v8/src/heap-snapshot-generator.cc

// Copyright 2013 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/v8.h"

#include "src/heap-snapshot-generator-inl.h"

#include "src/allocation-tracker.h"
#include "src/code-stubs.h"
#include "src/conversions.h"
#include "src/debug.h"
#include "src/heap-profiler.h"
#include "src/types.h"

namespace v8 {
namespace internal {


HeapGraphEdge::HeapGraphEdge(Type type, const char* name, int from, int to)
    : type_(type),
      from_index_(from),
      to_index_(to),
      name_(name) {
  ASSERT(type == kContextVariable
      || type == kProperty
      || type == kInternal
      || type == kShortcut
      || type == kWeak);
}


HeapGraphEdge::HeapGraphEdge(Type type, int index, int from, int to)
    : type_(type),
      from_index_(from),
      to_index_(to),
      index_(index) {
  ASSERT(type == kElement || type == kHidden);
}


void HeapGraphEdge::ReplaceToIndexWithEntry(HeapSnapshot* snapshot) {
  to_entry_ = &snapshot->entries()[to_index_];
}


const int HeapEntry::kNoEntry = -1;

HeapEntry::HeapEntry(HeapSnapshot* snapshot,
                     Type type,
                     const char* name,
                     SnapshotObjectId id,
                     size_t self_size,
                     unsigned trace_node_id)
    : type_(type),
      children_count_(0),
      children_index_(-1),
      self_size_(self_size),
      snapshot_(snapshot),
      name_(name),
      id_(id),
      trace_node_id_(trace_node_id) { }


void HeapEntry::SetNamedReference(HeapGraphEdge::Type type,
                                  const char* name,
                                  HeapEntry* entry) {
  HeapGraphEdge edge(type, name, this->index(), entry->index());
  snapshot_->edges().Add(edge);
  ++children_count_;
}


void HeapEntry::SetIndexedReference(HeapGraphEdge::Type type,
                                    int index,
                                    HeapEntry* entry) {
  HeapGraphEdge edge(type, index, this->index(), entry->index());
  snapshot_->edges().Add(edge);
  ++children_count_;
}


void HeapEntry::Print(
    const char* prefix, const char* edge_name, int max_depth, int indent) {
  STATIC_ASSERT(sizeof(unsigned) == sizeof(id()));
  base::OS::Print("%6" V8PRIuPTR " @%6u %*c %s%s: ", self_size(), id(), indent,
                  ' ', prefix, edge_name);
  if (type() != kString) {
    base::OS::Print("%s %.40s\n", TypeAsString(), name_);
  } else {
    base::OS::Print("\"");
    const char* c = name_;
    while (*c && (c - name_) <= 40) {
      if (*c != '\n')
        base::OS::Print("%c", *c);
      else
        base::OS::Print("\\n");
      ++c;
    }
    base::OS::Print("\"\n");
  }
  if (--max_depth == 0) return;
  Vector<HeapGraphEdge*> ch = children();
  for (int i = 0; i < ch.length(); ++i) {
    HeapGraphEdge& edge = *ch[i];
    const char* edge_prefix = "";
    EmbeddedVector<char, 64> index;
    const char* edge_name = index.start();
    switch (edge.type()) {
      case HeapGraphEdge::kContextVariable:
        edge_prefix = "#";
        edge_name = edge.name();
        break;
      case HeapGraphEdge::kElement:
        SNPrintF(index, "%d", edge.index());
        break;
      case HeapGraphEdge::kInternal:
        edge_prefix = "$";
        edge_name = edge.name();
        break;
      case HeapGraphEdge::kProperty:
        edge_name = edge.name();
        break;
      case HeapGraphEdge::kHidden:
        edge_prefix = "$";
        SNPrintF(index, "%d", edge.index());
        break;
      case HeapGraphEdge::kShortcut:
        edge_prefix = "^";
        edge_name = edge.name();
        break;
      case HeapGraphEdge::kWeak:
        edge_prefix = "w";
        edge_name = edge.name();
        break;
      default:
        SNPrintF(index, "!!! unknown edge type: %d ", edge.type());
    }
    edge.to()->Print(edge_prefix, edge_name, max_depth, indent + 2);
  }
}


const char* HeapEntry::TypeAsString() {
  switch (type()) {
    case kHidden: return "/hidden/";
    case kObject: return "/object/";
    case kClosure: return "/closure/";
    case kString: return "/string/";
    case kCode: return "/code/";
    case kArray: return "/array/";
    case kRegExp: return "/regexp/";
    case kHeapNumber: return "/number/";
    case kNative: return "/native/";
    case kSynthetic: return "/synthetic/";
    case kConsString: return "/concatenated string/";
    case kSlicedString: return "/sliced string/";
    case kSymbol: return "/symbol/";
    default: return "???";
  }
}


// It is very important to keep objects that form a heap snapshot
// as small as possible.
namespace {  // Avoid littering the global namespace.

template <size_t ptr_size> struct SnapshotSizeConstants;

template <> struct SnapshotSizeConstants<4> {
  static const int kExpectedHeapGraphEdgeSize = 12;
  static const int kExpectedHeapEntrySize = 28;
};

template <> struct SnapshotSizeConstants<8> {
  static const int kExpectedHeapGraphEdgeSize = 24;
  static const int kExpectedHeapEntrySize = 40;
};

}  // namespace


HeapSnapshot::HeapSnapshot(HeapProfiler* profiler,
                           const char* title,
                           unsigned uid)
    : profiler_(profiler),
      title_(title),
      uid_(uid),
      root_index_(HeapEntry::kNoEntry),
      gc_roots_index_(HeapEntry::kNoEntry),
      natives_root_index_(HeapEntry::kNoEntry),
      max_snapshot_js_object_id_(0) {
  STATIC_ASSERT(
      sizeof(HeapGraphEdge) ==
      SnapshotSizeConstants<kPointerSize>::kExpectedHeapGraphEdgeSize);
  STATIC_ASSERT(
      sizeof(HeapEntry) ==
      SnapshotSizeConstants<kPointerSize>::kExpectedHeapEntrySize);
  USE(SnapshotSizeConstants<4>::kExpectedHeapGraphEdgeSize);
  USE(SnapshotSizeConstants<4>::kExpectedHeapEntrySize);
  USE(SnapshotSizeConstants<8>::kExpectedHeapGraphEdgeSize);
  USE(SnapshotSizeConstants<8>::kExpectedHeapEntrySize);
  for (int i = 0; i < VisitorSynchronization::kNumberOfSyncTags; ++i) {
    gc_subroot_indexes_[i] = HeapEntry::kNoEntry;
  }
}


void HeapSnapshot::Delete() {
  profiler_->RemoveSnapshot(this);
  delete this;
}


void HeapSnapshot::RememberLastJSObjectId() {
  max_snapshot_js_object_id_ = profiler_->heap_object_map()->last_assigned_id();
}


HeapEntry* HeapSnapshot::AddRootEntry() {
  ASSERT(root_index_ == HeapEntry::kNoEntry);
  ASSERT(entries_.is_empty());  // Root entry must be the first one.
  HeapEntry* entry = AddEntry(HeapEntry::kSynthetic,
                              "",
                              HeapObjectsMap::kInternalRootObjectId,
                              0,
                              0);
  root_index_ = entry->index();
  ASSERT(root_index_ == 0);
  return entry;
}


HeapEntry* HeapSnapshot::AddGcRootsEntry() {
  ASSERT(gc_roots_index_ == HeapEntry::kNoEntry);
  HeapEntry* entry = AddEntry(HeapEntry::kSynthetic,
                              "(GC roots)",
                              HeapObjectsMap::kGcRootsObjectId,
                              0,
                              0);
  gc_roots_index_ = entry->index();
  return entry;
}


HeapEntry* HeapSnapshot::AddGcSubrootEntry(int tag) {
  ASSERT(gc_subroot_indexes_[tag] == HeapEntry::kNoEntry);
  ASSERT(0 <= tag && tag < VisitorSynchronization::kNumberOfSyncTags);
  HeapEntry* entry = AddEntry(
      HeapEntry::kSynthetic,
      VisitorSynchronization::kTagNames[tag],
      HeapObjectsMap::GetNthGcSubrootId(tag),
      0,
      0);
  gc_subroot_indexes_[tag] = entry->index();
  return entry;
}


HeapEntry* HeapSnapshot::AddEntry(HeapEntry::Type type,
                                  const char* name,
                                  SnapshotObjectId id,
                                  size_t size,
                                  unsigned trace_node_id) {
  HeapEntry entry(this, type, name, id, size, trace_node_id);
  entries_.Add(entry);
  return &entries_.last();
}


void HeapSnapshot::FillChildren() {
  ASSERT(children().is_empty());
  children().Allocate(edges().length());
  int children_index = 0;
  for (int i = 0; i < entries().length(); ++i) {
    HeapEntry* entry = &entries()[i];
    children_index = entry->set_children_index(children_index);
  }
  ASSERT(edges().length() == children_index);
  for (int i = 0; i < edges().length(); ++i) {
    HeapGraphEdge* edge = &edges()[i];
    edge->ReplaceToIndexWithEntry(this);
    edge->from()->add_child(edge);
  }
}


class FindEntryById {
 public:
  explicit FindEntryById(SnapshotObjectId id) : id_(id) { }
  int operator()(HeapEntry* const* entry) {
    if ((*entry)->id() == id_) return 0;
    return (*entry)->id() < id_ ? -1 : 1;
  }
 private:
  SnapshotObjectId id_;
};


HeapEntry* HeapSnapshot::GetEntryById(SnapshotObjectId id) {
  List<HeapEntry*>* entries_by_id = GetSortedEntriesList();
  // Perform a binary search by id.
  int index = SortedListBSearch(*entries_by_id, FindEntryById(id));
  if (index == -1)
    return NULL;
  return entries_by_id->at(index);
}


template<class T>
static int SortByIds(const T* entry1_ptr,
                     const T* entry2_ptr) {
  if ((*entry1_ptr)->id() == (*entry2_ptr)->id()) return 0;
  return (*entry1_ptr)->id() < (*entry2_ptr)->id() ? -1 : 1;
}


List<HeapEntry*>* HeapSnapshot::GetSortedEntriesList() {
  if (sorted_entries_.is_empty()) {
    sorted_entries_.Allocate(entries_.length());
    for (int i = 0; i < entries_.length(); ++i) {
      sorted_entries_[i] = &entries_[i];
    }
    sorted_entries_.Sort(SortByIds);
  }
  return &sorted_entries_;
}


void HeapSnapshot::Print(int max_depth) {
  root()->Print("", "", max_depth, 0);
}


size_t HeapSnapshot::RawSnapshotSize() const {
  return
      sizeof(*this) +
      GetMemoryUsedByList(entries_) +
      GetMemoryUsedByList(edges_) +
      GetMemoryUsedByList(children_) +
      GetMemoryUsedByList(sorted_entries_);
}


// We split IDs on evens for embedder objects (see
// HeapObjectsMap::GenerateId) and odds for native objects.
const SnapshotObjectId HeapObjectsMap::kInternalRootObjectId = 1;
const SnapshotObjectId HeapObjectsMap::kGcRootsObjectId =
    HeapObjectsMap::kInternalRootObjectId + HeapObjectsMap::kObjectIdStep;
const SnapshotObjectId HeapObjectsMap::kGcRootsFirstSubrootId =
    HeapObjectsMap::kGcRootsObjectId + HeapObjectsMap::kObjectIdStep;
const SnapshotObjectId HeapObjectsMap::kFirstAvailableObjectId =
    HeapObjectsMap::kGcRootsFirstSubrootId +
    VisitorSynchronization::kNumberOfSyncTags * HeapObjectsMap::kObjectIdStep;


static bool AddressesMatch(void* key1, void* key2) {
  return key1 == key2;
}


HeapObjectsMap::HeapObjectsMap(Heap* heap)
    : next_id_(kFirstAvailableObjectId),
      entries_map_(AddressesMatch),
      heap_(heap) {
  // This dummy element solves a problem with entries_map_.
  // When we do lookup in HashMap we see no difference between two cases:
  // it has an entry with NULL as the value or it has created
  // a new entry on the fly with NULL as the default value.
  // With such dummy element we have a guaranty that all entries_map_ entries
  // will have the value field grater than 0.
  // This fact is using in MoveObject method.
  entries_.Add(EntryInfo(0, NULL, 0));
}


bool HeapObjectsMap::MoveObject(Address from, Address to, int object_size) {
  ASSERT(to != NULL);
  ASSERT(from != NULL);
  if (from == to) return false;
  void* from_value = entries_map_.Remove(from, ComputePointerHash(from));
  if (from_value == NULL) {
    // It may occur that some untracked object moves to an address X and there
    // is a tracked object at that address. In this case we should remove the
    // entry as we know that the object has died.
    void* to_value = entries_map_.Remove(to, ComputePointerHash(to));
    if (to_value != NULL) {
      int to_entry_info_index =
          static_cast<int>(reinterpret_cast<intptr_t>(to_value));
      entries_.at(to_entry_info_index).addr = NULL;
    }
  } else {
    HashMap::Entry* to_entry = entries_map_.Lookup(to, ComputePointerHash(to),
                                                   true);
    if (to_entry->value != NULL) {
      // We found the existing entry with to address for an old object.
      // Without this operation we will have two EntryInfo's with the same
      // value in addr field. It is bad because later at RemoveDeadEntries
      // one of this entry will be removed with the corresponding entries_map_
      // entry.
      int to_entry_info_index =
          static_cast<int>(reinterpret_cast<intptr_t>(to_entry->value));
      entries_.at(to_entry_info_index).addr = NULL;
    }
    int from_entry_info_index =
        static_cast<int>(reinterpret_cast<intptr_t>(from_value));
    entries_.at(from_entry_info_index).addr = to;
    // Size of an object can change during its life, so to keep information
    // about the object in entries_ consistent, we have to adjust size when the
    // object is migrated.
    if (FLAG_heap_profiler_trace_objects) {
      PrintF("Move object from %p to %p old size %6d new size %6d\n",
             from,
             to,
             entries_.at(from_entry_info_index).size,
             object_size);
    }
    entries_.at(from_entry_info_index).size = object_size;
    to_entry->value = from_value;
  }
  return from_value != NULL;
}


void HeapObjectsMap::UpdateObjectSize(Address addr, int size) {
  FindOrAddEntry(addr, size, false);
}


