bug#58158: 29.0.50; [overlay] Interval tree iteration considered harmful

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: monnier@iro.umontreal.ca,  58158@debbugs.gnu.org
> Date: Thu, 29 Sep 2022 12:05:50 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Can you propose a fix?
> 
> Other than completely rewrite at least this part, no.
> 
> > I guess the begin_iteration/end_iteration dance is because the tree
> > could be in inconsistent state in-between?  If so, what would it take
> > to avoid the inconsistency?
> 
> I find it very hard to tell why this is done the way it is.  If someone
> knowing the code can think of a reason, please speak up.

I may be missing something, but it looks like the sole purpose of the
iter_start/iter_finish dance is to ensure only one iteration per tree
is running at any given time, and that's because the iteration uses
some state variable(s) of which there's only one instance per tree.

Stefan, am I missing something?