sdk/runtime/vm/heap.cc

// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#include "vm/heap.h"

#include "platform/assert.h"
#include "platform/utils.h"
#include "vm/flags.h"
#include "vm/isolate.h"
#include "vm/lockers.h"
#include "vm/object.h"
#include "vm/object_set.h"
#include "vm/os.h"
#include "vm/pages.h"
#include "vm/raw_object.h"
#include "vm/scavenger.h"
#include "vm/service.h"
#include "vm/service_event.h"
#include "vm/stack_frame.h"
#include "vm/tags.h"
#include "vm/timeline.h"
#include "vm/verifier.h"
#include "vm/virtual_memory.h"
#include "vm/weak_table.h"

namespace dart {

DEFINE_FLAG(bool, disable_alloc_stubs_after_gc, false, "Stress testing flag.");
DEFINE_FLAG(bool, gc_at_alloc, false, "GC at every allocation.");
DEFINE_FLAG(int, new_gen_ext_limit, 64,
            "maximum total external size (MB) in new gen before triggering GC");
DEFINE_FLAG(int, pretenure_interval, 10,
            "Back off pretenuring after this many cycles.");
DEFINE_FLAG(int, pretenure_threshold, 98,
            "Trigger pretenuring when this many percent are promoted.");
DEFINE_FLAG(bool, verbose_gc, false, "Enables verbose GC.");
DEFINE_FLAG(int, verbose_gc_hdr, 40, "Print verbose GC header interval.");
DEFINE_FLAG(bool, verify_after_gc, false,
            "Enables heap verification after GC.");
DEFINE_FLAG(bool, verify_before_gc, false,
            "Enables heap verification before GC.");
DEFINE_FLAG(bool, pretenure_all, false, "Global pretenuring (for testing).");


Heap::Heap(Isolate* isolate,
           intptr_t max_new_gen_semi_words,
           intptr_t max_old_gen_words,
           intptr_t max_external_words)
    : isolate_(isolate),
      new_space_(this, max_new_gen_semi_words, kNewObjectAlignmentOffset),
      old_space_(this, max_old_gen_words, max_external_words),
      read_only_(false),
      gc_new_space_in_progress_(false),
      gc_old_space_in_progress_(false),
      pretenure_policy_(0) {
  for (int sel = 0;
       sel < kNumWeakSelectors;
       sel++) {
    new_weak_tables_[sel] = new WeakTable();
    old_weak_tables_[sel] = new WeakTable();
  }
  stats_.num_ = 0;
}


Heap::~Heap() {
  for (int sel = 0;
       sel < kNumWeakSelectors;
       sel++) {
    delete new_weak_tables_[sel];
    delete old_weak_tables_[sel];
  }
}


uword Heap::AllocateNew(intptr_t size) {
  ASSERT(Thread::Current()->no_safepoint_scope_depth() == 0);
  // Currently, only the Dart thread may allocate in new space.
  isolate()->AssertCurrentThreadIsMutator();
  uword addr = new_space_.TryAllocate(size);
  if (addr == 0) {
    // This call to CollectGarbage might end up "reusing" a collection spawned
    // from a different thread and will be racing to allocate the requested
    // memory with other threads being released after the collection.
    CollectGarbage(kNew);
    addr = new_space_.TryAllocate(size);
    if (addr == 0) {
      return AllocateOld(size, HeapPage::kData);
    }
  }
  return addr;
}


