c# - ネジ止め付きソケット

Question

ソケットとスレッドによって管理されるクライアント/サーバー アプリケーションを作成しています。ソケットと関連するスレッドを適切に閉じる方法を知りたいです。これは私のコードです：

protected override void OnFormClosing(FormClosingEventArgs e)
{
    base.OnFormClosing(e);

    try
    {
        if (UserList.Count > 0)
        {
            foreach (User user in UserList)
            {
                Socket socketUser = user.getSocket();
                socketUser.Send(Encoding.ASCII.GetBytes("!close"));
                socketUser.Close();
            }
        }
        thrAccept.Abort();
        thrReceive.Abort();
        socket.Close();
        incoming.Close();

        Application.Exit();
    }
    catch
    {
        MessageBox.Show("aasa");
    }
}

private void connectBtn_Click(object sender, EventArgs e)
{
    string port=portNum.Text;
    string welcome = "Server up and running - " + System.DateTime.Now.GetDateTimeFormats()[0] + "  " + DateTime.Now.ToString("HH:mm") + "\n" + "Listening Port: " + port + "\n";
    socket.Bind(new IPEndPoint(IPAddress.Any, Convert.ToInt32(portNum.Text)));
    socket.Listen(3);

    thrAccept = new Thread(new ThreadStart(Accept));
    serverLog.AppendText(welcome + "\n");
    thrAccept.Start();
    connectBtn.Enabled = false;
}

private void Accept()
{
    while (true)
    {
        incoming = socket.Accept();
        thrReceive = new Thread(new ThreadStart(Receive));
        thrReceive.Start();
    }
}

private void Receive()
{
    User user = new User();//create an istance for the class User

    while (true)
    {
        byte[] buffer = new byte[64];
        incoming.Receive(buffer);
        // the program continue....

ソケットを正しく閉じるにはどうすればよいですか?

クラス ユーザー

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

namespace HW2_SERVER
{
    class User
    {
        public string username;
        public Socket S;
        public string role;
        public bool managed;
        public User()
        {
            username = "";
            S = null;
            role = "";
            managed = false;

        }

        public void setManage(bool i)
        {
            managed = i;
        }
        public void setUsername(string u)
        {
            username = u;
        }
        public void setSocket(Socket sock)
        {
            S = sock;
        }
        public void setRole(string r)
        {
            role = r;
        }
        public bool getManaged()
        {
            return managed;
        }
        public string getUsername()
        {
            return username;

        }
        public Socket getSocket()
        {
            return S;
        }
        public string getRole()
        {
            return role;
        }
    }
}