libevent是一个事件触发的网络库 ，适用于windows、linux、bsd等多种平台，内部使用select、epoll、kqueue等系统调用管理事件机制-The libevent API provides a mechanism to a callback function when a specific event occurs on a file descr iptor or after a timeout has been reached. Furthermore, libevent also support callbacks due to signals or regular timeouts.