require 'thread'

semaphore = Mutex.new
data = {}

getter = Thread.new do
  gettercount = 0
  loop do
    puts "#{data[:foo]} #{gettercount}"
    gettercount += 1
  end
end

setter = Thread.new do
  settercount = 0
  loop do
    d = { foo: settercount }
    semaphore.synchronize do
      data = d
    end
    settercount += 1
  end

end

setter.join
getter.join