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

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support601 No2

573 4

55 — 57

46 — 555

No No10.1 —?
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support601601 ?

573 4

55 — 57

46 — 555

No No No

1. 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.

2. Support was removed to mitigate speculative execution side-channel attacks (Windows blog).

3. Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog).

4. 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.

5. From version 46 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.

See also

Document Tags and Contributors

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