SnapshotObjectId HeapObjectsMap::FindEntry(Address addr) {
  HashMap::Entry* entry = entries_map_.Lookup(addr, ComputePointerHash(addr),
                                              false);
  if (entry == NULL) return 0;
  int entry_index = static_cast<int>(reinterpret_cast<intptr_t>(entry->value));
  EntryInfo& entry_info = entries_.at(entry_index);
  ASSERT(static_cast<uint32_t>(entries_.length()) > entries_map_.occupancy());
  return entry_info.id;
}


SnapshotObjectId HeapObjectsMap::FindOrAddEntry(Address addr,
                                                unsigned int size,
                                                bool accessed) {
  ASSERT(static_cast<uint32_t>(entries_.length()) > entries_map_.occupancy());
  HashMap::Entry* entry = entries_map_.Lookup(addr, ComputePointerHash(addr),
                                              true);
  if (entry->value != NULL) {
    int entry_index =
        static_cast<int>(reinterpret_cast<intptr_t>(entry->value));
    EntryInfo& entry_info = entries_.at(entry_index);
    entry_info.accessed = accessed;
    if (FLAG_heap_profiler_trace_objects) {
      PrintF("Update object size : %p with old size %d and new size %d\n",
             addr,
             entry_info.size,
             size);
    }
    entry_info.size = size;
    return entry_info.id;
  }
  entry->value = reinterpret_cast<void*>(entries_.length());
  SnapshotObjectId id = next_id_;
  next_id_ += kObjectIdStep;
  entries_.Add(EntryInfo(id, addr, size, accessed));
  ASSERT(static_cast<uint32_t>(entries_.length()) > entries_map_.occupancy());
  return id;
}


void HeapObjectsMap::StopHeapObjectsTracking() {
  time_intervals_.Clear();
}


void HeapObjectsMap::UpdateHeapObjectsMap() {
  if (FLAG_heap_profiler_trace_objects) {
    PrintF("Begin HeapObjectsMap::UpdateHeapObjectsMap. map has %d entries.\n",
           entries_map_.occupancy());
  }
  heap_->CollectAllGarbage(Heap::kMakeHeapIterableMask,
                          "HeapObjectsMap::UpdateHeapObjectsMap");
  HeapIterator iterator(heap_);
  for (HeapObject* obj = iterator.next();
       obj != NULL;
       obj = iterator.next()) {
    FindOrAddEntry(obj->address(), obj->Size());
    if (FLAG_heap_profiler_trace_objects) {
      PrintF("Update object      : %p %6d. Next address is %p\n",
             obj->address(),
             obj->Size(),
             obj->address() + obj->Size());
    }
  }
  RemoveDeadEntries();
  if (FLAG_heap_profiler_trace_objects) {
    PrintF("End HeapObjectsMap::UpdateHeapObjectsMap. map has %d entries.\n",
           entries_map_.occupancy());
  }
}


namespace {


struct HeapObjectInfo {
  HeapObjectInfo(HeapObject* obj, int expected_size)
    : obj(obj),
      expected_size(expected_size) {
  }

  HeapObject* obj;
  int expected_size;

  bool IsValid() const { return expected_size == obj->Size(); }

  void Print() const {
    if (expected_size == 0) {
      PrintF("Untracked object   : %p %6d. Next address is %p\n",
             obj->address(),
             obj->Size(),
             obj->address() + obj->Size());
    } else if (obj->Size() != expected_size) {
      PrintF("Wrong size %6d: %p %6d. Next address is %p\n",
             expected_size,
             obj->address(),
             obj->Size(),
             obj->address() + obj->Size());
    } else {
      PrintF("Good object      : %p %6d. Next address is %p\n",
             obj->address(),
             expected_size,
             obj->address() + obj->Size());
    }
  }
};


static int comparator(const HeapObjectInfo* a, const HeapObjectInfo* b) {
  if (a->obj < b->obj) return -1;
  if (a->obj > b->obj) return 1;
  return 0;
}


}  // namespace


int HeapObjectsMap::FindUntrackedObjects() {
  List<HeapObjectInfo> heap_objects(1000);

  HeapIterator iterator(heap_);
  int untracked = 0;
  for (HeapObject* obj = iterator.next();
       obj != NULL;
       obj = iterator.next()) {
    HashMap::Entry* entry = entries_map_.Lookup(
      obj->address(), ComputePointerHash(obj->address()), false);
    if (entry == NULL) {
      ++untracked;
      if (FLAG_heap_profiler_trace_objects) {
        heap_objects.Add(HeapObjectInfo(obj, 0));
      }
    } else {
      int entry_index = static_cast<int>(
          reinterpret_cast<intptr_t>(entry->value));
      EntryInfo& entry_info = entries_.at(entry_index);
      if (FLAG_heap_profiler_trace_objects) {
        heap_objects.Add(HeapObjectInfo(obj,
                         static_cast<int>(entry_info.size)));
        if (obj->Size() != static_cast<int>(entry_info.size))
          ++untracked;
      } else {
        CHECK_EQ(obj->Size(), static_cast<int>(entry_info.size));
      }
    }
  }
  if (FLAG_heap_profiler_trace_objects) {
    PrintF("\nBegin HeapObjectsMap::FindUntrackedObjects. %d entries in map.\n",
           entries_map_.occupancy());
    heap_objects.Sort(comparator);
    int last_printed_object = -1;
    bool print_next_object = false;
    for (int i = 0; i < heap_objects.length(); ++i) {
      const HeapObjectInfo& object_info = heap_objects[i];
      if (!object_info.IsValid()) {
        ++untracked;
        if (last_printed_object != i - 1) {
          if (i > 0) {
            PrintF("%d objects were skipped\n", i - 1 - last_printed_object);
            heap_objects[i - 1].Print();
          }
        }
        object_info.Print();
        last_printed_object = i;
        print_next_object = true;
      } else if (print_next_object) {
        object_info.Print();
        print_next_object = false;
        last_printed_object = i;
      }
    }
    if (last_printed_object < heap_objects.length() - 1) {
      PrintF("Last %d objects were skipped\n",
             heap_objects.length() - 1 - last_printed_object);
    }
    PrintF("End HeapObjectsMap::FindUntrackedObjects. %d entries in map.\n\n",
           entries_map_.occupancy());
  }
  return untracked;
}


SnapshotObjectId HeapObjectsMap::PushHeapObjectsStats(OutputStream* stream) {
  UpdateHeapObjectsMap();
  time_intervals_.Add(TimeInterval(next_id_));
  int prefered_chunk_size = stream->GetChunkSize();
  List<v8::HeapStatsUpdate> stats_buffer;
  ASSERT(!entries_.is_empty());
  EntryInfo* entry_info = &entries_.first();
  EntryInfo* end_entry_info = &entries_.last() + 1;
  for (int time_interval_index = 0;
       time_interval_index < time_intervals_.length();
       ++time_interval_index) {
    TimeInterval& time_interval = time_intervals_[time_interval_index];
    SnapshotObjectId time_interval_id = time_interval.id;
    uint32_t entries_size = 0;
    EntryInfo* start_entry_info = entry_info;
    while (entry_info < end_entry_info && entry_info->id < time_interval_id) {
      entries_size += entry_info->size;
      ++entry_info;
    }
    uint32_t entries_count =
        static_cast<uint32_t>(entry_info - start_entry_info);
    if (time_interval.count != entries_count ||
        time_interval.size != entries_size) {
      stats_buffer.Add(v8::HeapStatsUpdate(
          time_interval_index,
          time_interval.count = entries_count,
          time_interval.size = entries_size));
      if (stats_buffer.length() >= prefered_chunk_size) {
        OutputStream::WriteResult result = stream->WriteHeapStatsChunk(
            &stats_buffer.first(), stats_buffer.length());
        if (result == OutputStream::kAbort) return last_assigned_id();
        stats_buffer.Clear();
      }
    }
  }
  ASSERT(entry_info == end_entry_info);
  if (!stats_buffer.is_empty()) {
    OutputStream::WriteResult result = stream->WriteHeapStatsChunk(
        &stats_buffer.first(), stats_buffer.length());
    if (result == OutputStream::kAbort) return last_assigned_id();
  }
  stream->EndOfStream();
  return last_assigned_id();
}


void HeapObjectsMap::RemoveDeadEntries() {
  ASSERT(entries_.length() > 0 &&
         entries_.at(0).id == 0 &&
         entries_.at(0).addr == NULL);
  int first_free_entry = 1;
  for (int i = 1; i < entries_.length(); ++i) {
    EntryInfo& entry_info = entries_.at(i);
    if (entry_info.accessed) {
      if (first_free_entry != i) {
        entries_.at(first_free_entry) = entry_info;
      }
      entries_.at(first_free_entry).accessed = false;
      HashMap::Entry* entry = entries_map_.Lookup(
          entry_info.addr, ComputePointerHash(entry_info.addr), false);
      ASSERT(entry);
      entry->value = reinterpret_cast<void*>(first_free_entry);
      ++first_free_entry;
    } else {
      if (entry_info.addr) {
        entries_map_.Remove(entry_info.addr,
                            ComputePointerHash(entry_info.addr));
      }
    }
  }
  entries_.Rewind(first_free_entry);
  ASSERT(static_cast<uint32_t>(entries_.length()) - 1 ==
         entries_map_.occupancy());
}


SnapshotObjectId HeapObjectsMap::GenerateId(v8::RetainedObjectInfo* info) {
  SnapshotObjectId id = static_cast<SnapshotObjectId>(info->GetHash());
  const char* label = info->GetLabel();
  id ^= StringHasher::HashSequentialString(label,
                                           static_cast<int>(strlen(label)),
                                           heap_->HashSeed());
  intptr_t element_count = info->GetElementCount();
  if (element_count != -1)
    id ^= ComputeIntegerHash(static_cast<uint32_t>(element_count),
                             v8::internal::kZeroHashSeed);
  return id << 1;
}


size_t HeapObjectsMap::GetUsedMemorySize() const {
  return
      sizeof(*this) +
      sizeof(HashMap::Entry) * entries_map_.capacity() +
      GetMemoryUsedByList(entries_) +
      GetMemoryUsedByList(time_intervals_);
}


HeapEntriesMap::HeapEntriesMap()
    : entries_(HashMap::PointersMatch) {
}


int HeapEntriesMap::Map(HeapThing thing) {
  HashMap::Entry* cache_entry = entries_.Lookup(thing, Hash(thing), false);
  if (cache_entry == NULL) return HeapEntry::kNoEntry;
  return static_cast<int>(reinterpret_cast<intptr_t>(cache_entry->value));
}


void HeapEntriesMap::Pair(HeapThing thing, int entry) {
  HashMap::Entry* cache_entry = entries_.Lookup(thing, Hash(thing), true);
  ASSERT(cache_entry->value == NULL);
  cache_entry->value = reinterpret_cast<void*>(static_cast<intptr_t>(entry));
}


HeapObjectsSet::HeapObjectsSet()
    : entries_(HashMap::PointersMatch) {
}


void HeapObjectsSet::Clear() {
  entries_.Clear();
}


bool HeapObjectsSet::Contains(Object* obj) {
  if (!obj->IsHeapObject()) return false;
  HeapObject* object = HeapObject::cast(obj);
  return entries_.Lookup(object, HeapEntriesMap::Hash(object), false) != NULL;
}


void HeapObjectsSet::Insert(Object* obj) {
  if (!obj->IsHeapObject()) return;
  HeapObject* object = HeapObject::cast(obj);
  entries_.Lookup(object, HeapEntriesMap::Hash(object), true);
}


const char* HeapObjectsSet::GetTag(Object* obj) {
  HeapObject* object = HeapObject::cast(obj);
  HashMap::Entry* cache_entry =
      entries_.Lookup(object, HeapEntriesMap::Hash(object), false);
  return cache_entry != NULL
      ? reinterpret_cast<const char*>(cache_entry->value)
      : NULL;
}


void HeapObjectsSet::SetTag(Object* obj, const char* tag) {
  if (!obj->IsHeapObject()) return;
  HeapObject* object = HeapObject::cast(obj);
  HashMap::Entry* cache_entry =
      entries_.Lookup(object, HeapEntriesMap::Hash(object), true);
  cache_entry->value = const_cast<char*>(tag);
}


HeapObject* const V8HeapExplorer::kInternalRootObject =
    reinterpret_cast<HeapObject*>(
        static_cast<intptr_t>(HeapObjectsMap::kInternalRootObjectId));
HeapObject* const V8HeapExplorer::kGcRootsObject =
    reinterpret_cast<HeapObject*>(
        static_cast<intptr_t>(HeapObjectsMap::kGcRootsObjectId));
HeapObject* const V8HeapExplorer::kFirstGcSubrootObject =
    reinterpret_cast<HeapObject*>(
        static_cast<intptr_t>(HeapObjectsMap::kGcRootsFirstSubrootId));
HeapObject* const V8HeapExplorer::kLastGcSubrootObject =
    reinterpret_cast<HeapObject*>(
        static_cast<intptr_t>(HeapObjectsMap::kFirstAvailableObjectId));


V8HeapExplorer::V8HeapExplorer(
    HeapSnapshot* snapshot,
    SnapshottingProgressReportingInterface* progress,
    v8::HeapProfiler::ObjectNameResolver* resolver)
    : heap_(snapshot->profiler()->heap_object_map()->heap()),
      snapshot_(snapshot),
      names_(snapshot_->profiler()->names()),
      heap_object_map_(snapshot_->profiler()->heap_object_map()),
      progress_(progress),
      filler_(NULL),
      global_object_name_resolver_(resolver) {
}


V8HeapExplorer::~V8HeapExplorer() {
}


HeapEntry* V8HeapExplorer::AllocateEntry(HeapThing ptr) {
  return AddEntry(reinterpret_cast<HeapObject*>(ptr));
}


