a.rb

$port = 10000

require "socket"
server = TCPServer.open($port)
loop do
  Thread.start(server.accept) do |cli|
    puts "connected: " + cli.__id__.to_s
    while line = cli.gets
      puts cli.__id__.to_s + ": " + line.chomp
    end
    cli.close
    puts "disconnected: " + cli.__id__.to_s
  end
end