Redislock

redislock (GitHub: danielstjules/redislock, License: MIT) by Daniel St. Jules is a module for distributed locking powered by Redis. This utility is very helpful when you are building a distributed application, or even a basic CPU cluster to take advantage of multiple cores. One of the cool features is ability to set maximum number of retries and amount of time between them.

 

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npm install redislock

Usage

Locking is performed using the following redis command:

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SET key uuid PX timeout NX

If the SET returns OK, the lock has been acquired on the given key, and an expiration has been set. Then, releasing a lock uses the following redis script:

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if redis.call('GET', KEYS[1]) == ARGV[1] then
  return redis.call('DEL', KEYS[1])
end
return 0

This ensures that the key is deleted only if it is currently holding the lock, by passing its UUID as an argument.

Example below creates a lock and then tries to acquire it second time. The second attempt will fail.

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var redis = require('redis');
var redislock = require('redislock');
var client = redis.createClient();
var lock = redislock.createLock(client, {
  timeout: 20000,
  retries: 3,
  delay: 100
});
function doStuff(done) {
  lock.acquire('my:lock-name', function (err) {
    if (err) {
      console.log('Failed to get a lock...', err.message);
      return;
    }
    // tring to get the same lock second time will trigger an error.
    doStuff(done);
    lock.release(function (err) {
      console.log('Do work here...');
      done();
    });
  });
}
doStuff(function() {
  console.log('Done working...');
  client.end();
});