Lock on asynchronous code
- ES6 promise supported
- Multiple keys lock supported
- Timeout supported
- Pending task limit supported
- Domain reentrant supported
- 100% code coverage
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){
});
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
});
// 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
});
lock.acquire([key1, key2], fn, cb);
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
});
});
});
// 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 library instead of the global Promise variable
var lock = new AsyncLock({Promise : require('bluebird')}); // Bluebird
var lock = new AsyncLock({Promise : require('q')}); // Q
See Changelog
See isse tracker.
MIT, see LICENSE