[Fontconfig] thread problem with fontconfig

[Patrick Lam]

Christian Krause wrote:
> Hi,
> 
> Recently I found a problem with evince and a special pdf file ([1]).
> The backtrace (see below, [2]) indicates that 2 threads call at the
> same time functions of the fontconfig library when the crash occurs.
> 
> So I have 2 questions:
> 
> 1. Is fontconfig thread-safe? Is there something special where
> developers of multi-threaded applications must take care of?
> 
> 2. Please can you have a look at the backtrace and give me a hint
> where I can start looking for the problem?

fontconfig is not thread-safe.  One way to fix this problem would be to 
have a lock which surrounds all calls to fontconfig.

I can't actually see in the trace what might be causing the crash.  But 
I'm sure that arbitrary things can happen when you call fontconfig from 
multiple threads.

pat