conn.rb

require 'thread'

queues = Array.new(10){ Queue.new }

list_of_hosts.each_slice(10).map{|s| s.each_with_index{|h,i| queues[i] << h }  }

threads = 10.times.map do |i|
  Thread.new do
    while host = queues[i].pop
      check host
    end
  end
end

threads.each(&:join)