SDL_SemTryWait - Man Page

Attempt to lock a semaphore but don't suspend the thread.


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

int SDL_SemTryWait(SDL_sem *sem);


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.

Return Value

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



See Also

SDL_CreateSemaphore, SDL_DestroySemaphore, SDL_SemWait, SDL_SemWaitTimeout, SDL_SemPost, SDL_SemValue

Referenced By

SDL_CreateSemaphore(3), SDL_DestroySemaphore(3), SDL_SemPost(3), SDL_SemValue(3), SDL_SemWait(3), SDL_SemWaitTimeout(3).

Tue 11 Sep 2001, 23:00 SDL API Reference