SDL_CondWait- Wait on a condition variable
int SDL_CondWait(SDL_cond *cond, SDL_mutex *mut);
Wait on the condition variable cond and unlock the provided mutex. The mutex
must the locked before entering this function. Returns 0 when it is signalled,
or -1 on an error.
SDL_CondWaitTimeout, SDL_CondSignal, SDL_mutexP