IWbemServices::CancelAsyncCall method (wbemcli.h)

Article
10/13/2021

The IWbemServices::CancelAsyncCall method cancels any currently pending asynchronous calls based on the IWbemObjectSink pointer, which was originally passed to the asynchronous method. The outstanding IWbemObjectSink pointer can be released prior to the call or after the call returns. The CancelAsyncCall method is not operational from within a sink and is not supported by method providers. This means only the client end of the call is canceled. The implementing provider is not notified that the call was canceled and runs to completion. You should consider this before canceling methods that take a long time to complete, such as the Defrag and Format methods in the Win32_Volume class.

Syntax

HRESULT CancelAsyncCall(
  [in] IWbemObjectSink *pSink
);

Parameters

[in] pSink

Pointer to the IWbemObjectSink implementation provided by the client to any of the asynchronous methods of IWbemServices.

Return value

This method returns an HRESULT that indicates the status of the method call. The following list lists the value contained within an HRESULT.

On failure, you can obtain available information from the COM function GetErrorInfo.

COM-specific error codes can also be returned if network problems cause you to lose the remote connection to Windows Management.

Note If SetStatus has not been called on the application's sink by the time WMI processes CancelAsyncCall, WMI calls SetStatus on that sink with WBEM_E_CALL_CANCELLED as the value for the hResult parameter.

Timing, and the nature of an asynchronous operation, can affect whether WMI is able to cancel the operation. Only lengthy queries are likely to be successfully canceled before they have completed. Faster operations, such as asynchronous deletions or modifications, typically complete before WMI can process a CancelAsyncCall call. So while CancelAsyncCall attempts to cancel the current operation, sometimes all that can be done is to release the IWbemObjectSink pointer.

Note It is possible to make numerous asynchronous calls using the same object sink. In this case, the CancelAsyncCall method cancels all asynchronous calls sharing this object sink. It is strongly recommended that you create one instance of an object sink for each outstanding asynchronous call.

Remarks

Because the call-back to the sink might not be returned at the same authentication level as the client requires, it is recommended that you use semisynchronous instead of asynchronous communication. For more information, see Calling a Method. Calling CancelAsyncCall from within an implementation of IWbemObjectSink::Indicate or IWbemObjectSink::SetStatus can interfere with the WMI state and is not recommended.

In the case of a method call such as ExecMethodAsync, only the client end of the call is canceled. The implementing provider is not notified that the call was canceled and runs to completion.

For more information on how to use asynchronous calls, see Making an Asynchronous Call with C++ and Receiving Asynchronous Event Notifications

Examples

For a full example that uses CancelAsyncCall, see Example: Receiving Event Notifications Through WMI

The following C++ sample, taken from the \\Program Files\Microsoft SDKs\Windows\v7.0\Samples\sysmgmt\wmi\vc\decoupled\instance_provider sample, demonstrates an implementation of CancelAsyncCall.

HRESULT CProvider_IWbemServices :: CancelAsyncCall ( 
  
 IWbemObjectSink *a_Sink
)
{
 HRESULT t_Result = WBEM_E_NOT_AVAILABLE ;
 return t_Result ;
}

Requirements

Requirement	Value
Minimum supported client	Windows Vista
Minimum supported server	Windows Server 2008
Target Platform	Windows
Header	wbemcli.h (include Wbemidl.h)
Library	Wbemuuid.lib
DLL	Fastprox.dll; Esscli.dll; FrameDyn.dll; FrameDynOS.dll; Ntevt.dll; Stdprov.dll; Viewprov.dll; Wbemcomn.dll; Wbemcore.dll; Wbemess.dll; Wbemsvc.dll; Wmipicmp.dll; Wmidcprv.dll; Wmipjobj.dll; Wmiprvsd.dll