bug#15876: 24.3.50; Highly degraded performance between rev 114715 and 115006

[Eli Zaretskii]

> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Cc: Jan Djärv <jan.h.d@swipnet.se>,
>         sva-news@mygooglest.com, 15876@debbugs.gnu.org, dmantipov@yandex.ru
> Date: Fri, 13 Dec 2013 11:50:49 -0500
> 
> >  . I also tried a different approach: compact only those font-entities
> >    that don't match any font that is still used by some face on some
> >    frame.  (I used font_match_p for that.)  This seems to work, except
> >    that font_match_p is evidently not safe enough to be used in the
> >    middle of GC -- I got crashes a few times.  When it did work, it
> >    again prevented the compaction, as if the compacting code were not
> >    there at all.
> 
> Maybe a better way goes along the lines of:
> - every time we use a font, we set an "in_use" bit.

The problem is not with fonts, it is with font-entities (a different
type of object) stored within the font cache.

I couldn't find any code that marks them "in use" or records them in
some other Lisp object (which would have prevented them from being
GC'ed).

> - every now and then (ha ha!), we let the GC collect fonts that don't
>   have their "in_use" bit set.

You didn't say who will reset that bit.