CSE2410 Fall 2014 Bounce

// Copyright 2012 the V8 project authors. All rights reserved.

// Redistribution and use in source and binary forms, with or without

// modification, are permitted provided that the following conditions are

// met:

//

//     * Redistributions of source code must retain the above copyright

//       notice, this list of conditions and the following disclaimer.

//     * Redistributions in binary form must reproduce the above

//       copyright notice, this list of conditions and the following

//       disclaimer in the documentation and/or other materials provided

//       with the distribution.

//     * Neither the name of Google Inc. nor the names of its

//       contributors may be used to endorse or promote products derived

//       from this software without specific prior written permission.

//

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include "v8.h"

#include "incremental-marking.h"

#include "code-stubs.h"

#include "compilation-cache.h"

#include "objects-visiting.h"

#include "objects-visiting-inl.h"

#include "v8conversions.h"

namespace v8 {

namespace internal {

IncrementalMarking::IncrementalMarking(Heap* heap)

    : heap_(heap),

      state_(STOPPED),

      marking_deque_memory_(NULL),

      marking_deque_memory_committed_(false),

      steps_count_(0),

      steps_took_(0),

      longest_step_(0.0),

      old_generation_space_available_at_start_of_incremental_(0),

      old_generation_space_used_at_start_of_incremental_(0),

      steps_count_since_last_gc_(0),

      steps_took_since_last_gc_(0),

      should_hurry_(false),

      marking_speed_(0),

      allocated_(0),

      no_marking_scope_depth_(0),

      unscanned_bytes_of_large_object_(0) {

}

void IncrementalMarking::TearDown() {

  delete marking_deque_memory_;

}

void IncrementalMarking::RecordWriteSlow(HeapObject* obj,

                                         Object** slot,

                                         Object* value) {

  if (BaseRecordWrite(obj, slot, value) && slot != NULL) {

    MarkBit obj_bit = Marking::MarkBitFrom(obj);

    if (Marking::IsBlack(obj_bit)) {

      // Object is not going to be rescanned we need to record the slot.

      heap_->mark_compact_collector()->RecordSlot(

          HeapObject::RawField(obj, 0), slot, value);

    }

  }

}

void IncrementalMarking::RecordWriteFromCode(HeapObject* obj,

                                             Object** slot,

                                             Isolate* isolate) {

  ASSERT(obj->IsHeapObject());

  IncrementalMarking* marking = isolate->heap()->incremental_marking();

  ASSERT(!marking->is_compacting_);

  MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());

  int counter = chunk->write_barrier_counter();

  if (counter < (MemoryChunk::kWriteBarrierCounterGranularity / 2)) {

    marking->write_barriers_invoked_since_last_step_ +=

        MemoryChunk::kWriteBarrierCounterGranularity -

            chunk->write_barrier_counter();

    chunk->set_write_barrier_counter(

        MemoryChunk::kWriteBarrierCounterGranularity);

  }

  marking->RecordWrite(obj, slot, *slot);

}

void IncrementalMarking::RecordWriteForEvacuationFromCode(HeapObject* obj,

                                                          Object** slot,

                                                          Isolate* isolate) {

  ASSERT(obj->IsHeapObject());

  IncrementalMarking* marking = isolate->heap()->incremental_marking();

  ASSERT(marking->is_compacting_);

  MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());

  int counter = chunk->write_barrier_counter();

  if (counter < (MemoryChunk::kWriteBarrierCounterGranularity / 2)) {

    marking->write_barriers_invoked_since_last_step_ +=

        MemoryChunk::kWriteBarrierCounterGranularity -

            chunk->write_barrier_counter();

    chunk->set_write_barrier_counter(

        MemoryChunk::kWriteBarrierCounterGranularity);

  }

  marking->RecordWrite(obj, slot, *slot);

}

void IncrementalMarking::RecordCodeTargetPatch(Code* host,

                                               Address pc,

                                               HeapObject* value) {

  if (IsMarking()) {

    RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);

    RecordWriteIntoCode(host, &rinfo, value);

  }

}

void IncrementalMarking::RecordCodeTargetPatch(Address pc, HeapObject* value) {

  if (IsMarking()) {

    Code* host = heap_->isolate()->inner_pointer_to_code_cache()->

        GcSafeFindCodeForInnerPointer(pc);

    RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);

    RecordWriteIntoCode(host, &rinfo, value);

  }

}

void IncrementalMarking::RecordWriteOfCodeEntrySlow(JSFunction* host,

                                                    Object** slot,

                                                    Code* value) {

  if (BaseRecordWrite(host, slot, value)) {

    ASSERT(slot != NULL);

    heap_->mark_compact_collector()->

        RecordCodeEntrySlot(reinterpret_cast<Address>(slot), value);

