Threading problem

[greatchap]

Hi Guys,

I am using VB.NET (2008). I have tried using threading before and I did encounter issues. Then I wrote in this forum and jmcilhinney helped me. It did solve my problem and I am grateful for that. The thread can be found here
Thread here

My current problem is as follows :-

- I have a form with various controls incl a timer control.
- Task: when i click on start , timer starts and at regular intervals it downloads a file and processes it.
- Then it becomes idle for a while before repeating it.
- No threading used in this form so far.

Now when the timer is idle then I need to do some processing. So I thought that I can create a thread and use that thread to do the processing so that the application remains responsive.

I wrote the following code :

' General
Dim DataThread as Thread

Private Sub TimerMain_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles TimerMain.Tick

If timerjobdone = True then
Call ExecuteThreadCode()
TimerMain.Interval = 10000
end if

End Sub

Private Sub ExecuteThreadCode()

DataThread = new thread(addressof DoProcessing)
Datathread.start


End Sub

Private sub DoProcessing()

' Here I need to access the label of the form so i need to do invoke method
' I do some file reading and other processing here

End sub

Now when the code segment executes my application becomes unresponsive. I mean i used threading to make program more accessible to user or responsive but it does not work.

Will be glad if anyone can help me out.

Thanks a lot,

GR

[Shaggy Hiker]

You don't actually need the ExecuteThreadCode method, as you could move what is inside of it into the timer. It doesn't hurt, though, if you find it cleaner this way.

I would say that the issue lies in the part that you didn't post: The thread method itself.

[greatchap]

The code inside the thread method is bit long and complex. It's basically opening files, processing them and downloading some small files and processing them.

What I wanted to know is why it is not working like an independant thread? why does my program become unresponsive.

[Shaggy Hiker]

You also mentioned interacting with form controls from the background thread. Perhaps that was done in a way that blocks the UI. The code you have shown doesn't have any obvious issues in it. However, you can put a breakpoint on the first line in the timer event, and step through it. If it is blocking somewhere, you will see it. If it isn't, and the timer event code finishes up normally, then it is the background thread itself that is blocking the UI thread. Without seeing the code, nobody can answer that definitively. However, if there is lots of code...perhaps nobody can answer definitively anyhow.

The first thing I would do would be to step through the timer event. That shouldn't cause a problem as you have it now, so the next thing I would do would be to take a look at any interactions between the thread and the UI.

[szlamany]

Wouldn't this be a good time to put some Debug.Writeline statements into the main code, the timer events and the thread methods?

Won't all these Debug.Writeline's appear in the OUTPUT window telling you exactly where the flow of the code is going?

[greatchap]

The code for the sub that does the processing (which I didnt write before) is :

Private Sub DoProcessing()
 If Me.InvokeRequired = True Then
            Me.lblstatus.Invoke(New MethodInvoker(AddressOf DoProcessing))
        Else
            Try
                ' this function will check for data. 

                ' CHECKS/Validation
                If Now.DayOfWeek = DayOfWeek.Saturday Then Exit Sub

                Dim FPath As String = DataPath & "\Abc.txt"
                If File.Exists(FPath) = False Then Exit Sub

                Dim CTime As DateTime = Now, GoAhead As Boolean = False, Cnt As Integer = 0

                If Format$(CTime, "HHmm").ToString.Substring(3, 1) = "5" Or Format$(CTime, "HHmm").ToString.Substring(3, 1) = "0" Then
                    GoAhead = True  ' means we have 5 min in hand and we can go ahead and check
                Else
                    Do
                        Cnt = Cnt + 1
                        CTime = CTime.AddMinutes(1)
                        If Format$(CTime, "HHmm").ToString.Substring(3, 1) = "5" Or Format$(CTime, "HHmm").ToString.Substring(3, 1) = "0" Then Exit Do
                        If Cnt > 5 Then Exit Do ' EMERGENCY EXIT
                    Loop
                    If Cnt >= 3 Then GoAhead = True Else GoAhead = False
                End If

