Simple example of concurrency in Ruby with Fiber.

simple_fiber_concurrency.rb

require "fiber"

f1 = Fiber.new do |f2|
  while true
    puts "A"
    sleep 2
    f2.transfer
  end
end

f2 = Fiber.new do |f1|
  f1.resume Fiber.current
  while true
    puts "B"
    sleep 2
    f1.transfer
  end
end

f2.resume f1