sockets - 异常，但仅在第 3 次 - IAsyncResult 对象未从此类上的相应异步方法返回

Question

我有一个旧版 (2008) Windows 服务应用程序(使用 System.ServiceProcess.ServiceBase)，我需要以与现在的工作方式略有不同的方式使用它。目前，它启动并在特定端口上创建一个 TCPLISTENER，供客户端应用程序连接(它只连接一次)，以便向监听端口发送/接收请求。这一切都很好。但是，适配需要使用 web 应用程序连接到监听器端口，然后正常发送/rcv，但接收后必须 DISCONNECT(*)

(* - 如果 Web 应用程序不必在每次测试后断开与监听套接字的连接会更好，但我如何实现这一点超出了我的能力范围。我可以将 TCP 连接保持在 session 状态以供重复使用吗？ )

无论如何，对于第一个 的改编一切正常。两个 connect/send/rcv/disconnect 测试，但在 第三该服务在 Socket 类的 EndAccept 中引发 ArgumentException。

我不明白为什么它在第三次测试中失败了。

这是简单的测试客户端。

      Public Class ConnectDisconnectTCP
    Inherits System.Web.UI.Page
    Private IP As String = "127.0.0.1"
    Private port As Int32 = 10002
    Private mTCP As System.Net.Sockets.TcpClient
    Private netStrm As NetworkStream

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    End Sub

    Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim oEnc As New ASCIIEncoding
        Dim ScanText As String = "100000000093001X" + vbLf
        Dim mTCP As System.Net.Sockets.TcpClient

        'connect and create a tcpclient
        mTCP = New System.Net.Sockets.TcpClient(IP, port)
        netStrm = mTCP.GetStream()
        netStrm.WriteAsync(oEnc.GetBytes(ScanText.ToString), 0, ScanText.ToString.Length)

        If netStrm.CanRead Then

            Dim myReadBuffer(1024) As Byte
            Dim myCompleteMessage As StringBuilder = New StringBuilder()
            Dim numberOfBytesRead As Integer = 0

            ' Incoming message may be larger than the buffer size.
            Do
                numberOfBytesRead = netStrm.Read(myReadBuffer, 0, myReadBuffer.Length)
                myCompleteMessage.AppendFormat("{0}", Encoding.ASCII.GetString(myReadBuffer, 0, numberOfBytesRead))
            Loop While netStrm.DataAvailable

        End If

       'CLOSE
        netStrm.Close()
        mTCP.Close() 'Disposes this TcpClient instance and requests that the underlying TCP connection be closed.
        mTCP = Nothing
        Label1.Text = "Closed"
    End Sub End Class

这是完成所有工作的服务上的 TCPListener 类

   Imports System
    Imports System.IO
    Imports System.Net
    Imports System.Net.Sockets
    Imports System.Threading
    Imports System.Text

    Public Class TCPListenerPort

    Private currentAsynchResult As IAsyncResult
    Private cState As ClientState
    Private servSock As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
    Private m_connectionstate As Int32 = 0
    Dim sData As String = String.Empty

    'counters
    Public cnt As Int32 = 0
    Public rcvcnt As Int32 = 0
    Public acccnt As Int32 = 0
    Public sndcnt As Int32 = 0
    Public sndcal As Int32 = 0
    Public cncnt As Int32 = 0

    'Public Events
    Public Event ConnectionState(ByVal enmState As Int32)
    Public Event DataArrived(ByVal strData As Object)

    Public Sub New()
    End Sub

    Public Sub New(ByVal dr As DataRow)

    End Sub

    Protected Overrides Sub Finalize()
        Try
            If Not cState Is Nothing Then
                cState.ClntSock.Close()
            End If
            If Not servSock Is Nothing Then
                servSock.Close()
            End If
        Catch ex As Exception
            Throw ex
        Finally
            MyBase.Finalize()
        End Try
    End Sub

    Private Class ClientState

        Public Const BUFSIZE As Integer = 1024

        Public mrcvBuffer As Byte() = New Byte(BUFSIZE - 1) {}
        Public mSendBuffer As Byte() = New Byte(BUFSIZE - 1) {}