uword Heap::AllocateOld(intptr_t size, HeapPage::PageType type) {
  ASSERT(Thread::Current()->no_safepoint_scope_depth() == 0);
  uword addr = old_space_.TryAllocate(size, type);
  if (addr != 0) {
    return addr;
  }
  // If we are in the process of running a sweep wait for the sweeper to free
  // memory.
  {
    MonitorLocker ml(old_space_.tasks_lock());
    addr = old_space_.TryAllocate(size, type);
    while ((addr == 0) && (old_space_.tasks() > 0)) {
      ml.Wait();
      addr = old_space_.TryAllocate(size, type);
    }
  }
  if (addr != 0) {
    return addr;
  }
  Thread* thread = Thread::Current();
  if (thread->CanCollectGarbage()) {
    // All GC tasks finished without allocating successfully. Run a full GC.
    CollectAllGarbage();
    addr = old_space_.TryAllocate(size, type);
    if (addr != 0) {
      return addr;
    }
    // Wait for all of the concurrent tasks to finish before giving up.
    {
      MonitorLocker ml(old_space_.tasks_lock());
      addr = old_space_.TryAllocate(size, type);
      while ((addr == 0) && (old_space_.tasks() > 0)) {
        ml.Wait();
        addr = old_space_.TryAllocate(size, type);
      }
    }
    if (addr != 0) {
      return addr;
    }
    // Force growth before attempting another synchronous GC.
    addr = old_space_.TryAllocate(size, type, PageSpace::kForceGrowth);
    if (addr != 0) {
      return addr;
    }
    // Before throwing an out-of-memory error try a synchronous GC.
    CollectAllGarbage();
    {
      MonitorLocker ml(old_space_.tasks_lock());
      while (old_space_.tasks() > 0) {
        ml.Wait();
      }
    }
  }
  addr = old_space_.TryAllocate(size, type, PageSpace::kForceGrowth);
  if (addr != 0) {
    return addr;
  }
  // Give up allocating this object.
  OS::PrintErr(
      "Exhausted heap space, trying to allocate %" Pd " bytes.\n", size);
  return 0;
}


uword Heap::AllocatePretenured(intptr_t size) {
  ASSERT(Thread::Current()->no_safepoint_scope_depth() == 0);
  uword addr = old_space_.TryAllocateDataBump(size, PageSpace::kControlGrowth);
  if (addr != 0) return addr;
  return AllocateOld(size, HeapPage::kData);
}


void Heap::AllocateExternal(intptr_t size, Space space) {
  ASSERT(Thread::Current()->no_safepoint_scope_depth() == 0);
  if (space == kNew) {
    isolate()->AssertCurrentThreadIsMutator();
    new_space_.AllocateExternal(size);
    if (new_space_.ExternalInWords() > (FLAG_new_gen_ext_limit * MBInWords)) {
      // Attempt to free some external allocation by a scavenge. (If the total
      // remains above the limit, next external alloc will trigger another.)
      CollectGarbage(kNew);
    }
  } else {
    ASSERT(space == kOld);
    old_space_.AllocateExternal(size);
    if (old_space_.NeedsGarbageCollection()) {
      CollectAllGarbage();
    }
  }
}

void Heap::FreeExternal(intptr_t size, Space space) {
  if (space == kNew) {
    new_space_.FreeExternal(size);
  } else {
    ASSERT(space == kOld);
    old_space_.FreeExternal(size);
  }
}

void Heap::PromoteExternal(intptr_t size) {
  new_space_.FreeExternal(size);
  old_space_.AllocateExternal(size);
}

bool Heap::Contains(uword addr) const {
  return new_space_.Contains(addr) ||
      old_space_.Contains(addr);
}


bool Heap::NewContains(uword addr) const {
  return new_space_.Contains(addr);
}


bool Heap::OldContains(uword addr) const {
  return old_space_.Contains(addr);
}


bool Heap::CodeContains(uword addr) const {
  return old_space_.Contains(addr, HeapPage::kExecutable);
}


void Heap::VisitObjects(ObjectVisitor* visitor) const {
  new_space_.VisitObjects(visitor);
  old_space_.VisitObjects(visitor);
}


HeapIterationScope::HeapIterationScope()
    : StackResource(Thread::Current()),
      old_space_(isolate()->heap()->old_space()) {
  // It's not yet safe to iterate over a paged space while it's concurrently
  // sweeping, so wait for any such task to complete first.
  MonitorLocker ml(old_space_->tasks_lock());
#if defined(DEBUG)
  // We currently don't support nesting of HeapIterationScopes.
  ASSERT(old_space_->iterating_thread_ != thread());
#endif
  while (old_space_->tasks() > 0) {
    ml.Wait();
  }
#if defined(DEBUG)
  ASSERT(old_space_->iterating_thread_ == NULL);
  old_space_->iterating_thread_ = thread();
#endif
  old_space_->set_tasks(1);
}


