在这里介绍程序主要实现的功能以及流程。
程序在启动后会开启1个线程，1个定时器，一个线程用来接受来自客户端的连接，定时器用来检测当前有多少个客户连接，当有一个客户连接是，会开启一个线程用来与客户传送消息。为了简单起见，服务器发送消息为广播发送。

全局变量：

  Dim listen_thread As Thread'监听线程
    Dim listener As Socket '套接字
    Public allDone As New ManualResetEvent(False)
    Dim Thread_listen As Thread

    Dim So As New ArrayList'已连接客户的集合
    Dim thread_lock As Object = New Object()'用于线程锁
    Dim Time As Timers.Time'定时器

   Public Class StateObject
        ' Client  socket.
        Public workSocket As Socket = Nothing
        ' Size of receive buffer.
        Public Const BufferSize As Integer = 1024
        ' Receive buffer.
        Public buffer(BufferSize) As Byte
        ' Received data string.
        Public sb As New StringBuilder
        Public size As Int32
    End Class 'StateObject

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接受连接的线程过程;

    Public Sub listen_handle()
        TextBox3.AppendText(vbNewLine & "服务器启动")
        TextBox3.ScrollToCaret()
        While 1

            allDone.Reset()
            Try
                listener.BeginAccept(New AsyncCallback(AddressOf Accept_callback), listener)
            Catch e As Exception
                Exit Sub
            End Try
            allDone.WaitOne()
        End While
    End Sub

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处理连接的线程过程：

 Public Sub Accept_callback(ar As IAsyncResult)
        allDone.Set() '让线程开始

        Dim waitDone As New ManualResetEvent(False)
        Dim socketi As Socket

        Try
            socketi = listener.EndAccept(ar)
        Catch ie As Exception
            Exit Sub
        End Try
        '显示出来
        TextBox3.AppendText(vbNewLine & "加入一个" & socketi.RemoteEndPoint.ToString)
        TextBox3.ScrollToCaret()
        Dim State As New StateObject()
        State.workSocket = socketi
        SyncLock thread_lock '/加入集合
            So.Add(socketi)
        End SyncLock
        State.size = 0
        Dim err As Int32 = 0
        While 1
            Try
                err = socketi.Receive(State.buffer)
            Catch e As Exception'接受异常说明客户端终止
                TextBox3.AppendText(vbNewLine & "客户端终止")
                TextBox3.ScrollToCaret()
                socketi.Close()
                SyncLock thread_lock
                    So.Remove(socketi)
                End SyncLock
                Exit Sub
            End Try
            If err > 0 Then '接收到消息并回调
                State.sb.Clear()
                State.sb.Append(Encoding.ASCII.GetString(State.buffer, 0, err))
                Dim str As String
                str = State.sb.ToString()
                TextBox1.AppendText(vbNewLine & str)
                TextBox1.ScrollToCaret()
            End If
        End While
    End Sub

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定时器过程：

    Public Sub Time_hande()
        Dim str As String = ""
        SyncLock thread_lock '
            For Each member As Socket In So
                str = str & member.RemoteEndPoint.ToString() & vbNewLine
            Next
        End SyncLock
        TextBox6.Text = str
    End Sub

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界面：

github:https://github.com/fengasdf/WindowsApplication4/blob/master/WindowsApplication4/Form1.vb