[libevent源码分析] event_add

标签：c   linux   libevent   源码   socket   

event_add 把event往当前event中的ev_base追加,如果需要定时，那么tv不能为空

int
event_add(struct event *ev, const struct timeval *tv)
{
	struct event_base *base = ev->ev_base;      //event_add 会把event加入到他的ev_base成员里
	const struct eventop *evsel = base->evsel;  //对应linux的epoll相关函数
	void *evbase = base->evbase;                //对应linux为 struct epollop
    /*
     * struct epollop
     * {
     *      struct evepoll *fds;                //分配nfiles个evepoll对象
     *      int nfds;                           //支持的最大软限制数的句柄(上面的数组个数)
     *      struct epoll_event* events;         //分配nfiles(软限制数) epoll_event对象
     *      int nevents;                        //nevents保存着上面events个数
     *      int epfd;                           //保存着epoll_create的句柄
     * }
     */
	int res = 0;

	event_debug((
		 "event_add: event: %p, %s%s%scall %p",
		 ev,
		 ev->ev_events & EV_READ ? "EV_READ " : " ",
		 ev->ev_events & EV_WRITE ? "EV_WRITE " : " ",
		 tv ? "EV_TIMEOUT " : " ",
		 ev->ev_callback));

	assert(!(ev->ev_flags & ~EVLIST_ALL));

	if (tv != NULL && !(ev->ev_flags & EVLIST_TIMEOUT)) {
		if (min_heap_reserve(&base->timeheap,
			1 + min_heap_size(&base->timeheap)) == -1)
			return (-1);  /* ENOMEM == errno */
	}

	if ((ev->ev_events & (EV_READ|EV_WRITE|EV_SIGNAL)) &&
	    !(ev->ev_flags & (EVLIST_INSERTED|EVLIST_ACTIVE))) {
		res = evsel->add(evbase, ev);           //注册or修改事件到epoll中去
		if (res != -1)
			event_queue_insert(base, ev, EVLIST_INSERTED);  //把ev插入到eventqeue中去
	}

    /*
     * 如果说插入事件成功同时设置了超时时间
     */
	if (res != -1 && tv != NULL) {
		struct timeval now;

        /* 
         *如果已经存在了超时时间,那么就删除这个超时节点
         */ 
		if (ev->ev_flags & EVLIST_TIMEOUT)
			event_queue_remove(base, ev, EVLIST_TIMEOUT);

		/* Check if it is active due to a timeout.  Rescheduling
		 * this timeout before the callback can be executed
		 * removes it from the active list. */
		if ((ev->ev_flags & EVLIST_ACTIVE) &&
		    (ev->ev_res & EV_TIMEOUT)) {
			/* See if we are just active executing this
			 * event in a loop
			 */
			if (ev->ev_ncalls && ev->ev_pncalls) {
				/* Abort loop */
				*ev->ev_pncalls = 0;
			}
			
			event_queue_remove(base, ev, EVLIST_ACTIVE);
		}

		gettime(base, &now);
		evutil_timeradd(&now, tv, &ev->ev_timeout);

		event_debug((
			 "event_add: timeout in %ld seconds, call %p",
			 tv->tv_sec, ev->ev_callback));

		event_queue_insert(base, ev, EVLIST_TIMEOUT);//加入到最小超时堆中去
	}

	return (res);
}

如果事件是EV_READ、EV_WRITE、EV_SIGNAL,并且事件不是插入or激活状态，那么就加入事件
以epoll为例

static int
epoll_add(void *arg, struct event *ev)
{
	struct epollop *epollop = arg;
	struct epoll_event epev = {0, {0}};
	struct evepoll *evep;
	int fd, op, events;

