Adding call to sleep blocks stage in pipeline

[RaelB 4]

In the SimplePipeline project (from HL-III presentation), if I add a call to sleep in AddOne stage, the program (i.e. UI) blocks for 5 seconds.

 

procedure AddOne(const input, output: IOmniBlockingCollection);
var
  v: TOmniValue;
begin
  for v in input do
  begin
    output.Add(v.AsInteger + 1);
    Sleep(1000);
  end;
end;

I would expect this to not block the UI, since it is running in a Thread/Task?

[Primož Gabrijelčič 218]

SimplePipeline is, well, simple. This is the TButton event handler:

procedure TfrmSimplePipeline.btnPipelineClick(Sender: TObject);
var
  pipeline: IOmniPipeline;
  i: Integer;
  v: TOmniValue;
begin
  pipeline := Parallel.Pipeline;
  pipeline.Stage(AddOne);
  pipeline.Stage(Invert);
  pipeline.Run;

  for i := 1 to 5 do
    pipeline.Input.Add(i);
  pipeline.Input.CompleteAdding;

  for v in pipeline.Output do
    lbLog.Items.Add(Format('%.3f', [v.AsDouble]));

  pipeline := nil;
end;

As you can see, the code starts the pipeline and then runs the loop that processes the results. This loop is run in a main thread and therefore blocks the UI. If you slow down the pipeline, it needs more time to generate the results and UI is blocked.

[RaelB 4]

Thanks, got it.