Linux下udp并发服务器的实现。服务器循环接收客户端的消息，每收到一个消息，fork（）一次，通过子进程来完成客户端的消息。与tcp并发不一样，他不必listen（）和accept（）。-Udp under Linux to achieve concurrent server. Server receives the client' s message loop, each receives a message, fork () once the child process to be completed by the client' s message. Concurrent with the tcp not the same, he does not listen () and accept ().