How to properly exit background thread with loop when class exported via MEF?

Question

I implemented class that serves as TcpCLient server. Looks like this:

{

[Export]
public class MessageListener
{
    private readonly TcpListener tcpListener;
    private readonly Thread listenThread;

    private DataRepository DataRepository { get; set; }

    private IEventAggregator EventAggregator { get; set; }

    [ImportingConstructor]
    public MessageListener(DataRepository dataRepository, IEventAggregator eventAggregator)
    {
        this.DataRepository = dataRepository;
        this.EventAggregator = eventAggregator;

        // TODO: Need to put proper Port number
        this.tcpListener = new TcpListener(IPAddress.Any, 3000);
        this.listenThread = new Thread(this.ListenForClients);
        this.listenThread.Start();
    }

    private void ListenForClients()
    {
        this.tcpListener.Start();

        while (true)
        {
            // blocks until a client has connected to the server
            var client = this.tcpListener.AcceptTcpClient();

            // create a thread to handle communication with connected client
            var clientThread = new Thread(this.HandleClientComm);
            clientThread.Start(client);
        }
    }

This listener imported in my Shell view model. Works good.

When I close WPF window - MEF won't dispose this object. Windows closes but process still running. How do I properly shutdown this "server"? It waits for var client ..

Answer 1

The process won't exit until all foreground threads complete.

In this case, since you're starting a new thread, you can just make it a background thread:

this.listenThread = new Thread(this.ListenForClients);
this.listenThread.IsBackground = true;
this.listenThread.Start();

Background threads won't keep the process alive.

Answer 2

Mark your class as implementing IDisposable , and set a disposed flag in the Dispose implementation. Then change your loop where you accept connections like this:

    while (!this.disposed)
    {
        Thread.Sleep(1); // to avoid spinning a core 100%
        if (this.tcpListener.Pending)
        {
            // shouldn't block because we checked tcpListener.Pending
            var client = this.tcpListener.AcceptTcpClient();
            var clientThread = new Thread(this.HandleClientComm);
            clientThread.Start(client);
        }
    }

MEF will take care of calling Dispose on any disposable components it created, provided that you dispose the MEF container itself when the application exits.

Answer 3

It doesnt stop because of the infinite loop. You need to use a flag, a mutex or something like that, so that the loop stops and the thread will return and stop properly.