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

[Eli Zaretskii]

> Date: Wed, 10 Dec 2014 18:50:01 -0500
> From: Kirill Ignatiev <kirill.ignatiev@gmail.com>
> Cc: Sebastian Wiesner <swiesner@lunaryorn.com>, 19266@debbugs.gnu.org
> 
> Can someone familiar with emacs' font internals check if this makes
> sense as the cause of the problem, please? I really don't understand
> how/where fonts are stored/cached/used; I did read
> font/fontset/macfont/alloc.c, but I'm still unclear.

Unfortunately, we don't have too many experts on this, to put it
mildly.  Dmitry, could you please take a look?

> To summarize: My interpretation of what's happening is that when emacs
> looks at some fonts to see if they contain a certain characters and
> neither of them does, emacs *does not* cache the fonts. So the next
> time redisplay happens after those fonts are garbage-collected, emacs
> has to load the fonts all over again, causing a noticeable redisplay
> delay.

This does sound like the truth, although I'm not sure.

> For testing, how do I turn off font garbage collection, so that no
> font is ever closed?

Comment out the call to cleanup_vector?

> How do I trigger font garbage collection manually?

Did you try "M-x garbage-collect RET"?

> Is this the right mailing list for this?

Yes, it is.