Custom Request timeout issue?

Question

User1040660288 posted

I basically want to start a timer at the beginning of a request, and if it is takes longer than X, throw an exception, catch it, display a nice message to the user, and move on.  I have almost got what i want working with the following code: 

'Delegate
Dim timerDelegate As TimerCallback = AddressOf TimeLimiter

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    Try
        Dim timer As New Threading.Timer(timerDelegate, Nothing, 5000, System.Threading.Timeout.Infinite)

        RunBigCalculation()

    Catch ex As Exception
        'Display nice message
    End Try
End Sub

Private Sub TimeLimiter(ByVal stateInfo As Object)
    Throw New Exception("Load taking too long")
End Sub

The problem i am having with the above is that I get an "unhandled error" exception.  The Try/Catch block never catches it. I think this is essentially a threading question. 

If anyone can shed any light on what i am doing wrong, and how i can fix it, that would be great. 

Answer 1

User2104673743 posted

Whe you run a timer, the timer lives on a different thread, so throwing an exception on a different thread wont be caught by the catch method you have.

I could suggest that you adjust this page scriptTimeOut property so the page will stop executing (do this before calling the "RunBigCalculation" method and catch the exception just as you are doing now.

Hope this helps.

Answer 2

User1040660288 posted

Hey jportelas - thanks for your response.

For a couple of different reasons I would like to find another way (lack of control over environment etc).  I have very limited experience working with threads.  Is there a way to use threads to achieve what i am trying to do?

Thanks

James

Answer 3

User2104673743 posted

The scriptTimeOut property is perfect for you, you can set it programmatically to the time you expect it to run for and then (in the finally block for example) restablish its old value.

Check this out:

http://msdn.microsoft.com/en-us/library/system.web.httpserverutility.scripttimeout.aspx

It is easier than using threads [;)]

Answer 4

User1040660288 posted

I didn't want to complicate the question, but it is not so much full page postbacks that i am working with, but partial page postbacks via an updatepanel.  I want very fine control over the max time for an update panel refresh.

The trouble with scriptTimeOut is that it actually works on a 15 second timeout test cycle (so timeout could be +/- 15 seconds from time specified) - see here: http://blogs.msdn.com/pedram/archive/2007/10/02/how-the-execution-timeout-is-managed-in-asp-net.aspx?CommentPosted=true#commentmessage

I think the answer lies in calling the thread.abort on the main HTTP thread, and somehow passing enough info (via a stateInfo object) to get it to throw a TimeOut Exception instead of an Abort Excepton.  The trouble is, I am not sure how to hook these things up, or even find the main HTTP thread again from within the spawned thread.

Any further advice appreciated.

Answer 5

User1040660288 posted

Another problem with the standard RequestTimeout is that it basically aborts the thread.  As far as i can tell, there is no opportunity to catch the exception and handle any differently than redirecting the user to an error page.  In my case I would simply like to display something different in the update panel.

 Any ideas anyone?

Answer 6

User1616291716 posted

Hi jshallard,

It seems that you want to send a friendly message to the user when the request is TimeOut, If yes, I suggest you try to achieve it by refering to the following code:

 

Imports System 
Imports System.Collections.Generic 
Imports System.Linq 
Imports System.Text 
Imports System.Web 

Public Class MyHttpModule 
    Implements IHttpModule 
    Public Sub Init(ByVal ap As HttpApplication) 
        AddHandler ap.PreSendRequestHeaders, AddressOf ap_PreSendRequestHeaders 
    End Sub 
    
    
    Private Sub ap_PreSendRequestHeaders(ByVal sender As Object, ByVal e As EventArgs) 
        Dim hr As HttpResponse = DirectCast(sender, HttpApplication).Context.Response 
        If hr.StatusCode = 408 Then ' The request time out
            hr.Redirect("TimeOut.htm") 
        End If 
    End Sub 
    Public Sub Dispose() 
    End Sub 
End Class