Simple example of concurrency in Ruby with Fiber.

simple_fiber_concurrency.rb

require "fiber"

f1 = Fiber.new { |f2| f2.resume Fiber.current; while true; puts "A"; f2.transfer; end }
f2 = Fiber.new { |f1| f1.transfer; while true; puts "B"; f1.transfer; end }

f1.resume f2

require "fiber"

f1 = Fiber.new { |f2| f2.resume Fiber.current; while true; puts "A"; f2.transfer; end }
f2 = Fiber.new { |f1| f1.transfer; while true; puts "B"; f1.transfer; end }

f1.resume f2

A-ha! That was really pretty obvious, I guess, having re-read the docs. Too busy thinking about Fibers and not enough focus elsewhere.