Thread-safe ?

I still have to figure out:
which openCV functions are pthread-safe (on a linux platform, for instance kernel 2.6.x)?!
Pardon! Je parle Francais seulement un petit peu!
Je n'ai pas comprenu si opencv functiones sont pthread-safe

By pthread-safe I mean that
(1) opencv functions can be called by different threads on different
data with no unexpected result
(2) opencv functions can be called by different threads on the same
data provided the ordinary use of pthread_mutex_lock()/trylock()/unlock
()/etc.

A specific example: what to do if I wanna call cvGetTickCount() by
different threads? Do I have to use mutexes??!! (that would spoil the
measure)