Cohesion

Elegant process clustering for node.js

Features

• Controller <-> Child Event Transference

Installation

cohesion package is available for node through npm.

npm install cohesion

Getting Started

To ensure consistency, the following language will used throughout the documentation.

• Controller - the node script the is initially started and manages all child processes
• Child - a script & javascript object that is started as a child processes of the controller
• Master - the javascript object api that manages macro setting for the cohesion cluster
• Worker - from the context of the controller, the javascript object api for each child process

Controller

The controller is the master process of a cohesion process cluster. Through it you can manage pre- and post- worker hooks, set number of workers, and listen for events.

To begin, construct a new worker by passing the path to the child script. An additional settings object can also be included to further modify a master behavior.

The most important event that the constructed master will emit is the worker event; this will be emitted for each new constructed worker. Events that are triggered on a worker process will be emitted on child process, and visa-versa.

The following example demonstrates a simple counter which will round-robin a countdown between each spawned child.

/**
 * controller.js
 */

// create master
var cohesion = require('cohesion')
  , master = new cohesion.Master(__dirname + '/child.js');

// example counter
var count = 30;

// event for when each worker spawns
master.on('worker', function (worker) {

  // emitted by child on start
  worker.on('ready', function () {
    worker.emit('calc', count);
  });

  // emitted by child after a calculation
  worker.on('next', function () {
    if (count > 0 ) {
      worker.emit('count', count);
      count--;
    } else {
      worker.stop();
    }
  });

});

// event for when all workers have stopped
master.on('stopped', function () {
  console.log('all done');
});

// start all the workers
master.spawnWorkers();

Child

The child is a small wrapper around the child-process api that turns each child process into a remote event listener and emitter.

The follow example demonstrates the child side of the previous counter example.

/**
 * child.js
 */

// mount child listener
var child = require('cohesion').child();

// emitted by controller
child.on('count', function (n) {
  setTimeout(function () {
    console.log('pid %d - %d', child.pid, n);
    child.emit('next');
  }, 100);
});

// start the calculations
child.emit('ready');

API Reference

Master

Events

• worker

.beforeEach (fn)

Provide a function that is be called before a worker is started. Function can be asyncronous and should be used to establish configuration. It will be called once before each worker is started, but not on restarts. Multiple calls will queue multiple before each functions that will be invoked in the order they are defined.

The following example uses harbor to assign a port to each worker.

var harbor = require('harbor')(1227, 1337)
  , n = 0;

master.beforeEach(function (config, done) {
  var name = 'child-' + (++n);
  config.name = name;
  harbor.claim(name, function (err, port) {
    if (err) return done(err);
    console.log('clamed 
    config.port = port;
    done();
  });
});

As you can see, config is a simple JSON object that will be serialized and provided to the child after startup. See the Child API for more information on how to access the config on the server side.

.afterEach (fn)

Works like .beforeEach(), but queue functions to be invoked after a worker has completed it's shutdown sequence. This occurs either when worker.stop() is called or when a worker has reached it's maximum restart attempts and the startup sequence is abandoned.

master.afterEach(function (config, done) {
  harbor.release(config.name);
  done();
});

.spawnWorkers (max, cb)

.spawnWorker (cb)

Child API

Contributing

Interested in contributing? Fork to get started. Contact @logicalparadox if you are interested in being regular contributor.

Contibutors

• Jake Luer (@logicalparadox)

License

(The MIT License)

Copyright (c) 2012 Jake Luer [email protected]

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.