redis中有兩類事件，一類是IO事件統一封裝成aeFileEvent，底層呼叫系統支援的多路複用層（evport、epoll、kqueue、select），一類是定時器事件，以aeTimeEvent描述，巧妙借用系統函式epoll_wait等阻塞函式設定阻塞時間以達到觸發條件

/* Include the best multiplexing layer supported by this system.
 * The following should be ordered by performances, descending. */
// 根據巨集定義包含系統支援的多路複用模型，從上到下按效能高低排序
#ifdef HAVE_EVPORT
#include "ae_evport.c"
#else
    #ifdef HAVE_EPOLL
    #include "ae_epoll.c"
    #else
        #ifdef HAVE_KQUEUE
        #include "ae_kqueue.c"
        #else
        #include "ae_select.c"
        #endif
    #endif
#endif
 

AE迴圈的主要函式：

建立AE迴圈

主要是結構體成員申請記憶體和設定初始值

aeEventLoop *aeCreateEventLoop(int setsize) {
    aeEventLoop *eventLoop;
    int i;

    if ((eventLoop = zmalloc(sizeof(*eventLoop))) == NULL) goto err;
    eventLoop->events = zmalloc(sizeof(aeFileEvent)*setsize);
    eventLoop->fired = zmalloc(sizeof(aeFiredEvent)*setsize);
    if (eventLoop->events == NULL || eventLoop->fired == NULL) goto err;
    eventLoop->setsize = setsize;
    eventLoop->lastTime = time(NULL);
    eventLoop->timeEventHead = NULL;
    eventLoop->timeEventNextId = 0;
    eventLoop->stop = 0;
    eventLoop->maxfd = -1;
    eventLoop->beforesleep = NULL;
    eventLoop->aftersleep = NULL;
    if (aeApiCreate(eventLoop) == -1) goto err;
    /* Events with mask == AE_NONE are not set. So let's initialize the
     * vector with it. */
    for (i = 0; i < setsize; i++)
        eventLoop->events[i].mask = AE_NONE;
    return eventLoop;

err:
    if (eventLoop) {
        zfree(eventLoop->events);
        zfree(eventLoop->fired);
        zfree(eventLoop);
    }
    return NULL;
}
 

主迴圈

void aeMain(aeEventLoop *eventLoop) {
    eventLoop->stop = 0;
    while (!eventLoop->stop) {  //迴圈監聽事件
        // 阻塞之前的處理
        if (eventLoop->beforesleep != NULL)
            eventLoop->beforesleep(eventLoop);
        // 事件處理，第二個引數決定處理哪類事件
        aeProcessEvents(eventLoop, AE_ALL_EVENTS|AE_CALL_AFTER_SLEEP);
    }
}
 

事件處理函式

int aeProcessEvents(aeEventLoop *eventLoop, int flags)
{
    int processed = 0, numevents;

    /* Nothing to do? return ASAP */
    // 如果不處理定時器事件，也不處理檔案事件，就直接返回
    if (!(flags & AE_TIME_EVENTS) && !(flags & AE_FILE_EVENTS)) return 0;

    /* Note that we want call select() even if there are no
     * file events to process as long as we want to process time
     * events, in order to sleep until the next time event is ready
     * to fire. */
    // 如果有監控檔案事件，或者要處理定時器事件並且沒有設定不阻塞標誌
    if (eventLoop->maxfd != -1 ||
        ((flags & AE_TIME_EVENTS) && !(flags & AE_DONT_WAIT))) {
        int j;
        aeTimeEvent *shortest = NULL;
        struct timeval tv, *tvp;
        
        // 如果處理定時器事件且沒有設定不阻塞標誌，取最快到達的定時器時間
        if (flags & AE_TIME_EVENTS && !(flags & AE_DONT_WAIT))
            shortest = aeSearchNearestTimer(eventLoop);
        if (shortest) {
            long now_sec, now_ms;

            aeGetTime(&now_sec, &now_ms);
            tvp = &tv;