HeapIterationScope::~HeapIterationScope() {
  MonitorLocker ml(old_space_->tasks_lock());
#if defined(DEBUG)
  ASSERT(old_space_->iterating_thread_ == thread());
  old_space_->iterating_thread_ = NULL;
#endif
  ASSERT(old_space_->tasks() == 1);
  old_space_->set_tasks(0);
  ml.Notify();
}


void Heap::IterateObjects(ObjectVisitor* visitor) const {
  // The visitor must not allocate from the heap.
  NoSafepointScope no_safepoint_scope_;
  new_space_.VisitObjects(visitor);
  IterateOldObjects(visitor);
}


void Heap::IterateOldObjects(ObjectVisitor* visitor) const {
  HeapIterationScope heap_iteration_scope;
  old_space_.VisitObjects(visitor);
}


void Heap::VisitObjectPointers(ObjectPointerVisitor* visitor) const {
  new_space_.VisitObjectPointers(visitor);
  old_space_.VisitObjectPointers(visitor);
}


RawInstructions* Heap::FindObjectInCodeSpace(FindObjectVisitor* visitor) const {
  // Only executable pages can have RawInstructions objects.
  RawObject* raw_obj = old_space_.FindObject(visitor, HeapPage::kExecutable);
  ASSERT((raw_obj == Object::null()) ||
         (raw_obj->GetClassId() == kInstructionsCid));
  return reinterpret_cast<RawInstructions*>(raw_obj);
}


RawObject* Heap::FindOldObject(FindObjectVisitor* visitor) const {
  HeapIterationScope heap_iteration_scope;
  return old_space_.FindObject(visitor, HeapPage::kData);
}


RawObject* Heap::FindNewObject(FindObjectVisitor* visitor) const {
  return new_space_.FindObject(visitor);
}


RawObject* Heap::FindObject(FindObjectVisitor* visitor) const {
  // The visitor must not allocate from the heap.
  NoSafepointScope no_safepoint_scope;
  RawObject* raw_obj = FindNewObject(visitor);
  if (raw_obj != Object::null()) {
    return raw_obj;
  }
  raw_obj = FindOldObject(visitor);
  if (raw_obj != Object::null()) {
    return raw_obj;
  }
  raw_obj = FindObjectInCodeSpace(visitor);
  return raw_obj;
}


bool Heap::BeginNewSpaceGC() {
  MonitorLocker ml(&gc_in_progress_monitor_);
  bool start_gc_on_thread = true;
  while (gc_new_space_in_progress_ ||
         gc_old_space_in_progress_) {
    start_gc_on_thread = !gc_new_space_in_progress_;
    ml.Wait();
  }
  if (start_gc_on_thread) {
    gc_new_space_in_progress_ = true;
    return true;
  }
  return false;
}


void Heap::EndNewSpaceGC() {
  MonitorLocker ml(&gc_in_progress_monitor_);
  ASSERT(gc_new_space_in_progress_);
  gc_new_space_in_progress_ = false;
  ml.NotifyAll();
}


bool Heap::BeginOldSpaceGC() {
  MonitorLocker ml(&gc_in_progress_monitor_);
  bool start_gc_on_thread = true;
  while (gc_new_space_in_progress_ ||
         gc_old_space_in_progress_) {
    start_gc_on_thread = !gc_old_space_in_progress_;
    ml.Wait();
  }
  if (start_gc_on_thread) {
    gc_old_space_in_progress_ = true;
    return true;
  }
  return false;
}


void Heap::EndOldSpaceGC() {
  MonitorLocker ml(&gc_in_progress_monitor_);
  ASSERT(gc_old_space_in_progress_);
  gc_old_space_in_progress_ = false;
  ml.NotifyAll();
}


void Heap::UpdateClassHeapStatsBeforeGC(Heap::Space space) {
  ClassTable* class_table = isolate()->class_table();
  if (space == kNew) {
    class_table->ResetCountersNew();
  } else {
    class_table->ResetCountersOld();
  }
}


