[html5] Web Workers: Race-Condition setting onmessage handler?

[Tobias Sauerwein]

Hi!

I am wondering what prevents a web worker from running into race-conditions
when setting the onmessage handlers. I am worried about that a web worker
posts a message before the main script has set up the onmessage handler, or
the other way around, that the web worker posts a message before the main
script has set up its onmessage handler.

I know that there is a message queue [1], but you can easily make up an
example where a message is not enqueued:

Main Script:

var worker = new Worker("webworker.js");
> worker.onmessage = function(event) {
>     console.log('onmessage ' + event.data)
> };
> worker.postMessage("start");
>


'webworker.js':

setTimeout(
>     function() {
>         onmessage = function(event) {
>             postMessage("message received");
>         };
>         postMessage("done");
>     }, 1000);
>


The output is (in Chromium 6.0.475.0 and Firefox 4.01b, Opera 10.70 also
outputs "onmessage message received"):

onmessage done
>

So the "onmessage" handler of the web worker is never called.


Is this the behavior the specification requests, or is it a bug in
Chrome/Chromium and Firefox?

Tobias



[1]:
http://www.whatwg.org/specs/web-apps/current-work/multipage/comms.html#port-message-queue
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