  }

}

void IncrementalMarking::RecordWriteIntoCodeSlow(HeapObject* obj,

                                                 RelocInfo* rinfo,

                                                 Object* value) {

  MarkBit value_bit = Marking::MarkBitFrom(HeapObject::cast(value));

  if (Marking::IsWhite(value_bit)) {

    MarkBit obj_bit = Marking::MarkBitFrom(obj);

    if (Marking::IsBlack(obj_bit)) {

      BlackToGreyAndUnshift(obj, obj_bit);

      RestartIfNotMarking();

    }

    // Object is either grey or white.  It will be scanned if survives.

    return;

  }

  if (is_compacting_) {

    MarkBit obj_bit = Marking::MarkBitFrom(obj);

    if (Marking::IsBlack(obj_bit)) {

      // Object is not going to be rescanned.  We need to record the slot.

      heap_->mark_compact_collector()->RecordRelocSlot(rinfo,

                                                       Code::cast(value));

    }

  }

}

static void MarkObjectGreyDoNotEnqueue(Object* obj) {

  if (obj->IsHeapObject()) {

    HeapObject* heap_obj = HeapObject::cast(obj);

    MarkBit mark_bit = Marking::MarkBitFrom(HeapObject::cast(obj));

    if (Marking::IsBlack(mark_bit)) {

      MemoryChunk::IncrementLiveBytesFromGC(heap_obj->address(),

                                            -heap_obj->Size());

    }

    Marking::AnyToGrey(mark_bit);

  }

}

static inline void MarkBlackOrKeepGrey(HeapObject* heap_object,

                                       MarkBit mark_bit,

                                       int size) {

  ASSERT(!Marking::IsImpossible(mark_bit));

  if (mark_bit.Get()) return;

  mark_bit.Set();

  MemoryChunk::IncrementLiveBytesFromGC(heap_object->address(), size);

  ASSERT(Marking::IsBlack(mark_bit));

}

static inline void MarkBlackOrKeepBlack(HeapObject* heap_object,

                                        MarkBit mark_bit,

                                        int size) {

  ASSERT(!Marking::IsImpossible(mark_bit));

  if (Marking::IsBlack(mark_bit)) return;

  Marking::MarkBlack(mark_bit);

  MemoryChunk::IncrementLiveBytesFromGC(heap_object->address(), size);

  ASSERT(Marking::IsBlack(mark_bit));

}

class IncrementalMarkingMarkingVisitor

    : public StaticMarkingVisitor<IncrementalMarkingMarkingVisitor> {

 public:

  static void Initialize() {

    StaticMarkingVisitor<IncrementalMarkingMarkingVisitor>::Initialize();

    table_.Register(kVisitFixedArray, &VisitFixedArrayIncremental);

    table_.Register(kVisitNativeContext, &VisitNativeContextIncremental);

    table_.Register(kVisitJSRegExp, &VisitJSRegExp);

  }

  static const int kProgressBarScanningChunk = 32 * 1024;

  static void VisitFixedArrayIncremental(Map* map, HeapObject* object) {

    MemoryChunk* chunk = MemoryChunk::FromAddress(object->address());

    // TODO(mstarzinger): Move setting of the flag to the allocation site of

    // the array. The visitor should just check the flag.

    if (FLAG_use_marking_progress_bar &&

        chunk->owner()->identity() == LO_SPACE) {

      chunk->SetFlag(MemoryChunk::HAS_PROGRESS_BAR);

    }

    if (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR)) {

      Heap* heap = map->GetHeap();

      // When using a progress bar for large fixed arrays, scan only a chunk of

      // the array and try to push it onto the marking deque again until it is

      // fully scanned. Fall back to scanning it through to the end in case this

      // fails because of a full deque.

      int object_size = FixedArray::BodyDescriptor::SizeOf(map, object);

      int start_offset = Max(FixedArray::BodyDescriptor::kStartOffset,

                             chunk->progress_bar());

      int end_offset = Min(object_size,

                           start_offset + kProgressBarScanningChunk);

      int already_scanned_offset = start_offset;

      bool scan_until_end = false;

      do {

        VisitPointersWithAnchor(heap,

                                HeapObject::RawField(object, 0),

                                HeapObject::RawField(object, start_offset),

                                HeapObject::RawField(object, end_offset));

        start_offset = end_offset;

        end_offset = Min(object_size, end_offset + kProgressBarScanningChunk);

        scan_until_end = heap->incremental_marking()->marking_deque()->IsFull();

      } while (scan_until_end && start_offset < object_size);

      chunk->set_progress_bar(start_offset);

      if (start_offset < object_size) {

        heap->incremental_marking()->marking_deque()->UnshiftGrey(object);

        heap->incremental_marking()->NotifyIncompleteScanOfObject(

            object_size - (start_offset - already_scanned_offset));

      }

    } else {

      FixedArrayVisitor::Visit(map, object);

    }

  }

  static void VisitNativeContextIncremental(Map* map, HeapObject* object) {

    Context* context = Context::cast(object);

    // We will mark cache black with a separate pass

    // when we finish marking.

