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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)

Public class methods

attach_to(namespace, subscriber = new, notifier = ActiveSupport::Notifications, inherit_all: false)

Attach the subscriber to a namespace.

Source code GitHub 
# File activesupport/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

detach_from(namespace, notifier = ActiveSupport::Notifications)

Detach the subscriber from a namespace.

Source code GitHub 
# File activesupport/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

method_added(event)

Adds event subscribers for all new methods added to the class.

Source code GitHub 
# File activesupport/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

new()

Source code GitHub 
# File activesupport/lib/active_support/subscriber.rb, line 131
def initialize
  @patterns  = {}
  super
end

subscribers()

Source code GitHub 
# File activesupport/lib/active_support/subscriber.rb, line 79
def subscribers
  @@subscribers ||= []
end

Private class methods

add_event_subscriber(event)

Source code GitHub 
# File activesupport/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

remove_event_subscriber(event)

Source code GitHub 
# File activesupport/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

call(event)

Source code GitHub 
# File activesupport/lib/active_support/subscriber.rb, line 136
def call(event)
  method = event.name[0, event.name.index(".")]
  send(method, event)
end

Definition files