Use the new ActiveSupport::FileUpdateChecker instead of RoutesReloader.

actionpack/lib/action_dispatch/railtie.rb

@@ -10,7 +10,7 @@ class Railtie < Rails::Railtie
 
     # Prepare dispatcher callbacks and run 'prepare' callbacks
     initializer "action_dispatch.prepare_dispatcher" do |app|
-      ActionDispatch::Callbacks.to_prepare { app.routes_reloader.reload_if_changed }
+      ActionDispatch::Callbacks.to_prepare { app.routes_reloader.execute_if_updated }
     end
   end
 end
\ No newline at end of file

railties/lib/rails/application.rb

 require 'active_support/core_ext/hash/reverse_merge'
+require 'active_support/file_update_checker'
 require 'fileutils'
 require 'rails/plugin'
 require 'rails/engine'
@@ -46,7 +47,6 @@ class Application < Engine
     autoload :Configuration,  'rails/application/configuration'
     autoload :Finisher,       'rails/application/finisher'
     autoload :Railties,       'rails/application/railties'
-    autoload :RoutesReloader, 'rails/application/routes_reloader'
 
     class << self
       private :new
@@ -121,11 +121,18 @@ def railties
     end
 
     def routes_reloader
-      @routes_reloader ||= RoutesReloader.new
+      @routes_reloader ||= ActiveSupport::FileUpdateChecker.new([]){ reload_routes! }
     end
 
     def reload_routes!
-      routes_reloader.reload!
+      routes = Rails::Application.routes
+      routes.disable_clear_and_finalize = true
+
+      routes.clear!
+      routes_reloader.paths.each { |path| load(path) }
+      ActiveSupport.on_load(:action_controller) { routes.finalize! }
+    ensure
+      routes.disable_clear_and_finalize = false
     end
 
     def initialize!

railties/lib/rails/application/routes_reloader.rb

-module Rails
-  class Application
-    class RoutesReloader
-      attr_reader :paths
-
-      def initialize
-        @paths, @last_change_at = [], nil
-      end
-
-      def changed_at
-        routes_changed_at = nil
-
-        paths.each do |path|
-          config_changed_at = File.stat(path).mtime
-
-          if routes_changed_at.nil? || config_changed_at > routes_changed_at
-            routes_changed_at = config_changed_at
-          end
-        end
-
-        routes_changed_at
-      end
-
-      def reload!
-        routes = Rails::Application.routes
-        routes.disable_clear_and_finalize = true
-
-        routes.clear!
-        paths.each { |path| load(path) }
-        ActiveSupport.on_load(:action_controller) { routes.finalize! }
-
-        nil
-      ensure
-        routes.disable_clear_and_finalize = false
-      end
-
-      def reload_if_changed
-        current_change_at = changed_at
-        if @last_change_at != current_change_at
-          @last_change_at = current_change_at
-          reload!
-        end
-      end
-    end
-  end
-end
\ No newline at end of file