COM Queued Components for the ASP Developer - Why and How By Christopher S. Blexrud Blex Consulting, Inc.

2. Topics to be Covered Recap traditional synchronous programming in the Microsoft world (COM/DCOM), focusing on the need for asynchronous communication Quick introduction to Message Queuing (MSMQ) and what it brings to developers In-depth look into Queued Components (QC) Architecture built on top of MSMQ Asynchronous communication How to create objects through QC Demonstration

3. Synchronous Programming

4. Traditional COM and DCOM Component Object Model (COM) Binary standard of interfaces Provides a foundation to build component based applications upon Distributed COM (DCOM) Use Remote Procedure Calls (RPC) Utilizes a Proxy and Stud to handle marshalling Transparent to the programmer, but not within the architecture

6. Sample Sync Programming - Code

7. Sample Sync Programming � Diagram

8. Long processing time, especially on the web Page time outs (ASP) Data access time outs Why hold the client up when they could be processing other transactions? Availability What if a server is unavailable and/or unreliable? Should this stop the users from using the system? Does the client care? No feedback that is require to send back to the user Where Does Synchronous Processing Fail?

9. MSMQ

10. Message Queuing MSMQ 1.0 appeared with the NT 4.0 Option pack MSMQ 2.0 comes with Windows 2000 and is intergraded into the Active Directory Allows for distributed applications to communicate using a reliable and secure architecture Allows asynchronous communication among applications Great for situations that do not require immediate responses

12. Main Parts of Message Queuing Queues Designed to hold messages, Contain security rights (send, receive, admin, etc.) Messages Label - similar to a subject on an email. Usually used to distinguish various types of messages in a single queue. Body � a versatile part of a MSMQ message. It can hold a single numeric value, string, array, or even an COM object that supports the IPersistStream or the IPersistStorage interface (like an ADODB Recordset) Many Others such as Priority, Delivery Mode, and various security and privacy settings, just to name a few.

13. Main Parts of Message Queuing � Cont. Sender Usually the requester of some functionality Comprises the message and sends it off to the queue Receiver Cares out the request from the sender. This work is usually what would have been processed on the client (client-side executable, IIS, etc.), but has been asynchronously moved another process. Also the communication between the client and server is asynchronous; the receiver can response to the messages from MSMQ both synchronously and asynchronously.

14. Typical MSMQ Interaction in a Web App

15. Sample MSMQ Code � Sending

16. Sample MSMQ Code � Receiving

17. COM+ QC

18. COM+ Queued Components COM+ QC form a very exciting architecture for all COM developers. Provides most of the benefits from MSMQ, with out the headache of MSMQ and handling all of the exceptions it brings Asynchronous communication without the hassle! Work well in a disconnected environment or when resources are not always available Configurable via the Component Administrator in Windows 2000

19. QC Benefits Component Lifetimes � The server and client do not have to exist at the same time, they communicate asynchronously Availability � The desired component may not be available due to an unreliable network or pure overload Disconnected Application � Great for laptops! Message Reliability � Pulls the benefits of guaranteed message delivery from MSMQ Scheduling � QC can be configured to only process messages during set times, which is a great way to move processor intensive tasks to nightly processing.

20. What are Queued Components? QC's are actually just an architecture to build upon Comprised of four parts: Recorder, MSMQ, Listener, Player Recorder - Logs the interaction (method calls) between the the client and that the client thinks is the component. It takes this log and builds a message and sends it to MSMQ. Actually the recorder is able to impersonate the object the consumer request. MSMQ � Holds the message in series of queues.

22. Queued Components Interaction

23. How to Use Queued Components

25. How to Configure Queued Components Use Component Service MMC snap-in Mark COM+ application as queued Mark interface as queued

26. Queued Components Restrictions No ByRef Parameters No return values Sub-routines only The client (IIS in the web / client-side executable in a tradition client-server application) and server must both be Windows 2000

27. Demonstration

29. Recap COM+ Queued Components Why Synchronous programming not tolerant to unavailable resources and long processing time, and does not support disconnected users If you want a lot of control and have a lot of custom requirements, or just have upgraded from Windows NT 4.0 use MSMQ If you need to get things done and do not require a lot of immediate feedback COM+ Queued Component is a great solution.