.Net 4.0 Async Serial Comm - exception: “The I/O operation has been aborted because of either a thread exit or an application request”

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VB

.NET

.NET4

communication

As I've encountered an advice not to use the SerialPort.DataReceived event, nor the BytesToRead() (www.sparxeng.com/blog/software/must-use-net-system-io-ports-serialport), I am trying to implement a reader from a serial port with BeginRead & End Read. When the application reached the line:

Dim numBytesRead As Integer = Me._stream.EndRead(ar)

the following exception occurs:
System.IO.IOException: The I/O operation has been aborted because of either a thread exit or an application request.
at System.IO.Ports.InternalResources.WinIOError(Int32 errorCode, String str)
at System.IO.Ports.SerialStream.EndRead(IAsyncResult asyncResult)
at X_SerialComm.CSerialCommMng.ReadCallback(IAsyncResult ar)
That's where I need your assistance.
Thanks for any advice,
Amir

The full code:

Imports System.IO
Imports System.IO.Ports
Public Class CSerialCommMng
   Public WithEvents m_port As SerialPort
   Private _readBuffer(20000) As Byte
   Private _stream As Stream
   '
   Public Sub New(pName As String)
        Try
            m_portName = pName
            If m_port IsNot Nothing Then
                If m_port.IsOpen Then
                    ClosePort()
                End If
                m_port = Nothing
            End If
            m_port = New SerialPort(pName)
            _stream = m_port.BaseStream
            SetPortAttrb() ' baudRate, stopBit, ect
        Catch ex As Exception
            RaiseEvent PortDoesNotExists(m_portName)
            m_portName = ""
        End Try
    End Sub
    Public Function Open() As Boolean
            If m_port Is Nothing Then
                RaiseEvent PortClosed()
                Return False
            End If
            If m_port.IsOpen Then Return True
            With m_port
                GC.SuppressFinalize(m_port)
                .Open()
                Thread.Sleep(10)
                GC.SuppressFinalize(.BaseStream)
            End With
            ReadFromSerial() 
            Return True
    End Function
    Private Sub ReadFromSerial()
            Dim response As New CommsResponse()
            Me._stream.BeginRead(Me._readBuffer, 0, Me._readBuffer.Length, New AsyncCallback(AddressOf Me.ReadCallback), response)
    End Sub
    Private Sub ReadCallback(ar As IAsyncResult)
        Try
            Dim numBytesRead As Integer = Me._stream.EndRead(ar)
            If numBytesRead > 0 Then
                HandleText(Me._readBuffer) ' which raises the relevant event
            End If
        Catch ex As IOException
            Console.WriteLine("-cb- rcv serial 1: " & ex.ToString)
        Catch ex As ObjectDisposedException
            Console.WriteLine("-cb- rcv serial 2: " & ex.ToString)
        End Try
    End Sub
    Private Class CommsResponse
        Implements IAsyncResult
        Private ReadOnly _state As Object
        Private _isCompleted As [Boolean]
        Private ReadOnly _locker As Object = New Object()
        Private _evt As ManualResetEvent
        Public ReadOnly Property AsyncState As Object Implements IAsyncResult.AsyncState
            Get
                Return _state
            End Get
        End Property
        Public ReadOnly Property AsyncWaitHandle As WaitHandle Implements IAsyncResult.AsyncWaitHandle
            Get
                Return GetEvtHandle()
            End Get
        End Property
        Public ReadOnly Property CompletedSynchronously As Boolean Implements IAsyncResult.CompletedSynchronously
            Get
                Return False
            End Get
        End Property
        Public ReadOnly Property IsCompleted As Boolean Implements IAsyncResult.IsCompleted
            Get
                Return _isCompleted
            End Get
        End Property
        Private Function GetEvtHandle() As ManualResetEvent
            SyncLock _locker
                If _evt Is Nothing Then
                    _evt = New ManualResetEvent(False)
                End If
                If _isCompleted Then
                    _evt.[Set]()
                End If
            End SyncLock
            Return _evt
        End Function
    End Class
End Class