X server not responding when querying X pointer position

[Thierry Reding]

* Daniel Stone wrote:
> Hi,
> 
> On Thu, Jul 07, 2011 at 11:17:57AM +0200, Thierry Reding wrote:
> > I see strange behaviour with a program I'm developing. Basically the program
> > embeds WebKit to display a graphical user-interface. Sometimes during testing
> > (which is just playing around with some buttons on the screen) it happens that
> > the GUI gets stuck completely.
> > 
> > Attaching to the program at runtime after reproducing the hang, I was able to
> > get the following backtrace (paths shortened for readability):
> > 
> > 	(gdb) bt
> > 	#2  0xb56939aa in poll () from /lib/libc.so.6
> > 	#3  0xb55c2640 in _xcb_conn_wait (c=0x867a748, cond=0xbfe46ec0, vector=0x0, count=0x0)
> > 	    at .../build/packages/xorg/lib/xcb/libxcb-1.7/src/xcb_conn.c:313
> > 	#4  0xb55c3f87 in xcb_wait_for_reply (c=0x867a748, request=6396, e=0xbfe46f5c)
> > 	    at .../build/packages/xorg/lib/xcb/libxcb-1.7/src/xcb_in.c:378
> > 	#5  0xb761b458 in _XReply () from /usr/lib/libX11.so.6
> > 	#6  0xb7610b5e in XQueryPointer () from /usr/lib/libX11.so.6
> >       [...]
> > 
> > Looking at this there seems to be a problem when trying to display tooltips,
> > possibly for one of the buttons being pressed/hovered over. My best guess is
> > that for some reason, the X server is not responding to the XQueryPointer
> > request.
> > 
> > I'm running this on X.Org server 1.10.2, with libX11 1.4.3 and libxcb 1.7. I'm
> > also cross-compiling this from x86_64 to i786 if that is at all important.
> > 
> > Does anybody have any ideas about what might be the cause or do you have any
> > pointers as to where I should look further? I can provide more information if
> > needed. Also I wasn't sure whether or not to Cc the XCB mailing list on this
> > because it seems more of an X server problem. I could be completely wrong of
> > course.
> 
> The two most pertinent questions I can think of are:
>     * are you using threads at all?

I try to keep the number of threads used to a minimum, but since WebKit is
involved and the program also uses libvlc as well, several threads will be in
use.

>     * has someone else called XGrabServer()?

Apart from _gdk_windowing_window_at_pointer() listed in the trace, not that I
know of. Perhaps libvlc could be the culprit here. I will try to trace all
calls to XGrabServer, see where that leads.

Thanks,
Thierry
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