procedure TForm1.Button1Click(Sender: TObject);
var
  task: ITask;
begin
  FAccessor.Enter();
  try
    if (FWorkInProgress) then Exit;
    FWorkInProgress := true;
  finally
    FAccessor.Leave();
  end;

  FNeedShowText := cbShowText.Checked;
  task := TTask.Create(procedure()
var
  html: TStrings;
begin
  html := TStringList.Create();
  try
    TThread.Synchronize(nil, procedure()
    begin
      Memo1.Lines.Clear();
    end);
    clHttp1.Get(edtUrl.Text, html);

    if FNeedShowText then
    begin
      clHtmlParser1.Parse(html);
    end else
    begin
      TThread.Synchronize(nil, procedure()
      begin
        Memo1.Lines.Assign(html);
      end);
    end;

  finally
    FAccessor.Enter();
    try
      FWorkInProgress := False;
    finally
      FAccessor.Leave();
    end;
    html.Free();
  end;
end);
  task.Start();
end;

procedure TForm1.FormCloseQuery(Sender: TObject; var CanClose: Boolean);
begin
 FAccessor.Enter();
  try
    if (FWorkInProgress) then
    begin
      ShowMessage('The work is in progress, cannot close the program.');
      CanClose := False;
    end;
  finally
    FAccessor.Leave();
  end;
end;

procedure TForm1.clHtmlParser1ParseTag(Sender: TObject; ATag: TclHtmlTag);
begin
  if (Trim(ATag.Text) <> '') then
  TThread.Synchronize(nil, procedure()
  begin
    Memo1.Lines.Add(ATag.Text);
  end);
end;