bug#71454: 30.0.50; Performance issues with font selection

[Eli Zaretskii <eliz@gnu.org>]

> From: Kai Ma <justksqsf@gmail.com>
> Date: Mon, 10 Jun 2024 14:35:50 +0200
> Cc: Jeremy Bryant <jb@jeremybryant.net>,
>  71454@debbugs.gnu.org
> 
> 
> 
> > On Jun 10, 2024, at 13:55, Eli Zaretskii <eliz@gnu.org> wrote:
> > 
> >> Cc: 71454@debbugs.gnu.org
> >> From: Kai Ma <justksqsf@gmail.com>
> >> Date: Mon, 10 Jun 2024 00:17:55 +0200
> >> 
> >> 
> >>> On Jun 10, 2024, at 00:10, Jeremy Bryant <jb@jeremybryant.net> wrote:
> >>> 
> >>> Would you be able to provide a self-contained series of steps starting
> >>> from emacs -Q?
> >> 
> >> On my machine it is extremely easy to reproduce by simply:
> >> 
> >> 1. emacs -Q
> >> 2. Switch to *scratch*
> >> 3. Copy the provided text into *scratch*
> >> 4. Emacs will freeze for 17 seconds or so, and it cannot be interrupted by C-g
> > 
> > I cannot reproduce this, I get an almost instantaneous redisplay with
> > those characters.
> > 
> > When your Emacs eventually displays the text, how many characters are
> > shown as boxes with hex code, and which ones are those?
> 
> None are hex code here. They eventually get displayed, but it takes a long time.

Then it definitely sounds like macOS specific.  Does anyone know how
Emacs on macOS searches for fonts, and whether there are any
font-caching facilities, either in Emacs or by the OS?