Transacted Queues

This topic applies to Windows Workflow Foundation 4 (WF4).

This sample shows how to integrate queues and transactions in Windows Workflow Foundation (WF) to create reliable and scalable services. A TransactionScope is used in the client workflow to send message to a queue under a transaction using the NetMsmqBinding. A TransactedReceiveScope is used on the server to receive messages from the queue and update the state of the workflow under the same transaction.

Demonstrates

TransactionScope, TransactedReceiveScope, NetMsmqBinding, Receive, and content-based correlation.

Discussion

To demonstrate the features covered in this sample, a RewardsPoints workflow service is created, which keeps track of the points earned and used for a given account. The client uses WorkflowInvoker to simulate posting various requests to the queue. To post a message to the queue under a transaction, the Send activity can be placed inside the Body of a TransactionScope. In this sample, the client runs first, followed by the server, to demonstrate how queued messages can decouple the client and server applications.

Once the client completes, the service is configured and hosted. As soon as it opens, it starts processing the messages that have already been placed in the queue. Each message is received and processed under the same server transaction. In this sample, the first message received is a CreateAccount request that creates the instance and initializes the content correlation based on the account name passed as part of the request message. To model the kind of service you might expect in the real world, the following two TransactedReceiveScope activities that process the AddPoints and UsePoints messages are placed in parallel branches within a while loop so that they can process these messages repeatedly in any order.

TransactionScope and TransactedReceiveScope each have an implicit persistence point at the end of their scopes, so using these activities in WF combined with queues is a reliable way to move your workflow from one consistent state to the next, while ensuring that messages are never lost.

To set up, build, and run the sample

1. Install and configure MSMQ. See Installing Message Queuing for details.

2. Ensure that MSDTC is running by executing the following command on a command line. net start msdtc

3. Compile the project and open the executable, or open the project in Visual Studio 2010 and select a start option from the debug menu. First, the queue is created, then the client runs and posts messages to the queue, and finally the service starts and the messages are processed. To exit the program, press ENTER.

Note:

The samples may already be installed on your computer. Check for the following (default) directory before continuing. <InstallDrive>:\WF_WCF_Samples If this directory does not exist, go to Windows Communication Foundation (WCF) and Windows Workflow Foundation (WF) Samples for .NET Framework 4 to download all Windows Communication Foundation (WCF) and WF samples. This sample is located in the following directory. <InstallDrive>:\WF_WCF_Samples\WF\Scenario\Transactions\TransactedQueues