The Atomics.waitAsync() static method waits asynchronously on a shared memory location and returns a Promise.

Unlike Atomics.wait, waitAsync is non-blocking and usable on the main thread.

Note: This operation only works with an Int32Array or BigInt64Array that views a SharedArrayBuffer.

Syntax

Atomics.waitAsync(typedArray, index, value)
Atomics.waitAsync(typedArray, index, value, timeout)

Parameters

• typedArray
  • : An Int32Array or BigInt64Array that views a SharedArrayBuffer.
• index
  • : The position in the typedArray to wait on.
• value
  • : The expected value to test.

• timeout

  • : Time to wait in milliseconds. NaN (and values that get converted to NaN, such as undefined) becomes Infinity. Negative values become 0.

Return value

An Object with the following properties:

• async
  • : A boolean indicating whether the value property is a Promise or not.
• value
  • : If async is false, it will be a string which is either "not-equal" or "timed-out" (only when the timeout parameter is 0). If async is true, it will be a Promise which is fulfilled with a string value, either "ok" or "timed-out". The promise is never rejected.

Exceptions

• TypeError
  • : Thrown if typedArray is not an Int32Array or BigInt64Array that views a SharedArrayBuffer.
• RangeError
  • : Thrown if index is out of bounds in the typedArray.

Examples

Using waitAsync()

Given a shared Int32Array.

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

A reading thread is sleeping and waiting on location 0 which is expected to be 0. The result.value will be a promise.

const result = Atomics.waitAsync(int32, 0, 0, 1000);
// { async: true, value: Promise {<pending>} }

In the reading thread or in another thread, the memory location 0 is called and the promise can be resolved with "ok".

Atomics.notify(int32, 0);
// { async: true, value: Promise {<fulfilled>: 'ok'} }

If it isn't resolving to "ok", the value in the shared memory location wasn't the expected (the value would be "not-equal" instead of a promise) or the timeout was reached (the promise will resolve to "time-out").

Specifications

Browser compatibility

See also

• Atomics
• Atomics.wait
• Atomics.notify