Async Semaphore

A counting semaphore based on Java's Concurrent Semaphore.

Install

Install the module via npm:

npm install ts-async-semaphore

Quick Example

// fairness false

import { Semaphore } from 'ts-async-semaphore';
const semaphore = new Semaphore(0);

semaphore.acquire(2).then(() => {
    console.log('Hello');
});

semaphore.acquire().then(() => {
    console.log('World');

    semaphore.release(2);
});

setTimeout(function () {
    semaphore.release();
}, 2000);

// fairness true

import { Semaphore } from 'ts-async-semaphore';
const semaphore = new Semaphore(0, true);

semaphore.acquire(2).then(() => {
    console.log('Hello');
});

semaphore.acquire().then(() => {
    console.log('World');
});

semaphore.release(1);

setTimeout(function () {
    semaphore.release(2);
}, 2000);

import { Semaphore } from 'ts-async-semaphore';
const semaphore = new Semaphore(0, true);

semaphore.tryAcquire(1, 50).then((val) => {
    console.log(`Acquire ${val ? 'success' : 'fail'}`);
});

Documentation

Constructor: Semaphore([permits], [fairness])

permits: Integer Initial available permits of semaphore. Default: 0.

fairness: Boolean Fairness of semaphore. If set to true, a FIFO rules applied, else, look on each acquirers permit value.

#availablePermits()

Returns the current number of permits available in this semaphore.

Returns: number

#acquire([permits])

Acquires the given number of permits from this semaphore.

permits: number The number of permits to acquire. Default: 0.

Returns: Promise<void>

#getQueuedAcquirers()

Returns an estimate of the number of acquirers waiting to acquire.

Returns: Function[]

#getQueueLength()

Returns an estimate of the number of acquirers waiting to acquire.

Returns: number

#release([permits])

Releases the given number of permits, returning them to the semaphore.

permits: number The number of permits to release. Default: 0.

#drainPermits()

Acquires and returns all permits that are immediately available.

Returns: number

#reducePermits(permits)

Shrinks the number of available permits by the indicated reduction.

permits: number The number of permits to remove.

#tryAcquire([permits], [timeoutMs])

Acquires the given number of permits from this semaphore.

permits: number The number of permits to acquire. Default: 0. timeoutMs: number The timeout after which the acquire will fail

Returns: Boolean Promise true if success, false false if fail