C++ GenCollectedHeap::next_gen方法代码示例

void CardTableRS::clear_into_gen_and_younger(Generation* gen) {
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  // Gen and all younger have been evacuated. We can clear
  // remembered set entries for the next highest generation
  // (we know that it has no pointers to younger gens) and
  // those below.
  Generation* g = gch->next_gen(gen);
  while (g != NULL) {
    clear(g->reserved());
    g = gch->prev_gen(gen);
  }
}

bool DefNewGeneration::collection_attempt_is_safe() {
  if (!to()->is_empty()) {
    if (Verbose && PrintGCDetails) {
      gclog_or_tty->print(" :: to is not empty :: ");
    }
    return false;
  }
  if (_next_gen == NULL) {
    GenCollectedHeap* gch = GenCollectedHeap::heap();
    _next_gen = gch->next_gen(this);
  }
  return _next_gen->promotion_attempt_is_safe(used());
}

bool DefNewGeneration::full_promotion_would_succeed() {
  if (_next_gen == NULL) {
    GenCollectedHeap* gch = GenCollectedHeap::heap();
    _next_gen = gch->next_gen(this);
    assert(_next_gen != NULL, 
           "This must be the youngest gen, and not the only gen");
  }

  // Decide if there's enough room for a full promotion
  // When using extremely large edens, we effectively lose a large amount of old space.
  // Use the "MaxLiveObjectEvacuationRatio" flag to reduce the minimum evacuation space
  // requirements. If there is not enough space to evacuate eden during a scavenge, the
  // VM will immediately exit with an out of memory error. This flag has not been tested
  // with collectors other than simple mark & sweep.
  const double evacuation_ratio = MaxLiveObjectEvacuationRatio / 100.0;
  size_t worst_case_evacuation = (size_t)(used() * evacuation_ratio);

  return _next_gen->max_contiguous_available() >= worst_case_evacuation;
}

bool DefNewGeneration::collection_attempt_is_safe() {
  if (!to()->is_empty()) {
    return false;
  }
  if (_next_gen == NULL) {
    GenCollectedHeap* gch = GenCollectedHeap::heap();
    _next_gen = gch->next_gen(this);
    assert(_next_gen != NULL,
           "This must be the youngest gen, and not the only gen");
  }

  // Decide if there's enough room for a full promotion
  // When using extremely large edens, we effectively lose a
  // large amount of old space.  Use the "MaxLiveObjectEvacuationRatio"
  // flag to reduce the minimum evacuation space requirements. If
  // there is not enough space to evacuate eden during a scavenge,
  // the VM will immediately exit with an out of memory error.
  // This flag has not been tested
  // with collectors other than simple mark & sweep.
  //
  // Note that with the addition of promotion failure handling, the
  // VM will not immediately exit but will undo the young generation
  // collection.  The parameter is left here for compatibility.
  const double evacuation_ratio = MaxLiveObjectEvacuationRatio / 100.0;

  // worst_case_evacuation is based on "used()".  For the case where this
  // method is called after a collection, this is still appropriate because
  // the case that needs to be detected is one in which a full collection
  // has been done and has overflowed into the young generation.  In that
  // case a minor collection will fail (the overflow of the full collection
  // means there is no space in the old generation for any promotion).
  size_t worst_case_evacuation = (size_t)(used() * evacuation_ratio);

  return _next_gen->promotion_attempt_is_safe(worst_case_evacuation,
                                              HandlePromotionFailure);
}

void DefNewGeneration::collect(bool   full,
                               bool   clear_all_soft_refs,
                               size_t size,
                               bool   is_tlab) {
  assert(full || size > 0, "otherwise we don't want to collect");

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  _gc_timer->register_gc_start();
  DefNewTracer gc_tracer;
  gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());

  _next_gen = gch->next_gen(this);

  // If the next generation is too full to accommodate promotion
  // from this generation, pass on collection; let the next generation
  // do it.
  if (!collection_attempt_is_safe()) {
    if (Verbose && PrintGCDetails) {
      gclog_or_tty->print(" :: Collection attempt not safe :: ");
    }
    gch->set_incremental_collection_failed(); // Slight lie: we did not even attempt one
    return;
  }
  assert(to()->is_empty(), "Else not collection_attempt_is_safe");

  init_assuming_no_promotion_failure();

  GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL);
  // Capture heap used before collection (for printing).
  size_t gch_prev_used = gch->used();

  gch->trace_heap_before_gc(&gc_tracer);

  SpecializationStats::clear();

  // These can be shared for all code paths
  IsAliveClosure is_alive(this);
  ScanWeakRefClosure scan_weak_ref(this);

  age_table()->clear();
  to()->clear(SpaceDecorator::Mangle);

  gch->rem_set()->prepare_for_younger_refs_iterate(false);

  assert(gch->no_allocs_since_save_marks(0),
         "save marks have not been newly set.");