HeapEntry* V8HeapExplorer::AddEntry(HeapObject* object) {
  if (object == kInternalRootObject) {
    snapshot_->AddRootEntry();
    return snapshot_->root();
  } else if (object == kGcRootsObject) {
    HeapEntry* entry = snapshot_->AddGcRootsEntry();
    return entry;
  } else if (object >= kFirstGcSubrootObject && object < kLastGcSubrootObject) {
    HeapEntry* entry = snapshot_->AddGcSubrootEntry(GetGcSubrootOrder(object));
    return entry;
  } else if (object->IsJSFunction()) {
    JSFunction* func = JSFunction::cast(object);
    SharedFunctionInfo* shared = func->shared();
    const char* name = shared->bound() ? "native_bind" :
        names_->GetName(String::cast(shared->name()));
    return AddEntry(object, HeapEntry::kClosure, name);
  } else if (object->IsJSRegExp()) {
    JSRegExp* re = JSRegExp::cast(object);
    return AddEntry(object,
                    HeapEntry::kRegExp,
                    names_->GetName(re->Pattern()));
  } else if (object->IsJSObject()) {
    const char* name = names_->GetName(
        GetConstructorName(JSObject::cast(object)));
    if (object->IsJSGlobalObject()) {
      const char* tag = objects_tags_.GetTag(object);
      if (tag != NULL) {
        name = names_->GetFormatted("%s / %s", name, tag);
      }
    }
    return AddEntry(object, HeapEntry::kObject, name);
  } else if (object->IsString()) {
    String* string = String::cast(object);
    if (string->IsConsString())
      return AddEntry(object,
                      HeapEntry::kConsString,
                      "(concatenated string)");
    if (string->IsSlicedString())
      return AddEntry(object,
                      HeapEntry::kSlicedString,
                      "(sliced string)");
    return AddEntry(object,
                    HeapEntry::kString,
                    names_->GetName(String::cast(object)));
  } else if (object->IsSymbol()) {
    return AddEntry(object, HeapEntry::kSymbol, "symbol");
  } else if (object->IsCode()) {
    return AddEntry(object, HeapEntry::kCode, "");
  } else if (object->IsSharedFunctionInfo()) {
    String* name = String::cast(SharedFunctionInfo::cast(object)->name());
    return AddEntry(object,
                    HeapEntry::kCode,
                    names_->GetName(name));
  } else if (object->IsScript()) {
    Object* name = Script::cast(object)->name();
    return AddEntry(object,
                    HeapEntry::kCode,
                    name->IsString()
                        ? names_->GetName(String::cast(name))
                        : "");
  } else if (object->IsNativeContext()) {
    return AddEntry(object, HeapEntry::kHidden, "system / NativeContext");
  } else if (object->IsContext()) {
    return AddEntry(object, HeapEntry::kObject, "system / Context");
  } else if (object->IsFixedArray() ||
             object->IsFixedDoubleArray() ||
             object->IsByteArray() ||
             object->IsExternalArray()) {
    return AddEntry(object, HeapEntry::kArray, "");
  } else if (object->IsHeapNumber()) {
    return AddEntry(object, HeapEntry::kHeapNumber, "number");
  }
  return AddEntry(object, HeapEntry::kHidden, GetSystemEntryName(object));
}


HeapEntry* V8HeapExplorer::AddEntry(HeapObject* object,
                                    HeapEntry::Type type,
                                    const char* name) {
  return AddEntry(object->address(), type, name, object->Size());
}


HeapEntry* V8HeapExplorer::AddEntry(Address address,
                                    HeapEntry::Type type,
                                    const char* name,
                                    size_t size) {
  SnapshotObjectId object_id = heap_object_map_->FindOrAddEntry(
      address, static_cast<unsigned int>(size));
  unsigned trace_node_id = 0;
  if (AllocationTracker* allocation_tracker =
      snapshot_->profiler()->allocation_tracker()) {
    trace_node_id =
        allocation_tracker->address_to_trace()->GetTraceNodeId(address);
  }
  return snapshot_->AddEntry(type, name, object_id, size, trace_node_id);
}


class SnapshotFiller {
 public:
  explicit SnapshotFiller(HeapSnapshot* snapshot, HeapEntriesMap* entries)
      : snapshot_(snapshot),
        names_(snapshot->profiler()->names()),
        entries_(entries) { }
  HeapEntry* AddEntry(HeapThing ptr, HeapEntriesAllocator* allocator) {
    HeapEntry* entry = allocator->AllocateEntry(ptr);
    entries_->Pair(ptr, entry->index());
    return entry;
  }
  HeapEntry* FindEntry(HeapThing ptr) {
    int index = entries_->Map(ptr);
    return index != HeapEntry::kNoEntry ? &snapshot_->entries()[index] : NULL;
  }
  HeapEntry* FindOrAddEntry(HeapThing ptr, HeapEntriesAllocator* allocator) {
    HeapEntry* entry = FindEntry(ptr);
    return entry != NULL ? entry : AddEntry(ptr, allocator);
  }
  void SetIndexedReference(HeapGraphEdge::Type type,
                           int parent,
                           int index,
                           HeapEntry* child_entry) {
    HeapEntry* parent_entry = &snapshot_->entries()[parent];
    parent_entry->SetIndexedReference(type, index, child_entry);
  }
  void SetIndexedAutoIndexReference(HeapGraphEdge::Type type,
                                    int parent,
                                    HeapEntry* child_entry) {
    HeapEntry* parent_entry = &snapshot_->entries()[parent];
    int index = parent_entry->children_count() + 1;
    parent_entry->SetIndexedReference(type, index, child_entry);
  }
  void SetNamedReference(HeapGraphEdge::Type type,
                         int parent,
                         const char* reference_name,
                         HeapEntry* child_entry) {
    HeapEntry* parent_entry = &snapshot_->entries()[parent];
    parent_entry->SetNamedReference(type, reference_name, child_entry);
  }
  void SetNamedAutoIndexReference(HeapGraphEdge::Type type,
                                  int parent,
                                  HeapEntry* child_entry) {
    HeapEntry* parent_entry = &snapshot_->entries()[parent];
    int index = parent_entry->children_count() + 1;
    parent_entry->SetNamedReference(
        type,
        names_->GetName(index),
        child_entry);
  }

 private:
  HeapSnapshot* snapshot_;
  StringsStorage* names_;
  HeapEntriesMap* entries_;
};


class GcSubrootsEnumerator : public ObjectVisitor {
 public:
  GcSubrootsEnumerator(
      SnapshotFiller* filler, V8HeapExplorer* explorer)
      : filler_(filler),
        explorer_(explorer),
        previous_object_count_(0),
        object_count_(0) {
  }
  void VisitPointers(Object** start, Object** end) {
    object_count_ += end - start;
  }
  void Synchronize(VisitorSynchronization::SyncTag tag) {
    // Skip empty subroots.
    if (previous_object_count_ != object_count_) {
      previous_object_count_ = object_count_;
      filler_->AddEntry(V8HeapExplorer::GetNthGcSubrootObject(tag), explorer_);
    }
  }
 private:
  SnapshotFiller* filler_;
  V8HeapExplorer* explorer_;
  intptr_t previous_object_count_;
  intptr_t object_count_;
};


void V8HeapExplorer::AddRootEntries(SnapshotFiller* filler) {
  filler->AddEntry(kInternalRootObject, this);
  filler->AddEntry(kGcRootsObject, this);
  GcSubrootsEnumerator enumerator(filler, this);
  heap_->IterateRoots(&enumerator, VISIT_ALL);
}


const char* V8HeapExplorer::GetSystemEntryName(HeapObject* object) {
  switch (object->map()->instance_type()) {
    case MAP_TYPE:
      switch (Map::cast(object)->instance_type()) {
#define MAKE_STRING_MAP_CASE(instance_type, size, name, Name) \
        case instance_type: return "system / Map (" #Name ")";
      STRING_TYPE_LIST(MAKE_STRING_MAP_CASE)
#undef MAKE_STRING_MAP_CASE
        default: return "system / Map";
      }
    case CELL_TYPE: return "system / Cell";
    case PROPERTY_CELL_TYPE: return "system / PropertyCell";
    case FOREIGN_TYPE: return "system / Foreign";
    case ODDBALL_TYPE: return "system / Oddball";
#define MAKE_STRUCT_CASE(NAME, Name, name) \
    case NAME##_TYPE: return "system / "#Name;
  STRUCT_LIST(MAKE_STRUCT_CASE)
#undef MAKE_STRUCT_CASE
    default: return "system";
  }
}


int V8HeapExplorer::EstimateObjectsCount(HeapIterator* iterator) {
  int objects_count = 0;
  for (HeapObject* obj = iterator->next();
       obj != NULL;
       obj = iterator->next()) {
    objects_count++;
  }
  return objects_count;
}


class IndexedReferencesExtractor : public ObjectVisitor {
 public:
  IndexedReferencesExtractor(V8HeapExplorer* generator,
                             HeapObject* parent_obj,
                             int parent)
      : generator_(generator),
        parent_obj_(parent_obj),
        parent_(parent),
        next_index_(0) {
  }
  void VisitCodeEntry(Address entry_address) {
     Code* code = Code::cast(Code::GetObjectFromEntryAddress(entry_address));
     generator_->SetInternalReference(parent_obj_, parent_, "code", code);
     generator_->TagCodeObject(code);
  }
  void VisitPointers(Object** start, Object** end) {
    for (Object** p = start; p < end; p++) {
      ++next_index_;
      if (CheckVisitedAndUnmark(p)) continue;
      generator_->SetHiddenReference(parent_obj_, parent_, next_index_, *p);
    }
  }
  static void MarkVisitedField(HeapObject* obj, int offset) {
    if (offset < 0) return;
    Address field = obj->address() + offset;
    ASSERT(Memory::Object_at(field)->IsHeapObject());
    intptr_t p = reinterpret_cast<intptr_t>(Memory::Object_at(field));
    ASSERT(!IsMarked(p));
    intptr_t p_tagged = p | kTag;
    Memory::Object_at(field) = reinterpret_cast<Object*>(p_tagged);
  }

 private:
  bool CheckVisitedAndUnmark(Object** field) {
    intptr_t p = reinterpret_cast<intptr_t>(*field);
    if (IsMarked(p)) {
      intptr_t p_untagged = (p & ~kTaggingMask) | kHeapObjectTag;
      *field = reinterpret_cast<Object*>(p_untagged);
      ASSERT((*field)->IsHeapObject());
      return true;
    }
    return false;
  }

  static const intptr_t kTaggingMask = 3;
  static const intptr_t kTag = 3;

  static bool IsMarked(intptr_t p) { return (p & kTaggingMask) == kTag; }

  V8HeapExplorer* generator_;
  HeapObject* parent_obj_;
  int parent_;
  int next_index_;
};


bool V8HeapExplorer::ExtractReferencesPass1(int entry, HeapObject* obj) {
  if (obj->IsFixedArray()) return false;  // FixedArrays are processed on pass 2

  if (obj->IsJSGlobalProxy()) {
    ExtractJSGlobalProxyReferences(entry, JSGlobalProxy::cast(obj));
  } else if (obj->IsJSArrayBuffer()) {
    ExtractJSArrayBufferReferences(entry, JSArrayBuffer::cast(obj));
  } else if (obj->IsJSWeakSet()) {
    ExtractJSWeakCollectionReferences(entry, JSWeakSet::cast(obj));
  } else if (obj->IsJSWeakMap()) {
    ExtractJSWeakCollectionReferences(entry, JSWeakMap::cast(obj));
  } else if (obj->IsJSObject()) {
    ExtractJSObjectReferences(entry, JSObject::cast(obj));
  } else if (obj->IsString()) {
    ExtractStringReferences(entry, String::cast(obj));
  } else if (obj->IsSymbol()) {
    ExtractSymbolReferences(entry, Symbol::cast(obj));
  } else if (obj->IsMap()) {
    ExtractMapReferences(entry, Map::cast(obj));
  } else if (obj->IsSharedFunctionInfo()) {
    ExtractSharedFunctionInfoReferences(entry, SharedFunctionInfo::cast(obj));
  } else if (obj->IsScript()) {
    ExtractScriptReferences(entry, Script::cast(obj));
  } else if (obj->IsAccessorPair()) {
    ExtractAccessorPairReferences(entry, AccessorPair::cast(obj));
  } else if (obj->IsCodeCache()) {
    ExtractCodeCacheReferences(entry, CodeCache::cast(obj));
  } else if (obj->IsCode()) {
    ExtractCodeReferences(entry, Code::cast(obj));
  } else if (obj->IsBox()) {
    ExtractBoxReferences(entry, Box::cast(obj));
  } else if (obj->IsCell()) {
    ExtractCellReferences(entry, Cell::cast(obj));
  } else if (obj->IsPropertyCell()) {
    ExtractPropertyCellReferences(entry, PropertyCell::cast(obj));
  } else if (obj->IsAllocationSite()) {
    ExtractAllocationSiteReferences(entry, AllocationSite::cast(obj));
  }
  return true;
}


bool V8HeapExplorer::ExtractReferencesPass2(int entry, HeapObject* obj) {
  if (!obj->IsFixedArray()) return false;

  if (obj->IsContext()) {
    ExtractContextReferences(entry, Context::cast(obj));
  } else {
    ExtractFixedArrayReferences(entry, FixedArray::cast(obj));
  }
  return true;
}


void V8HeapExplorer::ExtractJSGlobalProxyReferences(
    int entry, JSGlobalProxy* proxy) {
  SetInternalReference(proxy, entry,
                       "native_context", proxy->native_context(),
                       JSGlobalProxy::kNativeContextOffset);
}


