C# problem with multi-clients server application

Question

I have a server application and a client application. I'm using socket to communicate between server and client. Everything works fine if there's only one client connect: uploading, downloading all work well.

But if there's another client connect (I start the client application again, which means there're 2 client apps and 1 server app running on my computer), my server starts to mess up: server doesn't receive file upload from client, client couldn't download from server.

In server code, I already used multithreading for each client connection so I can't figure out the problem. Here is my server code:

    private void ServerForm_Load(object sender, System.EventArgs e)
            {

                //...
                Thread th = new Thread(new ThreadStart(ListenForPeers));
                th.Start();
            }

    public void ListenForPeers()
            {
                    serversocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                    serversocket.Blocking = true;
                    IPHostEntry IPHost = Dns.GetHostEntry(server);
                    string[] aliases = IPHost.Aliases;
                    IPAddress[] addr = IPHost.AddressList;
                    IPEndPoint ipepServer = new IPEndPoint(addr[0], 8090);
                    serversocket.Bind(ipepServer);
                    serversocket.Listen(-1);
                    while (true)
                    {
                        clientsock = serversocket.Accept();
                        if (clientsock.Connected)
                        {
                            total_clients_connected++;
                            AppendText("Client connected...");
                            Thread tc = new Thread(new ThreadStart(listenclient));
                            tc.Start();
                        }
             }


    void listenclient()
        {
             // start communication
        }

Is there something wrong with my server code that makes it unable to become a multi-clients server system? Help is really appreciated. Thanks in advance.

Answer 1

It looks like you've defined your clientSocket as a global variable to be used by all server threads, instead you want it to be a local reference for each thread. You can do this with a ParameterizedThreadStart:

public void listenForPeers()
{
  //Setup the server socket

  while(true){
    Socket newClient = serverSock.Accept();
    if(newClient.Connected){
      Thread tc = new Thread(new ParameterizedThreadStart(listenclient));
      tc.start(newClient);
    }
  }
}

void listenclient(object clientSockObj)
{
  Socket clientSock = (Socket)clientSockObj;

  //communication to client via clientSock.
}

Answer 2

First, you're setting your socket's Blocking property to true. This will block any requests until the previous ones finish...

See here: http://msdn.microsoft.com/en-us/library/system.net.sockets.socket.blocking(VS.80).aspx

If you are in blocking mode, and you make a method call which does not complete immediately, your application will block execution until the requested operation completes. If you want execution to continue even though the requested operation is not complete, change the Blocking property to false. The Blocking property has no effect on asynchronous methods. If you are sending and receiving data asynchronously and want to block execution, use the ManualResetEvent class.

You might want to reconsider doing it this way, and instead use WCF or maybe a web service for uploading the files... it'll be a lot easier, and IIS will handle the threading for you. It's pretty easy to write a web service to upload a file...

http://www.c-sharpcorner.com/UploadFile/scottlysle/UploadwithCSharpWS05032007121259PM/UploadwithCSharpWS.aspx

Answer 3

try this

const int noOfClients = 5;

for(int i=0;i<noOfClients;i++)
{
  Thread th = new Thread(new ThreadStart(ListenForPeers));
  th.Start();
}