  // Not very pretty.
  CollectorPolicy* cp = gch->collector_policy();

  FastScanClosure fsc_with_no_gc_barrier(this, false);
  FastScanClosure fsc_with_gc_barrier(this, true);

  KlassScanClosure klass_scan_closure(&fsc_with_no_gc_barrier,
                                      gch->rem_set()->klass_rem_set());

  set_promo_failure_scan_stack_closure(&fsc_with_no_gc_barrier);
  FastEvacuateFollowersClosure evacuate_followers(gch, _level, this,
                                                  &fsc_with_no_gc_barrier,
                                                  &fsc_with_gc_barrier);

  assert(gch->no_allocs_since_save_marks(0),
         "save marks have not been newly set.");

  int so = SharedHeap::SO_AllClasses | SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;

  gch->gen_process_strong_roots(_level,
                                true,  // Process younger gens, if any,
                                       // as strong roots.
                                true,  // activate StrongRootsScope
                                true,  // is scavenging
                                SharedHeap::ScanningOption(so),
                                &fsc_with_no_gc_barrier,
                                true,   // walk *all* scavengable nmethods
                                &fsc_with_gc_barrier,
                                &klass_scan_closure);

  // "evacuate followers".
  evacuate_followers.do_void();

  FastKeepAliveClosure keep_alive(this, &scan_weak_ref);
  ReferenceProcessor* rp = ref_processor();
  rp->setup_policy(clear_all_soft_refs);
  const ReferenceProcessorStats& stats =
  rp->process_discovered_references(&is_alive, &keep_alive, &evacuate_followers,
                                    NULL, _gc_timer);
  gc_tracer.report_gc_reference_stats(stats);

  if (!_promotion_failed) {
    // Swap the survivor spaces.
    eden()->clear(SpaceDecorator::Mangle);
    from()->clear(SpaceDecorator::Mangle);
    if (ZapUnusedHeapArea) {
      // This is now done here because of the piece-meal mangling which
      // can check for valid mangling at intermediate points in the
      // collection(s).  When a minor collection fails to collect
      // sufficient space resizing of the young generation can occur
      // an redistribute the spaces in the young generation.  Mangle
      // here so that unzapped regions don't get distributed to
//.........这里部分代码省略.........

void DefNewGeneration::collect(bool   full,
                               bool   clear_all_soft_refs,
                               size_t size,
                               bool   is_tlab) {
  assert(full || size > 0, "otherwise we don't want to collect");
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  _next_gen = gch->next_gen(this);
  assert(_next_gen != NULL,
    "This must be the youngest gen, and not the only gen");

  // If the next generation is too full to accomodate promotion
  // from this generation, pass on collection; let the next generation
  // do it.
  if (!collection_attempt_is_safe()) {
    gch->set_incremental_collection_will_fail();
    return;
  }
  assert(to()->is_empty(), "Else not collection_attempt_is_safe");

  init_assuming_no_promotion_failure();

  TraceTime t1("GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);
  // Capture heap used before collection (for printing).
  size_t gch_prev_used = gch->used();

  SpecializationStats::clear();

  // These can be shared for all code paths
  IsAliveClosure is_alive(this);
  ScanWeakRefClosure scan_weak_ref(this);

  age_table()->clear();
  to()->clear(SpaceDecorator::Mangle);

  gch->rem_set()->prepare_for_younger_refs_iterate(false);

  assert(gch->no_allocs_since_save_marks(0),
         "save marks have not been newly set.");

  // Not very pretty.
  CollectorPolicy* cp = gch->collector_policy();

  FastScanClosure fsc_with_no_gc_barrier(this, false);
  FastScanClosure fsc_with_gc_barrier(this, true);

  set_promo_failure_scan_stack_closure(&fsc_with_no_gc_barrier);
  FastEvacuateFollowersClosure evacuate_followers(gch, _level, this,
                                                  &fsc_with_no_gc_barrier,
                                                  &fsc_with_gc_barrier);

  assert(gch->no_allocs_since_save_marks(0),
         "save marks have not been newly set.");

  gch->gen_process_strong_roots(_level,
                                true,  // Process younger gens, if any,
                                       // as strong roots.
                                true,  // activate StrongRootsScope
                                false, // not collecting perm generation.
                                SharedHeap::SO_AllClasses,
                                &fsc_with_no_gc_barrier,
                                true,   // walk *all* scavengable nmethods
                                &fsc_with_gc_barrier);

  // "evacuate followers".
  evacuate_followers.do_void();