void V8HeapExplorer::ExtractJSObjectReferences(
    int entry, JSObject* js_obj) {
  HeapObject* obj = js_obj;
  ExtractClosureReferences(js_obj, entry);
  ExtractPropertyReferences(js_obj, entry);
  ExtractElementReferences(js_obj, entry);
  ExtractInternalReferences(js_obj, entry);
  SetPropertyReference(
      obj, entry, heap_->proto_string(), js_obj->GetPrototype());
  if (obj->IsJSFunction()) {
    JSFunction* js_fun = JSFunction::cast(js_obj);
    Object* proto_or_map = js_fun->prototype_or_initial_map();
    if (!proto_or_map->IsTheHole()) {
      if (!proto_or_map->IsMap()) {
        SetPropertyReference(
            obj, entry,
            heap_->prototype_string(), proto_or_map,
            NULL,
            JSFunction::kPrototypeOrInitialMapOffset);
      } else {
        SetPropertyReference(
            obj, entry,
            heap_->prototype_string(), js_fun->prototype());
        SetInternalReference(
            obj, entry, "initial_map", proto_or_map,
            JSFunction::kPrototypeOrInitialMapOffset);
      }
    }
    SharedFunctionInfo* shared_info = js_fun->shared();
    // JSFunction has either bindings or literals and never both.
    bool bound = shared_info->bound();
    TagObject(js_fun->literals_or_bindings(),
              bound ? "(function bindings)" : "(function literals)");
    SetInternalReference(js_fun, entry,
                         bound ? "bindings" : "literals",
                         js_fun->literals_or_bindings(),
                         JSFunction::kLiteralsOffset);
    TagObject(shared_info, "(shared function info)");
    SetInternalReference(js_fun, entry,
                         "shared", shared_info,
                         JSFunction::kSharedFunctionInfoOffset);
    TagObject(js_fun->context(), "(context)");
    SetInternalReference(js_fun, entry,
                         "context", js_fun->context(),
                         JSFunction::kContextOffset);
    SetWeakReference(js_fun, entry,
                     "next_function_link", js_fun->next_function_link(),
                     JSFunction::kNextFunctionLinkOffset);
    STATIC_ASSERT(JSFunction::kNextFunctionLinkOffset
                 == JSFunction::kNonWeakFieldsEndOffset);
    STATIC_ASSERT(JSFunction::kNextFunctionLinkOffset + kPointerSize
                 == JSFunction::kSize);
  } else if (obj->IsGlobalObject()) {
    GlobalObject* global_obj = GlobalObject::cast(obj);
    SetInternalReference(global_obj, entry,
                         "builtins", global_obj->builtins(),
                         GlobalObject::kBuiltinsOffset);
    SetInternalReference(global_obj, entry,
                         "native_context", global_obj->native_context(),
                         GlobalObject::kNativeContextOffset);
    SetInternalReference(global_obj, entry,
                         "global_context", global_obj->global_context(),
                         GlobalObject::kGlobalContextOffset);
    SetInternalReference(global_obj, entry,
                         "global_proxy", global_obj->global_proxy(),
                         GlobalObject::kGlobalProxyOffset);
    STATIC_ASSERT(GlobalObject::kHeaderSize - JSObject::kHeaderSize ==
                 4 * kPointerSize);
  } else if (obj->IsJSArrayBufferView()) {
    JSArrayBufferView* view = JSArrayBufferView::cast(obj);
    SetInternalReference(view, entry, "buffer", view->buffer(),
                         JSArrayBufferView::kBufferOffset);
    SetWeakReference(view, entry, "weak_next", view->weak_next(),
                     JSArrayBufferView::kWeakNextOffset);
  }
  TagObject(js_obj->properties(), "(object properties)");
  SetInternalReference(obj, entry,
                       "properties", js_obj->properties(),
                       JSObject::kPropertiesOffset);
  TagObject(js_obj->elements(), "(object elements)");
  SetInternalReference(obj, entry,
                       "elements", js_obj->elements(),
                       JSObject::kElementsOffset);
}


void V8HeapExplorer::ExtractStringReferences(int entry, String* string) {
  if (string->IsConsString()) {
    ConsString* cs = ConsString::cast(string);
    SetInternalReference(cs, entry, "first", cs->first(),
                         ConsString::kFirstOffset);
    SetInternalReference(cs, entry, "second", cs->second(),
                         ConsString::kSecondOffset);
  } else if (string->IsSlicedString()) {
    SlicedString* ss = SlicedString::cast(string);
    SetInternalReference(ss, entry, "parent", ss->parent(),
                         SlicedString::kParentOffset);
  }
}


void V8HeapExplorer::ExtractSymbolReferences(int entry, Symbol* symbol) {
  SetInternalReference(symbol, entry,
                       "name", symbol->name(),
                       Symbol::kNameOffset);
}


void V8HeapExplorer::ExtractJSWeakCollectionReferences(
    int entry, JSWeakCollection* collection) {
  MarkAsWeakContainer(collection->table());
  SetInternalReference(collection, entry,
                       "table", collection->table(),
                       JSWeakCollection::kTableOffset);
}


void V8HeapExplorer::ExtractContextReferences(int entry, Context* context) {
  if (context == context->declaration_context()) {
    ScopeInfo* scope_info = context->closure()->shared()->scope_info();
    // Add context allocated locals.
    int context_locals = scope_info->ContextLocalCount();
    for (int i = 0; i < context_locals; ++i) {
      String* local_name = scope_info->ContextLocalName(i);
      int idx = Context::MIN_CONTEXT_SLOTS + i;
      SetContextReference(context, entry, local_name, context->get(idx),
                          Context::OffsetOfElementAt(idx));
    }
    if (scope_info->HasFunctionName()) {
      String* name = scope_info->FunctionName();
      VariableMode mode;
      int idx = scope_info->FunctionContextSlotIndex(name, &mode);
      if (idx >= 0) {
        SetContextReference(context, entry, name, context->get(idx),
                            Context::OffsetOfElementAt(idx));
      }
    }
  }

#define EXTRACT_CONTEXT_FIELD(index, type, name) \
  if (Context::index < Context::FIRST_WEAK_SLOT || \
      Context::index == Context::MAP_CACHE_INDEX) { \
    SetInternalReference(context, entry, #name, context->get(Context::index), \
        FixedArray::OffsetOfElementAt(Context::index)); \
  } else { \
    SetWeakReference(context, entry, #name, context->get(Context::index), \
        FixedArray::OffsetOfElementAt(Context::index)); \
  }
  EXTRACT_CONTEXT_FIELD(CLOSURE_INDEX, JSFunction, closure);
  EXTRACT_CONTEXT_FIELD(PREVIOUS_INDEX, Context, previous);
  EXTRACT_CONTEXT_FIELD(EXTENSION_INDEX, Object, extension);
  EXTRACT_CONTEXT_FIELD(GLOBAL_OBJECT_INDEX, GlobalObject, global);
  if (context->IsNativeContext()) {
    TagObject(context->jsfunction_result_caches(),
              "(context func. result caches)");
    TagObject(context->normalized_map_cache(), "(context norm. map cache)");
    TagObject(context->runtime_context(), "(runtime context)");
    TagObject(context->embedder_data(), "(context data)");
    NATIVE_CONTEXT_FIELDS(EXTRACT_CONTEXT_FIELD);
    EXTRACT_CONTEXT_FIELD(OPTIMIZED_FUNCTIONS_LIST, unused,
                          optimized_functions_list);
    EXTRACT_CONTEXT_FIELD(OPTIMIZED_CODE_LIST, unused, optimized_code_list);
    EXTRACT_CONTEXT_FIELD(DEOPTIMIZED_CODE_LIST, unused, deoptimized_code_list);
    EXTRACT_CONTEXT_FIELD(NEXT_CONTEXT_LINK, unused, next_context_link);
#undef EXTRACT_CONTEXT_FIELD
    STATIC_ASSERT(Context::OPTIMIZED_FUNCTIONS_LIST ==
                  Context::FIRST_WEAK_SLOT);
    STATIC_ASSERT(Context::NEXT_CONTEXT_LINK + 1 ==
                  Context::NATIVE_CONTEXT_SLOTS);
    STATIC_ASSERT(Context::FIRST_WEAK_SLOT + 5 ==
                  Context::NATIVE_CONTEXT_SLOTS);
  }
}


void V8HeapExplorer::ExtractMapReferences(int entry, Map* map) {
  if (map->HasTransitionArray()) {
    TransitionArray* transitions = map->transitions();
    int transitions_entry = GetEntry(transitions)->index();
    Object* back_pointer = transitions->back_pointer_storage();
    TagObject(back_pointer, "(back pointer)");
    SetInternalReference(transitions, transitions_entry,
                         "back_pointer", back_pointer);

    if (FLAG_collect_maps && map->CanTransition()) {
      if (!transitions->IsSimpleTransition()) {
        if (transitions->HasPrototypeTransitions()) {
          FixedArray* prototype_transitions =
              transitions->GetPrototypeTransitions();
          MarkAsWeakContainer(prototype_transitions);
          TagObject(prototype_transitions, "(prototype transitions");
          SetInternalReference(transitions, transitions_entry,
                               "prototype_transitions", prototype_transitions);
        }
        // TODO(alph): transitions keys are strong links.
        MarkAsWeakContainer(transitions);
      }
    }

    TagObject(transitions, "(transition array)");
    SetInternalReference(map, entry,
                         "transitions", transitions,
                         Map::kTransitionsOrBackPointerOffset);
  } else {
    Object* back_pointer = map->GetBackPointer();
    TagObject(back_pointer, "(back pointer)");
    SetInternalReference(map, entry,
                         "back_pointer", back_pointer,
                         Map::kTransitionsOrBackPointerOffset);
  }
  DescriptorArray* descriptors = map->instance_descriptors();
  TagObject(descriptors, "(map descriptors)");
  SetInternalReference(map, entry,
                       "descriptors", descriptors,
                       Map::kDescriptorsOffset);

  MarkAsWeakContainer(map->code_cache());
  SetInternalReference(map, entry,
                       "code_cache", map->code_cache(),
                       Map::kCodeCacheOffset);
  SetInternalReference(map, entry,
                       "prototype", map->prototype(), Map::kPrototypeOffset);
  SetInternalReference(map, entry,
                       "constructor", map->constructor(),
                       Map::kConstructorOffset);
  TagObject(map->dependent_code(), "(dependent code)");
  MarkAsWeakContainer(map->dependent_code());
  SetInternalReference(map, entry,
                       "dependent_code", map->dependent_code(),
                       Map::kDependentCodeOffset);
}


void V8HeapExplorer::ExtractSharedFunctionInfoReferences(
    int entry, SharedFunctionInfo* shared) {
  HeapObject* obj = shared;
  String* shared_name = shared->DebugName();
  const char* name = NULL;
  if (shared_name != *heap_->isolate()->factory()->empty_string()) {
    name = names_->GetName(shared_name);
    TagObject(shared->code(), names_->GetFormatted("(code for %s)", name));
  } else {
    TagObject(shared->code(), names_->GetFormatted("(%s code)",
        Code::Kind2String(shared->code()->kind())));
  }

  SetInternalReference(obj, entry,
                       "name", shared->name(),
                       SharedFunctionInfo::kNameOffset);
  SetInternalReference(obj, entry,
                       "code", shared->code(),
                       SharedFunctionInfo::kCodeOffset);
  TagObject(shared->scope_info(), "(function scope info)");
  SetInternalReference(obj, entry,
                       "scope_info", shared->scope_info(),
                       SharedFunctionInfo::kScopeInfoOffset);
  SetInternalReference(obj, entry,
                       "instance_class_name", shared->instance_class_name(),
                       SharedFunctionInfo::kInstanceClassNameOffset);
  SetInternalReference(obj, entry,
                       "script", shared->script(),
                       SharedFunctionInfo::kScriptOffset);
  const char* construct_stub_name = name ?
      names_->GetFormatted("(construct stub code for %s)", name) :
      "(construct stub code)";
  TagObject(shared->construct_stub(), construct_stub_name);
  SetInternalReference(obj, entry,
                       "construct_stub", shared->construct_stub(),
                       SharedFunctionInfo::kConstructStubOffset);
  SetInternalReference(obj, entry,
                       "function_data", shared->function_data(),
                       SharedFunctionInfo::kFunctionDataOffset);
  SetInternalReference(obj, entry,
                       "debug_info", shared->debug_info(),
                       SharedFunctionInfo::kDebugInfoOffset);
  SetInternalReference(obj, entry,
                       "inferred_name", shared->inferred_name(),
                       SharedFunctionInfo::kInferredNameOffset);
  SetInternalReference(obj, entry,
                       "optimized_code_map", shared->optimized_code_map(),
                       SharedFunctionInfo::kOptimizedCodeMapOffset);
  SetInternalReference(obj, entry,
                       "feedback_vector", shared->feedback_vector(),
                       SharedFunctionInfo::kFeedbackVectorOffset);
}


void V8HeapExplorer::ExtractScriptReferences(int entry, Script* script) {
  HeapObject* obj = script;
  SetInternalReference(obj, entry,
                       "source", script->source(),
                       Script::kSourceOffset);
  SetInternalReference(obj, entry,
                       "name", script->name(),
                       Script::kNameOffset);
  SetInternalReference(obj, entry,
                       "context_data", script->context_data(),
                       Script::kContextOffset);
  TagObject(script->line_ends(), "(script line ends)");
  SetInternalReference(obj, entry,
                       "line_ends", script->line_ends(),
                       Script::kLineEndsOffset);
}


void V8HeapExplorer::ExtractAccessorPairReferences(
    int entry, AccessorPair* accessors) {
  SetInternalReference(accessors, entry, "getter", accessors->getter(),
                       AccessorPair::kGetterOffset);
  SetInternalReference(accessors, entry, "setter", accessors->setter(),
                       AccessorPair::kSetterOffset);
}


void V8HeapExplorer::ExtractCodeCacheReferences(
    int entry, CodeCache* code_cache) {
  TagObject(code_cache->default_cache(), "(default code cache)");
  SetInternalReference(code_cache, entry,
                       "default_cache", code_cache->default_cache(),
                       CodeCache::kDefaultCacheOffset);
  TagObject(code_cache->normal_type_cache(), "(code type cache)");
  SetInternalReference(code_cache, entry,
                       "type_cache", code_cache->normal_type_cache(),
                       CodeCache::kNormalTypeCacheOffset);
}


void V8HeapExplorer::TagBuiltinCodeObject(Code* code, const char* name) {
  TagObject(code, names_->GetFormatted("(%s builtin)", name));
}


void V8HeapExplorer::TagCodeObject(Code* code) {
  if (code->kind() == Code::STUB) {
    TagObject(code, names_->GetFormatted(
        "(%s code)", CodeStub::MajorName(
            static_cast<CodeStub::Major>(code->major_key()), true)));
  }
}


void V8HeapExplorer::ExtractCodeReferences(int entry, Code* code) {
  TagCodeObject(code);
  TagObject(code->relocation_info(), "(code relocation info)");
  SetInternalReference(code, entry,
                       "relocation_info", code->relocation_info(),
                       Code::kRelocationInfoOffset);
  SetInternalReference(code, entry,
                       "handler_table", code->handler_table(),
                       Code::kHandlerTableOffset);
  TagObject(code->deoptimization_data(), "(code deopt data)");
  SetInternalReference(code, entry,
                       "deoptimization_data", code->deoptimization_data(),
                       Code::kDeoptimizationDataOffset);
  if (code->kind() == Code::FUNCTION) {
    SetInternalReference(code, entry,
                         "type_feedback_info", code->type_feedback_info(),
                         Code::kTypeFeedbackInfoOffset);
  }
  SetInternalReference(code, entry,
                       "gc_metadata", code->gc_metadata(),
                       Code::kGCMetadataOffset);
  SetInternalReference(code, entry,
                       "constant_pool", code->constant_pool(),
                       Code::kConstantPoolOffset);
  if (code->kind() == Code::OPTIMIZED_FUNCTION) {
    SetWeakReference(code, entry,
                     "next_code_link", code->next_code_link(),
                     Code::kNextCodeLinkOffset);
  }
}


void V8HeapExplorer::ExtractBoxReferences(int entry, Box* box) {
  SetInternalReference(box, entry, "value", box->value(), Box::kValueOffset);
}