    MarkObjectGreyDoNotEnqueue(context->normalized_map_cache());

    VisitNativeContext(map, context);

  }

  static void VisitWeakCollection(Map* map, HeapObject* object) {

    Heap* heap = map->GetHeap();

    VisitPointers(heap,

                  HeapObject::RawField(object,

                                       JSWeakCollection::kPropertiesOffset),

                  HeapObject::RawField(object, JSWeakCollection::kSize));

  }

  static void BeforeVisitingSharedFunctionInfo(HeapObject* object) {}

  INLINE(static void VisitPointer(Heap* heap, Object** p)) {

    Object* obj = *p;

    if (obj->NonFailureIsHeapObject()) {

      heap->mark_compact_collector()->RecordSlot(p, p, obj);

      MarkObject(heap, obj);

    }

  }

  INLINE(static void VisitPointers(Heap* heap, Object** start, Object** end)) {

    for (Object** p = start; p < end; p++) {

      Object* obj = *p;

      if (obj->NonFailureIsHeapObject()) {

        heap->mark_compact_collector()->RecordSlot(start, p, obj);

        MarkObject(heap, obj);

      }

    }

  }

  INLINE(static void VisitPointersWithAnchor(Heap* heap,

                                             Object** anchor,

                                             Object** start,

                                             Object** end)) {

    for (Object** p = start; p < end; p++) {

      Object* obj = *p;

      if (obj->NonFailureIsHeapObject()) {

        heap->mark_compact_collector()->RecordSlot(anchor, p, obj);

        MarkObject(heap, obj);

      }

    }

  }

  // Marks the object grey and pushes it on the marking stack.

  INLINE(static void MarkObject(Heap* heap, Object* obj)) {

    HeapObject* heap_object = HeapObject::cast(obj);

    MarkBit mark_bit = Marking::MarkBitFrom(heap_object);

    if (mark_bit.data_only()) {

      MarkBlackOrKeepGrey(heap_object, mark_bit, heap_object->Size());

    } else if (Marking::IsWhite(mark_bit)) {

      heap->incremental_marking()->WhiteToGreyAndPush(heap_object, mark_bit);

    }

  }

  // Marks the object black without pushing it on the marking stack.

  // Returns true if object needed marking and false otherwise.

  INLINE(static bool MarkObjectWithoutPush(Heap* heap, Object* obj)) {

    HeapObject* heap_object = HeapObject::cast(obj);

    MarkBit mark_bit = Marking::MarkBitFrom(heap_object);

    if (Marking::IsWhite(mark_bit)) {

      mark_bit.Set();

      MemoryChunk::IncrementLiveBytesFromGC(heap_object->address(),

                                            heap_object->Size());

      return true;

    }

    return false;

  }

};

class IncrementalMarkingRootMarkingVisitor : public ObjectVisitor {

 public:

  explicit IncrementalMarkingRootMarkingVisitor(

      IncrementalMarking* incremental_marking)

      : incremental_marking_(incremental_marking) {

  }

  void VisitPointer(Object** p) {

    MarkObjectByPointer(p);

  }

  void VisitPointers(Object** start, Object** end) {

    for (Object** p = start; p < end; p++) MarkObjectByPointer(p);

  }

 private:

  void MarkObjectByPointer(Object** p) {

    Object* obj = *p;

    if (!obj->IsHeapObject()) return;

    HeapObject* heap_object = HeapObject::cast(obj);

    MarkBit mark_bit = Marking::MarkBitFrom(heap_object);

    if (mark_bit.data_only()) {

      MarkBlackOrKeepGrey(heap_object, mark_bit, heap_object->Size());

    } else {

      if (Marking::IsWhite(mark_bit)) {

        incremental_marking_->WhiteToGreyAndPush(heap_object, mark_bit);

      }

    }

  }

  IncrementalMarking* incremental_marking_;

};

void IncrementalMarking::Initialize() {

  IncrementalMarkingMarkingVisitor::Initialize();

}

void IncrementalMarking::SetOldSpacePageFlags(MemoryChunk* chunk,

                                              bool is_marking,

                                              bool is_compacting) {

  if (is_marking) {

    chunk->SetFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);

    chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);

    // It's difficult to filter out slots recorded for large objects.

    if (chunk->owner()->identity() == LO_SPACE &&

        chunk->size() > static_cast<size_t>(Page::kPageSize) &&

        is_compacting) {

      chunk->SetFlag(MemoryChunk::RESCAN_ON_EVACUATION);

