Question

I’m sure that this question has already been asked, but I don’t really see it.

Using asp.net and C#, how does one track the pages that are open/closed?

I have tried all sorts of things, including:

• modifying the global.asax file application/session start/end operations
• setting a page’s destructor to report back to the application
• static variables (which persist globally rather than on a session by session basis)
• Javascript window.onload and window.onbeforeunload event handlers

It’s been educational, but so far no real solution has emerged.

The reason I want to do this is to prevent multiple users from modifying the same table at the same time. That is, I have a list of links to tables, and when a user clicks to modify a table, I would like to set that link to be locked so that NO USER can then modify that table. If the user closes the table modification page, I have no way to unlock the link to that table.

Answer 1

You should not worry about tracking pages open or closed. Once a webpage is rendered by IIS it’s as good as “closed”.

What you need to do is protect from two users updating your table at the same time by using locks…For example:

    using (Mutex m = new Mutex(false, "Global\\TheNameOfTheMutex")) 
    {
            // If you want to wait for 5 seconds for other page to finish, 
            // you can do m.WaitOne(TimeSpan.FromSeconds(5),false)

            if (!m.WaitOne(TimeSpan.Zero, false))
                Response.Write("Another Page is updating database.");
            else
                UpdateDatabase();                              

    } 

What this above snippet does is, it will not allow any other webpage to call on the UpdateDatabase method while another page is already runing the UpdateDatabase call.So no two pages can call updatedatabase at the same exact time.

But this does not protect the second user from running UpdateDatabase AFTER the first call has finished, so you need to make sure your UpdateDatabase method has proper checks in place ie. it does not allow stale data to be updated.