Three Fibers Dancing in a Clock

clock.rb

require 'fiber'

module Clock
  DEFAULT_SECONDS = 4

  module_function

  def run seconds: DEFAULT_SECONDS
    timer.resume tick, tock, seconds: seconds
  end
  alias call run

  def timer
    Fiber.new do |ticker, tocker, seconds: DEFAULT_SECONDS|
      beats = [ticker, tocker].cycle
      seconds.times do
        sleep 1
        beats.next.transfer Fiber.current
      end

      'en fin'
    end
  end

  def tick
    Fiber.new do |time|
      loop do
        puts 'tick'
        time.transfer
      end
    end
  end

  def tock
    Fiber.new do |time|
      loop do
        puts 'tock'
        time.transfer
      end
    end
  end
end

2.times.map { Thread.new { Clock.run } }.map &:value