C#

class ClientState
{
    // Holds client state: I/O buffer, socket, IP endpoint etc...
}

class NetworkServer
{
    // Holds list of client states
    private List<clientstate> clientList;
    private object lockObject = new object();

    // Start server node
    public void Start(int backlog)
    {
        clientList = new List<clientstate>();
    
       // Listen to incoming connections asynchronously
        serverSocket.Listen(backlog);
        serverSocket.BeginAccept(new AsyncCallback(OnClientConnect), null);   
    }

    // Callback on client connection
    private void OnClientConnect(IAsyncResult state)
    {
        // Accepts incoming connection
        Socket clientSocket = serverSocket.EndAccept(state);
    
        // Create client state and fill it with state values    
        ClientState clientState = new ClientState();
        ...

        // Add to client list
        lock(lockObject)
        {
            clientList.Add(clientState);
        }
        
        // Start receiving from client
        clientSocket.BeginReceive(clientState.Buffer, 
                                  0,
                                  clientState.Buffer.Length, 
                                  SocketFlags.None,
                                  new AsyncCallback(OnClientRead),
                                  clientState);
    
        // Listen for a new incoming connection
        serverSocket.BeginAccept(new AsyncCallback(OnClientConnect), null);
    }

    // Callback on data ready from a client
    private void OnClientRead(IAsyncResult state)
    {
        // Terminate async read
        SocketError socketError;
        int numBytes = clientSocket.EndReceive(state, out socketError);
    
        if ((numBytes == 0) || (socketError != SocketError.Success))
        {
            // Client closed or receive error: close client socket
            clientSocket.Shutdown(SocketShutdown.Both);
            clientSocket.Close();

            // Remove client from list
            lock(lockObject)
            {
                clientList.Remove(clientState);
            }
        } 
        else 
        {
            // Process data 
            ...

            // Launch a new async read from the client
            clientSocket.BeginReceive(clientState.Buffer,
                                  0,
                                  clientState.Buffer.Length,
                                  SocketFlags.None,
                                  new AsyncCallback(OnClientRead),
                                  clientState); 
        }
    }
}</clientstate></clientstate>