async-lock

Lock on asynchronous code

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

Disclaimer

I did not create this package. I was granted the ownership because it was no longer being maintained, and I volunteered to fix a bug. I will not do any maintenance on it other than merge PRs.

DO NOT EXPECT ME TO ADD FEATURES OR FIX BUGS. PRs WELCOME

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

1redis.get('key', function(err, value) {
2	redis.set('key', value * 2);
3});

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

1lock.acquire('key', function(cb) {
2	// Concurrency safe
3	redis.get('key', function(err, value) {
4		redis.set('key', value * 2, cb);
5	});
6}, function(err, ret) {
7});

Get Started

1var AsyncLock = require('async-lock');
2var lock = new AsyncLock();
3
4/**
5 * @param {String|Array} key 	resource key or keys to lock
6 * @param {function} fn 	execute function
7 * @param {function} cb 	(optional) callback function, otherwise will return a promise
8 * @param {Object} opts 	(optional) options
9 */
10lock.acquire(key, function(done) {
11	// async work
12	done(err, ret);
13}, function(err, ret) {
14	// lock released
15}, opts);
16
17// Promise mode
18lock.acquire(key, function() {
19	// return value or promise
20}, opts).then(function() {
21	// lock released
22});

Error Handling

1// Callback mode
2lock.acquire(key, function(done) {
3	done(new Error('error'));
4}, function(err, ret) {
5	console.log(err.message) // output: error
6});
7
8// Promise mode
9lock.acquire(key, function() {
10	throw new Error('error');
11}).catch(function(err) {
12	console.log(err.message) // output: error
13});

Acquire multiple keys

1lock.acquire([key1, key2], fn, cb);

Domain reentrant lock

Lock is reentrant in the same domain

1var domain = require('domain');
2var lock = new AsyncLock({domainReentrant : true});
3
4var d = domain.create();
5d.run(function() {
6	lock.acquire('key', function() {
7		//Enter lock
8		return lock.acquire('key', function() {
9			//Enter same lock twice
10		});
11	});
12});

Options

1// Specify timeout - max amount of time an item can remain in the queue before acquiring the lock
2var lock = new AsyncLock({timeout: 5000});
3lock.acquire(key, fn, function(err, ret) {
4	// timed out error will be returned here if lock not acquired in given time
5});
6
7// Specify max occupation time - max amount of time allowed between entering the queue and completing execution
8var lock = new AsyncLock({maxOccupationTime: 3000});
9lock.acquire(key, fn, function(err, ret) {
10	// occupation time exceeded error will be returned here if job not completed in given time
11});
12
13// Specify max execution time - max amount of time allowed between acquiring the lock and completing execution
14var lock = new AsyncLock({maxExecutionTime: 3000});
15lock.acquire(key, fn, function(err, ret) {
16	// execution time exceeded error will be returned here if job not completed in given time
17});
18
19// Set max pending tasks - max number of tasks allowed in the queue at a time
20var lock = new AsyncLock({maxPending: 1000});
21lock.acquire(key, fn, function(err, ret) {
22	// Handle too much pending error
23})
24
25// Whether there is any running or pending async function
26lock.isBusy();
27
28// Use your own promise library instead of the global Promise variable
29var lock = new AsyncLock({Promise: require('bluebird')}); // Bluebird
30var lock = new AsyncLock({Promise: require('q')}); // Q
31
32// Add a task to the front of the queue waiting for a given lock
33lock.acquire(key, fn1, cb); // runs immediately
34lock.acquire(key, fn2, cb); // added to queue
35lock.acquire(key, priorityFn, cb, {skipQueue: true}); // jumps queue and runs before fn2

Changelog

See Changelog

Issues

See issue tracker.

License

MIT, see LICENSE