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.
}