Step through app, stop, restart, now get "Only one useage of socket permitted"

So I'm opening a TCPListener on socket 8000. Debugging code, finding bugs, stopping the app and debugging again.

Somehow I'm causing a problem such that it's not closing the TCP port, and it's causing a major problem such that even after I stop my program and restart it the code to open the TCP port the app is still throwing an exception, and it keeps happening until I reboot.

It's going to be real hard to find the bug when I have to reboot each time to debug the app!

I used netstat -b and it does Not show port 8000 open.

Of course I can try changing the port each time I run the app... But I really want to know why the app is still throwing an exception on a fresh run and netstat doesn't show the port open?

Help. And Thanks!

I've found it only happens if Stop the program using the Stop button in Visual Studio Or if my application terminates without first executing the code that closes the TCPListener. If my program exits properly it does not occur.

Edit: Shouldn't the built-in garbage collection handle closing the port properly when an unexpected termination occurs where I have no way of handling the termination (such as an End Task)?

Where is the code that closes the listener located?

I can't say that I have ever had this problem, though that might be that I don't use TCP much, but I have used UDP a fair amount, and that listens to ports, and has a similar issue. In my case, the easiest solution was to change a setting on the socket such that there can be multiple shared users of the same port. I had to do that because I had multiple modules communicating via UDP on the same port on the same computer. That solution might work for you (it can be found by searching the networking forum for threads started by me, and having the word UDP, it is the thread with 7-8 replies).

However, that's not a good solution in this case, because you have an actual problem, and getting around the problem by sharing a port is nothing but a hack (and not the super moderator here, either). A better solution would be to solve the problem, which is why I asked that first question. If your TCP is in a class, then does it implement IDisposable, and is the socket closing code in the Dispose method? If not, then I think it should be, or at least the Dispose method should ensure that the socket is closed.

Quote:

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Originally Posted by Shaggy Hiker

Where is the code that closes the listener located?

I can't say that I have ever had this problem, though that might be that I don't use TCP much, but I have used UDP a fair amount, and that listens to ports, and has a similar issue. In my case, the easiest solution was to change a setting on the socket such that there can be multiple shared users of the same port. I had to do that because I had multiple modules communicating via UDP on the same port on the same computer. That solution might work for you (it can be found by searching the networking forum for threads started by me, and having the word UDP, it is the thread with 7-8 replies).

However, that's not a good solution in this case, because you have an actual problem, and getting around the problem by sharing a port is nothing but a hack (and not the super moderator here, either). A better solution would be to solve the problem, which is why I asked that first question. If your TCP is in a class, then does it implement IDisposable, and is the socket closing code in the Dispose method? If not, then I think it should be, or at least the Dispose method should ensure that the socket is closed.

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I'm checking and closing the socket in 2 places:
1) At a subroutine that handles application exit
2) The socket runs in a thread, and I have a ThreadDone event which gets triggered when the thread completes, which also closes the socket.

Yes, the socket is in a class. No, I've not implemented IDisposable. I've never used it before cause I didn't know why I would want to use it... I guess now I know one reason ;)

So in IDisposable, basically I'll just check if tcplistener is nothing and if not, close it? Seems easy enough.

Thanks!

Looking at this link: http://msdn.microsoft.com/en-us/libr...isposable.aspx

I'm trying to understand Dispose... But it looks like if I implement it I also have to manually dispose of all managed resources too?

I REALLY need some help with this same issue. I've tried everything I can think of, and nothing is working.

Here's some basic code, and what happens is that if it crashes or the program in any way stops unexpectedly, then run the program again, I get the error "Only one useage of socket permitted". However the socket is NOT open! Netstat -b does Not list the port. Even if I then exit the program properly (which calls oComms.Stop()) I still get the error the next time I run the program. Note that this code has been cut down to make it easier to read...

I have even tried implementing idisposable to no avail.

