Can not stop async TCP sever Windows service

Question

I have a TCP server windows service developed in .net 4.0 with asynchronous server sockets.

It works, but about 90 % of the time I simply can not stop it: after pressing stop button in Windows Service console, it hangs and stops after about a minute, but its process goes on and TCP communication continues. It hangs at _listener.Close(). Only thing I can do to close the communication is to restart Windows. There can be something with closing sockets. I tried to figure out but I simply can not find the root of the problem.

Client side is not under my control, they are some 100 gadgets sending data via TCP.

Here is my code (updated).

Thanks a lot, any suggestions are highly appreciated!

    public class DeviceTCPServer
{
    public readonly IPAddress IPAddress;
    public readonly int Port;
    public readonly int InputBufferSize;
    public readonly ConcurrentDictionary<Guid, StateObject> Connections;

    public event EventHandler OnStarted;
    public event EventHandler OnStopped;
    public event ServerEventHandler OnConnected;
    public event ServerEventHandler OnDisconnected;
    public event RecievedEventHandler OnRecieved;
    public event DroppedEventHandler OnDropped;
    public event ExceptionEventHandler OnException;
    public event ServerLogEventHandler ServerLog;

    private volatile bool _iAmListening;
    private Socket _listener;
    private Thread _listenerThread;
    private readonly ManualResetEvent _allDone = new ManualResetEvent(false);

    public bool Listening
    {
        get { return _iAmListening; }
    }

    public DeviceTCPServer(IPAddress ipAddress,
                         int port,
                         int inputBufferSize)
    {
        IPAddress = ipAddress;
        Port = port;
        InputBufferSize = inputBufferSize;

        Connections = new ConcurrentDictionary<Guid, StateObject>();
    }

    public void ThreadedStart()
    {
        _listenerThread = new Thread(Start)
        {
            CurrentUICulture = Thread.CurrentThread.CurrentUICulture,
            IsBackground = true
        };

        _listenerThread.Start();
    }

    private void Start()
    {
        try
        {
            var localEP = new IPEndPoint(IPAddress, Port);
            _listener = new Socket(localEP.Address.AddressFamily, SocketType.Stream, ProtocolType.Tcp);

            _listener.Bind(localEP);
            _listener.Listen(10000);

            if (OnStarted != null)
                OnStarted(this, new EventArgs());

            _iAmListening = true;

            var listenerWithCultureInfo = new Tuple<Socket, CultureInfo>(_listener,
                                                                         Thread.CurrentThread.CurrentUICulture);

            while (_iAmListening)
            {
                _allDone.Reset();
                _listener.BeginAccept(AcceptCallback, listenerWithCultureInfo);
                _allDone.WaitOne();
            }
        }
        catch (Exception exc)
        {
            Debug.Assert(false, exc.Message);
            if (OnException != null)
                OnException(this, new ExceptionEventArgs(exc, "Start"));
        }
    }

    public void StopListening()
    {
        try
        {
            _iAmListening = false;
            _allDone.Set();
        }
        catch(Exception exc)
        {
            Debug.Assert(false, exc.Message);
            if (OnException != null)
                OnException(this, new ExceptionEventArgs(exc, "StopListening"));
        }
    }

    public void Stop()
    {
        try
        {
            _listener.Close(0);
            CloseAllConnections();
            _listenerThread.Abort();
        }
        catch (Exception exc)
        {
            Debug.Assert(false, exc.Message);
            if (OnException != null)
                OnException(this, new ExceptionEventArgs(exc, "Stop"));
        }
    }

    private void AcceptCallback(IAsyncResult ar)
    {
        var arTuple = (Tuple<Socket, CultureInfo>)ar.AsyncState;
        var state = new StateObject(arTuple.Item2, InputBufferSize);

        try
        {
            Connections.AddOrUpdate(state.Guid,
                                    state,
                                    (k, v) => v);

            Thread.CurrentThread.CurrentUICulture = state.CurrentUICulture;

            var listener = arTuple.Item1;
            var handler = listener.EndAccept(ar);

            _allDone.Set();
            if (!_iAmListening)
                return;

            state.WorkSocket = handler;
            handler.BeginReceive(state.Buffer, 0, state.InputBufferSize, 0,
                                 RecieveCallBack, state);

            if (OnConnected != null)
                OnConnected(this, new ServerEventArgs(state));
        }
        catch(ObjectDisposedException)
        {
            _allDone.Set();
            return;
        }
        catch (Exception exc)
        {
            Debug.Assert(false, exc.Message);
            if (OnException != null)
                OnException(this, new ExceptionEventArgs(exc, state, "AcceptCallback"));
        }
    }

    public void RecieveCallBack(IAsyncResult ar)
    {
        var state = (StateObject)ar.AsyncState;

        try
        {
            Thread.CurrentThread.CurrentUICulture = state.CurrentUICulture;

            var handler = state.WorkSocket;
            var read = handler.EndReceive(ar);

            var pBinayDataPocketCodecStore = new BinayDataPocketCodecStore();

            if (read > 0)
            {
                state.LastDataReceive = DateTime.Now;

                var data = new byte[read];
                Array.Copy(state.Buffer, 0, data, 0, read);
                state.AddBytesToInputDataCollector(data);

