module Parallel
  def cpu_cores
    2
  end

  def parallel_each(&block)
    t = []
    each_slice(cpu_cores).each do |items|
      t << Thread.new do
        items.each do |item|
          yield item
        end
      end
    end
    t.collect(&:join)
  end

  def parallel_sum
    t = []
    each_slice(cpu_cores).each do |items|
      puts "Thread.."
      t << Thread.new do
        Thread.current[:output] = items.inject(&:+)
      end
    end
    output = 0
    t.each do |thread|
      thread.join
      output += thread[:output]
    end
    output
  end

end


class Array
  prepend Parallel
end

Array.new([1,2,3,4,5]).parallel_each do |a|
  puts "#{a}"
  sleep (1..5).to_a.sample
end

puts Array.new([1,2,3,4,5]).parallel_sum