrintGCDetails
 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     NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 202     COMPILER2_PRESENT(DerivedPointerTable::clear());
 203 
 204     ref_processor()->enable_discovery();
 205     ref_processor()->setup_policy(clear_all_softrefs);
 206 
 207     mark_sweep_phase1(clear_all_softrefs);
 208 
 209     mark_sweep_phase2();
 210 
 211     // Don't add any more derived pointers during phase3
 212     COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
 213     COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
 214 
 215     mark_sweep_phase3();
 216 
 217     mark_sweep_phase4();
 218 
 219     restore_marks();
 220 
 221     deallocate_stacks();
 222 
 223     if (ZapUnusedHeapArea) {
 224       // Do a complete mangle (top to end) because the usage for
 225       // scratch does not maintain a top pointer.
 226       young_gen->to_space()->mangle_unused_area_complete();
 227     }
 228 
 229     eden_empty = young_gen->eden_space()->is_empty();
 230     if (!eden_empty) {
 231       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
 232     }
 233 
 234     // Update heap occupancy information which is used as
 235     // input to soft ref clearing policy at the next gc.
 236     Universe::update_heap_info_at_gc();
 237 
 238     survivors_empty = young_gen->from_space()->is_empty() &&
 239                       young_gen->to_space()->is_empty();
 240     young_gen_empty = eden_empty && survivors_empty;
 241 
 242     BarrierSet* bs = heap->barrier_set();
 243     if (bs->is_a(BarrierSet::ModRef)) {
 244       ModRefBarrierSet* modBS = (ModRefBarrierSet*)bs;
 245       MemRegion old_mr = heap->old_gen()->reserved();
 246       MemRegion perm_mr = heap->perm_gen()->reserved();
 247       assert(perm_mr.end() <= old_mr.start(), "Generations out of order");
 248 
 249       if (young_gen_empty) {
 250         modBS->clear(MemRegion(perm_mr.start(), old_mr.end()));
 251       } else {
 252         modBS->invalidate(MemRegion(perm_mr.start(), old_mr.end()));
 253       }
 254     }
 255 
 256     BiasedLocking::restore_marks();
 257     Threads::gc_epilogue();
 258     CodeCache::gc_epilogue();
 259     JvmtiExport::gc_epilogue();
 260 
 261     COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
 262 
 263     ref_processor()->enqueue_discovered_references(NULL);
 264 
 265     // Update time of last GC
 266     reset_millis_since_last_gc();
 267 
 268     // Let the size policy know we're done
 269     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
 270 
 271     if (UseAdaptiveSizePolicy) {
 272 
 273       if (PrintAdaptiveSizePolicy) {
 274         gclog_or_tty->print("AdaptiveSizeStart: ");
 275         gclog_or_tty->stamp();
 276         gclog_or_tty->print_cr(" collection: %d ",
 277                        heap->total_collections());
 278         if (Verbose) {
 279           gclog_or_tty->print("old_gen_capacity: %d young_gen_capacity: %d"
 280             " perm_gen_capacity: %d ",
 281             old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes(),
 282             perm_gen->capacity_in_bytes());
 283         }
 284       }
 285 
 286       // Don't check if the size_policy is ready here.  Let
 287       // the size_policy check that internally.
 288       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
 289           ((gc_cause != GCCause::_java_lang_system_gc) ||
 290             UseAdaptiveSizePolicyWithSystemGC)) {
 291         // Calculate optimal free space amounts
 292         assert(young_gen->max_size() >
 293           young_gen->from_space()->capacity_in_bytes() +
 294           young_gen->to_space()->capacity_in_bytes(),
 295           "Sizes of space in young gen are out-of-bounds");
 296         size_t max_eden_size = young_gen->max_size() -
 297           young_gen->from_space()->capacity_in_bytes() -
 298           young_gen->to_space()->capacity_in_bytes();
 299         size_policy->compute_generation_free_space(young_gen->used_in_bytes(),
 300                                  young_gen->eden_space()->used_in_bytes(),
 301                                  old_gen->used_in_bytes(),
 302                                  perm_gen->used_in_bytes(),
 303                                  young_gen->eden_space()->capacity_in_bytes(),
 304                                  old_gen->max_gen_size(),
 305                                  max_eden_size,
 306                                  true /* full gc*/,
 307                                  gc_cause,
 308                                  heap->collector_policy());
 309 
 310         heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
 311 
 312         // Don't resize the young generation at an major collection.  A
 313         // desired young generation size may have been calculated but
 314         // resizing the young generation complicates the code because the
 315         // resizing of the old generation may have moved the boundary
 316         // between the young generation and the old generation.  Let the
 317         // young generation resizing happen at the minor collections.
