[RESOLVED] complicated timer loop

[markhorgan1]

i have the following code to ping a list of switches , basically i want to add a timer to run at the end once the pings are finished and when the timer reaches a pre-determined value (long frequency) i want the ping process to start again , i want this process to keep repeating until btnoff is pressed. im having trouble because the code uses multithreading and ui threads whcih im not too familiar with.

ive tried adding in the timer below which ive commented out because it was giving an error when the pings were completed.
any ideas ?

**code is posted below

[markhorgan1]

Imports System.Data
Imports System.Data.OleDb
Public Class Form5

    Dim frequency As Long
    Private Sub btnON_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnON.Click

        If ComboBox1.Text = "" Then    ' ensures combo box is not left blank

            MsgBox("Please select scan frequency", [vbOKOnly])       ' prompts user to enter scan frequency

            'sets scan frequency
        Else
            btnBack.Enabled = False
            ComboBox1.Enabled = False
            lblMin.Enabled = False
            lblFrequency.Enabled = False
            btnOff.Enabled = True
            btnON.Enabled = False
            lblOff.Visible = False
            PictureBox1.Visible = False
            lblOn.Visible = True
            PictureBox2.Visible = True               'enables/hides the relevant picture boxs, labels and buttons based on user selection

        RichTextBox1.Visible = True

       Counter = 0 'reset the counter in case this is not the first time the ping button has been clicked


            Dim bgthread As New Threading.Thread(AddressOf BG_CollectData)  'Create a new background thread
            bgthread.IsBackground = True  'Make the thread end if the program is closed
            bgthread.Start()              'Start the background thread

        End If

        If ComboBox1.Text = "15" Then
            frequency = 900000

        ElseIf ComboBox1.Text = "20" Then            ' 60000ms in minute
            frequency = 1200000

        ElseIf ComboBox1.Text = "30" Then
            frequency = 1800000

        ElseIf ComboBox1.Text = "60" Then
            frequency = 3600000000

        End If

    End Sub

    Private Sub btnOff_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOff.Click

        btnBack.Enabled = True
        ComboBox1.Enabled = True
        lblMin.Enabled = True
        lblFrequency.Enabled = True
        btnON.Enabled = True
        btnOff.Enabled = False
        lblOn.Visible = False
        PictureBox2.Visible = False
        lblOff.Visible = True
        PictureBox1.Visible = True                   'enables/hides the relevant picture boxs, labels and buttons based on user selection

    End Sub

    Private Sub btnBack_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBack.Click

        Me.Hide()          'hides current form
        Form3.Show()       'displays selected form

    End Sub
    ''' <summary>
    ''' Represents a network switch (or any device with an IP) that is in the database
    ''' </summary>
    Private Class NetworkSwitch
        Private _IPAddress As String
        Private _SwitchID As Integer
        Private _SwitchName As String
        Private _Result As Boolean
        Private _ResponseTime As Integer

        Public Property IPAddress() As String
            Get
                Return _IPAddress
            End Get
            Set(ByVal value As String)
                _IPAddress = value
            End Set
        End Property
        Public Property ResponseTime() As Integer
            Get
                Return _ResponseTime
            End Get
            Set(ByVal value As Integer)
                _ResponseTime = value
            End Set
        End Property
        Public Property SwitchName() As String
            Get
                Return _SwitchName
            End Get
            Set(ByVal value As String)
                _SwitchName = value
            End Set
        End Property

        Public Property SwitchID() As Integer
            Get
                Return _SwitchID
            End Get
            Set(ByVal value As Integer)
                _SwitchID = value
            End Set
        End Property

        Public Property Result() As Boolean
            Get
                Return _Result
            End Get
            Set(ByVal value As Boolean)
                _Result = value
            End Set
        End Property
 End Class

    'Set up some variables that we will use from various functions/subs
    Private PingList As List(Of NetworkSwitch)

