Does a Firefox Workers limit exist?

Question

Im trying to create web Workers and post messages to them in cycle:

array.forEach(function (data) {
        this.createWorker();
        this.workers[this.workersPointer].postMessage({task: 'someTask', data: string});
    }, this);

createWorker function:

createWorker: function () {
    this.workersPointer++;
    var worker = this.workers[this.workersPointer] = new Worker('Worker.js'),
        storage = this;
    worker.onmessage = function (event) {
        if (event.data.error) {
            storage[event.data.task + 'Errback'](event.data.error);
        }
        else {
            storage[event.data.task + 'Callback'](event.data.data);
        }
    };
    worker.onerror = function (error) {
        storage.workerErrback(error);
    };
}

Worker code:

self.addEventListener('message', function (event) {
self.postMessage({
    data: data,
    error: err,
    task: event.data.task
});

}, false);

It works perfectly in Google Chrome. When I'm trying to run it in Firefox, it works only 20 times. Do Firefox web workers have a limit? I can't find information about it on mozilla.org. If there is no limit, what's the problem? Any ideas?

Answer 1

Just did some test of my own. For this, i changed the code a little bit:

Cycle:

for(var i=0;i<200;i++){
   this.createWorker();
   this.workers[this.workersPointer].postMessage({task: 'someTask', number:i});
};

createWorker function:

this.workers =[];
this.workersPointer = 0;
storage=[];


var createWorker= function () {
    workersPointer++;
    var myPointer = workersPointer;
    var worker = this.workers[this.workersPointer] = new Worker('Worker.js');

    worker.onmessage = function (event) {
        if (event.data.error) {
            alert(event.data.error);
        }
        else {
            document.cookie=event.data.task+"["+myPointer+"]="+event.data.number;
        }
    };
    worker.onerror = function (event) {
        alert("Error: " + event.error);
    };
}

Worker:

onmessage = function(event) {
    postMessage({number:event.data.number*2, task: event.data.task});
};

After i run this, in chrome i got 66 cookies (including a nice blue crash window), in firefox i got 20. So both browsers seem to have worker limitations.

EDIT:

In Opera i get a console message:

Maximum number of Web Worker instances(16) exceeded for this window.

Answer 2

There is a setting in Firefox, called "dom.workers.maxPerDomain" which is by default 20.

However, there might not be any real performance gain in using more workers than you have cores in the computer. With a modern computer today that has hyper threading, I think using around 8 workers would be sufficient. Otherwise you might cause to much context switching that would instead introduce a bottleneck.

It all depends though, what you want to achieve.

Answer 3

For futher reference check out in Firefox

about:config

There's a parameter called :

dom.workers.maxPerDomain

Wich (at least in FF 33) is set to a default value of 20.

gl.

And as noted on this other stackoverflow question:

Each browser has web workers limitations (Firefox has 20, Chrome 60+, Opera 16); however, you can change it in Firefox -> dom.workers.maxPerDomain; as for your actual question, if you can or cannot avoid this limitation, I'm not sure. "Workers (as these background scripts are called herein) are relatively heavy-weight, and are not intended to be used in large numbers." Can you give an exact situation where you would want to use more than 20 workers? – Marius Balaban Nov 26 '12 at 22:34

Answer 4

I also played around with workers and tried to find an optimum for my case (encryption of strings). It was 8 too.

Similar question and discussion: Number of Web Workers Limit