SDL Wiki
(This is the documentation for SDL3, which is under heavy development and the API is changing! SDL2 is the current stable version!)


Wait until a semaphore has a positive value and then decrements it.


int SDL_SemWaitTimeout(SDL_sem *sem, Sint32 timeoutMS);

Function Parameters

sem the semaphore to wait on
timeoutMS the length of the timeout, in milliseconds

Return Value

Returns 0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait does not succeed in the allotted time, or a negative error code on failure; call SDL_GetError() for more information.


This function suspends the calling thread until either the semaphore pointed to by sem has a positive value, the call is interrupted by a signal or error, or the specified time has elapsed. If the call is successful it will atomically decrement the semaphore value.


This function is available since SDL 3.0.0.

Code Examples

SDL_atomic_t done;
SDL_sem *sem;

SDL_AtomicSet(&done, 0);
sem = SDL_CreateSemaphore(0);
Thread A:
    while (!SDL_AtomicGet(&done)) {

Thread B:
    const Uint32 timeout = 1000; /* wake up every second */

    while (!SDL_AtomicGet(&done)) {
        if (SDL_SemWaitTimeout(sem, timeout) == 0 && data_available()) {
        ... do other processing
SDL_AtomicSet(&done, 1);

CategoryAPI, CategoryMutex

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