A CommonJS module providing the ability to pause program flow until a set of asynchronous operations have completed.

Latch.js

/**
 * Provides the ability to have a set of asynchronous operations wait after their
 * respective execution until all of the operations in the group have completed.
 * 
 * Sample usage:
 *     // Define some operations that will run asynchronously.
 *     var worker1 = function(announceComplete) {
 *         // Do some work here ...
 *         announceComplete();
 *     };
 *     var worker2 = function(announceComplete) {
 *         // Do some work here ...
 *         announceComplete();
 *     };
 * 
 *     // Callback for when all workers have completed.
 *     var allCompleteCB = function() {
 *         alert('All operations completed, Latch is released.');
 *     };
 * 
 *     // Use the Latch to run the workers asynchronously.
 *     var latch = require('Latch');
 *     latch.start([worker1, worker2], allCompleteCB);
 *
 * @author Patrick Seda
 */
var Latch = (function() {
	// Start all operations asynchronously.
	var start = function(workers, allCompleteCB) {
		var counter = workers.length;
		
		// Decrement counter and fire the CB when all workers are finished.
		var announceComplete = function() {
			if (--counter === 0) {
				allCompleteCB && allCompleteCB();
			}
		};
		
		// Start each worker, handing them the announceComplete method.
		for (var i = 0, len = workers.length; i < len; i++) {
			workers[i](announceComplete);
		}
	};
	
	// Public API
	return {
		start : start
	};
})();

module.exports = Latch;