SharedArrayBuffer

In This Article

The SharedArrayBuffer object is used to represent a generic, fixed-length raw binary data buffer, similar to the ArrayBuffer object, but in a way that they can be used to create views on shared memory. Unlike an ArrayBuffer, a SharedArrayBuffer cannot become detached.

Syntax

new SharedArrayBuffer(length)

Parameters

length: The size, in bytes, of the array buffer to create.

Return value

A new SharedArrayBuffer object of the specified size. Its contents are initialized to 0.

Description

Allocating and sharing memory

To share memory using SharedArrayBuffer objects from one agent in the cluster to another (an agent is either the web page’s main program or one of its web workers), postMessage and structured cloning is used.

The structured clone algorithm accepts SharedArrayBuffers and TypedArrays mapped onto SharedArrayBuffers. In both cases, the SharedArrayBuffer object is transmitted to the receiver resulting in a new, private SharedArrayBuffer object in the receiving agent (just as for ArrayBuffer). However, the shared data block referenced by the two SharedArrayBuffer objects is the same data block, and a side effect to the block in one agent will eventually become visible in the other agent.

var sab = new SharedArrayBuffer(1024);
worker.postMessage(sab);

Updating and synchronizing shared memory with Atomic operations

Shared memory can be created and updated simultaneously in workers or the main thread. Depending on the system (the CPU, the OS, the Browser) it can take a while until the change is propagated to all contexts. To synchronize, atomic operations are needed.

APIs accepting `SharedArrayBuffer` objects

Constructing is required with `new` operator

SharedArrayBuffer constructors require to be constructed with a new operator. Calling a SharedArrayBuffer constructor as a function without new, will throw a TypeError.

var sab = SharedArrayBuffer(1024);
// TypeError: calling a builtin SharedArrayBuffer constructor 
// without new is forbidden

var sab = new SharedArrayBuffer(1024);

Properties

SharedArrayBuffer.length: The SharedArrayBuffer constructor's length property whose value is 1.
SharedArrayBuffer.prototype: Allows the addition of properties to all SharedArrayBuffer objects.