The static Atomics.wait() method verifies that a given position in an Int32Array still contains a given value and if so sleeps, awaiting a wakeup or a timeout. It returns a string which is either "ok", "not-equal", or "timed-out".

Note: This operation only works with a shared Int32Array and may not be allowed on the main thread.

Syntax

Atomics.wait(typedArray, index, value[, timeout])

Parameters

typedArray
A shared Int32Array.
index
The position in the typedArray to wait on.
value
The expected value to test .
timeout Optional
Time to wait in milliseconds. Infinity, if no time is provided.

Return value

A String which is either "ok", "not-equal", or "timed-out".

Exceptions

Examples

Given a shared Int32Array:

var sab = new SharedArrayBuffer(1024);
var int32 = new Int32Array(sab);

A reading thread is sleeping and waiting on location 0 which is expected to be 0. As long as that is true, it will not go on. However, once the writing thread has stored a new value, it will be woken up by the writing thread and return the new value (123).

Atomics.wait(int32, 0, 0);
console.log(int32[0]); // 123

A writing thread stores a new value and wakes up the waiting thread once it has written:

console.log(int32[0]); // 0;
Atomics.store(int32, 0, 123); 
Atomics.wake(int32, 0, 1);

Specifications

Specification Status Comment
ECMAScript Latest Draft (ECMA-262)
The definition of 'Atomics.wait' in that specification.
Draft Initial definition in ES2017.

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung InternetNode.js
Basic supportChrome Full support 68
Full support 68
No support 60 — 63
Notes
Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.
Edge Full support 16
Notes
Full support 16
Notes
Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).
Firefox Full support 57
Notes Disabled
Full support 57
Notes Disabled
Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog).
Disabled From version 57: this feature is behind the javascript.options.shared_memory preference (needs to be set to true). To change preferences in Firefox, visit about:config.
No support 55 — 57
No support 48 — 55
Disabled
Disabled From version 48 until version 55 (exclusive): this feature is behind the javascript.options.shared_memory preference (needs to be set to true). To change preferences in Firefox, visit about:config.
No support 46 — 48
Notes Alternate Name Disabled
Notes The method returns values Atomics.OK, Atomics.TIMEDOUT, and Atomics.NOTEQUAL, instead of the later-specified strings.
Alternate Name Uses the non-standard name: futexWait
Disabled From version 46 until version 48 (exclusive): this feature is behind the javascript.options.shared_memory preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE No support NoOpera No support NoSafari No support 10.1 — ?WebView Android No support 60 — 63
Notes
No support 60 — 63
Notes
Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.
Chrome Android No support 60 — 63
Notes
No support 60 — 63
Notes
Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.
Edge Mobile ? Firefox Android Full support 57
Notes Disabled
Full support 57
Notes Disabled
Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog).
Disabled From version 57: this feature is behind the javascript.options.shared_memory preference (needs to be set to true). To change preferences in Firefox, visit about:config.
No support 55 — 57
No support 48 — 55
Disabled
Disabled From version 48 until version 55 (exclusive): this feature is behind the javascript.options.shared_memory preference (needs to be set to true). To change preferences in Firefox, visit about:config.
No support 46 — 48
Notes Alternate Name Disabled
Notes The method returns values Atomics.OK, Atomics.TIMEDOUT, and Atomics.NOTEQUAL, instead of the later-specified strings.
Alternate Name Uses the non-standard name: futexWait
Disabled From version 46 until version 48 (exclusive): this feature is behind the javascript.options.shared_memory preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support Nonodejs Full support 8.10.0

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.
Uses a non-standard name.
Uses a non-standard name.

See also

Document Tags and Contributors

Contributors to this page: graingert, fscholz, lth
Last updated by: graingert,