gistfile1.rb

equire 'celluloid'

module Observable
  def start_notifier
    receive do |it|
      if it.is_a? Celluloid::Actor
        wait :done
        it.signal :notification
      end 
    end 
  end 
end

class Foo 
  include Celluloid
  include Observable

  def initialize
    start_notifier!
  end 

  def work
    sleep 10
    puts 'Foo finished'
    signal :done
  end 
end

class Bar 
  include Celluloid

  def work_after(actor)
    actor.mailbox << self
    wait :notification
    puts 'Bar finished'
  end 
end

foo = Foo.new
bar = Bar.new

foo.work!
bar.work_after foo