em.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-

require 'eventmachine'

class UpdateEvent
  include EM::Deferrable

  def fire(msg)
    p "update: #{msg}"
  end

  def canceled(msg)
    p "cancel: #{msg}"
  end
end 

def enqueue(msg, sec = 3)
  defer = UpdateEvent.new
  defer.callback do |msg|
    defer.fire msg
  end

  defer.errback do
    defer.canceled msg
  end

  EM.add_timer(sec) do
    defer.succeed msg
  end

  defer
end

EM.run do
  d1 = enqueue 'hogehoge'
  d2 = enqueue 'fugafuga'

  sleep 2
  d2.fail # cancel
end