请问关于vb.net socket的连接问题

我这里有一个server程序，还有一个client程序，程序代码如下，非常简单。我的问题是，如果我现在运行server，然后运行一个client，他们能顺利建立connection,然后如果我再运行一个client程序，这个client同样是connect到这个server的ip和port，然后我希望这个client程序能报错，因为我这个server不是多线程的，他的端口已经正在和一个client通信了，可是我运行了第二个client程序后，没有报错，是被socket的read方法block了，也就是表面上看去也和server程序连接上了，这就是我奇怪的地方，为什么一个端口能同时和不同的client的连上呢？不是一次只能建一个connection吗？请指教。

server代码：
Public Class Server
  Inherits Form
  ' TextBoxes for receiving user input and displaying information
  Private connection As Socket ' Socket object handles connection
  Private readThread As Thread ' server thread
  'Friend WithEvents txtInput As TextBox
  'Friend WithEvents txtInput As TextBox
  ' Stream through which to transfer data
  Private socketStream As NetworkStream
  ' objects for writing and reading data
  Private writer As BinaryWriter
  Private reader As BinaryReader
  Dim counter As Integer = 1

  Public Sub New()
  MyBase.New()
  ' equired by the Windows Form Designer.
  InitializeComponent()
  ' Server portion of a client/server stream-socket connection (part 1 of 4)
  ' add any initialization after the
  ' InitializeComponent call
  ' create thread from server
  Control.CheckForIllegalCrossThreadCalls = False
  readThread = New Thread(AddressOf RunServer)
  readThread.Start()
  End Sub ' New

  ' Visual Studio .NET generated code
  ' invoked when user closes server
  Private Sub FrmServer_Closing(ByVal sender As System.Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
  System.Environment.Exit(System.Environment.ExitCode)
  End Sub ' FrmServer_Closing

  ' send server text to client
  Private Sub txtInput_KeyDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles txtInput.KeyDown
  ' send text to client
  Try
  ' send text if user pressed Enter and connection exists
  If (e.KeyCode = Keys.Enter AndAlso Not connection Is Nothing) Then
  writer.Write("SERVER>>> " & txtInput.Text) ' send data
  StatusTxtBx.Text &= vbCrLf & "SERVER>>> " & _
  txtInput.Text
  ' close connection if server’s user signals termination
  If txtInput.Text = "TERMINATE" Then
  connection.Close()
  End If
  txtInput.Clear()
  End If
  ' handle exception if error occurs when server sends data
  Catch exception As SocketException
  StatusTxtBx.Text &= vbCrLf & "Error writing object"
  End Try
  End Sub ' txtInput_KeyDown
  ' allow client to connect and display text sent by user
  Public Sub RunServer()
  Dim listener As TcpListener
  ' wait for request, then establish connection
  Try
  ' Step 1: create TcpListener
  listener = New TcpListener(5000)
  listener.ExclusiveAddressUse = True
  ' Step 2: TcpListener waits for connection request
  listener.Start()
  ' Step 3: establish connection upon client request
  While True
  StatusTxtBx.Text = "Waiting for connection" & vbCrLf
  ' accept an incoming connection
  connection = listener.AcceptSocket()
  ' create NetworkStream object associated with socket
  socketStream = New NetworkStream(connection)
  ' create objects for transferring data across stream
  writer = New BinaryWriter(socketStream)
  reader = New BinaryReader(socketStream)

  StatusTxtBx.Text &= "Connection " & counter & _
  " received." & vbCrLf
  ' inform client that connection was successfull
  writer.Write("SERVER>>> Connection successful")

