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 # attach_to :active_record # # def sql(event) # Statsd.timing("sql.#{event.payload[:name]}", event.duration) # end # end # end # # 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('.'.freeze).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 ActiveSupport::PerThreadRegistry # for further details. class SubscriberQueueRegistry # :nodoc: extend PerThreadRegistry def initialize @registry = {} end def get_queue(queue_key) @registry[queue_key] ||= [] end end end