1 files changed, 14 insertions, 10 deletions
diff --git a/activesupport/lib/active_support/subscriber.rb b/activesupport/lib/active_support/subscriber.rb
index 4b9b48539f..1cd4b807ad 100644
--- a/activesupport/lib/active_support/subscriber.rb
+++ b/activesupport/lib/active_support/subscriber.rb
@@ -5,24 +5,19 @@ module ActiveSupport
   # ActiveSupport::Notifications. The subscriber dispatches notifications to
   # a registered object based on its given namespace.
   #
-  # An example would be Active Record subscriber responsible for collecting
+  # An example would be an Active Record subscriber responsible for collecting
   # statistics about queries:
   #
   #   module ActiveRecord
   #     class StatsSubscriber < ActiveSupport::Subscriber
+  #       attach_to :active_record
+  #
   #       def sql(event)
   #         Statsd.timing("sql.#{event.payload[:name]}", event.duration)
   #       end
   #     end
   #   end
   #
-  # And it's finally registered as:
-  #
-  #   ActiveRecord::StatsSubscriber.attach_to :active_record
-  #
-  # Since we need to know all instance methods before attaching the log
-  # subscriber, the line above should be called after your subscriber definition.
-  #
   # After configured, whenever a "sql.active_record" notification is published,
   # it will properly dispatch the event (ActiveSupport::Notifications::Event) to
   # the +sql+ method.
@@ -64,12 +59,21 @@ module ActiveSupport
       def add_event_subscriber(event)
         return if %w{ start finish }.include?(event.to_s)
 
-        notifier.subscribe("#{event}.#{namespace}", subscriber)
+        pattern = "#{event}.#{namespace}"
+
+        # Don't add multiple subscribers (eg. if methods are redefined).
+        return if subscriber.patterns.include?(pattern)
+
+        subscriber.patterns << pattern
+        notifier.subscribe(pattern, subscriber)
       end
     end
 
+    attr_reader :patterns # :nodoc:
+
     def initialize
       @queue_key = [self.class.name, object_id].join "-"
+      @patterns  = []
       super
     end
 
@@ -87,7 +91,7 @@ module ActiveSupport
       event.end = finished
       event.payload.merge!(payload)
 
-      method = name.split('.').first
+      method = name.split('.'.freeze).first
       send(method, event)
     end