bug#51490: Show an indicator when Emacs is busy somewhere in the Emacs window

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: stefan@marxist.se,  51490@debbugs.gnu.org
> Date: Wed, 21 Sep 2022 13:06:25 +0200
> 
> > If so, what are you trying to save by "modifying the glyphs directly",
> > and why do you think doing so will produce some savings, as opposed to
> > just update the mode line normally?
> 
> Because this will be happening from an alarm while Lisp code is running,
> and we can't run other Lisp code while that is happening.

Mode line is drawn in C, not in Lisp.

And if the problem is that we cannot run the display code, either,
then how would it help to poke the glyph?  It won't be shown on the
glass, because redisplay cannot run.  Right?  Or what am I missing?