delayed_render

# File actionview/lib/action_view/renderer/streaming_template_renderer.rb, line 59
    def delayed_render(buffer, template, layout, view, locals)
      # Wrap the given buffer in the StreamingBuffer and pass it to the
      # underlying template handler. Now, every time something is concatenated
      # to the buffer, it is not appended to an array, but streamed straight
      # to the client.
      output  = ActionView::StreamingBuffer.new(buffer)
      yielder = lambda { |*name| view._layout_for(*name) }

      instrument(:template, :identifier => template.identifier, :layout => layout.try(:virtual_path)) do
        fiber = Fiber.new do
          if layout
            layout.render(view, locals, output, &yielder)
          else
            # If you don't have a layout, just render the thing
            # and concatenate the final result. This is the same
            # as a layout with just <%= yield %>
            output.safe_concat view._layout_for
          end
        end

        # Set the view flow to support streaming. It will be aware
        # when to stop rendering the layout because it needs to search
        # something in the template and vice-versa.
        view.view_flow = StreamingFlow.new(view, fiber)

        # Yo! Start the fiber!
        fiber.resume

        # If the fiber is still alive, it means we need something
        # from the template, so start rendering it. If not, it means
        # the layout exited without requiring anything from the template.
        if fiber.alive?
          content = template.render(view, locals, &yielder)

          # Once rendering the template is done, sets its content in the :layout key.
          view.view_flow.set(:layout, content)

          # In case the layout continues yielding, we need to resume
          # the fiber until all yields are handled.
          fiber.resume while fiber.alive?
        end
      end
    end