require 'active_support/notifications/instrumenter'
require 'active_support/notifications/fanout'
module ActiveSupport
# = Notifications
#
# <tt>ActiveSupport::Notifications</tt> provides an instrumentation API for
# Ruby.
#
# == Instrumenters
#
# To instrument an event you just need to do:
#
# ActiveSupport::Notifications.instrument('render', extra: :information) do
# render text: 'Foo'
# end
#
# That executes the block first and notifies all subscribers once done.
#
# In the example above +render+ is the name of the event, and the rest is called
# the _payload_. The payload is a mechanism that allows instrumenters to pass
# extra information to subscribers. Payloads consist of a hash whose contents
# are arbitrary and generally depend on the event.
#
# == Subscribers
#
# You can consume those events and the information they provide by registering
# a subscriber.
#
# ActiveSupport::Notifications.subscribe('render') do |name, start, finish, id, payload|
# name # => String, name of the event (such as 'render' from above)
# start # => Time, when the instrumented block started execution
# finish # => Time, when the instrumented block ended execution
# id # => String, unique ID for this notification
# payload # => Hash, the payload
# end
#
# For instance, let's store all "render" events in an array:
#
# events = []
#
# ActiveSupport::Notifications.subscribe('render') do |*args|
# events << ActiveSupport::Notifications::Event.new(*args)
# end
#
# That code returns right away, you are just subscribing to "render" events.
# The block is saved and will be called whenever someone instruments "render":
#
# ActiveSupport::Notifications.instrument('render', extra: :information) do
# render text: 'Foo'
# end
#
# event = events.first
# event.name # => "render"
# event.duration # => 10 (in milliseconds)
# event.payload # => { extra: :information }
#
# The block in the <tt>subscribe</tt> call gets the name of the event, start
# timestamp, end timestamp, a string with a unique identifier for that event
# (something like "535801666f04d0298cd6"), and a hash with the payload, in
# that order.
#
# If an exception happens during that particular instrumentation the payload will
# have a key <tt>:exception</tt> with an array of two elements as value: a string with
# the name of the exception class, and the exception message.
#
# As the previous example depicts, the class <tt>ActiveSupport::Notifications::Event</tt>
# is able to take the arguments as they come and provide an object-oriented
# interface to that data.
#
# It is also possible to pass an object as the second parameter passed to the
# <tt>subscribe</tt> method instead of a block:
#
# module ActionController
# class PageRequest
# def call(name, started, finished, unique_id, payload)
# Rails.logger.debug ['notification:', name, started, finished, unique_id, payload].join(' ')
# end
# end
# end
#
# ActiveSupport::Notifications.subscribe('process_action.action_controller', ActionController::PageRequest.new)
#
# resulting in the following output within the logs including a hash with the payload:
#
# notification: process_action.action_controller 2012-04-13 01:08:35 +0300 2012-04-13 01:08:35 +0300 af358ed7fab884532ec7 {
# :controller=>"Devise::SessionsController",
# :action=>"new",
# :params=>{"action"=>"new", "controller"=>"devise/sessions"},
# :format=>:html,
# :method=>"GET",
# :path=>"/login/sign_in",
# :status=>200,
# :view_runtime=>279.3080806732178,
# :db_runtime=>40.053
# }
#
# You can also subscribe to all events whose name matches a certain regexp:
#
# ActiveSupport::Notifications.subscribe(/render/) do |*args|
# ...
# end
#
# and even pass no argument to <tt>subscribe</tt>, in which case you are subscribing
# to all events.
#
# == Temporary Subscriptions
#
# Sometimes you do not want to subscribe to an event for the entire life of
# the application. There are two ways to unsubscribe.
#
# WARNING: The instrumentation framework is designed for long-running subscribers,
# use this feature sparingly because it wipes some internal caches and that has
# a negative impact on performance.
#
# === Subscribe While a Block Runs
#
# You can subscribe to some event temporarily while some block runs. For
# example, in
#
# callback = lambda {|*args| ... }
# ActiveSupport::Notifications.subscribed(callback, "sql.active_record") do
# ...
# end
#
# the callback will be called for all "sql.active_record" events instrumented
# during the execution of the block. The callback is unsubscribed automatically
# after that.
#
# === Manual Unsubscription
#
# The +subscribe+ method returns a subscriber object:
#
# subscriber = ActiveSupport::Notifications.subscribe("render") do |*args|
# ...
# end
#
# To prevent that block from being called anymore, just unsubscribe passing
# that reference:
#
# ActiveSupport::Notifications.unsubscribe(subscriber)
#
# == Default Queue
#
# Notifications ships with a queue implementation that consumes and publish events
# to log subscribers in a thread. You can use any queue implementation you want.
#
module Notifications
class << self
attr_accessor :notifier
def publish(name, *args)
notifier.publish(name, *args)
end
def instrument(name, payload = {})
if notifier.listening?(name)
instrumenter.instrument(name, payload) { yield payload if block_given? }
else
yield payload if block_given?
end
end
def subscribe(*args, &block)
notifier.subscribe(*args, &block)
end
def subscribed(callback, *args, &block)
subscriber = subscribe(*args, &callback)
yield
ensure
unsubscribe(subscriber)
end
def unsubscribe(args)
notifier.unsubscribe(args)
end
def instrumenter
Thread.current[:"instrumentation_#{notifier.object_id}"] ||= Instrumenter.new(notifier)
end
end
self.notifier = Fanout.new
end
end
