Have a single connection with netTcpBinding between client and WCF service - wcf-binding

Question

I came across a page on MSDN explaining transaction in WCF Services here. I tweaked the binding settings and used netTcpBinding. Here is the serviceModel section of my app.config file:
<system.serviceModel>
<bindings>
<netTcpBinding>
<binding name="netTcpBindingConfiguration1" transactionFlow="true">
<security mode="Message" />
</binding>
</netTcpBinding>
</bindings>
<services>
<service name="OrderingService.OrderService">
<clear />
<endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"
listenUriMode="Explicit">
</endpoint>
<endpoint address="net.tcp://localhost:8880/OrderingService"
binding="netTcpBinding" bindingConfiguration="netTcpBindingConfiguration1"
contract="OrderingService.IOrderService" />
<host>
<baseAddresses>
<add baseAddress="http://localhost:8888/OrderingService/" />
</baseAddresses>
</host>
</service>
</services>
<behaviors>
<serviceBehaviors>
<behavior>
<serviceMetadata httpGetEnabled="True" />
<serviceDebug includeExceptionDetailInFaults="False" />
</behavior>
</serviceBehaviors>
</behaviors>
I created a windows application as the client of the service. I used netstat command to see the TCP connections between the client and the service (hosted in a console application). I realized for each operation (which was a button click in my client app that places a new order by invoking the methods of the service's proxy class), a new connection is created and all previous connections still remain ESTABLISHED. Obviously, this is not an ideal condition. I wondered what I did wrong and what setting or configuration would work out this problem by reducing the number of connections to only one. By the way, the service class that implements the service interface has InstanceContextMode set to PerSession. Here are the contract interface and the service class:
[ServiceContract(SessionMode=SessionMode.Required)]
public interface IOrderService
{
[OperationContract]
[TransactionFlow(TransactionFlowOption.NotAllowed)]
List<Customer> GetCustomers();
[OperationContract]
[TransactionFlow(TransactionFlowOption.NotAllowed)]
List<Product> GetProducts();
[OperationContract]
[TransactionFlow(TransactionFlowOption.Mandatory)]
string PlaceOrder(Order order);
[OperationContract]
[TransactionFlow(TransactionFlowOption.Mandatory)]
string AdjustInventory(int productId, int quantity);
[OperationContract]
[TransactionFlow(TransactionFlowOption.Mandatory)]
string AdjustBalance(int customerId, decimal amount);
}
[ServiceBehavior(TransactionIsolationLevel = IsolationLevel.Serializable,
TransactionTimeout = "00:00:20",
InstanceContextMode = InstanceContextMode.PerSession,
TransactionAutoCompleteOnSessionClose = true)]
public class OrderService : IOrderService
{...}
Here is the code the uses the proxy class in the client app:
using (TransactionScope scope = new TransactionScope())
{
try
{
proxy = new OrderServiceClient("NetTcpBinding_IOrderService");
result = proxy.PlaceOrder(order);
MessageBox.Show(result);
result = proxy.AdjustInventory(product.ProductId, quantity);
MessageBox.Show(result);
result = proxy.AdjustBalance(customer.CustomerId, product.Price * quantity);
MessageBox.Show(result);
proxy.Close();
scope.Complete();
}
catch (Exception exc)
{
MessageBox.Show("Error occurred: " + exc.Message);
}
}

Answer 1

With regards to the TCP connection remaining ESTABLISHED - are you calling .Close() on your instance of the client when you are finished with it?
If you want to use a single connection you should change the instance context mode to 'Single' and reuse the connection you establish in the client to process all your service calls. This suits an architecture where you want to maintain state within your service.
[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)]
public class Service : IService
{
}
I found this link very helpful when I was learning about context modes in WCF: CodeProject link
As you are currently using PerSession context mode you should be able to limit it to a single connection by adding a setting for maxConcurrentSessions in your behaviors section. You can do it like this:
<serviceBehaviors>
<behavior>
<serviceMetadata httpGetEnabled="True" />
<serviceDebug includeExceptionDetailInFaults="False" />
<serviceThrottling maxConcurrentSessions="1" />
</behavior>
</serviceBehaviors>
This would only be a good idea if you have a single client.