1 files changed, 37 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/file_update_checker.rb b/activesupport/lib/active_support/file_update_checker.rb
new file mode 100644
index 0000000000..5f5b264eb9
--- /dev/null
+++ b/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 = calculate ? updated_at : nil
+    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