cancel System.Threading.Tasks.Task on Form_closing

[LuckyLuke82]

Hi,

I run a new thread on Form1_Load, like this:

   Private cancel_task As New CancellationTokenSource
   Private new_task As Task
  
 Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
       
       '....some code before calling new thread - not relevant IMHO

        cancel_task = New CancellationTokenSource

        new_task = Task.Factory.StartNew(Sub() Get_Data(SQL), cancel_task.Token)

  End Sub

Task in another thread fills Datatable, and I need to cancel that if user closes Form1. I tried this but It doesn't work, I receive error "Invoke or BeginInvoke cannot be called on a control until the window handle has been created.in at System.Windows.Forms.Control.MarshaledInvoke(Control caller, Delegate method, Object[] args, Boolean synchronous)
at System.Windows.Forms.Control.BeginInvoke(Delegate method, Object[] args)" :

  Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        
        cancel_task.Cancel()
      
    End Sub

I'm not sure If I correctly assigned CancellationToken to Task, or If problem is that inside called Sub() I invoke back to UI thread (in order to bind filled datatable to Datagridview). Or If I'm missing
something in that Sub() which is called from new thread. Here is my Get_Data Sub():

 Sub Get_Data(ByVal Sql As String)

        'Fill dataTable
        Try

            Using conn = New OracleConnection(conn_string)
       

                Using cmd As OracleCommand = New OracleCommand("my_stored_procedure")
                    cmd.Connection = conn
                    cmd.CommandType = CommandType.StoredProcedure

                    cmd.Parameters.Add(New OracleParameter("SqL_query", OracleDbType.NVarchar2) With {
                    .Direction = ParameterDirection.Input,
                    .Value = Sql})

                    cmd.Parameters.Add(New OracleParameter("result", OracleDbType.RefCursor)).Direction = ParameterDirection.Output

                     Using da As New OracleDataAdapter
                            da.SelectCommand = cmd
                            da.Fill(dt) '- global datatable
                     End Using


                    'back to UI thread and set Datagridview datasource to filled datatable
                     Me.BeginInvoke(Sub() Bind_Datagrid())

           Catch ex As Exception
            Console.WriteLine(ex.Message + "in " + ex.StackTrace)
        End Try

    End Sub

Can somebody tell me how to properly cancel working thread ? Thanks in advance !

[LuckyLuke82]

I think I solved my problem. I was missing a lines in Get_Data:

Sub Get_Data(ByVal Sql As String)

        'Fill dataTable
        Try

            Using conn = New OracleConnection(conn_string)
       

                Using cmd As OracleCommand = New OracleCommand("my_stored_procedure")
                    cmd.Connection = conn
                    cmd.CommandType = CommandType.StoredProcedure

                    cmd.Parameters.Add(New OracleParameter("SqL_query", OracleDbType.NVarchar2) With {
                    .Direction = ParameterDirection.Input,
                    .Value = Sql})

                    cmd.Parameters.Add(New OracleParameter("result", OracleDbType.RefCursor)).Direction = ParameterDirection.Output

                     Using da As New OracleDataAdapter
                            da.SelectCommand = cmd
                            da.Fill(dt) '- global datatable
                     End Using
                   
                       If cancel_task.IsCancellationRequested Then 'This lines are added
                        Console.WriteLine("thread ended...")
                        cmd.Cancel()
                        dt.Rows.Clear()
                        Exit Sub
                       End If

                    'back to UI thread and set Datagridview datasource to filled datatable
                     Me.BeginInvoke(Sub() Bind_Datagrid())
                  End using
           Catch ex As Exception
            Console.WriteLine(ex.Message + "in " + ex.StackTrace)
        End Try

    End Sub

Please correct me If I'm wrong, but this ends async thread If close Form before Datagridview is bounded with Datatable, which is exactly what I want.