void Heap::CollectNewSpaceGarbage(Thread* thread,
                                  ApiCallbacks api_callbacks,
                                  GCReason reason) {
  if (BeginNewSpaceGC()) {
    bool invoke_api_callbacks = (api_callbacks == kInvokeApiCallbacks);
    RecordBeforeGC(kNew, reason);
    VMTagScope tagScope(thread, VMTag::kGCNewSpaceTagId);
    TimelineDurationScope tds(thread,
                              isolate()->GetGCStream(),
                              "CollectNewGeneration");
    UpdateClassHeapStatsBeforeGC(kNew);
    new_space_.Scavenge(invoke_api_callbacks);
    isolate()->class_table()->UpdatePromoted();
    UpdatePretenurePolicy();
    RecordAfterGC(kNew);
    PrintStats();
    EndNewSpaceGC();
    if (old_space_.NeedsGarbageCollection()) {
      // Old collections should call the API callbacks.
      CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kPromotion);
    }
  }
}


void Heap::CollectOldSpaceGarbage(Thread* thread,
                                  ApiCallbacks api_callbacks,
                                  GCReason reason) {
  if (BeginOldSpaceGC()) {
    bool invoke_api_callbacks = (api_callbacks == kInvokeApiCallbacks);
    RecordBeforeGC(kOld, reason);
    VMTagScope tagScope(thread, VMTag::kGCOldSpaceTagId);
    TimelineDurationScope tds(thread,
                              isolate()->GetGCStream(),
                              "CollectOldGeneration");
    UpdateClassHeapStatsBeforeGC(kOld);
    old_space_.MarkSweep(invoke_api_callbacks);
    RecordAfterGC(kOld);
    PrintStats();
    EndOldSpaceGC();
  }
}


void Heap::CollectGarbage(Space space,
                          ApiCallbacks api_callbacks,
                          GCReason reason) {
  Thread* thread = Thread::Current();
  switch (space) {
    case kNew: {
      CollectNewSpaceGarbage(thread, api_callbacks, reason);
      break;
    }
    case kOld:
    case kCode: {
      CollectOldSpaceGarbage(thread, api_callbacks, reason);
      break;
    }
    default:
      UNREACHABLE();
  }
}


void Heap::CollectGarbage(Space space) {
  Thread* thread = Thread::Current();
  if (space == kOld) {
    CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kOldSpace);
  } else {
    ASSERT(space == kNew);
    CollectNewSpaceGarbage(thread, kInvokeApiCallbacks, kNewSpace);
  }
}


void Heap::CollectAllGarbage() {
  Thread* thread = Thread::Current();
  CollectNewSpaceGarbage(thread, kInvokeApiCallbacks, kFull);
  CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kFull);
}


bool Heap::ShouldPretenure(intptr_t class_id) const {
  if (class_id == kOneByteStringCid) {
    return pretenure_policy_ > 0;
  } else {
    return false;
  }
}


void Heap::UpdatePretenurePolicy() {
  if (FLAG_disable_alloc_stubs_after_gc) {
    ClassTable* table = isolate_->class_table();
    Zone* zone = Thread::Current()->zone();
    for (intptr_t cid = 1; cid < table->NumCids(); ++cid) {
      if (((cid >= kNumPredefinedCids) || (cid == kArrayCid)) &&
          table->IsValidIndex(cid) &&
          table->HasValidClassAt(cid)) {
        const Class& cls = Class::Handle(zone, table->At(cid));
        cls.DisableAllocationStub();
      }
    }
  }
  ClassHeapStats* stats =
      isolate_->class_table()->StatsWithUpdatedSize(kOneByteStringCid);
  int allocated = stats->pre_gc.new_count;
  int promo_percent = (allocated == 0) ? 0 :
      (100 * stats->promoted_count) / allocated;
  if (promo_percent >= FLAG_pretenure_threshold) {
    pretenure_policy_ += FLAG_pretenure_interval;
  } else {
    pretenure_policy_ = Utils::Maximum(0, pretenure_policy_ - 1);
  }
}


void Heap::UpdateGlobalMaxUsed() {
  ASSERT(isolate_ != NULL);
  // We are accessing the used in words count for both new and old space
  // without synchronizing. The value of this metric is approximate.
  isolate_->GetHeapGlobalUsedMaxMetric()->SetValue(
      (UsedInWords(Heap::kNew) * kWordSize) +
      (UsedInWords(Heap::kOld) * kWordSize));
}


void Heap::SetGrowthControlState(bool state) {
  old_space_.SetGrowthControlState(state);
}


bool Heap::GrowthControlState() {
  return old_space_.GrowthControlState();
}


void Heap::WriteProtect(bool read_only, bool include_code_pages) {
  read_only_ = read_only;
  new_space_.WriteProtect(read_only);
  old_space_.WriteProtect(read_only, include_code_pages);
}


