[SharedArrayBuffer] Add "AllowShared" extended attribute, used for WebGL

third_party/WebKit/Source/core/dom/ArrayBufferViewHelpers.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ArrayBufferViewHelpers_h
+#define ArrayBufferViewHelpers_h
+
+#include <type_traits>
+#include "core/dom/DOMArrayBufferView.h"
+#include "platform/heap/Handle.h"
+#include "platform/wtf/TypeTraits.h"
+
+namespace blink {
+
+template <typename T>
+class NotShared {
+  // A wrapper template type that is used to ensure that a TypedArray is not

[haraken, 2017/04/13 04:51:12]

Nit: Move the comment to above the class declaration.

[binji, 2017/04/13 18:41:59]

Done.

+  // backed by a SharedArrayBuffer.
+  //
+  // Typically this is used as an annotation on C++ functions that are called by
+  // the bindings layer, e.g.:
+  //
+  //   void Foo(NotShared<DOMUint32Array> param) {
+  //     DOMUint32Array* array = param.View();
+  //     ...
+  //   }
+  static_assert(WTF::IsSubclass<typename std::remove_const<T>::type,
+                                DOMArrayBufferView>::value,
+                "NotShared<T> must have T as subclass of DOMArrayBufferView");
+  STACK_ALLOCATED();
+
+ public:
+  using TypedArrayType = T;
+
+  NotShared() {}
+
+  explicit NotShared(T* typedArray) : typed_array_(typedArray) {
+    DCHECK(!(typedArray && typedArray->View()->IsShared()));
+  }
+  NotShared(const NotShared& other) = default;
+  template <typename U>
+  NotShared(const NotShared<U>& other) : typed_array_(other.View()) {}
+  template <typename U>
+  NotShared(const Member<U>& other) {
+    DCHECK(!other->View()->IsShared());
+    typed_array_ = other.Get();
+  }
+
+  NotShared& operator=(const NotShared& other) = default;
+  template <typename U>
+  NotShared& operator=(const NotShared<U>& other) {
+    typed_array_ = other.View();
+    return *this;
+  }
+
+  T* View() const { return typed_array_.Get(); }
+
+  bool operator!() const { return !typed_array_; }
+  explicit operator bool() const { return !!typed_array_; }
+
+ private:
+  // Must use an untraced member here since this object may be constructed on a
+  // thread without a ThreadState (e.g. an Audio worklet). It is safe in that
+  // case because the pointed-to ArrayBuffer is being kept alive another way
+  // (e.g. CrossThreadPersistent).
+  //
+  // TODO(binji): update to using Member, see crbug.com/710295.
+  UntracedMember<T> typed_array_;
+};
+
+template <typename T>
+class MaybeShared {
+  // A wrapper template type that specifies that a TypedArray may be backed by a

[haraken, 2017/04/13 04:51:12]

Ditto.

[binji, 2017/04/13 18:41:59]

Done.

+  // SharedArrayBuffer.
+  //
+  // Typically this is used as an annotation on C++ functions that are called by
+  // the bindings layer, e.g.:
+  //
+  //   void Foo(MaybeShared<DOMUint32Array> param) {
+  //     DOMUint32Array* array = param.View();
+  //     ...
+  //   }
+  static_assert(WTF::IsSubclass<typename std::remove_const<T>::type,
+                                DOMArrayBufferView>::value,
+                "MaybeShared<T> must have T as subclass of DOMArrayBufferView");
+  STACK_ALLOCATED();
+
+ public:
+  using TypedArrayType = T;
+
+  MaybeShared() {}
+
+  explicit MaybeShared(T* typedArray) : typed_array_(typedArray) {}
+  MaybeShared(const MaybeShared& other) = default;
+  template <typename U>
+  MaybeShared(const MaybeShared<U>& other) : typed_array_(other.View()) {}
+  template <typename U>
+  MaybeShared(const Member<U>& other) {
+    typed_array_ = other.Get();
+  }
+
+  MaybeShared& operator=(const MaybeShared& other) = default;
+  template <typename U>
+  MaybeShared& operator=(const MaybeShared<U>& other) {
+    typed_array_ = other.View();
+    return *this;
+  }
+
+  T* View() const { return typed_array_.Get(); }
+
+  bool operator!() const { return !typed_array_; }
+  explicit operator bool() const { return !!typed_array_; }
+
+ private:
+  Member<T> typed_array_;
+};
+
+}  // namespace blink
+
+#endif  // ArrayBufferViewHelpers_h