object_space.rb

require 'singleton'
require 'monitor'
require 'drb'

module DRb
  class DRbObjectSpace
    include Singleton
    include MonitorMixin

    def initialize
      super()
      @map = ObjectSpace::WeakMap.new
    end

    def to_id(obj)
      synchronize do
        @map[obj.__id__] = obj
        obj.__id__
      end
    end

    def to_obj(ref)
      synchronize do
        raise RangeError.new("invalid reference") unless @map.include?(ref)
        @map[ref]
      end
    end
  end

  class DRbIdConv
    def to_obj(ref)
      DRbObjectSpace.instance.to_obj(ref)
    end

    def to_id(obj)
      obj.nil? ? nil : DRbObjectSpace.instance.to_id(obj)
    end
  end

  WeakIdConv = DRbIdConv
end

if __FILE__ == $0
  DRb.start_service(nil, {'stdout' => $stdout, 'ENV' => ENV})
  puts DRb.uri
  DRb.thread.join
end

drb/drb.rbをこんな風に変更して、drb/weakidconv.rbの中身は40行目だけにしたいのだがどうしたらよいのか