I read from a serialport using a worker thread. Because the worker thread t
does not loop often, I cannot wait to terminate the worker thread using a
boolean in the While condition.
So I have a StopReader() method that simply aborts the worker thread (is
there a better way for the above situation?).
The StopReader creates an ObjectDisposedE xception when calling t.Abort(). WHY?
Public Sub StopReader()
'stop the thread running the reader code and wait for the stop to
complete
Try
If Not Me.stoppedReadi ng Then
If t.IsAlive AndAlso t IsNot Thread.CurrentT hread Then
t.Abort()
'=THIS Abort() CREATES "OBJECT DISPOSED EXCEPTION - Safe handle has been
disposed"
t.Join()
End If
End If
Catch ex As ThreadStateExce ption
Console.WriteLi ne("StopReader : ThreadStateExce ption")
Catch ex As Exception
Console.WriteLi ne("StopReader : " & ex.message)
Finally
Me.stoppedReadi ng = True 'flag that we stopped the reader
worker already
End Try
End Sub
Fine, so I include the lines:
Catch ex As ObjectDisposedE xception
Console.WriteLi ne("StopReader : ObjectDisposedE xception")
however the messages reappears and the catch doesn't work.
Here is the complete code:
Imports System.IO
Imports System.IO.Ports
Imports System.Threadin g
Public Class SerialPortReade r
Implements IDisposable
Private disposedValue As Boolean = False ' To detect redundant
calls
Private stoppedReading As Boolean = False ' false = reader is
working
Dim myPort As SerialPort
Dim t As Thread 'worker thread for reader
Public Sub New()
Try
'create, configure and open a serial port
myPort = New SerialPort("COM 4")
With myPort
.BaudRate = 9600
.DataBits = 8
.Parity = Parity.None
.StopBits = StopBits.One
.Handshake = Handshake.None
.DtrEnable = True
.Encoding = System.Text.Enc oding.UTF8
End With
myPort.Open()
'delete old data
myPort.DiscardO utBuffer()
myPort.DiscardI nBuffer()
'Catch ex As UnauthorizedAcc essException
'this happens sometimes and is a confirmed bug (not an issue
here).
Catch ex As Exception
Console.WriteLi ne("Constructor : Thread abort exception.")
Finally
End Try
End Sub
Public Sub StartReader()
'set up a worker thread to read from the serial port
t = New Thread(AddressO f ReceiveWorker)
t.Start()
End Sub
Public Sub StopReader()
'stop the thread running the reader code and wait for the stop to
complete
Try
If Not Me.stoppedReadi ng Then
If t.IsAlive AndAlso t IsNot Thread.CurrentT hread Then
t.Abort() 'THIS CREATES "OBJECT DISPOSED EXCEPTION -
Safe handle has been disposed"
t.Join()
End If
End If
Catch ex As ObjectDisposedE xception 'doesn't catch the exception
Console.WriteLi ne("StopReader : ObjectDisposedE xception")
Catch ex As ThreadStateExce ption
Console.WriteLi ne("StopReader : ThreadStateExce ption")
Catch ex As Exception
Console.WriteLi ne("StopReader : " & ex.message)
Finally
Me.stoppedReadi ng = True 'flag that we stopped the reader
worker already
End Try
End Sub
Public Sub ReceiveWorker()
'loop endlessly reading bytes from serial port
Dim myByte As Byte
Try
While (True)
myByte = CType(myPort.Re adByte, Byte) 'read
transparently from serial port
'... process received byte
End While
Catch ex As ThreadAbortExce ption
Console.WriteLi ne("ReceiveWork er: Thread abort exception.")
Catch ex As Exception
Console.WriteLi ne("ReceiveWork er: other exception.")
Finally
End Try
End Sub
#Region " IDisposable Support "
' IDisposable
Protected Overridable Sub Dispose(ByVal disposing As Boolean)
If Not Me.disposedValu e Then
If disposing Then
' TODO: free managed resources when explicitly called
If Not IsNothing(myPor t) Then
If Not Me.stoppedReadi ng Then StopReader()
myPort.Dispose( )
End If
End If
' TODO: free shared unmanaged resources
End If
Me.disposedValu e = True
End Sub
' This code added by Visual Basic to correctly implement the disposable
pattern.
Public Sub Dispose() Implements IDisposable.Dis pose
' Do not change this code. Put cleanup code in Dispose(ByVal
disposing As Boolean) above.
Dispose(True)
GC.SuppressFina lize(Me)
End Sub
#End Region
End Class
Thank you very much. herbert
