Re: checkX problems

[Jon TURNEY <jon dot turney at dronecode dot org dot uk>]

On 30/10/2009 13:48, Ken Brown wrote:
> I'm having trouble with checkX.  I haven't seen other people complain
> about this, so I assume it's something about my system, but I can't
> figure out what. There are two symptoms:
>
> 1. If I run checkX with a timeout, the timeout seems to be ignored. For
> example, with the X server *not* running:
>
> $ checkX -d 127.0.0.1:0.0 -t 100 --debug
> checkX.exe DEBUG: displayname : '127.0.0.1:0.0'
> checkX.exe DEBUG: opt_location: 0
> checkX.exe DEBUG: opt_loglevel: 7
> checkX.exe DEBUG: opt_nogui : 0
> checkX.exe DEBUG: opt_notty : 0
> checkX.exe DEBUG: opt_timeout : 100.00
> checkX.exe DEBUG: (adjust_path) path is :
> /usr/local/texlive/2009/bin/i386-cygwin:/usr/local/bin:/usr/bin:/c/Program
> Files/ThinkPad/Utilities:/c/WINDOWS/system32:/c/WINDOWS:/c/WINDOWS/System32/Wbem:/c/Program
> Files/Intel/Wireless/Bin/:/c/Program Files/IBM ThinkVantage/Client
> Security Solution:/c/Program Files/ThinkPad/ConnectUtilities:/c/Program
> Files/QuickTime/QTSystem/:/c/Program Files/Common
> Files/Lenovo:/usr/lib/lapack:/usr/X11R6/bin:/usr/bin
> checkX.exe DEBUG: (find_X11_lib) DLL is /usr/bin/cygX11-6.dll
> checkX.exe DEBUG: (dlopen_X11_lib) /usr/bin/cygX11-6.dll dlopen'ed
> successfully.
> checkX.exe DEBUG: (load_X11_symbols) symbol XOpenDisplay loaded ok
> checkX.exe DEBUG: (load_X11_symbols) symbol XCloseDisplay loaded ok
> checkX.exe DEBUG: (try_with_timeout) Using delay of 100 secs, 0 nanosecs
> (100.00)
> checkX.exe DEBUG: (try_with_timeout) xserver search was unsuccessful
> checkX.exe Info: could not open X display '127.0.0.1:0.0'
> checkX.exe DEBUG: returning with status 1
> checkX.exe Info: Exiting with status 1
>
> The problem is that it returns within a second, in spite of the timeout.
> Or am I misunderstanding what the timeout is supposed to do?

I think this is a misunderstanding here.

Looking at the source, the timeout is the maximum time checkX will wait for an 
XOpenDisplay() to complete.  If that fails immediately (e.g. due to with 
ECONNREFUSED), checkX will stop immediately.

This is pretty reasonable. If there is nothing listening on the socket for the 
X server, that is not going to get better if we wait...

... except if the server happens to be starting up when we execute checkX.

So, this is not quite what startxwin.bat requires, as the server may still be 
in the process of starting up.  Fortunately, the X server binds it's socket 
pretty early in the startup, so this probably works pretty well, but in theory 
at least there is still a possible timing window in startxwin.bat.

So it perhaps be useful if checkX retried the XOpenDisplay() periodically 
until the timeout was up (as xinit does)

> 2. If I start the X server by using the default startxwin.bat or
> startxwin.sh (both of which call checkX), the server is very unstable
> and crashes within a few minutes. This happens consistently, and it
> never happens if I comment out the line calling checkX.

I think I was able to reproduce this problem (it is not how I normally start 
the X server)

However, now I come back to look at this in detail, the problem no longer 
seems to exist. Are you still able to demonstrate it?

> I tried strace'ing checkX, but I don't know what to look for in the
> output. (I'll send it if it would be useful, but I don't want to spam
> the list otherwise.) I'm attaching cygcheck output.

--
Jon TURNEY
Volunteer Cygwin/X X Server maintainer

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