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    1.3.0 • Public • Published


    Lock on asynchronous code

    Build Status

    • ES6 promise supported
    • Multiple keys lock supported
    • Timeout supported
    • Occupation time limit supported
    • Pending task limit supported
    • Domain reentrant supported
    • 100% code coverage


    I did not create this package, and I will not add any features to it myself. I was granted the ownership because it was no longer being maintained, and I volunteered to fix a bug.

    If you have a new feature you would like to have incorporated, please send me a PR and I will be happy to work with you and get it merged. For any bugs, PRs are most welcome but when possible I will try to get them resolved as soon as possible.

    Why do you need locking on single threaded nodejs?

    Nodejs is single threaded, and the code execution never gets interrupted inside an event loop, so locking is unnecessary? This is true ONLY IF your critical section can be executed inside a single event loop. However, if you have any async code inside your critical section (it can be simply triggered by any I/O operation, or timer), your critical logic will across multiple event loops, therefore it's not concurrency safe!

    Consider the following code

    redis.get('key', function(err, value) {
    	redis.set('key', value * 2);

    The above code simply multiply a redis key by 2. However, if two users run concurrently, the execution order may like this

    user1: redis.get('key') -> 1
    user2: redis.get('key') -> 1
    user1: redis.set('key', 1 x 2) -> 2
    user2: redis.set('key', 1 x 2) -> 2

    Obviously it's not what you expected

    With asyncLock, you can easily write your async critical section

    lock.acquire('key', function(cb) {
    	// Concurrency safe
    	redis.get('key', function(err, value) {
    		redis.set('key', value * 2, cb);
    }, function(err, ret) {

    Get Started

    var AsyncLock = require('async-lock');
    var lock = new AsyncLock();
     * @param {String|Array} key 	resource key or keys to lock
     * @param {function} fn 	execute function
     * @param {function} cb 	(optional) callback function, otherwise will return a promise
     * @param {Object} opts 	(optional) options
    lock.acquire(key, function(done) {
    	// async work
    	done(err, ret);
    }, function(err, ret) {
    	// lock released
    }, opts);
    // Promise mode
    lock.acquire(key, function() {
    	// return value or promise
    }, opts).then(function() {
    	// lock released

    Error Handling

    // Callback mode
    lock.acquire(key, function(done) {
    	done(new Error('error'));
    }, function(err, ret) {
    	console.log(err.message) // output: error
    // Promise mode
    lock.acquire(key, function() {
    	throw new Error('error');
    }).catch(function(err) {
    	console.log(err.message) // output: error

    Acquire multiple keys

    lock.acquire([key1, key2], fn, cb);

    Domain reentrant lock

    Lock is reentrant in the same domain

    var domain = require('domain');
    var lock = new AsyncLock({domainReentrant : true});
    var d = domain.create(); {
    	lock.acquire('key', function() {
    		//Enter lock
    		return lock.acquire('key', function() {
    			//Enter same lock twice


    // Specify timeout
    var lock = new AsyncLock({timeout: 5000});
    lock.acquire(key, fn, function(err, ret) {
    	// timed out error will be returned here if lock not acquired in given time
    // Specify max occupation time
    var lock = new AsyncLock({maxOccupationTime: 3000});
    lock.acquire(key, fn, function(err, ret) {
    	// occupation time exceeded error will be returned here if job not completed in given time
    // Set max pending tasks
    var lock = new AsyncLock({maxPending: 1000});
    lock.acquire(key, fn, function(err, ret) {
    	// Handle too much pending error
    // Whether there is any running or pending async function
    // Use your own promise library instead of the global Promise variable
    var lock = new AsyncLock({Promise: require('bluebird')}); // Bluebird
    var lock = new AsyncLock({Promise: require('q')}); // Q
    // Add a task to the front of the queue waiting for a given lock
    lock.acquire(key, fn1, cb); // runs immediately
    lock.acquire(key, fn2, cb); // added to queue
    lock.acquire(key, priorityFn, cb, {skipQueue: true}); // jumps queue and runs before fn2


    See Changelog


    See issue tracker.


    MIT, see LICENSE


    npm i async-lock

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    • rogierschouten