SDL_SemWaitTimeout -- Lock a semaphore, but only wait up to a specified maximum time.


#include "SDL.h"
#include "SDL_thread.h"

int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout);


SDL_SemWaitTimeout is a variant of SDL_SemWait with a maximum timeout value. 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 wait up to timeout milliseconds trying to lock the semaphore. This function is to be avoided if possible since on some platforms it is implemented by polling the semaphore every millisecond in a busy loop.

After SDL_SemWaitTimeout is successful, the semaphore can be released and its count atomically incremented by a successful call to SDL_SemPost.

Return Value


If the semaphore was not successfully locked, the semaphore will be unchanged.


res = SDL_SemWaitTimeout(my_sem, WAIT_TIMEOUT_MILLISEC);

if (res == SDL_MUTEX_TIMEDOUT) {
        return TRY_AGAIN;
if (res == -1) {
        return WAIT_ERROR;



See Also

SDL_CreateSemaphore, SDL_DestroySemaphore, SDL_SemWait, SDL_SemTryWait, SDL_SemPost, SDL_SemValue

SDL_SemWaitTimeout (last edited 2008-04-17 08:18:14 by localhost)