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Date:	Sat, 16 Oct 2010 14:06:56 -0400
From:	Ken Brown <kbrown AT cornell DOT edu>
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To:	cygwin <cygwin AT cygwin DOT com>
Subject:	Re: Sending signals to a subprocess
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On 10/16/2010 1:17 PM, Ken Brown wrote:
> I could use some help fixing a longstanding bug in the Cygwin build of
> emacs, in which emacs is unable to send signals to subprocesses.  A
> symptom from the user's point of view is that one cannot interrupt a
> process in shell mode by typing C-c C-c.  I've found a workaround that
> handles that case (SIGINT), as well as SIGQUIT and SIGTSTP.  But as long
> as I'm fixing this, I'd like to do it right and figure out how to handle
> all signals.
>
> This boils down to finding the right process group ID to pass to 'kill'.
> On systems that have TIOCGPGRP, emacs uses the following code (in
> src/process.c) to get this ID:
>
> /* Return the foreground process group for the tty/pty that
>      the process P uses.  */
> static int
> emacs_get_tty_pgrp (p)
>        struct Lisp_Process *p;
> {
>     int gid = -1;
>
> #ifdef TIOCGPGRP
>     if (ioctl (p->infd, TIOCGPGRP,&gid) == -1&&  ! NILP (p->tty_name))
>       {
>         int fd;
>         /* Some OS:es (Solaris 8/9) does not allow TIOCGPGRP from the
> 	 master side.  Try the slave side.  */
>         fd = emacs_open (SDATA (p->tty_name), O_RDONLY, 0);
>
>         if (fd != -1)
> 	{
> 	  ioctl (fd, TIOCGPGRP,&gid);
> 	  emacs_close (fd);
> 	}
>       }
> #endif /* defined (TIOCGPGRP ) */
>
>     return gid;
> }
>
> What's the right way to do this in Cygwin?

I guess it's clear from the context, but I should have said that the 
problem only arises when emacs has to communicate with the subprocess 
through a tty that is not the controlling tty of emacs.  So tcgetpgrp() 
doesn't work.

Ken

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