Code:

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In main form:
    Dim oThread
    Dim oComms
    Public Sub StartThread()
        If oComms Is Nothing Then
            oComms= New myDataComms()
        End If
        'exit sub if thread already running and not done
        If Not oThread Is Nothing Then
            If oThread.ThreadState = ThreadState.Running Or oThread.ThreadState = ThreadState.Suspended Or oThread.ThreadState = ThreadState.WaitSleepJoin Then
                Exit Sub
            End If
        End If
        oThread = New Thread(AddressOf oComms.Listen)
        oComms.run = True
        oThread.Start()
    End Sub

Public Class myDataComms
    'Implements IDisposable
    Private disposed As Boolean = False

    Dim tcpListener As TcpListener
    Dim tcpClient As TcpClient
    Dim networkStream As NetworkStream
    Public run As Boolean = False
    Public Event ThreadProcess()
    Public Event ThreadDone()

    Public Sub Stop()
        run = False
        If (Not IsNothing(tcpListener)) Then
            Try
                If tcpListener.Server.IsBound Then
                    tcpListener.Server.Close()
                End If
            Catch ex As Exception
            End Try
            tcpListener.Stop()
        End If
        If (Not IsNothing(networkStream)) Then
            networkStream.Close()
        End If
        If (Not IsNothing(tcpClient)) Then
            tcpClient.Close()
        End If
    End Sub
    Public Sub Listen()
        Try
            tcpListener = New TcpListener(IPAddress.Any, 8001)
            'tcpListener.ExclusiveAddressUse = True
            tcpListener.Start()
            While run
                If tcpListener.Pending Then
                    'Accept the pending client connection and return a TcpClient initialized for communication.
                    tcpClient = tcpListener.AcceptTcpClient()
                    ' Get the stream
                    networkStream = tcpClient.GetStream()
                    ' Read the stream into a byte array
                    Dim bytes(tcpClient.ReceiveBufferSize) As Byte
                    'networkStream.Read(bytes, 0, CInt(tcpClient.ReceiveBufferSize))
                    '' Return the data received from the client to the console.
                   
                    Dim myCompleteMessage As StringBuilder = New StringBuilder()

                    Do
                        numberOfBytesRead = networkStream.Read(bytes, 0, bytes.Length)
                        myCompleteMessage.AppendFormat("{0}", Encoding.ASCII.GetString(bytes, 0, numberOfBytesRead))
                    Loop While networkStream.DataAvailable

                    Dim responseString As String = "blah blah"
                            RaiseEvent ThreadProcess()
                        End If
                    Catch ex As Exception
                        responseString = "error"
                    End Try

                    Dim sendBytes As [Byte]() = Encoding.ASCII.GetBytes(responseString)
                    networkStream.Write(sendBytes, 0, sendBytes.Length)
                    'Any communication with the remote client using the TcpClient can go here.
                    'Close TcpListener and TcpClient.
                    networkStream.Close()
                    tcpClient.Close()
                End If
                Thread.Sleep(200)
            End While

        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
        RaiseEvent ThreadDone()
    End Sub
    '' Implement IDisposable.
    '' Do not make this method virtual.
    '' A derived class should not be able to override this method.
    'Public Overloads Sub Dispose() Implements IDisposable.Dispose
    '    Stop()
    '    Dispose(True)
    '    ' This object will be cleaned up by the Dispose method.
    '    ' Therefore, you should call GC.SupressFinalize to
    '    ' take this object off the finalization queue
    '    ' and prevent finalization code for this object
    '    ' from executing a second time.
    '    GC.SuppressFinalize(Me)
    'End Sub
    '' Dispose(bool disposing) executes in two distinct scenarios.
    '' If disposing equals true, the method has been called directly
    '' or indirectly by a user's code. Managed and unmanaged resources
    '' can be disposed.
    '' If disposing equals false, the method has been called by the
    '' runtime from inside the finalizer and you should not reference
    '' other objects. Only unmanaged resources can be disposed.
    'Private Overloads Sub Dispose(ByVal disposing As Boolean)
    '    ' Check to see if Dispose has already been called.
    '    If Not Me.disposed Then
    '        ' If disposing equals true, dispose all managed
    '        ' and unmanaged resources.
    '        If disposing Then
    '            ' Dispose managed resources.
    '        End If

    '        ' Call the appropriate methods to clean up
    '        ' unmanaged resources here.
    '        ' If disposing is false,
    '        ' only the following code is executed.
    '        Stop()

    '        ' Note disposing has been done.
    '        disposed = True

    '    End If
    'End Sub
    '' This finalizer will run only if the Dispose method
    '' does not get called.
    '' It gives your base class the opportunity to finalize.
    '' Do not provide finalize methods in types derived from this class.
    'Protected Overrides Sub Finalize()
    '    ' Do not re-create Dispose clean-up code here.
    '    ' Calling Dispose(false) is optimal in terms of
    '    ' readability and maintainability.
    '    Dispose(False)
    '    MyBase.Finalize()
    'End Sub

End Class

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Take a look at my TCP Client & Server class in my signature. I had a similar issue but I managed to solve it by doing a few different things.