On 09.03.2010, at 9:45, Drew Wilson wrote:
Yeah, it's a race condition - it seems to all depend on whether the
worker resource gets loaded before the postMessage loop starts.
Failure rate is around 30-50% on my machine.
It would help to have a more detailed description of the problem. I've
been following the discussion in bugs and in this thread, but I'm
still unsure about some aspects of it.
Seems that there are two issues at hand:
1) We feel the need to change how Document::postTask() behaves,
because otherwise, the patch for <https://bugs.webkit.org/show_bug.cgi?id=34726
> doesn't work. We feel the need because it makes little sense for it
to have drastically different behavior depending on what thread it's
called from.
It feels like a good change to make indeed, but I'm surprised that it
apparently went through review unmentioned and unquestioned. The
questions to ask are why exactly it was needed, and whether there are
other ways to fix bug 34726.
2) if we make that change, the worker-cloneport.html test starts to
fail.
I didn't attempt to debug this myself, and I don't quite understand
the problem description. I see only one postMessage loop in the test,
and it's in worker code. How can it be executed before the worker
resource gets loaded?
It looks like events have priority in Cocoa, and I'm guessing that
performSelectorOnMainThread() creates events with a higher priority
than those generated by URLConnection, which can lead to starvation.
I'm not certain what the right fix is, other than to maybe use a
different method of dispatching events other than
performSelectorOnMainThread that lets us set a lower priority?
These main thread calls do not use events for processing. CF/NSRunLoop
has a concept of run loop sources, which can generate events or
perform other actions, see <http://developer.apple.com/mac/library/documentation/CoreFoundation/Reference/CFRunLoopRef/Reference/reference.html
> and <http://developer.apple.com/Mac/library/documentation/CoreFoundation/Reference/CFRunLoopSourceRef/Reference/reference.html
>.
- WBR, Alexey Proskuryakov
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