bug#19266: 24.4; Font-related window redrawing delays on OS X

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 4 Dec 2014 02:41:34 -0500
> From: Kirill Ignatiev <kirill.ignatiev@gmail.com>
> Cc: 19266@debbugs.gnu.org
> 
> > AFAICT, these delays are due to Emacs searching the system for
> > appropriate fonts needed to display those unusual symbols.
> 
> I understand that this needs to happen once.

It can happen once for each portion of a buffer that was not yet
displayed.

> The description of what triggers the delays is unclear because for me
> it's only reproducible incidentally, during normal work. I have
> fold-mode that hides large portions of text, and a number of frames.
> If I hide some previously-displayed text, go work in another frame,
> then come back and unhide the text, then there is the font-searching
> delay. Something similar happens if I switch to a different buffer,
> then some time later switch back.

Emacs releases unused font slots from time to time, which might be the
reason here.

But this is speculation; a reproducible recipe is required to
investigate and come up with specifics.  And yes, it could be a bug.

> Is it reasonable to expect to keep all recently used fonts in memory
> and not search for them again?

For some value of "recently", yes.  Again, more data is needed to
determine whether this is an Emacs bug or a system configuration
issue.