Libevent 事件循环(1)
// 事件的dispatch
int event_base_loop(struct event_base *base, int flags) {
//得到采用的事件模型 epoll/epoll/select const struct eventop *evsel = base->evsel; struct timeval tv; struct timeval *tv_p; int res, done, retval = 0; /* Grab the lock. We will release it inside evsel.dispatch, and again * as we invoke user callbacks. */ EVBASE_ACQUIRE_LOCK(base, th_base_lock);
//判断是否loop正在running 如果由则退出 if (base->running_loop) { event_warnx("%s: reentrant invocation. Only one event_base_loop" " can run on each event_base at once.", __func__); EVBASE_RELEASE_LOCK(base, th_base_lock); return -1; } base->running_loop = 1; //清理时间缓存 clear_time_cache(base); if (base->sig.ev_signal_added && base->sig.ev_n_signals_added) evsig_set_base_(base); done = 0; #ifndef EVENT__DISABLE_THREAD_SUPPORT base->th_owner_id = EVTHREAD_GET_ID(); #endif //终止和中断标志至0 base->event_gotterm = base->event_break = 0; //事件循环 与 平时我们自己写的epoll_wait select 等待事件一样 在一个死循环中 while (!done) { base->event_continue = 0; base->n_deferreds_queued = 0; /* Terminate the loop if we have been asked to */
//被其他线程中断 if (base->event_gotterm) { break; } if (base->event_break) { break; } tv_p = &tv;
//当前没有激活的事件 if (!N_ACTIVE_CALLBACKS(base) && !(flags & EVLOOP_NONBLOCK)) { timeout_next(base, &tv_p);//判断小根堆中的root是否已经超时， 如果超时 就将tv清0. 如果没有的话就将root的时间减去现在时间的结果赋值给tv(定时器触发的剩余
的时间长度) } else { /* * if we have active events, we just poll new events * without waiting. */
//如果有激活事件 就将tv清空 evutil_timerclear(&tv); } /* If we have no events, we just exit */
//未注册事件就退出循环 if (0==(flags&EVLOOP_NO_EXIT_ON_EMPTY) && !event_haveevents(base) && !N_ACTIVE_CALLBACKS(base)) { event_debug(("%s: no events registered.", __func__)); retval = 1; goto done; } event_queue_make_later_events_active(base); //清理时间缓存 clear_time_cache(base); // 调用模型的epoll_wait/select/poll 等 tv_p 是刚才计算的最小时间间隔 res = evsel->dispatch(base, tv_p); //以epoll 为例详细说明 if (res == -1) { event_debug(("%s: dispatch returned unsuccessfully.", __func__)); retval = -1; goto done; } //更新base中的时间， 下面就是调用定时事件和IO事件。 update_time_cache(base); //判断定时器事件是否发生了，若发生就将事件加入激活队列 timeout_process(base); //见下文 if (N_ACTIVE_CALLBACKS(base)) {
//执行激活队列中的事件 int n = event_process_active(base); //见下文 if ((flags & EVLOOP_ONCE) && N_ACTIVE_CALLBACKS(base) == 0 && n != 0) done = 1; } else if (flags & EVLOOP_NONBLOCK) done = 1; } event_debug(("%s: asked to terminate loop.", __func__)); done: clear_time_cache(base); base->running_loop = 0; EVBASE_RELEASE_LOCK(base, th_base_lock); return (retval); }
以 epoll 模型的dispatch 看一下evsel->dispatch(base, tv_p);
static int epoll_dispatch(struct event_base *base, struct timeval *tv) { struct epollop *epollop = base->evbase; struct epoll_event *events = epollop->events; int i, res; long timeout = -1; if (tv != NULL) { timeout = evutil_tv_to_msec_(tv); //将tv 话为 msec传递给epoll_wait if (timeout < 0 || timeout > MAX_EPOLL_TIMEOUT_MSEC) { /* Linux kernels can wait forever if the timeout is * too big; see comment on MAX_EPOLL_TIMEOUT_MSEC. */ timeout = MAX_EPOLL_TIMEOUT_MSEC; } } epoll_apply_changes(base); event_changelist_remove_all_(&base->changelist, base); EVBASE_RELEASE_LOCK(base, th_base_lock);//多线程下防止惊群而加锁 res = epoll_wait(epollop->epfd, events, epollop->nevents, timeout);//等待事件 EVBASE_ACQUIRE_LOCK(base, th_base_lock); if (res == -1) { if (errno != EINTR) { event_warn("epoll_wait"); return (-1); } return (0); } event_debug(("%s: epoll_wait reports %d", __func__, res)); EVUTIL_ASSERT(res <= epollop->nevents); //依次处理事件 for (i = 0; i < res; i++) { int what = events[i].events; short ev = 0; if (what & (EPOLLHUP|EPOLLERR)) { ev = EV_READ | EV_WRITE; } else { if (what & EPOLLIN) ev |= EV_READ; if (what & EPOLLOUT) ev |= EV_WRITE; if (what & EPOLLRDHUP) ev |= EV_CLOSED; } if (!ev) continue; //根据fd找到相应的位置 将event_callback加入到激活queue等待被调用 evmap_io_active_(base, events[i].data.fd, ev | EV_ET); } // 拓展事件容量 if (res == epollop->nevents && epollop->nevents < MAX_NEVENT) { /* We used all of the event space this time. We should be ready for more events next time. */ int new_nevents = epollop->nevents * 2; struct epoll_event *new_events; new_events = mm_realloc(epollop->events, new_nevents * sizeof(struct epoll_event)); if (new_events) { epollop->events = new_events; epollop->nevents = new_nevents; } } return (0); }
再看一下timeout_process.
static void timeout_process(struct event_base *base) { /* Caller must hold lock. */ struct timeval now; struct event *ev; //没有定时事件直接退出 if (min_heap_empty_(&base->timeheap)) { return; } gettime(base, &now); //取堆顶最小 while ((ev = min_heap_top_(&base->timeheap))) {
//没有超时就直接退出 if (evutil_timercmp(&ev->ev_timeout, &now, >)) break; /* delete this event from the I/O queues */
//有超时事件发生就将事件从io中删除 event_del_nolock_(ev, EVENT_DEL_NOBLOCK); event_debug(("timeout_process: event: %p, call %p", ev, ev->ev_callback));
//加入激活队列中 最终会调用 event_queue_insert_timeout，被激活的计时和IO都放在同一个queue中 event_active_nolock_(ev, EV_TIMEOUT, 1); } }