        Private mclntSock As Socket = Nothing


        Public Sub New(ByRef clntSock As Socket)
            mclntSock = clntSock
            ReDim mrcvBuffer(BUFSIZE)
            ReDim mSendBuffer(BUFSIZE)
        End Sub

        Public ReadOnly Property SckConnected() As Boolean
            Get
                SckConnected = mclntSock.Connected
            End Get
        End Property

        Public ReadOnly Property RcvBuffer() As Byte()
            Get
                RcvBuffer = mrcvBuffer
            End Get
        End Property

        Public ReadOnly Property SendBuffer() As Byte()
            Get
                SendBuffer = mSendBuffer
            End Get
        End Property

        Public ReadOnly Property ClntSock() As Socket
            Get
                ClntSock = mclntSock
            End Get
        End Property

    End Class

    Public Sub Connect(ByVal TCPPort As Int32, ByVal Backlog As Int32)



        Try
            cState = New ClientState(servSock)
            cState.ClntSock.Bind(New IPEndPoint(System.Net.IPAddress.Any, TCPPort))
            cState.ClntSock.Listen(100) '5

            While True
                cncnt = cncnt + 1
                System.Diagnostics.Debug.WriteLine("in connect WHILE " + cncnt.ToString)
                currentAsynchResult = servSock.BeginAccept(New AsyncCallback(AddressOf AcceptCallback), cState)
                currentAsynchResult.AsyncWaitHandle.WaitOne()
            End While

        Catch __unusedObjectDisposedException1__ As ObjectDisposedException
        Catch e As Exception
        End Try
    End Sub

    Private Sub AcceptCallback(ByVal asyncResult As IAsyncResult)


        Try

            acccnt = acccnt + 1
            System.Diagnostics.Debug.WriteLine("AcceptCallback Start" + acccnt.ToString)

            'obtain the Socket on which the connection attempt is being made
            Dim servSock As ClientState = asyncResult.AsyncState 'Asyncstate gets a user defined object that qualifies or contains info about an async operation
            Dim clntSock As Socket

            clntSock = servSock.ClntSock.EndAccept(asyncResult)

            System.Diagnostics.Debug.WriteLine(clntSock.RemoteEndPoint)

            Dim cs As New ClientState(clntSock)
            clntSock.BeginReceive(cs.RcvBuffer, 0, cs.RcvBuffer.Length, SocketFlags.None, New AsyncCallback(AddressOf ReceiveCallback), cs)

        Catch ar As ArgumentException

            '!!!!!Test 3 errors here with
            'The IAsyncResult object was not returned from the corresponding asynchronous method on this class.

        Catch ex As Exception

        End Try

        System.Diagnostics.Debug.WriteLine("AcceptCallback End " + acccnt.ToString)

    End Sub

    Private Sub ReceiveCallback(ByVal asyncResult As IAsyncResult)
        rcvcnt = rcvcnt + 1
        System.Diagnostics.Debug.WriteLine("ReceiveCallback In " + rcvcnt.ToString)
        Dim cs As ClientState = asyncResult.AsyncState
        Dim AE As New System.Text.ASCIIEncoding
        Dim recvMsgSize As Int32 = 0
        Dim strTmp As String = String.Empty
        Dim strSend As String = String.Empty

        Try

            recvMsgSize = cs.ClntSock.EndReceive(asyncResult)
            strTmp = Replace(AE.GetString(cs.RcvBuffer), vbNullChar, "")
            If recvMsgSize > 0 Then
                System.Diagnostics.Debug.WriteLine("ReceiveCallback receiveMsgSize " + recvMsgSize.ToString)
                If Right(strTmp, 1) = vbLf Or Right(strTmp, 1) = vbCr Then
                    strSend = sData + strTmp
                    strSend = strSend.Replace(vbLf, "")
                    strSend = strSend.Replace(vbCr, "")
                    cState = cs
                    sData = String.Empty

                    RaiseEvent DataArrived(strSend)
                Else

                End If

            Else

            End If


        Catch ex As Exception

            Throw ex
        End Try

        System.Diagnostics.Debug.WriteLine("ReceiveCallback Exit " + rcvcnt.ToString)

