Volatile Queued Communication

Straipsnis
09/15/2021

The Volatile sample demonstrates how to perform volatile queued communication over the Message Queuing (MSMQ) transport. This sample uses NetMsmqBinding. The service in this case is a self-hosted console application to enable you to observe the service receiving queued messages.

Note

The setup procedure and build instructions for this sample are located at the end of this topic.

In queued communication, the client communicates to the service using a queue. More precisely, the client sends messages to a queue. The service receives messages from the queue. The service and client therefore, do not have to be running at the same time to communicate using a queue.

When you send a message with no assurances, MSMQ only makes a best effort to deliver the message, unlike with Exactly Once assurances where MSMQ ensures that the message gets delivered or, if it cannot be delivered, lets you know that the message cannot be delivered.

In certain scenarios, you may want to send a volatile message with no assurances over a queue, when timely delivery is more important than losing messages. Volatile messages do not survive queue manager crashes. Therefore if the queue manager crashes, the non-transactional queue used to store volatile messages survives but the messages themselves do not because the messages are not stored on the disk.

Note

You cannot send volatile messages with no assurances within the scope of a transaction using MSMQ. You also must create a non-transactional queue to send volatile messages.

The service contract in this sample is IStockTicker that defines one-way services that are best suited for use with queuing.

[ServiceContract(Namespace = "http://Microsoft.ServiceModel.Samples")]
public interface IStockTicker
{
    [OperationContract(IsOneWay = true)]
    void StockTick(string symbol, float price);
}

The service operation displays the stock ticker symbol and price, as shown in the following sample code:

public class StockTickerService : IStockTicker
{
    public void StockTick(string symbol, float price)
    {
        Console.WriteLine("Stock Tick {0}:{1} ", symbol, price);
     }
     …
}

The service is self hosted. When using the MSMQ transport, the queue used must be created in advance. This can be done manually or through code. In this sample, the service contains code to check for the existence of the queue and create it if required. The queue name is read from the configuration file. The base address is used by the ServiceModel Metadata Utility Tool (Svcutil.exe) to generate the proxy for the service.

// Host the service within this EXE console application.
public static void Main()
{
    // Get MSMQ queue name from app settings in configuration.
    string queueName = ConfigurationManager.AppSettings["queueName"];

    // Create the transacted MSMQ queue if necessary.
    if (!MessageQueue.Exists(queueName))
        MessageQueue.Create(queueName);

    // Create a ServiceHost for the StockTickerService type.
    using (ServiceHost serviceHost = new ServiceHost(typeof(StockTickerService)))
    {
        // Open the ServiceHost to create listeners and start listening for messages.
        serviceHost.Open();

        // The service can now be accessed.
        Console.WriteLine("The service is ready.");
        Console.WriteLine("Press <ENTER> to terminate service.");
        Console.WriteLine();
        Console.ReadLine();

        // Close the ServiceHost to shutdown the service.
        serviceHost.Close();
    }
}

The MSMQ queue name is specified in the appSettings section of the configuration file. The endpoint for the service is defined in the system.serviceModel section of the configuration file and specifies the netMsmqBinding binding.

Note

The queue name uses a dot (.) for the local machine and backslash separators in its path when creating a queue using System.Messaging. The Windows Communication Foundation (WCF) endpoint address specifies a net.msmq: scheme, uses "localhost" for the local machine and forward slashes in its path.

The assurances and durability or volatility of messages are also specified in the configuration.

<appSettings>
  <!-- use appSetting to configure MSMQ queue name -->
  <add key="queueName" value=".\private$\ServiceModelSamplesVolatile" />
</appSettings>

<system.serviceModel>
  <services>
    <service name="Microsoft.ServiceModel.Samples.StockTickerService"
             behaviorConfiguration="CalculatorServiceBehavior">
    ...
      <!-- Define NetMsmqEndpoint -->
      <endpoint address="net.msmq://localhost/private/ServiceModelSamplesVolatile"
                binding="netMsmqBinding"
                bindingConfiguration="volatileBinding"
                contract="Microsoft.ServiceModel.Samples.IStockTicker" />
    ...
    </service>
  </services>

  <bindings>
    <netMsmqBinding>
      <binding name="volatileBinding"
             durable="false"
           exactlyOnce="false"/>
    </netMsmqBinding>
  </bindings>
  ...
</system.serviceModel>

Because the sample sends queued messages by using a non-transactional queue, transacted messages cannot be sent to the queue.

