[Xcb] [Bug 26511] Assertion while calling XPending() (xcb_io.c:242)

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Wed Feb 10 11:17:12 PST 2010


--- Comment #4 from Jamey Sharp <jamey at minilop.net>  2010-02-10 11:17:12 PST ---
This assert means that libX11 got responses from the X server for requests that
it doesn't believe have been sent. I don't have a hypothesis yet about how that
could happen.

I don't immediately see how the architecture of either machine could matter
here. Can you check whether you can reproduce this bug on either the ppc32
machine or the x86-64 machine alone?

I'll probably need you to print the values of dpy->last_request_read and
dpy->request at the point where the assertion fails, and it may help if you
could attach a capture of the X network traffic in the same failing session
using something like wireshark.

Judging by the assert line number, I think your libX11 must be at least version, but no later than 1.3. The only more recent change to xcb_io.c is a
Cygwin build fix, which had better not matter.

I hope the two commits in between those versions don't matter on a 32-bit
client, but I'm not certain that "Avoid datatype overflow on AMD64 and friends"
was correct, so it'd be nice to know if that commit is involved. (I hadn't
noticed it before today.)

Is OpenSUSE applying any patches to libX11's xcb_io.c? I'd guess not, but if so
that would be important to know.

I suspect the versions of the server and libxcb don't matter, which is
fortunate since the OpenSUSE version numbers are meaningless to me.

> Something that might be relevant: here, the x86_64 machine is a laptop. If I'm
> running on AC power and disconnect the cable, the browsers will die
> immediately.

Sounds like the problem occurs when an event arrives, which makes sense. I'm
curious what event your desktop environment is triggering on the switch to
battery, but it doesn't matter.

I'm also curious how you got a Python traceback in the middle of a gdb stack

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