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 :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. 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 will be called asynchronously 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 +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. # # 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. # # 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. # # === 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 autoload :Instrumenter, 'active_support/notifications/instrumenter' autoload :Event, 'active_support/notifications/instrumenter' autoload :Fanout, 'active_support/notifications/fanout' @instrumenters = Hash.new { |h,k| h[k] = notifier.listening?(k) } class << self attr_accessor :notifier def publish(name, *args) notifier.publish(name, *args) end def instrument(name, payload = {}) if @instrumenters[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).tap do @instrumenters.clear end end def subscribed(callback, *args, &block) subscriber = subscribe(*args, &callback) yield ensure unsubscribe(subscriber) end def unsubscribe(args) notifier.unsubscribe(args) @instrumenters.clear end def instrumenter Thread.current[:"instrumentation_#{notifier.object_id}"] ||= Instrumenter.new(notifier) end end self.notifier = Fanout.new end end