Implement SharedArrayBuffer.

This adds a new external type (v8::SharedArrayBuffer) that uses a JSArrayBuffer under the hood. It can be distinguished from an ArrayBuffer by the newly-added is_shared() bit.

Currently there is no difference in functionality between a SharedArrayBuffer and an ArrayBuffer. However, a future CL will add the Atomics API, which is only available on an SharedArrayBuffer. All non-atomic accesses are identical to ArrayBuffer accesses.

BUG=

Review URL: https://codereview.chromium.org/1136553006

Cr-Commit-Position: refs/heads/master@{#28588}

BUILD.gn

@@ -276,7 +276,8 @@ action("js2c_experimental") {
     "src/harmony-regexp.js",
     "src/harmony-reflect.js",
     "src/harmony-spread.js",
-    "src/harmony-object.js"
+    "src/harmony-object.js",
+    "src/harmony-sharedarraybuffer.js"
   ]
 
   outputs = [

include/v8.h

@@ -1920,6 +1920,13 @@ class V8_EXPORT Value : public Data {
    */
   bool IsDataView() const;
 
+  /**
+   * Returns true if this value is a SharedArrayBuffer.
+   * This is an experimental feature.
+   */
+  bool IsSharedArrayBuffer() const;
+
+
   V8_WARN_UNUSED_RESULT MaybeLocal<Boolean> ToBoolean(
       Local<Context> context) const;
   V8_WARN_UNUSED_RESULT MaybeLocal<Number> ToNumber(
@@ -3344,7 +3351,7 @@ class V8_EXPORT ArrayBuffer : public Object {
       ArrayBufferCreationMode mode = ArrayBufferCreationMode::kExternalized);
 
   /**
-   * Returns true if ArrayBuffer is extrenalized, that is, does not
+   * Returns true if ArrayBuffer is externalized, that is, does not
    * own its memory block.
    */
   bool IsExternal() const;
@@ -3630,6 +3637,105 @@ class V8_EXPORT DataView : public ArrayBufferView {
 };
 
 
+/**
+ * An instance of the built-in SharedArrayBuffer constructor.
+ * This API is experimental and may change significantly.
+ */
+class V8_EXPORT SharedArrayBuffer : public Object {
+ public:
+  /**
+   * The contents of an |SharedArrayBuffer|. Externalization of
+   * |SharedArrayBuffer| returns an instance of this class, populated, with a
+   * pointer to data and byte length.
+   *
+   * The Data pointer of SharedArrayBuffer::Contents is always allocated with
+   * |ArrayBuffer::Allocator::Allocate| by the allocator specified in
+   * v8::Isolate::CreateParams::array_buffer_allocator.
+   *
+   * This API is experimental and may change significantly.
+   */
+  class V8_EXPORT Contents {  // NOLINT
+   public:
+    Contents() : data_(NULL), byte_length_(0) {}
+
+    void* Data() const { return data_; }
+    size_t ByteLength() const { return byte_length_; }
+
+   private:
+    void* data_;
+    size_t byte_length_;
+
+    friend class SharedArrayBuffer;
+  };
+
+
+  /**
+   * Data length in bytes.
+   */
+  size_t ByteLength() const;
+
+  /**
+   * Create a new SharedArrayBuffer. Allocate |byte_length| bytes.
+   * Allocated memory will be owned by a created SharedArrayBuffer and
+   * will be deallocated when it is garbage-collected,
+   * unless the object is externalized.
+   */
+  static Local<SharedArrayBuffer> New(Isolate* isolate, size_t byte_length);
+
+  /**
+   * Create a new SharedArrayBuffer over an existing memory block.  The created
+   * array buffer is immediately in externalized state unless otherwise
+   * specified. The memory block will not be reclaimed when a created
+   * SharedArrayBuffer is garbage-collected.
+   */
+  static Local<SharedArrayBuffer> New(
+      Isolate* isolate, void* data, size_t byte_length,
+      ArrayBufferCreationMode mode = ArrayBufferCreationMode::kExternalized);
+
+  /**
+   * Returns true if SharedArrayBuffer is externalized, that is, does not
+   * own its memory block.
+   */
+  bool IsExternal() const;
+
+  /**
+   * Make this SharedArrayBuffer external. The pointer to underlying memory
+   * block and byte length are returned as |Contents| structure. After
+   * SharedArrayBuffer had been etxrenalized, it does no longer owns the memory
+   * block. The caller should take steps to free memory when it is no longer
+   * needed.
+   *
+   * The memory block is guaranteed to be allocated with |Allocator::Allocate|
+   * by the allocator specified in
+   * v8::Isolate::CreateParams::array_buffer_allocator.
+   *
+   */
+  Contents Externalize();
+
+  /**
+   * Get a pointer to the ArrayBuffer's underlying memory block without
+   * externalizing it. If the ArrayBuffer is not externalized, this pointer
+   * will become invalid as soon as the ArrayBuffer became garbage collected.
+   *
+   * The embedder should make sure to hold a strong reference to the
+   * ArrayBuffer while accessing this pointer.
+   *
+   * The memory block is guaranteed to be allocated with |Allocator::Allocate|
+   * by the allocator specified in
+   * v8::Isolate::CreateParams::array_buffer_allocator.
+   */
+  Contents GetContents();
+
+  V8_INLINE static SharedArrayBuffer* Cast(Value* obj);
+
+  static const int kInternalFieldCount = V8_ARRAY_BUFFER_INTERNAL_FIELD_COUNT;
+
+ private:
+  SharedArrayBuffer();
+  static void CheckCast(Value* obj);
+};
+
+
 /**
  * An instance of the built-in Date constructor (ECMA-262, 15.9).
  */
@@ -7817,6 +7923,14 @@ DataView* DataView::Cast(v8::Value* value) {
 }
 
