Multithread unsafe

multi_unsafe.rb

def add_range_unsafe
  c = StatefulCalculator.new

  threads = (1..256).each_slice(16).map do |range|
    Thread.new do
      range.each { |n| c.add n }
    end
  end

  threads.map(&:join)

  c.result
end

puts add_range_unsafe # 24399
puts add_range_unsafe # 26126
puts add_range_unsafe # 25674