module ActiveRecord::AttributeMethods::ClassMethods

def define_attribute_methods # :nodoc:
  # Use a mutex; we don't want two thread simultaneously trying to define
  # attribute methods.
  generated_attribute_methods.synchronize do
    return if attribute_methods_generated?
    superclass.define_attribute_methods unless self == base_class
    super(column_names)
    @attribute_methods_generated = true
  end
end