    Private Counter As Integer = 0
    Private ConnString As New OleDbConnectionStringBuilder("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=H:\FYP-trial\NetworkMap\Network Map.mdb;User Id=admin;Password=;")
    'This is the Delegate that will be used to pass data between the threads safely
    Private Delegate Sub PingComplete(ByVal sw As NetworkSwitch)
  Private Sub BG_CollectData()
        'Create our connection that will be used to connect to the Access database
        Dim AccessConnection As New OleDbConnection(ConnString.ConnectionString)

        'Create the command that will be used to select all of the data in the IP and ID columns
        Dim SelectCommand As New OleDbCommand("SELECT * FROM tblSwitch ", AccessConnection)

 'Create a new instance of a list of our NetworkSwitch class
        PingList = New List(Of NetworkSwitch)
 'Open the connection to the database
        AccessConnection.Open()

 'Use a DataReader to access the data that the SELECT command returns
        Dim Reader As OleDbDataReader = SelectCommand.ExecuteReader
        'Start to loop through the results
        'This loop will be restarted for each row in the database
        Do While Reader.Read
 'Create a new instance of our NetworkSwitch class and populate the ID and IP properties
            'with data from the current row in the database that we are looping through
            Dim CurrentSwitch As New NetworkSwitch
            With CurrentSwitch
                .SwitchID = Reader("SwitchID")
                .SwitchName = Reader("SwitchName")
                .IPAddress = Reader("IPAddress")
 End With
            'Add the new instance of the NetworkSwitch to our list
            PingList.Add(CurrentSwitch)
        Loop 'Start the loop again for the next record in the database

        'Close the connection because we have now processed all rows in the database
        AccessConnection.Close()

        'Give the threadpool a limit so that no more than 30 threads are running at the same time
        Threading.ThreadPool.SetMaxThreads(30, 400)

        'Loop through our list of NetworkSwitch instances and start (well, queue up) a new background
        'thread for each item in the list and passes it the current item in the loop (which is a NetworkSwitch object)
        For Each switchobject As NetworkSwitch In PingList
            Threading.ThreadPool.QueueUserWorkItem(New Threading.WaitCallback(AddressOf DoPing), switchobject)
        Next
End Sub

    ''' <summary>
    ''' Performs the ping and updates the Result property of the NetworkSwitch object that was passed to this 
    ''' </summary>
 Private Sub DoPing(ByVal Switch As NetworkSwitch)
 Dim Result As Net.NetworkInformation.PingReply
        Dim SendPing As New Net.NetworkInformation.Ping
        Dim ResponseTime As Integer
 Result = SendPing.Send(Switch.IPAddress)
        ResponseTime = Result.RoundtripTime

        If Result.Status = Net.NetworkInformation.IPStatus.Success Then
            Switch.Result = True
            Switch.ResponseTime = ResponseTime
        Else
            Switch.Result = False
        End If
  UpdateDatabase(Switch)
        Counter += 1
        Me.Invoke(New PingComplete(AddressOf UI_PingComplete), Switch)

    End Sub
 ''' <summary>
    ''' This is executed each time a ping completes and the database has been updated.
    ''' It is executed on the UI thread because we used Me.Invoke to call it so it can access
    ''' controls on the UI thread without a problem
    ''' </summary>
    Private Sub UI_PingComplete(ByVal sw As NetworkSwitch)

        If sw.Result = True Then
            RichTextBox1.SelectionColor = Color.DarkBlue
        ElseIf sw.Result = False Then

            RichTextBox1.SelectionColor = Color.Red

        End If

        RichTextBox1.AppendText(sw.SwitchID & "--" & sw.SwitchName & " -- " & sw.IPAddress & " -- Reply -> " & sw.Result & "--ResponseTime--" & sw.ResponseTime & "ms" & vbNewLine) 'update our log textbox

        If Counter = PingList.Count Then
            RichTextBox1.AppendText(vbNewLine & vbNewLine & "Finished re-trying devices" & vbNewLine)

            MsgBox("Finished re-trying devices", [vbOKOnly])
            '  Timer1 = Nothing
            PingList = Nothing 'clean up
            '  Timer1.Enabled = True
            ' Timer1.Start()

