Multi threading webrequests? - vb.net

Question

I'm programming a tool that'll go through a lot of websites and see if they contain a text that's in a textbox.
Now I wan't to add multi threading so it goes quite a lot faster, most preferably I'd dynamically add threads.
This is my code now but it didn't work because it says index ouf of range. And I doubt it work anyways.
Dim clsThreads As New Generic.List(Of System.Threading.Thread)
Dim numberOfthreads As Integer = 1
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
For Each strLine1 As String In TextBox1.Text.Split({vbCr, vbLf}, StringSplitOptions.RemoveEmptyEntries)
For Each strLine2 As String In TextBox2.Text.Split({vbCr, vbLf}, StringSplitOptions.RemoveEmptyEntries)
clsThreads(numberOfthreads) = New Thread(Sub() Me.request(strLine1, strLine2))
clsThreads(numberOfthreads).Name = "Thread: " + numberOfthreads.ToString
clsThreads(numberOfthreads).IsBackground = True
clsThreads(numberOfthreads).Start()
numberOfthreads = numberOfthreads + 1
If (numberOfthreads.Equals(20)) Then
numberOfthreads = 0
End If
Next
Next
End Sub
So, how do I implement multi threading in a smart way?
This is my request sub:
Public Sub request(ByVal username, ByVal mail)
Dim req As WebRequest = WebRequest.Create("http://localhost/" + username)
req.Method = "GET"
Dim res As WebResponse = req.GetResponse()
Dim dataStream As Stream = res.GetResponseStream()
Dim reader As New StreamReader(dataStream)
Dim responseFromServer As String = reader.ReadToEnd()
If responseFromServer.Contains(mail) Then
TextBox3.Text = TextBox3.Text + vbNewLine + username
End If
End Sub
End Class

Answer 1

Something like this?
Option Strict On
Option Explicit On
Option Infer Off
Public Class Form1
Dim ActiveThreads As New List(Of System.Threading.Thread)
Delegate Sub delRemoveThread(thread As Threading.Thread)
Sub removeThread(thread As Threading.Thread)
If Me.InvokeRequired Then
Me.Invoke(New delRemoveThread(AddressOf removeThread), thread)
Else
ActiveThreads.Remove(thread)
End If
End Sub
Private Sub Button1_Click3(sender As Object, e As EventArgs) Handles Button1.Click
For i As Integer = 1 To 20
Dim th As New Threading.Thread(New Threading.ParameterizedThreadStart(Sub()
request("username", "mail")
removeThread(Threading.Thread.CurrentThread)
End Sub))
th.Start()
Next
End Sub
Public Sub request(ByVal username As String, ByVal mail As String)
Dim req As Net.WebRequest = Net.WebRequest.Create("http://localhost/" + username)
req.Method = "GET"
Dim res As Net.WebResponse = req.GetResponse()
Dim dataStream As IO.Stream = res.GetResponseStream()
Dim reader As New IO.StreamReader(dataStream)
Dim responseFromServer As String = reader.ReadToEnd()
If responseFromServer.Contains(mail) Then
TextBox3.Text = TextBox3.Text + vbNewLine + username
End If
End Sub
End Class