redis-locking-worker

Overview

An event driven implementation of global locks using Redis.

Install

npm install redis-locking-worker

Usage

var RedisLockingWorker = require("redis-locking-worker");

var worker = new RedisLockingWorker({
	"lockKey" : "mylock",
	"statusLevel" : RedisLockingWorker.StatusLevels.Verbose,
	"lockTimeout" : 5000,
	"maxAttempts" : 5
});

worker.on("acquired", function(lastAttempt) {
	if (Math.random() <= SUCCESS_CHANCE) {
		console.log("Completed work successfully, cleaning up!");
		lock.done(lastAttempt);
	} else {
		// oh no, we failed to do work!
		console.log("Failed to do work, hopefully someone else will have better luck!");
	}	
});

worker.on("locked", function() {
	console.log("Someone else acquired the lock");
});

worker.on("error", function(error) {
	console.error("Error from lock: %j", error);
});

worker.on("status", function(message) {
	console.log("Status message from lock: %s", message);
});

worker.acquire();

Options

You can specify a variety of options when creating a new lock instance:

{
	"client" : null,										/* Instance of a node-redis redis client (https://github.com/mranney/node_redis) */
	"host" : "localhost",									/* Redis host to connect to if a client wasn't explicitly passed in */
	"port" : 6379,											/* Redis port to connect to if a client wasn't explicitly passed in */
	"lockKey" : null,										/* Name of the key to use for this lock, defaults to null, not optional */
	"statusLevel" : RedisLockingWorker.StatusLevel.Normal,	/* Verbosity to use when emitting status events */
	"lockTimeout" : 5000,									/* Time, in milliseconds, before a lock should expire. */
	"maxAttempts" : 5,										/* Number of attempts to complete work before giving up */
}

Example

You can run:

node examples/cluster.js

For an example implementation that uses cluster to fork one worker per CPU core, each one with a 15% chance of completing the "work" successfully. You should see output along these lines:

Worker 1 failed to do work
Worker 2 did not acquire lock
Worker 3 did not acquire lock
Worker 5 did not acquire lock
Worker 4 did not acquire lock
Worker 6 did not acquire lock
Worker 7 did not acquire lock
Worker 8 did not acquire lock
Worker 2 Status message from lock: Checking status of work from attempt #1
Worker 2 Status message from lock: Work was not completed, trying to reacquire lock for attempt #1
Worker 2 Status message from lock: Trying to reacquire lock
Worker 2 Status message from lock: Current attempt count: 1
Worker 2 Status message from lock: This is attempt #2
Worker 2 failed to do work
Worker 3 Status message from lock: Checking status of work from attempt #1
Worker 3 Status message from lock: Attempt count has been incremented (expected 1, but it's 2), someone else got the lock
Worker 5 Status message from lock: Checking status of work from attempt #1
Worker 5 Status message from lock: Attempt count has been incremented (expected 1, but it's 2), someone else got the lock
Worker 4 Status message from lock: Checking status of work from attempt #1
Worker 4 Status message from lock: Attempt count has been incremented (expected 1, but it's 2), someone else got the lock
Worker 6 Status message from lock: Checking status of work from attempt #1
Worker 6 Status message from lock: Attempt count has been incremented (expected 1, but it's 2), someone else got the lock
Worker 7 Status message from lock: Checking status of work from attempt #1
Worker 7 Status message from lock: Attempt count has been incremented (expected 1, but it's 2), someone else got the lock
Worker 8 Status message from lock: Checking status of work from attempt #1
Worker 8 Status message from lock: Attempt count has been incremented (expected 1, but it's 2), someone else got the lock
Worker 3 Status message from lock: Checking status of work from attempt #2
Worker 3 Status message from lock: Work was not completed, trying to reacquire lock for attempt #2
Worker 3 Status message from lock: Trying to reacquire lock
Worker 3 Status message from lock: Current attempt count: 2
Worker 3 Status message from lock: This is attempt #3
Worker 3 failed to do work
Worker 5 Status message from lock: Checking status of work from attempt #2
Worker 5 Status message from lock: Attempt count has been incremented (expected 2, but it's 3), someone else got the lock
Worker 4 Status message from lock: Checking status of work from attempt #2
Worker 4 Status message from lock: Attempt count has been incremented (expected 2, but it's 3), someone else got the lock
Worker 6 Status message from lock: Checking status of work from attempt #2
Worker 6 Status message from lock: Attempt count has been incremented (expected 2, but it's 3), someone else got the lock
Worker 7 Status message from lock: Checking status of work from attempt #2
Worker 7 Status message from lock: Attempt count has been incremented (expected 2, but it's 3), someone else got the lock
Worker 8 Status message from lock: Checking status of work from attempt #2
Worker 8 Status message from lock: Attempt count has been incremented (expected 2, but it's 3), someone else got the lock
Worker 5 Status message from lock: Checking status of work from attempt #3
Worker 5 Status message from lock: Work was not completed, trying to reacquire lock for attempt #3
Worker 5 Status message from lock: Trying to reacquire lock
Worker 5 Status message from lock: Current attempt count: 3
Worker 5 Status message from lock: This is attempt #4
Worker 5 completed work successfully, last attempt? false
Worker 4 Status message from lock: Checking status of work from attempt #3
Worker 4 Status message from lock: Work completed successfully by primary process, deleting lock
Worker 6 Status message from lock: Checking status of work from attempt #3
Worker 6 Status message from lock: Lock key is gone, someone else completed the work and deleted the lock
Worker 7 Status message from lock: Checking status of work from attempt #3
Worker 7 Status message from lock: Lock key is gone, someone else completed the work and deleted the lock
Worker 8 Status message from lock: Checking status of work from attempt #3
Worker 8 Status message from lock: Lock key is gone, someone else completed the work and deleted the lock