title: Celluloid callback
body: <p>How can I get notified when an async method has finished it's job (callback) when using Celluloid?</p>
  
  <p>Sample code:</p>
  
  <pre><code>  require 'celluloid/autostart'
  
    class Test
      include Celluloid
  
      def initialize(aaa)
        @aaa = aaa
      end
  
      def foo
        sleep 20
        @bbb = 'asdasd'
      end
  
      def bar
        "aaa is: #{@aaa}, bbb is: #{@bbb}"
      end
    end
    x = Test.new 111
    x.async.foo
  </code></pre>
  
  <p>I would like to get notified as soon as the job inside foo is done.</p>