@openally/mutex

Mutex

Another Mutex/Semaphore implementation with first-class support of AbortSignal

Requirements

• Node.js v16 or higher

Getting Started

This package is available in the Node Package Repository and can be easily installed with npm or yarn.

$ npm i @openally/mutex
# or
$ yarn add @openally/mutex

Usage example

import timers from "node:timers/promises";

import { Mutex } from "@openally/mutex";

const lock = new Mutex({ concurrency: 2 });

async function asynchronousTask() {
  const free = await lock.acquire({
    signal: AbortSignal.timeout(5_000),

    // Release if your asynchronous task never give the hand back (leak/bug for example)
    delayBeforeAutomaticRelease: 30_000
  });

  try {
    // Do Asynchronous job here
    await timers.setTimeout(100);
    console.log("one job done!");
  }
  finally {
    free();
  }
}

await Promise.allSettled([
  asynchronousTask(),
  asynchronousTask(),
  asynchronousTask(),
  asynchronousTask(),
  asynchronousTask()
]);
console.log("all done!");

API

declare class Mutex {
  static readonly MaximumConcurrency: number;

  public readonly concurrency: number;
  public readonly running: number;
  public readonly locked: boolean;
}

Note The maximum concurrency defined on the class is 1000

constructor(options: IMutexOptions)

The options payload is described by the following TypeScript interface:

export interface IMutexOptions {
  /**
   * @default 5
   */
  concurrency?: number;

  /**
   * If disabled it will unref() Node.js timers (allowing to not keep event loop alive).
   *
   * @default true
   */
  keepReferencingTimers?: boolean;
}

acquire(options: IMutexAcquireOptions): Promise< () => void >

Acquire one lock. The `options` payload is described by the following TypeScript interface:

export interface IMutexAcquireOptions {
  /**
   * AbortSignal to be able to define a maximum time to wait before abortion of lock acquisition.
   */
  signal?: AbortSignal;

  /**
   * When acquired, define a maximum delay before automatic release.
   *
   * No automatic release by default
   */
  delayBeforeAutomaticRelease?: number;
}

The acquire method return a callback function that will allow the developer to manually release.

release(): this

Manually release one lock. If there is no lock it will just return.

A event is emitted when release is triggered (the event itself is a Symbol exported by the package).

import { once } from "node:events";
import { Mutex, MutexRelease } from "@openally/mutex";

const lock = new Mutex();

const free = await lock.acquire();
// free will automatically trigger .release()
setImmediate(() => free());

await once(lock, MutexRelease);
console.log("done!");

cancel(): this

Cancel all running locks (will provoke dispatch MutexCanceledError to all promises).

reset(): this

Reset instance state (and remove cancellation if enabled). It will trigger cancel() if there is still promises running.

Error management

When cancelled the acquire method will throw a MutexCanceledError error.

import { Mutex, MutexCanceledError } from "@openally/mutex";

const lock = new Mutex().cancel();

try {
  await lock.acquire();
}
catch (err) {
  console.log(err instanceof MutexCanceledError);
}

License

MIT