bug#26333: 26.0.50; Hang when displaying some special characters for the first time

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Sun, 23 Jan 2022 17:17:15 +0100
> Cc: 26333@debbugs.gnu.org
> 
> Steven Allen <steven@stebalien.com> writes:
> 
> > 1. Start `emacs -Q` (GUI mode, GTK3).
> > 2. Open a scratch buffer.
> > 3. Insert a MATHMATICAL SANS-SERIF BOLD SMALL LAMBDA (0x1D77A): 𝝺
> >
> > The first time this character is displayed, Emacs hangs for ~15 seconds
> > pegging the CPU at 100%. Unfortunately, the profiler doesn't seem to
> > notice/record this hang.
> 
> (I'm going through old bug reports that unfortunately weren't resolved
> at the time.)
> 
> I'm unable to reproduce this problem in Emacs 28, but then again, this
> problem seems to rely on a particular set of fonts being installed.

It could be that those 15 sec is what Emacs needs to search the
available fonts before it finds the one that can display the
character.