Stopping an asynchronous TCP server on separate thread in C#

Question

I have implemented an asynchronous TCP server that is spawned by another process. It starts fine and operates as expected, however I am having trouble terminating the server when I end the process that started it.

The following is my current TCP server and stopping function from the other process.

TCP Server

    public class StateObject
    {
        //Client socket.
        public Socket workSocket = null;
        //Size of receive buffer.
        public const int BufferSize = 1024;
        //Receive buffer.
        public byte[] buffer = new byte[BufferSize];
        //Received data string.
        public StringBuilder sb = new StringBuilder();
    }

    public class AsynchronousSocketListener : Strategy
    {
        //Thread signal.
        public static ManualResetEvent allDone = new ManualResetEvent(false);
        public volatile bool listening = true;

        //User-specified port number.
        private int Port;

        public AsynchronousSocketListener(int port)
        {
            Port = port;
        }

        public void StopListening()
        {
            listening = false;
        }

        public void StartListening()
        {
            //Data buffer for incoming data.
            byte[] bytes = new Byte[1024];

            //Establish the local endpoint for the socket.
            IPHostEntry ipHostInfo = Dns.Resolve(Dns.GetHostName());
            IPAddress ipAddress = ipHostInfo.AddressList[0];
            IPEndPoint localEndPoint = new IPEndPoint(ipAddress, Port);

            //Create a TCP/IP socket.
            Socket listener = new Socket(AddressFamily.InterNetwork,
                SocketType.Stream, ProtocolType.Tcp);

            //Bind the socket to the local endpoint and listen for
            //incoming connections.
            try
            {
                listener.Bind(localEndPoint);
                listener.Listen(100);

                while (listening)
                {
                    //Set the event to nonsignaled state.
                    allDone.Reset();    

                    //Start an asychronous socket to listen for connections.
                    Print("Waiting for a connection...");
                    listener.BeginAccept(
                    new AsyncCallback(AcceptCallback),
                        listener);

                    //Wait until a connection is made before continuing.
                    allDone.WaitOne();
                }
            }
            catch (Exception e)
            {
                Print(e.ToString());    
            }
        }

        public void AcceptCallback(IAsyncResult arg)
        {
            //Signal the main thread to continue.
            allDone.Set();

            //Get the socket that handles the client request.
            Socket listener = (Socket) arg.AsyncState;
            Socket handler = listener.EndAccept(arg);

            //Create the state object.
            StateObject state = new StateObject();
            state.workSocket = handler;
            handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
                new AsyncCallback(ReadCallback), state);
        }

        public void ReadCallback(IAsyncResult arg)
        {
            String content = String.Empty;

            //Retrieve the state object and the handler socket
            //from the asynchronous state object.
            StateObject state = (StateObject) arg.AsyncState;
            Socket handler = state.workSocket;

            //Read data from the client socket.
            int bytesRead = handler.EndReceive(arg);

            if (bytesRead > 0)
            {
                //There might be more data, so store the data received so far.
                state.sb.Append(Encoding.ASCII.GetString(
                    state.buffer,0,bytesRead));

                //Check for end-of-file tag. If it is not there, read
                //more data.
                content = state.sb.ToString();
                if (content.IndexOf("<EOF>") > -1)
                {
                    //All the data has been read from the
                    //client. Display it on the console.
                    Print("Read " + content.Length + " bytes from socket. \n Data : " + content);
                    //Echo the data back to the client.
                    Send(handler, content);
                }
                else
                {
                    //Not all data received. Get more.
                    handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
                        new AsyncCallback(ReadCallback), state);
                }
            }
        }

        private void Send(Socket handler, String data)
        {
            //Convert the string data to byte data using ASCII encoding.
            byte[] byteData = Encoding.ASCII.GetBytes(data);

            //Begin sending the data to the remote device.
            handler.BeginSend(byteData,0,byteData.Length,0,
                new AsyncCallback(SendCallback),handler);
        }

        private void SendCallback(IAsyncResult arg)
        {
            try
            {
                //Retrieve the socket from the state object.
                Socket handler = (Socket) arg.AsyncState;

                //Complete sending the data to the remote device.
                int bytesSent = handler.EndSend(arg);
                Print("Sent " + bytesSent + " bytes to client.");

                handler.Shutdown(SocketShutdown.Both);
                handler.Close();
            }
            catch (Exception e)
            {
                Print(e.ToString());    
            }
        }
    }

Spawning process

//private NinjaTerminal.Server server;
        private NinjaTerminal.AsynchronousSocketListener    server;
        private Thread                                      listenThread;
        private int                                         _Port = 8080;

    protected override void OnStartUp() 
    {
        server = new NinjaTerminal.AsynchronousSocketListener(Port);
        listenThread = new Thread(new ThreadStart(server.StartListening));
        listenThread.Start();
    }

    protected override void OnTermination() 
    {
        listenThread.stopListening();
        listenThread.Join();
    }

Now I've verified that OnTermination() gets called, and it does join to the server thread, however the server thread never ends.

I would love some insights as to why, and suggestions to a better architecture or more than welcome. At this stage I haven't invested much into anything but setting up the TCP server, so if you have a different/better idea I'd love to hear it.

Also, I've searched high and low through StackOverflow for an answer already and none of them really applied to an asynchronous TCP server. And I'm using .NET 3.5

Code addition to Reed's answer

public void StopListening() { listening = false; allDone.Set(); }

    public void StartListening()
    {
        //Data buffer for incoming data.
        byte[] bytes = new Byte[1024];

        //Establish the local endpoint for the socket.
        IPHostEntry ipHostInfo = Dns.Resolve(Dns.GetHostName());
        IPAddress ipAddress = ipHostInfo.AddressList[0];
        IPEndPoint localEndPoint = new IPEndPoint(ipAddress, Port);

        //Create a TCP/IP socket.
        Socket listener = new Socket(AddressFamily.InterNetwork,
            SocketType.Stream, ProtocolType.Tcp);

        //Bind the socket to the local endpoint and listen for
        //incoming connections.
        try
        {
            listener.Bind(localEndPoint);
            listener.Listen(100);

            while (listening)
            {
                //Set the event to nonsignaled state.
                allDone.Reset();    

                //Start an asychronous socket to listen for connections.
                Print("Waiting for a connection...");
                listener.BeginAccept(
                new AsyncCallback(AcceptCallback),
                    listener);

                //Wait until a connection is made before continuing.
                allDone.WaitOne();
            }
            listener.Close();
        }
        catch (Exception e)
        {
            Print(e.ToString());    
        }
    }

Answer 1

You need to change StopListening to also include a call to signal your WaitHandle:

public void StopListening()
{
    this.listening = false;
    this.allDone.Set();
}

Without this, your StartListening routine will hang forever here:

//Wait until a connection is made before continuing.
allDone.WaitOne();