            '  If Timer1.Equals(frequency) Then
            'Dim bgthread As New Threading.Thread(AddressOf BG_CollectData)  'Create a new background thread
            ' bgthread.IsBackground = True  'Make the thread end if the program is closed
            'bgthread.Start()              'Start the background thread
            ' End If
        End If
    End Sub

    Private Sub UpdateDatabase(ByVal sw As NetworkSwitch)

        Dim AccessConnection As New OleDbConnection(ConnString.ConnectionString)

        Dim UpdateCommand As New OleDbCommand("UPDATE tblSwitch SET Result=@Result, LastTested=@CurrentTime, ResponseTime=@ResponseTime WHERE SwitchID=@SwitchID", AccessConnection)

        With UpdateCommand.Parameters
            .Add("@Result", OleDbType.Boolean).Value = sw.Result
            .Add("@CurrentTime", OleDbType.Char).Value = Now.ToString
            .Add("@ResponseTime", OleDbType.Integer).Value = sw.ResponseTime
            .Add("@SwitchID", OleDbType.Integer).Value = sw.SwitchID

        End With
        AccessConnection.Open()   'dont delete

        UpdateCommand.ExecuteNonQuery()  'Execute the command that updates the database
 AccessConnection.Close()   'dont delete
End Sub

End Class

[Megalith]

Ah i see it:- this is the code you have wrong

           MsgBox("Finished re-trying devices", [vbOKOnly])
            '  Timer1 = Nothing
            PingList = Nothing 'clean up
            '  Timer1.Enabled = True
            ' Timer1.Start()

            '  If Timer1.Equals(frequency) Then
            'Dim bgthread As New Threading.Thread(AddressOf BG_CollectData)  'Create a new background thread
            ' bgthread.IsBackground = True  'Make the thread end if the program is closed
            'bgthread.Start()              'Start the background thread
            ' End If

the first part is right so keep this

           MsgBox("Finished re-trying devices", [vbOKOnly])
           Timer1 = Nothing
           PingList = Nothing 'clean up
           Timer1.Enabled = True
           Timer1.Start()

go onto the Design page for the form ands double click the timer, this creates a timer Tick sub to deal with when the timer has ticked. within this block paste this

Dim bgthread As New Threading.Thread(AddressOf BG_CollectData)  'Create a new background thread
bgthread.IsBackground = True  'Make the thread end if the program is closed
bgthread.Start()              'Start the background thread
Timer1.Stop()                  'Stop the timer till you need to do the count again

[markhorgan1]

thanks megalith ive made those changes one last thing tho i cant seem to find how the timer knows when to tick ?

is it done by setting the interval on the timer or do i set a value that the timer compares itself to ? e.g. like i originally had below

If Timer1.Equals(frequency) Then ....

[Megalith]

yes you set the interval on the timer (which is in millseconds) you can do it either in design or while the code runs, with this example, unless you do plan to change the delay) i'd do it in design.

[markhorgan1]

yeah i need to do it while the code runs because the interval is selected by the user before the loop runs for the first time. i tried setting the interval but I am now getting a nullreference error(object reference not set to an instance of an object) at this line after code runs for first time.

Me.Invoke(New PingComplete(AddressOf UI_PingComplete), Switch)

** ive posted the code with the timer changes below

[markhorgan1]

Imports System.Data
Imports System.Data.OleDb
Public Class Form5

    Dim frequency As Long

    Private Sub btnON_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnON.Click

        If ComboBox1.Text = "" Then    ' ensures combo box is not left blank

            MsgBox("Please select scan frequency", [vbOKOnly])       ' prompts user to enter scan frequency



            'sets scan frequency


        Else
            btnBack.Enabled = False
            ComboBox1.Enabled = False
            lblMin.Enabled = False
            lblFrequency.Enabled = False
            btnOff.Enabled = True
            btnON.Enabled = False
            lblOff.Visible = False
            PictureBox1.Visible = False
            lblOn.Visible = True
            PictureBox2.Visible = True               'enables/hides the relevant picture boxs, labels and buttons based on user selection


            RichTextBox1.Visible = True

            Counter = 0 'reset the counter in case this is not the first time the ping button has been clicked


