[libevent]event_base_loop()

intevent_base_loop(struct event_base *base, int flags){const struct eventop *evsel = base->evsel;//选择了epoll机制（如果之前选择了epoll）void *evbase = base->evbase;//epoll.c的epollop对象struct timeval tv;struct timeval *tv_p;int res, done;/* clear time cache */base->tv_cache.tv_sec = 0;//清除时间缓存，好让下面的gettime获得当前系统时间而不是获得缓存的时间if (base->sig.ev_signal_added)evsignal_base = base;//该变量也是一个全局的变量，赋值后关于信号的一些操作默认用到这个basedone = 0;while (!done) {/* Terminate the loop if we have been asked to */if (base->event_gotterm) {//这两个是用来中断循环的标识base->event_gotterm = 0;break;}if (base->event_break) {base->event_break = 0;break;}timeout_correct(base, &tv);//如果使用了monotonic时钟类型则这个函数就没用了tv_p = &tv;if (!base->event_count_active && !(flags & EVLOOP_NONBLOCK)) {//如果没有就绪的事件，则获得接下来需要最小等待时间，用作epoll_wait的时间参数timeout_next(base, &tv_p);} else {/*  * if we have active events, we just poll new events * without waiting. */evutil_timerclear(&tv);//有就绪事件则无需等待epoll_wait，时间设置为0}/* If we have no events, we just exit *///无事件注册了则退出循环if (!event_haveevents(base)) {event_debug(("%s: no events registered.", __func__));return (1);}/* update last old time */gettime(base, &base->event_tv);//如果使用了monotonic时钟，则这个也没什么意义/* clear time cache */base->tv_cache.tv_sec = 0;res = evsel->dispatch(base, evbase, tv_p);//内部使用epoll_wait()等待事件，不过仅仅处理读写事件，信号事件在evsignal_process()函数处理if (res == -1)return (-1);gettime(base, &base->tv_cache);//获得当前时间，更新缓存，缓存的作用是无需调用系统调用获得时间，省时timeout_process(base);//检查小根堆的事件是否到时，并进行删除过期事件和插入就绪链表的动作if (base->event_count_active) {//有就绪事件则调用事件注册的回调函数event_process_active(base);if (!base->event_count_active && (flags & EVLOOP_ONCE))done = 1;} else if (flags & EVLOOP_NONBLOCK)done = 1;}/* clear time cache */base->tv_cache.tv_sec = 0;event_debug(("%s: asked to terminate loop.", __func__));return (0);}