 318       }
 319       if (PrintAdaptiveSizePolicy) {
 320         gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",
 321                        heap->total_collections());
 322       }
 323     }
 324 
 325     if (UsePerfData) {
 326       heap->gc_policy_counters()->update_counters();
 327       heap->gc_policy_counters()->update_old_capacity(
 328         old_gen->capacity_in_bytes());
 329       heap->gc_policy_counters()->update_young_capacity(
 330         young_gen->capacity_in_bytes());
 331     }
 332 
 333     heap->resize_all_tlabs();
 334 
 335     // We collected the perm gen, so we'll resize it here.
 336     perm_gen->compute_new_size(perm_gen_prev_used);
 337 
 338     if (TraceGen1Time) accumulated_time()->stop();
 339 
 340     if (PrintGC) {
 341       if (PrintGCDetails) {
 342         // Don't print a GC timestamp here.  This is after the GC so
 343         // would be confusing.
 344         young_gen->print_used_change(young_gen_prev_used);
 345         old_gen->print_used_change(old_gen_prev_used);
 346       }
 347       heap->print_heap_change(prev_used);
 348       // Do perm gen after heap becase prev_used does
 349       // not include the perm gen (done this way in the other
 350       // collectors).
 351       if (PrintGCDetails) {
 352         perm_gen->print_used_change(perm_gen_prev_used);
 353       }
 354     }
 355 
 356     // Track memory usage and detect low memory
 357     MemoryService::track_memory_usage();
 358     heap->update_counters();
 359   }
 360 
 361   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
 362     HandleMark hm;  // Discard invalid handles created during verification
 363     gclog_or_tty->print(" VerifyAfterGC:");
 364     Universe::verify(false);
 365   }
 366 
 367   // Re-verify object start arrays
 368   if (VerifyObjectStartArray &&
 369       VerifyAfterGC) {
 370     old_gen->verify_object_start_array();
 371     perm_gen->verify_object_start_array();
 372   }
 373 
 374   if (ZapUnusedHeapArea) {
 375     old_gen->object_space()->check_mangled_unused_area_complete();
 376     perm_gen->object_space()->check_mangled_unused_area_complete();
 377   }
 378 
 379   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 380 
 381   if (PrintHeapAtGC) {
 382     Universe::print_heap_after_gc();
 383   }
 384 
 385   heap->post_full_gc_dump();
 386 
 387 #ifdef TRACESPINNING
 388   ParallelTaskTerminator::print_termination_counts();
 389 #endif
 390 }
 391 
 392 bool PSMarkSweep::absorb_live_data_from_eden(PSAdaptiveSizePolicy* size_policy,
 393                                              PSYoungGen* young_gen,
 394                                              PSOldGen* old_gen) {
 395   MutableSpace* const eden_space = young_gen->eden_space();
 396   assert(!eden_space->is_empty(), "eden must be non-empty");
 397   assert(young_gen->virtual_space()->alignment() ==
 398          old_gen->virtual_space()->alignment(), "alignments do not match");
 399 
 400   if (!(UseAdaptiveSizePolicy && UseAdaptiveGCBoundary)) {
 401     return false;
 402   }
 403 
 404   // Both generations must be completely committed.
