[Fontconfig] fontconfig performance problems + FcConfigUptoDate() bug

[Keith Packard]

Around 9 o'clock on Aug 10, Lubos Lunak wrote:

> and moreover if I comprehend it correctly this data can be modified at
runtime in the app.

No, the cache data is loaded at startup time and (for each directory at 
least) cannot change during the program run, except when reloading the 
cache to discover changes in the system.

> That looks more like a complete rewrite of a part of
> fontconfig to me, and that'd be probably better be done by somebody who's
> not completely clueless about it (hmm, does that include also somebody else
> than you?). Can you estimate the extent of work this would require?

Yes, it's certainly a significant reworking of the fontconfig internals. 

I suspect it will require the ability for internal functions to handle two 
separate representations for the basic FcPattern datatype; one which 
contains a maze of pointers (the current structure) and one which uses 
only offsets or somesuch.  That datatype is hidden from applications, so 
it should be possible to completely replace it if necessary, or at least 
extend it significantly without ABI/API changes.

I suspect this will take a couple of weeks of occasional tinkering to 
figure out how the data structures should work and then probably a week or 
so of solid coding to get it implemented, followed by a couple of weeks of 
testing and fixing.  But, these are just WAGs; I haven't even started the 
design process...

-keith


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