Question about pipeline progress indicator

[RaelB 4]

Hi,

I have a simple pipeline, that takes in a list of 20 items, and has one stage. For each item, the stage waits 1 second, and then sends a message to the main UI, which will add the item to a Memo, and update a ProgressBar.

 

The code is looking like this:

procedure TForm1.AddDownloadItems;
var
  DownloadItem: TDownloadItem;
  I: Integer;
begin
  for I := 0 to 19 do
  begin
    DownloadItem := TDownloadItem.Create;
    DownloadItem.Id := I;
    FDownloadItems.Add(DownloadItem);
  end;
end;

procedure TForm1.Stage1(const input, output: IOmniBlockingCollection; const
  Task: IOmniTask);
var
  Item: TDownloadItem;
  InputItem: TOmniValue;
begin
  for InputItem in Input do
  begin
    Item := TDownloadItem(InputItem.AsObject);
    Sleep(1000);
    Task.Comm.Send(0, Item.Id);
    Output.Add(InputItem);
  end;
end;

procedure TForm1.UpdateProgress(const task: IOmniTaskControl; const msg: TOmniMessage);
begin
  Inc(Progress);
  Memo1.Lines.Add(msg.MsgData.AsString);
  ProgressBar1.Position := Progress;
end;

procedure TForm1.GetDownloadsPipline;
var
  Item: TDownloadItem;
begin
  { ====== Start Pipeline ========= }

  Screen.Cursor := crHourGlass;
  StartTime := GetTickCount;
  FPipeline := Parallel.Pipeline
    .Stage(Stage1, Parallel.TaskConfig.OnMessage(UpdateProgress)).NumTasks(4) //Environment.Process.Affinity.Count)
    .OnStop(
      procedure
      begin
        PostMessage(Form1.Handle, WM_STOPPED, 0, 0);
      end)
    .Run;

  Self.AddDownloadItems;
  for Item in FDownloadItems do
    FPipeline.Input.Add(Item);
  FPipeline.Input.CompleteAdding;
end;

When the program runs, a few items get added to the Memo, and only afterwards the progressbar updates. This seems strange. I would expect the progress bar to update simultaneously with the memo. Please see attached video. Any ideas?

 

Thanks