 405   if (young_gen->virtual_space()->uncommitted_size() != 0) {
 406     return false;
 407   }
 408   if (old_gen->virtual_space()->uncommitted_size() != 0) {
 409     return false;
 410   }
 411 
 412   // Figure out how much to take from eden.  Include the average amount promoted
 413   // in the total; otherwise the next young gen GC will simply bail out to a
 414   // full GC.
 415   const size_t alignment = old_gen->virtual_space()->alignment();
 416   const size_t eden_used = eden_space->used_in_bytes();
 417   const size_t promoted = (size_t)size_policy->avg_promoted()->padded_average();
 418   const size_t absorb_size = align_size_up(eden_used + promoted, alignment);
 419   const size_t eden_capacity = eden_space->capacity_in_bytes();
 420 
 421   if (absorb_size >= eden_capacity) {
 422     return false; // Must leave some space in eden.
 423   }
 424 
 425   const size_t new_young_size = young_gen->capacity_in_bytes() - absorb_size;
 426   if (new_young_size < young_gen->min_gen_size()) {
 427     return false; // Respect young gen minimum size.
 428   }
 429 
 430   if (TraceAdaptiveGCBoundary && Verbose) {
 431     gclog_or_tty->print(" absorbing " SIZE_FORMAT "K:  "
 432                         "eden " SIZE_FORMAT "K->" SIZE_FORMAT "K "
 433                         "from " SIZE_FORMAT "K, to " SIZE_FORMAT "K "
 434                         "young_gen " SIZE_FORMAT "K->" SIZE_FORMAT "K ",
 435                         absorb_size / K,
 436                         eden_capacity / K, (eden_capacity - absorb_size) / K,
 437                         young_gen->from_space()->used_in_bytes() / K,
 438                         young_gen->to_space()->used_in_bytes() / K,
 439                         young_gen->capacity_in_bytes() / K, new_young_size / K);
 440   }
 441 
 442   // Fill the unused part of the old gen.
 443   MutableSpace* const old_space = old_gen->object_space();
 444   HeapWord* const unused_start = old_space->top();
 445   size_t const unused_words = pointer_delta(old_space->end(), unused_start);
 446 
 447   if (unused_words > 0) {
 448     if (unused_words < CollectedHeap::min_fill_size()) {
 449       return false;  // If the old gen cannot be filled, must give up.
 450     }
 451     CollectedHeap::fill_with_objects(unused_start, unused_words);
 452   }
 453 
 454   // Take the live data from eden and set both top and end in the old gen to
 455   // eden top.  (Need to set end because reset_after_change() mangles the region
 456   // from end to virtual_space->high() in debug builds).
 457   HeapWord* const new_top = eden_space->top();
 458   old_gen->virtual_space()->expand_into(young_gen->virtual_space(),
 459                                         absorb_size);
 460   young_gen->reset_after_change();
 461   old_space->set_top(new_top);
 462   old_space->set_end(new_top);
 463   old_gen->reset_after_change();
 464 
 465   // Update the object start array for the filler object and the data from eden.
 466   ObjectStartArray* const start_array = old_gen->start_array();
 467   for (HeapWord* p = unused_start; p < new_top; p += oop(p)->size()) {
 468     start_array->allocate_block(p);
 469   }
 470 
 471   // Could update the promoted average here, but it is not typically updated at
 472   // full GCs and the value to use is unclear.  Something like
 473   //
 474   // cur_promoted_avg + absorb_size / number_of_scavenges_since_last_full_gc.
 475 
 476   size_policy->set_bytes_absorbed_from_eden(absorb_size);
 477   return true;
 478 }
 479 
 480 void PSMarkSweep::allocate_stacks() {
 481   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 482   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 483 
 484   PSYoungGen* young_gen = heap->young_gen();
 485 
 486   MutableSpace* to_space = young_gen->to_space();
 487   _preserved_marks = (PreservedMark*)to_space->top();
 488   _preserved_count = 0;
 489 
 490   // We want to calculate the size in bytes first.
