class ActiveSupport::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

namespace[R]
notifier[R]
subscriber[R]

Public Class Methods

attach_to(namespace, subscriber = new, notifier = ActiveSupport::Notifications, inherit_all: false) click to toggle source

Attach the subscriber to a namespace.

# File lib/active_support/subscriber.rb, line 33
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) click to toggle source

Detach the subscriber from a namespace.

# File lib/active_support/subscriber.rb, line 48
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) click to toggle source

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

# File lib/active_support/subscriber.rb, line 67
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
new() click to toggle source
Calls superclass method
# File lib/active_support/subscriber.rb, line 128
def initialize
  @queue_key = [self.class.name, object_id].join "-"
  @patterns  = {}
  super
end
subscribers() click to toggle source
# File lib/active_support/subscriber.rb, line 76
def subscribers
  @@subscribers ||= []
end

Private Class Methods

add_event_subscriber(event) click to toggle source
# File lib/active_support/subscriber.rb, line 83
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
fetch_public_methods(subscriber, inherit_all) click to toggle source
# File lib/active_support/subscriber.rb, line 121
def fetch_public_methods(subscriber, inherit_all)
  subscriber.public_methods(inherit_all) - Subscriber.public_instance_methods(true)
end
find_attached_subscriber() click to toggle source
# File lib/active_support/subscriber.rb, line 105
def find_attached_subscriber
  subscribers.find { |attached_subscriber| attached_subscriber.instance_of?(self) }
end
invalid_event?(event) click to toggle source
# File lib/active_support/subscriber.rb, line 109
def invalid_event?(event)
  %i{ start finish }.include?(event.to_sym)
end
pattern_subscribed?(pattern) click to toggle source
# File lib/active_support/subscriber.rb, line 117
def pattern_subscribed?(pattern)
  subscriber.patterns.key?(pattern)
end
prepare_pattern(event) click to toggle source
# File lib/active_support/subscriber.rb, line 113
def prepare_pattern(event)
  "#{event}.#{namespace}"
end
remove_event_subscriber(event) click to toggle source
# File lib/active_support/subscriber.rb, line 94
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

finish(name, id, payload) click to toggle source
# File lib/active_support/subscriber.rb, line 143
def finish(name, id, payload)
  event = event_stack.pop
  event.finish!
  event.payload.merge!(payload)

  method = name.split(".").first
  send(method, event)
end
start(name, id, payload) click to toggle source
# File lib/active_support/subscriber.rb, line 134
def start(name, id, payload)
  event = ActiveSupport::Notifications::Event.new(name, nil, nil, id, payload)
  event.start!
  parent = event_stack.last
  parent << event if parent

  event_stack.push event
end

Private Instance Methods

event_stack() click to toggle source
# File lib/active_support/subscriber.rb, line 158
def event_stack
  registry = ActiveSupport::IsolatedExecutionState[:active_support_subscriber_queue_registry] ||= {}
  registry[@queue_key] ||= []
end