 
+SharedArrayBuffer* SharedArrayBuffer::Cast(v8::Value* value) {
+#ifdef V8_ENABLE_CHECKS
+  CheckCast(value);
+#endif
+  return static_cast<SharedArrayBuffer*>(value);
+}
+
+
 Function* Function::Cast(v8::Value* value) {
 #ifdef V8_ENABLE_CHECKS
   CheckCast(value);

src/api.cc

@@ -2679,7 +2679,8 @@ bool Value::IsArray() const {
 
 
 bool Value::IsArrayBuffer() const {
-  return Utils::OpenHandle(this)->IsJSArrayBuffer();
+  i::Handle<i::Object> obj = Utils::OpenHandle(this);
+  return obj->IsJSArrayBuffer() && !i::JSArrayBuffer::cast(*obj)->is_shared();
 }
 
 
@@ -2700,6 +2701,7 @@ bool Value::IsTypedArray() const {
            i::JSTypedArray::cast(*obj)->type() == i::kExternal##Type##Array; \
   }
 
+
 TYPED_ARRAYS(VALUE_IS_TYPED_ARRAY)
 
 #undef VALUE_IS_TYPED_ARRAY
@@ -2710,6 +2712,12 @@ bool Value::IsDataView() const {
 }
 
 
+bool Value::IsSharedArrayBuffer() const {
+  i::Handle<i::Object> obj = Utils::OpenHandle(this);
+  return obj->IsJSArrayBuffer() && i::JSArrayBuffer::cast(*obj)->is_shared();
+}
+
+
 bool Value::IsObject() const {
   return Utils::OpenHandle(this)->IsJSObject();
 }
@@ -3086,9 +3094,9 @@ void v8::Promise::Resolver::CheckCast(Value* that) {
 
 void v8::ArrayBuffer::CheckCast(Value* that) {
   i::Handle<i::Object> obj = Utils::OpenHandle(that);
-  Utils::ApiCheck(obj->IsJSArrayBuffer(),
-                  "v8::ArrayBuffer::Cast()",
-                  "Could not convert to ArrayBuffer");
+  Utils::ApiCheck(
+      obj->IsJSArrayBuffer() && !i::JSArrayBuffer::cast(*obj)->is_shared(),
+      "v8::ArrayBuffer::Cast()", "Could not convert to ArrayBuffer");
 }
 
 
@@ -3131,6 +3139,15 @@ void v8::DataView::CheckCast(Value* that) {
 }
 
 
+void v8::SharedArrayBuffer::CheckCast(Value* that) {
+  i::Handle<i::Object> obj = Utils::OpenHandle(that);
+  Utils::ApiCheck(
+      obj->IsJSArrayBuffer() && i::JSArrayBuffer::cast(*obj)->is_shared(),
+      "v8::SharedArrayBuffer::Cast()",
+      "Could not convert to SharedArrayBuffer");
+}
+
+
 void v8::Date::CheckCast(v8::Value* that) {
   i::Handle<i::Object> obj = Utils::OpenHandle(that);
   i::Isolate* isolate = NULL;
@@ -6305,7 +6322,7 @@ Local<ArrayBuffer> v8::ArrayBuffer::New(Isolate* isolate, size_t byte_length) {
   LOG_API(i_isolate, "v8::ArrayBuffer::New(size_t)");
   ENTER_V8(i_isolate);
   i::Handle<i::JSArrayBuffer> obj =
-      i_isolate->factory()->NewJSArrayBuffer();
+      i_isolate->factory()->NewJSArrayBuffer(i::SharedFlag::kNotShared);
   i::Runtime::SetupArrayBufferAllocatingData(i_isolate, obj, byte_length);
   return Utils::ToLocal(obj);
 }
@@ -6318,7 +6335,7 @@ Local<ArrayBuffer> v8::ArrayBuffer::New(Isolate* isolate, void* data,
   LOG_API(i_isolate, "v8::ArrayBuffer::New(void*, size_t)");
   ENTER_V8(i_isolate);
   i::Handle<i::JSArrayBuffer> obj =
-      i_isolate->factory()->NewJSArrayBuffer();
+      i_isolate->factory()->NewJSArrayBuffer(i::SharedFlag::kNotShared);
   i::Runtime::SetupArrayBuffer(i_isolate, obj,
                                mode == ArrayBufferCreationMode::kExternalized,
                                data, byte_length);
@@ -6424,6 +6441,66 @@ Local<DataView> DataView::New(Handle<ArrayBuffer> array_buffer,
 }
 
