.NET Winform Program Terminating without any valid reason on End Sub

Question

I'm using agsXMPP in my .NET project (WinForms) I have the following Code block, this is executed whenever a message is received from any client. Now whenever a message is received, this block executes and the program terminates.. :( I've no idea as to what's happening. Help!

Has this something to do with threads? (I've heard that agsXMPP encapsulates a thread on which it works)

   Private Sub messageReceived(ByVal sender As Object, ByVal msg As protocol.client.Message)
    Dim chatMessage() As String
    Static Dim Hi_ed As Integer = 0
    chatMessage = msg.From.ToString.Split("/")
    Dim chatSender As String = chatMessage(0)

    If Not IsWorking Then
        IsWorking = True
        If Not ProcessCommands(msg.Body, chatSender) Then
            Dim sStr As String = ParseEnglish(msg.Body)

            Select Case sStr
                Case "HI"
                    If Hi_ed = False Then
                        SendGTalkMsg("Hi. How do you do?", chatSender)
                        Hi_ed = True
                    Else
                        SendGTalkMsg("हाय वाई कुछ नहीं हम तो !!!", chatSender)
                    End If
                Case "DETAILS PLEASE"
                    SendGTalkMsg(". Currently there are N no of sams running on me: :)", chatSender)
            End Select
        End If
        IsWorking = False

        Exit Sub
    Else
        SendGTalkMsg("I'm working right now. Please have patience.", chatSender)
    End If
End Sub

** EDIT **** Now, when I run the EXE file generated, after this event is done the "not-responding" error comes, which clearly means that there is an exception but it's escaping the try catch block. :(

This is the error which I get:

Problem signature:
Problem Event Name: CLR20r3
Problem Signature 01:   updatecheck.exe
Problem Signature 02:   1.0.0.0
Problem Signature 03:   4e8ed73e
Problem Signature 04:   mscorlib
Problem Signature 05:   4.0.0.0
Problem Signature 06:   4dd23522
Problem Signature 07:   1526
Problem Signature 08:   4f
Problem Signature 09:   System.InvalidOperationException
OS Version:  6.1.7600.2.0.0.256.1
Locale ID:  1033
Additional Information 1:   0a9e
Additional Information 2:   0a9e372d3b4ad19135b953a78882e789
Additional Information 3:   0a9e
Additional Information 4:   0a9e372d3b4ad19135b953a78882e789

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Answer 1

Well, well, well. It was all because of a silly dialog box for the

My.Computer.Network.DownloadFile(SourceZipFile, DestinationZipFile, "<userid>", "<password>", True, 100000, True)

was set to true. So whenever the file download progress box appeared, it used to mess up with the threads. When I changed the ShowUI parameter of DownloadFile to False everything worked fine. :)

But do we have a clear explanation to this?

Answer 2

Most likely this is due to the combination of threads and an unhandled exception. There seems to be no way to control the behavior for unhandled exceptions for any but the main thread, so it is imperative that you handle all exceptions that might arise outside the main thread. This include asynchronous call-backs, such as the above, as these are often made off the main thread. If an exception goes unhandled on a non-main thread, the application will simply terminate; no message.

I would recommend wrapping all call-back and other async methods in a try...catch block that logs the error or writes it to the debug trace window.