Heap::Space Heap::SpaceForAllocation(intptr_t cid) {
  return FLAG_pretenure_all ? kPretenured : kNew;
}


intptr_t Heap::TopOffset(Heap::Space space) {
  if (space == kNew) {
    return OFFSET_OF(Heap, new_space_) + Scavenger::top_offset();
  } else {
    ASSERT(space == kPretenured);
    return OFFSET_OF(Heap, old_space_) + PageSpace::top_offset();
  }
}


intptr_t Heap::EndOffset(Heap::Space space) {
  if (space == kNew) {
    return OFFSET_OF(Heap, new_space_) + Scavenger::end_offset();
  } else {
    ASSERT(space == kPretenured);
    return OFFSET_OF(Heap, old_space_) + PageSpace::end_offset();
  }
}


void Heap::Init(Isolate* isolate,
                intptr_t max_new_gen_words,
                intptr_t max_old_gen_words,
                intptr_t max_external_words) {
  ASSERT(isolate->heap() == NULL);
  Heap* heap = new Heap(isolate,
                        max_new_gen_words,
                        max_old_gen_words,
                        max_external_words);
  isolate->set_heap(heap);
}


void Heap::GetMergedAddressRange(uword* start, uword* end) const {
  if (new_space_.CapacityInWords() != 0) {
    uword new_start;
    uword new_end;
    new_space_.StartEndAddress(&new_start, &new_end);
    *start = Utils::Minimum(new_start, *start);
    *end = Utils::Maximum(new_end, *end);
  }
  if (old_space_.CapacityInWords() != 0) {
    uword old_start;
    uword old_end;
    old_space_.StartEndAddress(&old_start, &old_end);
    *start = Utils::Minimum(old_start, *start);
    *end = Utils::Maximum(old_end, *end);
  }
  ASSERT(*start <= *end);
}


ObjectSet* Heap::CreateAllocatedObjectSet(
    MarkExpectation mark_expectation) const {
  uword start = static_cast<uword>(-1);
  uword end = 0;
  Isolate* vm_isolate = Dart::vm_isolate();
  vm_isolate->heap()->GetMergedAddressRange(&start, &end);
  this->GetMergedAddressRange(&start, &end);

  ObjectSet* allocated_set = new ObjectSet(start, end);
  {
    VerifyObjectVisitor object_visitor(
        isolate(), allocated_set, mark_expectation);
    this->VisitObjects(&object_visitor);
  }
  {
    // VM isolate heap is premarked.
    VerifyObjectVisitor vm_object_visitor(
        isolate(), allocated_set, kRequireMarked);
    vm_isolate->heap()->VisitObjects(&vm_object_visitor);
  }
  return allocated_set;
}


bool Heap::Verify(MarkExpectation mark_expectation) const {
  HeapIterationScope heap_iteration_scope;
  return VerifyGC(mark_expectation);
}


bool Heap::VerifyGC(MarkExpectation mark_expectation) const {
  ObjectSet* allocated_set = CreateAllocatedObjectSet(mark_expectation);
  VerifyPointersVisitor visitor(isolate(), allocated_set);
  VisitObjectPointers(&visitor);
  delete allocated_set;
  // Only returning a value so that Heap::Validate can be called from an ASSERT.
  return true;
}


void Heap::PrintSizes() const {
  OS::PrintErr("New space (%" Pd64 "k of %" Pd64 "k) "
               "Old space (%" Pd64 "k of %" Pd64 "k)\n",
               (UsedInWords(kNew) / KBInWords),
               (CapacityInWords(kNew) / KBInWords),
               (UsedInWords(kOld) / KBInWords),
               (CapacityInWords(kOld) / KBInWords));
}


int64_t Heap::UsedInWords(Space space) const {
  return space == kNew ? new_space_.UsedInWords() : old_space_.UsedInWords();
}


int64_t Heap::CapacityInWords(Space space) const {
  return space == kNew ? new_space_.CapacityInWords() :
                         old_space_.CapacityInWords();
}


