Atomics.compareExchange()
This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.
The static Atomics
.compareExchange()
method exchanges a given replacement value at a given position in the array, and returns the old value at that position, if a given expected value equals the old value. This atomic operation guarantees that no other write happens until the modified value is written back.
Syntax
Atomics.compareExchange(typedArray, index, expectedValue, replacementValue)
Parameters
typedArray
- A shared integer typed array. One of
Int8Array
,Uint8Array
,Int16Array
,Uint16Array
,Int32Array
, orUint32Array
. index
- The position in the
typedArray
to exchange avalue
. expectedValue
- The value to check for equality.
- replacementValue
- The number to exchange.
Return value
The old value at the given position (typedArray[index]
).
Exceptions
- Throws a
TypeError
, iftypedArray
is not one of the allowed integer types. - Throws a
TypeError
, iftypedArray
is not a shared typed array type. - Throws a
RangeError
, ifindex
is out of bounds in thetypedArray
.
Examples
var sab = new SharedArrayBuffer(1024); var ta = new Uint8Array(sab); ta[0] = 7; Atomics.compareExchange(ta, 0, 7, 12); // returns 7, the old value Atomics.load(ta, 0); // 12
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript Shared Memory and Atomics The definition of 'Atomics.compareExchange' in that specification. |
Draft | Initial definition. |
Browser compatibility
Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|---|
Basic support | No support [2] | No support | 46 (46) [1] | No support | No support | No support |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | No support | No support | 46.0 (46) [1] | No support | No support | No support |
[1] This feature is disabled by a preference setting. In about:config, set javascript.options.shared_memory
to true
.
[2] The implementation is under development and needs these runtime flags: --js-flags=--harmony-sharedarraybuffer --enable-blink-feature=SharedArrayBuffer
See also
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/javascript/reference/global_objects/atomics/compareexchange