Performance optimizations to handle cases of instrumentors that are not listened to. Also, fix a possible concurrency issue.

2 files changed, 9 insertions, 4 deletions

diff --git a/activesupport/lib/active_support/notifications/fanout.rb b/activesupport/lib/active_support/notifications/fanout.rb
index 64f315cb6a..adc34f3286 100644
--- a/activesupport/lib/active_support/notifications/fanout.rb
+++ b/activesupport/lib/active_support/notifications/fanout.rb
@@ -9,15 +9,16 @@ module ActiveSupport
       end
 
       def subscribe(pattern = nil, block = Proc.new)
-        @listeners_for.clear
-        Subscriber.new(pattern, block).tap do |s|
+        subscriber = Subscriber.new(pattern, block).tap do |s|
           @subscribers << s
         end
+        @listeners_for.clear
+        subscriber
       end
 
       def unsubscribe(subscriber)
-        @listeners_for.clear
         @subscribers.reject! {|s| s.matches?(subscriber)}
+        @listeners_for.clear
       end
 
       def publish(name, *args)
@@ -28,6 +29,10 @@ module ActiveSupport
         @listeners_for[name] ||= @subscribers.select { |s| s.subscribed_to?(name) }
       end
 
+      def listening?(name)
+        listeners_for(name).any?
+      end
+
       # This is a sync queue, so there is not waiting.
       def wait
       end
diff --git a/activesupport/lib/active_support/notifications/instrumenter.rb b/activesupport/lib/active_support/notifications/instrumenter.rb
index e98189f899..713d5a5f25 100644
--- a/activesupport/lib/active_support/notifications/instrumenter.rb
+++ b/activesupport/lib/active_support/notifications/instrumenter.rb
@@ -19,7 +19,7 @@ module ActiveSupport
       def instrument(name, payload={})
         begin
           @started = Time.now
-          yield(payload) if block_given?
+          yield
         rescue Exception => e
           payload[:exception] = [e.class.name, e.message]
           raise e