// Create a client.
Random r = new Random(137);

StockTickerClient client = new StockTickerClient();

float price = 43.23F;
for (int i = 0; i < 10; i++)
{
    float increment = 0.01f * (r.Next(10));
    client.StockTick("zzz" + i, price + increment);
}

//Closing the client gracefully cleans up resources.
client.Close();

When you run the sample, the client and service activities are displayed in both the service and client console windows. You can see the service receive messages from the client. Press ENTER in each console window to shut down the service and client. Note that because queuing is in use, the client and service do not have to be up and running at the same time. You can run the client, shut it down, and then start up the service and it still receives its messages.

The service is ready.
Press <ENTER> to terminate service.

Stock Tick zzz0:43.25
Stock Tick zzz1:43.23
Stock Tick zzz2:43.28
Stock Tick zzz3:43.3
Stock Tick zzz4:43.23
Stock Tick zzz5:43.25
Stock Tick zzz6:43.25
Stock Tick zzz7:43.24
Stock Tick zzz8:43.32
Stock Tick zzz9:43.3

To set up, build, and run the sample

Ensure that you have performed the One-Time Setup Procedure for the Windows Communication Foundation Samples.
To build the C# or Visual Basic .NET edition of the solution, follow the instructions in Building the Windows Communication Foundation Samples.
To run the sample in a single- or cross-machine configuration, follow the instructions in Running the Windows Communication Foundation Samples.

By default with the NetMsmqBinding, transport security is enabled. There are two pertinent properties for MSMQ transport security, MsmqAuthenticationMode and MsmqProtectionLevel. By default, the authentication mode is set to Windows and the protection level is set to Sign. For MSMQ to provide the authentication and signing feature, it must be part of a domain and the active directory integration option for MSMQ must be installed. If you run this sample on a computer that does not satisfy these criteria you receive an error.

To run the sample on a computer joined to a workgroup or without active directory integration

If your computer is not part of a domain or does not have active directory integration installed, turn off transport security by setting the authentication mode and protection level to None as shown in the following sample configuration code:

<system.serviceModel>
    <services>
      <service name="Microsoft.ServiceModel.Samples.StockTickerService"
               behaviorConfiguration="StockTickerServiceBehavior">
        <host>
          <baseAddresses>
            <add baseAddress="http://localhost:8000/ServiceModelSamples/service"/>
          </baseAddresses>
        </host>

        <!-- Define NetMsmqEndpoint -->
        <endpoint address="net.msmq://localhost/private/ServiceModelSamplesVolatile"
                  binding="netMsmqBinding"
                  bindingConfiguration="volatileBinding"
                  contract="Microsoft.ServiceModel.Samples.IStockTicker" />
        <!-- the mex endpoint is exposed at http://localhost:8000/ServiceModelSamples/service/mex -->
        <endpoint address="mex"
                  binding="mexHttpBinding"
                  contract="IMetadataExchange" />

      </service>
    </services>

    <bindings>
      <netMsmqBinding>
        <binding name="volatileBinding"
              durable="false"
              exactlyOnce="false">
          <security mode="None" />
        </binding>
      </netMsmqBinding>
    </bindings>

    <behaviors>
      <serviceBehaviors>
        <behavior name="StockTickerServiceBehavior">
          <serviceMetadata httpGetEnabled="True"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>

  </system.serviceModel>

Ensure that you change the configuration on both the server and the client before you run the sample.

Note

Setting security mode to None is equivalent to setting MsmqAuthenticationMode, MsmqProtectionLevel, and Message security to None.

Bendrinti naudojant

Volatile Queued Communication

To set up, build, and run the sample

To run the sample on a computer joined to a workgroup or without active directory integration

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