Cooperative concurrency in ruby

async_kitchen.rb

require 'fiber'

class EventLoop
  def initialize
    @tasks = {}
    @state = {}
  end

  def call(&block)
    instance_eval &block

    loop do
      @tasks.each { |name, fiber|
        unless fiber.alive?
          @tasks.delete(name)
          next
        end
        fiber.resume
      }
    end
  end

  def task(name, &block)
    @tasks[name] = Fiber.new do
      instance_eval(&block)
    end
  end

  def set(key, value)
    @state[key] ||= []
    @state[key] << value
    Fiber.yield
  end

  def get(key, *args)
    loop do
      return @state[key].pop if @state.key?(key) && @state[key].any?
      Fiber.yield
    end
  end
end


# A cooperatively concurrent restaurant
EventLoop.new.call do
  task :open_restaurant do
    set(:free_table, 1)
    set(:free_table, 2)
  end

  task :server do
    loop do
      puts "server - setting table"
      table = get(:free_table)
      set(:table, table)
      puts "server - giving menu"
      set(:menu, '...')
      puts "server - taking order"
      order = get(:order)
      puts "server - sending #{order} order to kitchen"
      set(:kitchen_order, order)
      puts "server - serving #{order}"
      order = get(:ready_order)
      set(order, order)
    end
  end

  task :chef do
    loop do
      order = get(:kitchen_order)
      puts "chef - making #{order}"
      set(:ready_order, order)
    end
  end

  task :customer1 do
    puts "customer 1 - waiting for table"
    table = get(:table)
    puts "customer 1 - waiting for menu"
    get(:menu)
    puts "customer 1 - ordering"
    set(:order, :filet_mignon)
    order = get(:filet_mignon)
    puts "customer 1 - finished #{order}"
    set(:free_table, table)
  end

  task :customer2 do
    puts "customer 2 - waiting for table"
    table = get(:table)
    puts "customer 2 - waiting for menu"
    get(:menu)
    puts "customer 2 - ordering"
    set(:order, :lobster_bisque)
    order = get(:lobster_bisque)
    puts "customer 2 - finished #{order}"
    set(:free_table, table)
  end
end