[whatwg] Workers: what should happen when exceeding worker limit?

Thu Sep 23 02:06:20 PDT 2010

What should happen when instantiating a Worker that cannot be started
because of the limit on the number of workers?  Chrome 6 and Chromium
7.0.532.0 (60255) put the 17th worker in a queue, to be created when
some existing worker terminates.  This queue seems to be limitless in
size (or at least it is large).  In Opera 10.70 (9049), instantiating
the 17th Worker throws "Error: QUOTA_EXCEEDED_ERR".

I'd much prefer that it failed immediately, rather than being put in a
queue.  I use a SharedWorker as an enhancement, and I don't want to
implement a timeout for the Worker spawning (I'd rather have it fail,
so that I can immediately do something else).  I can avoid spawning
more than 16 workers, but I never know if another tab has already
created enough workers to exhaust the global worker limit (64 in
Chrome, ~118 in Opera).  And if I really want to spawn the worker, I
can always try spawning it again soon.

This message describes why Chromium queues up excessive workers:
http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2009-July/020865.html

I'm not sure that making it work like a "sea of XHRs" is the right
thing, for two reasons:
1) Workers often stay running for a long time; XHRs are usually short-lived.
2) Most web applications don't expect to definitely have access to a
Worker, so they work around it by running code in the page instead of
the worker.  This same code path could be used when the worker limit
is exhausted.  With XHRs, there's generally no workaround: you need
the data, no matter what.

Here's a crude test page that instantiates 17 workers:
<!doctype html>
<div id="log"></div>
<script>
var workers = [];
for(var i=0; i < 17; i++) {
  try {
    workers.push(new Worker('empty.js'));
    document.getElementById('log').innerHTML +=
        'Worker #' + i + ' instantiated.<br>';
  } catch(e) {
    document.getElementById('log').innerHTML += e.toString() + '<br>';
  }
}
</script>

Any thoughts would be appreciated.

Thanks,

Ivan