Make dispatcher instances immutable

actionpack/lib/action_controller/dispatch/dispatcher.rb

@@ -66,7 +66,8 @@ module ActionController
     define_callbacks :prepare_dispatch, :before_dispatch, :after_dispatch
 
     def initialize
-      @app = @@middleware.build(lambda { |env| self.dup._call(env) })
+      @app = @@middleware.build(lambda { |env| self._call(env) })
+      freeze
     end
 
     def call(env)
@@ -74,8 +75,18 @@ module ActionController
     end
 
     def _call(env)
-      @env = env
-      dispatch
+      begin
+        run_callbacks :before_dispatch
+        Routing::Routes.call(env)
+      rescue Exception => exception
+        if controller ||= (::ApplicationController rescue Base)
+          controller.call_with_exception(env, exception).to_a
+        else
+          raise exception
+        end
+      ensure
+        run_callbacks :after_dispatch, :enumerator => :reverse_each
+      end
     end
 
     def flush_logger