when/lib/Scheduler.js

/** @license MIT License (c) copyright 2010-2014 original author or authors */
/** @author Brian Cavalier */
/** @author John Hann */

(function(define) { 'use strict';
define(function(require) {

	var Queue = require('./Queue');

	// Credit to Twisol (https://github.com/Twisol) for suggesting
	// this type of extensible queue + trampoline approach for next-tick conflation.

	/**
	 * Async task scheduler
	 * @param {function} async function to schedule a single async function
	 * @constructor
	 */
	function Scheduler(async) {
		this._async = async;
		this._queue = new Queue(15);
		this._afterQueue = new Queue(5);
		this._running = false;

		var self = this;
		this.drain = function() {
			self._drain();
		};
	}

	/**
	 * Enqueue a task
	 * @param {{ run:function }} task
	 */
	Scheduler.prototype.enqueue = function(task) {
		this._add(this._queue, task);
	};

	/**
	 * Enqueue a task to run after the main task queue
	 * @param {{ run:function }} task
	 */
	Scheduler.prototype.afterQueue = function(task) {
		this._add(this._afterQueue, task);
	};

	/**
	 * Drain the handler queue entirely, and then the after queue
	 */
	Scheduler.prototype._drain = function() {
		runQueue(this._queue);
		this._running = false;
		runQueue(this._afterQueue);
	};

	/**
	 * Add a task to the q, and schedule drain if not already scheduled
	 * @param {Queue} queue
	 * @param {{run:function}} task
	 * @private
	 */
	Scheduler.prototype._add = function(queue, task) {
		queue.push(task);
		if(!this._running) {
			this._running = true;
			this._async(this.drain);
		}
	};

	/**
	 * Run all the tasks in the q
	 * @param queue
	 */
	function runQueue(queue) {
		while(queue.length > 0) {
			queue.shift().run();
		}
	}

	return Scheduler;

});
}(typeof define === 'function' && define.amd ? define : function(factory) { module.exports = factory(require); }));