[Xcb] xcb_wait_for_reply deadlocking with xcb_property_changed call

Nicholas Allen nick.allen at onlinehome.de
Sat Mar 27 04:30:43 PDT 2010

Unfortunately, I'm also experiencing these deadlocks when I call
xcb_wait_for_event even though I've called xcb_flush just before. I
thought it was only happening when I used the property util functions
but I now caught it under the debugger outside of this function. This
doesn't happen as often as with the property change helper library but
it still happens occasionally.

So it seems there is a major thread deadlocking bug in XCB. I don't
really know how to debug it though. Any suggestions? I'm not at all
familiar with the XCB code base so any pointers greatly appreciated...



Nicholas Allen wrote:
> Hi,
> I had a problem a while ago with deadlocking that seems to have been
> solved by moving from xlib to XCB and calling xcb_flush before
> xcb_wait_for_event. However, I recently started experiencing this
> deadlocking again. I've noticed it always happens when I call the
> xcb_property_changed function from the property utils and the deadlock
> happens inside xcb_wait_for_reply.
> I only recently added this to the code so it could be that I'm doing
> something wrong. The last time I had deadlocking problems it was because
> I wasn't calling xcb_flush before waiting for the next event. Should I
> be doing the same before calling xcb_property_changed function? Or
> perhaps the xcb_property_changed function should be doing this itself
> (this would make more sense to me). Couldn't xcb_wait_for_reply
> automatically flush the connection first to prevent these kinds of problems?
> Cheers,
> Nick
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