diff options
Diffstat (limited to 'activesupport/lib/active_support/notifications.rb')
| -rw-r--r-- | activesupport/lib/active_support/notifications.rb | 244 |
1 files changed, 244 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/notifications.rb b/activesupport/lib/active_support/notifications.rb new file mode 100644 index 0000000000..7ccc333463 --- /dev/null +++ b/activesupport/lib/active_support/notifications.rb @@ -0,0 +1,244 @@ +# frozen_string_literal: true + +require "active_support/notifications/instrumenter" +require "active_support/notifications/fanout" +require "active_support/per_thread_registry" + +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 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 the instrumenter that fired the event + # 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 <tt>subscribe</tt> call gets the name of the event, start + # timestamp, end timestamp, a string with a unique identifier for that event's instrumenter + # (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. + # The <tt>:exception_object</tt> key of the payload will have the exception + # itself as the value: + # + # event.payload[:exception] # => ["ArgumentError", "Invalid value"] + # event.payload[:exception_object] # => #<ArgumentError: Invalid value> + # + # As the earlier 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 which responds to <tt>call</tt> method + # as the second parameter 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) + # + # 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 + + # Subscribe to a given event name with the passed +block+. + # + # You can subscribe to events by passing a String to match exact event + # names, or by passing a Regexp to match all events that match a pattern. + # + # ActiveSupport::Notifications.subscribe(/render/) do |*args| + # @event = ActiveSupport::Notifications::Event.new(*args) + # end + # + # The +block+ will receive five parameters with information about the event: + # + # 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 the instrumenter that fired the event + # payload # => Hash, the payload + # end + # + # If the block passed to the method only takes one parameter, + # it will yield an event object to the block: + # + # ActiveSupport::Notifications.subscribe(/render/) do |event| + # @event = event + # 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 |