int64_t Heap::ExternalInWords(Space space) const {
  return space == kNew ? new_space_.ExternalInWords() :
                         old_space_.ExternalInWords();
}


int64_t Heap::GCTimeInMicros(Space space) const {
  if (space == kNew) {
    return new_space_.gc_time_micros();
  }
  return old_space_.gc_time_micros();
}


intptr_t Heap::Collections(Space space) const {
  if (space == kNew) {
    return new_space_.collections();
  }
  return old_space_.collections();
}


const char* Heap::GCReasonToString(GCReason gc_reason) {
  switch (gc_reason) {
    case kNewSpace:
      return "new space";
    case kPromotion:
      return "promotion";
    case kOldSpace:
      return "old space";
    case kFull:
      return "full";
    case kGCAtAlloc:
      return "debugging";
    case kGCTestCase:
      return "test case";
    default:
      UNREACHABLE();
      return "";
  }
}


int64_t Heap::PeerCount() const {
  return new_weak_tables_[kPeers]->count() + old_weak_tables_[kPeers]->count();
}


int64_t Heap::HashCount() const {
  return new_weak_tables_[kHashes]->count() +
      old_weak_tables_[kHashes]->count();
}


int64_t Heap::ObjectIdCount() const {
  return new_weak_tables_[kObjectIds]->count() +
      old_weak_tables_[kObjectIds]->count();
}


void Heap::ResetObjectIdTable() {
  new_weak_tables_[kObjectIds]->Reset();
  old_weak_tables_[kObjectIds]->Reset();
}


intptr_t Heap::GetWeakEntry(RawObject* raw_obj, WeakSelector sel) const {
  if (raw_obj->IsNewObject()) {
    return new_weak_tables_[sel]->GetValue(raw_obj);
  }
  ASSERT(raw_obj->IsOldObject());
  return old_weak_tables_[sel]->GetValue(raw_obj);
}


void Heap::SetWeakEntry(RawObject* raw_obj, WeakSelector sel, intptr_t val) {
  if (raw_obj->IsNewObject()) {
    new_weak_tables_[sel]->SetValue(raw_obj, val);
  } else {
    ASSERT(raw_obj->IsOldObject());
    old_weak_tables_[sel]->SetValue(raw_obj, val);
  }
}


void Heap::PrintToJSONObject(Space space, JSONObject* object) const {
  if (space == kNew) {
    new_space_.PrintToJSONObject(object);
  } else {
    old_space_.PrintToJSONObject(object);
  }
}


void Heap::RecordBeforeGC(Space space, GCReason reason) {
  ASSERT((space == kNew && gc_new_space_in_progress_) ||
         (space == kOld && gc_old_space_in_progress_));
  stats_.num_++;
  stats_.space_ = space;
  stats_.reason_ = reason;
  stats_.before_.micros_ = OS::GetCurrentTimeMicros();
  stats_.before_.new_ = new_space_.GetCurrentUsage();
  stats_.before_.old_ = old_space_.GetCurrentUsage();
  stats_.times_[0] = 0;
  stats_.times_[1] = 0;
  stats_.times_[2] = 0;
  stats_.times_[3] = 0;
  stats_.data_[0] = 0;
  stats_.data_[1] = 0;
  stats_.data_[2] = 0;
  stats_.data_[3] = 0;
}


void Heap::RecordAfterGC(Space space) {
  stats_.after_.micros_ = OS::GetCurrentTimeMicros();
  int64_t delta = stats_.after_.micros_ - stats_.before_.micros_;
  if (stats_.space_ == kNew) {
    new_space_.AddGCTime(delta);
    new_space_.IncrementCollections();
  } else {
    old_space_.AddGCTime(delta);
    old_space_.IncrementCollections();
  }
  stats_.after_.new_ = new_space_.GetCurrentUsage();
  stats_.after_.old_ = old_space_.GetCurrentUsage();
  ASSERT((space == kNew && gc_new_space_in_progress_) ||
         (space == kOld && gc_old_space_in_progress_));
  if (Service::gc_stream.enabled()) {
    ServiceEvent event(Isolate::Current(), ServiceEvent::kGC);
    event.set_gc_stats(&stats_);
    Service::HandleEvent(&event);
  }
}


