The root cause of Global Session_End not being executed(triggered)

If the website is to implement the online user function, the users must be added to the online list in the Session_Start method when they login, and they needs to be deleted from the online list in the Session_End method when they logout. Sometimes, the user is deleted in the Session_End method, but they cannot be deleted. It seems that the Session_End is not executed. We often think that there is a problem with the deletion code, but the user can be deleted normally without executing the delete user code in the Session_End method, indicating the code no problem, but there is a problem with the Session_End method. What is the root cause of the problem?

Let's first look at how the C# language stipulates the Session_End method:

1. If there is an error in the code in the Session_End method, it will return immediately, and it will not record the error or throw any exception, and the Respone.Write method cannot be used to output the error;

2. Methods or classes such as Server.MapPath, Request, Cache, HttpContext.Current cannot be used in the Session_End method;

3. It is necessary to set the sessionState mode="InProc" mode in the Web.Config configuration file to InProc.

So, if you encounter Session_End not being executed(triggered), you may wish to check whether the above regulations are violated first. The common mistake is to use Server.MapPath, Request, Cache, HttpContext.Curren in the Session_End method or the method it calls; if they are used, the code can be executed normally if they are implemented in another way.

Examples of Global Session_End not being executed(triggered)

1. Server.MapPath is used in the Session_End method

protected void Session_End(object sender, EventArgs e)
       {
              string path = "/temp/map.txt";
              path = Server.MapPath(path);//Server.MapPath is not allowed in the Session_End method
       }

2. The method called in the Session_End method uses HttpContext.Curren

protected void Session_End(object sender, EventArgs e)
       {
              string path = "/temp/map.txt";
              path = Server.MapPath(path);//Server.MapPath is not allowed in the Session_End method
       }

public void delOnline()
       {
              if(HttpContext.Current.Cache["user"] != null)
                     {
                             //It is not allowed to use HttpContext.Current and Cache in the method called in the Session_End method
                            string user = (HttpContext.Current.Cache["user"]).ToString();
                     }
       }