@Override
  public void handleHistoryUpdated() {
    synchronized (this) {
      update_needed = true;
    }

    draw_area.repaint();
  }
  /** ***************************************************************************** */
  @Override
  public void handleHistoryStarted() {
    synchronized (this) {
      update_needed = true;
      restart_needed = true;
      thread_colors.clear();
    }

    draw_area.repaint();
  }