Re: W2K Terminal Services and multiple users running X

[Igor Pechtchanski <pechtcha at cs dot nyu dot edu>]

On Wed, 24 Mar 2004, Harold L Hunt II wrote:

> Igor Pechtchanski wrote:
>
> > Harold,
> >
> >>... but the true difficulty in that is communicating the assigned
> >>display number back to the shell from which XWin was launched so that X
> >>programs can know the correct display to connect to.
> >
> > Why not have XWin write its display number to a file in /var/run, e.g.,
> > /var/run/XWin.$$.display, where "$$" stands for the PID of the XWin
> > process?  Since anyone who started XWin in the background from a shell
> > script will have access to its PID via $!, the following idiom will work:
> >
> >       XWin -multiwindow -emulate3buttons &
> >       XWINPID=$!
> >       DISPLAY_FILE=/var/run/XWin.$XWINPID.display
> >       while [ ! -e "$DISPLAY_FILE" ]; do sleep 1; done
> >       DISPLAY="`cat "$DISPLAY_FILE"`"
> >
> > Unfortunately, this approach won't work from .bat scripts (since they
> > aren't aware of Cygwin process IDs).  It also won't work if "cygstart
> > XWin" is used.  Any ideas on how to address it?
> >       Igor
>
> Batch scripts was more of my concern... it would be possible to do from
> a Cygwin shell like you describe (though I did not have all of the
> tricks in mind).
>
> Maybe the solution is to make the batch files just launch a shell script
> to do the heavy lifting... sort of cheating but if it makes it possible
> then it is acceptable to me.
>
> Harold

Harold,

It might be possible to have the batch file check for the existence of the
display file.  A rather crude first approximation would be (1) "sleep" for
a bit, then (2) do "dir /b /o:-d c:\cygwin\var\run\XWin.*.display" and (3)
extract the first file, then (4) "type" this file to get the display
number.

There may also be a way of guessing whether the file was created by the
current instance of XWin I don't have it fleshed out yet, but something
like: (1) check if c:\cygwin\var\run\XWin.lock.display exists, (2) if not,
create it, (3) run XWin, (4) sleep in a loop while the first file returned
by "dir /b /o:-d c:\cygwin\var\run\XWin.*.display" is XWin.lock.display;
finally, (5) extract the first file and (6) "type" the file to get the
display number.  The XWin.lock.display will serve as both a lock file for
concurrent invocations (still not foolproof, but much better than
nothing), and also as a marker (it will be the newest such file until XWin
creates one, so it will be first in the list).  Of course, step (7) is to
remove the lock file...

Hope this makes sense.  I think I can implement the above with the NT
command subset (cmd.exe commands).  I'm not sure if the limited
expressiveness of command.com on Win9x systems will allow this.  Any
takers?
	Igor
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