ASP.net显示当前系统在线人数

void Application_Start(object sender, EventArgs e) ???????{ ???????????// 在应用程序启动时运行的代码 ???????????Application.Lock(); ???????????if (Application["visitor_counter"] == null) ???????????{ ???????????????Application["visitor_counter"] = 1; ???????????} ???????????else ???????????{ ???????????????Application["visitor_counter"] = (int)Application["visitor_counter"] + 1; ???????????} ???????????Application.UnLock(); ???????} ???????void Application_End(object sender, EventArgs e) ???????{ ???????????// ?在应用程序关闭时运行的代码 ???????????Application.Lock(); ???????????Application["visitor_counter"] = (int)Application["visitor_counter"] - 1; ???????????Application.UnLock(); ???????}