2 files changed, 33 insertions, 3 deletions
diff --git a/activesupport/lib/active_support/concurrency/latch.rb b/activesupport/lib/active_support/concurrency/latch.rb
new file mode 100644
index 0000000000..1507de433e
--- /dev/null
+++ b/activesupport/lib/active_support/concurrency/latch.rb
@@ -0,0 +1,27 @@
+require 'thread'
+require 'monitor'
+
+module ActiveSupport
+  module Concurrency
+    class Latch
+      def initialize(count = 1)
+        @count = count
+        @lock = Monitor.new
+        @cv = @lock.new_cond
+      end
+
+      def release
+        @lock.synchronize do
+          @count -= 1 if @count > 0
+          @cv.broadcast if @count.zero?
+        end
+      end
+
+      def await
+        @lock.synchronize do
+          @cv.wait_while { @count > 0 }
+        end
+      end
+    end
+  end
+end
diff --git a/activesupport/lib/active_support/core_ext/class/attribute.rb b/activesupport/lib/active_support/core_ext/class/attribute.rb
index da0a12136c..7b6f8ab0a1 100644
--- a/activesupport/lib/active_support/core_ext/class/attribute.rb
+++ b/activesupport/lib/active_support/core_ext/class/attribute.rb
@@ -79,12 +79,14 @@ class Class
 
         def self.#{name}=(val)
           singleton_class.class_eval do
-            redefine_method(:#{name}) { val }
+            remove_possible_method(:#{name})
+            define_method(:#{name}) { val }
           end
 
           if singleton_class?
             class_eval do
-              redefine_method(:#{name}) do
+              remove_possible_method(:#{name})
+              def #{name}
                 defined?(@#{name}) ? @#{name} : singleton_class.#{name}
               end
             end
@@ -93,7 +95,8 @@ class Class
         end
 
         if instance_reader
-          redefine_method(:#{name}) do
+          remove_possible_method :#{name}
+          def #{name}
             defined?(@#{name}) ? @#{name} : self.class.#{name}
           end