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// Copyright 2015 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 <unordered_map>
#include "src/base/platform/mutex.h"
#include "src/common/globals.h"
#include "src/objects/js-array-buffer.h"
#include "src/utils/allocation.h"
namespace v8 {
namespace internal {
class MarkingState;
class Page;
class Space;
class ArrayBufferTracker : public AllStatic {
enum ProcessingMode {
// The following methods are used to track raw C++ pointers to externally
// allocated memory used as backing store in live array buffers.
// Register/unregister a new JSArrayBuffer |buffer| for tracking. Guards all
// access to the tracker by taking the page lock for the corresponding page.
inline static void RegisterNew(Heap* heap, JSArrayBuffer buffer);
inline static void Unregister(Heap* heap, JSArrayBuffer buffer);
// Identifies all backing store pointers for dead JSArrayBuffers in new space.
// Does not take any locks and can only be called during Scavenge.
static void PrepareToFreeDeadInNewSpace(Heap* heap);
// Frees all backing store pointers for dead JSArrayBuffer on a given page.
// Requires marking information to be present. Requires the page lock to be
// taken by the caller.
template <typename MarkingState>
static void FreeDead(Page* page, MarkingState* marking_state);
// Frees all remaining, live or dead, array buffers on a page. Only useful
// during tear down.
static void FreeAll(Page* page);
// Processes all array buffers on a given page. |mode| specifies the action
// to perform on the buffers. Returns whether the tracker is empty or not.
static bool ProcessBuffers(Page* page, ProcessingMode mode);
// Returns whether a buffer is currently tracked.
V8_EXPORT_PRIVATE static bool IsTracked(JSArrayBuffer buffer);
// Tears down the tracker and frees up all registered array buffers.
static void TearDown(Heap* heap);
// LocalArrayBufferTracker tracks internalized array buffers.
// Never use directly but instead always call through |ArrayBufferTracker|.
class LocalArrayBufferTracker {
enum CallbackResult { kKeepEntry, kUpdateEntry, kRemoveEntry };
enum FreeMode { kFreeDead, kFreeAll };
explicit LocalArrayBufferTracker(Page* page) : page_(page) {}
inline void Add(JSArrayBuffer buffer, size_t length);
inline void Remove(JSArrayBuffer buffer, size_t length);
// Frees up array buffers.
// Sample usage:
// Free([](HeapObject array_buffer) {
// if (should_free_internal(array_buffer)) return true;
// return false;
// });
template <typename Callback>
void Free(Callback should_free);
// Processes buffers one by one. The CallbackResult of the callback decides
// what action to take on the buffer.
// Callback should be of type:
// CallbackResult fn(JSArrayBuffer buffer, JSArrayBuffer* new_buffer);
template <typename Callback>
void Process(Callback callback);
bool IsEmpty() const { return array_buffers_.empty(); }
bool IsTracked(JSArrayBuffer buffer) const {
return array_buffers_.find(buffer) != array_buffers_.end();
class Hasher {
size_t operator()(JSArrayBuffer buffer) const {
return static_cast<size_t>(buffer.ptr() >> 3);
// Keep track of the backing store and the corresponding length at time of
// registering. The length is accessed from JavaScript and can be a
// HeapNumber. The reason for tracking the length is that in the case of
// length being a HeapNumber, the buffer and its length may be stored on
// different memory pages, making it impossible to guarantee order of freeing.
using TrackingData =
std::unordered_map<JSArrayBuffer, JSArrayBuffer::Allocation, Hasher>;
// Internal version of add that does not update counters. Requires separate
// logic for updating external memory counters.
inline void AddInternal(JSArrayBuffer buffer, size_t length);
Page* page_;
// The set contains raw heap pointers which are removed by the GC upon
// processing the tracker through its owning page.
TrackingData array_buffers_;
} // namespace internal
} // namespace v8