Wait until a semaphore has a positive value and then decrements it.
Defined in <SDL3/SDL_mutex.h>
| sem | the semaphore wait on |
Returns 0 on success 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 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_WaitSemaphoreTimeout() with a time length of -1.
This function is available since SDL 3.0.0.
// BEWARE: This code example was migrated from the SDL2 Wiki, by only updating the names.
void create_and_wait_threads(void);
#define NB_WAITER 10
SDL_Semaphore *sem;
// Increments the semaphore every 2s
int poster_thread() {
for (int i = 0; i < NB_WAITER; i++) {
SDL_PostSemaphore(sem);
SDL_Delay(2 * 1000);
}
return 0;
}
int waiter_thread() {
int status;
status = SDL_WaitSemaphore(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);
}