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.

Header File

Defined in <SDL3/SDL_mutex.h>


int SDL_WaitSemaphore(SDL_Semaphore *sem);

Function Parameters

SDL_Semaphore * sem the semaphore wait on.

Return Value

(int) 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.

Code Examples

// 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_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

See Also

CategoryAPI, CategoryAPIFunction, CategoryMutex

[ edit | delete | history | feedback | raw ]

[ front page | index | search | recent changes | git repo | offline html ]

All wiki content is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0).
Wiki powered by ghwikipp.