Re: poor handling of multiple C-g with multi-tty (apparent hangs)

["Ami Fischman" <ami@fischman.org>]

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This was never checked in, even though it is strictly an improvement to the
current situation (see my original email for why I believe this is an
improvement to emacs users as a whole).  Are you still working on refining
it or would you mind checking it in as it is?

-a

On Mon, Aug 11, 2008 at 10:40 AM, Chong Yidong <cyd@stupidchicken.com>wrote:

> "Ami Fischman" <ami@fischman.org> writes:
>
> > Emacs has code to deal with C-g being entered while a quit is already
> > in progress, meant to suspend emacs and drop the user to the superior
> > shell or debugger (see section 59.7 Emergency Escape of the emacs
> > info).  This is done if emacs believes it's a good idea, which
> > criteria includes "running in tty mode".  Unfortunately this was never
> > updated to work correctly with the multi-tty patch.
>
> Thanks for pointing this out.
>
> IIUC, the "emergency C-g" behavior is geared towards the traditional
> setup where there's only one text-only terminal available.  There, the
> emergency C-g is the only way to drop back to the shell if Emacs gets
> stuck.
>
> It's disabled for graphical terminals because there, you can open up a
> separate terminal to kill/suspend the Emacs process.
>
> This implies that we should disable the emergency C-g if Emacs is
> running on more than one terminal, as in the following patch.
>
> *** trunk/src/keyboard.c.~1.969.~       2008-08-05 17:08:23.000000000 -0400
> --- trunk/src/keyboard.c        2008-08-11 13:35:43.000000000 -0400
> ***************
> *** 10953,10958 ****
> --- 10953,10976 ----
>    errno = old_errno;
>  }
>
> + /* If there is exactly one terminal active, return it.  Otherwise,
> +    return NULL.  */
> +
> + static struct terminal *
> + just_one_tty_p ()
> + {
> +   struct terminal *t, *found = NULL;
> +   for (t = terminal_list; t; t = t->next_terminal)
> +     if (TERMINAL_ACTIVE_P (t))
> +       {
> +       if (found)
> +         return NULL;
> +       else
> +         found = t;
> +       }
> +   return found;
> + }
> +
>  /* This routine is called at interrupt level in response to C-g.
>
>     It is called from the SIGINT handler or kbd_buffer_store_event.
> ***************
> *** 10968,10980 ****
>  handle_interrupt ()
>  {
>    char c;
>
>    cancel_echoing ();
>
> -   /* XXX This code needs to be revised for multi-tty support. */
>    if (!NILP (Vquit_flag)
>  #ifndef MSDOS
> !       && get_named_tty ("/dev/tty")
>  #endif
>        )
>      {
> --- 10986,10999 ----
>  handle_interrupt ()
>  {
>    char c;
> +   struct terminal *t;
>
>    cancel_echoing ();
>
>    if (!NILP (Vquit_flag)
>  #ifndef MSDOS
> !       && (t = just_one_tty_p (), t)
> !       && t->type == output_termcap
>  #endif
>        )
>      {
>

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