Notifications provides an instrumentation API for Ruby. To instrument an action in Ruby you just need to do:

ActiveSupport::Notifications.instrument(:render, :extra => :information) do
  render :text => "Foo"
end

You can consume those events and the information they provide by registering a log subscriber. For instance, let’s store all instrumented events in an array:

@events = []

ActiveSupport::Notifications.subscribe do |*args|
  @events << ActiveSupport::Notifications::Event.new(*args)
end

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 }

When subscribing to Notifications, you can pass a pattern, to only consume events that match the pattern:

ActiveSupport::Notifications.subscribe(/render/) do |event|
  @render_events << event
end

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.

Namespace
Methods
I
P
S
U
Attributes
[RW] notifier
Class Public methods
instrument(name, payload = {})

Source: show 

# File activesupport/lib/active_support/notifications.rb, line 51
def instrument(name, payload = {})
  if @instrumenters[name]
    instrumenter.instrument(name, payload) { yield payload if block_given? }
  else
    yield payload if block_given?
  end
end
instrumenter()

Source: show 

# File activesupport/lib/active_support/notifications.rb, line 70
def instrumenter
  Thread.current[:"instrumentation_#{notifier.object_id}"] ||= Instrumenter.new(notifier)
end
publish(name, *args)

Source: show 

# File activesupport/lib/active_support/notifications.rb, line 47
def publish(name, *args)
  notifier.publish(name, *args)
end
subscribe(*args, &block)

Source: show 

# File activesupport/lib/active_support/notifications.rb, line 59
def subscribe(*args, &block)
  notifier.subscribe(*args, &block).tap do
    @instrumenters.clear
  end
end
unsubscribe(args)

Source: show 

# File activesupport/lib/active_support/notifications.rb, line 65
def unsubscribe(args)
  notifier.unsubscribe(args)
  @instrumenters.clear
end