2 files changed, 10 insertions, 6 deletions
diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index 31cd2edc12..f3200aa78a 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -1,6 +1,5 @@
 require 'active_support/core_ext/enumerable'
 require 'active_support/deprecation'
-require 'thread'
 
 module ActiveRecord
   # = Active Record Attribute Methods
@@ -39,8 +38,6 @@ module ActiveRecord
       def define_attribute_methods
         # Use a mutex; we don't want two thread simaltaneously trying to define
         # attribute methods.
-        @attribute_methods_mutex ||= Mutex.new
-
         @attribute_methods_mutex.synchronize do
           return if attribute_methods_generated?
           superclass.define_attribute_methods unless self == base_class
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index fa5846de39..198db715b2 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -5,6 +5,7 @@ end
 
 require 'yaml'
 require 'set'
+require 'thread'
 require 'active_support/benchmarkable'
 require 'active_support/dependencies'
 require 'active_support/descendants_tracker'
@@ -390,12 +391,18 @@ module ActiveRecord #:nodoc:
 
     class << self # Class methods
       def inherited(child_class) #:nodoc:
-        # force attribute methods to be higher in inheritance hierarchy than other generated methods
-        child_class.generated_attribute_methods
-        child_class.generated_feature_methods
+        child_class.initialize_generated_modules
         super
       end
 
+      def initialize_generated_modules #:nodoc:
+        @attribute_methods_mutex = Mutex.new
+
+        # force attribute methods to be higher in inheritance hierarchy than other generated methods
+        generated_attribute_methods
+        generated_feature_methods
+      end
+
       def generated_feature_methods
         @generated_feature_methods ||= begin
           mod = const_set(:GeneratedFeatureMethods, Module.new)