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() {

	// 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._running = false;

		this._queue = this;
		this._queueLen = 0;
		this._afterQueue = {};
		this._afterQueueLen = 0;

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

	/**
	 * Enqueue a task
	 * @param {{ run:function }} task
	 */
	Scheduler.prototype.enqueue = function(task) {
		this._queue[this._queueLen++] = task;
		this.run();
	};

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

	Scheduler.prototype.run = function() {
		if (!this._running) {
			this._running = true;
			this._async(this.drain);
		}
	};

	/**
	 * Drain the handler queue entirely, and then the after queue
	 */
	Scheduler.prototype._drain = function() {
		var i = 0;
		for (; i < this._queueLen; ++i) {
			this._queue[i].run();
			this._queue[i] = void 0;
		}

		this._queueLen = 0;
		this._running = false;

		for (i = 0; i < this._afterQueueLen; ++i) {
			this._afterQueue[i].run();
			this._afterQueue[i] = void 0;
		}

		this._afterQueueLen = 0;
	};

	return Scheduler;

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