            Dim bgthread As New Threading.Thread(AddressOf BG_CollectData)  'Create a new background thread
            bgthread.IsBackground = True  'Make the thread end if the program is closed
            bgthread.Start()              'Start the background thread

        End If


        If ComboBox1.Text = "15" Then
            frequency = 600000 ' should be 90 but 60 for demo sake
            'frequency = Timer1.Interval
        ElseIf ComboBox1.Text = "20" Then            ' 60000ms in minute
            frequency = 1200000

        ElseIf ComboBox1.Text = "30" Then
            frequency = 1800000

        ElseIf ComboBox1.Text = "60" Then
            frequency = 3600000000


        End If

    End Sub


    Private Sub btnOff_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOff.Click

        btnBack.Enabled = True
        ComboBox1.Enabled = True
        lblMin.Enabled = True
        lblFrequency.Enabled = True
        btnON.Enabled = True
        btnOff.Enabled = False
        lblOn.Visible = False
        PictureBox2.Visible = False
        lblOff.Visible = True
        PictureBox1.Visible = True                   'enables/hides the relevant picture boxs, labels and buttons based on user selection

    End Sub

    Private Sub btnBack_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBack.Click

        Me.Hide()          'hides current form
        Form3.Show()       'displays selected form

    End Sub




    Private Class NetworkSwitch
        Private _IPAddress As String
        Private _SwitchID As Integer
        Private _SwitchName As String
        Private _Result As Boolean
        Private _ResponseTime As Integer


        Public Property IPAddress() As String
            Get
                Return _IPAddress
            End Get
            Set(ByVal value As String)
                _IPAddress = value
            End Set
        End Property
        Public Property ResponseTime() As Integer
            Get
                Return _ResponseTime
            End Get
            Set(ByVal value As Integer)
                _ResponseTime = value
            End Set
        End Property
        Public Property SwitchName() As String
            Get
                Return _SwitchName
            End Get
            Set(ByVal value As String)
                _SwitchName = value
            End Set
        End Property

        Public Property SwitchID() As Integer
            Get
                Return _SwitchID
            End Get
            Set(ByVal value As Integer)
                _SwitchID = value
            End Set
        End Property

        Public Property Result() As Boolean
            Get
                Return _Result
            End Get
            Set(ByVal value As Boolean)
                _Result = value
            End Set
        End Property

    End Class

    
    Private PingList As List(Of NetworkSwitch)

    Private Counter As Integer = 0
    Private ConnString As New OleDbConnectionStringBuilder("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=H:\FYP-trial\NetworkMap\Network Map.mdb;User Id=admin;Password=;")
    'This is the Delegate that will be used to pass data between the threads safely
    Private Delegate Sub PingComplete(ByVal sw As NetworkSwitch)


   
    Private Sub BG_CollectData()
   
        Dim AccessConnection As New OleDbConnection(ConnString.ConnectionString)

 
        Dim SelectCommand As New OleDbCommand("SELECT * FROM tblSwitch ", AccessConnection)

        'Create a new instance of a list of our NetworkSwitch class
        PingList = New List(Of NetworkSwitch)


      
        AccessConnection.Open()

        'Use a DataReader to access the data that the SELECT command returns
        Dim Reader As OleDbDataReader = SelectCommand.ExecuteReader
        'Start to loop through the results
        'This loop will be restarted for each row in the database
        Do While Reader.Read

            'Create a new instance of our NetworkSwitch class and populate the ID and IP properties
            'with data from the current row in the database that we are looping through
            Dim CurrentSwitch As New NetworkSwitch
            With CurrentSwitch
                .SwitchID = Reader("SwitchID")
                .SwitchName = Reader("SwitchName")
                .IPAddress = Reader("IPAddress")

            End With
            'Add the new instance of the NetworkSwitch to our list
            PingList.Add(CurrentSwitch)
        Loop 'Start the loop again for the next record in the database

        'Close the connection because we have now processed all rows in the database
        AccessConnection.Close()

        'Give the threadpool a limit so that no more than 30 threads are running at the same time
        Threading.ThreadPool.SetMaxThreads(30, 400)

