User count

i wrote the below codes for visitors count (online users) for my application :

reference :
http://aspdotnetfaq.com/Faq/How-to-show-number-of-online-users-visitors-for-ASP-NET-website.aspx

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.SessionState;
using CardCharge.Classes;

namespace CardCharge
{
    public class Global : System.Web.HttpApplication
    {

        protected void Application_Start(object sender, EventArgs e)
        {
            Application["OnlineUsers"] = 0;
        }

        protected void Session_Start(object sender, EventArgs e)
        {
            Application.Lock();
            Application["OnlineUsers"] = (int)Application["OnlineUsers"] + 1;
            Application.UnLock();
        }

        protected void Application_BeginRequest(object sender, EventArgs e)
        {

        }

        protected void Application_AuthenticateRequest(object sender, EventArgs e)
        {

        }

        protected void Application_Error(object sender, EventArgs e)
        {

        }

        protected void Session_End(object sender, EventArgs e)
        {
            Application.Lock();
            Application["OnlineUsers"] = (int)Application["OnlineUsers"] - 1;
            Application.UnLock();
        }

        protected void Application_End(object sender, EventArgs e)
        {

        }
    }
}