gin/array_buffer.cc

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include <stdlib.h>
   6
   7 #include "base/logging.h"
   8 #include "gin/array_buffer.h"
   9 #include "gin/per_isolate_data.h"
  10
  11 namespace gin {
  12
  13 namespace {
  14
  15 gin::WrapperInfo g_array_buffer_wrapper_info = {gin::kEmbedderNativeGin};
  16
  17 }  // namespace
  18
  19 COMPILE_ASSERT(V8_ARRAY_BUFFER_INTERNAL_FIELD_COUNT == 2,
  20                array_buffers_must_have_two_internal_fields);
  21
  22 // ArrayBufferAllocator -------------------------------------------------------
  23
  24 void* ArrayBufferAllocator::Allocate(size_t length) {
  25   return calloc(1, length);
  26 }
  27
  28 void* ArrayBufferAllocator::AllocateUninitialized(size_t length) {
  29   return malloc(length);
  30 }
  31
  32 void ArrayBufferAllocator::Free(void* data, size_t length) {
  33   free(data);
  34 }
  35
  36 ArrayBufferAllocator* ArrayBufferAllocator::SharedInstance() {
  37   static ArrayBufferAllocator* instance = new ArrayBufferAllocator();
  38   return instance;
  39 }
  40
  41 // ArrayBuffer::Private -------------------------------------------------------
  42
  43 // This class exists to solve a tricky lifetime problem. The V8 API doesn't
  44 // want to expose a direct view into the memory behind an array buffer because
  45 // V8 might deallocate that memory during garbage collection. Instead, the V8
  46 // API forces us to externalize the buffer and take ownership of the memory.
  47 // In order to know when to free the memory, we need to figure out both when
  48 // we're done with it and when V8 is done with it.
  49 //
  50 // To determine whether we're done with the memory, every view we have into
  51 // the array buffer takes a reference to the ArrayBuffer::Private object that
  52 // actually owns the memory. To determine when V8 is done with the memory, we
  53 // open a weak handle to the ArrayBuffer object. When we receive the weak
  54 // callback, we know the object is about to be garbage collected and we can
  55 // drop V8's implied reference to the memory.
  56 //
  57 // The final subtlety is that we need every ArrayBuffer into the same array
  58 // buffer to AddRef the same ArrayBuffer::Private. To make that work, we store
  59 // a pointer to the ArrayBuffer::Private object in an internal field of the
  60 // ArrayBuffer object.
  61 //
  62 class ArrayBuffer::Private : public base::RefCounted<ArrayBuffer::Private> {
  63  public:
  64   static scoped_refptr<Private> From(v8::Isolate* isolate,
  65                                      v8::Handle<v8::ArrayBuffer> array);
  66
  67   void* buffer() const { return buffer_; }
  68   size_t length() const { return length_; }
  69
  70  private:
  71   friend class base::RefCounted<Private>;
  72
  73   Private(v8::Isolate* isolate, v8::Handle<v8::ArrayBuffer> array);
  74   ~Private();
  75
  76   static void WeakCallback(
  77       const v8::WeakCallbackData<v8::ArrayBuffer, Private>& data);
  78
  79   v8::Persistent<v8::ArrayBuffer> array_buffer_;
  80   scoped_refptr<Private> self_reference_;
  81   v8::Isolate* isolate_;
  82   void* buffer_;
  83   size_t length_;
  84 };
  85
  86 scoped_refptr<ArrayBuffer::Private> ArrayBuffer::Private::From(
  87     v8::Isolate* isolate, v8::Handle<v8::ArrayBuffer> array) {
  88   if (array->IsExternal()) {
  89     CHECK_EQ(WrapperInfo::From(v8::Handle<v8::Object>::Cast(array)),
  90              &g_array_buffer_wrapper_info)
  91         << "Cannot mix blink and gin ArrayBuffers";
  92     return make_scoped_refptr(static_cast<Private*>(
  93         array->GetAlignedPointerFromInternalField(kEncodedValueIndex)));
  94   }
  95   return make_scoped_refptr(new Private(isolate, array));
  96 }
  97
  98 ArrayBuffer::Private::Private(v8::Isolate* isolate,
  99                               v8::Handle<v8::ArrayBuffer> array)
 100     : array_buffer_(isolate, array), isolate_(isolate) {
 101   // Take ownership of the array buffer.
