merge-sort-async/mergesort.js

merge sort using cluster module completely async

/**
 * Created by pariskshitdutt on 08/03/15.
 */

/**
 * imports required by the code
 * async module needs to be installed using npm
 */
var async=require('async');
var cluster = require('cluster');

/**
 * cluster module setup creates merge.js as child processes
 */
    cluster.setupMaster({
        exec : __dirname+"/merge.js"
    });
var workers=[];
/**
 * performs mergesort and returns the sorted array in callback
 * @param unsorted array
 * @param callback returns err and sorted array
 */

    module.exports.mergeSort=function mergeSort(arr,callback) {

        var len = arr.length, firstHalf, secondHalf;        //different variables required

        if (len >= 2) {

            firstHalf = arr.slice(0, len / 2);      //slices the array in first half
            secondHalf = arr.slice(len / 2, len);   //slices the array in second half

            //performs both the recursive calls and combines and
            // gives back a combined callback whick spawns a worker which performs the merge

            async.parallel([
                function(callback){mergeSort(firstHalf,callback)},
                function(callback){mergeSort(secondHalf,callback)}
            ], function(err,results){
                //spawns a worker thread using cluster module
                try {
                    spawn(err, results, callback);
                }catch(e){
                    var wait = setInterval(function () {
                        try{
                            spawn(err,results,callback);
                            clearInterval(wait);
                        }catch(e){}
                    }, 1);
                }
            });

        } else {
            //passes the single object array to the callback because its already sorted
            callback(null,arr);
        }
    };
    function spawn(err,results,callback){
        var worker = cluster.fork();
        workers.push(worker);
        //passes the spliced arrays to the worker for processing
        worker.send({first: results[0], second: results[1]});
        //handles the messages recieved from the worker
        worker.on('message', function (msg) {

            //completes the merge and passes the result to the callback
            callback(null, msg.result);
            //the job of the worker is done here so its killed
            worker.kill();
            delete workers[worker];
        });
    }