From: Ken Brown <kbrown@cornell.edu>
To: Eli Zaretskii <eliz@gnu.org>
Cc: "7225@debbugs.gnu.org" <7225@debbugs.gnu.org>
Subject: bug#7225: 23.2.50; [PATCH] C-c C-c doesn't work in shell mode (Cygwin)
Date: Mon, 18 Oct 2010 07:58:35 -0400 [thread overview]
Message-ID: <4CBC366B.9060906@cornell.edu> (raw)
In-Reply-To: <E1P7jhN-0004eE-4E@fencepost.gnu.org>
On 10/18/2010 2:59 AM, Eli Zaretskii wrote:
>> Date: Sun, 17 Oct 2010 19:11:15 -0400
>> From: Ken Brown<kbrown@cornell.edu>
>> CC: "7225@debbugs.gnu.org"<7225@debbugs.gnu.org>
>>
>>> The problem that code is trying to solve is how to send a signal to
>>> the whole process group starting at the shell (or whatever process is
>>> the group leader). Failure to do so could mean that the immediate
>>> subprocess of Emacs will get the signal, but its children will not.
>>> If the signal kills the subprocess, its children may remain behind as
>>> orphans.
>>
>> Am I misunderstanding the comment preceding the definition of
>> emacs_get_tty_pgrp?
>
> No, you understand it correctly.
>
>> Here's what it says:
>>
>> /* Return the foreground process group for the tty/pty that
>> the process P uses. */
>>
>> That's not the same as the process group of the shell, at least in
>> Cygwin.
>
> Right, these are in general two different groups.
>
>> You seem to be assuming that the process group of the shell will
>> include all of the shell's children.
>
> No, I didn't assume that, sorry for possibly confusing wording.
>
> There's a misunderstanding here: you were talking about the case of
> interrupting a command run by a shell, whereas I was talking about the
> case of sending a signal to a process that is not the shell, or
> perhaps about signaling the shell itself.
>
> For the case you ware talking about, sending the signal to the shell
> is indeed the wrong thing, because the shell makes any foreground
> command it runs into a separate process group, and it's that process
> group that we want to send the signal to. But for that case, you
> already found the right solution: use SIGNALS_VIA_CHARACTERS. This
> does exactly the right thing, like the INTR character typed on the
> tty.
>
> What's left is the case of signals other that SIGINT/SIGQUIT/SIGTSTP.
> In that case, in the absence of TIOCGPGRP, the code in process.c
> supports sending the signal only to p->pid's process group (if p->pid
> is not a group leader, only it itself will be signaled). I think this
> is better than punting, because if there _is_ a process group of which
> p->pid is the leader, doing what the code does now will not leave
> orphans, processes other than p->pid that belonged to p->pid's group.
> It is true that this group might not be the foreground process group,
> but with signals other than SIGINT/SIGQUIT/SIGTSTP, this matters much
> less, I think.
OK, I'm glad we understand each other now. But I still think line 6233
is wrong. That code gets executed only when current_group is non-nil.
(As far as I know, the only use case for this is in shell mode, when
we're trying to signal the foreground process; but I haven't done an
exhaustive search to see if there are other cases.) According to the
documentation preceding process_send_signal, we should not be sending a
signal to p->pid in that case. So I think punting is better than what's
done now. When current_group is nil, on the other hand, we do want to
send a signal to p->pid and its process group, and this is correctly
taken care of in line 6104.
As a practical matter, I don't think the problem is serious, but I do
think it's a bug. Anyway, I'll go ahead with my patch, since we both
agree that it's the right fix for the original bug I reported.
next prev parent reply other threads:[~2010-10-18 11:58 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-15 23:36 bug#7225: 23.2.50; [PATCH] C-c C-c doesn't work in shell mode (Cygwin) Ken Brown
2010-10-16 7:32 ` Eli Zaretskii
2010-10-16 12:44 ` Ken Brown
2010-10-16 13:26 ` Eli Zaretskii
2010-10-16 18:22 ` Ken Brown
2010-10-17 21:40 ` Ken Brown
2010-10-17 22:08 ` Eli Zaretskii
2010-10-17 23:11 ` Ken Brown
2010-10-17 23:39 ` Ken Brown
2010-10-18 6:59 ` Eli Zaretskii
2010-10-18 11:58 ` Ken Brown [this message]
2010-10-18 17:37 ` Ken Brown
2010-10-18 5:49 ` Jan Djärv
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