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# XTaskQueueSubmitDelayedCallback

> XTaskQueueSubmitDelayedCallback

# XTaskQueueSubmitDelayedCallback

Submits a callback to the queue for the given port.

## Syntax

```cpp theme={null}
HRESULT XTaskQueueSubmitDelayedCallback(  
         XTaskQueueHandle queue,  
         XTaskQueuePort port,  
         uint32_t delayMs,  
         void* callbackContext,  
         XTaskQueueCallback* callback  
)  
```

### Parameters

*queue*   \_In\_\
Type: XTaskQueueHandle

The queue to submit the callback to.

*port*   \_In\_\
Type: [XTaskQueuePort](/reference/system/xtaskqueue/enums/xtaskqueueport)

The port to submit the callback to. Callbacks can be assigned to work or completion ports.

*delayMs*   \_In\_\
Type: uint32\_t

The number of milliseconds to delay before submitting the callback to the queue.

<Note>A callback can be submitted to be added to the queue some time in the future. If *delayMs* is non-zero the callback will be placed on a pending list and a timer is initialized with the next closest wait time. When the time elapses, the callback with the next time will be placed on the execution list. The queue will raise a [XTaskQueueMonitorCallback](/reference/system/xtaskqueue/functions/xtaskqueuemonitorcallback), and if the queue is running in a thread pool dispatch mode, thread pool work will be submitted.</Note>

*callbackContext*   \_In\_opt\_\
Type: void\*

An optional context pointer that will be passed to the callback.

*callback*   \_In\_\
Type: [XTaskQueueCallback\*](/reference/system/xtaskqueue/functions/xtaskqueuecallback)

A pointer to the callback function.

### Return value

Type: HRESULT

HRESULT success or error code.

## Remarks

This callback will be added to the queue after *delayMs* milliseconds.

<img src="https://mintcdn.com/microsoft-4404708b/gzrdvT5kpqAXKEQt/images/gdk/reference/note.gif?s=6c1a4c009b25ad5315c45ce51bc83983" alt="alert" width="10" height="10" data-path="images/gdk/reference/note.gif" /> **Performance Note:**\
Adding an item to a queue needs to be lock and wait free in order to satisfy the performance requirements of upstream code. The following APIs are lock free:

* [XTaskQueueSubmitCallback](/reference/system/xtaskqueue/functions/xtaskqueuesubmitcallback)
* [XTaskQueueSubmitDelayedCallback](/reference/system/xtaskqueue/functions/xtaskqueuesubmitdelayedcallback)
* [XTaskQueueDispatch](/reference/system/xtaskqueue/functions/xtaskqueuedispatch), provided that 0 is passed for *timeoutInMs*

The following example allows callbacks to be submitted in the future by using the **XTaskQueueSubmitDelayedCallback** function. This is a great way to retry a failed call after a short delay; it can also be used as a cheap timer for periodic events.

<Note>**SubmitCallback** is a helper function that is defined in the code example for the [XTaskQueueSubmitCallback](/reference/system/xtaskqueue/functions/xtaskqueuesubmitcallback) function.</Note>

```cpp theme={null}
void SubmittingDelayedCallback()
{
    XTaskQueueHandle queue;

    HRESULT hr = XTaskQueueCreate(
        XTaskQueueDispatchMode::ThreadPool,
        XTaskQueueDispatchMode::ThreadPool, 
        &queue);

    if (FAILED(hr))
    {
        printf("failed to create task queue: 0x%x\r\n", hr);
        return;
    }

    struct CallContext
    {
        DWORD count;
        XTaskQueueHandle queue;
        XTaskQueueCallback* callback;
    } callContext;

    auto callback = [](void* context, bool cancel)
    {
        CallContext *callContext = static_cast<CallContext*>(context);
        callContext->count++;
        printf("Periodic callback %d\r\n", callContext->count);
        if (callContext->count != 10 && !cancel)
        {
            HRESULT hr = XTaskQueueSubmitDelayedCallback(
                callContext->queue, 
                XTaskQueuePort::Completion, 
                500, 
                callContext, 
                callContext->callback);

            if (FAILED(hr))
            {
                printf("Failed submitting next callback: 0x%x\r\n", hr);
                callContext->count = 10; // Prevent us from waiting forever.
            }
        }
    };

    callContext.count = 0;
    callContext.queue = queue;
    callContext.callback = callback;

    // Use the task queue to make 10 periodic calls
    hr = XTaskQueueSubmitDelayedCallback(
        queue,
        XTaskQueuePort::Completion,
        500,
        &callContext,
        callback);

    if (FAILED(hr))
    {
        printf("Failed submitting delayed callback: 0x%x\r\n", hr);
        XTaskQueueCloseHandle(queue);
        return;
    }

    // Now wait for all the calls to complete.
    while (callContext.count != 10)
    {
        Sleep(1000);
    }

    XTaskQueueTerminate(queue, true, nullptr, nullptr);
    XTaskQueueCloseHandle(queue);
}
```

## Requirements

**Header:** XTaskQueue.h

**Library:** xgameruntime.lib

**Supported platforms:** Windows, XBOX One family consoles and XBOX Series consoles

## See also

[XTaskQueue members](/reference/system/xtaskqueue/xtaskqueue_members)\
[Asynchronous Programming Model](/build/core-features/common/async/async-programming-model)\
[Async Task Queue design](/build/core-features/common/async/async-task-queue-design)


## Related topics

- [How to: Using delayed callbacks](/build/core-features/common/async/async-task-queue-design-howto/using-delayed-callbacks.md)
- [XTaskQueueSubmitCallback](/reference/system/xtaskqueue/functions/xtaskqueuesubmitcallback.md)
- [XTaskQueuePort](/reference/system/xtaskqueue/enums/xtaskqueueport.md)
- [XTaskQueueMonitorCallback](/reference/system/xtaskqueue/functions/xtaskqueuemonitorcallback.md)
- [XTaskQueueCallback](/reference/system/xtaskqueue/functions/xtaskqueuecallback.md)