SharedArrayBuffer
对象用来表示一个通用的,固定长度的原始二进制数据缓冲区,类似于 ArrayBuffer
对象,它们都可以用来在共享内存(shared memory)上创建视图。与 ArrayBuffer
不同的是,SharedArrayBuffer
不能被分离。
请注意,由于能够轻易地利用《边信道(side-channel)读取未授权内存的攻击技术》中提到的Spectre漏洞——一种利用现代 CPU 使用的执行优化功能的新攻击技术, SharedArrayBuffer
功能将在 Chrome 和 FireFox 的新版本中禁用,并将逐渐被所有浏览器禁用。
但该API并不会被废弃,chrome团队声明在未来解决因web时钟导致的安全问题后,该API将会恢复。
语法
new SharedArrayBuffer(length)
参数
-
length
- 所创建的数组缓冲区的大小,以字节(byte)为单位。
返回值
一个大小指定的新 SharedArrayBuffer
对象。其内容被初始化为 0。
描述
分配及共享内存
为了将一个structured cloning )。
结构化克隆算法接收被映射到一个新的 SharedArrayBuffers
对象上的 SharedArrayBuffers
对象与 TypedArrays
对象。在这两种映射下,这个新的 SharedArrayBuffer
对象会被传递到目标用户代理的接收函数上,导致在目标用户代理产生了一个新的私有 SharedArrayBuffer
对象(正如 ArrayBuffer
一样)。然而,这两个 SharedArrayBuffer
对象指向的共享数据块其实是同一个,并且在某一代理中的一个块的副作用将最终导致另一个代理具有可见性。
let sab = new SharedArrayBuffer(1024); worker.postMessage(sab);
在早期版本的特性中,结构化克隆期间 SharedArrayBuffers
需要被精确转化。然而,从HTML的意义上来讲,SharedArrayBuffer
s 并非一个 Transferable object
。因此,如果一个 SharedArrayBuffer
对象位于转化队列,postMessage
将会抛出一个 DataCloneError
或 一个 DOMException
:
var sab = new SharedArrayBuffer(1024); worker.postMessage(sab, [sab]); // Uncaught DOMException: Failed to execute 'postMessage' on 'Worker': A SharedArrayBuffer could not be cloned.
通过原子操作更新及同步来共享内存
共享内存能被同时创建和更新于工作者线程或主线程。依赖于系统(CPU,操作系统,浏览器),变化传递给环境需要一段时间。需要通过 atomic 操作来进行同步。
接受 SharedArrayBuffer
对象的API
WebGLRenderingContext.bufferData()
WebGLRenderingContext.bufferSubData()
WebGL2RenderingContext.getBufferSubData()
需要 new
运算符来构造
SharedArrayBuffer
需要 TypeError
异常。
var sab = SharedArrayBuffer(1024); // TypeError: calling a builtin SharedArrayBuffer constructor // 必须用 new 来构造
var sab = new SharedArrayBuffer(1024);
属性
-
SharedArrayBuffer.length
-
SharedArrayBuffer
构造函数的 length 属性值为1。 -
SharedArrayBuffer.prototype
-
允许所有
SharedArrayBuffer
对象的附加属性。
SharedArrayBuffer
原型对象
所有 SharedArrayBuffer
实例继承自 SharedArrayBuffer.prototype
。
属性
- SharedArrayBuffer.prototype.constructor
-
Specifies the function that creates an object's prototype. The initial value is the standard built-in
SharedArrayBuffer
constructor. -
SharedArrayBuffer.prototype.byteLength
只读 - The size, in bytes, of the array. This is established when the array is constructed and cannot be changed. Read only.
方法
-
SharedArrayBuffer.prototype.slice(begin, end)
-
Returns a new
SharedArrayBuffer
whose contents are a copy of thisSharedArrayBuffer
's bytes frombegin
, inclusive, up toend
, exclusive. If eitherbegin
orend
is negative, it refers to an index from the end of the array, as opposed to from the beginning.
规范
规范 | 状态 | 备注 |
---|---|---|
ECMAScript Latest Draft (ECMA-262) SharedArrayBuffer |
Draft | Initial definition in ES2017. |
ECMAScript 2017 (ECMA-262) SharedArrayBuffer |
Standard |
浏览器兼容性
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | Android webview | Chrome for Android | Firefox for Android | Opera for Android | Safari on iOS | Samsung Internet | Node.js | |
SharedArrayBuffer |
Chrome Full support 68
|
Edge No support 16 — 17
Notes
|
Firefox Full support 57
Notes
Disabled
|
IE No support No | Opera No support No | Safari No support 10.1 — ? | WebView Android No support 60 — 63
Notes
|
Chrome Android No support 60 — 63
Notes
|
Firefox Android Full support 57
Notes
Disabled
|
Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No
Notes
|
nodejs Full support 8.10.0 |
byteLength |
Chrome Full support 68
|
Edge No support 16 — 17
Notes
|
Firefox Full support 57
Notes
Disabled
|
IE No support No | Opera No support No | Safari No support 10.1 — ? | WebView Android No support 60 — 63
Notes
|
Chrome Android No support 60 — 63
Notes
|
Firefox Android Full support 57
Notes
Disabled
|
Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No
Notes
|
nodejs Full support 8.10.0 |
prototype |
Chrome Full support 68
|
Edge No support 16 — 17
Notes
|
Firefox Full support 57
Notes
Disabled
|
IE No support No | Opera No support No | Safari No support 10.1 — ? | WebView Android No support 60 — 63
Notes
|
Chrome Android No support 60 — 63
Notes
|
Firefox Android Full support 57
Notes
Disabled
|
Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No
Notes
|
nodejs No support No |
SharedArrayBuffer in DataView |
Chrome Full support 68
|
Edge No support No | Firefox Full support 57
Notes
Disabled
|
IE No support No | Opera No support No | Safari No support 10.1 — ? | WebView Android No support 60 — 63
Notes
|
Chrome Android No support 60 — 63
Notes
|
Firefox Android Full support 57
Notes
Disabled
|
Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No
Notes
|
nodejs No support No |
slice |
Chrome Full support 68
|
Edge No support 16 — 17
Notes
|
Firefox Full support 57
Notes
Disabled
|
IE No support No | Opera No support No | Safari No support 10.1 — ? | WebView Android No support 60 — 63
Notes
|
Chrome Android No support 60 — 63
Notes
|
Firefox Android Full support 57
Notes
Disabled
|
Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No
Notes
|
nodejs Full support 8.10.0 |
Legend
- Full support
- Full support
- No support
- No support
- See implementation notes.
- See implementation notes.
- User must explicitly enable this feature.
- User must explicitly enable this feature.
相关链接
Atomics
ArrayBuffer
- JavaScript typed arrays
- Web Workers
- parlib-simple – a simple library providing synchronization and work distribution abstractions.
- Shared Memory – a brief tutorial
-
A Taste of JavaScript’s New Parallel Primitives – Mozilla Hacks