    }

  } else if (chunk->owner()->identity() == CELL_SPACE ||

             chunk->owner()->identity() == PROPERTY_CELL_SPACE ||

             chunk->scan_on_scavenge()) {

    chunk->ClearFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);

    chunk->ClearFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);

  } else {

    chunk->ClearFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);

    chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);

  }

}

void IncrementalMarking::SetNewSpacePageFlags(NewSpacePage* chunk,

                                              bool is_marking) {

  chunk->SetFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);

  if (is_marking) {

    chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);

  } else {

    chunk->ClearFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);

  }

  chunk->SetFlag(MemoryChunk::SCAN_ON_SCAVENGE);

}

void IncrementalMarking::DeactivateIncrementalWriteBarrierForSpace(

    PagedSpace* space) {

  PageIterator it(space);

  while (it.has_next()) {

    Page* p = it.next();

    SetOldSpacePageFlags(p, false, false);

  }

}

void IncrementalMarking::DeactivateIncrementalWriteBarrierForSpace(

    NewSpace* space) {

  NewSpacePageIterator it(space);

  while (it.has_next()) {

    NewSpacePage* p = it.next();

    SetNewSpacePageFlags(p, false);

  }

}

void IncrementalMarking::DeactivateIncrementalWriteBarrier() {

  DeactivateIncrementalWriteBarrierForSpace(heap_->old_pointer_space());

  DeactivateIncrementalWriteBarrierForSpace(heap_->old_data_space());

  DeactivateIncrementalWriteBarrierForSpace(heap_->cell_space());

  DeactivateIncrementalWriteBarrierForSpace(heap_->property_cell_space());

  DeactivateIncrementalWriteBarrierForSpace(heap_->map_space());

  DeactivateIncrementalWriteBarrierForSpace(heap_->code_space());

  DeactivateIncrementalWriteBarrierForSpace(heap_->new_space());

  LargePage* lop = heap_->lo_space()->first_page();

  while (lop->is_valid()) {

    SetOldSpacePageFlags(lop, false, false);

    lop = lop->next_page();

  }

}

void IncrementalMarking::ActivateIncrementalWriteBarrier(PagedSpace* space) {

  PageIterator it(space);

  while (it.has_next()) {

    Page* p = it.next();

    SetOldSpacePageFlags(p, true, is_compacting_);

  }

}

void IncrementalMarking::ActivateIncrementalWriteBarrier(NewSpace* space) {

  NewSpacePageIterator it(space->ToSpaceStart(), space->ToSpaceEnd());

  while (it.has_next()) {

    NewSpacePage* p = it.next();

    SetNewSpacePageFlags(p, true);

  }

}

void IncrementalMarking::ActivateIncrementalWriteBarrier() {

  ActivateIncrementalWriteBarrier(heap_->old_pointer_space());

  ActivateIncrementalWriteBarrier(heap_->old_data_space());

  ActivateIncrementalWriteBarrier(heap_->cell_space());

  ActivateIncrementalWriteBarrier(heap_->property_cell_space());

  ActivateIncrementalWriteBarrier(heap_->map_space());

  ActivateIncrementalWriteBarrier(heap_->code_space());

  ActivateIncrementalWriteBarrier(heap_->new_space());

  LargePage* lop = heap_->lo_space()->first_page();

  while (lop->is_valid()) {

    SetOldSpacePageFlags(lop, true, is_compacting_);

    lop = lop->next_page();

  }

}

bool IncrementalMarking::WorthActivating() {

#ifndef DEBUG

  static const intptr_t kActivationThreshold = 8 * MB;

#else

  // TODO(gc) consider setting this to some low level so that some

  // debug tests run with incremental marking and some without.

  static const intptr_t kActivationThreshold = 0;

#endif

  // Only start incremental marking in a safe state: 1) when expose GC is

  // deactivated, 2) when incremental marking is turned on, 3) when we are

  // currently not in a GC, and 4) when we are currently not serializing

  // or deserializing the heap.

  return !FLAG_expose_gc &&

      FLAG_incremental_marking &&

      FLAG_incremental_marking_steps &&

      heap_->gc_state() == Heap::NOT_IN_GC &&

      !Serializer::enabled() &&

      heap_->isolate()->IsInitialized() &&

      heap_->PromotedSpaceSizeOfObjects() > kActivationThreshold;

}

void IncrementalMarking::ActivateGeneratedStub(Code* stub) {

  ASSERT(RecordWriteStub::GetMode(stub) ==

         RecordWriteStub::STORE_BUFFER_ONLY);

  if (!IsMarking()) {

    // Initially stub is generated in STORE_BUFFER_ONLY mode thus

    // we don't need to do anything if incremental marking is

    // not active.

