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

[Kirill Ignatiev]

On 4 December 2014 at 03:03, Eli Zaretskii <eliz@gnu.org> wrote:
>> Date: Thu, 4 Dec 2014 02:41:34 -0500
>> From: Kirill Ignatiev <kirill.ignatiev@gmail.com>
>> Cc: 19266@debbugs.gnu.org
>
> 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.

Okay, here's one attempt to reproduce it (sorry about the length). The
idea is to view lots of files, then later viewing a buffer that was
previously displayed causes a delay.

1. Start with -Q.
2. Open file uncommon_symbols.txt (attached). There's a delay but it opens fine.
3. Select the entire file; there is another delay (presumably font for
selected region is loaded separately).
4. C-h h to view hello file. Scroll all the way down with C-v.
5. Mark entire hello file, scroll all the way up from bottom.
6. View src/font.c (in emacs source), scroll all the way down to
render the whole file.
7. Mark the entire file, scroll all the way up, to view the entire
file in selected color.

Now:
8. View uncommon_symbols.txt: no delay.
9. Mark the entire file: no delay again.
10. View hello file: there is a noticeable delay of a few seconds with
the stack trace attached below.

This delay is, I think, identical to what I sometimes experience. Also
the reproduction's length can maybe be reduced somehow. I don't think
viewing three unicode-rich files should lead to such a noticeable
redrawing delay.

It's not so much that the delay is terribly long, it's that it
interrupts typing and normal workflow.

uncommon_symbols_bt.txt
Description: Text document

uncommon_symbols.txt
Description: Text document