bug#28542: Temporary failure in name resolution while quitting emacs

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: bshanks3@hotmail.com,  28542@debbugs.gnu.org
> Date: Sun, 06 Dec 2020 13:50:14 +0100
> 
> Sure, a prompt with a timeout would be fine by me.
> 
> Looking at the code again:
> 
>   /* Fsignal calls emacs_abort () if it sees that waiting_for_input is
>      set.  */
>   waiting_for_input = 0;
>   if (noninteractive)
>     safe_run_hooks (Qkill_emacs_hook);
>   else
>     run_hook (Qkill_emacs_hook);
> 
> Would it make sense to create a new Lisp-level function to do the
> run-hook/prompting stuff, and call out to that?  And move the setting of
> waiting_for_input into the "then" branch?

I think it'd be good to have a run_hook_with_timeout function, yes.
Whether it should be exposed to Lisp, I'm less certain: what would be
the use case that isn't this single place?

As for zeroing waiting_for_input: it's almost certainly shouldn't be
part of that, since it should always be zero when Emacs signals an
error.  We do this here because this might be exiting due to a fatal
signal, in which case all bets are off, and we should better be safe
than sorry.