IWbemObjectSink interface

Article
01/07/2021

The IWbemObjectSink interface creates a sink interface that can receive all types of notifications within the WMI programming model. Clients must implement this interface to receive both the results of the asynchronous methods of IWbemServices, and specific types of event notifications. Providers use, but do not implement this interface to provide events and objects to WMI.

Typically, providers call an implementation provided to them by WMI. In these cases, call Indicate to provide objects to the WMI service. After that, call SetStatus to indicate the end of the notification sequence. You can also call SetStatus to indicate errors when the sink does not have any objects.

When programming asynchronous clients of WMI, the user provides the implementation. WMI calls the methods to deliver objects and set the status of the result.

Note

If a client application passes the same sink interface in two different overlapping asynchronous calls, WMI does not guarantee the order of the callback. Client applications that make overlapping asynchronous calls should either pass different sink objects, or serialize their calls.

Note

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.

Members

The IWbemObjectSink interface has these types of members:

Methods

Methods

The IWbemObjectSink interface has these methods.

Method	Description
Indicate	Receives notification objects.
SetStatus	Called by sources to indicate the end of a notification sequence, or to send other status codes to the sink.

Remarks

When implementing an event subscription sink (IWbemObjectSink or IWbemEventSink), do not call into WMI from within the Indicate or SetStatus methods on the sink object. For example, calling IWbemServices::CancelAsyncCall to cancel the sink from within an implementation of Indicate can interfere with the WMI state. To cancel an event subscription, set a flag and call IWbemServices::CancelAsyncCall from another thread or object. For implementations that are not related to an event sink, such as object, enum, and query retrievals, you can call back into WMI.

Sink implementations should process the event notification within 100 MSEC because the WMI thread that delivers the event notification cannot do other work until the sink object has completed processing. If the notification requires a large amount of processing, the sink can use an internal queue for another thread to handle the processing.

Examples

The following code example is a simple implementation of an object sink. This sample can be used with IWbemServices::ExecQueryAsync or IWbemServices::CreateInstanceEnumAsync to receive the returned instances:

#include <iostream>
#include <wbemidl.h>
#pragma comment(lib, "wbemuuid.lib")

class QuerySink : public IWbemObjectSink
{
    LONG m_lRef;
    bool bDone; 

public:
    QuerySink() { m_lRef = 0; }
   ~QuerySink() { bDone = TRUE; }

    virtual ULONG STDMETHODCALLTYPE AddRef();
    virtual ULONG STDMETHODCALLTYPE Release();        
    virtual HRESULT STDMETHODCALLTYPE 
        QueryInterface(REFIID riid, void** ppv);

    virtual HRESULT STDMETHODCALLTYPE Indicate( 
            /* [in] */
            LONG lObjectCount,
            /* [size_is][in] */
            IWbemClassObject __RPC_FAR *__RPC_FAR *apObjArray
            );
        
    virtual HRESULT STDMETHODCALLTYPE SetStatus( 
            /* [in] */ LONG lFlags,
            /* [in] */ HRESULT hResult,
            /* [in] */ BSTR strParam,
            /* [in] */ IWbemClassObject __RPC_FAR *pObjParam
            );
};


ULONG QuerySink::AddRef()
{
    return InterlockedIncrement(&m_lRef);
}

ULONG QuerySink::Release()
{
    LONG lRef = InterlockedDecrement(&m_lRef);
    if(lRef == 0)
        delete this;
    return lRef;
}

HRESULT QuerySink::QueryInterface(REFIID riid, void** ppv)
{
    if (riid == IID_IUnknown || riid == IID_IWbemObjectSink)
    {
        *ppv = (IWbemObjectSink *) this;
        AddRef();
        return WBEM_S_NO_ERROR;
    }
    else return E_NOINTERFACE;
}


HRESULT QuerySink::Indicate(long lObjCount, IWbemClassObject **pArray)
{
    for (long i = 0; i < lObjCount; i++)
    {
        IWbemClassObject *pObj = pArray[i];

        // ... use the object.

        // AddRef() is only required if the object will be held after
        // the return to the caller.
    }

    return WBEM_S_NO_ERROR;
}

HRESULT QuerySink::SetStatus(
            /* [in] */ LONG lFlags,
            /* [in] */ HRESULT hResult,
            /* [in] */ BSTR strParam,
            /* [in] */ IWbemClassObject __RPC_FAR *pObjParam
        )
{
    printf("QuerySink::SetStatus hResult = 0x%X\n", hResult);
    return WBEM_S_NO_ERROR;
}

Requirements

Requirement	Value
Minimum supported client	Windows Vista
Minimum supported server	Windows Server 2008
Header	Wbemcli.h (include Wbemidl.h)
Library	Wbemuuid.lib
DLL	Fastprox.dll