Sending signals to a subprocess

Ken Brown
Sat Oct 16 18:07:00 GMT 2010

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;

   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?


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