Linux下tcp并发服务器的实现。服务器端监听是否有请求，并循环接受收到的请求，每收到一个请求，fork（）一次，通过子进程来完成客户端的请求。-Under Linux tcp achieve concurrent server. Monitor whether the server requests and circulation accept requests received, each receives a request, fork () once, by a child process to complete the client' s request.