Class: ActiveSupport::Subscriber

Inherits:
Object
  • Object
show all
Defined in:
lib/active_support/subscriber.rb

Overview

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)

Direct Known Subclasses

LogSubscriber

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initializeSubscriber

Returns a new instance of Subscriber.


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# File 'lib/active_support/subscriber.rb', line 129

def initialize
  @queue_key = [self.class.name, object_id].join "-"
  @patterns  = {}
  super
end

Instance Attribute Details

#patternsObject (readonly)

:nodoc:


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# File 'lib/active_support/subscriber.rb', line 127

def patterns
  @patterns
end

Class Method Details

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

Attach the subscriber to a namespace.


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# File 'lib/active_support/subscriber.rb', line 34

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) ⇒ Object

Detach the subscriber from a namespace.


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# File 'lib/active_support/subscriber.rb', line 49

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) ⇒ Object

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


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# File 'lib/active_support/subscriber.rb', line 68

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

.subscribersObject


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# File 'lib/active_support/subscriber.rb', line 77

def subscribers
  @@subscribers ||= []
end

Instance Method Details

#finish(name, id, payload) ⇒ Object


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# File 'lib/active_support/subscriber.rb', line 144

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) ⇒ Object


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# File 'lib/active_support/subscriber.rb', line 135

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