Add ActiveSupport::FileUpdateChecker.

2 files changed, 40 insertions, 1 deletions

diff --git a/activesupport/lib/active_support.rb b/activesupport/lib/active_support.rb
index f93b351655..3ce5476bbd 100644
--- a/activesupport/lib/active_support.rb
+++ b/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
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..c0b5ca4deb
--- /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 = 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
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