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

[Ami Fischman]

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 <address@hidden> wrote:

"Ami Fischman" <address@hidden> 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
       )
     {