                //check, if pocket is complete
                var allData = state.InputDataCollector.ToArray();
                var codecInitRes = pBinayDataPocketCodecStore.Check(allData);

                if (codecInitRes.Generic.Complete)
                {
                    if (!codecInitRes.Generic.Drop)
                    {
                        if (OnRecieved != null)
                            OnRecieved(this, new RecievedEventArgs(state, allData));
                    }
                    else
                    {
                        if (OnDropped != null)
                            OnDropped(this, new DroppedEventArgs(state, codecInitRes.Generic));

                        //get new data
                        state.ResetInputDataCollector();

                        handler.BeginReceive(state.Buffer, 0, state.InputBufferSize, 0,
                                             RecieveCallBack, state);
                    }
                }
                else
                {
                    //get more data
                    handler.BeginReceive(state.Buffer, 0, state.InputBufferSize, 0,
                                         RecieveCallBack, state);
                }
            }
            else
            {
                if ((handler.Connected == false) || (handler.Available == 0))
                {
                    Close(state);
                }
            }
        }
        catch (Exception exc)
        {
            Debug.Assert(false, exc.Message);
            if (OnException != null)
                OnException(this, new ExceptionEventArgs(exc, state, "RecieveCallBack"));
        }
    }

    public void Send(StateObject state, byte[] data)
    {
        try
        {
            var handler = state.WorkSocket;

            handler.BeginSend(data, 0, data.Length, 0,
                              SendCallback, state);
        }
        catch (Exception exc)
        {
            Debug.Assert(false, exc.Message);
            if (OnException != null)
                OnException(this, new ExceptionEventArgs(exc, state, "Send"));
        }
    }

    private void SendCallback(IAsyncResult ar)
    {
        var state = (StateObject)ar.AsyncState;

        try
        {
            Thread.CurrentThread.CurrentUICulture = state.CurrentUICulture;
            var handler = state.WorkSocket;

            handler.EndSend(ar);
            handler.BeginReceive(state.Buffer, 0, state.InputBufferSize, 0,
                                 RecieveCallBack, state);
        }
        catch (Exception exc)
        {
            Debug.Assert(false, exc.Message);
            if (OnException != null)
                OnException(this, new ExceptionEventArgs(exc, state, "SendCallback"));
        }
    }

    public void Close(StateObject state)
    {
        try
        {
            if (state == null)
                return;

            var handler = state.WorkSocket;

            if (handler == null)
                return;

            if (!handler.Connected)
                return;

            if (handler.Available > 0)
            {
                var data = new byte[handler.Available];
                handler.Receive(data);
            }

            handler.Shutdown(SocketShutdown.Both);
            handler.Close(0);

            if (OnDisconnected != null)
                OnDisconnected(this, new ServerEventArgs(state));

            StateObject removed;
            var removeResult = Connections.TryRemove(state.Guid, out removed);
        }
        catch (Exception exc)
        {
            Debug.Assert(false, exc.Message);
            if (OnException != null)
                OnException(this, new ExceptionEventArgs(exc, "Close"));
        }
    }

    private void CloseAllConnections()
    {
        try
        {
            var connections = Connections.Select(c => c.Value);

            foreach(var connection in connections)
            {
                Close(connection);
            }
        }
        catch(Exception exc)
        {
            Debug.Assert(false, exc.Message);
            if (OnException != null)
                OnException(this, new ExceptionEventArgs(exc, "CloseAllConnections"));
        }
    }

    public override string ToString()
    {
        return string.Format("{0}:{1}", IPAddress, Port);
    }
}

Answer 1

Since this is a service, the usual "wait for the non-background threads to exit" rule doesn't apply, and it is your job to kill the workers (which can including pending async operations). Now; at the moment, you're killing the listener , but that only prevents new sockets from attaching. You should ideally keep track of your clients somewhere, so that you can also kill all the client sockets. When you've done that , you should be fine. Remember to synchronize access to any collection of clients, or use a thread-safe collection type.

Answer 2

I think you should use the Socket.Shutdown method before closing the socket. As it is stated in the documentation:

When using a connection-oriented Socket, always call the Shutdown method before closing the Socket. This ensures that all data is sent and received on the connected socket before it is closed.

Moreover, maybe I am wrong, but I can not see any calls to the StopListening() method. Since then the _iAmListening field is not set to false, and the callback (AcceptCallback(IAsyncResult ar)) is still responding to the incoming calls.

Answer 3

So, finally the problem is solve, there were no any problem with my Windows service!

It was caused by a Microsoft Windows update:

Microsoft KB4338815, which caused closesocket tо hang forever on Intel Xeon processors: https://forum.filezilla-project.org/viewtopic.php?t=49308

Thanks all your efforts to try to help me!