Example of using Deferrable to provide an asynchronous API to a synchronous method.

synchronous_deferrable.rb

def do_funky_stuff
  d = EM::DefaultDeferrable.new
  # do some long-running thing synchronously
  d.succeed
  return d
end

do_funky_stuff.callback { sleep 5; puts 'Done!' }  # blocks for 5 seconds
# prints "Done!"