TCP server in C# causing 100% CPU usage after 2-3 days

Question

Here's my code for a very simple TCP Server (basically the sample Asynchronous Server Socket example - http://goo.gl/Ix5C - modified slightly):

    public static void InitiateListener()
    {
        try
        {
            allDone = new ManualResetEvent(false);
            configFile = new XmlConfig();                
            StartListening();
        }
        catch (Exception exc)
        {
            LogsWriter f = new LogsWriter(configFile.ErrorLogsPath);
            f.WriteToFile(exc.Message);
            f.CloseFile();
        }

    }

    private static void StartListening()
    {      
        try
        {
            IPEndPoint localEndPoint = new IPEndPoint(IPAddress.Any, configFile.Port);
            Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

            listener.Bind(localEndPoint);
            listener.Listen(100);                

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

                // Start an asynchronous socket to listen for connections.
                listener.BeginAccept(new AsyncCallback(AcceptCallback), listener);

                // Wait until a connection is made before continuing.
                allDone.WaitOne();
            }
        }
        catch (Exception exc)
        {
            throw exc;
        }
    }

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

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

        // Create the state object.
        StateObject state = new StateObject();
        state.workSocket = handler;

        handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReadCallback), state);
    }

    public static void ReadCallback(IAsyncResult ar)
    {
        string hexData = string.Empty;

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

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

            if (bytesRead > 0)
            {
                hexData = BitConverter.ToString(state.buffer);

                if (hexData.Contains("FA-F8")) //heartbeat - echo the data back to the client.
                {
                    byte[] byteData = state.buffer.Take(bytesRead).ToArray();
                    handler.Send(byteData);
                }
                else if (hexData.Contains("0D-0A")) //message
                {
                    state.AsciiData = Encoding.ASCII.GetString(state.buffer, 0, bytesRead);
                    state.ParseMessage(configFile);
                }
            }
            handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReadCallback), state);                
        }
        catch (Exception)
        {
            handler.Shutdown(SocketShutdown.Both);
            handler.Close();
        }
    }

This is all in a Windows service. And the CPU maxes to 100% after about 2 and a half days of running perfectly acceptably. This has happened 3 times now - the windows service always works fine and functions as it's supposed to, utlizing almost no CPU resources but sometime on the 3rd day goes to 100% and stays there until the service is resarted.

I get very simple CSV packets, that I parse quickly and send it off to a database via a webservice in this method: state.ParseMessage(configFile); Even when the CPU is 100%, the database gets filled up pretty reliably. But I understand this could be one place where I need to investigate?

Which other areas of the code seem like they could be causing the problem? I'm new to async programming, so I don't know if I need to close threads manually. Also, this might be another problem: handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReadCallback), state);
Calling that line within ReadCallback itself. I do this to maintain the connection with the client and continue to receive the data, but maybe I should close to the socket and force a new connection?

Could you please offer some suggestions? Thanks

Answer 1

Instead of loop while(true) in startlistening method we need to call

listener.BeginAccept(new AsyncCallback(AcceptCallback), listener);

from AcceptCallback method once completion of accepting new client.

Answer 2

You need to detect disconnection through bytesRead == 0 . Right now you don't and instead issue another read.

Looks like you have copied MSDN sample code. I can tell because of the insightless combination of async IO and events. All this code becomes simpler when you use synchronous IO.