Question

I have a aspx page in which i create reports and charts on the fly. Creation of these charts and reports takes a lot of time because of which a blank screen is shown to the user until the creation completes.

To solve this problem I am trying to trigger report generation in a separate thread on page load and when the reportgeneration completes i am trying to set a session variable to indicate completion. I have a AJAX timer which keeps checking for this flag.

protected void Page_Load( object sender, EventArgs e )
{
    if ( !IsPostBack )
    {
        ThreadPool.QueueUserWorkItem( new WaitCallback( DoLongRunningProcess ) );
    }
}
public void GenerateReport( object state )
{
    ///generate report
    Session[ "done" ] = true;
}

The problem is that Session is null(Session state can only be used when enableSessionState is set to true, either in a configuration file or in the Page directive. Please also make sure that System.Web.SessionStateModule or a custom session state module is included in the <configuration>\<system.web>\<httpModules> section in the application configuration.) when i am trying set the completion flag.

Can you guys tell me how to workaround this problem.

Answer 1

The problem is that in a new thread, HttpContext.Current (and Session in it) is not available.

One solution is to create an instance that you pout in Session and also sens to worker thread as a parameter:

1. Declare a Status class:

   public class MyStatus {
   public Exception Exception { get; set; }
   public bool IsDone { get; set; }
   }

2. Before start processing, put an instance in the Session that your ajax callback can check. Also gives object as argument to worker thread.

   protected void Page_Load( object sender, EventArgs e )
   {
   if ( !IsPostBack )
   {
   MyStatus myStatus = new MyStatus();
   Session[“MyStatus”] = myStatus;
   ThreadPool.QueueUserWorkItem(DoLongRunningProcess , myStatus );
   }
   }

3. In your worker thread, set the flag that processing is done.

   public void GenerateReport( object state )
   {
   MyStatus myStatus = state as MyState;

   ///generate report
   myStatus.IsDone = true;
   

   }

4. In your ajax callback, check status. If you are done, also remove status from Session.

   MyStatus myStatus = Session[“MyStatus”] as MyState;
   if (myStatus.IsDone)
   {
   // do something.

   // cleanup.
   Session.Remove("MyStatus");
   

   }