C# Sockets and Multithreading

Question

I am trying to learn more about sockets and threading in c#. I have come across a lot of good resources online to help get me started. The program I made so far, is a simple "man-in-the-middle" application. It's designed as the following: client <--> [application] <--> server

Given the following code, how can I prevent this thread from running at 100% CPU? How can I have the thread wait and block for data and not exit when the client / server is idle?

while (true)
       {
            lock (ClientState)
            {
                checkConnectionStatus(client, server);
            }

            if (clientStream.CanRead && clientStream.DataAvailable)
            {
                Byte[] bytes = new Byte[(client.ReceiveBufferSize)];

                IAsyncResult result = clientStream.BeginRead(bytes, 0, client.ReceiveBufferSize, null, null);
                int size = clientStream.EndRead(result);

                sendData(bytes, serverStream, size);
            }
            if (serverStream.CanRead && serverStream.DataAvailable)
            {
                Byte[] bytes = new byte[(server.ReceiveBufferSize)];

                IAsyncResult result = serverStream.BeginRead(bytes, 0, server.ReceiveBufferSize, null, null);
                int size = serverStream.EndRead(result);

                sendData(bytes, clientStream, size);
            }
        }

EDIT: Decided to post the entire "Connection.cs" class for anyone interested. I'm a beginner programming, so I know there are some bad coding practices here. Basically this whole class is ran in another thread and should die when the connection (to either the client socket or server socket) drops.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.Sockets;
using System.Threading;
using System.Net;

namespace TCPRelay
{
public class Connection
{
    public delegate void delThreadSafeHandleException(System.Exception ex);
    public delegate void ConnectionDelegate(Connection conn);
    public int DataGridIndex;

    Main pMain;

    public TcpClient client { get; set; }
    public TcpClient server { get; set; }
    public String ClientState { get; set; }

    public string ListenPort { get; set; }
    public string remotePort { get; set; }

    public string listenAddress { get; set; }
    public string remoteAddress { get; set; }

    private TcpListener service { get; set; }

    private Main Form
    {
        get
        {
            return pMain;
        }
    }
    private NetworkStream clientStream { get; set; }
    private NetworkStream serverStream { get; set; }


    public Connection(TcpClient client, TcpClient server)
    {
        clientStream = client.GetStream();
        serverStream = server.GetStream();
    }

    public Connection(String srcAddress, int srcPort, String dstAddress, int dstPort, Main caller)
    {
        try
        {
            pMain = caller;
            TcpListener _service = new TcpListener((IPAddress.Parse(srcAddress)), srcPort);

            //Start the client service and add to connection property
            _service.Start();
            service = _service;


            //Set other useful parameters
            listenAddress = srcAddress;
            ListenPort = srcPort.ToString();

            remoteAddress = dstAddress;
            remotePort = dstPort.ToString();

            this.ClientState = "Listening";
        }
        catch (Exception ex)
        {
            pMain.HandleException(ex);
            Thread.CurrentThread.Abort();
        }

    }

    private TcpClient getServerConnection(String address, int port)
    {
        TcpClient client = new TcpClient(address, port);
        if (client.Connected)
        {
            return client;
        }
        else
        {
            throw new Exception(
                String.Format("Unable to connect to {0} on port {0}",
                address,
                port)
                );
        }
    }
    private void sendData(Byte[] databuf, NetworkStream stream, int size)
    {
        bool waiting = true;
        while (waiting)
        {
            if (stream.CanWrite)
            {
                waiting = false;
                stream.Write(databuf, 0, size);
            }
            else { throw new Exception("Unable to write to network stream"); }
        }
    }

    //Main Looping and data processing goes here
    public void ProcessClientRequest()
    {
        try
        {
            //Wait for a connection to the client
            TcpClient client = service.AcceptTcpClient();

            //Get the streams and set the peer endpoints
            this.clientStream = client.GetStream();
            this.client = client;

            //Now that we have a client, lets connect to our server endpoint
            TcpClient server = getServerConnection(remoteAddress, int.Parse(remotePort));

            //Set some useful parameters
            this.server = server;
            this.serverStream = server.GetStream();
        }
        catch (Exception ex)
        {
            lock (ClientState)
            {
                this.ClientState = ex.Message;    
            }