  } else if (IsCompacting()) {

    RecordWriteStub::Patch(stub, RecordWriteStub::INCREMENTAL_COMPACTION);

  } else {

    RecordWriteStub::Patch(stub, RecordWriteStub::INCREMENTAL);

  }

}

static void PatchIncrementalMarkingRecordWriteStubs(

    Heap* heap, RecordWriteStub::Mode mode) {

  UnseededNumberDictionary* stubs = heap->code_stubs();

  int capacity = stubs->Capacity();

  for (int i = 0; i < capacity; i++) {

    Object* k = stubs->KeyAt(i);

    if (stubs->IsKey(k)) {

      uint32_t key = NumberToUint32(k);

      if (CodeStub::MajorKeyFromKey(key) ==

          CodeStub::RecordWrite) {

        Object* e = stubs->ValueAt(i);

        if (e->IsCode()) {

          RecordWriteStub::Patch(Code::cast(e), mode);

        }

      }

    }

  }

}

void IncrementalMarking::EnsureMarkingDequeIsCommitted() {

  if (marking_deque_memory_ == NULL) {

    marking_deque_memory_ = new VirtualMemory(4 * MB);

  }

  if (!marking_deque_memory_committed_) {

    bool success = marking_deque_memory_->Commit(

        reinterpret_cast<Address>(marking_deque_memory_->address()),

        marking_deque_memory_->size(),

        false);  // Not executable.

    CHECK(success);

    marking_deque_memory_committed_ = true;

  }

}

void IncrementalMarking::UncommitMarkingDeque() {

  if (state_ == STOPPED && marking_deque_memory_committed_) {

    bool success = marking_deque_memory_->Uncommit(

        reinterpret_cast<Address>(marking_deque_memory_->address()),

        marking_deque_memory_->size());

    CHECK(success);

    marking_deque_memory_committed_ = false;

  }

}

void IncrementalMarking::Start(CompactionFlag flag) {

  if (FLAG_trace_incremental_marking) {

    PrintF("[IncrementalMarking] Start\n");

  }

  ASSERT(FLAG_incremental_marking);

  ASSERT(FLAG_incremental_marking_steps);

  ASSERT(state_ == STOPPED);

  ASSERT(heap_->gc_state() == Heap::NOT_IN_GC);

  ASSERT(!Serializer::enabled());

  ASSERT(heap_->isolate()->IsInitialized());

  ResetStepCounters();

  if (heap_->IsSweepingComplete()) {

    StartMarking(flag);

  } else {

    if (FLAG_trace_incremental_marking) {

      PrintF("[IncrementalMarking] Start sweeping.\n");

    }

    state_ = SWEEPING;

  }

  heap_->new_space()->LowerInlineAllocationLimit(kAllocatedThreshold);

}

void IncrementalMarking::StartMarking(CompactionFlag flag) {

  if (FLAG_trace_incremental_marking) {

    PrintF("[IncrementalMarking] Start marking\n");

  }

  is_compacting_ = !FLAG_never_compact && (flag == ALLOW_COMPACTION) &&

      heap_->mark_compact_collector()->StartCompaction(

          MarkCompactCollector::INCREMENTAL_COMPACTION);

  state_ = MARKING;

  RecordWriteStub::Mode mode = is_compacting_ ?

      RecordWriteStub::INCREMENTAL_COMPACTION : RecordWriteStub::INCREMENTAL;

  PatchIncrementalMarkingRecordWriteStubs(heap_, mode);

  EnsureMarkingDequeIsCommitted();

  // Initialize marking stack.

  Address addr = static_cast<Address>(marking_deque_memory_->address());

  size_t size = marking_deque_memory_->size();

  if (FLAG_force_marking_deque_overflows) size = 64 * kPointerSize;

  marking_deque_.Initialize(addr, addr + size);

  ActivateIncrementalWriteBarrier();

  // Marking bits are cleared by the sweeper.

#ifdef VERIFY_HEAP

  if (FLAG_verify_heap) {

    heap_->mark_compact_collector()->VerifyMarkbitsAreClean();

  }

#endif

  heap_->CompletelyClearInstanceofCache();

  heap_->isolate()->compilation_cache()->MarkCompactPrologue();

  if (FLAG_cleanup_code_caches_at_gc) {

    // We will mark cache black with a separate pass

    // when we finish marking.

    MarkObjectGreyDoNotEnqueue(heap_->polymorphic_code_cache());

  }

  // Mark strong roots grey.

