parallel.js for phantomjs

parallel.js

const QUEUE_LENGTH = 1;

var numRunningJobs = 0;
var numWaitingJobs = 0;

var parrallelCallback = function() {
    numRunningJobs --;

    if (numRunningJobs === 0 && numWaitingJobs === 0) {
        phantom.exit();
    }
};

var addToQueue = function(func, obj, isWaiting) {
    if (numRunningJobs >= QUEUE_LENGTH) {
        if (!isWaiting) {
            numWaitingJobs ++;
        }
        setTimeout(function() {
            addToQueue(func, obj, true);
        }, 100);
    } else {
        if (isWaiting) {
            numWaitingJobs --;
        }
        numRunningJobs ++;
        func(obj, parrallelCallback);
    }
};

/* following is an example */

// a test function. it must call the callback function when work is done.
var testFunc = function(url, callback) {
    var page = require('webpage').create();
    page.settings.loadImages = false;
    page.onConsoleMessage = function(msg) { console.log(msg); };
    page.onLoadFinished = function() {
        page.evaluate(function() {
            console.log(document.title);
        });
        callback && callback();
    };
    page.open(url);
};

// some test data
var testObjs = [ 'http://www.google.com/', 'http://www.bing.com/', 'http://www.yahoo.com/' ];

// add to the queue
for (var i = 0; i < testObjs.length; i++) {
    addToQueue(testFunc, testObjs[i]);
}