 
+bool v8::SharedArrayBuffer::IsExternal() const {
+  return Utils::OpenHandle(this)->is_external();
+}
+
+
+v8::SharedArrayBuffer::Contents v8::SharedArrayBuffer::Externalize() {
+  i::Handle<i::JSArrayBuffer> self = Utils::OpenHandle(this);
+  i::Isolate* isolate = self->GetIsolate();
+  Utils::ApiCheck(!self->is_external(), "v8::SharedArrayBuffer::Externalize",
+                  "SharedArrayBuffer already externalized");
+  self->set_is_external(true);
+  isolate->heap()->UnregisterArrayBuffer(self->backing_store());
+  return GetContents();
+}
+
+
+v8::SharedArrayBuffer::Contents v8::SharedArrayBuffer::GetContents() {
+  i::Handle<i::JSArrayBuffer> self = Utils::OpenHandle(this);
+  size_t byte_length = static_cast<size_t>(self->byte_length()->Number());
+  Contents contents;
+  contents.data_ = self->backing_store();
+  contents.byte_length_ = byte_length;
+  return contents;
+}
+
+
+size_t v8::SharedArrayBuffer::ByteLength() const {
+  i::Handle<i::JSArrayBuffer> obj = Utils::OpenHandle(this);
+  return static_cast<size_t>(obj->byte_length()->Number());
+}
+
+
+Local<SharedArrayBuffer> v8::SharedArrayBuffer::New(Isolate* isolate,
+                                                    size_t byte_length) {
+  i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
+  LOG_API(i_isolate, "v8::SharedArrayBuffer::New(size_t)");
+  ENTER_V8(i_isolate);
+  i::Handle<i::JSArrayBuffer> obj =
+      i_isolate->factory()->NewJSArrayBuffer(i::SharedFlag::kShared);
+  i::Runtime::SetupArrayBufferAllocatingData(i_isolate, obj, byte_length, true,
+                                             i::SharedFlag::kShared);
+  return Utils::ToLocalShared(obj);
+}
+
+
+Local<SharedArrayBuffer> v8::SharedArrayBuffer::New(
+    Isolate* isolate, void* data, size_t byte_length,
+    ArrayBufferCreationMode mode) {
+  i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
+  LOG_API(i_isolate, "v8::SharedArrayBuffer::New(void*, size_t)");
+  ENTER_V8(i_isolate);
+  i::Handle<i::JSArrayBuffer> obj =
+      i_isolate->factory()->NewJSArrayBuffer(i::SharedFlag::kShared);
+  i::Runtime::SetupArrayBuffer(i_isolate, obj,
+                               mode == ArrayBufferCreationMode::kExternalized,
+                               data, byte_length, i::SharedFlag::kShared);
+  return Utils::ToLocalShared(obj);
+}
+
+
 Local<Symbol> v8::Symbol::New(Isolate* isolate, Local<String> name) {
   i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
   LOG_API(i_isolate, "Symbol::New()");

src/api.h

@@ -159,6 +159,7 @@ class RegisteredExtension {
   V(Float32Array, JSTypedArray)              \
   V(Float64Array, JSTypedArray)              \
   V(DataView, JSDataView)                    \
+  V(SharedArrayBuffer, JSArrayBuffer)        \
   V(Name, Name)                              \
   V(String, String)                          \
   V(Symbol, Symbol)                          \
@@ -230,6 +231,9 @@ class Utils {
   static inline Local<Float64Array> ToLocalFloat64Array(
       v8::internal::Handle<v8::internal::JSTypedArray> obj);
 
