Ping using VB (performance issues)

i have this code to ping a list of over 400 switches , the program works fine but for some reason the first time i ping all the switches alot of the attempts time-out(even tho they shouldnt) which makes the program alot slower , if i click ping again less of the attempts time-out(and as a result the program runs faster) and if i click it a third time i usually get a completely accurate result with all the switches pinging back "success" (except for a few which i know for a fact are down anyway) any ideas why this is ??

Code:

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Public Class SwitchMonitor
    Dim Ping As Net.NetworkInformation.Ping
    Dim pReply As Net.NetworkInformation.PingReply



    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim i As Integer
        Dim ds As New DataSet
        Dim da As OleDb.OleDbDataAdapter
        Dim sql As String
        Dim con As New OleDb.OleDbConnection

        Label1.Visible = True
        Label2.Visible = True
        Label3.Visible = True
        Label4.Visible = True
        Label5.Visible = True



        con.ConnectionString = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = C:\Documents and Settings\mhorgan\Desktop\Network Map.mdb"
        con.Open()

        sql = "SELECT * FROM tblSwitch"
        da = New OleDb.OleDbDataAdapter(sql, con)
        da.Fill(ds, "monitor")

        Dim cb As New OleDb.OleDbCommandBuilder(da)
        Ping = New Net.NetworkInformation.Ping
        Dim dgvr As DataGridViewRow

        ProgressBar1.Minimum = 0                                      'sets minimum value of progress bar
        ProgressBar1.Maximum = ds.Tables("monitor").Rows.Count - 1    'sets maximum value of progress bar

        For i = 0 To ds.Tables("monitor").Rows.Count - 1

            Application.DoEvents()

            ' Set up the progress bar's properties
            ProgressBar1.Value = i


            dgvr = New DataGridViewRow 'Creates a new row           
            DataGridView1.Rows.Add(dgvr) 'Add the row           

            Try

                pReply = Ping.Send(ds.Tables("monitor").Rows(i).Item(5)) 'Sends the ping to the current item               



                DataGridView1.Rows.Item(i).Cells(0).Value = ds.Tables("monitor").Rows(i).Item(1) 'read in switch name from column 2

                DataGridView1.Rows.Item(i).Cells(1).Value = ds.Tables("monitor").Rows(i).Item(5) 'Updates the value of the new Item               

                DataGridView1.Rows.Item(i).Cells(2).Value = pReply.Status  'The value of the status returned               

                DataGridView1.Rows.Item(i).Cells(3).Value = Now.ToString() 'show the last time checked with Now.ToString() method




                If pReply.Status <> Net.NetworkInformation.IPStatus.Success Then 'Sets the color of the cell       

                    DataGridView1.Rows.Item(i).Cells(2).Style.BackColor = Color.Red
                Else
                    DataGridView1.Rows.Item(i).Cells(2).Style.BackColor = Color.Green
                End If

                ds.Tables("monitor").Rows(i).Item(6) = pReply.Status 'Write in the original datatable
                ds.Tables("monitor").Rows(i).Item(7) = Now.ToString() 'added code for date/time
                da.Update(ds, "monitor") 'Updates the database
            Catch ex As Exception
                MessageBox.Show(ex.ToString())
            End Try
        Next
    End Sub


    Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExit.Click
        Dim con As New OleDb.OleDbConnection
        con.ConnectionString = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = C:\Documents and Settings\mhorgan\Desktop\Network Map.mdb"
        con.Close()
        End
    End Sub

    Private Sub SwitchMonitor_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub
End Class

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I would suggest you to use separate threads for pinging each switch. In case, there is no response from any of the switch, ur app would continue pinging other switches in separate thread.

As well as spawning a few extra threads, you might also want to consider having a slight time offset between each ping so that it is not trying to send a lot of pings all at the same time.
You need to do a bit of reading up on multi-threading because it is not just a simple change in your code, you will have to change how you are updating the user interface (because the UI runs on a separate thread that only it can access) amongst other things. jmcilhinney wrote a good in depth tutorial on background threads, you can find it in the codebank on these forums. There is one here about using background workers (which are a component that wrap up the functionality of a background thread and add some handy methods and event handlers): http://www.vbforums.com/showthread.php?t=471889
Having said that, a background worker is probably not appropriate in your situation because you need to be launching multiple threads to handle all these pings. Using the System.Threading.Thread and ThreadPool classes are probably your best bet.

EDIT: here is the one about accessing controls from background threads: http://www.vbforums.com/showthread.php?t=498387

thanks will start lookin at multi-threading so ! any ideas why it takes around 3 pings to get an accurate result (i.e why alot of switches time out on the first ping but if i run program again they succed) is it just because im only using the one thread and its so long ??

also would it be difficult to change the code to just have the loop running as one background thread as you mentioned earlier to make it a little more responsive (just to allow it to be minimized while it runs basically) if so would having it run as a background thread slow it down in anyway ?

Well you could have the loop running as one background thread but the idea that pvbangera and myself were suggesting was to have more than one background thread so that you can do more than one ping at a time. Doing that will make your UI more responsive because the ping is no longer being done in your UI thread so you will be able to minimise it or whatever at any time.
Oh and using multiple threads will not slow it down, it will in your case make the whole process complete much faster because you are not having to wait for each ping before another one can be sent :)

I've created an example for you that uses one background thread to gather the data from the Access database and then once it has collected all of the necessary info from the database it loops through the in-memory copy of the data and sends a ping to all of the IPs in the collection using the ThreadPool. Each time a ping completes (either successfully or not) it adds 1 to a counter and checks to see if the counter now equals the same amount that was in the list of IPs to ping, if so then we know it is the last ping to respond so we can output a message saying "all tests finished" and do whatever you like. Will upload it in a minute after I have added comments to the code.

EDIT: See file attached to this post :)

Attached example project file to previous post, let me know if you have any questions (obviously you need to change a few column names and the path to the database etc etc but its more for you to learn from rather than just start using instead of what you have got already. Also there is no error handling at all in there so if you are going to try and use my version then you need to at least add a few Try, Catch, Finally blocks ;)