[Xcb] Display freeze hanging in xcb_wait_for_reply

Christian Linhart chris at DemoRecorder.com
Thu Sep 25 07:16:30 PDT 2014

Hi Daniel,

Since you are using a pretty old version of libxcb, I suggest that you download 
* the newest HEAD from the libxcb-git together with the HEAD from proto:
  and try it with that.

* and/or the newest offical releases of libxcb and proto ( 1.11. )
  and try it with that.

If it works with the newer version, then it is an old bug which was fixed after release 1.9.
If the problem still exists, then we know there is still a problem in the current release.

>From your problem description, the problem may also be in the X-Server.
I suggest that you try to set the DISPLAY to a remote machine with a different X-Server version.
If it works there, this may hint to an X.Server problem.

In any case, a backtrace, as suggested by Uli Schlachter, will be helpful.


On 09/25/14 12:21, Daniel Kuhne wrote:
> We are facing display freeze with libxcb-1.9 in multithreaded environment.
> We see this freeze when we set resolution of our application to display resolution,
> graphic drivers performs a flip instead of a blit operation. In that case, after some frames,
> we will never come back from xcb_wait_for_reply() in XReply() inside xcb_io.c. If 
> we set resolution not to fullscreen, we do get a blit for each frame, we never fall into 
> a display freeze. We are wondering if this a known issue with xcb? 
> Could you please say how we should provide more information. Where should we do some 
> debug prints?
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> Xcb at lists.freedesktop.org
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