kill_sub_thread

# File lib/drb/drb.rb, line 1415
    def kill_sub_thread
      Thread.new do
        grp = ThreadGroup.new
        grp.add(Thread.current)
        list = @grp.list
        while list.size > 0
          list.each do |th|
            th.kill if th.alive?
          end
          list = @grp.list
        end
      end
    end