1 files changed, 125 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/subscriber.rb b/activesupport/lib/active_support/subscriber.rb
new file mode 100644
index 0000000000..98be78b41b
--- /dev/null
+++ b/activesupport/lib/active_support/subscriber.rb
@@ -0,0 +1,125 @@
+require 'active_support/per_thread_registry'
+
+module ActiveSupport
+  # ActiveSupport::Subscriber is an object set to consume
+  # 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
+  # statistics about queries:
+  #
+  #   module ActiveRecord
+  #     class StatsSubscriber < ActiveSupport::Subscriber
+  #       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.
+  class Subscriber
+    class << self
+
+      # Attach the subscriber to a namespace.
+      def attach_to(namespace, subscriber=new, notifier=ActiveSupport::Notifications)
+        @namespace  = namespace
+        @subscriber = subscriber
+        @notifier   = notifier
+
+        subscribers << subscriber
+
+        # Add event subscribers for all existing methods on the class.
+        subscriber.public_methods(false).each do |event|
+          add_event_subscriber(event)
+        end
+      end
+
+      # Adds event subscribers for all new methods added to the class.
+      def method_added(event)
+        # Only public methods are added as subscribers, and only if a notifier
+        # has been set up. This means that subscribers will only be set up for
+        # classes that call #attach_to.
+        if public_method_defined?(event) && notifier
+          add_event_subscriber(event)
+        end
+      end
+
+      def subscribers
+        @@subscribers ||= []
+      end
+
+      protected
+
+      attr_reader :subscriber, :notifier, :namespace
+
+      def add_event_subscriber(event)
+        return if %w{ start finish }.include?(event.to_s)
+
+        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
+
+    def start(name, id, payload)
+      e = ActiveSupport::Notifications::Event.new(name, Time.now, nil, id, payload)
+      parent = event_stack.last
+      parent << e if parent
+
+      event_stack.push e
+    end
+
+    def finish(name, id, payload)
+      finished  = Time.now
+      event     = event_stack.pop
+      event.end = finished
+      event.payload.merge!(payload)
+
+      method = name.split('.').first
+      send(method, event)
+    end
+
+    private
+
+      def event_stack
+        SubscriberQueueRegistry.instance.get_queue(@queue_key)
+      end
+  end
+
+  # This is a registry for all the event stacks kept for subscribers.
+  #
+  # See the documentation of <tt>ActiveSupport::PerThreadRegistry</tt>
+  # for further details.
+  class SubscriberQueueRegistry # :nodoc:
+    extend PerThreadRegistry
+
+    def initialize
+      @registry = {}
+    end
+
+    def get_queue(queue_key)
+      @registry[queue_key] ||= []
+    end
+  end
+end