void V8HeapExplorer::ExtractCellReferences(int entry, Cell* cell) {
  SetInternalReference(cell, entry, "value", cell->value(), Cell::kValueOffset);
}


void V8HeapExplorer::ExtractPropertyCellReferences(int entry,
                                                   PropertyCell* cell) {
  ExtractCellReferences(entry, cell);
  SetInternalReference(cell, entry, "type", cell->type(),
                       PropertyCell::kTypeOffset);
  MarkAsWeakContainer(cell->dependent_code());
  SetInternalReference(cell, entry, "dependent_code", cell->dependent_code(),
                       PropertyCell::kDependentCodeOffset);
}


void V8HeapExplorer::ExtractAllocationSiteReferences(int entry,
                                                     AllocationSite* site) {
  SetInternalReference(site, entry, "transition_info", site->transition_info(),
                       AllocationSite::kTransitionInfoOffset);
  SetInternalReference(site, entry, "nested_site", site->nested_site(),
                       AllocationSite::kNestedSiteOffset);
  MarkAsWeakContainer(site->dependent_code());
  SetInternalReference(site, entry, "dependent_code", site->dependent_code(),
                       AllocationSite::kDependentCodeOffset);
  // Do not visit weak_next as it is not visited by the StaticVisitor,
  // and we're not very interested in weak_next field here.
  STATIC_ASSERT(AllocationSite::kWeakNextOffset >=
               AllocationSite::BodyDescriptor::kEndOffset);
}


class JSArrayBufferDataEntryAllocator : public HeapEntriesAllocator {
 public:
  JSArrayBufferDataEntryAllocator(size_t size, V8HeapExplorer* explorer)
      : size_(size)
      , explorer_(explorer) {
  }
  virtual HeapEntry* AllocateEntry(HeapThing ptr) {
    return explorer_->AddEntry(
        static_cast<Address>(ptr),
        HeapEntry::kNative, "system / JSArrayBufferData", size_);
  }
 private:
  size_t size_;
  V8HeapExplorer* explorer_;
};


void V8HeapExplorer::ExtractJSArrayBufferReferences(
    int entry, JSArrayBuffer* buffer) {
  SetWeakReference(buffer, entry, "weak_next", buffer->weak_next(),
                   JSArrayBuffer::kWeakNextOffset);
  SetWeakReference(buffer, entry,
                   "weak_first_view", buffer->weak_first_view(),
                   JSArrayBuffer::kWeakFirstViewOffset);
  // Setup a reference to a native memory backing_store object.
  if (!buffer->backing_store())
    return;
  size_t data_size = NumberToSize(heap_->isolate(), buffer->byte_length());
  JSArrayBufferDataEntryAllocator allocator(data_size, this);
  HeapEntry* data_entry =
      filler_->FindOrAddEntry(buffer->backing_store(), &allocator);
  filler_->SetNamedReference(HeapGraphEdge::kInternal,
                             entry, "backing_store", data_entry);
}


void V8HeapExplorer::ExtractFixedArrayReferences(int entry, FixedArray* array) {
  bool is_weak = weak_containers_.Contains(array);
  for (int i = 0, l = array->length(); i < l; ++i) {
    if (is_weak) {
      SetWeakReference(array, entry,
                       i, array->get(i), array->OffsetOfElementAt(i));
    } else {
      SetInternalReference(array, entry,
                           i, array->get(i), array->OffsetOfElementAt(i));
    }
  }
}


void V8HeapExplorer::ExtractClosureReferences(JSObject* js_obj, int entry) {
  if (!js_obj->IsJSFunction()) return;

  JSFunction* func = JSFunction::cast(js_obj);
  if (func->shared()->bound()) {
    FixedArray* bindings = func->function_bindings();
    SetNativeBindReference(js_obj, entry, "bound_this",
                           bindings->get(JSFunction::kBoundThisIndex));
    SetNativeBindReference(js_obj, entry, "bound_function",
                           bindings->get(JSFunction::kBoundFunctionIndex));
    for (int i = JSFunction::kBoundArgumentsStartIndex;
         i < bindings->length(); i++) {
      const char* reference_name = names_->GetFormatted(
          "bound_argument_%d",
          i - JSFunction::kBoundArgumentsStartIndex);
      SetNativeBindReference(js_obj, entry, reference_name,
                             bindings->get(i));
    }
  }
}


void V8HeapExplorer::ExtractPropertyReferences(JSObject* js_obj, int entry) {
  if (js_obj->HasFastProperties()) {
    DescriptorArray* descs = js_obj->map()->instance_descriptors();
    int real_size = js_obj->map()->NumberOfOwnDescriptors();
    for (int i = 0; i < real_size; i++) {
      switch (descs->GetType(i)) {
        case FIELD: {
          Representation r = descs->GetDetails(i).representation();
          if (r.IsSmi() || r.IsDouble()) break;
          int index = descs->GetFieldIndex(i);

          Name* k = descs->GetKey(i);
          if (index < js_obj->map()->inobject_properties()) {
            Object* value = js_obj->InObjectPropertyAt(index);
            if (k != heap_->hidden_string()) {
              SetPropertyReference(
                  js_obj, entry,
                  k, value,
                  NULL,
                  js_obj->GetInObjectPropertyOffset(index));
            } else {
              TagObject(value, "(hidden properties)");
              SetInternalReference(
                  js_obj, entry,
                  "hidden_properties", value,
                  js_obj->GetInObjectPropertyOffset(index));
            }
          } else {
            FieldIndex field_index =
                FieldIndex::ForDescriptor(js_obj->map(), i);
            Object* value = js_obj->RawFastPropertyAt(field_index);
            if (k != heap_->hidden_string()) {
              SetPropertyReference(js_obj, entry, k, value);
            } else {
              TagObject(value, "(hidden properties)");
              SetInternalReference(js_obj, entry, "hidden_properties", value);
            }
          }
          break;
        }
        case CONSTANT:
          SetPropertyReference(
              js_obj, entry,
              descs->GetKey(i), descs->GetConstant(i));
          break;
        case CALLBACKS:
          ExtractAccessorPairProperty(
              js_obj, entry,
              descs->GetKey(i), descs->GetValue(i));
          break;
        case NORMAL:  // only in slow mode
        case HANDLER:  // only in lookup results, not in descriptors
        case INTERCEPTOR:  // only in lookup results, not in descriptors
          break;
        case NONEXISTENT:
          UNREACHABLE();
          break;
      }
    }
  } else {
    NameDictionary* dictionary = js_obj->property_dictionary();
    int length = dictionary->Capacity();
    for (int i = 0; i < length; ++i) {
      Object* k = dictionary->KeyAt(i);
      if (dictionary->IsKey(k)) {
        Object* target = dictionary->ValueAt(i);
        // We assume that global objects can only have slow properties.
        Object* value = target->IsPropertyCell()
            ? PropertyCell::cast(target)->value()
            : target;
        if (k == heap_->hidden_string()) {
          TagObject(value, "(hidden properties)");
          SetInternalReference(js_obj, entry, "hidden_properties", value);
          continue;
        }
        if (ExtractAccessorPairProperty(js_obj, entry, k, value)) continue;
        SetPropertyReference(js_obj, entry, String::cast(k), value);
      }
    }
  }
}


bool V8HeapExplorer::ExtractAccessorPairProperty(
    JSObject* js_obj, int entry, Object* key, Object* callback_obj) {
  if (!callback_obj->IsAccessorPair()) return false;
  AccessorPair* accessors = AccessorPair::cast(callback_obj);
  Object* getter = accessors->getter();
  if (!getter->IsOddball()) {
    SetPropertyReference(js_obj, entry, String::cast(key), getter, "get %s");
  }
  Object* setter = accessors->setter();
  if (!setter->IsOddball()) {
    SetPropertyReference(js_obj, entry, String::cast(key), setter, "set %s");
  }
  return true;
}


void V8HeapExplorer::ExtractElementReferences(JSObject* js_obj, int entry) {
  if (js_obj->HasFastObjectElements()) {
    FixedArray* elements = FixedArray::cast(js_obj->elements());
    int length = js_obj->IsJSArray() ?
        Smi::cast(JSArray::cast(js_obj)->length())->value() :
        elements->length();
    for (int i = 0; i < length; ++i) {
      if (!elements->get(i)->IsTheHole()) {
        SetElementReference(js_obj, entry, i, elements->get(i));
      }
    }
  } else if (js_obj->HasDictionaryElements()) {
    SeededNumberDictionary* dictionary = js_obj->element_dictionary();
    int length = dictionary->Capacity();
    for (int i = 0; i < length; ++i) {
      Object* k = dictionary->KeyAt(i);
      if (dictionary->IsKey(k)) {
        ASSERT(k->IsNumber());
        uint32_t index = static_cast<uint32_t>(k->Number());
        SetElementReference(js_obj, entry, index, dictionary->ValueAt(i));
      }
    }
  }
}


void V8HeapExplorer::ExtractInternalReferences(JSObject* js_obj, int entry) {
  int length = js_obj->GetInternalFieldCount();
  for (int i = 0; i < length; ++i) {
    Object* o = js_obj->GetInternalField(i);
    SetInternalReference(
        js_obj, entry, i, o, js_obj->GetInternalFieldOffset(i));
  }
}


String* V8HeapExplorer::GetConstructorName(JSObject* object) {
  Heap* heap = object->GetHeap();
  if (object->IsJSFunction()) return heap->closure_string();
  String* constructor_name = object->constructor_name();
  if (constructor_name == heap->Object_string()) {
    // Look up an immediate "constructor" property, if it is a function,
    // return its name. This is for instances of binding objects, which
    // have prototype constructor type "Object".
    Object* constructor_prop = NULL;
    Isolate* isolate = heap->isolate();
    LookupResult result(isolate);
    object->LookupOwnRealNamedProperty(
        isolate->factory()->constructor_string(), &result);
    if (!result.IsFound()) return object->constructor_name();

    constructor_prop = result.GetLazyValue();
    if (constructor_prop->IsJSFunction()) {
      Object* maybe_name =
          JSFunction::cast(constructor_prop)->shared()->name();
      if (maybe_name->IsString()) {
        String* name = String::cast(maybe_name);
        if (name->length() > 0) return name;
      }
    }
  }
  return object->constructor_name();
}


HeapEntry* V8HeapExplorer::GetEntry(Object* obj) {
  if (!obj->IsHeapObject()) return NULL;
  return filler_->FindOrAddEntry(obj, this);
}


class RootsReferencesExtractor : public ObjectVisitor {
 private:
  struct IndexTag {
    IndexTag(int index, VisitorSynchronization::SyncTag tag)
        : index(index), tag(tag) { }
    int index;
    VisitorSynchronization::SyncTag tag;
  };

 public:
  explicit RootsReferencesExtractor(Heap* heap)
      : collecting_all_references_(false),
        previous_reference_count_(0),
        heap_(heap) {
  }

  void VisitPointers(Object** start, Object** end) {
    if (collecting_all_references_) {
      for (Object** p = start; p < end; p++) all_references_.Add(*p);
    } else {
      for (Object** p = start; p < end; p++) strong_references_.Add(*p);
    }
  }

  void SetCollectingAllReferences() { collecting_all_references_ = true; }

  void FillReferences(V8HeapExplorer* explorer) {
    ASSERT(strong_references_.length() <= all_references_.length());
    Builtins* builtins = heap_->isolate()->builtins();
    for (int i = 0; i < reference_tags_.length(); ++i) {
      explorer->SetGcRootsReference(reference_tags_[i].tag);
    }
    int strong_index = 0, all_index = 0, tags_index = 0, builtin_index = 0;
    while (all_index < all_references_.length()) {
      bool is_strong = strong_index < strong_references_.length()
          && strong_references_[strong_index] == all_references_[all_index];
      explorer->SetGcSubrootReference(reference_tags_[tags_index].tag,
                                      !is_strong,
                                      all_references_[all_index]);
      if (reference_tags_[tags_index].tag ==
          VisitorSynchronization::kBuiltins) {
        ASSERT(all_references_[all_index]->IsCode());
        explorer->TagBuiltinCodeObject(
            Code::cast(all_references_[all_index]),
            builtins->name(builtin_index++));
      }
      ++all_index;
      if (is_strong) ++strong_index;
      if (reference_tags_[tags_index].index == all_index) ++tags_index;
    }
  }

  void Synchronize(VisitorSynchronization::SyncTag tag) {
    if (collecting_all_references_ &&
        previous_reference_count_ != all_references_.length()) {
      previous_reference_count_ = all_references_.length();
      reference_tags_.Add(IndexTag(previous_reference_count_, tag));
    }
  }

 private:
  bool collecting_all_references_;
  List<Object*> strong_references_;
  List<Object*> all_references_;
  int previous_reference_count_;
  List<IndexTag> reference_tags_;
  Heap* heap_;
};


bool V8HeapExplorer::IterateAndExtractReferences(
    SnapshotFiller* filler) {
  filler_ = filler;

  // Make sure builtin code objects get their builtin tags
  // first. Otherwise a particular JSFunction object could set
  // its custom name to a generic builtin.
  SetRootGcRootsReference();
  RootsReferencesExtractor extractor(heap_);
  heap_->IterateRoots(&extractor, VISIT_ONLY_STRONG);
  extractor.SetCollectingAllReferences();
  heap_->IterateRoots(&extractor, VISIT_ALL);
  extractor.FillReferences(this);

  // We have to do two passes as sometimes FixedArrays are used
  // to weakly hold their items, and it's impossible to distinguish
  // between these cases without processing the array owner first.
  bool interrupted =
      IterateAndExtractSinglePass<&V8HeapExplorer::ExtractReferencesPass1>() ||
      IterateAndExtractSinglePass<&V8HeapExplorer::ExtractReferencesPass2>();

  if (interrupted) {
    filler_ = NULL;
    return false;
  }

  filler_ = NULL;
  return progress_->ProgressReport(true);
}


template<V8HeapExplorer::ExtractReferencesMethod extractor>
bool V8HeapExplorer::IterateAndExtractSinglePass() {
  // Now iterate the whole heap.
  bool interrupted = false;
  HeapIterator iterator(heap_, HeapIterator::kFilterUnreachable);
  // Heap iteration with filtering must be finished in any case.
  for (HeapObject* obj = iterator.next();
       obj != NULL;
       obj = iterator.next(), progress_->ProgressStep()) {
    if (interrupted) continue;

