SDL_CreateSemaphore() creates a new semaphore and initializes it with the value initial_value. Each locking operation on the semaphore by SDL_SemWait, SDL_SemTryWait or SDL_SemWaitTimeout will atomically decrement the semaphore value. The locking operation will be blocked if the semaphore value is not positive (greater than zero). Each unlock operation by SDL_SemPost will atomically increment the semaphore value.
SDL_sem *my_sem;
my_sem = SDL_CreateSemaphore(INITIAL_SEM_VALUE);
if (my_sem == NULL) {
return CREATE_SEM_FAILED;
}