 491   _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));
 492   // Now divide by the size of a PreservedMark
 493   _preserved_count_max /= sizeof(PreservedMark);
 494 }
 495 
 496 
 497 void PSMarkSweep::deallocate_stacks() {
 498   _preserved_mark_stack.clear(true);
 499   _preserved_oop_stack.clear(true);
 500   _marking_stack.clear();
 501   _objarray_stack.clear(true);
 502   _revisit_klass_stack.clear(true);
 503   _revisit_mdo_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   EventMark m("1 mark object");
 509   TraceTime tm("phase 1", PrintGCDetails && Verbose, true, gclog_or_tty);
 510   trace(" 1");
 511 
 512   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 513   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 514 
 515   // General strong roots.
 516   {
 517     ParallelScavengeHeap::ParStrongRootsScope psrs;
 518     Universe::oops_do(mark_and_push_closure());
 519     ReferenceProcessor::oops_do(mark_and_push_closure());
 520     JNIHandles::oops_do(mark_and_push_closure());   // Global (strong) JNI handles
 521     CodeBlobToOopClosure each_active_code_blob(mark_and_push_closure(), /*do_marking=*/ true);
 522     Threads::oops_do(mark_and_push_closure(), &each_active_code_blob);
 523     ObjectSynchronizer::oops_do(mark_and_push_closure());
 524     FlatProfiler::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     // Do not treat nmethods as strong roots for mark/sweep, since we can unload them.
 529     //CodeCache::scavenge_root_nmethods_do(CodeBlobToOopClosure(mark_and_push_closure()));
 530   }
 531 
 532   // Flush marking stack.
 533   follow_stack();
 534 
 535   // Process reference objects found during marking
 536   {
 537     ref_processor()->setup_policy(clear_all_softrefs);
 538     ref_processor()->process_discovered_references(
 539       is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL);
 540   }
 541 
 542   // Follow system dictionary roots and unload classes
 543   bool purged_class = SystemDictionary::do_unloading(is_alive_closure());
 544 
 545   // Follow code cache roots
 546   CodeCache::do_unloading(is_alive_closure(), mark_and_push_closure(),
 547                           purged_class);
 548   follow_stack(); // Flush marking stack
 549 
 550   // Update subklass/sibling/implementor links of live klasses
 551   follow_weak_klass_links();
 552   assert(_marking_stack.is_empty(), "just drained");
 553 
 554   // Visit memoized mdo's and clear unmarked weak refs
 555   follow_mdo_weak_refs();
 556   assert(_marking_stack.is_empty(), "just drained");
 557 
 558   // Visit interned string tables and delete unmarked oops
 559   StringTable::unlink(is_alive_closure());
 560   // Clean up unreferenced symbols in symbol table.
 561   SymbolTable::unlink();
 562 
 563   assert(_marking_stack.is_empty(), "stack should be empty by now");
 564 }
 565 
 566 
 567 void PSMarkSweep::mark_sweep_phase2() {
 568   EventMark m("2 compute new addresses");
 569   TraceTime tm("phase 2", PrintGCDetails && Verbose, true, gclog_or_tty);
 570   trace("2");
 571 
 572   // Now all live objects are marked, compute the new object addresses.
 573 
 574   // It is imperative that we traverse perm_gen LAST. If dead space is
 575   // allowed a range of dead object may get overwritten by a dead int
 576   // array. If perm_gen is not traversed last a klassOop may get
 577   // overwritten. This is fine since it is dead, but if the class has dead
 578   // instances we have to skip them, and in order to find their size we
 579   // need the klassOop!
 580   //
 581   // It is not required that we traverse spaces in the same order in
 582   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 583   // tracking expects us to do so. See comment under phase4.
 584 
 585   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 586   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 587 
 588   PSOldGen* old_gen = heap->old_gen();
 589   PSPermGen* perm_gen = heap->perm_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   // Compact the perm gen into the perm gen
 598   PSMarkSweepDecorator::set_destination_decorator_perm_gen();
 599 
 600   perm_gen->precompact();
 601 }
 602 
 603 // This should be moved to the shared markSweep code!