    End Sub

    Public Function SendData(ByVal strData As Object) As Boolean

        ' Change the data to a byte array if necessary, then send it via the socket
        Dim oEncoder As New System.Text.ASCIIEncoding
        Dim bytes As Byte()
        Dim Result As IAsyncResult

        Try

            Select Case strData.GetType().ToString
                Case "System.String" ' Convert a string to a byte array
                    bytes = oEncoder.GetBytes(strData)
                Case "System.Byte[]" ' Send a byte array directly
                    bytes = strData
                Case Else ' And just send anything else as-is
                    bytes = strData
            End Select

            sndcnt = sndcnt + 1
            Result = cState.ClntSock.BeginSend(bytes, 0, bytes.Length, SocketFlags.None, New AsyncCallback(AddressOf SendCallback), cState)
            System.Diagnostics.Debug.WriteLine("SendData " + sndcnt + " " + Result.ToString)

            Result.AsyncWaitHandle.WaitOne()

        Catch ex As Exception
            Throw ex
        End Try
        Return True

    End Function

    Private Sub SendCallback(ByVal asyncResult As IAsyncResult)

        Dim cs As ClientState = asyncResult.AsyncState
        Dim bytesSent As Int32 = 0

        Try
            bytesSent = cs.ClntSock.EndSend(asyncResult)
            sndcal = sndcal + 1

            cs.ClntSock.BeginReceive(cs.RcvBuffer, 0, cs.RcvBuffer.Length, SocketFlags.None, New AsyncCallback(AddressOf ReceiveCallback), cs)
            System.Diagnostics.Debug.WriteLine("SendCallBack " + sndcal.ToString + " " + bytesSent.ToString)

        Catch ex As Exception
            Throw (ex)
        End Try

    End Sub


    End Class

打开 .net 跟踪，加上代码的系统诊断 debug.write，这里是 TEST1、TEST2、TEST3/CRASH 操作的完整日志。注意 '<-- SCANTEXT RECEIVED' 和 '<-- RESPONSE RECEIVED' 注释。 'in connect WHILE 4' 注释显示了第三次请求尝试的到来。

