fiber.rb

require 'socket'
require 'fiber'

class Selector
  def initialize
    @readable = {}
    @writeable = {}
  end

  def wait_readable(io)
    @readable[io] = Fiber.current
    Fiber.yield
    @readable.delete(io)
    true
  end

  def run
    while @readable.any? || @writeable.any?
      readable, writable = IO.select(@readable.keys, @writeable.keys)

      readable.each do |io|
        @readable[io].resume
      end

      writable.each do |io|
        @writeable[io].resume
      end
    end
  end
end

class Client
  def initialize(io, selector)
    @io = io
    @selector = selector
  end

  def read(*args)
    while result = @io.read_nonblock(*args, exception: false)
      case result
      when :wait_readable
        @selector.wait_readable(@io)
      else
        return result
      end
    end
  end
end

class FiberChat < TCPServer
  def initialize(*args)
    super

    @selector = Selector.new
  end

  def handle(conn)
    client =  Client.new(conn, @selector)

    Fiber.new do
      msg = ''
      loop do
        msg += client.read(1).to_s until msg.end_with?("\n")
        Kernel.puts msg
        msg = ''
      end
    end.resume
  end

  def run(&block)
    Fiber.new do
      while conn = accept_nonblock(exception: false)
        case conn
        when :wait_readable
          @selector.wait_readable(self)
        else
          handle(conn)
        end
      end
    end.resume

    @selector.run
  end
end

srv = FiberChat.new 8080
srv.run