[Fontconfig] Missing font issue due to broken caches

[David Lattimore]

Hi Akira,

I have a slightly unusual usage of FontConfig in that I store fonts on a
server and get FontConfig to scan them to produce a cache, then transfer
the cache to a client which loads it, matches fonts then requests those
fonts from the server. Currently in order to load the cache on the client,
we create an empty font directory with the same mtime as the font directory
on the server. This is already pretty hacky, but it works. I fear with the
above change we'd find ourselves creating N dummy files in our client-side
"font directory". So if there were some way around these checks, that would
be good. Perhaps an API to just load a cache file without needing any font
directory at all? I've been meaning to see if I could implement such an API
in FontConfig, but haven't gotten to it yet.

Thanks,
David

On 29 July 2015 at 12:31, Akira TAGOH <akira at tagoh.org> wrote:

> Hi,
>
> I need some comments about making a change in FcCache to work around the
> kinda race condition in updating caches. please read comments in
> https://bugs.freedesktop.org/show_bug.cgi?id=69845
> <https://bugs.freedesktop.org/show_bug.cgi?id=69845>for more details of
> the background.
>
> As attached at https://bugs.freedesktop.org/attachment.cgi?id=116870 I'm
> proposing the change to store the number of files in a directory to FcCache
> so that fontconfig can detect this fault; AFAICS the number of font files
> being reported from the cache and the actual one is different and it is
> same or newer than the mtime of directory so fontconfig doesn't update then.
>
> The change itself is quite simple and no extra cost to store it. even if
> it is going to update the cache by this change, it is supposed to be
> updated per se. the concern is, it may be likely to happen during running
> applications.
>
> Any other concerns or comment on this change?
>
> --
> Akira TAGOH
>
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