                If GoAhead = False Then Exit Sub

                ' Checks Done
                Dim FileData() As String = File.ReadAllLines(FPath), FTemp() As String
                Dim FileTime As DateTime, FileDate As Date, Ticks() As String, EndTime As DateTime
                Dim RecCount As Long = 0, ReadCounter As Long = 0

                ReDim Ticks(0)

                If UBound(FileData) < 3 Then
                    Exit Sub ' get out
                End If

               lblstatus.Text = "Status: Checking for data..." : lblstatus.Refresh()

                For i As Long = UBound(FileData) To LBound(FileData) Step -1
                    If FileData(i).Trim = "" Then Continue For
                    ReadCounter += 1
                    FileDate = New Date(FileData(i).ToString.Substring(6, 4), FileData(i).ToString.Substring(3, 2), FileData(i).ToString.Substring(0, 2))
                    RecCount = i

                    If ReadCounter = 1 Then ' Get End Time
                        FTemp = FileData(i).Split(",")
                        EndTime = New DateTime(Now.Date.Year, Now.Date.Month, Now.Date.Day, FTemp(1).Substring(0, 2), FTemp(1).Substring(2, 2), 0)
                    End If

                    If Format$(FileDate, "yyyyMMdd") <> Format$(Now.Date, "yyyyMMdd") Then
                        Exit For
                    End If
                Next

                If RecCount = UBound(FileData) Then
                    ' no rec found display message and get out
                    lblstatus.Text = "Status: Data check completed"  lblstatus.Refresh()
                    Exit Sub
                End If

                ReadCounter = 0 : RecCount += 1
                FileTime = New DateTime(Now.Date.Year, Now.Date.Month, Now.Date.Day, "09", "05", "0")

                Do
                    ReadCounter = ReadCounter + 1
                    If RecExistsInArray(FileData, RecCount, Format$(FileTime, "HHmm")) = True Then
                        FileTime = FileTime.AddMinutes(5)
                    Else
                        ReDim Preserve Ticks(UBound(Ticks) + 1)
                        Ticks(UBound(Ticks)) = Format$(FileTime, "HHmm")
                        FileTime = FileTime.AddMinutes(5)
                    End If
                    If FileTime = EndTime Then Exit Do
                    If ReadCounter > 70 Then Exit Do ' Emergency Exit
                Loop

                ' NOW DOWNLOAD THOSE Files
                Dim DownloadedTicks() As String : ReDim DownloadedTicks(0)

                For i As Integer = 1 To UBound(Ticks)
                    Try
                        If File.Exists(Application.StartupPath & "\" & Ticks(i) & ".dat") = True Then File.Delete(Application.StartupPath & "\" & Ticks(i) & ".dat")
                        My.Computer.Network.DownloadFile("www.mysite.com/" & Format(DateTimePicker1.Value.Date, "ddMMyy") & "/" & Ticks(i) & ".dat", Application.StartupPath & "\" & Ticks(i) & ".dat")
                        ReDim Preserve DownloadedTicks(UBound(DownloadedTicks) + 1) ' tick downloaded
                        DownloadedTicks(UBound(DownloadedTicks)) = Ticks(i)
                    Catch ex As Exception
                        ' means couldnt download or find file
                    End Try
                Next

                If UBound(DownloadedTicks) = 0 Then
                    ' didnt find file so quit/exit
                    lblstatus.Text = "Status: Data check completed" : lblstatus.Refresh()
                    Exit Sub
                End If

                ' Found some/all missed ticks
                ' Read them

                ' File Reading routine not pasted right now


               lblstatus.Text = "Status: Data updated successfully " 

            Catch ex As Exception
                Threading.Thread.Sleep(1500)
            End Try
        End If       ' Endif for Me.Invoke Required
End Sub

Now inspite of executing the above code in thread, the application locks up till processing does not finish. Why? Do i need to use doevents or I dunno why? I did use debug to check the flow and found no problems in the flow.

