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
SharedArrayBuffer cannot become detached.
SharedArrayBuffer was disabled by default in all major browsers on 5 January, 2018 in response to Spectre. Chrome re-enabled it in v67 on platforms where its site-isolation feature is enabled to protect against Spectre-style vulnerabilities.
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
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 which use SharedArrayBuffer objects
Always use the new operator to create a SharedArrayBuffer
var sab = SharedArrayBuffer(1024); // TypeError: calling a builtin SharedArrayBuffer constructor // without new is forbidden
var sab = new SharedArrayBuffer(1024);
- Creates a new
SharedArrayBufferconstructor's length property whose value is 1.
- Allows the addition of properties to all
SharedArrayBuffer prototype object
SharedArrayBuffer instances inherit from
- Specifies the function that creates an object's prototype. The initial value is the standard built-in
- The size, in bytes, of the array. This is established when the array is constructed and cannot be changed. Read only.
- Returns a new
SharedArrayBufferwhose contents are a copy of this
SharedArrayBuffer's bytes from
begin, inclusive, up to
end, exclusive. If either
endis negative, it refers to an index from the end of the array, as opposed to from the beginning.
|ECMAScript Latest Draft (ECMA-262)
The definition of 'SharedArrayBuffer' in that specification.