[webkit-dev] FrameLoader::stopAllLoaders and sync XHR

[Brady Eidson]

On Apr 22, 2013, at 8:37 AM, Joe Mason <jmason at blackberry.com> wrote:

> I'm trying to debug a deadlock on exit in a BlackBerry app that uses webkit (which is pretty hard to reproduce, so I don't have a cut-down test case yet). Right now my suspicions are on this behaviour:
> 
> a synchronous XMLHttpRequest starts loading (from a script running in the main frame)
> ResourceHandle::platformLoadResourceSynchronously gets called
> On BlackBerry, this is implemented by creating a nested EventLoop and calling loop.cycle()
> While in the nested event loop, BlackBerry::WebPage::stopLoading is called

There's your problem - loadResourceSynchronously is supposed to guarantee that - from WebCore's perspective - the main web thread is waiting on the resource load.

The nested event loop needs to be configured to *not* call back in to WebCore and *only* to service the load.

Note that this expectation re: sync XHR is why single-process, Web-thread-is-UI-thread browsers are expected to become completely non responsive during the sync XHR.

The proper way to allowing such an app to exit while a sync XHR is outstanding would be to cause the sync XHR load to fail at the networking layer *then* exit.

~Brady


> This is implemented by calling m_mainFrame->loader()->stopAllLoaders()
> 
> As far as I can see, FrameLoader::stopAllLoaders does NOT stop any XMLHttpRequest started from this frame - it just stops the provisionalDocumentLoader and documentLoader for the frame itself, and recursively does the same for all subframes. Is that correct?
> 
> Is there a way to find and stop all synchronous requests associated with a frame? (There should be only one...)
> 
> Thanks,
> Joe
> 
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