###### (This is the documentation for SDL3, which is under heavy development and the API is changing! [SDL2](https://wiki.libsdl.org/SDL2/) is the current stable version!) # SDL_SemWait Wait until a semaphore has a positive value and then decrements it. ## Syntax ```c int SDL_SemWait(SDL_sem *sem); ``` ## Function Parameters | | | | ----------- | --------------------- | | **sem** | the semaphore wait on | ## Return Value Returns 0 on success or a negative error code on failure; call [SDL_GetError](SDL_GetError)() for more information. ## Remarks This function suspends the calling thread until either the semaphore pointed to by `sem` has a positive value or the call is interrupted by a signal or error. If the call is successful it will atomically decrement the semaphore value. This function is the equivalent of calling [SDL_SemWaitTimeout](SDL_SemWaitTimeout)() with a time length of [`SDL_MUTEX_MAXWAIT`](SDL_MUTEX_MAXWAIT). ## Version This function is available since SDL 3.0.0. ## Code Examples ```c #define NB_WAITER 10 SDL_sem *sem; // Increments the semaphore every 2s int poster_thread() { for (int i = 0; i < NB_WAITER; i++) { SDL_SemPost(sem); SDL_Delay(2 * 1000); } return 0; } int waiter_thread() { int status; status = SDL_SemWait(sem); if (status == 0) { SDL_Log("Semaphore was decremented.\n"); } else { SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "An error has occured while waiting: %s\n", SDL_GetError()); } return 0; } int main() { sem = SDL_CreateSemaphore(0); create_and_wait_threads(); // 1 poster, 10 waiters SDL_DestroySemaphore(sem); } ``` ## Related Functions * [SDL_CreateSemaphore](SDL_CreateSemaphore) * [SDL_DestroySemaphore](SDL_DestroySemaphore) * [SDL_SemPost](SDL_SemPost) * [SDL_SemTryWait](SDL_SemTryWait) * [SDL_SemValue](SDL_SemValue) * [SDL_SemWait](SDL_SemWait) * [SDL_SemWaitTimeout](SDL_SemWaitTimeout) ---- [CategoryAPI](CategoryAPI), [CategoryMutex](CategoryMutex)