有没有现成的可以实现在 OS X 上 on-demand launching 的轮子

[lululau]

类似这样的功能：

services = [
  {:port => 3306, :cmd => 'mysqld_safe xxxxx'},
  {:port => 6379, :cmd => 'redis-server xxxx'}
]

while true
  services.each do |service|
    if service[:port].not_in_use?
      Thread.new(service) do |service|
        server_sock = TCPServer.new(serivce[:port])
        server_sock.listen(backlog)
        server_sock.accept
        server_sock.close()
        system(service[:cmd])
      end
    end
  end
  sleep(interval)
end

launchd 可以实现 on-demand launching，但是需要被启动的 service 程序支持才行