XML FeedsToday I wanted a way to see which of my cameras were online at a certain point in time. Pinging them is a great way of doing that, it at least says they are there and the first two layers of the OSI model are working (if I remember correctly).
Doing a ping to another computer in VB.Net is easy.
- Dim _ping As New Ping
- Dim _pingreply = _ping.Send(IpAddress, 2000)
- If _pingreply.Status = IPStatus.Success Then
- Like this.
The first parameter of Ping.Send is the IpAddress as string and the second is the timeout in this case 2 seconds.
I want to ping 5 cameras at a time to worst case this will take 10 seconds. 10 seconds is a long time to wait for a user who's attention span is 3 seconds. So we need a way to do this asynchronously.
So I create a grid with 2 columns and 5 rows. First column has the Ipaddresses and the second will show the result.
Here is how.
- Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
- fGrid.Columns.Add("Ip", "Ip")
- fGrid.Columns.Add("Ping", "Ping")
- fGrid.Columns(0).Width = 100
- fGrid.Columns(1).AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill
- For i As Integer = 0 To 4
- Dim myRowIndex = fGrid.Rows.Add()
- fGrid.Rows(myRowIndex).Cells(0).Value = "10.216.110." & (11 + myRowIndex).ToString
- Next
- End Sub
Looks like this.
So now that we have that we can do the pings in another thread. So I made a button to spawn this thread and begin the process.
- Private fThread = New Thread(New ThreadStart(AddressOf ThreadProc))
- fThread.IsBackground = True
- fThread.Start()
and this will use the following things.
- Private Sub ThreadProc()
- Parallel.For(0, 5, Sub(b)
- CheckOnline(b)
- End Sub)
- End Sub
- Private Sub CheckOnline(ByVal rowindex As Integer)
- Dim _ping As New Ping
- Try
- Dim _pingreply = _ping.Send("10.216.110." & (11 + rowindex).ToString, 2000)
- If _pingreply.Status = IPStatus.Success Then
- SyncLock success
- success.Add(rowindex)
- End SyncLock
- End If
- Catch ex As Exception
- End Try
- End Sub
Yep I used a parallel foreach that will spawn 5 more threads to do the pings in parallel for me.
But I also needed a way to tell my users I was doing something and a way to tell them it was all finished and the result.
I did that with a second thread that check the result in a list and sees if they are done, making sure I synchronize the lists add method because that is not threadsafe.
- Imports System.Threading
- Imports System.Threading.Tasks
- Imports System.Net.NetworkInformation
- Partial Public Class Form1
- Private fThread As Thread
- Private fThread2 As Thread
- Public Delegate Sub AddRowDelegate(ByVal column As Integer)
- Delegate Sub CheckOnlineDelegate(ByVal rowindex As Integer)
- Delegate Sub SetOnlineDelegate(ByVal rowindex As Integer)
- Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
- fGrid.Columns.Add("Ip", "Ip")
- fGrid.Columns.Add("Ping", "Ping")
- fGrid.Columns(0).Width = 100
- fGrid.Columns(1).AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill
- For i As Integer = 0 To 4
- Dim myRowIndex = fGrid.Rows.Add()
- fGrid.Rows(myRowIndex).Cells(0).Value = "10.216.110." & (11 + myRowIndex).ToString
- Next
- End Sub
- Private Sub ThreadProc()
- Parallel.For(0, 5, Sub(b)
- Do While Not done.Contains(b)
- fGrid.Invoke(New AddRowDelegate(AddressOf AddRow), New Object() {b})
- Thread.Sleep(300)
- Loop
- fGrid.Invoke(New SetOnlineDelegate(AddressOf SetOnline), New Object() {b})
- End Sub)
- End Sub
- Private Sub ThreadProc2()
- Parallel.For(0, 5, Sub(b)
- CheckOnline(b)
- End Sub)
- End Sub
- Private Sub AddRow(ByVal rowindex As Integer)
- If fGrid.Rows(rowindex).Cells(1).Value Is Nothing OrElse fGrid.Rows(rowindex).Cells(1).Value.ToString.Contains(".....") OrElse Not fGrid.Rows(rowindex).Cells(1).Value.ToString.Contains("Pinging") Then
- fGrid.Rows(rowindex).Cells(1).Value = "Pinging 10.216.110." & (11 + rowindex).ToString & " "
- Else
- fGrid.Rows(rowindex).Cells(1).Value = fGrid.Rows(rowindex).Cells(1).Value.ToString & "."
- End If
- fGrid.Rows(rowindex).Cells(1).Style.BackColor = Drawing.Color.White
- End Sub
- Private success As New List(Of Integer)
- Private done As New List(Of Integer)
- Private Sub CheckOnline(ByVal rowindex As Integer)
- Dim _ping As New Ping
- Try
- Dim _pingreply = _ping.Send("10.216.110." & (11 + rowindex).ToString, 2000)
- If _pingreply.Status = IPStatus.Success Then
- SyncLock success
- success.Add(rowindex)
- End SyncLock
- End If
- Catch ex As Exception
- End Try
- SyncLock done
- done.Add(rowindex)
- End SyncLock
- End Sub
- Private Sub SetOnline(ByVal rowindex As Integer)
- If Not success.Contains(rowindex) Then
- fGrid.Rows(rowindex).Cells(1).Value = "Offline"
- fGrid.Rows(rowindex).Cells(1).Style.BackColor = Drawing.Color.Red
- Else
- fGrid.Rows(rowindex).Cells(1).Value = "Online"
- fGrid.Rows(rowindex).Cells(1).Style.BackColor = Drawing.Color.Green
- End If
- End Sub
- Private Sub PingToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PingToolStripMenuItem.Click
- done = New List(Of Integer)
- success = New List(Of Integer)
- fThread = New Thread(New ThreadStart(AddressOf ThreadProc))
- fThread.IsBackground = True
- fThread.Start()
- fThread2 = New Thread(New ThreadStart(AddressOf ThreadProc2))
- fThread2.IsBackground = True
- fThread2.Start()
- End Sub
- End Class
As you can see I invoke the SetOnline and AddRow methods via the grid so that it can be handled in a thread safe way. I also use delegates for that.
While running it you will see that if one is online it will turn green immediately or very fast.
Look also that the Parallel For second parameter is Exclusive To so it does not translate into For i as integer = 0 to 5 but it translates into For i as integer = 0 to 4.
And that you have to wait for about 2 (timeout we used) seconds for all the others to turn red.
Writing thread safe code is tricky but I think I covered all the bases to make this as thread safe as possible without getting race conditions.
Any questions?
Chris is awesome.
That, sir, is very cool! I can see a ton of applicable uses for this for someone like me that probably would have a hard time writing it on my own. (now I just need to convert it to C# :P )
Great post! 
Exactly what i'm looking for
Do you have this as a project to download? I'm looking to use this as a base for server monitor software. I wrote one using 3 columns(up/down/rebooted), but it is not threaded. 
Hi,
You need to change a lot since you need to have a way to tell when the 5 previous threads have finished. Not something that is going to be to easy, I might look at it later this week. 
It's layer 2 if you are pinging in the same VLAN. Otherwise your testing up to layer 3 :-) 
Hi Christiaan,
Hi,
Here is a multithreaded chat programming in vb.net
Hi great blog
LTD Social Sitings
Note: Watch for social icons on posts by your favorite authors to follow their postings on these and other social sites.