Threading problem

[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.