    HeapEntry* heap_entry = GetEntry(obj);
    int entry = heap_entry->index();
    if ((this->*extractor)(entry, obj)) {
      SetInternalReference(obj, entry,
                           "map", obj->map(), HeapObject::kMapOffset);
      // Extract unvisited fields as hidden references and restore tags
      // of visited fields.
      IndexedReferencesExtractor refs_extractor(this, obj, entry);
      obj->Iterate(&refs_extractor);
    }

    if (!progress_->ProgressReport(false)) interrupted = true;
  }
  return interrupted;
}


bool V8HeapExplorer::IsEssentialObject(Object* object) {
  return object->IsHeapObject()
      && !object->IsOddball()
      && object != heap_->empty_byte_array()
      && object != heap_->empty_fixed_array()
      && object != heap_->empty_descriptor_array()
      && object != heap_->fixed_array_map()
      && object != heap_->cell_map()
      && object != heap_->global_property_cell_map()
      && object != heap_->shared_function_info_map()
      && object != heap_->free_space_map()
      && object != heap_->one_pointer_filler_map()
      && object != heap_->two_pointer_filler_map();
}


void V8HeapExplorer::SetContextReference(HeapObject* parent_obj,
                                         int parent_entry,
                                         String* reference_name,
                                         Object* child_obj,
                                         int field_offset) {
  ASSERT(parent_entry == GetEntry(parent_obj)->index());
  HeapEntry* child_entry = GetEntry(child_obj);
  if (child_entry != NULL) {
    filler_->SetNamedReference(HeapGraphEdge::kContextVariable,
                               parent_entry,
                               names_->GetName(reference_name),
                               child_entry);
    IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
  }
}


void V8HeapExplorer::SetNativeBindReference(HeapObject* parent_obj,
                                            int parent_entry,
                                            const char* reference_name,
                                            Object* child_obj) {
  ASSERT(parent_entry == GetEntry(parent_obj)->index());
  HeapEntry* child_entry = GetEntry(child_obj);
  if (child_entry != NULL) {
    filler_->SetNamedReference(HeapGraphEdge::kShortcut,
                               parent_entry,
                               reference_name,
                               child_entry);
  }
}


void V8HeapExplorer::SetElementReference(HeapObject* parent_obj,
                                         int parent_entry,
                                         int index,
                                         Object* child_obj) {
  ASSERT(parent_entry == GetEntry(parent_obj)->index());
  HeapEntry* child_entry = GetEntry(child_obj);
  if (child_entry != NULL) {
    filler_->SetIndexedReference(HeapGraphEdge::kElement,
                                 parent_entry,
                                 index,
                                 child_entry);
  }
}


void V8HeapExplorer::SetInternalReference(HeapObject* parent_obj,
                                          int parent_entry,
                                          const char* reference_name,
                                          Object* child_obj,
                                          int field_offset) {
  ASSERT(parent_entry == GetEntry(parent_obj)->index());
  HeapEntry* child_entry = GetEntry(child_obj);
  if (child_entry == NULL) return;
  if (IsEssentialObject(child_obj)) {
    filler_->SetNamedReference(HeapGraphEdge::kInternal,
                               parent_entry,
                               reference_name,
                               child_entry);
  }
  IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
}


void V8HeapExplorer::SetInternalReference(HeapObject* parent_obj,
                                          int parent_entry,
                                          int index,
                                          Object* child_obj,
                                          int field_offset) {
  ASSERT(parent_entry == GetEntry(parent_obj)->index());
  HeapEntry* child_entry = GetEntry(child_obj);
  if (child_entry == NULL) return;
  if (IsEssentialObject(child_obj)) {
    filler_->SetNamedReference(HeapGraphEdge::kInternal,
                               parent_entry,
                               names_->GetName(index),
                               child_entry);
  }
  IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
}


void V8HeapExplorer::SetHiddenReference(HeapObject* parent_obj,
                                        int parent_entry,
                                        int index,
                                        Object* child_obj) {
  ASSERT(parent_entry == GetEntry(parent_obj)->index());
  HeapEntry* child_entry = GetEntry(child_obj);
  if (child_entry != NULL && IsEssentialObject(child_obj)) {
    filler_->SetIndexedReference(HeapGraphEdge::kHidden,
                                 parent_entry,
                                 index,
                                 child_entry);
  }
}


void V8HeapExplorer::SetWeakReference(HeapObject* parent_obj,
                                      int parent_entry,
                                      const char* reference_name,
                                      Object* child_obj,
                                      int field_offset) {
  ASSERT(parent_entry == GetEntry(parent_obj)->index());
  HeapEntry* child_entry = GetEntry(child_obj);
  if (child_entry == NULL) return;
  if (IsEssentialObject(child_obj)) {
    filler_->SetNamedReference(HeapGraphEdge::kWeak,
                               parent_entry,
                               reference_name,
                               child_entry);
  }
  IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
}


void V8HeapExplorer::SetWeakReference(HeapObject* parent_obj,
                                      int parent_entry,
                                      int index,
                                      Object* child_obj,
                                      int field_offset) {
  ASSERT(parent_entry == GetEntry(parent_obj)->index());
  HeapEntry* child_entry = GetEntry(child_obj);
  if (child_entry == NULL) return;
  if (IsEssentialObject(child_obj)) {
    filler_->SetNamedReference(HeapGraphEdge::kWeak,
                               parent_entry,
                               names_->GetFormatted("%d", index),
                               child_entry);
  }
  IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
}


void V8HeapExplorer::SetPropertyReference(HeapObject* parent_obj,
                                          int parent_entry,
                                          Name* reference_name,
                                          Object* child_obj,
                                          const char* name_format_string,
                                          int field_offset) {
  ASSERT(parent_entry == GetEntry(parent_obj)->index());
  HeapEntry* child_entry = GetEntry(child_obj);
  if (child_entry != NULL) {
    HeapGraphEdge::Type type =
        reference_name->IsSymbol() || String::cast(reference_name)->length() > 0
            ? HeapGraphEdge::kProperty : HeapGraphEdge::kInternal;
    const char* name = name_format_string != NULL && reference_name->IsString()
        ? names_->GetFormatted(
              name_format_string,
              String::cast(reference_name)->ToCString(
                  DISALLOW_NULLS, ROBUST_STRING_TRAVERSAL).get()) :
        names_->GetName(reference_name);

    filler_->SetNamedReference(type,
                               parent_entry,
                               name,
                               child_entry);
    IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
  }
}


void V8HeapExplorer::SetRootGcRootsReference() {
  filler_->SetIndexedAutoIndexReference(
      HeapGraphEdge::kElement,
      snapshot_->root()->index(),
      snapshot_->gc_roots());
}


void V8HeapExplorer::SetUserGlobalReference(Object* child_obj) {
  HeapEntry* child_entry = GetEntry(child_obj);
  ASSERT(child_entry != NULL);
  filler_->SetNamedAutoIndexReference(
      HeapGraphEdge::kShortcut,
      snapshot_->root()->index(),
      child_entry);
}


void V8HeapExplorer::SetGcRootsReference(VisitorSynchronization::SyncTag tag) {
  filler_->SetIndexedAutoIndexReference(
      HeapGraphEdge::kElement,
      snapshot_->gc_roots()->index(),
      snapshot_->gc_subroot(tag));
}


void V8HeapExplorer::SetGcSubrootReference(
    VisitorSynchronization::SyncTag tag, bool is_weak, Object* child_obj) {
  HeapEntry* child_entry = GetEntry(child_obj);
  if (child_entry != NULL) {
    const char* name = GetStrongGcSubrootName(child_obj);
    if (name != NULL) {
      filler_->SetNamedReference(
          HeapGraphEdge::kInternal,
          snapshot_->gc_subroot(tag)->index(),
          name,
          child_entry);
    } else {
      if (is_weak) {
        filler_->SetNamedAutoIndexReference(
            HeapGraphEdge::kWeak,
            snapshot_->gc_subroot(tag)->index(),
            child_entry);
      } else {
        filler_->SetIndexedAutoIndexReference(
            HeapGraphEdge::kElement,
            snapshot_->gc_subroot(tag)->index(),
            child_entry);
      }
    }

    // Add a shortcut to JS global object reference at snapshot root.
    if (child_obj->IsNativeContext()) {
      Context* context = Context::cast(child_obj);
      GlobalObject* global = context->global_object();
      if (global->IsJSGlobalObject()) {
        bool is_debug_object = false;
        is_debug_object = heap_->isolate()->debug()->IsDebugGlobal(global);
        if (!is_debug_object && !user_roots_.Contains(global)) {
          user_roots_.Insert(global);
          SetUserGlobalReference(global);
        }
      }
    }
  }
}


const char* V8HeapExplorer::GetStrongGcSubrootName(Object* object) {
  if (strong_gc_subroot_names_.is_empty()) {
#define NAME_ENTRY(name) strong_gc_subroot_names_.SetTag(heap_->name(), #name);
#define ROOT_NAME(type, name, camel_name) NAME_ENTRY(name)
    STRONG_ROOT_LIST(ROOT_NAME)
#undef ROOT_NAME
#define STRUCT_MAP_NAME(NAME, Name, name) NAME_ENTRY(name##_map)
    STRUCT_LIST(STRUCT_MAP_NAME)
#undef STRUCT_MAP_NAME
#define STRING_NAME(name, str) NAME_ENTRY(name)
    INTERNALIZED_STRING_LIST(STRING_NAME)
#undef STRING_NAME
#undef NAME_ENTRY
    CHECK(!strong_gc_subroot_names_.is_empty());
  }
  return strong_gc_subroot_names_.GetTag(object);
}


void V8HeapExplorer::TagObject(Object* obj, const char* tag) {
  if (IsEssentialObject(obj)) {
    HeapEntry* entry = GetEntry(obj);
    if (entry->name()[0] == '\0') {
      entry->set_name(tag);
    }
  }
}


void V8HeapExplorer::MarkAsWeakContainer(Object* object) {
  if (IsEssentialObject(object) && object->IsFixedArray()) {
    weak_containers_.Insert(object);
  }
}


class GlobalObjectsEnumerator : public ObjectVisitor {
 public:
  virtual void VisitPointers(Object** start, Object** end) {
    for (Object** p = start; p < end; p++) {
      if ((*p)->IsNativeContext()) {
        Context* context = Context::cast(*p);
        JSObject* proxy = context->global_proxy();
        if (proxy->IsJSGlobalProxy()) {
          Object* global = proxy->map()->prototype();
          if (global->IsJSGlobalObject()) {
            objects_.Add(Handle<JSGlobalObject>(JSGlobalObject::cast(global)));
          }
        }
      }
    }
  }
  int count() { return objects_.length(); }
  Handle<JSGlobalObject>& at(int i) { return objects_[i]; }

 private:
  List<Handle<JSGlobalObject> > objects_;
};


// Modifies heap. Must not be run during heap traversal.
void V8HeapExplorer::TagGlobalObjects() {
  Isolate* isolate = heap_->isolate();
  HandleScope scope(isolate);
  GlobalObjectsEnumerator enumerator;
  isolate->global_handles()->IterateAllRoots(&enumerator);
  const char** urls = NewArray<const char*>(enumerator.count());
  for (int i = 0, l = enumerator.count(); i < l; ++i) {
    if (global_object_name_resolver_) {
      HandleScope scope(isolate);
      Handle<JSGlobalObject> global_obj = enumerator.at(i);
      urls[i] = global_object_name_resolver_->GetName(
          Utils::ToLocal(Handle<JSObject>::cast(global_obj)));
    } else {
      urls[i] = NULL;
    }
  }

  DisallowHeapAllocation no_allocation;
  for (int i = 0, l = enumerator.count(); i < l; ++i) {
    objects_tags_.SetTag(*enumerator.at(i), urls[i]);
  }

  DeleteArray(urls);
}


class GlobalHandlesExtractor : public ObjectVisitor {
 public:
  explicit GlobalHandlesExtractor(NativeObjectsExplorer* explorer)
      : explorer_(explorer) {}
  virtual ~GlobalHandlesExtractor() {}
  virtual void VisitPointers(Object** start, Object** end) {
    UNREACHABLE();
  }
  virtual void VisitEmbedderReference(Object** p, uint16_t class_id) {
    explorer_->VisitSubtreeWrapper(p, class_id);
  }
 private:
  NativeObjectsExplorer* explorer_;
};


class BasicHeapEntriesAllocator : public HeapEntriesAllocator {
 public:
  BasicHeapEntriesAllocator(
      HeapSnapshot* snapshot,
      HeapEntry::Type entries_type)
    : snapshot_(snapshot),
      names_(snapshot_->profiler()->names()),
      heap_object_map_(snapshot_->profiler()->heap_object_map()),
      entries_type_(entries_type) {
  }
  virtual HeapEntry* AllocateEntry(HeapThing ptr);
 private:
  HeapSnapshot* snapshot_;
  StringsStorage* names_;
  HeapObjectsMap* heap_object_map_;
  HeapEntry::Type entries_type_;
};


HeapEntry* BasicHeapEntriesAllocator::AllocateEntry(HeapThing ptr) {
  v8::RetainedObjectInfo* info = reinterpret_cast<v8::RetainedObjectInfo*>(ptr);
  intptr_t elements = info->GetElementCount();
  intptr_t size = info->GetSizeInBytes();
  const char* name = elements != -1
      ? names_->GetFormatted(
            "%s / %" V8_PTR_PREFIX "d entries", info->GetLabel(), elements)
      : names_->GetCopy(info->GetLabel());
  return snapshot_->AddEntry(
      entries_type_,
      name,
      heap_object_map_->GenerateId(info),
      size != -1 ? static_cast<int>(size) : 0,
      0);
}


NativeObjectsExplorer::NativeObjectsExplorer(
    HeapSnapshot* snapshot,
    SnapshottingProgressReportingInterface* progress)
    : isolate_(snapshot->profiler()->heap_object_map()->heap()->isolate()),
      snapshot_(snapshot),
      names_(snapshot_->profiler()->names()),
      progress_(progress),
      embedder_queried_(false),
      objects_by_info_(RetainedInfosMatch),
      native_groups_(StringsMatch),
      filler_(NULL) {
  synthetic_entries_allocator_ =
      new BasicHeapEntriesAllocator(snapshot, HeapEntry::kSynthetic);
  native_entries_allocator_ =
      new BasicHeapEntriesAllocator(snapshot, HeapEntry::kNative);
}


