FILE: MqPers.exe Sending Persistent COM Objects Using MSMQ in C+

• Microsoft Message Queue Server version 1.0

SUMMARY

With Microsoft Message Queuing Server it's possible to send the state of COM objects supporting the IPersistStream or IPersistStorage interface. This article discusses what is necessary to take advantage of this feature using Visual C++ and ATL.

MORE INFORMATION

The following file is available for download from the Microsoft Software Library:

 ~ MQPers.exe (size: 71772 bytes) 

   ARTICLE-ID: Q119591
   TITLE     : How to Obtain Microsoft Support Files from Online Services

The sample has two ActiveX components, Point and Line, which are implemented using ATL and Visual C++. In addition to the code generated by the ATL wizard, some additional lines have to be added for IPersistStream implementation. An object that implements IPersistStream is ready for sending its state over a MSMQ's queue.

Sending the Objects State Over the Queue

We use the #import directive in Visual C++ to manipulate the MSQM COM and the Point and Line objects. For additional information on how to initialize OLE when using the #import directive, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q169496
   TITLE     : INFO: Using ActiveX Data Objects (ADO) via #import in VC++"

   // For these ActiveX components we need only smart interface pointer
   IMSMQQueueInfosPtr   pQueueInfos;
   IMSMQQueueInfoPtr      pQueueInfo;
   IMSMQQueuePtr      pQueue;
   IUnknownPtr      pIUnknown;

   // Instantiate the following ActiveX components
   IMSMQQueryPtr      pQuery(__uuidof(MSMQQuery));
   IMSMQMessagePtr      pMessage(__uuidof(MSMQMessage));
   ILinePtr         pLine(__uuidof(Line));
   IPointPtr         pPoint(__uuidof(Point));

   ...

   if (n == 1) {
   // Initialize point object
      pPoint->x = 8;
      pPoint->y = 9;

       // The message body gets the IUnknown pointer
       pMessage->Body = static_cast<IUnknown*>(pPoint);

   } else {

      ...

   }

   pMessage->Send(pQueue);

   ...

Receiving the Objects State from the Queue

When an MSMQMessage instructs an ActiveX component to save its state to a stream, it also asks the component to save its CLSID to the stream. When receiving an object state, this enables the Microsoft Message Queue Server to instantiate the ActiveX component belonging to the transmitted CLSID.

The message body property of the received message actually is a VARIANT containing an IUnknown pointer to the interface of newly created object. Now it's up to the program to determine which object state was received and which object was created. One way to do this is to ask the IUnknown for ILine or the IPoint interface.

   ...

   // Get the next message
   pMessage = pQueue->Receive();

   IPointPtr      pPoint((IUnknown*)pMessage->Body);

   // Check if it's a Point object
   if (pPoint != NULL) {
         cout << "\nGot a Point Object: " << pPoint->x << "  " << \
   pPoint->y << "\n";

   }
   else {
      ILinePtr   pLine((IUnknown*)pMessage->Body);

      // Check if it's a Line object
      if (pLine != NULL) {
   cout << "\nGot a Line Object: " << pLine->x1 << " "
   <<  \       pLine->y1 << " " << pLine->x2 << " " << pLine->y2 << "\n";
      }
      else
         cout << "\nUnknown Object !!!\n";
   }
   pQueue->Close();

   ...

REFERENCES

MSMQ Online SDK help file

(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Michael Zill, Microsoft Corporation

Keywords          : MQVC
Version           : WINNT:1.0
Platform          : winnt
Issue type        : kbfile
Solution Type     : kbsample