  IncrementalMarkingRootMarkingVisitor visitor(this);

  heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);

  heap_->mark_compact_collector()->MarkWeakObjectToCodeTable();

  // Ready to start incremental marking.

  if (FLAG_trace_incremental_marking) {

    PrintF("[IncrementalMarking] Running\n");

  }

}

void IncrementalMarking::PrepareForScavenge() {

  if (!IsMarking()) return;

  NewSpacePageIterator it(heap_->new_space()->FromSpaceStart(),

                          heap_->new_space()->FromSpaceEnd());

  while (it.has_next()) {

    Bitmap::Clear(it.next());

  }

}

void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {

  if (!IsMarking()) return;

  int current = marking_deque_.bottom();

  int mask = marking_deque_.mask();

  int limit = marking_deque_.top();

  HeapObject** array = marking_deque_.array();

  int new_top = current;

  Map* filler_map = heap_->one_pointer_filler_map();

  while (current != limit) {

    HeapObject* obj = array[current];

    ASSERT(obj->IsHeapObject());

    current = ((current + 1) & mask);

    if (heap_->InNewSpace(obj)) {

      MapWord map_word = obj->map_word();

      if (map_word.IsForwardingAddress()) {

        HeapObject* dest = map_word.ToForwardingAddress();

        array[new_top] = dest;

        new_top = ((new_top + 1) & mask);

        ASSERT(new_top != marking_deque_.bottom());

#ifdef DEBUG

        MarkBit mark_bit = Marking::MarkBitFrom(obj);

        ASSERT(Marking::IsGrey(mark_bit) ||

               (obj->IsFiller() && Marking::IsWhite(mark_bit)));

#endif

      }

    } else if (obj->map() != filler_map) {

      // Skip one word filler objects that appear on the

      // stack when we perform in place array shift.

      array[new_top] = obj;

      new_top = ((new_top + 1) & mask);

      ASSERT(new_top != marking_deque_.bottom());

#ifdef DEBUG

        MarkBit mark_bit = Marking::MarkBitFrom(obj);

        MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());

        ASSERT(Marking::IsGrey(mark_bit) ||

               (obj->IsFiller() && Marking::IsWhite(mark_bit)) ||

               (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR) &&

                Marking::IsBlack(mark_bit)));

#endif

    }

  }

  marking_deque_.set_top(new_top);

  steps_took_since_last_gc_ = 0;

  steps_count_since_last_gc_ = 0;

  longest_step_ = 0.0;

}

void IncrementalMarking::VisitObject(Map* map, HeapObject* obj, int size) {

  MarkBit map_mark_bit = Marking::MarkBitFrom(map);

  if (Marking::IsWhite(map_mark_bit)) {

    WhiteToGreyAndPush(map, map_mark_bit);

  }

  IncrementalMarkingMarkingVisitor::IterateBody(map, obj);

  MarkBit mark_bit = Marking::MarkBitFrom(obj);

#if ENABLE_SLOW_ASSERTS

  MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());

  SLOW_ASSERT(Marking::IsGrey(mark_bit) ||

              (obj->IsFiller() && Marking::IsWhite(mark_bit)) ||

              (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR) &&

               Marking::IsBlack(mark_bit)));

#endif

  MarkBlackOrKeepBlack(obj, mark_bit, size);

}

void IncrementalMarking::ProcessMarkingDeque(intptr_t bytes_to_process) {

  Map* filler_map = heap_->one_pointer_filler_map();

  while (!marking_deque_.IsEmpty() && bytes_to_process > 0) {

    HeapObject* obj = marking_deque_.Pop();

    // Explicitly skip one word fillers. Incremental markbit patterns are

    // correct only for objects that occupy at least two words.

    Map* map = obj->map();

    if (map == filler_map) continue;

    int size = obj->SizeFromMap(map);

    unscanned_bytes_of_large_object_ = 0;

    VisitObject(map, obj, size);

    bytes_to_process -= (size - unscanned_bytes_of_large_object_);

  }

}

void IncrementalMarking::ProcessMarkingDeque() {

  Map* filler_map = heap_->one_pointer_filler_map();

  while (!marking_deque_.IsEmpty()) {

    HeapObject* obj = marking_deque_.Pop();

    // Explicitly skip one word fillers. Incremental markbit patterns are

    // correct only for objects that occupy at least two words.

    Map* map = obj->map();

    if (map == filler_map) continue;

    VisitObject(map, obj, obj->SizeFromMap(map));

  }

}

void IncrementalMarking::Hurry() {

  if (state() == MARKING) {

    double start = 0.0;

    if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {

      start = OS::TimeCurrentMillis();

      if (FLAG_trace_incremental_marking) {

        PrintF("[IncrementalMarking] Hurry\n");

      }

    }

    // TODO(gc) hurry can mark objects it encounters black as mutator

    // was stopped.

