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.
Attach the subscriber to a namespace.
# File lib/active_support/subscriber.rb, line 33 def attach_to(namespace, subscriber=new, notifier=ActiveSupport::Notifications) subscribers << subscriber subscriber.public_methods(false).each do |event| next if %w{ start finish }.include?(event.to_s) notifier.subscribe("#{event}.#{namespace}", subscriber) end end
# File lib/active_support/subscriber.rb, line 48 def initialize @queue_key = [self.class.name, object_id].join "-" super end
# File lib/active_support/subscriber.rb, line 43 def subscribers @@subscribers ||= [] end
# File lib/active_support/subscriber.rb, line 61 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
# File lib/active_support/subscriber.rb, line 53 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
# File lib/active_support/subscriber.rb, line 73 def event_stack SubscriberQueueRegistry.get_queue(@queue_key) end