[Fontconfig] Application startup performance

[Keith Packard]

u-pnrz at aetey.se writes:

> I would rather postulate fc-cache to be run and risk ignoring some fonts
> until this is done. Is the risk really significant? Distros run fc-cache,
> users who add fonts on their own would know they have to run fc-cache.

Yes, it's pretty clear we've gotten distros to understand that running
fc-cache is required after installing fonts.

> What makes me unconfortable is applications doing huge i/o operation at
> startup just because of a certain library being used. Then neither
> the application developer nor the user have some real power over the
> behaviour.

It's failures within fontconfig that cause this

> I would be even more uncomfortable if there will be some locks involved
> or some daemons would be expected to run just to be able to rely on
> fontconfig. Explicit cache creation looks like the cleanest solution.

Here's another alternative -- cache creation could be the responsibility
of fc-cache, but perhaps applications could validate the cache by
checking directory timestamps and loading directories which were out of
date manually (as they do today) but *not* write out that information
back to the disk which would avoid the race conditions present in the
current environment. fc-cache could then use some kind of per-directory
locking to avoid races in generating the information there, which should
make the directory timestamps reliable enough to not need applications
to scan every directory manually at startup time.

-- 
-keith
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