StopAcknowledge method

[Warning: UMDF 2 is the latest version of UMDF and supersedes UMDF 1. All new UMDF drivers should be written using UMDF 2. No new features are being added to UMDF 1 and there is limited support for UMDF 1 on newer versions of Windows 10. Universal Windows drivers must use UMDF 2. For more info, see Getting Started with UMDF.]

The StopAcknowledge method informs the framework that the driver has stopped processing a specified I/O request.


void StopAcknowledge(
  [in] BOOL Requeue



A Boolean value that, if TRUE, causes the framework to requeue the request into the queue so that the framework will deliver it to the driver again. If FALSE, the framework does not requeue the request. For more information, see the following Remarks section.

Return Value



If a driver registers an IQueueCallbackIoStop::OnIoStop callback function for an I/O queue, the framework calls it when the queue's underlying device is leaving its working (D0) state. The framework calls this callback function for every I/O request that the driver owns at the time when the queue is being stopped. The driver must complete, cancel, or postpone processing of each request by doing one of the following:

  • If the driver owns the request, it can call IWDFIoRequest::Complete to complete or cancel the request.

  • If the driver has forwarded the request to an I/O target, it can call IWDFIoRequest::CancelSentRequest to attempt to cancel the request.

  • If the driver postpones processing the request, it must call StopAcknowledge.

If your driver calls StopAcknowledge, it must call this method from within its IQueueCallbackIoStop::OnIoStop callback function.

If the driver does not call IWDFIoRequest::Complete or StopAcknowledge for every request that an IQueueCallbackIoStop::OnIoStop callback function receives, the framework does not allow the device to leave its working (D0) state. Potentially, this inaction can prevent a system from entering its hibernation state or another low system power state.

When a driver's IQueueCallbackIoStop::OnIoStop callback function calls StopAcknowledge, it can set the Requeue parameter to TRUE or FALSE:

  • Setting Requeue to TRUE causes the framework to place the request back into its I/O queue.

    When the underlying device returns to its working (D0) state, the framework will redeliver the request to the driver.

  • Setting Requeue to FALSE causes ownership of the request to remain with the driver. The driver must stop doing any I/O processing that requires hardware access.

    When the underlying device returns to its working (D0) state, the framework will call the driver's IQueueCallbackIoResume::OnIoResume callback function, so that the driver can continue processing the request.

If the driver had previously called IWDFIoRequest::MarkCancelable, it must call IWDFIoRequest::UnmarkCancelable before calling StopAcknowledge with Requeue set to TRUE.

Before calling StopAcknowledge, the driver's IQueueCallbackIoStop::OnIoStop callback function must stop all processing of the I/O request that requires accessing the underlying device, because the device is about to enter a low-power state.


The following code example is an IQueueCallbackIoStop::OnIoStop callback function that checks to see if a received request is cancelable and, if it is, calls IWDFIoRequest::UnmarkCancelable. If IWDFIoRequest::UnmarkCancelable returns HRESULT_FROM_WIN32(ERROR_OPERATION_ABORTED), the example just returns because the driver's IRequestCallbackCancel::OnCancel callback function will handle the request. Otherwise, the example calls StopAcknowledge and specifies FALSE so that the framework will eventually call the driver's IQueueCallbackIoResume::OnIoResume callback function.

    __in IWDFIoQueue*  pWdfQueue,
    __in IWDFIoRequest*  pWdfRequest,
    __in ULONG  ActionFlags
{ HRESULT status;

    if (ActionFlags & WdfRequestStopRequestCancelable) {
        status = pWdfRequest->UnmarkCancelable();
    // Declare an IWDFIoRequest2 interface pointer and obtain the
    // IWDFIoRequest2 interface from the IWDFIoRequest interface.
    CComQIPtr<IWDFIoRequest2> r2 = pWdfRequest;



End of support Unavailable in UMDF 2.0 and later.
Target Platform Desktop
Minimum UMDF version 1.9
Header wudfddi.h (include Wudfddi.h)
Library wudfddi.h

See Also




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