simple_pool.rb

require 'thread'

class Pool
  def initialize(csv, get, set)
    @get = get
    @set = set
    @csv = csv
    @queue = Queue.new
    @mutex = Mutex.new
  end

  def <<(work)
    @queue << work
  end

  def wait
    @threads = 20.times.map do |id|
      Thread.new(&method(:work))
    end
    @threads.map(&:join)
  end

  def work
    loop do
      break if @queue.empty?
      row = @queue.shift
      res = instance_eval { @get.call(row, @mutex) }
      @mutex.synchronize { @csv << instance_eval { @set.call(res) }; }
    end
  end
end