Imports System
Imports System.Threading
Imports System.Net.Sockets
Imports System.Text
Public Class TcpSvr
    Public MaxThreads As System.Int16
    Private ActiveThreads As Long
    Private ThreadIndex As System.Int16
    Private StopListener As System.Boolean
    Private Listener As TcpListener
    Public Port As System.Int32
    Private ASCII As ASCIIEncoding
 
    Public Sub New()
        StopListener = False
        ActiveThreads = 0
        ASCII = New ASCIIEncoding
    End Sub
 
    Public Sub Start()
        Console.WriteLine("Listener starten...")
        Dim ipAdd = System.Net.IPAddress.Parse("192.168.16.16")
        Listener = New TcpListener(ipAdd, Port)
        Listener.Start()
        MultiThread()
        Console.WriteLine("Listener stoppen...")
        Listener.Stop()
    End Sub
 
    Public Sub MultiThread()
        Dim CurThreadStart As ThreadStart
        Dim CurThread As Thread
        Dim ThreadCount As System.Int16
        Console.WriteLine("MaxThreads: " + MaxThreads.ToString)
        Console.WriteLine("Threading starten...")
        While StopListener = False
            If Listener.Pending = False Then
                ' continue 
            End If
            If ActiveThreads = MaxThreads Then
                ' continue 
            End If
            Console.WriteLine("Request 1")
            CurThreadStart = AddressOf Request
            CurThread = New Thread(CurThreadStart)
            CurThread.Start()
            SyncLock CurThread
                System.Math.Min(System.Threading.Interlocked.Increment( _
                  ActiveThreads), ActiveThreads - 1)
            End SyncLock
        End While
    End Sub
 
    Public Sub Request()
        Console.WriteLine("Request bearbeiten")
        Dim CurThread As Thread
        Dim CurSocket As Socket
        Dim Buffer As Byte()
        Dim Bytes As System.Int32
        Dim Temp As System.String
        Buffer = New Byte(256) {}
        CurThread = Thread.CurrentThread
        CurSocket = Listener.AcceptSocket
 
        While StopListener = False
            If CurSocket.Available > 0 Then
                Try
                    Bytes = CurSocket.Receive(Buffer, Buffer.Length, 0)
                    Temp = ASCII.GetString(Buffer, 0, Bytes)
                    Console.WriteLine("Eingabe: " + Temp)
 
                    If Temp.Substring(0, 1) = "q" Then
                        CurSocket.Send(ASCII.GetBytes("schon Schluss?"))
                        StopListener = True
                    End If
                Catch e As Exception
                    Console.WriteLine("Fehler: " + e.Message)
                End Try
            End If
        End While
 
        CurSocket.Close()
 
        SyncLock CurThread
            System.Math.Max(System.Threading.Interlocked.Decrement( _
              ActiveThreads), ActiveThreads + 1)
        End SyncLock
    End Sub
End Class

Public Shared Sub Main()
        Dim TcpSvr As TcpSvr
        TcpSvr = New TcpSvr
        TcpSvr.MaxThreads = 500
        TcpSvr.Port = 25
        Console.WriteLine("TcpServer starten...")
        TcpSvr.Start()
    End Sub

Eine nicht behandelte Ausnahme des Typs 'System.Net.Sockets.SocketException' _
  ist in system.dll aufgetreten.
 
Zusätzliche Informationen: Ein Blockierungsvorgang wurde durch einen Aufruf von _
  WSACancelBlockingCall unterbrochen