Part 46 - WCF throttling

Suggested Videos
Part 43 - Single concurrency mode in WCF
Part 44 - Multiple concurrency mode in WCF
Part 45 - Reentrant concurrency mode in WCF



In this video we will discuss throttling in WCF with examples.



Let's understand throttling with an example
Step 1: Create a class library project with name = SimpleService. Delete the autogenerated class1.cs file.

Step 2: Right click on SimpleService project in solution explorer and add a WCF service with name = SimpleService. 

Step 3: Copy and paste the following code in ISimpleService.cs file

using System.ServiceModel;

namespace SimpleService

{

    [ServiceContract]

    public interface ISimpleService

    {

        [OperationContract(IsOneWay = true)]

        void DoWork();

    }

}

Step 4: Copy and paste the following code in SimpleService.cs file

using System;

using System.ServiceModel;

using System.Threading;

namespace SimpleService

{

    [ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Multiple,

        InstanceContextMode = InstanceContextMode.PerCall)]

    public class SimpleService : ISimpleService

    {

        public void DoWork()

        {

            Thread.Sleep(1000);

            Console.WriteLine("Thread {0} processing request @ {1}",

                Thread.CurrentThread.ManagedThreadId, DateTime.Now);

        }

    }

}

Step 5: Right click on SimpleService solution in solution explorer and add a console project with name = Host. We will use this project to host the WCF service.

Step 6: Right click on References folder under Host project and add a reference to SimpleService project and System.ServiceModel assembly.

Step 7:  Right click on Host project and add Application Configuration file. This should add App.config file.

Step 8: Copy and paste the following configuration in App.config file

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

  <system.serviceModel>

    <behaviors>

      <serviceBehaviors>

        <behavior name="mexBehavior">

          <serviceMetadata httpGetEnabled="true" />

        </behavior>

      </serviceBehaviors>

    </behaviors>

    <services>

      <service behaviorConfiguration="mexBehavior"

               name="SimpleService.SimpleService">

        <endpoint address="SimpleService"

                  binding="basicHttpBinding"

                  contract="SimpleService.ISimpleService"

                  />

        <host>

          <baseAddresses>

            <add baseAddress="http://localhost:8080" />

          </baseAddresses>

        </host>

      </service>

    </services>

  </system.serviceModel>

</configuration>

Step 9: Copy and paste the following code in Program.cs file in the Host project.

using System.ServiceModel;

using System;

namespace Host

{

    class Program

    {

        public static void Main()

        {

            using (ServiceHost host = new

                ServiceHost(typeof(SimpleService.SimpleService)))

            {

                host.Open();

                Console.WriteLine("Host started @ " + DateTime.Now.ToString());

                Console.ReadLine();

            }

        }

    }

}

Step 10: Set Host project as the startup project and run the application by pressing CTRL + F5 key. At this point we have the WCF service up and running.

Step 11: Now let's create a client for the WCF service. Create a new Console application with name = Client

Step 12: Add a service reference to SimpleService. Right click on References folder and select Add Service Reference. In the Add Service Reference window type Address = http://localhost:8080/ and click GO button. This should bring up the SimpleService. In the Namespace textbox type SimpleService and click OK.

Step 13: Copy and paste the following code in Program.cs file.

using System.Threading;

namespace Client

{

    class Program

    {

        static void Main()

        {

            SimpleService.SimpleServiceClient client = new SimpleService.SimpleServiceClient();

            for (int i = 1; i <= 100; i++)

            {

                Thread thread = new Thread(client.DoWork);

                thread.Start();

            }

        }

    }

}

What is throughput?
Throughput is the amount of work done in a given time. In addition to Service Instance Context Mode and Concurrency Mode, Throttling settings also influence the throughput of a WCF service.

Throttling settings can be specified either in the config file or in code

Throttling settings in config file

<behaviors>

  <serviceBehaviors>

    <behavior name="throttlingBehavior">

      <serviceThrottling

        maxConcurrentCalls="3"

        maxConcurrentInstances="3"

        maxConcurrentSessions="100"/>

    </behavior>

  </serviceBehaviors>

</behaviors>

Throttling settings in code

using (ServiceHost host = new ServiceHost(typeof(SimpleService.SimpleService)))

{

    ServiceThrottlingBehavior throttlingBehavior = new ServiceThrottlingBehavior

    {

        MaxConcurrentCalls = 3,

        MaxConcurrentInstances = 3,

        MaxConcurrentSessions = 100

    };

    host.Description.Behaviors.Add(throttlingBehavior);

    host.Open();

    Console.WriteLine("Host started @ " + DateTime.Now.ToString());

    Console.ReadLine();

}

Please Note: ServiceThrottlingBehavior class is present in System.ServiceModel.Description namespace

With the above throttling settings a maximum of 3 concurrent calls are processed.

In addition to maxConcurrentCalls property, maxConcurrentInstances and maxConcurrentSessions may also impact the number of calls processed concurrently.

For example, if we set maxConcurrentCalls="3", maxConcurrentInstances="2", and maxConcurrentSessions="100", 
With a PerCall instance context mode, only 2 calls are processed concurrently. This is because every call requires a new service instance, and here we are allowing only a maximum of 2 concurrent instances to be created.

With a Single instance context mode, 3 calls are processed concurrently. This is because with a singleton service there is only one service instance which handles all the requests from all the clients. With singleton maxConcurrentInstances property does not have any influence.

Please note: maxConcurrentSessions is the sum of all types of sessions, that is 
1. Application sessions
2. Transport sessions
3. Reliable sessions
4. Secure sessions

Defaults:
Before WCF 4.0
        MaxConcurrentCalls: 16
        MaxConcurrentSessions: 10
        MaxConcurrentInstances: MaxConcurrentCalls + MaxConcurrentSessions (26)

WCF 4.0 and later
        MaxConcurrentCalls: 16 * processor count
        MaxConcurrentSessions: 100 * processor count
        MaxConcurrentInstances: MaxConcurrentCalls + MaxConcurrentSessions