###### (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_WaitSemaphore

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

## Header File

Defined in [<SDL3/SDL_mutex.h>](https://github.com/libsdl-org/SDL/blob/main/include/SDL3/SDL_mutex.h)

## Syntax

```c
int SDL_WaitSemaphore(SDL_Semaphore *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_WaitSemaphoreTimeout](SDL_WaitSemaphoreTimeout)() with a time length
of -1.

## Version

This function is available since SDL 3.0.0.

## Code Examples

```c
// BEWARE: This code example was migrated from the SDL2 Wiki, by only updating the names.

#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);
}

```

## See Also

* [SDL_PostSemaphore](SDL_PostSemaphore)
* [SDL_TryWaitSemaphore](SDL_TryWaitSemaphore)
* [SDL_WaitSemaphoreTimeout](SDL_WaitSemaphoreTimeout)

----
[CategoryAPI](CategoryAPI), [CategoryAPIFunction](CategoryAPIFunction)