            CloseConnection();
            Thread.CurrentThread.Abort();
        }
        while (true)
       {
            lock (ClientState)
            {
                checkConnectionStatus(client, server);
            }

            if (clientStream.CanRead && clientStream.DataAvailable)
            {
                Byte[] bytes = new Byte[(client.ReceiveBufferSize)];

                IAsyncResult result = clientStream.BeginRead(bytes, 0, client.ReceiveBufferSize, null, null);
                int size = clientStream.EndRead(result);

                sendData(bytes, serverStream, size);
            }
            if (serverStream.CanRead && serverStream.DataAvailable)
            {
                Byte[] bytes = new byte[(server.ReceiveBufferSize)];

                IAsyncResult result = serverStream.BeginRead(bytes, 0, server.ReceiveBufferSize, null, null);
                int size = serverStream.EndRead(result);

                sendData(bytes, clientStream, size);
            }
        }
    }

    private void checkConnectionStatus(TcpClient _client, TcpClient _server)
    {
        try
        {
            if (_client.Client.Poll(0, SelectMode.SelectRead))
            {
                byte[] buff = new byte[1];
                if (_client.Client.Receive(buff, SocketFlags.Peek) == 0)
                {
                    this.ClientState = "Closed";
                    CloseConnection();
                    Thread.CurrentThread.Abort();
                }
            }
            else if (_server.Client.Poll(0, SelectMode.SelectRead))
            {
                byte[] buff = new byte[1];
                if (_server.Client.Receive(buff, SocketFlags.Peek) == 0)
                {
                    this.ClientState = "Closed";
                    CloseConnection();
                    Thread.CurrentThread.Abort();
                }
            }
            else { this.ClientState = "Connected"; }
        }
        catch (System.Net.Sockets.SocketException ex)
        {
            this.ClientState = ex.SocketErrorCode.ToString();
            CloseConnection();
            Thread.CurrentThread.Abort();
        }
    }

    public void CloseConnection()
    {
        if (clientStream != null)
        {
            clientStream.Close();
            clientStream.Dispose();
        }

        if (client != null)
        {
            client.Close();
        }

        if (serverStream != null)
        {
            serverStream.Close();
            serverStream.Dispose();
        }

        if (server != null)
        {
            server.Close();
        }

        if (service != null)
        {
            service.Stop();
        }
    }       
}

}

I also have a "Main" form and a "ConnectionManager" class that i'm playing around with.

Answer 1

The most efficient way of handling this would be to issue a read with a callback, on each stream.

After issuing both reads, sit waiting forever on an object that you use to signal that the thread should stop its work (a ManualResetEvent is the traditional one to use - can be used to signal many threads at once).

When data is received, the OS will call your callback function(s), and you would do your processing in there and then (importantly) queue another read.

This means that your thread is forever idle, waiting on a signal object that tells it that it's time to go away (in a "wake up - time to die" kind of way), and is only ever doing work when the OS tells it that there is data to process.

To be REALLY friendly, you would also do the writes asynchronously, so that one connection cannot starve the other of processing time (in the current implementation, if one write blocks, the other stream never gets serviced).

Finally, to be super good, you would encapsulate this behaviour in an object that takes as a parameter the stream to use, and then simply instantiate two of them, instead of having two streams and doing everything twice in the main code.

Answer 2

After accepting the socket in the middle man I do the following:

 private void WaitForData()
    {
        try
        {
            if (socketReadCallBack == null)
            {
                socketReadCallBack = new AsyncCallback(OnDataReceived);
            }

            ReceiveState rState = new ReceiveState();
            rState.Client = mySocket;

            mySocket.BeginReceive(rState.Buffer, 0, rState.Buffer.Length, SocketFlags.None,
                new AsyncCallback(socketReadCallBack), rState);

        }
        catch (SocketException excpt)
        {
            // Process Exception
        }

    }

Receive State is:

public class ReceiveState
  {
    public byte[] Buffer = new byte[1024]; //buffer for network i/o
    public int DataSize = 0; //data size to be received by the server
    public bool DataSizeReceived = false; //whether prefix was received
    public MemoryStream Data = new MemoryStream(); //place where data is stored
    public Socket Client;   //client socket
   }

Once data is received my routine "OnDataReceived" processes it. I'm not experiencing any CPU problems with this.

Same code used for both the client and middleman.