# SDL_CreateSemaphore

Create a semaphore.

## Header File

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

## Syntax

```c
SDL_Semaphore * SDL_CreateSemaphore(Uint32 initial_value);
```

## Function Parameters

|                  |                   |                                      |
| ---------------- | ----------------- | ------------------------------------ |
| [Uint32](Uint32) | **initial_value** | the starting value of the semaphore. |

## Return Value

([SDL_Semaphore](SDL_Semaphore) *) Returns a new semaphore or NULL on
failure; call [SDL_GetError](SDL_GetError)() for more information.

## Remarks

This function creates a new semaphore and initializes it with the value
`initial_value`. Each wait operation on the semaphore will atomically
decrement the semaphore value and potentially block if the semaphore value
is 0. Each post operation will atomically increment the semaphore value and
wake waiting threads and allow them to retry the wait operation.

## Thread Safety

It is safe to call this function from any thread.

## Version

This function is available since SDL 3.2.0.

## Code Examples

Typical use of semaphores:

```c
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_SetAtomicInt(&done, 0);
sem = SDL_CreateSemaphore(0);


Thread_A:
    while (!SDL_GetAtomicInt(&done)) {
        add_data_to_queue();
        SDL_SignalSemaphore(sem);
    }

Thread_B:
    while (!SDL_GetAtomicInt(&done)) {
        SDL_WaitSemaphore(sem);
        if (data_available()) {
            get_data_from_queue();
        }
    }


SDL_SetAtomicInt(&done, 1);
SDL_SignalSemaphore(sem);
wait_for_threads();
SDL_DestroySemaphore(sem);
```

## See Also

- [SDL_DestroySemaphore](SDL_DestroySemaphore)
- [SDL_SignalSemaphore](SDL_SignalSemaphore)
- [SDL_TryWaitSemaphore](SDL_TryWaitSemaphore)
- [SDL_GetSemaphoreValue](SDL_GetSemaphoreValue)
- [SDL_WaitSemaphore](SDL_WaitSemaphore)
- [SDL_WaitSemaphoreTimeout](SDL_WaitSemaphoreTimeout)

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

