SDL_SemWait
From SDL Library
SDL_SemWait
Description
SDL_SemWait() suspends the calling thread until either
the semaphore pointed to by sem has a positive value,
the call is interrupted by a signal or error. If the call is successful it
will atomically decrement the semaphore value.
After SDL_SemWait() is successful, the semaphore
can be released and its count atomically incremented by a successful call to
SDL_SemPost.