Please help me here.
Thank you.

[jmcilhinney]

The problem is that you're NOT executing that code in a separate thread. You start a new thread and call DoProcessing, then the very first thing that DoProcessing does is invoke a call back to the UI thread and ALL the work is done there.

You are supposed to do all your work on the worker thread and then invoke a call back to the UI thread ONLY to access the UI. Get rid of any that If block and any interaction with the UI from that method. Then that whole method will be executed on the worker thread. You then write a new method ONLY for interaction with the UI, e.g.

Private Sub UpdateLabel(ByVal text As String)
    If Me.lblstatus.InvokeRequired Then
        Me.lblstatus.Invoke(New MethodInvoker(AddressOf DoProcessing), text)
    Else
        Me.lblstatus.Text = text
    End If
End Sub

You can then call that method from DoProcessing to update lblstatus.

[greatchap]

The problem is that you're NOT executing that code in a separate thread. You start a new thread and call DoProcessing, then the very first thing that DoProcessing does is invoke a call back to the UI thread and ALL the work is done there.

You are supposed to do all your work on the worker thread and then invoke a call back to the UI thread ONLY to access the UI. Get rid of any that If block and any interaction with the UI from that method. Then that whole method will be executed on the worker thread. You then write a new method ONLY for interaction with the UI, e.g.

Private Sub UpdateLabel(ByVal text As String)
    If Me.lblstatus.InvokeRequired Then
        Me.lblstatus.Invoke(New MethodInvoker(AddressOf DoProcessing), text)
    Else
        Me.lblstatus.Text = text
    End If
End Sub

You can then call that method from DoProcessing to update lblstatus.

Thanks buddy for your help. I removed the invoke call to UI thread statements. The DoProcessing sub now does not directly access the UI.
But still the application behaves like before that is it locks up till the processing isn't over. I am unable to understand why?.

 Private Sub DoProcessing()
        Try
            ' this function will check for data. 
            ' CHECKS/Validation

            If ProgramSettings.CheckForMissedData = False Then Exit Sub
            If Now.DayOfWeek = DayOfWeek.Saturday Then Exit Sub

            Dim FPath As String = DataPath & "\Abc.txt"
            If File.Exists(FPath) = False Then Exit Sub

            Dim CTime As DateTime = Now, GoAhead As Boolean = False, Cnt As Integer = 0

            If Format$(CTime, "HHmm").ToString.Substring(3, 1) = "5" Or Format$(CTime, "HHmm").ToString.Substring(3, 1) = "0" Then
                GoAhead = True  ' means we have 5 min in hand and we can go ahead and check
            Else
                Do
                    Cnt = Cnt + 1
                    CTime = CTime.AddMinutes(1)
                    If Format$(CTime, "HHmm").ToString.Substring(3, 1) = "5" Or Format$(CTime, "HHmm").ToString.Substring(3, 1) = "0" Then Exit Do
                    If Cnt > 5 Then Exit Do ' EMERGENCY EXIT
                Loop
                If Cnt >= 3 Then GoAhead = True Else GoAhead = False
            End If

            If GoAhead = False Then Exit Sub

            ' Checks Done
            Dim FileData() As String = File.ReadAllLines(FPath), FTemp() As String
            Dim FileTime As DateTime, FileDate As Date, Ticks() As String, EndTime As DateTime
            Dim RecCount As Long = 0, ReadCounter As Long = 0

            ReDim Ticks(0)

            If UBound(FileData) < 3 Then
                Exit Sub ' get out
            End If

            Call LabelReset("Status: Checking for missed data")

            For i As Long = UBound(FileData) To LBound(FileData) Step -1
                If FileData(i).Trim = "" Then Continue For
                ReadCounter += 1
                FileDate = New Date(FileData(i).ToString.Substring(6, 4), FileData(i).ToString.Substring(3, 2), FileData(i).ToString.Substring(0, 2))
                RecCount = i

