C# thread started in another class

Question

I have one main form class and another class. In the second class, I have a thread loop:

    public void StartListening()
    {
        listening = true;
        listener = new Thread(new ThreadStart(DoListening));
        listener.Start();
    }


    // Listening for udp datagrams thread loop
    /*=====================================================*/
    private void DoListening()
    {
        while (listening)
        {
            IPEndPoint remoteIPEndPoint = new IPEndPoint(IPAddress.Any, port);
            byte[] content = udpClient.Receive(ref remoteIPEndPoint);

            if (content.Length > 0)
            {
                string message = Encoding.ASCII.GetString(content);
                delegMessage(message);
            }
        }
    }

    // Stop listening for udp datagrams
    /*=====================================================*/
    public void StopListening()
    {
        lock (locker)
        {
            listening = false;
        }
    }

In main form class, I start this listening in class constructor

       udp.StartListening();

And than, in this main form class, I have key hook event, too. In this event, I wan to stop thread running in the second class.

    private void hook_KeyPressed(int key)
    {
        if (key == (int)Keys.LMenu)
            altPressed = true;
        if (key == (int)Keys.F4 && altPressed == true)
        udp.StopListening();
    } 

Unfortunetely, the thread is still running. Do you have some ideas about this??

Thank you very much.

Answer 1

Your thread is blocking at the byte[] content = udpClient.Receive(ref remoteIPEndPoint); line. The Receive method blocks until something is received.

You should use the asynchronous version ( BeginReceive ) instead.

Answer 2

Also, another flaw in your code - you check for the stopping condition without any synchronization. Here:

   private void DoListening()
   {
    while (listening){ //this condition could stuck forever in 'false'
   }

Actually, without a memory barrier, there is no guarantee, that a thread, that is running DoListening will ever see the change to listening var from other thread. You should at least use locking here (which provides memory barrier)

Answer 3

As @igelineau pointed out - your code is blocking on the receive call. If you don;t want to go down the async route (which I'd recommend) just send something to the udp port in your stop listening method.