 102   CHECK(!array->IsExternal());
 103   v8::ArrayBuffer::Contents contents = array->Externalize();
 104   buffer_ = contents.Data();
 105   length_ = contents.ByteLength();
 106
 107   array->SetAlignedPointerInInternalField(kWrapperInfoIndex,
 108                                           &g_array_buffer_wrapper_info);
 109   array->SetAlignedPointerInInternalField(kEncodedValueIndex, this);
 110
 111   self_reference_ = this;  // Cleared in WeakCallback.
 112   array_buffer_.SetWeak(this, WeakCallback);
 113 }
 114
 115 ArrayBuffer::Private::~Private() {
 116   PerIsolateData::From(isolate_)->allocator()->Free(buffer_, length_);
 117 }
 118
 119 void ArrayBuffer::Private::WeakCallback(
 120     const v8::WeakCallbackData<v8::ArrayBuffer, Private>& data) {
 121   Private* parameter = data.GetParameter();
 122   parameter->array_buffer_.Reset();
 123   parameter->self_reference_ = NULL;
 124 }
 125
 126 // ArrayBuffer ----------------------------------------------------------------
 127
 128 ArrayBuffer::ArrayBuffer()
 129     : bytes_(0),
 130       num_bytes_(0) {
 131 }
 132
 133 ArrayBuffer::ArrayBuffer(v8::Isolate* isolate,
 134                          v8::Handle<v8::ArrayBuffer> array) {
 135   private_ = ArrayBuffer::Private::From(isolate, array);
 136   bytes_ = private_->buffer();
 137   num_bytes_ = private_->length();
 138 }
 139
 140 ArrayBuffer::~ArrayBuffer() {
 141 }
 142
 143 ArrayBuffer& ArrayBuffer::operator=(const ArrayBuffer& other) {
 144   private_ = other.private_;
 145   bytes_ = other.bytes_;
 146   num_bytes_ = other.num_bytes_;
 147   return *this;
 148 }
 149
 150 // Converter<ArrayBuffer> -----------------------------------------------------
 151
 152 bool Converter<ArrayBuffer>::FromV8(v8::Isolate* isolate,
 153                                     v8::Handle<v8::Value> val,
 154                                     ArrayBuffer* out) {
 155   if (!val->IsArrayBuffer())
 156     return false;
 157   *out = ArrayBuffer(isolate, v8::Handle<v8::ArrayBuffer>::Cast(val));
 158   return true;
 159 }
 160
 161 // ArrayBufferView ------------------------------------------------------------
 162
 163 ArrayBufferView::ArrayBufferView()
 164     : offset_(0),
 165       num_bytes_(0) {
 166 }
 167
 168 ArrayBufferView::ArrayBufferView(v8::Isolate* isolate,
 169                                  v8::Handle<v8::ArrayBufferView> view)
 170     : array_buffer_(isolate, view->Buffer()),
 171       offset_(view->ByteOffset()),
 172       num_bytes_(view->ByteLength()) {
 173 }
 174
 175 ArrayBufferView::~ArrayBufferView() {
 176 }
 177
 178 // Converter<ArrayBufferView> -------------------------------------------------
 179
 180 bool Converter<ArrayBufferView>::FromV8(v8::Isolate* isolate,
 181                                         v8::Handle<v8::Value> val,
 182                                         ArrayBufferView* out) {
 183   if (!val->IsArrayBufferView())
 184     return false;
 185   *out = ArrayBufferView(isolate, v8::Handle<v8::ArrayBufferView>::Cast(val));
 186   return true;
 187 }
 188
 189 }  // namespace gin