void Heap::PrintStats() {
  if (!FLAG_verbose_gc) return;

  if ((FLAG_verbose_gc_hdr != 0) &&
      (((stats_.num_ - 1) % FLAG_verbose_gc_hdr) == 0)) {
    OS::PrintErr("[    GC    |  space  | count | start | gc time | "
                 "new gen (KB) | old gen (KB) | timers | data ]\n"
                 "[ (isolate)| (reason)|       |  (s)  |   (ms)  | "
                 "used,cap,ext | used,cap,ext |  (ms)  |      ]\n");
  }

  const char* space_str = stats_.space_ == kNew ? "Scavenge" : "Mark-Sweep";
  OS::PrintErr(
    "[ GC(%" Pd64 "): %s(%s), "  // GC(isolate), space(reason)
    "%" Pd ", "  // count
    "%.3f, "  // start time
    "%.3f, "  // total time
    "%" Pd ", %" Pd ", "  // new gen: in use before/after
    "%" Pd ", %" Pd ", "  // new gen: capacity before/after
    "%" Pd ", %" Pd ", "  // new gen: external before/after
    "%" Pd ", %" Pd ", "  // old gen: in use before/after
    "%" Pd ", %" Pd ", "  // old gen: capacity before/after
    "%" Pd ", %" Pd ", "  // old gen: external before/after
    "%.3f, %.3f, %.3f, %.3f, "  // times
    "%" Pd ", %" Pd ", %" Pd ", %" Pd ", "  // data
    "]\n",  // End with a comma to make it easier to import in spreadsheets.
    isolate()->main_port(), space_str, GCReasonToString(stats_.reason_),
    stats_.num_,
    MicrosecondsToSeconds(stats_.before_.micros_ - isolate()->start_time()),
    MicrosecondsToMilliseconds(stats_.after_.micros_ -
                                    stats_.before_.micros_),
    RoundWordsToKB(stats_.before_.new_.used_in_words),
    RoundWordsToKB(stats_.after_.new_.used_in_words),
    RoundWordsToKB(stats_.before_.new_.capacity_in_words),
    RoundWordsToKB(stats_.after_.new_.capacity_in_words),
    RoundWordsToKB(stats_.before_.new_.external_in_words),
    RoundWordsToKB(stats_.after_.new_.external_in_words),
    RoundWordsToKB(stats_.before_.old_.used_in_words),
    RoundWordsToKB(stats_.after_.old_.used_in_words),
    RoundWordsToKB(stats_.before_.old_.capacity_in_words),
    RoundWordsToKB(stats_.after_.old_.capacity_in_words),
    RoundWordsToKB(stats_.before_.old_.external_in_words),
    RoundWordsToKB(stats_.after_.old_.external_in_words),
    MicrosecondsToMilliseconds(stats_.times_[0]),
    MicrosecondsToMilliseconds(stats_.times_[1]),
    MicrosecondsToMilliseconds(stats_.times_[2]),
    MicrosecondsToMilliseconds(stats_.times_[3]),
    stats_.data_[0],
    stats_.data_[1],
    stats_.data_[2],
    stats_.data_[3]);
}


NoHeapGrowthControlScope::NoHeapGrowthControlScope()
    : StackResource(Thread::Current()) {
    Heap* heap = reinterpret_cast<Isolate*>(isolate())->heap();
    current_growth_controller_state_ = heap->GrowthControlState();
    heap->DisableGrowthControl();
}


NoHeapGrowthControlScope::~NoHeapGrowthControlScope() {
    Heap* heap = reinterpret_cast<Isolate*>(isolate())->heap();
    heap->SetGrowthControlState(current_growth_controller_state_);
}


WritableVMIsolateScope::WritableVMIsolateScope(Thread* thread,
                                               bool include_code_pages)
    : StackResource(thread), include_code_pages_(include_code_pages) {
  Dart::vm_isolate()->heap()->WriteProtect(false, include_code_pages_);
}


WritableVMIsolateScope::~WritableVMIsolateScope() {
  ASSERT(Dart::vm_isolate()->heap()->UsedInWords(Heap::kNew) == 0);
  Dart::vm_isolate()->heap()->WriteProtect(true, include_code_pages_);
}

}  // namespace dart