echo.rb

require 'celluloid'
require 'celluloid/io'

class EchoServer
  include Celluloid::IO

  finalizer :echo_finalize

  def initialize(host, port)
    puts "*** Starting echo server on #{host}:#{port}"

    # Since we included Celluloid::IO, we're actually making a
    # Celluloid::IO::TCPServer here
    @server = TCPServer.new(host, port)
    async.run
  end

  def echo_finalize
    @server.close if @server
  end

  private
  def run
    loop { async.handle_connection @server.accept }
  end

  def handle_connection(socket)
    _, port, host = socket.peeraddr
    puts "*** Received connection from #{host}:#{port}"
    loop { socket.write socket.readpartial(4096) }
  rescue EOFError
    puts "*** #{host}:#{port} disconnected"
  end
end

server = EchoServer.new('localhost', 9000)
Celluloid.join(server)

output

D, [2013-02-15T21:48:41.958060 #27596] DEBUG -- : Terminating 5 actors...
D, [2013-02-15T21:48:41.959060 #27596] DEBUG -- : Shutdown completed cleanly
echo.rb:37:in `<main>': undefined method `join' for Celluloid:Module (NoMethodError)