[libevent源码分析] event_add

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

intevent_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);}

如果新加的事件不为空，当前事件不是timeout时间，就为他在时间最小堆上分配一块可用空间(如果最小堆有空间，就不会重新分配)
关于最小堆可以连接我的githup,libevent用最小堆来管理定时事件，根节点永远是最小的而且算法时间最小

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 intepoll_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);}

信号追加，libevent对信号采用sockpair 创建两个互连socket，信号激发写可写sock，可读加入到事件循环中去
根据信号ev_base->sig.evsigcaught[signumber]来判断该信号是否发生,下面是信号追加函数

intevsignal_add(struct event *ev){int evsignal;struct event_base *base = ev->ev_base;          //信号event的basestruct 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numberassert(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);}

信号回调函数

/* * 所有的信号都通用一个信号处理函数 */static voidevsignal_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_SIGACTIONsignal(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