比select好用的工具，异步触发机制，可以同时检查若干描述符-The libevent API provides a mechanism to execute 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.



libevent is meant to replace the event loop found in event driven network servers. An application just needs to call event_dispatch() and then add or remove events dynamically without having to change the event loop.



Currently, libevent supports /dev/poll, kqueue(2), event ports, POSIX select(2), Windows select(), poll(2), and epoll(4). The internal event mechanism is completely independent of the exposed event API, and a simple update of libevent can provide new functionality without having to redesign the applications. As a result, Libevent allows for portable application development and provides the most scalable event notification mechanism available on an operating system. Libevent can also be used for multi-threaded applications, either by i