    /*
     * 信号的原理
     * 1 设置信号处理函数，保存原来的信号处理函数到event的ev_base->sh_old中去
     * 2 如果是首次添加信号，那么需要为所有信号追加一个信号事件来源自event->ev_base->ev_signal
     *   同时设置event->ev_base->ev_signal->ev_signal_added,表示信号回调事件已经设置了
     * 3 同时把事件追加到event->ev_base->ev_signal->evsigevents[signno]链表中去
     */
	if (ev->ev_events & EV_SIGNAL)  //如果是加入的信号
		return (evsignal_add(ev));

	fd = ev->ev_fd;
	if (fd >= epollop->nfds) {
		/* Extent the file descriptor array as necessary */
        //如果说当前的epoll中已经满足不了新加入的句柄
		if (epoll_recalc(ev->ev_base, epollop, fd) == -1)
			return (-1);
	}

	evep = &epollop->fds[fd];
	op = EPOLL_CTL_ADD;
	events = 0;
    //如果事件之前是可读
	if (evep->evread != NULL) {
		events |= EPOLLIN;
		op = EPOLL_CTL_MOD;
	}
    //如果事件之前是可写
	if (evep->evwrite != NULL) {
		events |= EPOLLOUT;
		op = EPOLL_CTL_MOD;
	}

    //新加入事件设置的是可读事件
	if (ev->ev_events & EV_READ)
		events |= EPOLLIN;
    //新加入事件设置的是可写事件
	if (ev->ev_events & EV_WRITE)
		events |= EPOLLOUT;

	epev.data.ptr = evep;
	epev.events = events;
	if (epoll_ctl(epollop->epfd, op, ev->ev_fd, &epev) == -1)
			return (-1);

	/* Update events responsible */
	if (ev->ev_events & EV_READ)
		evep->evread = ev;
	if (ev->ev_events & EV_WRITE)
		evep->evwrite = ev;

	return (0);
}

int
evsignal_add(struct event *ev)
{
	int evsignal;
	struct event_base *base = ev->ev_base;          //信号event的base
	struct evsignal_info *sig = &ev->ev_base->sig;  //信号在ev_base的管理结构

	if (ev->ev_events & (EV_READ|EV_WRITE))         //信号事件不支持可读可写事件
		event_errx(1, "%s: EV_SIGNAL incompatible use", __func__);
	evsignal = EVENT_SIGNAL(ev);                    //信号的fd就是信号number
	assert(evsignal >= 0 && evsignal < NSIG);       //信号不能超过NSIG这个数
	if (TAILQ_EMPTY(&sig->evsigevents[evsignal])) { //如果说该信号链表为空
		event_debug(("%s: %p: changing signal handler", __func__, ev));
        //设置信号处理函数，同时，保存原来的信号处理函数到ev_base->sh_old中去
		if (_evsignal_set_handler(
			    base, evsignal, evsignal_handler) == -1)
			return (-1);

		/* catch signals if they happen quickly */
		evsignal_base = base;

		if (!sig->ev_signal_added) {
			if (event_add(&sig->ev_signal, NULL))
				return (-1);
			sig->ev_signal_added = 1;               //加入epoll_wait中去
		}
	}

    //把ev->ev_signal_next加入到sig->evsigevents[evsignal]的链表末端
	/* multiple events may listen to the same signal */
	TAILQ_INSERT_TAIL(&sig->evsigevents[evsignal], ev, ev_signal_next);

	return (0);
}

/*
 * 所有的信号都通用一个信号处理函数
 */
static void
evsignal_handler(int sig)
{
	int save_errno = errno;     //保存错误码

	if (evsignal_base == NULL) {
		event_warn(
			"%s: received signal %d, but have no base configured",
			__func__, sig);
		return;
	}

	evsignal_base->sig.evsigcaught[sig]++;  //引起的信号number++
	evsignal_base->sig.evsignal_caught = 1; //设置信号标志，表示信号已经触发

#ifndef HAVE_SIGACTION
	signal(sig, evsignal_handler);
#endif

	/* Wake up our notification mechanism */
	send(evsignal_base->sig.ev_signal_pair[0], "a", 1, 0);  //通过写sockpair写数据来触发epoll_wait返回
	errno = save_errno;
}

定时事件采用最小堆，定时值+当前事件最为左后超时时间，加入到最小堆中去，主要在event_base_dispatch中使用

libeven 整个源码分析和sample都在我的 githup

[libevent源码分析] event_add

标签：c   linux   libevent   源码   socket   

原文地址：http://blog.csdn.net/youkuxiaobin/article/details/44112779