        'Loop through our list of NetworkSwitch instances and start (well, queue up) a new background
        'thread for each item in the list and passes it the current item in the loop (which is a NetworkSwitch object)
        For Each switchobject As NetworkSwitch In PingList
            Threading.ThreadPool.QueueUserWorkItem(New Threading.WaitCallback(AddressOf DoPing), switchobject)
        Next

    End Sub


    Private Sub DoPing(ByVal Switch As NetworkSwitch)

        Dim Result As Net.NetworkInformation.PingReply
        Dim SendPing As New Net.NetworkInformation.Ping
        Dim ResponseTime As Integer


        Result = SendPing.Send(Switch.IPAddress)
        ResponseTime = Result.RoundtripTime

        If Result.Status = Net.NetworkInformation.IPStatus.Success Then
            Switch.Result = True
            Switch.ResponseTime = ResponseTime
        Else
            Switch.Result = False
        End If

        UpdateDatabase(Switch)
        Counter += 1
        Me.Invoke(New PingComplete(AddressOf UI_PingComplete), Switch)

    End Sub

  
    Private Sub UI_PingComplete(ByVal sw As NetworkSwitch)

        If sw.Result = True Then
            RichTextBox1.SelectionColor = Color.DarkBlue
        ElseIf sw.Result = False Then

            RichTextBox1.SelectionColor = Color.Red

        End If

        RichTextBox1.AppendText(sw.SwitchID & "--" & sw.SwitchName & " -- " & sw.IPAddress & " -- Reply -> " & sw.Result & "--ResponseTime--" & sw.ResponseTime & "ms" & vbNewLine) 'update our log textbox

        If Counter = PingList.Count Then
            RichTextBox1.AppendText(vbNewLine & vbNewLine & "Finished re-trying devices" & vbNewLine)

            MsgBox("Finished re-trying devices", [vbOKOnly])
            Timer1 = Nothing
            PingList = Nothing 'clean up
            Timer1.Enabled = True
            frequency = Timer1.Interval
            Timer1.Start()

            '  If Timer1.Equals(frequency) Then
            'Dim bgthread As New Threading.Thread(AddressOf BG_CollectData)  'Create a new background thread
            ' bgthread.IsBackground = True  'Make the thread end if the program is closed
            'bgthread.Start()              'Start the background thread
            ' End If
        End If
    End Sub

 
    Private Sub UpdateDatabase(ByVal sw As NetworkSwitch)

        Dim AccessConnection As New OleDbConnection(ConnString.ConnectionString)

        Dim UpdateCommand As New OleDbCommand("UPDATE tblSwitch SET Result=@Result, LastTested=@CurrentTime, ResponseTime=@ResponseTime WHERE SwitchID=@SwitchID", AccessConnection)

        With UpdateCommand.Parameters
            .Add("@Result", OleDbType.Boolean).Value = sw.Result
            .Add("@CurrentTime", OleDbType.Char).Value = Now.ToString
            .Add("@ResponseTime", OleDbType.Integer).Value = sw.ResponseTime
            .Add("@SwitchID", OleDbType.Integer).Value = sw.SwitchID

        End With
        AccessConnection.Open()   'dont delete

        UpdateCommand.ExecuteNonQuery()  'Execute the command that updates the database

        AccessConnection.Close()   'dont delete

    End Sub




    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        Dim bgthread As New Threading.Thread(AddressOf BG_CollectData)  'Create a new background thread
        bgthread.IsBackground = True  'Make the thread end if the program is closed
        bgthread.Start()              'Start the background thread
        Timer1.Stop()                  'Stop the timer till you need to do the count again
    End Sub
End Class

[markhorgan1]

i have the timer working now,few things were in the wrong place, but it only works when i set the interval in design view is there a way to set it equal to a long which the user specifies ? before / after the timer is enabled

[Megalith]

yes you simply use

Timer1.Interval = someTimeInMilliseconds

glad you have it working though

[markhorgan1]

perfect , problem wasnt what i had but was where i was putting it

thanks megalith

[Megalith]

no probs, glad i could help