vb.net - TCP 上的超时异常未处理

Question

由于 VS 2010 不支持 TCP 连接的超时，因此我从网站获取了此代码：

Private Function ConnectWithTimeout() As Boolean
    Dim ar As IAsyncResult = TCPClient.BeginConnect(IPAddress, TCPPort, Nothing, Nothing)
    Dim wh As System.Threading.WaitHandle = ar.AsyncWaitHandle

    Try
        If Not ar.AsyncWaitHandle.WaitOne(TimeSpan.FromSeconds(2), False) Then
            TCPClient.Close()
            TCPClient = New System.Net.Sockets.TcpClient
            Throw New TimeoutException()
        End If
    Catch ex As Exception
        ThrowError("Timeout on connecting to " & IPAddress & " at port " & TCPPort & ".")
        Return False
    Finally
        wh.Close()
    End Try

    Return True
End Function

它工作正常，但每次，它都会在调试输出上给我这个：

“发生了‘System.TimeoutException’类型的第一次机会异常”

即使我抓住了所有的例外。有没有办法在处理此异常消息时摆脱它？

我试过这个：

    Dim connectDone As New System.Threading.AutoResetEvent(False)
    TCPClient.BeginConnect(IPAddress, TCPPort, New AsyncCallback(Sub(ar As IAsyncResult)
                                                                     TCPClient.EndConnect(ar)
                                                                     connectDone.Set()
                                                                 End Sub), TCPClient)
    'client.BeginConnect("127.0.0.1", 80, new AsyncCallback(delegate( IAsyncResult ar ) { client.EndConnect( ar );  connectDone.Set(); }), client);

    If Not connectDone.WaitOne(2000) Then
        Debug.WriteLine("TIMEOUT")
        Return False
    End If

    Return True

但它在 beginconnect 行上给了我 InvalidOperationException：当另一个异步操作在同一个 Socket 上进行时，无法调用 BeginConnect。

Answer 1

Private Function ConnectWithTimeout() As Boolean
    Dim ar As IAsyncResult 
    Dim wh As System.Threading.WaitHandle  

    Try
          ar = TCPClient.BeginConnect(IPAddress, TCPPort, Nothing, Nothing)
          wh = ar.AsyncWaitHandle
    Cath ex as Exception
          'Code to catch exception
    End Try

    Try
        If Not ar.AsyncWaitHandle.WaitOne(TimeSpan.FromSeconds(2), False) Then
            TCPClient.Close()
            TCPClient = New System.Net.Sockets.TcpClient
            Throw New TimeoutException()
    End If
    Catch ex As Exception
        ThrowError("Timeout on connecting to " & IPAddress & " at port " & TCPPort & ".")
        Return False
    Finally
        wh.Close()
    End Try

    Return True
End Function