SDL_SemTryWait is a non-blocking varient of SDL_SemWait. If the value of the semaphore pointed to by sem is positive it will atomically decrement the semaphore value and return 0, otherwise it will return SDL_MUTEX_TIMEOUT instead of suspending the thread.
After SDL_SemTryWait is successful, the semaphore can be released and its count atomically incremented by a successful call to SDL_SemPost.
Returns 0 if the semaphore was successfully locked or either SDL_MUTEX_TIMEOUT or -1 if the thread would have suspended or there was an error, respectivly.
If the semaphore was not successfully locked, the semaphore will be unchanged.
res := SDL_SemTryWait( my_sem );
if ( res = SDL_MUTEX_TIMEOUT ) then
Result := TRY_AGAIN;
if (res = -1) then
Result := WAIT_ERROR;
SDL_SemPost( my_sem );