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Subject:	Re: Bug in libX11 or something near ?
To:	The Cygwin Mailing List <cygwin AT cygwin DOT com>
References:	<CAC-34C0eHbNVnKT9HV1JGd3MJ4R=njABKWavXkiYLAUkjcXvKQ AT mail DOT gmail DOT com>
Cc:	Philippe <philippe DOT raven AT gmail DOT com>
From:	Jon Turney <jon DOT turney AT dronecode DOT org DOT uk>
Message-ID:	<5fa8b89e-1a9d-2619-f49f-c1680d587148@dronecode.org.uk>
Date:	Sun, 23 Jun 2019 18:57:38 +0100
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On 18/06/2019 17:07, Philippe wrote:
> I'm using Cygwin/X and identified a critical bug using some piece of
> software.
> I don't really know where to begin, but I'm able to crash some applications
> via the application's menu, only with Cygwin/X (no crash with Xming, and no
> crash under any Linux distributions).
> 
> For information, It goes through VirtualGL. I'll give the example on how to
> reproduce it with a free software : Paraview (under linux).
> 
> So you open Paraview, then clic on "View" > show the "Toolbars" submenu,
> then you move your mouse directly on the "Sources" or "Edit" menu, then it
> crashes immediately. The only error message in the linux shell (from where
> it was launched) is "paraview: Fatal IO error: client killed".
> 
> I got those lines in the XWin.0.log file :
> SetupSysMenu: GetSystemMenu() failed for HWND 0x130746
> winTopLevelWindowProc - WM_DESTROY - WM_WM_KILL

Thanks for reporting this problem, and the clear reproduction steps.

This is an interesting bug in the Cygwin X server's multiwindow mode. It 
seems that under some circumstances, when removing a WM_TRANSIENT_FOR 
window which in turn had a child WM_TRANSIENT_FOR window (e.g. a menu 
which has a sub-menu), the X server's integrated WM would get confused 
and think that the main window had been closed (so terminating the 
application).

I've has a go at fixing this and uploaded a snapshot at [1].  Perhaps 
you could try that and see if it improves things for you?

(I guessed you are using 64-bit Cygwin. If you need a 32-bit build 
instead, please let me know and I'll generate one)

[1] 
ftp://cygwin.com/pub/cygwinx/x86_64/XWin.20190623-git-210c90b328cf8f18.exe.bz2

-- 
Jon Turney
Volunteer Cygwin/X X Server maintainer

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