I have tried to upload +100 files to azure with Delphi. However, the calls block the main thread, so I want to do this with a async call or with a background thread.

This is what I do now (like explained here):

procedure TCloudManager.UploadTask(const input: TOmniValue;
  var output: TOmniValue);
var
  FileTask:TFileTask;
begin
  FileTask := input.AsRecord<TFileTask>;

  Upload(FileTask.BaseFolder, FileTask.LocalFile, FileTask.CloudFile);
end;

function TCloudManager.MassiveUpload(const BaseFolder: String;
  Files: TDictionary<String, String>): TStringList;
var
  pipeline: IOmniPipeline;
  FileInfo : TPair<String,String>;
  FileTask:TFileTask;
begin
  // set up pipeline
  pipeline := Parallel.Pipeline
    .Stage(UploadTask)
    .NumTasks(Environment.Process.Affinity.Count * 2)
    .Run;
  // insert URLs to be retrieved
  for FileInfo in Files do
  begin
    FileTask.LocalFile := FileInfo.Key;
    FileTask.CloudFile := FileInfo.Value;
    FileTask.BaseFolder := BaseFolder;

    pipeline.Input.Add(TOmniValue.FromRecord(FileTask));
  end;//for

  pipeline.Input.CompleteAdding;

  // wait for pipeline to complete
  pipeline.WaitFor(INFINITE);
end;

However this block too (why? I don't understand).