NativeObjectsExplorer::~NativeObjectsExplorer() {
  for (HashMap::Entry* p = objects_by_info_.Start();
       p != NULL;
       p = objects_by_info_.Next(p)) {
    v8::RetainedObjectInfo* info =
        reinterpret_cast<v8::RetainedObjectInfo*>(p->key);
    info->Dispose();
    List<HeapObject*>* objects =
        reinterpret_cast<List<HeapObject*>* >(p->value);
    delete objects;
  }
  for (HashMap::Entry* p = native_groups_.Start();
       p != NULL;
       p = native_groups_.Next(p)) {
    v8::RetainedObjectInfo* info =
        reinterpret_cast<v8::RetainedObjectInfo*>(p->value);
    info->Dispose();
  }
  delete synthetic_entries_allocator_;
  delete native_entries_allocator_;
}


int NativeObjectsExplorer::EstimateObjectsCount() {
  FillRetainedObjects();
  return objects_by_info_.occupancy();
}


void NativeObjectsExplorer::FillRetainedObjects() {
  if (embedder_queried_) return;
  Isolate* isolate = isolate_;
  const GCType major_gc_type = kGCTypeMarkSweepCompact;
  // Record objects that are joined into ObjectGroups.
  isolate->heap()->CallGCPrologueCallbacks(
      major_gc_type, kGCCallbackFlagConstructRetainedObjectInfos);
  List<ObjectGroup*>* groups = isolate->global_handles()->object_groups();
  for (int i = 0; i < groups->length(); ++i) {
    ObjectGroup* group = groups->at(i);
    if (group->info == NULL) continue;
    List<HeapObject*>* list = GetListMaybeDisposeInfo(group->info);
    for (size_t j = 0; j < group->length; ++j) {
      HeapObject* obj = HeapObject::cast(*group->objects[j]);
      list->Add(obj);
      in_groups_.Insert(obj);
    }
    group->info = NULL;  // Acquire info object ownership.
  }
  isolate->global_handles()->RemoveObjectGroups();
  isolate->heap()->CallGCEpilogueCallbacks(major_gc_type, kNoGCCallbackFlags);
  // Record objects that are not in ObjectGroups, but have class ID.
  GlobalHandlesExtractor extractor(this);
  isolate->global_handles()->IterateAllRootsWithClassIds(&extractor);
  embedder_queried_ = true;
}


void NativeObjectsExplorer::FillImplicitReferences() {
  Isolate* isolate = isolate_;
  List<ImplicitRefGroup*>* groups =
      isolate->global_handles()->implicit_ref_groups();
  for (int i = 0; i < groups->length(); ++i) {
    ImplicitRefGroup* group = groups->at(i);
    HeapObject* parent = *group->parent;
    int parent_entry =
        filler_->FindOrAddEntry(parent, native_entries_allocator_)->index();
    ASSERT(parent_entry != HeapEntry::kNoEntry);
    Object*** children = group->children;
    for (size_t j = 0; j < group->length; ++j) {
      Object* child = *children[j];
      HeapEntry* child_entry =
          filler_->FindOrAddEntry(child, native_entries_allocator_);
      filler_->SetNamedReference(
          HeapGraphEdge::kInternal,
          parent_entry,
          "native",
          child_entry);
    }
  }
  isolate->global_handles()->RemoveImplicitRefGroups();
}

List<HeapObject*>* NativeObjectsExplorer::GetListMaybeDisposeInfo(
    v8::RetainedObjectInfo* info) {
  HashMap::Entry* entry =
      objects_by_info_.Lookup(info, InfoHash(info), true);
  if (entry->value != NULL) {
    info->Dispose();
  } else {
    entry->value = new List<HeapObject*>(4);
  }
  return reinterpret_cast<List<HeapObject*>* >(entry->value);
}


bool NativeObjectsExplorer::IterateAndExtractReferences(
    SnapshotFiller* filler) {
  filler_ = filler;
  FillRetainedObjects();
  FillImplicitReferences();
  if (EstimateObjectsCount() > 0) {
    for (HashMap::Entry* p = objects_by_info_.Start();
         p != NULL;
         p = objects_by_info_.Next(p)) {
      v8::RetainedObjectInfo* info =
          reinterpret_cast<v8::RetainedObjectInfo*>(p->key);
      SetNativeRootReference(info);
      List<HeapObject*>* objects =
          reinterpret_cast<List<HeapObject*>* >(p->value);
      for (int i = 0; i < objects->length(); ++i) {
        SetWrapperNativeReferences(objects->at(i), info);
      }
    }
    SetRootNativeRootsReference();
  }
  filler_ = NULL;
  return true;
}


class NativeGroupRetainedObjectInfo : public v8::RetainedObjectInfo {
 public:
  explicit NativeGroupRetainedObjectInfo(const char* label)
      : disposed_(false),
        hash_(reinterpret_cast<intptr_t>(label)),
        label_(label) {
  }

  virtual ~NativeGroupRetainedObjectInfo() {}
  virtual void Dispose() {
    CHECK(!disposed_);
    disposed_ = true;
    delete this;
  }
  virtual bool IsEquivalent(RetainedObjectInfo* other) {
    return hash_ == other->GetHash() && !strcmp(label_, other->GetLabel());
  }
  virtual intptr_t GetHash() { return hash_; }
  virtual const char* GetLabel() { return label_; }

 private:
  bool disposed_;
  intptr_t hash_;
  const char* label_;
};


NativeGroupRetainedObjectInfo* NativeObjectsExplorer::FindOrAddGroupInfo(
    const char* label) {
  const char* label_copy = names_->GetCopy(label);
  uint32_t hash = StringHasher::HashSequentialString(
      label_copy,
      static_cast<int>(strlen(label_copy)),
      isolate_->heap()->HashSeed());
  HashMap::Entry* entry = native_groups_.Lookup(const_cast<char*>(label_copy),
                                                hash, true);
  if (entry->value == NULL) {
    entry->value = new NativeGroupRetainedObjectInfo(label);
  }
  return static_cast<NativeGroupRetainedObjectInfo*>(entry->value);
}


void NativeObjectsExplorer::SetNativeRootReference(
    v8::RetainedObjectInfo* info) {
  HeapEntry* child_entry =
      filler_->FindOrAddEntry(info, native_entries_allocator_);
  ASSERT(child_entry != NULL);
  NativeGroupRetainedObjectInfo* group_info =
      FindOrAddGroupInfo(info->GetGroupLabel());
  HeapEntry* group_entry =
      filler_->FindOrAddEntry(group_info, synthetic_entries_allocator_);
  filler_->SetNamedAutoIndexReference(
      HeapGraphEdge::kInternal,
      group_entry->index(),
      child_entry);
}


void NativeObjectsExplorer::SetWrapperNativeReferences(
    HeapObject* wrapper, v8::RetainedObjectInfo* info) {
  HeapEntry* wrapper_entry = filler_->FindEntry(wrapper);
  ASSERT(wrapper_entry != NULL);
  HeapEntry* info_entry =
      filler_->FindOrAddEntry(info, native_entries_allocator_);
  ASSERT(info_entry != NULL);
  filler_->SetNamedReference(HeapGraphEdge::kInternal,
                             wrapper_entry->index(),
                             "native",
                             info_entry);
  filler_->SetIndexedAutoIndexReference(HeapGraphEdge::kElement,
                                        info_entry->index(),
                                        wrapper_entry);
}


void NativeObjectsExplorer::SetRootNativeRootsReference() {
  for (HashMap::Entry* entry = native_groups_.Start();
       entry;
       entry = native_groups_.Next(entry)) {
    NativeGroupRetainedObjectInfo* group_info =
        static_cast<NativeGroupRetainedObjectInfo*>(entry->value);
    HeapEntry* group_entry =
        filler_->FindOrAddEntry(group_info, native_entries_allocator_);
    ASSERT(group_entry != NULL);
    filler_->SetIndexedAutoIndexReference(
        HeapGraphEdge::kElement,
        snapshot_->root()->index(),
        group_entry);
  }
}


void NativeObjectsExplorer::VisitSubtreeWrapper(Object** p, uint16_t class_id) {
  if (in_groups_.Contains(*p)) return;
  Isolate* isolate = isolate_;
  v8::RetainedObjectInfo* info =
      isolate->heap_profiler()->ExecuteWrapperClassCallback(class_id, p);
  if (info == NULL) return;
  GetListMaybeDisposeInfo(info)->Add(HeapObject::cast(*p));
}


HeapSnapshotGenerator::HeapSnapshotGenerator(
    HeapSnapshot* snapshot,
    v8::ActivityControl* control,
    v8::HeapProfiler::ObjectNameResolver* resolver,
    Heap* heap)
    : snapshot_(snapshot),
      control_(control),
      v8_heap_explorer_(snapshot_, this, resolver),
      dom_explorer_(snapshot_, this),
      heap_(heap) {
}


bool HeapSnapshotGenerator::GenerateSnapshot() {
  v8_heap_explorer_.TagGlobalObjects();

  // TODO(1562) Profiler assumes that any object that is in the heap after
  // full GC is reachable from the root when computing dominators.
  // This is not true for weakly reachable objects.
  // As a temporary solution we call GC twice.
  heap_->CollectAllGarbage(
      Heap::kMakeHeapIterableMask,
      "HeapSnapshotGenerator::GenerateSnapshot");
  heap_->CollectAllGarbage(
      Heap::kMakeHeapIterableMask,
      "HeapSnapshotGenerator::GenerateSnapshot");

#ifdef VERIFY_HEAP
  Heap* debug_heap = heap_;
  CHECK(debug_heap->old_data_space()->is_iterable());
  CHECK(debug_heap->old_pointer_space()->is_iterable());
  CHECK(debug_heap->code_space()->is_iterable());
  CHECK(debug_heap->cell_space()->is_iterable());
  CHECK(debug_heap->property_cell_space()->is_iterable());
  CHECK(debug_heap->map_space()->is_iterable());
#endif

#ifdef VERIFY_HEAP
  debug_heap->Verify();
#endif

  SetProgressTotal(2);  // 2 passes.

#ifdef VERIFY_HEAP
  debug_heap->Verify();
#endif

  if (!FillReferences()) return false;

  snapshot_->FillChildren();
  snapshot_->RememberLastJSObjectId();

  progress_counter_ = progress_total_;
  if (!ProgressReport(true)) return false;
  return true;
}


void HeapSnapshotGenerator::ProgressStep() {
  ++progress_counter_;
}


bool HeapSnapshotGenerator::ProgressReport(bool force) {
  const int kProgressReportGranularity = 10000;
  if (control_ != NULL
      && (force || progress_counter_ % kProgressReportGranularity == 0)) {
      return
          control_->ReportProgressValue(progress_counter_, progress_total_) ==
          v8::ActivityControl::kContinue;
  }
  return true;
}


void HeapSnapshotGenerator::SetProgressTotal(int iterations_count) {
  if (control_ == NULL) return;
  HeapIterator iterator(heap_, HeapIterator::kFilterUnreachable);
  progress_total_ = iterations_count * (
      v8_heap_explorer_.EstimateObjectsCount(&iterator) +
      dom_explorer_.EstimateObjectsCount());
  progress_counter_ = 0;
}


bool HeapSnapshotGenerator::FillReferences() {
  SnapshotFiller filler(snapshot_, &entries_);
  v8_heap_explorer_.AddRootEntries(&filler);
  return v8_heap_explorer_.IterateAndExtractReferences(&filler)
      && dom_explorer_.IterateAndExtractReferences(&filler);
}


template<int bytes> struct MaxDecimalDigitsIn;
template<> struct MaxDecimalDigitsIn<4> {
  static const int kSigned = 11;
  static const int kUnsigned = 10;
};
template<> struct MaxDecimalDigitsIn<8> {
  static const int kSigned = 20;
  static const int kUnsigned = 20;
};


class OutputStreamWriter {
 public:
  explicit OutputStreamWriter(v8::OutputStream* stream)
      : stream_(stream),
        chunk_size_(stream->GetChunkSize()),
        chunk_(chunk_size_),
        chunk_pos_(0),
        aborted_(false) {
    ASSERT(chunk_size_ > 0);
  }
  bool aborted() { return aborted_; }
  void AddCharacter(char c) {
    ASSERT(c != '\0');
    ASSERT(chunk_pos_ < chunk_size_);
    chunk_[chunk_pos_++] = c;
    MaybeWriteChunk();
  }
  void AddString(const char* s) {
    AddSubstring(s, StrLength(s));
  }
  void AddSubstring(const char* s, int n) {
    if (n <= 0) return;
    ASSERT(static_cast<size_t>(n) <= strlen(s));
    const char* s_end = s + n;
    while (s < s_end) {
      int s_chunk_size =
          Min(chunk_size_ - chunk_pos_, static_cast<int>(s_end - s));
      ASSERT(s_chunk_size > 0);
      MemCopy(chunk_.start() + chunk_pos_, s, s_chunk_size);
      s += s_chunk_size;
      chunk_pos_ += s_chunk_size;
      MaybeWriteChunk();
    }
  }
  void AddNumber(unsigned n) { AddNumberImpl<unsigned>(n, "%u"); }
  void Finalize() {
    if (aborted_) return;
    ASSERT(chunk_pos_ < chunk_size_);
    if (chunk_pos_ != 0) {
      WriteChunk();
    }
    stream_->EndOfStream();
  }

 private:
  template<typename T>
  void AddNumberImpl(T n, const char* format) {
    // Buffer for the longest value plus trailing \0
    static const int kMaxNumberSize =
        MaxDecimalDigitsIn<sizeof(T)>::kUnsigned + 1;
    if (chunk_size_ - chunk_pos_ >= kMaxNumberSize) {
      int result = SNPrintF(
          chunk_.SubVector(chunk_pos_, chunk_size_), format, n);
      ASSERT(result != -1);
      chunk_pos_ += result;
      MaybeWriteChunk();
    } else {
      EmbeddedVector<char, kMaxNumberSize> buffer;
      int result = SNPrintF(buffer, format, n);
      USE(result);
      ASSERT(result != -1);
      AddString(buffer.start());
    }
  }
  void MaybeWriteChunk() {
    ASSERT(chunk_pos_ <= chunk_size_);
    if (chunk_pos_ == chunk_size_) {
      WriteChunk();
    }
  }
  void WriteChunk() {
    if (aborted_) return;
    if (stream_->WriteAsciiChunk(chunk_.start(), chunk_pos_) ==
        v8::OutputStream::kAbort) aborted_ = true;
    chunk_pos_ = 0;
  }

  v8::OutputStream* stream_;
  int chunk_size_;
  ScopedVector<char> chunk_;
  int chunk_pos_;
  bool aborted_;
};


