dom/bindings/TypedArray.h
author James Teh <jteh@mozilla.com>
Thu, 07 Mar 2019 18:10:13 +0000
changeset 520910 c26d4a8d43c4d0d6f6e13135b8f35924123fe99e
parent 520218 f4e9e5429fd82f9c3787ca2d42798a2bf3d353f9
permissions -rw-r--r--
Bug 1527922: Ensure the Reload button is disabled when testing against blank tabs in the browser toolbar key nav tests. r=Gijs For a blank tab, the Reload button should be disabled. These tests depend on this. This seems to be true when setting the new tab page to blank in Firefox Options. However, when we open about:blank with BrowserTestUtils.withNewTab, this is unreliable. That is, sometimes the Reload button is enabled, sometimes it isn't. I don't understand why this happens. For the purposes of these tests, just force the Reload button to be disabled for new, blank tabs so we get consistent results. Differential Revision: https://phabricator.services.mozilla.com/D22449

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_dom_TypedArray_h
#define mozilla_dom_TypedArray_h

#include "jsfriendapi.h"  // js::Scalar
#include "js/ArrayBuffer.h"
#include "js/SharedArrayBuffer.h"
#include "js/GCAPI.h"       // JS::AutoCheckCannotGC
#include "js/RootingAPI.h"  // JS::Rooted
#include "mozilla/Attributes.h"
#include "mozilla/Move.h"
#include "mozilla/dom/BindingDeclarations.h"
#include "mozilla/dom/SpiderMonkeyInterface.h"
#include "nsWrapperCache.h"

namespace mozilla {
namespace dom {

/*
 * Various typed array classes for argument conversion.  We have a base class
 * that has a way of initializing a TypedArray from an existing typed array, and
 * a subclass of the base class that supports creation of a relevant typed array
 * or array buffer object.
 */
template <typename T, JSObject* UnwrapArray(JSObject*),
          void GetLengthAndDataAndSharedness(JSObject*, uint32_t*, bool*, T**)>
struct TypedArray_base : public SpiderMonkeyInterfaceObjectStorage,
                         AllTypedArraysBase {
  typedef T element_type;

  TypedArray_base()
      : mData(nullptr), mLength(0), mShared(false), mComputed(false) {}

  TypedArray_base(TypedArray_base&& aOther)
      : SpiderMonkeyInterfaceObjectStorage(std::move(aOther)),
        mData(aOther.mData),
        mLength(aOther.mLength),
        mShared(aOther.mShared),
        mComputed(aOther.mComputed) {
    aOther.mData = nullptr;
    aOther.mLength = 0;
    aOther.mShared = false;
    aOther.mComputed = false;
  }

 private:
  mutable T* mData;
  mutable uint32_t mLength;
  mutable bool mShared;
  mutable bool mComputed;

 public:
  inline bool Init(JSObject* obj) {
    MOZ_ASSERT(!inited());
    mImplObj = mWrappedObj = UnwrapArray(obj);
    return inited();
  }

  // About shared memory:
  //
  // Any DOM TypedArray as well as any DOM ArrayBufferView can map the
  // memory of either a JS ArrayBuffer or a JS SharedArrayBuffer.  If
  // the TypedArray maps a SharedArrayBuffer the Length() and Data()
  // accessors on the DOM view will return zero and nullptr; to get
  // the actual length and data, call the LengthAllowShared() and
  // DataAllowShared() accessors instead.
  //
  // Two methods are available for determining if a DOM view maps
  // shared memory.  The IsShared() method is cheap and can be called
  // if the view has been computed; the JS_GetTypedArraySharedness()
  // method is slightly more expensive and can be called on the Obj()
  // value if the view may not have been computed and if the value is
  // known to represent a JS TypedArray.
  //
  // (Just use JS::IsSharedArrayBuffer() to test if any object is of
  // that type.)
  //
  // Code that elects to allow views that map shared memory to be used
  // -- ie, code that "opts in to shared memory" -- should generally
  // not access the raw data buffer with standard C++ mechanisms as
  // that creates the possibility of C++ data races, which is
  // undefined behavior.  The JS engine will eventually export (bug
  // 1225033) a suite of methods that avoid undefined behavior.
  //
  // Callers of Obj() that do not opt in to shared memory can produce
  // better diagnostics by checking whether the JSObject in fact maps
  // shared memory and throwing an error if it does.  However, it is
  // safe to use the value of Obj() without such checks.
  //
  // The DOM TypedArray abstraction prevents the underlying buffer object
  // from being accessed directly, but JS_GetArrayBufferViewBuffer(Obj())
  // will obtain the buffer object.  Code that calls that function must
  // not assume the returned buffer is an ArrayBuffer.  That is guarded
  // against by an out parameter on that call that communicates the
  // sharedness of the buffer.
  //
  // Finally, note that the buffer memory of a SharedArrayBuffer is
  // not detachable.

