Bug 23521

Summary: XQueryPointer locks the display while it's executing
Product: xorg Reporter: Dima Ryazanov <dima>
Component: Lib/XlibAssignee: Xorg Project Team <xorg-team>
Status: RESOLVED NOTOURBUG QA Contact: Xorg Project Team <xorg-team>
Severity: normal    
Priority: medium CC: peter.hutterer
Version: unspecified   
Hardware: x86-64 (AMD64)   
OS: Linux (All)   
Whiteboard:
i915 platform: i915 features:

Description Dima Ryazanov 2009-08-25 23:46:21 UTC 
I'm using Kubuntu 9.04; not sure which version of X it has. The version of xorg-server itself is 1.6.

If an application stops in the middle of a call to XQueryPointer - e.g., hits a breakpoint in gdb - the whole desktop freezes until the application is resumed. That also makes it difficult to resume the application.
It looks like XQueryPointer calls LockDisplay, so if another application - such as the window manager - makes a call to XQueryPointer, the call won't return until the first application finishes executing it.

Steps to reproduce:
1. Start Firefox
2. Attach gdb to it
3. Set a breakpoint in XQueryService.
4. When the breakpoint gets hit, set another one at xcb_wait_for_reply
5. When the second breakpoint is hit, the desktop will be frozen

Another way, without gdb:
1. Start Firefox
2. Start "ksysguard"
3. Right-click the firefox process, and choose "Monitor Input&Output".
4. Go back to using Firefox, wait for about a minute, and the desktop will become frozen.
Comment 1 Peter Hutterer 2009-09-02 19:03:00 UTC 
LockDisplay is a library-internal function and only affects that client.

can you please try to replicate this issue using xeyes. it's about as simple an apps as you get and it uses XQueryPointer too.
Comment 2 Dima Ryazanov 2009-09-02 19:12:07 UTC 
Weird... I cannot reproduce it in xclock, only in Firefox. I'll see if I can come up with a simple testcase.

(Btw, I made a typo in step 3 - it's XQueryPointer, not XQueryService)
Comment 3 Peter Hutterer 2009-09-02 21:23:53 UTC 
xclock? or xeyes?

If you can't reproduce the issue with xeyes, please close as NOTOURBUG and report with firefox.
Comment 4 Dima Ryazanov 2009-09-02 21:46:29 UTC 
Oops, yes, xeyes.

Ok, I'll open a Firefox bug.

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