code: func (w *LogFile) Close() error {
  	w.mu.Lock()
  	defer w.mu.Unlock()
  	if w.closed {
  		return nil
  	}
  	if err := w.f.Close(); err != nil {
  		return err
  	}
  	w.closed = true
  	return nil
  }
docs: // Close closes underlying file and signals all readers to stop.