  inline bool IsShared() const {
    MOZ_ASSERT(mComputed);
    return mShared;
  }

  inline T* Data() const {
    MOZ_ASSERT(mComputed);
    if (mShared) return nullptr;
    return mData;
  }

  inline T* DataAllowShared() const {
    MOZ_ASSERT(mComputed);
    return mData;
  }

  inline uint32_t Length() const {
    MOZ_ASSERT(mComputed);
    if (mShared) return 0;
    return mLength;
  }

  inline uint32_t LengthAllowShared() const {
    MOZ_ASSERT(mComputed);
    return mLength;
  }

  inline void ComputeLengthAndData() const {
    MOZ_ASSERT(inited());
    MOZ_ASSERT(!mComputed);
    GetLengthAndDataAndSharedness(mImplObj, &mLength, &mShared, &mData);
    mComputed = true;
  }

 private:
  TypedArray_base(const TypedArray_base&) = delete;
};

template <typename T, JSObject* UnwrapArray(JSObject*),
          T* GetData(JSObject*, bool* isShared, const JS::AutoRequireNoGC&),
          void GetLengthAndDataAndSharedness(JSObject*, uint32_t*, bool*, T**),
          JSObject* CreateNew(JSContext*, uint32_t)>
struct TypedArray
    : public TypedArray_base<T, UnwrapArray, GetLengthAndDataAndSharedness> {
 private:
  typedef TypedArray_base<T, UnwrapArray, GetLengthAndDataAndSharedness> Base;

 public:
  TypedArray() : Base() {}

  TypedArray(TypedArray&& aOther) : Base(std::move(aOther)) {}

  static inline JSObject* Create(JSContext* cx, nsWrapperCache* creator,
                                 uint32_t length, const T* data = nullptr) {
    JS::Rooted<JSObject*> creatorWrapper(cx);
    Maybe<JSAutoRealm> ar;
    if (creator && (creatorWrapper = creator->GetWrapperPreserveColor())) {
      ar.emplace(cx, creatorWrapper);
    }

    return CreateCommon(cx, length, data);
  }

  static inline JSObject* Create(JSContext* cx, uint32_t length,
                                 const T* data = nullptr) {
    return CreateCommon(cx, length, data);
  }

 private:
  static inline JSObject* CreateCommon(JSContext* cx, uint32_t length,
                                       const T* data) {
    JSObject* obj = CreateNew(cx, length);
    if (!obj) {
      return nullptr;
    }
    if (data) {
      JS::AutoCheckCannotGC nogc;
      bool isShared;
      T* buf = static_cast<T*>(GetData(obj, &isShared, nogc));
      // Data will not be shared, until a construction protocol exists
      // for constructing shared data.
      MOZ_ASSERT(!isShared);
      memcpy(buf, data, length * sizeof(T));
    }
    return obj;
  }

  TypedArray(const TypedArray&) = delete;
};

template <JSObject* UnwrapArray(JSObject*),
          void GetLengthAndDataAndSharedness(JSObject*, uint32_t*, bool*,
                                             uint8_t**),
          js::Scalar::Type GetViewType(JSObject*)>
struct ArrayBufferView_base
    : public TypedArray_base<uint8_t, UnwrapArray,
                             GetLengthAndDataAndSharedness> {
 private:
  typedef TypedArray_base<uint8_t, UnwrapArray, GetLengthAndDataAndSharedness>
      Base;

 public:
  ArrayBufferView_base() : Base(), mType(js::Scalar::MaxTypedArrayViewType) {}