  txtInput.ReadOnly = False
  Dim theReply As String = ""
  ' Step 4: read String data sent from client
  Try
  ' loop until client signals termination
  Do
  theReply = reader.ReadString() ' read data
  ' display message
  StatusTxtBx.Text &= vbCrLf & theReply
  Loop While (theReply <> "CLIENT>>> TERMINATE" _
  AndAlso connection.Connected)
  ' handle exception if error reading data
  Catch inputOutputException As IOException
  MessageBox.Show("Client application closing")
  ' close connections
  Finally
  StatusTxtBx.Text &= vbCrLf & _
  "User terminated connection"
  txtInput.ReadOnly = True
  ' Step 5: close connection
  writer.Close()
  reader.Close()
  socketStream.Close()
  connection.Close()
  counter += 1
  End Try
  End While
  ' handle exception if error occurs in establishing connection
  Catch inputOutputException As IOException
  MessageBox.Show("Server application closing")
  End Try
  End Sub ' RunServer
End Class ' FrmServer

client代码：
Public Class Client
  Inherits Form

  ' TextBoxes for inputting and displaying information
  'Friend WithEvents txtInput As TextBox
  'Friend WithEvents txtDisplay As TextBox

  ' stream for sending data to server
  Private output As NetworkStream

  ' objects for writing and reading bytes to streams
  Private writer As BinaryWriter
  Private reader As BinaryReader

  Private message As String = "" ' message sent to server

  ' thread prevents client from blocking data transfer
  Private readThread As Thread

  Public Sub New()
  MyBase.New()

  ' equired by the Windows Form Designer.
  InitializeComponent()
  Control.CheckForIllegalCrossThreadCalls = False
  ' add any initialization after the
  ' InitializeComponent call

  readThread = New Thread(AddressOf RunClient)
  readThread.Start()
  End Sub ' New

  ' Visual Studio .NET generated code

  ' invoked when user closes application
  Private Sub FrmClient_Closing(ByVal sender As System.Object, _
  ByVal e As System.ComponentModel.CancelEventArgs) _
  Handles MyBase.Closing

  System.Environment.Exit(System.Environment.ExitCode)
  End Sub

  ' send user input to server
  Private Sub txtInput_KeyDown(ByVal sender As System.Object, _
  ByVal e As System.Windows.Forms.KeyEventArgs) _
  Handles txtInput.KeyDown

  ' send user input if user pressed Enter
  Try

  ' determine whether user pressed Enter
  If e.KeyCode = Keys.Enter Then

  ' send data to server
  writer.Write("CLIENT>>> " & txtInput.Text)
  txtDisplay.Text &= vbCrLf & "CLIENT>>> " & _
  txtInput.Text

  txtInput.Clear()
  End If

  ' handle exception if error occurs in sending data to server
  Catch exception As SocketException
  txtDisplay.Text &= vbCrLf & "Error writing object"
  End Try
  End Sub ' txtInput_KeyDown
  ' connect to server and display server-generated text
  Public Sub RunClient()
  Dim client As TcpClient
  ' instantiate TcpClient for sending data to server
  Try
  txtDisplay.Text &= "Attempting connection" & vbCrLf
  ' Step 1: create TcpClient and connect to server
  client = New TcpClient()
  client.Connect("127.0.0.1", 5000)
  client.SendTimeout = 1
  ' Step 2: get NetworkStream associated with TcpClient
  output = client.GetStream()
  ' create objects for writing and reading across stream
  writer = New BinaryWriter(output)
  reader = New BinaryReader(output)
  txtDisplay.Text &= vbCrLf & "Got I/O streams" & vbCrLf
  txtInput.ReadOnly = False
  ' Step 3: processing phase
  Try
  ' loop until server signals termination
  Do
  ' read message from server
  message = reader.ReadString
  txtDisplay.Text &= vbCrLf & message
  Loop While message <> "SERVER>>> TERMINATE"
  ' handle exception if error in reading server data
  : Catch inputOutputException As IOException
  MessageBox.Show("Client application closing")
  ' Step 4: close connection
  Finally
  txtDisplay.Text &= vbCrLf & "Closing connection." & vbCrLf
  writer.Close()
  reader.Close()
  output.Close()
  client.Close()
  End Try
  Application.Exit()
  ' handle exception if error in establishing connection
  Catch inputOutputException As Exception
  MessageBox.Show("Client application closing")
  End Try
  End Sub ' RunClient
End Class ' FrmClient

这么长？

顶，代码很简单的，直接复制粘贴然后建两个textexboxt就ok