// type, name|index, to_node.
const int HeapSnapshotJSONSerializer::kEdgeFieldsCount = 3;
// type, name, id, self_size, edge_count, trace_node_id.
const int HeapSnapshotJSONSerializer::kNodeFieldsCount = 6;

void HeapSnapshotJSONSerializer::Serialize(v8::OutputStream* stream) {
  if (AllocationTracker* allocation_tracker =
      snapshot_->profiler()->allocation_tracker()) {
    allocation_tracker->PrepareForSerialization();
  }
  ASSERT(writer_ == NULL);
  writer_ = new OutputStreamWriter(stream);
  SerializeImpl();
  delete writer_;
  writer_ = NULL;
}


void HeapSnapshotJSONSerializer::SerializeImpl() {
  ASSERT(0 == snapshot_->root()->index());
  writer_->AddCharacter('{');
  writer_->AddString("\"snapshot\":{");
  SerializeSnapshot();
  if (writer_->aborted()) return;
  writer_->AddString("},\n");
  writer_->AddString("\"nodes\":[");
  SerializeNodes();
  if (writer_->aborted()) return;
  writer_->AddString("],\n");
  writer_->AddString("\"edges\":[");
  SerializeEdges();
  if (writer_->aborted()) return;
  writer_->AddString("],\n");

  writer_->AddString("\"trace_function_infos\":[");
  SerializeTraceNodeInfos();
  if (writer_->aborted()) return;
  writer_->AddString("],\n");
  writer_->AddString("\"trace_tree\":[");
  SerializeTraceTree();
  if (writer_->aborted()) return;
  writer_->AddString("],\n");

  writer_->AddString("\"strings\":[");
  SerializeStrings();
  if (writer_->aborted()) return;
  writer_->AddCharacter(']');
  writer_->AddCharacter('}');
  writer_->Finalize();
}


int HeapSnapshotJSONSerializer::GetStringId(const char* s) {
  HashMap::Entry* cache_entry = strings_.Lookup(
      const_cast<char*>(s), StringHash(s), true);
  if (cache_entry->value == NULL) {
    cache_entry->value = reinterpret_cast<void*>(next_string_id_++);
  }
  return static_cast<int>(reinterpret_cast<intptr_t>(cache_entry->value));
}


namespace {

template<size_t size> struct ToUnsigned;

template<> struct ToUnsigned<4> {
  typedef uint32_t Type;
};

template<> struct ToUnsigned<8> {
  typedef uint64_t Type;
};

}  // namespace


template<typename T>
static int utoa_impl(T value, const Vector<char>& buffer, int buffer_pos) {
  STATIC_ASSERT(static_cast<T>(-1) > 0);  // Check that T is unsigned
  int number_of_digits = 0;
  T t = value;
  do {
    ++number_of_digits;
  } while (t /= 10);

  buffer_pos += number_of_digits;
  int result = buffer_pos;
  do {
    int last_digit = static_cast<int>(value % 10);
    buffer[--buffer_pos] = '0' + last_digit;
    value /= 10;
  } while (value);
  return result;
}


template<typename T>
static int utoa(T value, const Vector<char>& buffer, int buffer_pos) {
  typename ToUnsigned<sizeof(value)>::Type unsigned_value = value;
  STATIC_ASSERT(sizeof(value) == sizeof(unsigned_value));
  return utoa_impl(unsigned_value, buffer, buffer_pos);
}


void HeapSnapshotJSONSerializer::SerializeEdge(HeapGraphEdge* edge,
                                               bool first_edge) {
  // The buffer needs space for 3 unsigned ints, 3 commas, \n and \0
  static const int kBufferSize =
      MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned * 3 + 3 + 2;  // NOLINT
  EmbeddedVector<char, kBufferSize> buffer;
  int edge_name_or_index = edge->type() == HeapGraphEdge::kElement
      || edge->type() == HeapGraphEdge::kHidden
      ? edge->index() : GetStringId(edge->name());
  int buffer_pos = 0;
  if (!first_edge) {
    buffer[buffer_pos++] = ',';
  }
  buffer_pos = utoa(edge->type(), buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer_pos = utoa(edge_name_or_index, buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer_pos = utoa(entry_index(edge->to()), buffer, buffer_pos);
  buffer[buffer_pos++] = '\n';
  buffer[buffer_pos++] = '\0';
  writer_->AddString(buffer.start());
}


void HeapSnapshotJSONSerializer::SerializeEdges() {
  List<HeapGraphEdge*>& edges = snapshot_->children();
  for (int i = 0; i < edges.length(); ++i) {
    ASSERT(i == 0 ||
           edges[i - 1]->from()->index() <= edges[i]->from()->index());
    SerializeEdge(edges[i], i == 0);
    if (writer_->aborted()) return;
  }
}


void HeapSnapshotJSONSerializer::SerializeNode(HeapEntry* entry) {
  // The buffer needs space for 4 unsigned ints, 1 size_t, 5 commas, \n and \0
  static const int kBufferSize =
      5 * MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned  // NOLINT
      + MaxDecimalDigitsIn<sizeof(size_t)>::kUnsigned  // NOLINT
      + 6 + 1 + 1;
  EmbeddedVector<char, kBufferSize> buffer;
  int buffer_pos = 0;
  if (entry_index(entry) != 0) {
    buffer[buffer_pos++] = ',';
  }
  buffer_pos = utoa(entry->type(), buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer_pos = utoa(GetStringId(entry->name()), buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer_pos = utoa(entry->id(), buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer_pos = utoa(entry->self_size(), buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer_pos = utoa(entry->children_count(), buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer_pos = utoa(entry->trace_node_id(), buffer, buffer_pos);
  buffer[buffer_pos++] = '\n';
  buffer[buffer_pos++] = '\0';
  writer_->AddString(buffer.start());
}


void HeapSnapshotJSONSerializer::SerializeNodes() {
  List<HeapEntry>& entries = snapshot_->entries();
  for (int i = 0; i < entries.length(); ++i) {
    SerializeNode(&entries[i]);
    if (writer_->aborted()) return;
  }
}


void HeapSnapshotJSONSerializer::SerializeSnapshot() {
  writer_->AddString("\"title\":\"");
  writer_->AddString(snapshot_->title());
  writer_->AddString("\"");
  writer_->AddString(",\"uid\":");
  writer_->AddNumber(snapshot_->uid());
  writer_->AddString(",\"meta\":");
  // The object describing node serialization layout.
  // We use a set of macros to improve readability.
#define JSON_A(s) "[" s "]"
#define JSON_O(s) "{" s "}"
#define JSON_S(s) "\"" s "\""
  writer_->AddString(JSON_O(
    JSON_S("node_fields") ":" JSON_A(
        JSON_S("type") ","
        JSON_S("name") ","
        JSON_S("id") ","
        JSON_S("self_size") ","
        JSON_S("edge_count") ","
        JSON_S("trace_node_id")) ","
    JSON_S("node_types") ":" JSON_A(
        JSON_A(
            JSON_S("hidden") ","
            JSON_S("array") ","
            JSON_S("string") ","
            JSON_S("object") ","
            JSON_S("code") ","
            JSON_S("closure") ","
            JSON_S("regexp") ","
            JSON_S("number") ","
            JSON_S("native") ","
            JSON_S("synthetic") ","
            JSON_S("concatenated string") ","
            JSON_S("sliced string")) ","
        JSON_S("string") ","
        JSON_S("number") ","
        JSON_S("number") ","
        JSON_S("number") ","
        JSON_S("number") ","
        JSON_S("number")) ","
    JSON_S("edge_fields") ":" JSON_A(
        JSON_S("type") ","
        JSON_S("name_or_index") ","
        JSON_S("to_node")) ","
    JSON_S("edge_types") ":" JSON_A(
        JSON_A(
            JSON_S("context") ","
            JSON_S("element") ","
            JSON_S("property") ","
            JSON_S("internal") ","
            JSON_S("hidden") ","
            JSON_S("shortcut") ","
            JSON_S("weak")) ","
        JSON_S("string_or_number") ","
        JSON_S("node")) ","
    JSON_S("trace_function_info_fields") ":" JSON_A(
        JSON_S("function_id") ","
        JSON_S("name") ","
        JSON_S("script_name") ","
        JSON_S("script_id") ","
        JSON_S("line") ","
        JSON_S("column")) ","
    JSON_S("trace_node_fields") ":" JSON_A(
        JSON_S("id") ","
        JSON_S("function_info_index") ","
        JSON_S("count") ","
        JSON_S("size") ","
        JSON_S("children"))));
#undef JSON_S
#undef JSON_O
#undef JSON_A
  writer_->AddString(",\"node_count\":");
  writer_->AddNumber(snapshot_->entries().length());
  writer_->AddString(",\"edge_count\":");
  writer_->AddNumber(snapshot_->edges().length());
  writer_->AddString(",\"trace_function_count\":");
  uint32_t count = 0;
  AllocationTracker* tracker = snapshot_->profiler()->allocation_tracker();
  if (tracker) {
    count = tracker->function_info_list().length();
  }
  writer_->AddNumber(count);
}


static void WriteUChar(OutputStreamWriter* w, unibrow::uchar u) {
  static const char hex_chars[] = "0123456789ABCDEF";
  w->AddString("\\u");
  w->AddCharacter(hex_chars[(u >> 12) & 0xf]);
  w->AddCharacter(hex_chars[(u >> 8) & 0xf]);
  w->AddCharacter(hex_chars[(u >> 4) & 0xf]);
  w->AddCharacter(hex_chars[u & 0xf]);
}


void HeapSnapshotJSONSerializer::SerializeTraceTree() {
  AllocationTracker* tracker = snapshot_->profiler()->allocation_tracker();
  if (!tracker) return;
  AllocationTraceTree* traces = tracker->trace_tree();
  SerializeTraceNode(traces->root());
}


void HeapSnapshotJSONSerializer::SerializeTraceNode(AllocationTraceNode* node) {
  // The buffer needs space for 4 unsigned ints, 4 commas, [ and \0
  const int kBufferSize =
      4 * MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned  // NOLINT
      + 4 + 1 + 1;
  EmbeddedVector<char, kBufferSize> buffer;
  int buffer_pos = 0;
  buffer_pos = utoa(node->id(), buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer_pos = utoa(node->function_info_index(), buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer_pos = utoa(node->allocation_count(), buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer_pos = utoa(node->allocation_size(), buffer, buffer_pos);
  buffer[buffer_pos++] = ',';
  buffer[buffer_pos++] = '[';
  buffer[buffer_pos++] = '\0';
  writer_->AddString(buffer.start());

  Vector<AllocationTraceNode*> children = node->children();
  for (int i = 0; i < children.length(); i++) {
    if (i > 0) {
      writer_->AddCharacter(',');
    }
    SerializeTraceNode(children[i]);
  }
  writer_->AddCharacter(']');
}


// 0-based position is converted to 1-based during the serialization.
static int SerializePosition(int position, const Vector<char>& buffer,
                             int buffer_pos) {
  if (position == -1) {
    buffer[buffer_pos++] = '0';
  } else {
    ASSERT(position >= 0);
    buffer_pos = utoa(static_cast<unsigned>(position + 1), buffer, buffer_pos);
  }
  return buffer_pos;
}


void HeapSnapshotJSONSerializer::SerializeTraceNodeInfos() {
  AllocationTracker* tracker = snapshot_->profiler()->allocation_tracker();
  if (!tracker) return;
  // The buffer needs space for 6 unsigned ints, 6 commas, \n and \0
  const int kBufferSize =
      6 * MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned  // NOLINT
      + 6 + 1 + 1;
  EmbeddedVector<char, kBufferSize> buffer;
  const List<AllocationTracker::FunctionInfo*>& list =
      tracker->function_info_list();
  bool first_entry = true;
  for (int i = 0; i < list.length(); i++) {
    AllocationTracker::FunctionInfo* info = list[i];
    int buffer_pos = 0;
    if (first_entry) {
      first_entry = false;
    } else {
      buffer[buffer_pos++] = ',';
    }
    buffer_pos = utoa(info->function_id, buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(GetStringId(info->name), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(GetStringId(info->script_name), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    // The cast is safe because script id is a non-negative Smi.
    buffer_pos = utoa(static_cast<unsigned>(info->script_id), buffer,
        buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = SerializePosition(info->line, buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = SerializePosition(info->column, buffer, buffer_pos);
    buffer[buffer_pos++] = '\n';
    buffer[buffer_pos++] = '\0';
    writer_->AddString(buffer.start());
  }
}


void HeapSnapshotJSONSerializer::SerializeString(const unsigned char* s) {
  writer_->AddCharacter('\n');
  writer_->AddCharacter('\"');
  for ( ; *s != '\0'; ++s) {
    switch (*s) {
      case '\b':
        writer_->AddString("\\b");
        continue;
      case '\f':
        writer_->AddString("\\f");
        continue;
      case '\n':
        writer_->AddString("\\n");
        continue;
      case '\r':
        writer_->AddString("\\r");
        continue;
      case '\t':
        writer_->AddString("\\t");
        continue;
      case '\"':
      case '\\':
        writer_->AddCharacter('\\');
        writer_->AddCharacter(*s);
        continue;
      default:
        if (*s > 31 && *s < 128) {
          writer_->AddCharacter(*s);
        } else if (*s <= 31) {
          // Special character with no dedicated literal.
          WriteUChar(writer_, *s);
        } else {
          // Convert UTF-8 into \u UTF-16 literal.
          unsigned length = 1, cursor = 0;
          for ( ; length <= 4 && *(s + length) != '\0'; ++length) { }
          unibrow::uchar c = unibrow::Utf8::CalculateValue(s, length, &cursor);
          if (c != unibrow::Utf8::kBadChar) {
            WriteUChar(writer_, c);
            ASSERT(cursor != 0);
            s += cursor - 1;
          } else {
            writer_->AddCharacter('?');
          }
        }
    }
  }
  writer_->AddCharacter('\"');
}


void HeapSnapshotJSONSerializer::SerializeStrings() {
  ScopedVector<const unsigned char*> sorted_strings(
      strings_.occupancy() + 1);
  for (HashMap::Entry* entry = strings_.Start();
       entry != NULL;
       entry = strings_.Next(entry)) {
    int index = static_cast<int>(reinterpret_cast<uintptr_t>(entry->value));
    sorted_strings[index] = reinterpret_cast<const unsigned char*>(entry->key);
  }
  writer_->AddString("\"<dummy>\"");
  for (int i = 1; i < sorted_strings.length(); ++i) {
    writer_->AddCharacter(',');
    SerializeString(sorted_strings[i]);
    if (writer_->aborted()) return;
  }
}


} }  // namespace v8::internal