On Sat, Oct 16, 2010 at 02:06:56PM -0400, Ken Brown wrote:
>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.
I am a little confused as to the difference between tcgetpgrp and
TIOCGPGRP given this man page description from "man 4 tty_ioctl" on
linux:
TIOCGPGRP pid_t *argp
When successful, equivalent to *argp = tcgetpgrp(fd).
Get the process group ID of the foreground process group on this
terminal.
TIOCSPGRP const pid_t *argp
Equivalent to tcsetpgrp(fd, *argp).
Set the foreground process group ID of this terminal.
Do you have a simple test case which demonstrates the difference between
the calls? It seems odd that TIOCGPGRP would allow more access to a tty
than tcgetpgrp.
cgf
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