Libevent 事件管理和添加事件

/*
*   我们先来看一下事件的创建
*/
struct event *
event_new(struct event_base *base, evutil_socket_t fd, short events, void (*cb)(evutil_socket_t, short, void *), void *arg)
{
    struct event *ev;
    ev = mm_malloc(sizeof(struct event));
    if (ev == NULL)
        return (NULL);
    //调用assign 给ev 赋值
    if (event_assign(ev, base, fd, events, cb, arg) < ) {
        mm_free(ev);
        return (NULL);
    }

    return (ev);
}

int
event_assign(struct event *ev, struct event_base *base, evutil_socket_t fd, short events, void (*callback)(evutil_socket_t, short, void *), void *arg)
{
    if (!base)
        base = current_base;
    if (arg == &event_self_cbarg_ptr_)
        arg = ev;

    event_debug_assert_not_added_(ev);
    //设置ev结构体的各个参数
    ev->ev_base = base;

    ev->ev_callback = callback;
    ev->ev_arg = arg;
    ev->ev_fd = fd;
    ev->ev_events = events;
    ev->ev_res = ;
    ev->ev_flags = EVLIST_INIT;
    ev->ev_ncalls = ;
    ev->ev_pncalls = NULL;

    if (events & EV_SIGNAL) {
        //信号事件和io事件冲突
        if ((events & (EV_READ|EV_WRITE|EV_CLOSED)) != ) {
            event_warnx("%s: EV_SIGNAL is not compatible with "
                "EV_READ, EV_WRITE or EV_CLOSED", __func__);
            return -;
        }
        ev->ev_closure = EV_CLOSURE_EVENT_SIGNAL;
    } else {
        if (events & EV_PERSIST) {
            //如果事件是persist 清理记0
            evutil_timerclear(&ev->ev_io_timeout);
            ev->ev_closure = EV_CLOSURE_EVENT_PERSIST;
        } else {
            ev->ev_closure = EV_CLOSURE_EVENT;
        }
    }

    min_heap_elem_init_(ev);// 初始化最小堆索引为 -1 
　　//void min_heap_elem_init_(struct event* e) { e->ev_timeout_pos.min_heap_idx = -1; } 
    if (base != NULL) {
        /* by default, we put new events into the middle priority */
        ev->ev_pri = base->nactivequeues / ;
    }

    event_debug_note_setup_(ev);

    return ;
}

libevent事件管理结构
 IO 事件管理
　反应堆中event_base 中 
　　{
　　　　........
　　　　struct event_io_map io;  
　　　　struct event_signal_map sigmap;
　　　　........
　　}
                                             ________________
  event_base->io       event_io_map ------> |    evmap_io   |--->|   io  |----->|   io  |---||------  event_dlist events.
　　　　　　　　　　　　　　　　　　　　　　　　　　————————————————            此文件描述符关心的所有事件链表
　　　　　　　　　　　　　　　　　 　　　　　　　　|               |
　　　　　　　　　　　　　　　　　　　　　　　　　　————————————————
　　　　　　　　　　　　　　　　　 　　　　　　　　|               |
　　　　　　　　　　　　　　　　　　　　　        -----------------
          
            struct evmap_io {
    　　　　　　　　struct event_dlist events; //链表管理一个文件描述符所有关心的io事件
    　　　　　　　　ev_uint16_t nread;
    　　　　　　　　ev_uint16_t nwrite;
    　　　　　　　　ev_uint16_t nclose;
　　　　　　};
      
          struct evmap_signal {
    　　　　struct event_dlist events;//链表管理所有的信号事件
　　　　　　};

　　　　　　Linux 下的事件的hashmap io与signal相同。
　　　　　　#define event_io_map event_signal_map
　　　　　　struct event_signal_map {
    　　　　　　/* An array of evmap_io * or of evmap_signal *; empty entries are
     　　　　　　* set to NULL. */
    　　　　　　void **entries;     //entries 管理的是evmap_io \ evmap_signal
    　　　　　　/* The number of entries available in entries */
    　　　　　　int nentries;
　　　　　　};

下面是添加一个io事件的过程：
　　　　int　evmap_io_add_(struct event_base *base, evutil_socket_t fd, struct event *ev)
　　　　{
    　　const struct eventop *evsel = base->evsel;
    　　struct event_io_map *io = &base->io;
    　　struct evmap_io *ctx = NULL;
    　　int nread, nwrite, nclose, retval = 0;
    　　short res = 0, old = 0;
    　　struct event *old_ev;

