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require 'thread'

THREAD_NUM = 4

list = ['*',
        '_*',
        '__*',
        '___*',
        '____*',
        '_____*',
        '______*',
        '_______*',
        '________*',
        '_________*',]

locker = Mutex.new
list0 = list.dup
Array.new(THREAD_NUM) do
  Thread.new do
    while a = list0.shift
      locker.synchronize do
        # sleep 0.1
        puts a
      end
    end
  end
end.each(&:join)