    ProcessMarkingDeque();

    state_ = COMPLETE;

    if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {

      double end = OS::TimeCurrentMillis();

      double delta = end - start;

      heap_->AddMarkingTime(delta);

      if (FLAG_trace_incremental_marking) {

        PrintF("[IncrementalMarking] Complete (hurry), spent %d ms.\n",

               static_cast<int>(delta));

      }

    }

  }

  if (FLAG_cleanup_code_caches_at_gc) {

    PolymorphicCodeCache* poly_cache = heap_->polymorphic_code_cache();

    Marking::GreyToBlack(Marking::MarkBitFrom(poly_cache));

    MemoryChunk::IncrementLiveBytesFromGC(poly_cache->address(),

                                          PolymorphicCodeCache::kSize);

  }

  Object* context = heap_->native_contexts_list();

  while (!context->IsUndefined()) {

    // GC can happen when the context is not fully initialized,

    // so the cache can be undefined.

    HeapObject* cache = HeapObject::cast(

        Context::cast(context)->get(Context::NORMALIZED_MAP_CACHE_INDEX));

    if (!cache->IsUndefined()) {

      MarkBit mark_bit = Marking::MarkBitFrom(cache);

      if (Marking::IsGrey(mark_bit)) {

        Marking::GreyToBlack(mark_bit);

        MemoryChunk::IncrementLiveBytesFromGC(cache->address(), cache->Size());

      }

    }

    context = Context::cast(context)->get(Context::NEXT_CONTEXT_LINK);

  }

}

void IncrementalMarking::Abort() {

  if (IsStopped()) return;

  if (FLAG_trace_incremental_marking) {

    PrintF("[IncrementalMarking] Aborting.\n");

  }

  heap_->new_space()->LowerInlineAllocationLimit(0);

  IncrementalMarking::set_should_hurry(false);

  ResetStepCounters();

  if (IsMarking()) {

    PatchIncrementalMarkingRecordWriteStubs(heap_,

                                            RecordWriteStub::STORE_BUFFER_ONLY);

    DeactivateIncrementalWriteBarrier();

    if (is_compacting_) {

      LargeObjectIterator it(heap_->lo_space());

      for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {

        Page* p = Page::FromAddress(obj->address());

        if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {

          p->ClearFlag(Page::RESCAN_ON_EVACUATION);

        }

      }

    }

  }

  heap_->isolate()->stack_guard()->Continue(GC_REQUEST);

  state_ = STOPPED;

  is_compacting_ = false;

}

void IncrementalMarking::Finalize() {

  Hurry();

  state_ = STOPPED;

  is_compacting_ = false;

  heap_->new_space()->LowerInlineAllocationLimit(0);

  IncrementalMarking::set_should_hurry(false);

  ResetStepCounters();

  PatchIncrementalMarkingRecordWriteStubs(heap_,

                                          RecordWriteStub::STORE_BUFFER_ONLY);

  DeactivateIncrementalWriteBarrier();

  ASSERT(marking_deque_.IsEmpty());

  heap_->isolate()->stack_guard()->Continue(GC_REQUEST);

}

void IncrementalMarking::MarkingComplete(CompletionAction action) {

  state_ = COMPLETE;

  // We will set the stack guard to request a GC now.  This will mean the rest

  // of the GC gets performed as soon as possible (we can't do a GC here in a

  // record-write context).  If a few things get allocated between now and then

  // that shouldn't make us do a scavenge and keep being incremental, so we set

  // the should-hurry flag to indicate that there can't be much work left to do.

  set_should_hurry(true);

  if (FLAG_trace_incremental_marking) {

    PrintF("[IncrementalMarking] Complete (normal).\n");

  }

  if (action == GC_VIA_STACK_GUARD) {

    heap_->isolate()->stack_guard()->RequestGC();

  }

}

void IncrementalMarking::OldSpaceStep(intptr_t allocated) {

  if (IsStopped() && WorthActivating() && heap_->NextGCIsLikelyToBeFull()) {

    // TODO(hpayer): Let's play safe for now, but compaction should be

    // in principle possible.

    Start(PREVENT_COMPACTION);

  } else {

    Step(allocated * kFastMarking / kInitialMarkingSpeed, GC_VIA_STACK_GUARD);

  }

}

void IncrementalMarking::Step(intptr_t allocated_bytes,

                              CompletionAction action) {

  if (heap_->gc_state() != Heap::NOT_IN_GC ||

      !FLAG_incremental_marking ||

      !FLAG_incremental_marking_steps ||

      (state_ != SWEEPING && state_ != MARKING)) {

    return;

  }

  allocated_ += allocated_bytes;

  if (allocated_ < kAllocatedThreshold &&

      write_barriers_invoked_since_last_step_ <

          kWriteBarriersInvokedThreshold) {

    return;

  }

  if (state_ == MARKING && no_marking_scope_depth_ > 0) return;

  // The marking speed is driven either by the allocation rate or by the rate

  // at which we are having to check the color of objects in the write barrier.

