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require "active_support/per_thread_registry"
module ActiveSupport
# 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.
class Subscriber
class << self
# Attach the subscriber to a namespace.
def attach_to(namespace, subscriber = new, notifier = ActiveSupport::Notifications)
@namespace = namespace
@subscriber = subscriber
@notifier = notifier
subscribers << subscriber
# Add event subscribers for all existing methods on the class.
subscriber.public_methods(false).each do |event|
add_event_subscriber(event)
end
end
# Adds event subscribers for all new methods added to the class.
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
def subscribers
@@subscribers ||= []
end
protected
attr_reader :subscriber, :notifier, :namespace
def add_event_subscriber(event)
return if %w{ start finish }.include?(event.to_s)
pattern = "#{event}.#{namespace}"
# Don't add multiple subscribers (eg. if methods are redefined).
return if subscriber.patterns.include?(pattern)
subscriber.patterns << pattern
notifier.subscribe(pattern, subscriber)
end
end
attr_reader :patterns # :nodoc:
def initialize
@queue_key = [self.class.name, object_id].join "-"
@patterns = []
super
end
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
def finish(name, id, payload)
finished = Time.now
event = event_stack.pop
event.end = finished
event.payload.merge!(payload)
method = name.split(".".freeze).first
send(method, event)
end
private
def event_stack
SubscriberQueueRegistry.instance.get_queue(@queue_key)
end
end
# This is a registry for all the event stacks kept for subscribers.
#
# See the documentation of <tt>ActiveSupport::PerThreadRegistry</tt>
# for further details.
class SubscriberQueueRegistry # :nodoc:
extend PerThreadRegistry
def initialize
@registry = {}
end
def get_queue(queue_key)
@registry[queue_key] ||= []
end
end
end
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