await-mutex

Promised based Mutex for cases where you need to synchronize sequentially the access to a single resource from multiple locations.

A typical use case for a mutex is when multiple asynchronous processes are fired and all of them have to execute another, but the same, asynchronous process as they arrive, one at a time, waiting for previous call (if any) to finish before calling it again.

Examples

file-appender.js

Let you create an object to perform file appends one at a time.

import * as fs from "fs";
import Mutex from "await-mutex";

export default class FileAppender {

    constructor(filename) {

        this._filename = filename;
        this._mutex = new Mutex();
    }

    async append(data, options = undefined) {

        let unlock = await this._mutex.lock();

        fs.appendFile(this._filename, data, options, error => {

            unlock();

            if (error) {
                throw error;
            }
        });
    }
}

API

import Mutex from "await-mutex";

Mutex

Creates an instance of Mutex (can not be called without new).

let mutex = new Mutex();

Mutex.prototype.isLocked

Returns if the mutex instance is (true) or not locked (false).

let unlock = await mutex.lock();

console.log(mutex.isLocked()); // prints true

Mutex.prototype.lock: Promise

• Waits until the mutex is unlocked and then locks it.
• It returns an ES2015 standard Promise (this allows the use of async/await) which gets resolved once the mutex is unlocked.
• The promise resolution value is an unlock function that has to be called once the mutex needs to be unlocked.

async function someFunc(mutex) {

    let unlock = await mutex.lock(); // wait until mutex is unlocked

    setTimeout(unlock, 3000);

    console.log(someFunc.name);
}

async function someOtherFunc(mutex) {

    let unlock = await mutex.lock(); // wait until mutex is unlocked

    console.log(someOtherFunc.name);
}

let mutex = new Mutex();

someFunc(mutex); // prints SomeFunc inmediately
someOtherFunc(mutex); // waits 3 secs for mutex to be unlocked and then prints SomeOtherFunc

Installation

With npm do:

npm install --save await-mutex

Contributing

Contributors

• Mauro Titimoli

How to

Take a look to the Contributing Guide

license

Unlicense.