bug#45898: 27.1; wedged in redisplay again

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Date: Sat, 25 Jun 2022 13:10:14 +0200
> Cc: 45898@debbugs.gnu.org
> 
> > You mean, just update_ticks?  That's too general, IMO.  I'd like
> > people to have an idea what that does when they just see the call.
> > 
> > But I'm not good with names.
> 
> I love update_ticks!  And I'm good with names, trust me ;-).  And I'm 
> volunteering to do the work!

Fine with me, have fun.

> >> You mean a case, where small numbers of ticks sum up by calling these Lisp 
> >> functions often enough?
> > 
> > Actually, I meant something even simpler: a Lisp program that calls,
> > say, regexp search repeatedly, to accumulate enough ticks that would
> > signal an error, thus aborting that Lisp program.
> 
> That's 100% what I also meant.  Sorry for not being clear.
> 
> Do you think redisplaying_p would suffice as an indicator?  
> 
> That should be true if and only if redisplay_internal is in the call stack.  
> Also, redisplay_internal is a no-op if called recursively.  Or better said, 
> both used to be the case.

Yes, I know; and it's still the case.  Originally, I indeed only
looked at redisplaying_p.  But then cases with C-n and C-v wouldn't be
caught, because these commands, although they call the display code,
run without redisplay_internal in the call stack.  And very sluggish
response from these and similar commands is generally perceived as
"redisplay problems".  So I wanted to catch them as well, without
waiting for redisplay cycle they cause (which by itself may or may not
be "too slow" -- just moving the cursor is an optimization there, as
you know).