VB .NET Asynchronous Server Program Example

Create a new class library project and you might want to use the solution name, AsyncTcpServerVB and project name, AsyncTcpServer as shown in the following Figure.

Imports System

Imports System.Net

Imports System.Net.Sockets

Imports System.Collections

Imports System.Threading

Imports AsyncPacketClass.AsyncPacket

' Displays a simple usage information

    Shared Sub usage()

        Console.WriteLine("Executable_file_name [-a count] [-l address] [-p port]")

        Console.WriteLine("Available options:")

        Console.WriteLine("     -a count        Number of simultaneous asynch Accepts (BeginAccept) allowed")

        Console.WriteLine("     -l address      Local address to create a TCP server on (can be specified multiple times")

        Console.WriteLine("     -p port         Local port number each server listens on")

        Console.WriteLine()

    End Sub

    ' This is the main program that parses the command line parameters and sets up each TCP

    ' listening socket by creating a TcpServer object to handle client connections to each

    ' listening endpoint. The TcpServer object creates a AcceptedConection object for each

    ' established connection which handles IO operations from each client.

Shared Sub Main()

        Dim listenInterfaces As ArrayList = New ArrayList

        Dim tcpServerList As ArrayList = New ArrayList

        Dim asyncAcceptLimit As Integer = 10

        Dim listenPort As Integer = 5150

        ' Parse the command line

        Dim appArguments As String() = Environment.GetCommandLineArgs()

        Dim i As Integer

        usage()

        For i = 1 To appArguments.GetUpperBound(0)

            Try

                Dim CurArg() As Char = appArguments(i).ToCharArray(0, appArguments(i).Length)

                If (CurArg(0) = "-") Or (CurArg(0) = "/") Then

                    Select Case Char.ToLower(CurArg(1), System.Globalization.CultureInfo.CurrentCulture)

                        Case "a"

                            ' How many asynchronous accept (BeginAccepts) allowed simultaneously

                            i += 1

                            asyncAcceptLimit = System.Convert.ToInt32(appArguments(i))

                        Case "l"

                            ' Local interface(s) to bind to

                            i += 1

                            listenInterfaces.Add(IPAddress.Parse(appArguments(i)))

                        Case "p"

                            ' Port on which to listen

                            i += 1

                            listenPort = System.Convert.ToInt32(appArguments(i))

                        Case Else

                            usage()

                            Exit Sub

                    End Select

                End If

            Catch

                usage()

                Exit Sub

            End Try

        Next

        Dim ServerThread As RunServerThread = New RunServerThread

        Dim t As Thread

        ServerThread.asyncAcceptLimit = asyncAcceptLimit

        ServerThread.listenInterfaces = New ArrayList(listenInterfaces.Count)

        ServerThread.listenInterfaces.AddRange(listenInterfaces)

        ServerThread.listenPort = listenPort

        ServerThread.tcpServerList = New ArrayList(tcpServerList.Count)

        ServerThread.tcpServerList.AddRange(tcpServerList)

        ' Create a new thread and define its starting point.

        Console.WriteLine("Creating a new thread and define its starting point...")

        t = New Thread(AddressOf ServerThread.DoTheTask)

        t.Start()

    End Sub

    Class RunServerThread

    Public listenInterfaces As ArrayList

    Public tcpServerList As ArrayList

    Public asyncAcceptLimit As Integer

    Public listenPort As Integer

    Public Sub DoTheTask()

        ' Create an array of handles to signal when server sockets are finished

        Console.WriteLine("Creating an array of handles to signal when server sockets are finished...")

        Dim serverWaitHandles(listenInterfaces.Count - 1) As WaitHandle

        Dim i As Integer

        For i = 0 To listenInterfaces.Count - 1

            serverWaitHandles(i) = New ManualResetEvent(False)

        Next

        ' Create a TCP server socket for each local listen address passed to the application

        Console.WriteLine("Creating a TCP server socket for each local listen address passed to the application...")

        For i = 0 To listenInterfaces.Count - 1

            Dim listenEndPoint As IPEndPoint

            Dim listenServer As TcpServer

            Try

                listenEndPoint = New IPEndPoint(CType(listenInterfaces(i), IPAddress), listenPort)

                listenServer = New TcpServer(listenEndPoint, asyncAcceptLimit)

                serverWaitHandles(i) = listenServer.serverDone

                tcpServerList.Add(listenServer)

            Catch err As Exception

                Console.WriteLine("Error: {0}", err.Message)

            End Try

        Next

        Try

            ' Wait until all the TCP server sockets are done

            Console.WriteLine("Waiting until all the TCP server sockets are done...")

            While (True)

                If (ManualResetEvent.WaitAll(serverWaitHandles, 10000, False) = False) Then

                    ' Wait timed out so print some statistics

                    Console.WriteLine("                             Client Count                  Byte Count")

                    Console.WriteLine(" Server Address             Current/Total                 Sent/Received")

                    For i = 0 To tcpServerList.Count - 1

                        Console.WriteLine(" {0} {1} / {2} {3}/{4}", _

                            (CType(tcpServerList(i), TcpServer)).tcpSocket.LocalEndPoint.ToString().PadRight(20, " "), _

                            (CType(tcpServerList(i), TcpServer)).currentClientCount.ToString().PadLeft(12, " "), _

                            (CType(tcpServerList(i), TcpServer)).totalClientCount.ToString().PadRight(12, " "), _

                            (CType(tcpServerList(i), TcpServer)).TotalSendBytes.ToString().PadLeft(12, " "), _

                            (CType(tcpServerList(i), TcpServer)).TotalReceiveBytes.ToString().PadRight(12, " ") _

                            )

                    Next

                Else

                    Exit While

                End If

            End While

            Console.WriteLine("All listen sockets have been signaled...closing listen sockets...")

            For i = 0 To listenInterfaces.Count - 1

                Dim listenServer As TcpServer = CType(tcpServerList(i), TcpServer)

                listenServer.Shutdown()

                listenServer.tcpSocket.Close()

            Next

            Thread.Sleep(10000)

        Catch err As Exception

            Console.WriteLine("Error: {0}", err.Message)

        End Try

    End Sub

End Class