bug#21747: 25.0.50; while-no-input breaks kbd event handling when called from post-command-hook

[Eli Zaretskii]

> Date: Sat, 24 Oct 2015 11:30:42 +0100
> From: Artur Malabarba <bruce.connor.am@gmail.com>
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>, Kim Storm <storm@cua.dk>, 
> 21747@debbugs.gnu.org, 
>       Eli Zaretskii <eliz@gnu.org>
> 
> So maybe the docstring for post-command-hook should point out this detail and
> recommend that functions added to this hook call sit-for if they're going to 
> do
> potentially expensive processing. 

Just being potentially expensive is not enough to trigger the problem.
You need to actually hog Emacs (or close to that) to prevent redisplay
from eventually happening.

I agree that expensive processing in post-command-hook is not a good
idea (and said so several times in the past), but people are still
doing that, so I guess just advertising the problem is not enough.  (I
don't object to adding this to documentation, of course.)