Subscribe to event objects via `subscribe_event`

Fanout notifier can send event objects to subscribers now.  Also moved
`end` lower in the `finish!` method to guarantee that CPU time is
shorter than real time.

3 files changed, 56 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/notifications/fanout.rb b/activesupport/lib/active_support/notifications/fanout.rb
index 25aab175b4..91d8491c7e 100644
--- a/activesupport/lib/active_support/notifications/fanout.rb
+++ b/activesupport/lib/active_support/notifications/fanout.rb
@@ -27,6 +27,15 @@ module ActiveSupport
         subscriber
       end
 
+      def subscribe_event(pattern = nil, &block)
+        subscriber = Subscribers.event_object_subscriber pattern, block
+        synchronize do
+          @subscribers << subscriber
+          @listeners_for.clear
+        end
+        subscriber
+      end
+
       def unsubscribe(subscriber_or_name)
         synchronize do
           case subscriber_or_name
@@ -76,6 +85,14 @@ module ActiveSupport
             subscriber = Timed.new pattern, listener
           end
 
+          wrap_all pattern, subscriber
+        end
+
+        def self.event_object_subscriber(pattern, block)
+          wrap_all pattern, EventObject.new(pattern, block)
+        end
+
+        def self.wrap_all(pattern, subscriber)
           unless pattern
             AllMessages.new(subscriber)
           else
@@ -130,6 +147,27 @@ module ActiveSupport
           end
         end
 
+        class EventObject < Evented
+          def start(name, id, payload)
+            stack = Thread.current[:_event_stack] ||= []
+            event = build_event name, id, payload
+            event.start!
+            stack.push event
+          end
+
+          def finish(name, id, payload)
+            stack = Thread.current[:_event_stack]
+            event = stack.pop
+            event.finish!
+            @delegate.call event
+          end
+
+          private
+            def build_event(name, id, payload)
+              ActiveSupport::Notifications::Event.new name, nil, nil, id, payload
+            end
+        end
+
         class AllMessages # :nodoc:
           def initialize(delegate)
             @delegate = delegate
diff --git a/activesupport/lib/active_support/notifications/instrumenter.rb b/activesupport/lib/active_support/notifications/instrumenter.rb
index 259cb4db98..72e5064679 100644
--- a/activesupport/lib/active_support/notifications/instrumenter.rb
+++ b/activesupport/lib/active_support/notifications/instrumenter.rb
@@ -76,8 +76,8 @@ module ActiveSupport
       end
 
       def finish!
-        @end = now
         @cpu_time_finish = now_cpu
+        @end = now
         @allocation_count_finish = now_allocations
       end
 
diff --git a/activesupport/test/notifications_test.rb b/activesupport/test/notifications_test.rb
index d035f993f7..e28560d88b 100644
--- a/activesupport/test/notifications_test.rb
+++ b/activesupport/test/notifications_test.rb
@@ -26,6 +26,23 @@ module Notifications
     end
   end
 
+  class SubscribeEventObjects < TestCase
+    def test_subscribe_events
+      events = []
+      @notifier.subscribe_event do |event|
+        events << event
+      end
+
+      ActiveSupport::Notifications.instrument("foo")
+      event = events.first
+      assert event, "should have an event"
+      assert_operator event.allocations, :>, 0
+      assert_operator event.cpu_time, :>, 0
+      assert_operator event.idle_time, :>, 0
+      assert_operator event.duration, :>, 0
+    end
+  end
+
   class SubscribedTest < TestCase
     def test_subscribed
       name     = "foo"