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.