rails--rails/activesupport/lib/active_support/notifications/instrumenter.rb

require 'securerandom'

module ActiveSupport
  module Notifications
    # Instrumentors are stored in a thread local.
    class Instrumenter
      attr_reader :id

      def initialize(notifier)
        @id = unique_id
        @notifier = notifier
      end

      # Instrument the given block by measuring the time taken to execute it
      # and publish it. Notice that events get sent even if an error occurs
      # in the passed-in block.
      def instrument(name, payload={})
        @notifier.start(name, @id, payload)
        begin
          yield
        rescue Exception => e
          payload[:exception] = [e.class.name, e.message]
          raise e
        ensure
          @notifier.finish(name, @id, payload)
        end
      end

      private
        def unique_id
          SecureRandom.hex(10)
        end
    end

    class Event
      attr_reader :name, :time, :transaction_id, :payload, :children
      attr_accessor :end

      def initialize(name, start, ending, transaction_id, payload)
        @name           = name
        @payload        = payload.dup
        @time           = start
        @transaction_id = transaction_id
        @end            = ending
        @children       = []
      end

      def duration
        1000.0 * (self.end - time)
      end

      def <<(event)
        @children << event
      end

      def parent_of?(event)
        @children.include? event
      end
    end
  end
end