bug#7225: 23.2.50; [PATCH] C-c C-c doesn't work in shell mode (Cygwin)

[Ken Brown <kbrown@cornell.edu>]

On 10/16/2010 9:26 AM, Eli Zaretskii wrote:
>> Date: Sat, 16 Oct 2010 08:44:28 -0400
>> From: Ken Brown<kbrown@cornell.edu>
>> CC: "7225@debbugs.gnu.org"<7225@debbugs.gnu.org>
>>
>>>> C-c C-c
>>>> (The cat process doesn't get killed.)
>>>
>>> Is the reason for this known?  It looks like the `kill' syscall isn't
>>> doing its job, but if that's so, there should be a good reason for
>>> that.
>>
>> The problem is the group id in the call to 'kill'.  Cygwin doesn't
>> define TIOCGPGRP, and the group id as set in line 6233 of process.c
>> (emacs-23 branch) is the wrong group id.
>
> Does Cygwin have another way of getting the process group ID?  If so,
> can it be used in process_send_signal instead of emacs_get_tty_pgrp?
>
>>> Did you test it with a subprogram that puts its stdin into a mode
>>> where (speaking in termios terms) the ISIG flag in c_lflag passed to
>>> tcsetattr is unset?
>>
>> I don't know how to do this.  Can you give me a short test program to try?
>
> Sorry, no, not off-hand.
>
>>> In any case, I wouldn't recommend to take this workaround unless we
>>> understand why this doesn't work without it.
>>
>> I'm not sure why you call it a workaround.  The comments preceding (and
>> in) the definition of process_send_signal make it clear that
>> SIGNALS_VIA_CHARACTERS is the preferred method.  It's used by GNU/Linux
>> (see src/s/gnu-linux.h) and several other systems.
>
> SIGNALS_VIA_CHARACTERS is the preferred method for a few signals that
> are raised by keyboard characters.  But unless you find a way to send
> any signal to a subprocess on Cygwin, you will still have a bug,
> although not with SIGINT.

OK, now I understand.

> So I suggest to look into tweaking process_send_signal so that it
> works with Cygwin.  It looks like it makes all kinds of assumptions
> regarding systems that don't have TIOCGPGRP, and they are probably
> wrong for Cyugwin.  Or maybe you need something special in
> EMACS_KILLPG.
>
> When you have fixed process_send_signal, you can then introduce
> SIGNALS_VIA_CHARACTERS for Cygwin.
>
> However, this is just a suggestion.  If you don't feel like digging
> into these issues, go ahead and commit the change.

Thanks for the suggestion.  I would like to dig into this, but I don't 
really know enough.  I'll see if I can get some help on the Cygwin list.

Ken