require 'monitor'
class Counter < Monitor
    attr_reader :count
    def initialize
      @count = 0
      super
    end
    def tick
      synchronize do
        @count += 1
    end
  end
end
  
c = Counter.new
t1 = Thread.new { 100_000.times { c.tick }}
t1 = Thread.new { 100_000.times { c.tick }}
t1.join; t2.join
c.count