Multithreading cancellation Methode

Multithreading cancellation Methode

• RookieDBA

  Hi Freddy

  I am not familiar with the background worker class, but you seem to be suggesting that the worker thread is tied up in the database and therefore not actually 'running'.  If this is the case, I'd recommend you control the worker thread yourself and terminate it manually.

  You can spawn a worker thread yourself, and you can abort the thread manually which will raise an exception in the worker method (ThreadAbortException) that you can trap.  Note that the operation of closing a thread is not inherently synchronous, hence the call to the Join method. 

  It may not be the exact pattern you need but hopefully it is something that you may be able to consider/tweak.

  Private wt As Threading.Thread

  Private syncRoot As New Object

  Sub StartWork()

  SyncLock syncRoot

  wt = New Threading.Thread(AddressOf Me.DoWork)

  wt.IsBackground = True

  wt.Start()

  End SyncLock

  End Sub

  Sub StopIfWorking()

  SyncLock syncRoot

  If wt IsNot Nothing Then

  wt.Abort() : Threading.Thread.CurrentThread.Join(timeout)

  wt = Nothing

  End If

  End SyncLock

  End Sub

  Sub DoWork()

  Try

  Catch ex As Threading.ThreadAbortException

  End Try

  End Sub

  Richard

  
  

• karthik asok

  You could put an IF statement where it could check fairly often whether there's a cancelation pending. Maybe something like:

  For intK = 1 To 20
  If Worker.CancellationPending = True then
  e.Cancel = True
  SomeBooleanVariableForCancel = True 'maybe use a boolean so the other loops know the action's been cancelled
  e.Cancel = True
  Exit For
  Else
  counter = counter + 1
  'DO SOMETHING HERE
  End If
  Next
  Worker.ReportProgress(counter / 8000 * 100)

  In the RunWorkerCompleted routine, you can then check the e.Cancelled value to see if you had set it in the DoWork loop, and if it's set, process the cancelation accordingly.

  I haven't played with connecting to a database, but my guess is that you could do something similar:

  If Worker.CancellationPending = True then
  'Do the cancel stuff
  Else
  objDataTable = (Query to the huge database)
  End If

  Your main thread that started the background worker can trigger off the cancel button click to generate the BackgroundWorker.CancelAsync() that sets the CancellationPending flag to true.

  
  

• Sundararajan

  Dear Richard,I have try your methods, and it works like charming.Thank you very much.I do some experiment with your method with my second case.Your method can cancel a long thread that has been branch to database too.Superb....Regards,Freddy
  

• rKarthik

  dear Richard,
  Yeah, I try your solution it is work for my first case.
  But still i got problem report to progress bar since the thread is not interference with other ( thread safe).Here is my problem.
  Private Sub DoWork1()
  Try
  Dim objConnection As OleDbConnection
  Dim objCommand As OleDbCommand
  Dim intI As Integer
  Dim intJ As Integer
  Dim intK As Integer
  Dim counter As Integer
  objConnection = New OleDbConnection(vConnString)
  objConnection.Open()
  objCommand = objConnection.CreateCommand
  For intI = 1 To 20
  For intJ = 1 To 20
  For intK = 1 To 20
  counter = counter + 1
  Try
  objCommand.CommandText = "INSERT INTO tblTest(col1,col2,col3) VALUES " & _
  "('" & intI & "','" & intJ & "','" & intK & "')"
  objCommand.ExecuteNonQuery()
  Catch ex As Exception
  MessageBox.Show("Thread is closing")
  End Try
  Next
  ProgressBar1.Value = counter / 8000 * 100 <==== this is my error
  Next
  Next
  objConnection.Close()
  Catch ex As Threading.ThreadAbortException
  MessageBox.Show(ex.ToString)
  End Try
  End Sub
  
  Are there any solution
  Still the second case has no solution.If the thread query to a huge DB.How to cancel the thread.
  Are there any suggestion
  
  Dears,
  Freddy
  
  
  
  
  

• Glyn Darkin

  Hi Freddy

  I'm not 100% sure what you are asking. Hopefully, some of the following will prove relevant and make sense to you.

  DoWork1 is presumably running on a background thread. This means that it cannot interact directly with the progress bar as it is not the thread that created that control. What you need to do, is update the progress bar through another method and call that method via a delegate that is passed to the Invoke method of the progress control. Something like this should help ....

  private delegate sub updateprogressbardelegate (byval value as double)

  private sub updateprogressbar(byval value as double)

  if progressbar.invokerequired then

  progressbar.invoke(new updateprogressbardelegate(addressof updateprogressbar), value)

  else : progressbar.value = value

  end if

  end sub

  Simply replace the call to the setter ProgressBar1.Value = XXX to call the update progress bar method instead.

  If the above is not what you were looking for, please let me know and I will try to help.

  Richard

  
  

• Kapoulkine Arseny

  I have done your cancelation style in my first case, but still i got the thread is finished.Why the thread is not cancelled if we do "e.cancel = true"For the second case I observe the other system we used, that is SAP.SAP provide thread to DB cancellation via GUID(SM50).Is there anyone who know this in VS2005 area Thank you
  
• Multithreading cancellation Methode