  // It is possible for a tight non-allocating loop to run a lot of write

  // barriers before we get here and check them (marking can only take place on

  // allocation), so to reduce the lumpiness we don't use the write barriers

  // invoked since last step directly to determine the amount of work to do.

  intptr_t bytes_to_process =

      marking_speed_ * Max(allocated_, write_barriers_invoked_since_last_step_);

  allocated_ = 0;

  write_barriers_invoked_since_last_step_ = 0;

  bytes_scanned_ += bytes_to_process;

  double start = 0;

  if (FLAG_trace_incremental_marking || FLAG_trace_gc ||

      FLAG_print_cumulative_gc_stat) {

    start = OS::TimeCurrentMillis();

  }

  if (state_ == SWEEPING) {

    if (heap_->EnsureSweepersProgressed(static_cast<int>(bytes_to_process))) {

      bytes_scanned_ = 0;

      StartMarking(PREVENT_COMPACTION);

    }

  } else if (state_ == MARKING) {

    ProcessMarkingDeque(bytes_to_process);

    if (marking_deque_.IsEmpty()) MarkingComplete(action);

  }

  steps_count_++;

  steps_count_since_last_gc_++;

  bool speed_up = false;

  if ((steps_count_ % kMarkingSpeedAccellerationInterval) == 0) {

    if (FLAG_trace_gc) {

      PrintPID("Speed up marking after %d steps\n",

               static_cast<int>(kMarkingSpeedAccellerationInterval));

    }

    speed_up = true;

  }

  bool space_left_is_very_small =

      (old_generation_space_available_at_start_of_incremental_ < 10 * MB);

  bool only_1_nth_of_space_that_was_available_still_left =

      (SpaceLeftInOldSpace() * (marking_speed_ + 1) <

          old_generation_space_available_at_start_of_incremental_);

  if (space_left_is_very_small ||

      only_1_nth_of_space_that_was_available_still_left) {

    if (FLAG_trace_gc) PrintPID("Speed up marking because of low space left\n");

    speed_up = true;

  }

  bool size_of_old_space_multiplied_by_n_during_marking =

      (heap_->PromotedTotalSize() >

       (marking_speed_ + 1) *

           old_generation_space_used_at_start_of_incremental_);

  if (size_of_old_space_multiplied_by_n_during_marking) {

    speed_up = true;

    if (FLAG_trace_gc) {

      PrintPID("Speed up marking because of heap size increase\n");

    }

  }

  int64_t promoted_during_marking = heap_->PromotedTotalSize()

      - old_generation_space_used_at_start_of_incremental_;

  intptr_t delay = marking_speed_ * MB;

  intptr_t scavenge_slack = heap_->MaxSemiSpaceSize();

  // We try to scan at at least twice the speed that we are allocating.

  if (promoted_during_marking > bytes_scanned_ / 2 + scavenge_slack + delay) {

    if (FLAG_trace_gc) {

      PrintPID("Speed up marking because marker was not keeping up\n");

    }

    speed_up = true;

  }

  if (speed_up) {

    if (state_ != MARKING) {

      if (FLAG_trace_gc) {

        PrintPID("Postponing speeding up marking until marking starts\n");

      }

    } else {

      marking_speed_ += kMarkingSpeedAccelleration;

      marking_speed_ = static_cast<int>(

          Min(kMaxMarkingSpeed,

              static_cast<intptr_t>(marking_speed_ * 1.3)));

      if (FLAG_trace_gc) {

        PrintPID("Marking speed increased to %d\n", marking_speed_);

      }

    }

  }

  if (FLAG_trace_incremental_marking || FLAG_trace_gc ||

      FLAG_print_cumulative_gc_stat) {

    double end = OS::TimeCurrentMillis();

    double delta = (end - start);

    longest_step_ = Max(longest_step_, delta);

    steps_took_ += delta;

    steps_took_since_last_gc_ += delta;

    heap_->AddMarkingTime(delta);

  }

}

void IncrementalMarking::ResetStepCounters() {

  steps_count_ = 0;

  steps_took_ = 0;

  longest_step_ = 0.0;

  old_generation_space_available_at_start_of_incremental_ =

      SpaceLeftInOldSpace();

  old_generation_space_used_at_start_of_incremental_ =

      heap_->PromotedTotalSize();

  steps_count_since_last_gc_ = 0;

  steps_took_since_last_gc_ = 0;

  bytes_rescanned_ = 0;

  marking_speed_ = kInitialMarkingSpeed;

  bytes_scanned_ = 0;

  write_barriers_invoked_since_last_step_ = 0;

}

int64_t IncrementalMarking::SpaceLeftInOldSpace() {

  return heap_->MaxOldGenerationSize() - heap_->PromotedSpaceSizeOfObjects();

}

} }  // namespace v8::internal