Limiting number of users accessing asp.net website

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

void Session_Start(object sender, EventArgs e)
{
    try
    {
    	Application.Lock();

    	int activeSessions = (int) Application["ActiveSessions"] + 1;
    	int allowedSessions = 10; // retrieve the threshold here instead

    	Application["ActiveSessions"] = activeSessions;

    	if (activeSessions > allowedSessions)
    		System.Web.HttpContext.Current.Response.Redirect("~/UserLimitReached.aspx", false);
    }
    finally
    {
    	Application.UnLock();
    }
}

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