  FastKeepAliveClosure keep_alive(this, &scan_weak_ref);
  ReferenceProcessor* rp = ref_processor();
  rp->setup_policy(clear_all_soft_refs);
  rp->process_discovered_references(&is_alive, &keep_alive, &evacuate_followers,
                                    NULL);
  if (!promotion_failed()) {
    // Swap the survivor spaces.
    eden()->clear(SpaceDecorator::Mangle);
    from()->clear(SpaceDecorator::Mangle);
    if (ZapUnusedHeapArea) {
      // This is now done here because of the piece-meal mangling which
      // can check for valid mangling at intermediate points in the
      // collection(s).  When a minor collection fails to collect
      // sufficient space resizing of the young generation can occur
      // an redistribute the spaces in the young generation.  Mangle
      // here so that unzapped regions don't get distributed to
      // other spaces.
      to()->mangle_unused_area();
    }
    swap_spaces();

    assert(to()->is_empty(), "to space should be empty now");

    // Set the desired survivor size to half the real survivor space
    _tenuring_threshold =
      age_table()->compute_tenuring_threshold(to()->capacity()/HeapWordSize);

    if (PrintGC && !PrintGCDetails) {
      gch->print_heap_change(gch_prev_used);
    }
  } else {
    assert(HandlePromotionFailure,
      "Should not be here unless promotion failure handling is on");
    assert(_promo_failure_scan_stack != NULL &&
//.........这里部分代码省略.........

void DefNewGeneration::collect(bool   full,
                               bool   clear_all_soft_refs,
			       size_t size,
                               bool   is_large_noref,
                               bool   is_tlab) {
  assert(full || size > 0, "otherwise we don't want to collect");
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  _next_gen = gch->next_gen(this);
  assert(_next_gen != NULL, 
    "This must be the youngest gen, and not the only gen");
  // If the next generation is too full to accomodate worst-case promotion
  // from this generation, pass on collection; let the next generation
  // do it.
  if (!full_promotion_would_succeed()) {
    gch->set_incremental_collection_will_fail();
    if (PrintGC && Verbose) {
      gclog_or_tty->print_cr("DefNewGeneration::collect"
                    " contiguous_available: " SIZE_FORMAT " < used: " SIZE_FORMAT,
                    _next_gen->max_contiguous_available(), used());
    }
    return;
  }

  TraceTime t1("GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);
  // Capture heap used before collection (for printing).
  size_t gch_prev_used = gch->used();

  SpecializationStats::clear();

  // These can be shared for all code paths
  IsAliveClosure is_alive(this);
  ScanWeakRefClosure scan_weak_ref(this);

  age_table()->clear();
  to()->clear();

  gch->rem_set()->prepare_for_younger_refs_iterate(false);

  assert(gch->no_allocs_since_save_marks(0), 
	 "save marks have not been newly set.");

  // Weak refs.
  // FIXME: Are these storage leaks, or are they resource objects?
  NOT_COMPILER2(ReferencePolicy *soft_ref_policy = new LRUCurrentHeapPolicy());
  COMPILER2_ONLY(ReferencePolicy *soft_ref_policy = new LRUMaxHeapPolicy());
      
  // Not very pretty.
  CollectorPolicy* cp = gch->collector_policy();
  if (!cp->is_train_policy()) {
    FastScanClosure fsc_with_no_gc_barrier(this, false);
    FastScanClosure fsc_with_gc_barrier(this, true);

    FastEvacuateFollowersClosure evacuate_followers(gch, _level,
                                                    &fsc_with_no_gc_barrier, 
                                                    &fsc_with_gc_barrier);
    
    assert(gch->no_allocs_since_save_marks(0), 
           "save marks have not been newly set.");
    
    gch->process_strong_roots(_level,
                              true, // Process younger gens, if any, as
                              // strong roots.
                              false,// not collecting permanent generation.
                              GenCollectedHeap::CSO_AllClasses,
                              &fsc_with_gc_barrier, 
                              &fsc_with_no_gc_barrier);
    
    // "evacuate followers".
    evacuate_followers.do_void();
    
    FastKeepAliveClosure keep_alive(this, &scan_weak_ref);
    ref_processor()->process_discovered_references(soft_ref_policy,
                                                   &is_alive,
                                                   &keep_alive,
                                                   &evacuate_followers);
  } else { // Train policy
    ScanClosure sc_with_no_gc_barrier(this, false);
    ScanClosure sc_with_gc_barrier(this, true);
    
    EvacuateFollowersClosure evacuate_followers(gch, _level,
                                                &sc_with_no_gc_barrier, 
                                                &sc_with_gc_barrier);
    
    gch->process_strong_roots(_level,
                              true, // Process younger gens, if any, as
                              // strong roots.
                              false,// not collecting perm generation.
                              GenCollectedHeap::CSO_AllClasses,
                              &sc_with_gc_barrier, 
                              &sc_with_no_gc_barrier);
    
    // "evacuate followers".
    evacuate_followers.do_void();

    TrainPolicyKeepAliveClosure keep_alive((TrainGeneration*)_next_gen, 
                                           &scan_weak_ref);
    ref_processor()->process_discovered_references(soft_ref_policy,
                                                   &is_alive,
                                                   &keep_alive,
                                                   &evacuate_followers);
//.........这里部分代码省略.........