start

# File activesupport/lib/active_support/evented_file_update_checker.rb, line 113
      def start
        normalize_dirs!
        @dtw, @missing = [*@dtw, *@missing].partition(&:exist?)
        @listener = @dtw.any? ? Listen.to(*@dtw, &method(:changed)) : nil
        @listener&.start

        # Wait for the listener to be ready to avoid race conditions
        # Unfortunately this isn't quite enough on macOS because the Darwin backend
        # has an extra private thread we can't wait on.
        @listener&.wait_for_state(:processing_events)
      end