SDL_SemPost
Description
SDL_SemPost unlocks the semaphore pointed to by
sem and atomically increments the semaphores value.
Threads that were blocking on the semaphore may be scheduled after this call
succeeds.
SDL_SemPost should be called after a semaphore is locked by a successful call to
SDL_SemWait,
SDL_SemTryWait or
SDL_SemWaitTimeout.