Question

In my application I host a WCF service:

private void StartService()
{
    m_serviceHost = new ServiceHost(typeof(...));
    m_serviceHost.Open();
}

private void button1_Click(object sender, EventArgs e)
{                        
    Thread t = new Thread(StartService);
    t.IsBackground = true;
    t.Start();
    // ...
}

The service itself has just one method:

public void SendMessage(string message)
{
    MessageBox.Show(String.Format("Message '{0}' received on thread {1} : MessageLoop = 
        {2}", message, Thread.CurrentThread.GetHashCode(), Application.MessageLoop), 
        "MessagingService.SendMessage()");
}

When the client calls this operation I get the following responses:

Message 'hello client : message 9 recieved on thread **12**
Message 'hello client : message 9 recieved on thread **15**
Message 'hello client : message 9 recieved on thread **17**
...

Why does the thread id always change? When I created the ServiceHost I only put him on another thread! im not re-putting him on another thread each time… only once

How can i put the host in another thread (like i did) and to get only single background thread id ?

Answer 1

IIRC correctly the ConcurrencyMode.Single does not guarantee that a single thread is used…it guarantees that only a single thread can access the service instance…thus preventing concurrency issues that might arrise if two (or more) threads use the same service instance (state might get corrupted for instance).

I guess you want to enforce one thread to handle all the calls so everything gets done sequentially and no state gets corrupted. But with the default InstanceContextMode (PerCall) each call gets its own service instance anyway. And with the ConcurrencyMode set to single you are sure that only one thread accesses a service instance.

[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Single, 
    InstanceContextMode = InstanceContextMode.PerCall)]
public class MessageService : IMessageService
{
    public string ReturnMessage()
    {
        return String.Format("Thread {0}", Thread.CurrentThread.ManagedThreadId);
    }
}