    　　EVUTIL_ASSERT(fd == ev->ev_fd);

    　　if (fd < 0)
        　　return 0;
　　　　// Linux  use it
　　　　#ifndef EVMAP_USE_HT
    　　if (fd >= io->nentries) {
            //分配空间 
        　　if (evmap_make_space(io, fd, sizeof(struct evmap_io *)) == -1)
            return (-1);
    　　}
　　　　#endif
    　　//初始化一个evmap_io 并将ctx指针 指向这个结构体 linux下文件描述符即为key。
    　　GET_IO_SLOT_AND_CTOR(ctx, io, fd, evmap_io, evmap_io_init,
                         evsel->fdinfo_len);
    　　/*
            #define GET_SIGNAL_SLOT_AND_CTOR(x, map, slot, type, ctor, fdinfo_len)    \
        do {                                \
            if ((map)->entries[slot] == NULL) {            \
                (map)->entries[slot] =                \
                    mm_calloc(1,sizeof(struct type)+fdinfo_len); \
                if (EVUTIL_UNLIKELY((map)->entries[slot] == NULL)) \
                    return (-1);                \
                (ctor)((struct type *)(map)->entries[slot]);    \
            }                            \
            (x) = (struct type *)((map)->entries[slot]);        \
        } while (0)
    　　*/
    　　//一个event 可能对应多个事件
　　　　// 这里就是上一个的事件类型
   　　 nread = ctx->nread;
    　　nwrite = ctx->nwrite;
    　　nclose = ctx->nclose;

    　　if (nread)
        　　old |= EV_READ;
    　　if (nwrite)
        　　old |= EV_WRITE;
    　　if (nclose)
        　　old |= EV_CLOSED;
        //新的事件加入 若之前存在就不再设置res 但是会将各个事件个数加一
   　　 if (ev->ev_events & EV_READ) {
       　　 if (++nread == 1)
           　　 res |= EV_READ;
    　　}
    　　if (ev->ev_events & EV_WRITE) {
        　　if (++nwrite == 1)
           　　 res |= EV_WRITE;
    　　}
    　　if (ev->ev_events & EV_CLOSED) {
        　　if (++nclose == 1)
            res |= EV_CLOSED;
    　　}
    //一个描述符添加的事件个数不能超过oxffff.
    if (EVUTIL_UNLIKELY(nread > 0xffff || nwrite > 0xffff || nclose > 0xffff)) {
        event_warnx("Too many events reading or writing on fd %d",
            (int)fd);
        return -1;
    }

    ctx->nread = (ev_uint16_t) nread;
    ctx->nwrite = (ev_uint16_t) nwrite;
    ctx->nclose = (ev_uint16_t) nclose;
    //将新事件加入链表中
    LIST_INSERT_HEAD(&ctx->events, ev, ev_io_next);
    return (retval);
}

定时则是由min_heap最小堆的数据结构管理，每次取时间最短的事件。

添加事件：

int
event_add_nolock_(struct event *ev, const struct timeval *tv,
    int tv_is_absolute)
{
    struct event_base *base = ev->ev_base;
    int res = ;
    int notify = ;

    EVENT_BASE_ASSERT_LOCKED(base);
    event_debug_assert_is_setup_(ev);

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

    EVUTIL_ASSERT(!(ev->ev_flags & ~EVLIST_ALL));
    //若事件标志是终止事件， 就不再将事件加入
    if (ev->ev_flags & EVLIST_FINALIZING) {
        /* XXXX debug */
        return (-);
    }

    /*
     * prepare for timeout insertion further below, if we get a
     * failure on any step, we should not change any state.
     */
//先把堆空间准备好， 后续再插入定时事件
    if (tv != NULL && !(ev->ev_flags & EVLIST_TIMEOUT)) {
        if (min_heap_reserve_(&base->timeheap,
             + min_heap_size_(&base->timeheap)) == -)
            return (-);  /* ENOMEM == errno */
    }

    /* If the main thread is currently executing a signal event's
     * callback, and we are not the main thread, then we want to wait
     * until the callback is done before we mess with the event, or else
     * we can race on ev_ncalls and ev_pncalls below. */
#ifndef EVENT__DISABLE_THREAD_SUPPORT
    if (base->current_event == event_to_event_callback(ev) &&
        (ev->ev_events & EV_SIGNAL)
        && !EVBASE_IN_THREAD(base)) {
        ++base->current_event_waiters;
        EVTHREAD_COND_WAIT(base->current_event_cond, base->th_base_lock);
    }
#endif

    if ((ev->ev_events & (EV_READ|EV_WRITE|EV_CLOSED|EV_SIGNAL)) &&
        !(ev->ev_flags & (EVLIST_INSERTED|EVLIST_ACTIVE|EVLIST_ACTIVE_LATER))) {
        //如果事件是未被加入的 那么就先加入map中  上面所述
        if (ev->ev_events & (EV_READ|EV_WRITE|EV_CLOSED))
            res = evmap_io_add_(base, ev->ev_fd, ev);
        else if (ev->ev_events & EV_SIGNAL)
            res = evmap_signal_add_(base, (int)ev->ev_fd, ev);
        if (res != -)
            event_queue_insert_inserted(base, ev); //此处并没有将event加入到queue 只是将事件中的flag指为EVLIST_INSERTED  (base)->event_count += 1
        if (res == ) {
            /* evmap says we need to notify the main thread. */
            notify = ;
            res = ;
        }
    }