  ArrayBufferView_base(ArrayBufferView_base&& aOther)
      : Base(std::move(aOther)), mType(aOther.mType) {
    aOther.mType = js::Scalar::MaxTypedArrayViewType;
  }

 private:
  js::Scalar::Type mType;

 public:
  inline bool Init(JSObject* obj) {
    if (!Base::Init(obj)) {
      return false;
    }

    mType = GetViewType(this->Obj());
    return true;
  }

  inline js::Scalar::Type Type() const {
    MOZ_ASSERT(this->inited());
    return mType;
  }
};

typedef TypedArray<int8_t, js::UnwrapInt8Array, JS_GetInt8ArrayData,
                   js::GetInt8ArrayLengthAndData, JS_NewInt8Array>
    Int8Array;
typedef TypedArray<uint8_t, js::UnwrapUint8Array, JS_GetUint8ArrayData,
                   js::GetUint8ArrayLengthAndData, JS_NewUint8Array>
    Uint8Array;
typedef TypedArray<
    uint8_t, js::UnwrapUint8ClampedArray, JS_GetUint8ClampedArrayData,
    js::GetUint8ClampedArrayLengthAndData, JS_NewUint8ClampedArray>
    Uint8ClampedArray;
typedef TypedArray<int16_t, js::UnwrapInt16Array, JS_GetInt16ArrayData,
                   js::GetInt16ArrayLengthAndData, JS_NewInt16Array>
    Int16Array;
typedef TypedArray<uint16_t, js::UnwrapUint16Array, JS_GetUint16ArrayData,
                   js::GetUint16ArrayLengthAndData, JS_NewUint16Array>
    Uint16Array;
typedef TypedArray<int32_t, js::UnwrapInt32Array, JS_GetInt32ArrayData,
                   js::GetInt32ArrayLengthAndData, JS_NewInt32Array>
    Int32Array;
typedef TypedArray<uint32_t, js::UnwrapUint32Array, JS_GetUint32ArrayData,
                   js::GetUint32ArrayLengthAndData, JS_NewUint32Array>
    Uint32Array;
typedef TypedArray<float, js::UnwrapFloat32Array, JS_GetFloat32ArrayData,
                   js::GetFloat32ArrayLengthAndData, JS_NewFloat32Array>
    Float32Array;
typedef TypedArray<double, js::UnwrapFloat64Array, JS_GetFloat64ArrayData,
                   js::GetFloat64ArrayLengthAndData, JS_NewFloat64Array>
    Float64Array;
typedef ArrayBufferView_base<js::UnwrapArrayBufferView,
                             js::GetArrayBufferViewLengthAndData,
                             JS_GetArrayBufferViewType>
    ArrayBufferView;
typedef TypedArray<uint8_t, JS::UnwrapArrayBuffer, JS::GetArrayBufferData,
                   JS::GetArrayBufferLengthAndData, JS::NewArrayBuffer>
    ArrayBuffer;

typedef TypedArray<
    uint8_t, JS::UnwrapSharedArrayBuffer, JS::GetSharedArrayBufferData,
    JS::GetSharedArrayBufferLengthAndData, JS::NewSharedArrayBuffer>
    SharedArrayBuffer;

// A class for converting an nsTArray to a TypedArray
// Note: A TypedArrayCreator must not outlive the nsTArray it was created from.
//       So this is best used to pass from things that understand nsTArray to
//       things that understand TypedArray, as with ToJSValue.
template <typename TypedArrayType>
class TypedArrayCreator {
  typedef nsTArray<typename TypedArrayType::element_type> ArrayType;

 public:
  explicit TypedArrayCreator(const ArrayType& aArray) : mArray(aArray) {}

  JSObject* Create(JSContext* aCx) const {
    return TypedArrayType::Create(aCx, mArray.Length(), mArray.Elements());
  }

 private:
  const ArrayType& mArray;
};

}  // namespace dom
}  // namespace mozilla

#endif /* mozilla_dom_TypedArray_h */