    [12572] TcpClient#57416410::TcpClient(AddressFamily#2)
    [12572] Socket#61940669::Socket(AddressFamily#2)
    [12572] Exiting Socket#61940669::Socket() 
    [12572] Exiting TcpClient#57416410::TcpClient() 
    [12572] TcpClient#57416410::TcpClient()
    [12572] Exiting TcpClient#57416410::TcpClient() 
    [12572] Socket#15193904::Socket(AddressFamily#2)
    [12572] Exiting Socket#15193904::Socket() 
    [17872] Socket#40528290::Socket(AddressFamily#2)
    [17872] Exiting Socket#40528290::Socket() 
    [17872] Socket#40528290::Bind(0.0.0.0:10002#10002)
    [17872] Exiting Socket#40528290::Bind() 
    [17872] Socket#40528290::Listen(Int32#100)
    [17872] Exiting Socket#40528290::Listen() 
    in connect WHILE 1
    [17872] Socket#40528290::BeginAccept()
    [17872] Exiting Socket#40528290::BeginAccept()  -> AcceptAsyncResult#515737
    The thread '1' (0x6674) has exited with code 0 (0x0).
    The thread '<No Name>' (0x1df8) has exited with code 0 (0x0).
    The thread '<No Name>' (0x5dac) has exited with code 0 (0x0).
    [7984] Socket#49538252::Socket()
    [7984] Exiting Socket#49538252::Socket() 
    in connect WHILE 2
    AcceptCallback Start1
    [17872] Socket#40528290::BeginAccept()
    [7984] Socket#40528290::EndAccept(AcceptAsyncResult#515737)
    [17872] Exiting Socket#40528290::BeginAccept()  -> AcceptAsyncResult#27334100
    System.Net.Sockets Information: 0 : [7984] Socket#49538252 - Accepted connection from 127.0.0.1:63817 to 127.0.0.1:10002.
    [7984] Exiting Socket#40528290::EndAccept()     -> Socket#49538252
    127.0.0.1:63817
    [7984] Socket#49538252::BeginReceive()
    [7984] Exiting Socket#49538252::BeginReceive()  -> OverlappedAsyncResult#62696216
    AcceptCallback End 1
    [22168] Data from Socket#49538252::PostCompletion
    [22168] 00000000 : 32 30 30 30 30 30 30 30-30 30 38 33 30 30 31 58 : 100000000093001X <-- SCANTEXT RECEIVED, TEST1
    [22168] 00000010 : 0A                                              : .
    ReceiveCallback In 1
    [22168] Socket#49538252::EndReceive(OverlappedAsyncResult#62696216)
    [22168] Exiting Socket#49538252::EndReceive()   -> Int32#17
    ReceiveCallback receiveMsgSize 17
    [22168] Socket#49538252::BeginSend()
    [22168] Exiting Socket#49538252::BeginSend()    -> OverlappedAsyncResult#13462887
    A first chance exception of type 'System.FormatException' occurred in Microsoft.VisualBasic.dll
    [19228] Data from Socket#49538252::PostCompletion
    [19228] 00000000 : 07                                              : . <-- RESPONSE RECEIVED, TEST1
    [19228] Socket#49538252::EndSend(OverlappedAsyncResult#13462887)
    [19228] Exiting Socket#49538252::EndSend()  -> Int32#1
    [19228] Socket#49538252::BeginReceive()
    [19228] Exiting Socket#49538252::BeginReceive()     -> OverlappedAsyncResult#25961440
    SendCallBack 1 1
    [7984] Data from Socket#49538252::PostCompletion
    [7984] 00000000 :                                                 : 
    ReceiveCallback In 2
    [7984] Socket#49538252::EndReceive(OverlappedAsyncResult#25961440)
    [7984] Exiting Socket#49538252::EndReceive()    -> Int32#0
    ReceiveCallback Exit 2
    ReceiveCallback Exit 2
    [22168] Socket#31352595::Socket()
    [22168] Exiting Socket#31352595::Socket() 
    AcceptCallback Start2
    in connect WHILE 3
    [17872] Socket#40528290::BeginAccept()
    [22168] Socket#40528290::EndAccept(AcceptAsyncResult#27334100)
    [17872] Exiting Socket#40528290::BeginAccept()  -> AcceptAsyncResult#39421196
    System.Net.Sockets Information: 0 : [22168] Socket#31352595 - Accepted connection from 127.0.0.1:63820 to 127.0.0.1:10002.
    [22168] Exiting Socket#40528290::EndAccept()    -> Socket#31352595
    127.0.0.1:63820
    [22168] Socket#31352595::BeginReceive()
    [22168] Exiting Socket#31352595::BeginReceive()     -> OverlappedAsyncResult#28002689
    AcceptCallback End 2
    [7984] Data from Socket#31352595::PostCompletion
    [7984] 00000000 : 32 30 30 30 30 30 30 30-30 30 38 33 30 30 31 58 : 100000000093001X <-- SCANTEXT RECEIVED, TEST2
    [7984] 00000010 : 0A                                              : .
    ReceiveCallback In 3
    [7984] Socket#31352595::EndReceive(OverlappedAsyncResult#28002689)
    [7984] Exiting Socket#31352595::EndReceive()    -> Int32#17
    ReceiveCallback receiveMsgSize 17
    [7984] Socket#31352595::BeginSend()
    [7984] Exiting Socket#31352595::BeginSend()     -> OverlappedAsyncResult#31071611
    [22168] Data from Socket#31352595::PostCompletion
    A first chance exception of type 'System.FormatException' occurred in Microsoft.VisualBasic.dll
    [22168] 00000000 : 07                                              : . <-- RESULT RECEIVED, TEST2
    [22168] Socket#31352595::EndSend(OverlappedAsyncResult#31071611)
    [22168] Exiting Socket#31352595::EndSend()  -> Int32#1
    [22168] Socket#31352595::BeginReceive()
    [22168] Exiting Socket#31352595::BeginReceive()     -> OverlappedAsyncResult#51673536
    SendCallBack 2 1
    [4640] Data from Socket#31352595::PostCompletion
    [4640] 00000000 :                                                 : 
    ReceiveCallback Exit 3
    The thread '<No Name>' (0x4b1c) has exited with code 0 (0x0).
    ReceiveCallback In 4
    [4640] Socket#31352595::EndReceive(OverlappedAsyncResult#51673536)
    [4640] Exiting Socket#31352595::EndReceive()    -> Int32#0
    ReceiveCallback Exit 4
    [4640] Socket#37088038::Socket()
    [4640] Exiting Socket#37088038::Socket() 
    AcceptCallback Start3
    [4640] Socket#49538252::EndAccept(AcceptAsyncResult#39421196)
    in connect WHILE 4
    [17872] Socket#40528290::BeginAccept()
    [17872] Exiting Socket#40528290::BeginAccept()  -> AcceptAsyncResult#8948635
    //ERROR THROWN HERE
    AcceptCallback End 3

