move fanout back to a global variable, add a mutex for safety

activesupport/lib/active_support/notifications.rb

@@ -135,24 +135,9 @@ module ActiveSupport
   # to log subscribers in a thread. You can use any queue implementation you want.
   #
   module Notifications
-    class Registry # :nodoc:
-      def self.instance
-        Thread.current[name] ||= new
-      end
-
-      attr_reader :notifier, :instrumenter
-
-      def initialize
-        self.notifier = Fanout.new
-      end
-
-      def notifier=(notifier)
-        @notifier     = notifier
-        @instrumenter = Instrumenter.new(notifier)
-      end
-    end
-
     class << self
+      attr_accessor :notifier
+
       def publish(name, *args)
         notifier.publish(name, *args)
       end
@@ -181,16 +166,10 @@ def unsubscribe(args)
       end
 
       def instrumenter
-        Registry.instance.instrumenter
-      end
-
-      def notifier
-        Registry.instance.notifier
-      end
-
-      def notifier=(notifier)
-        Registry.instance.notifier = notifier
+        Thread.current[:"instrumentation_#{notifier.object_id}"] ||= Instrumenter.new(notifier)
       end
     end
+
+    self.notifier = Fanout.new
   end
 end

activesupport/lib/active_support/notifications/fanout.rb

+require 'mutex_m'
+
 module ActiveSupport
   module Notifications
     # This is a default queue implementation that ships with Notifications.
     # It just pushes events to all registered log subscribers.
     #
-    # Only one of these objects should instantiated per thread.  Concurrent
-    # access to this class is not allowed.
+    # This class is thread safe. All methods are reentrant.
     class Fanout
+      include Mutex_m
+
       def initialize
         @subscribers = []
         @listeners_for = {}
+        super
       end
 
       def subscribe(pattern = nil, block = Proc.new)
         subscriber = Subscribers.new pattern, block
-        @subscribers << subscriber
-        @listeners_for.clear
+        synchronize do
+          @subscribers << subscriber
+          @listeners_for.clear
+        end
         subscriber
       end
 
       def unsubscribe(subscriber)
-        @subscribers.reject! { |s| s.matches?(subscriber) }
-        @listeners_for.clear
+        synchronize do
+          @subscribers.reject! { |s| s.matches?(subscriber) }
+          @listeners_for.clear
+        end
       end
 
       def start(name, id, payload)
@@ -36,7 +44,9 @@ def publish(name, *args)
       end
 
       def listeners_for(name)
-        @listeners_for[name] ||= @subscribers.select { |s| s.subscribed_to?(name) }
+        synchronize do
+          @listeners_for[name] ||= @subscribers.select { |s| s.subscribed_to?(name) }
+        end
       end
 
       def listening?(name)