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Lock on asynchronous code for Nodejs
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README.md

async-lock

Lock on asynchronous code

Build Status Dependencies Status

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

Why you need locking on single threaded nodejs?

Nodejs is single threaded, and the code execution is never get 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 concurrency, 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();
d.run(function(){
	lock.acquire('key', function(){
		//Enter lock
		return lock.acquire('key', function(){
			//Enter same lock twice
		});
	});
});

Options

// 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
});

// 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
lock.isBusy();

// Use your own promise
var lock = new AsyncLock({Promise : require('bluebird')});

License

(The MIT License)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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