class ActiveSupport::Subscriber
Active Support Subscriber¶ ↑
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 an 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.
We can detach a subscriber as well:
ActiveRecord::StatsSubscriber.detach_from(:active_record)
Attributes
Public Class Methods
Source
# File lib/active_support/subscriber.rb, line 35 def attach_to(namespace, subscriber = new, notifier = ActiveSupport::Notifications, inherit_all: false) @namespace = namespace @subscriber = subscriber @notifier = notifier @inherit_all = inherit_all subscribers << subscriber # Add event subscribers for all existing methods on the class. fetch_public_methods(subscriber, inherit_all).each do |event| add_event_subscriber(event) end end
Attach the subscriber to a namespace.
Source
# File lib/active_support/subscriber.rb, line 50 def detach_from(namespace, notifier = ActiveSupport::Notifications) @namespace = namespace @subscriber = find_attached_subscriber @notifier = notifier return unless subscriber subscribers.delete(subscriber) # Remove event subscribers of all existing methods on the class. fetch_public_methods(subscriber, true).each do |event| remove_event_subscriber(event) end # Reset notifier so that event subscribers will not add for new methods added to the class. @notifier = nil end
Detach the subscriber from a namespace.
Source
# File lib/active_support/subscriber.rb, line 69 def method_added(event) super # 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
Adds event subscribers for all new methods added to the class.
Calls superclass method
Source
# File lib/active_support/subscriber.rb, line 131 def initialize @patterns = {} super end
Calls superclass method
Source
# File lib/active_support/subscriber.rb, line 79 def subscribers @@subscribers ||= [] end
Private Class Methods
Source
# File lib/active_support/subscriber.rb, line 86 def add_event_subscriber(event) # :doc: return if invalid_event?(event) pattern = prepare_pattern(event) # Don't add multiple subscribers (e.g. if methods are redefined). return if pattern_subscribed?(pattern) subscriber.patterns[pattern] = notifier.subscribe(pattern, subscriber) end
Source
# File lib/active_support/subscriber.rb, line 124 def fetch_public_methods(subscriber, inherit_all) subscriber.public_methods(inherit_all) - Subscriber.public_instance_methods(true) end
Source
# File lib/active_support/subscriber.rb, line 108 def find_attached_subscriber subscribers.find { |attached_subscriber| attached_subscriber.instance_of?(self) } end
Source
# File lib/active_support/subscriber.rb, line 112 def invalid_event?(event) %i{ start finish }.include?(event.to_sym) end
Source
# File lib/active_support/subscriber.rb, line 120 def pattern_subscribed?(pattern) subscriber.patterns.key?(pattern) end
Source
# File lib/active_support/subscriber.rb, line 116 def prepare_pattern(event) "#{event}.#{namespace}" end
Source
# File lib/active_support/subscriber.rb, line 97 def remove_event_subscriber(event) # :doc: return if invalid_event?(event) pattern = prepare_pattern(event) return unless pattern_subscribed?(pattern) notifier.unsubscribe(subscriber.patterns[pattern]) subscriber.patterns.delete(pattern) end
Public Instance Methods
Source
# File lib/active_support/subscriber.rb, line 136 def call(event) method = event.name[0, event.name.index(".")] send(method, event) end