+  static inline Local<SharedArrayBuffer> ToLocalShared(
+      v8::internal::Handle<v8::internal::JSArrayBuffer> obj);
+
   static inline Local<Message> MessageToLocal(
       v8::internal::Handle<v8::internal::Object> obj);
   static inline Local<Promise> PromiseToLocal(
@@ -360,6 +364,7 @@ MAKE_TO_LOCAL(ToLocal, JSArrayBuffer, ArrayBuffer)
 MAKE_TO_LOCAL(ToLocal, JSArrayBufferView, ArrayBufferView)
 MAKE_TO_LOCAL(ToLocal, JSDataView, DataView)
 MAKE_TO_LOCAL(ToLocal, JSTypedArray, TypedArray)
+MAKE_TO_LOCAL(ToLocalShared, JSArrayBuffer, SharedArrayBuffer)
 
 TYPED_ARRAYS(MAKE_TO_LOCAL_TYPED_ARRAY)
 

src/arraybuffer.js

@@ -28,7 +28,7 @@ utils.Import(function(from) {
 function ArrayBufferConstructor(length) { // length = 1
   if (%_IsConstructCall()) {
     var byteLength = $toPositiveInteger(length, kInvalidArrayBufferLength);
-    %ArrayBufferInitialize(this, byteLength);
+    %ArrayBufferInitialize(this, byteLength, kNotShared);
   } else {
     throw MakeTypeError(kConstructorNotFunction, "ArrayBuffer");
   }

src/bootstrapper.cc

@@ -1753,6 +1753,7 @@ EMPTY_NATIVE_FUNCTIONS_FOR_FEATURE(harmony_spreadcalls)
 EMPTY_NATIVE_FUNCTIONS_FOR_FEATURE(harmony_destructuring)
 EMPTY_NATIVE_FUNCTIONS_FOR_FEATURE(harmony_object)
 EMPTY_NATIVE_FUNCTIONS_FOR_FEATURE(harmony_spread_arrays)
+EMPTY_NATIVE_FUNCTIONS_FOR_FEATURE(harmony_sharedarraybuffer)
 
 
 void Genesis::InstallNativeFunctions_harmony_proxies() {
@@ -1846,6 +1847,20 @@ void Genesis::InitializeGlobal_harmony_tostring() {
 }
 
 
+void Genesis::InitializeGlobal_harmony_sharedarraybuffer() {
+  if (!FLAG_harmony_sharedarraybuffer) return;
+
+  Handle<JSGlobalObject> global(
+      JSGlobalObject::cast(native_context()->global_object()));
+
+  Handle<JSFunction> shared_array_buffer_fun = InstallFunction(
+      global, "SharedArrayBuffer", JS_ARRAY_BUFFER_TYPE,
+      JSArrayBuffer::kSizeWithInternalFields,
+      isolate()->initial_object_prototype(), Builtins::kIllegal);
+  native_context()->set_shared_array_buffer_fun(*shared_array_buffer_fun);
+}
+
+
 Handle<JSFunction> Genesis::InstallInternalArray(Handle<JSObject> target,
                                                  const char* name,
                                                  ElementsKind elements_kind) {
@@ -2410,6 +2425,8 @@ bool Genesis::InstallExperimentalNatives() {
   static const char* harmony_object_natives[] = {"native harmony-object.js",
                                                  NULL};
   static const char* harmony_spread_arrays_natives[] = {nullptr};
+  static const char* harmony_sharedarraybuffer_natives[] = {
+      "native harmony-sharedarraybuffer.js", NULL};
 
   for (int i = ExperimentalNatives::GetDebuggerCount();
        i < ExperimentalNatives::GetBuiltinsCount(); i++) {

src/contexts.h

@@ -103,6 +103,7 @@ enum BindingFlags {
   V(TO_LENGTH_FUN_INDEX, JSFunction, to_length_fun)                            \
   V(GLOBAL_EVAL_FUN_INDEX, JSFunction, global_eval_fun)                        \
   V(ARRAY_BUFFER_FUN_INDEX, JSFunction, array_buffer_fun)                      \
+  V(SHARED_ARRAY_BUFFER_FUN_INDEX, JSFunction, shared_array_buffer_fun)        \
   V(ARRAY_BUFFER_MAP_INDEX, Map, array_buffer_map)                             \
   V(UINT8_ARRAY_FUN_INDEX, JSFunction, uint8_array_fun)                        \
   V(INT8_ARRAY_FUN_INDEX, JSFunction, int8_array_fun)                          \
@@ -381,6 +382,7 @@ class Context: public FixedArray {
     FLOAT64_ARRAY_EXTERNAL_MAP_INDEX,
     UINT8_CLAMPED_ARRAY_EXTERNAL_MAP_INDEX,
     DATA_VIEW_FUN_INDEX,
+    SHARED_ARRAY_BUFFER_FUN_INDEX,
     MESSAGE_LISTENERS_INDEX,
     MAKE_MESSAGE_FUN_INDEX,
     GET_STACK_TRACE_LINE_INDEX,