Este program

require 'em-synchrony' ## v1.0.0                                                                                                                               
require 'em-hiredis'   ## v0.1.0                                                                                                                               

module EventMachine
  module Hiredis
    class Client

      def self.connect(host = 'localhost', port = 6379)
        conn = new(host, port)
        EM::Synchrony.sync conn.connect
    conn
      end

      alias :old_method_missing :method_missing
      def method_missing(sym, *args)
        EM::Synchrony.sync old_method_missing(sym, *args)
      end
    end
  end
end

EventMachine.synchrony do
  redis = EM::Hiredis.connect

  redis.set('foo', 'bar')
  puts redis.get('foo')

  EM.stop
end

dies como este

$ ruby /tmp/reddy.rb 
/home/blt/.rvm/gems/ruby-1.9.3-p0/gems/em-synchrony-1.0.0/lib/em-synchrony.rb:58:in `yield': can't yield from root fiber (FiberError)
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/em-synchrony-1.0.0/lib/em-synchrony.rb:58:in `sync'
    from /tmp/reddy.rb:16:in `method_missing'
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/em-hiredis-0.1.0/lib/em-hiredis/client.rb:119:in `select'
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/em-hiredis-0.1.0/lib/em-hiredis/client.rb:38:in `block in connect'
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/em-hiredis-0.1.0/lib/em-hiredis/event_emitter.rb:8:in `call'
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/em-hiredis-0.1.0/lib/em-hiredis/event_emitter.rb:8:in `block in emit'
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/em-hiredis-0.1.0/lib/em-hiredis/event_emitter.rb:8:in `each'
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/em-hiredis-0.1.0/lib/em-hiredis/event_emitter.rb:8:in `emit'
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/em-hiredis-0.1.0/lib/em-hiredis/connection.rb:15:in `connection_completed'
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/eventmachine-1.0.0.beta.4/lib/eventmachine.rb:179:in `run_machine'
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/eventmachine-1.0.0.beta.4/lib/eventmachine.rb:179:in `run'
    from /home/blt/.rvm/gems/ruby-1.9.3-p0/gems/em-synchrony-1.0.0/lib/em-synchrony.rb:27:in `synchrony'
    from /tmp/reddy.rb:22:in `<main>'

Acho isso profundamente confuso. Por que não funciona e eu tenho culpa? Se sim, o que posso fazer de diferente? A menos que eu tenha encoberto alguma coisa, isso é kosher, pelo README da em-sincroni