Destroy Thread with 'aborted' state - vb.net

Question

Using background worker in a winform program. Also communicating with somedevices
I have a stop button which tries to stop the background worker thread, which works, but sometimes, the background worker thread remains in state "Aborted"
I have to mention that I take care about the exception that rise, and also use a 'Finally' block to stop the communication with the devices
I need to stop the thread immediately, something like an emergency button...
Some code:
Private Sub BtnStopTest_Click(sender As Object, e As EventArgs) Handles btnStopTest.Click
Try
stoppedTesting = True
Log("Stopping operations safely. (You might have to wait some time )", Color.Blue, New Font("Microsoft Sans Serif", 9, FontStyle.Bold))
If bgWorkThread IsNot Nothing Then
'stop thread
'if thread is sleeping (waiting for a time)
If bgWorkThread.ThreadState = ThreadState.Background + ThreadState.WaitSleepJoin Then
bgWorkThread.Interrupt()
Else 'if thread is working normally
bgWorker.CancelAsync()
tEO.DoWorkEventArgs.cancel = True
bgWorkThread.Abort()
'sometimes, here the Thread has state 'Aborted
End If
ElseIf bgWorkThread Is Nothing Then
Dim ee As New System.ComponentModel.RunWorkerCompletedEventArgs(New Object, Nothing, False)
BgWorker_RunWorkerCompleted(New Object, ee)
End If
Catch ex As Exception
Utils.PreserveStackTrace(ex)
Log("Error when stopping testing" & vbCrLf & Utils.ReadException(ex), MessageType.ErrorMessage)
End Try
End Sub
Private Sub BgWorker_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles bgWorker.DoWork
Try
'some other things to do
For Each testStep In stepList
Try
'main operations and communication with device
' below functions are all different
'something like:
'CommunicationWithDevice1()
'CommunicationWithDevice2()
'CommunicationWithDevice3()
'CommunicationWithDevice4()
'....
'CommunicationWithDevice20()
Catch ex As Exception When TypeOf ex Is ThreadAbortException OrElse TypeOf ex Is ThreadInterruptedException
Utils.PreserveStackTrace(ex)
Log("Exception in thread" & vbCrLf & Utils.ReadException(ex), MessageType.ErrorMessage)
e.Cancel = True
If ex.GetType = GetType(ThreadAbortException) Then Thread.ResetAbort()
If stoppedTesting Then Exit For
Catch ex As Exception
If stoppedTesting Then Exit For
End Try
Catch ex As Exception When TypeOf ex Is ThreadAbortException OrElse TypeOf ex Is ThreadInterruptedException
e.Cancel = True
Log("Background worker thread was interrupted!")
Log("Background worker thread was interrupted!", Color.Red, New Font("Microsoft Sans Serif", 9, FontStyle.Bold))
Catch ex As Exception
Utils.PreserveStackTrace(ex)
Log("Error when doing background work!" & vbCrLf & Utils.ReadException(ex), Color.Red, New Font("Microsoft Sans Serif", 9, FontStyle.Bold))
Finally
StopCommunication()
End Try
End Sub
What can I do to completely destroy the thread?
If there is not possibility, any workaround to exit my 'DoWork' method immediately?

Answer 1

BackgroundWorker.CancelAsync() does not cancel the thread immediately, it actually posts the STOP message on the queue as you can check the BackgroundWorker.isCancellationPending is set to true, if you want to cancel immediately, you could have a global boolean and set it if you can to cancel the thread. In your Do_Work() method, you can regularly check the boolean and if it is set, run Exit Sub.
Something like this should do
Else 'if thread is working normally
cancelThread = true
tEO.DoWorkEventArgs.cancel = True
and inside your Do_Work sub
For Each testStep In stepList
Try
If cancelThread Then
Exit Sub
This will cleanly stop the BackgroundWorker and allow you to run the RunWorkerCompleted routine. Inside it, you can check for the cancelThread to know if the BackgroundWorker ran successfully or it was aborted.
UPDATE 2
After going through your code one more time, why do you need to use BackgroundWorker and Thread together? If you want immediate cancellation, use only Thread. Also, you only need one TRY..Catch for the entire function, that way it will ensure that the thread exits. You can always assign the thread to nothing and Garbage Collector will take care of freeing resources for you(If you are concerned with ABORTED)
Dim myThread As Thread = new Thread(new ThreadStart(yourFunctionForCommunication))
myThread.Start()
And in your function
Try
.. Do your work
Catch Ex As ThreadAbortException
Exit Sub;
Finally
//Do your cleanup code here
End Try
The abort call
myThread.Abort()
While mythread.ThreadState <> ThreadState.Aborted
End While
myThread = Nothing
But I should warn you that Aborting threads is not a safe process. See this MSDN Post.
If you would still want to use Background worker, i would suggest you to look into List<dynamic>. Add all the Communicatewithdevice1()....to 20() there then use that in a loop, that way you would not have to write the If conditional 20 times. See the post Here