    /*
     * we should change the timeout state only if the previous event
     * addition succeeded.
     */
    //添加定时器事件
    if (res != - && tv != NULL) {
        struct timeval now;
        int common_timeout;
#ifdef USE_REINSERT_TIMEOUT
        int was_common;
        int old_timeout_idx;
#endif

        /*
         * for persistent timeout events, we remember the
         * timeout value and re-add the event.
         *
         * If tv_is_absolute, this was already set.
         */
        if (ev->ev_closure == EV_CLOSURE_EVENT_PERSIST && !tv_is_absolute)
            ev->ev_io_timeout = *tv;

#ifndef USE_REINSERT_TIMEOUT
        if (ev->ev_flags & EVLIST_TIMEOUT) {
            event_queue_remove_timeout(base, ev); //已有定时事件将从最小堆中删除原先那个定时事件
        }
#endif

        /* Check if it is active due to a timeout.  Rescheduling
         * this timeout before the callback can be executed
         * removes it from the active list. */

         //如果此事件已经被激活并且返回了timeout事件就将事件终止， 并删除被激活的定时器事件 进而重新调度定时器
        if ((ev->ev_flags & EVLIST_ACTIVE) &&
            (ev->ev_res & EV_TIMEOUT)) {
            if (ev->ev_events & EV_SIGNAL) {
                /* See if we are just active executing
                 * this event in a loop
                 */
                if (ev->ev_ncalls && ev->ev_pncalls) {
                    /* Abort loop */
                    *ev->ev_pncalls = ;
                }
            }

            event_queue_remove_active(base, event_to_event_callback(ev));
        }
        //初始化定时器
        gettime(base, &now);
        //选用链表记时器还是最小堆
        common_timeout = is_common_timeout(tv, base);
#ifdef USE_REINSERT_TIMEOUT
        was_common = is_common_timeout(&ev->ev_timeout, base);
        old_timeout_idx = COMMON_TIMEOUT_IDX(&ev->ev_timeout);
#endif

        if (tv_is_absolute) {
            ev->ev_timeout = *tv;
        } else if (common_timeout) {
            struct timeval tmp = *tv;
            tmp.tv_usec &= MICROSECONDS_MASK;
            evutil_timeradd(&now, &tmp, &ev->ev_timeout);
            ev->ev_timeout.tv_usec |=
                (tv->tv_usec & ~MICROSECONDS_MASK);
        } else {
            evutil_timeradd(&now, tv, &ev->ev_timeout);
        }

        event_debug((
             "event_add: event %p, timeout in %d seconds %d useconds, call %p",
             ev, (int)tv->tv_sec, (int)tv->tv_usec, ev->ev_callback));

#ifdef USE_REINSERT_TIMEOUT
        event_queue_reinsert_timeout(base, ev, was_common, common_timeout, old_timeout_idx);
#else
        event_queue_insert_timeout(base, ev);//加入到最小堆
#endif
        //多线程定时器
        if (common_timeout) {
            //链表形式的计时器
            struct common_timeout_list *ctl =
                get_common_timeout_list(base, &ev->ev_timeout);
            if (ev == TAILQ_FIRST(&ctl->events)) {
                common_timeout_schedule(ctl, &now, ev);
            }
        } else {
            //最小堆计时器
            struct event* top = NULL;
            /* See if the earliest timeout is now earlier than it
             * was before: if so, we will need to tell the main
             * thread to wake up earlier than it would otherwise.
             * We double check the timeout of the top element to
             * handle time distortions due to system suspension.
             */
            if (min_heap_elt_is_top_(ev))
                notify = ;
            else if ((top = min_heap_top_(&base->timeheap)) != NULL &&
                     evutil_timercmp(&top->ev_timeout, &now, <))
                notify = ;
        }
    }

    /* if we are not in the right thread, we need to wake up the loop */
   //若为多线程 则需要唤醒主线程进行防止主线程仍阻塞在select/poll/epoll_wait. pipe/eventfd
    if (res != - && notify && EVBASE_NEED_NOTIFY(base))
        evthread_notify_base(base);

    event_debug_note_add_(ev);

    return (res);
}