ParallelRequests

parallel-requests.js

/*

This is just an exploration of idea. I don't think this solution is elegant
enough. I'm looking for something that would work without the add() and done()
methods. Something like this:
  new ParallelRequests(arrayOfRequests, callbackOnFinished);

The main idea is to work around delays when I need to aggregate data from
various sources before I can do something with them. Chaining is clearly not
the right way to go. 

CHAINED REQUESTS
  #1 |-----|
  #2       |-----|
  #3             |-----|
                       |<-- finally done!

PARELLEL REQUESTS
  #1 |-----|
  #2 |-----|
  #3 |-----|
           |<-- done already?

*/

function ParallelRequests(callback) {
    this.callback = callback || function () {};
    this.requests = [];
}

ParallelRequests.prototype = {
    add: function (request) {
        if (!request) { return; }
        var wrapped = this._wrap(request);
        this.requests.push(wrapped);
    },   
    _wrap: function(request) {
        var queue = this;
    	return function () {
     		try {
     			request();
     		} finally {
     			queue.done();
     		}
        };
	},
    done: function () {
        if (this.requests.length == 0) {
        	this.callback();
        }
    },
    start: function () {
        // ignore further modifications to requests
        var reqs = this.requests.slice(0);
        var request;
        while (request = reqs.pop()) {
            request();
        }
    }
}

var myBatchOfRequests = new ParallelRequests(function () {
    console.log('all requests finished correctly');
});

// just a sample function supporting callback
function generateRandomNumber(name) {
    var randomNumber = Math.round(Math.random() * 1000);
    console.log(name + ' generated ' + randomNumber);
}

myBatchOfRequests.add(function () {
    generateRandomNumber("1");
});
myBatchOfRequests.add(function () {
    generateRandomNumber("2");
});
myBatchOfRequests.add(function () {
    generateRandomNumber("3");
});
myBatchOfRequests.add(function () {
    generateRandomNumber("4");
});
myBatchOfRequests.add(function () {
    generateRandomNumber("5");
});


myBatchOfRequests.start();