require "active_support/notifications/instrumenter" require "active_support/notifications/fanout" require "active_support/per_thread_registry" module ActiveSupport # = Notifications # # ActiveSupport::Notifications provides an instrumentation API for # Ruby. # # == Instrumenters # # To instrument an event you just need to do: # # ActiveSupport::Notifications.instrument('render', extra: :information) do # render plain: 'Foo' # end # # That first executes the block and then 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 plain: 'Foo' # end # # event = events.first # event.name # => "render" # event.duration # => 10 (in milliseconds) # event.payload # => { extra: :information } # # The block in the subscribe 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 :exception with an array of two elements as value: a string with # the name of the exception class, and the exception message. # The :exception_object key of the payload will have the exception # itself as the value. # # As the previous example depicts, the class ActiveSupport::Notifications::Event # 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 which responds to call method # as the second parameter to the subscribe 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 subscribe, 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) # # You can also unsubscribe by passing the name of the subscriber object. Note # that this will unsubscribe all subscriptions with the given name: # # ActiveSupport::Notifications.unsubscribe("render") # # == Default Queue # # Notifications ships with a queue implementation that consumes and publishes events # to all log subscribers. 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(subscriber_or_name) notifier.unsubscribe(subscriber_or_name) end def instrumenter InstrumentationRegistry.instance.instrumenter_for(notifier) end end # This class is a registry which holds all of the +Instrumenter+ objects # in a particular thread local. To access the +Instrumenter+ object for a # particular +notifier+, you can call the following method: # # InstrumentationRegistry.instrumenter_for(notifier) # # The instrumenters for multiple notifiers are held in a single instance of # this class. class InstrumentationRegistry # :nodoc: extend ActiveSupport::PerThreadRegistry def initialize @registry = {} end def instrumenter_for(notifier) @registry[notifier] ||= Instrumenter.new(notifier) end end self.notifier = Fanout.new end end