Add ActiveSupport::FileUpdateChecker.

activesupport/lib/active_support.rb

@@ -39,6 +39,9 @@ require "active_support/dependencies/autoload"
 module ActiveSupport
   extend ActiveSupport::Autoload
 
+  autoload :DescendantsTracker
+  autoload :FileUpdateChecker
+
   # TODO: Narrow this list down
   eager_autoload do
     autoload :BacktraceCleaner
@@ -51,7 +54,6 @@ module ActiveSupport
     autoload :Concern
     autoload :Configurable
     autoload :Deprecation
-    autoload :DescendantsTracker
     autoload :Gzip
     autoload :Inflector
     autoload :JSON

activesupport/lib/active_support/file_update_checker.rb

@@ -0,0 +1,37 @@
+module ActiveSupport
+  # This class is responsible to track files and invoke the given block
+  # whenever one of these files are changed. For example, this class
+  # is used by Rails to reload routes whenever they are changed upon
+  # a new request.
+  #
+  #   routes_reloader = ActiveSupport::FileUpdateChecker.new(paths) do
+  #     paths.each { |p| load(p) }
+  #     Rails::Application.routes.reload!
+  #   end
+  #
+  #   ActionDispatch::Callbacks.to_prepare do
+  #     routes_reloader.execute_if_updated
+  #   end
+  #
+  class FileUpdateChecker
+    attr_reader :paths, :last_update_at
+
+    def initialize(paths, calculate=false, &block)
+      @paths = paths
+      @block = block
+      @last_update_at = updated_at if calculate
+    end
+
+    def updated_at
+      paths.map { |path| File.stat(path).mtime }.max
+    end
+
+    def execute_if_updated
+      current_update_at = self.updated_at
+      if @last_update_at != current_update_at
+        @last_update_at = current_update_at
+        @block.call
+      end
+    end
+  end
+end

activesupport/test/file_update_checker_test.rb

@@ -0,0 +1,56 @@
+require 'abstract_unit'
+require 'test/unit'
+require 'active_support'
+require 'fileutils'
+
+MTIME_FIXTURES_PATH = File.expand_path("../fixtures", __FILE__)
+
+class FileUpdateCheckerTest < Test::Unit::TestCase
+  FILES = %w(1.txt 2.txt 3.txt)
+
+  def setup
+    FileUtils.touch(FILES)
+  end
+
+  def teardown
+    FileUtils.rm(FILES)
+  end
+
+  def test_should_not_execute_the_block_if_no_paths_are_given
+    i = 0
+    checker = ActiveSupport::FileUpdateChecker.new([]){ i += 1 }
+    checker.execute_if_updated
+    assert_equal 0, i
+  end
+
+  def test_should_invoke_the_block_on_first_call_if_it_does_not_calculate_last_updated_at_on_load
+    i = 0
+    checker = ActiveSupport::FileUpdateChecker.new(FILES){ i += 1 }
+    checker.execute_if_updated
+    assert_equal 1, i
+  end
+
+  def test_should_not_invoke_the_block_on_first_call_if_it_calculates_last_updated_at_on_load
+    i = 0
+    checker = ActiveSupport::FileUpdateChecker.new(FILES, true){ i += 1 }
+    checker.execute_if_updated
+    assert_equal 0, i
+  end
+
+  def test_should_not_invoke_the_block_if_no_file_has_changed
+    i = 0
+    checker = ActiveSupport::FileUpdateChecker.new(FILES){ i += 1 }
+    5.times { checker.execute_if_updated }
+    assert_equal 1, i
+  end
+
+  def test_should_invoke_the_block_if_a_file_has_changed
+    i = 0
+    checker = ActiveSupport::FileUpdateChecker.new(FILES){ i += 1 }
+    checker.execute_if_updated
+    sleep(1)
+    FileUtils.touch(FILES)
+    checker.execute_if_updated
+    assert_equal 2, i
+  end
+end