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[Qmodem]

What is the correct procedure to terminate tasks if you need to cancel what they are doing?

I have a procedure that starts two tasks that can take 20-30 seconds each as they each process a dataset and create an output file.  If I want to cancel the output and close the dialog I have coded this in my formclosequery:

Code: [Select]

procedure TCCC100.FormCloseQuery(
  Sender       : TObject;
  var CanClose : Boolean);
begin
  inherited;
  GlobalOmniThreadPool.CancelAll;

  if Assigned(InventoryTask) then
    InventoryTask.Terminate;

  if Assigned(PartTask) then
    PartTask.Terminate;

  if Assigned(CountTasks) then
    while CountTasks.Value > 0 do
      Application.ProcessMessages;

  PartTask      := nil;
  InventoryTask := nil;
  Terminated    := true;
end;

The dialog gets stuck in an endless loop waiting for CountTasks.Value to reach 0;

The task is setup as such:

Code: [Select]

  InventoryTask := CreateTask(LoadInventoryRecords, 'LoadInventoryRecords')
    .OnMessage(InventoryHandleTaskMessage)
    .OnTerminated(InventoryHandleTaskTerminated)
    .SetParameter('TaskNumber', 1)
    .Schedule(GlobalOmniThreadPool);

and the OnTerminate method is:

Code: [Select]

procedure TCCC100.InventoryHandleTaskTerminated(
  const task : IOmniTaskControl);
begin
  LogMessages(Format('[%d/%s] %d|%s', [task.UniqueID, task.Name, 1, 'Inventory finished.']));
  CountTasks.Decrement;
end;

When the FormCloseQuery calls InventoryTask.Terminate, does that not tell the task to run its Terminated method and then decrement CountTasks as shown above? From what I can tell, it skips the OnTerminate method so i get stuck in the loop.  If I comment out the loop waiting for CountTasks to reach zero, I get an exception when I assign nil to the two tasks created.

Guess I need a lesson in cleaning up tasks!

Thanks in advance.

John

[Primoz Gabrijelcic]

You are doing everything by the book but you have stumbled upon a bug. I'll fix it as soon as possible - but first I have to understand what the real cause of the problem is.

For the time being, a workaround would be to call CountTasks.Decrement as a last thing in LoadInventoryRecords method (and other task methods).

[Primoz Gabrijelcic]

Fixed in the SVN. Thanks for finding this problem, it was a nasty one.

[Qmodem]

Thank you.  I will update from SVN and test today.

Cheers!

John

[Primoz Gabrijelcic]

Please report back with results.

[Qmodem]

I just tested the fix and it works perfectly.

Thanks again.

John

[Primoz Gabrijelcic]

Great! Again, thanks for the report - this bug would have bitten me sooner or later.