 604 class PSAlwaysTrueClosure: public BoolObjectClosure {
 605 public:
 606   void do_object(oop p) { ShouldNotReachHere(); }
 607   bool do_object_b(oop p) { return true; }
 608 };
 609 static PSAlwaysTrueClosure always_true;
 610 
 611 void PSMarkSweep::mark_sweep_phase3() {
 612   // Adjust the pointers to reflect the new locations
 613   EventMark m("3 adjust pointers");
 614   TraceTime tm("phase 3", PrintGCDetails && Verbose, true, gclog_or_tty);
 615   trace("3");
 616 
 617   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 618   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 619 
 620   PSYoungGen* young_gen = heap->young_gen();
 621   PSOldGen* old_gen = heap->old_gen();
 622   PSPermGen* perm_gen = heap->perm_gen();
 623 
 624   // General strong roots.
 625   Universe::oops_do(adjust_root_pointer_closure());
 626   ReferenceProcessor::oops_do(adjust_root_pointer_closure());
 627   JNIHandles::oops_do(adjust_root_pointer_closure());   // Global (strong) JNI handles
 628   Threads::oops_do(adjust_root_pointer_closure(), NULL);
 629   ObjectSynchronizer::oops_do(adjust_root_pointer_closure());
 630   FlatProfiler::oops_do(adjust_root_pointer_closure());
 631   Management::oops_do(adjust_root_pointer_closure());
 632   JvmtiExport::oops_do(adjust_root_pointer_closure());
 633   // SO_AllClasses
 634   SystemDictionary::oops_do(adjust_root_pointer_closure());
 635   //CodeCache::scavenge_root_nmethods_oops_do(adjust_root_pointer_closure());
 636 
 637   // Now adjust pointers in remaining weak roots.  (All of which should
 638   // have been cleared if they pointed to non-surviving objects.)
 639   // Global (weak) JNI handles
 640   JNIHandles::weak_oops_do(&always_true, adjust_root_pointer_closure());
 641 
 642   CodeCache::oops_do(adjust_pointer_closure());
 643   StringTable::oops_do(adjust_root_pointer_closure());
 644   ref_processor()->weak_oops_do(adjust_root_pointer_closure());
 645   PSScavenge::reference_processor()->weak_oops_do(adjust_root_pointer_closure());
 646 
 647   adjust_marks();
 648 
 649   young_gen->adjust_pointers();
 650   old_gen->adjust_pointers();
 651   perm_gen->adjust_pointers();
 652 }
 653 
 654 void PSMarkSweep::mark_sweep_phase4() {
 655   EventMark m("4 compact heap");
 656   TraceTime tm("phase 4", PrintGCDetails && Verbose, true, gclog_or_tty);
 657   trace("4");
 658 
 659   // All pointers are now adjusted, move objects accordingly
 660 
 661   // It is imperative that we traverse perm_gen first in phase4. All
 662   // classes must be allocated earlier than their instances, and traversing
 663   // perm_gen first makes sure that all klassOops have moved to their new
 664   // location before any instance does a dispatch through it's klass!
 665   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 666   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 667 
 668   PSYoungGen* young_gen = heap->young_gen();
 669   PSOldGen* old_gen = heap->old_gen();
 670   PSPermGen* perm_gen = heap->perm_gen();
 671 
 672   perm_gen->compact();
 673   old_gen->compact();
 674   young_gen->compact();
 675 }
 676 
 677 jlong PSMarkSweep::millis_since_last_gc() {
 678   jlong ret_val = os::javaTimeMillis() - _time_of_last_gc;
 679   // XXX See note in genCollectedHeap::millis_since_last_gc().
 680   if (ret_val < 0) {
 681     NOT_PRODUCT(warning("time warp: %d", ret_val);)
 682     return 0;
 683   }
 684   return ret_val;
 685 }
 686 
 687 void PSMarkSweep::reset_millis_since_last_gc() {
 688   _time_of_last_gc = os::javaTimeMillis();
 689 }