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From: mouse@lightning.mcrcim.mcgill.EDU
Newsgroups: comp.windows.x
Subject: Re:  Interrupting an X program... how?
Message-ID: <9103020240.AA05771@lightning.McRCIM.McGill.EDU>
Date: 2 Mar 91 02:40:37 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 41

> A traditional program under Unix can be interrupted by hitting
> Control-C (or whatever other character defined by stty).

> How do you send a signal to an X program?

The same way you send a signal to any other program.  Use kill (the
command or the syscall) or type one of the signal-generating characters
on the process' control tty when it's in the foreground.

> Specifically, a program which goes off and does lengthy calculations,
> and doesn't check for X events until the calculations are complete.

> Recasting this (existing) program to check for X events during the
> aforesaid lengthy computations is not really an option (among other
> things, the computations are in Fortran).  :-(

> So how can I arrange for the window manager or whatever to send a
> signal to a program running in an X window?

This is more or less impossible.  The program may be on a different
machine; it may even be running under an OS that doesn't have the
notion of signals at all.

In your particular case, since you have source to the program, you may
be able to do something like attaching a property to your top-level
window giving your process ID and some sort of machine identifier, then
implementing something which checks for these and, if running on the
same machine, sends the desired signal.

With a bit of care (ok, with a good deal of care :-), you should be
able to get away with checking for X events inside a SIGALRM handler,
then arranging for SIGALRM to be delivered periodically while inside
the crunching loop.  (This assumes (a) that you aren't already using
SIGALRM for anything, or can overload it, and (b) that you go to some
trouble to make certain you don't trip over any of the landmines
lurking in the use of Xlib from both mainline and signal handlers.)

					der Mouse

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