###### (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_WaitSemaphoreTimeout

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_WaitSemaphoreTimeout(SDL_Semaphore *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`](SDL_MUTEX_TIMEDOUT)
if the wait does not succeed in the allotted time, 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, 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.

## 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.

void add_data_to_queue(void);
void get_data_from_queue(void);
int data_available(void);
void wait_for_threads(void);

SDL_AtomicInt done;
SDL_Semaphore *sem;
SDL_AtomicSet(&done, 0);
sem = SDL_CreateSemaphore(0);

Thread_A:
    while (!SDL_AtomicGet(&done)) {
        add_data_to_queue();
        SDL_PostSemaphore(sem);
    }
Thread_B:
    const Uint32 timeout = 1000; /* wake up every second */
    while (!SDL_AtomicGet(&done)) {
        if (SDL_WaitSemaphoreTimeout(sem, timeout) == 0 && data_available()) {
            get_data_from_queue();
        }
        /* ... do other processing */
    }

SDL_AtomicSet(&done, 1);
SDL_PostSemaphore(sem);
wait_for_threads();
SDL_DestroySemaphore(sem);

```

## See Also

* [SDL_PostSemaphore](SDL_PostSemaphore)
* [SDL_TryWaitSemaphore](SDL_TryWaitSemaphore)
* [SDL_WaitSemaphore](SDL_WaitSemaphore)

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