使用 netstat 进行监控

服务启动时出现这个，表示服务正在监听10002端口

    TCP    0.0.0.0:10002 LON-WKS-ZER01:0      LISTENING

第一次和第二次扫描(即成功)一切正常。测试网络应用程序连接，发送“扫描文本”，各种回调委托(delegate)被触发，我们得到了很好的回复。

Netstat 在第一次测试期间，建立连接后:

    TCP    0.0.0.0:10002          LON-WKS-ZER01:0      LISTENING
    TCP    127.0.0.1:10002        apps:59574             ESTABLISHED
    TCP    127.0.0.1:59574        apps:10002             ESTABLISHED

(然后扫描#1完成)

调用 testApp mTCP.Close() 时，状态变为 CLOSE_WAIT 和 FIN_WAIT_2

   TCP    0.0.0.0:10002          LON-WKS-ZER01:0      LISTENING
   TCP    127.0.0.1:10002        apps:59574             CLOSE_WAIT
   TCP    127.0.0.1:59574        apps:10002             FIN_WAIT_2

几分钟后，CLOSE 和 FIN 连接消失，但仍有 LISTENER

 TCP    0.0.0.0:10002          LON-WKS-ZER01:0      LISTENING

接下来，发送scan#2，它重复上述序列，结果成功。

在第三次扫描中，当它尝试建立新连接时，在 AcceptCallback 的这一行中抛出异常:

clntSock = servSock.ClntSock.EndAccept(asyncResult)

具体来说，它是一个 ArgumentException，“asyncResult 不是通过调用 BeginAccept 创建的”(参见 EndAccept)

因此，由于我无法理解的原因，第三次测试的 IASyncResult 导致 EndAccept 方法抛出 ArgumentException。

总结一下这个错误 - Connect 调用的 BeginAccept 为 AcceptCallback 设置了一个委托(delegate)并传递了一个 IASyncResult。 AcceptCallBacks EndAccept 引发 ArgumentException

我意识到做事的方式不是很最新，我们最好用别的东西，但是一件事又另一件事(时间，资源)我需要尝试使轻微的适应工作。但我不明白为什么(现有客户端应用程序)连接、扫描、扫描、扫描、扫描等工作，但(网络应用程序)连接、扫描、断开连接、连接、扫描、断开连接在第三次扫描连接时失败

在此先感谢您的任何建议。

Answer 1

有人提出并回答了类似的问题 here

... you are holding the socket object in a class-scoped variable. So, if somehow the socket gets disconnected while the ReadCallback is executing and you reconnect it (thereby changing the socket object) - now they don't match, you are trying to complete the Async request using the new object when the old one is the one actually completing.

在您的情况下，它是变量 cState .在 Connect方法，如果您只是声明 cState 的新实例在本地保存套接字，则错误可能会停止发生。

Dim clientState As  New ClientState(servSock)
clientState.ClntSock.Bind(New IPEndPoint(System.Net.IPAddress.Any, TCPPort))
clientState.ClntSock.Listen(Backlog)

While True
    Dim result As IAsyncResult = servSock.BeginAccept(New AsyncCallback(AddressOf AcceptCallback), clientState)
    result.AsyncWaitHandle.WaitOne()
End While

还有， mTCP应该放在客户端。