                If ReadCounter = 1 Then ' Get End Time
                    FTemp = FileData(i).Split(",")
                    EndTime = New DateTime(Now.Date.Year, Now.Date.Month, Now.Date.Day, FTemp(1).Substring(0, 2), FTemp(1).Substring(2, 2), 0)
                End If

                If Format$(FileDate, "yyyyMMdd") <> Format$(Now.Date, "yyyyMMdd") Then
                    Exit For
                End If
            Next

            If RecCount = UBound(FileData) Then
                Exit Sub
            End If

            ReadCounter = 0 : RecCount += 1
            FileTime = New DateTime(Now.Date.Year, Now.Date.Month, Now.Date.Day, "09", "05", "0")

            Do
                ReadCounter = ReadCounter + 1
                If RecExistsInArray(FileData, RecCount, Format$(FileTime, "HHmm")) = True Then
                    FileTime = FileTime.AddMinutes(5)
                Else
                    ReDim Preserve Ticks(UBound(Ticks) + 1)
                    Ticks(UBound(Ticks)) = Format$(FileTime, "HHmm")
                    FileTime = FileTime.AddMinutes(5)
                End If
                If FileTime = EndTime Then Exit Do
                If ReadCounter > 70 Then Exit Do ' Emergency Exit
            Loop

            ' Done now check if there were missed ticks or not
            If UBound(Ticks) = 0 Then
                ' All ticks present so far 
                Call LabelReset("Status: No ticks missed so far")
                Exit Sub
            End If

            ' NOW DOWNLOAD THOSE TICKS
            Dim DownloadedTicks() As String : ReDim DownloadedTicks(0)

            For i As Integer = 1 To UBound(Ticks)
                Try
                    If File.Exists(Application.StartupPath & "\" & Ticks(i) & ".dat") = True Then File.Delete(Application.StartupPath & "\" & Ticks(i) & ".dat")
                    My.Computer.Network.DownloadFile("http://www.mysite.com/" & Format(DateTimePicker1.Value.Date, "ddMMyy") & "/" & Ticks(i) & ".dat", Application.StartupPath & "\" & Ticks(i) & ".dat")
                    ReDim Preserve DownloadedTicks(UBound(DownloadedTicks) + 1) ' tick downloaded
                    DownloadedTicks(UBound(DownloadedTicks)) = Ticks(i)
                Catch ex As Exception
                    ' means couldnt download or find file
                End Try
            Next

            If UBound(DownloadedTicks) = 0 Then
                ' didnt find file so quit/exit
                '    lblstatus.Text = "Status: Missed data check completed" : lblstatus.Refresh()
                ' commented above
                Exit Sub
            End If

            ' Found some/all ticks
            ' Read data files in array
            ' Code for Processing File Not Pasted
        
            Call LabelReset("Status: DONE")
        Catch ex As Exception
            
        End Try

    End Sub

 Private Sub LabelReset(ByVal text As String)
        If Me.InvokeRequired = True Then
            Me.lblstatus.Invoke(New MethodInvoker(AddressOf DoProcessing), text)
        Else
            lblstatus.Text = text : lblstatus.Refresh()
        End If
    End Sub

' Timer code

 Private Sub TimerMain_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles TimerMain.Tick
    
   If LastCheckOK() = True Then
            lblstatus.Text = "Status: Waiting for next data" : lblstatus.Refresh()
            TimerMain.Interval = GetTimerInterval()
           ' calling thread
            MissedTickThread = New Thread(AddressOf DoProcessing)
            MissedTickThread.Start()
            Exit Sub
        End If

End Sub

Cheers.

[greatchap]

I tried using background worker control but it didnt work the way I wanted. My app still locks up until processing is completed. Kinda strange isn't it ?