            /* How many milliseconds we need to wait for the next
             * time event to fire? */
            // 計算剩餘時間
            long long ms =
                (shortest->when_sec - now_sec)*1000 +
                shortest->when_ms - now_ms;

            if (ms > 0) {
                tvp->tv_sec = ms/1000;
                tvp->tv_usec = (ms % 1000)*1000;
            } else {
                tvp->tv_sec = 0;
                tvp->tv_usec = 0;
            }
        } else {
            /* If we have to check for events but need to return
             * ASAP because of AE_DONT_WAIT we need to set the timeout
             * to zero */
            // 如果設定了不阻塞標誌，阻塞時間為0，表示不阻塞
            if (flags & AE_DONT_WAIT) {
                tv.tv_sec = tv.tv_usec = 0;
                tvp = &tv;
            } else { //否則永久阻塞
                /* Otherwise we can block */
                tvp = NULL; /* wait forever */
            }
        }

        /* Call the multiplexing API, will return only on timeout or when
         * some event fires. */
        // 等待事件觸發或者超時
        numevents = aeApiPoll(eventLoop, tvp);

        /* After sleep callback. */
        // 阻塞後處理函式
        if (eventLoop->aftersleep != NULL && flags & AE_CALL_AFTER_SLEEP)
            eventLoop->aftersleep(eventLoop);

        // 迴圈處理觸發的檔案事件
        for (j = 0; j < numevents; j++) {
            aeFileEvent *fe = &eventLoop->events[eventLoop->fired[j].fd];
            int mask = eventLoop->fired[j].mask;
            int fd = eventLoop->fired[j].fd;
            int fired = 0; /* Number of events fired for current fd. */

            /* Normally we execute the readable event first, and the writable
             * event laster. This is useful as sometimes we may be able
             * to serve the reply of a query immediately after processing the
             * query.
             *
             * However if AE_BARRIER is set in the mask, our application is
             * asking us to do the reverse: never fire the writable event
             * after the readable. In such a case, we invert the calls.
             * This is useful when, for instance, we want to do things
             * in the beforeSleep() hook, like fsynching a file to disk,
             * before replying to a client. */
            // 如果設定了AE_BARRIER標誌，我們優先處理寫事件
            int invert = fe->mask & AE_BARRIER;

            /* Note the "fe->mask & mask & ..." code: maybe an already
             * processed event removed an element that fired and we still
             * didn't processed, so we check if the event is still valid.
             *
             * Fire the readable event if the call sequence is not
             * inverted. */
            // 沒有設定AE_BARRIER標誌，優先處理讀事件
            if (!invert && fe->mask & mask & AE_READABLE) {
                fe->rfileProc(eventLoop,fd,fe->clientData,mask);
                fired++;
            }

            /* Fire the writable event. */
            if (fe->mask & mask & AE_WRITABLE) {
                if (!fired || fe->wfileProc != fe->rfileProc) {
                    fe->wfileProc(eventLoop,fd,fe->clientData,mask);
                    fired++;
                }
            }

            /* If we have to invert the call, fire the readable event now
             * after the writable one. */
            // 如果需要反轉讀寫處理順序，處理完寫事件後，可以處理讀事件
            if (invert && fe->mask & mask & AE_READABLE) {
                if (!fired || fe->wfileProc != fe->rfileProc) {
                    fe->rfileProc(eventLoop,fd,fe->clientData,mask);
                    fired++;
                }
            }

            processed++;
        }
    }
    /* Check time events */
    // 處理定時器事件
    if (flags & AE_TIME_EVENTS)
        processed += processTimeEvents(eventLoop);

    return processed; /* return the number of processed file/time events */
}

處理定時器事件函式

/* Process time events */
static int processTimeEvents(aeEventLoop *eventLoop) {
    int processed = 0;
    aeTimeEvent *te;
    long long maxId;
    time_t now = time(NULL);

    /* If the system clock is moved to the future, and then set back to the
     * right value, time events may be delayed in a random way. Often this
     * means that scheduled operations will not be performed soon enough.
     *
     * Here we try to detect system clock skews, and force all the time
     * events to be processed ASAP when this happens: the idea is that
     * processing events earlier is less dangerous than delaying them
     * indefinitely, and practice suggests it is. */
    // 如果上次處理定時器事件的時間比當前時間還要大，說明時間有偏差，強制將所有的定時器儘快處理掉(將所有定時器的間隔秒數設定為0)
    if (now < eventLoop->lastTime) {
        te = eventLoop->timeEventHead;
        while(te) {
            te->when_sec = 0;
            te = te->next;
        }
    }
    // 更新最近處理定時器事件的時間
    eventLoop->lastTime = now;

    te = eventLoop->timeEventHead;
    maxId = eventLoop->timeEventNextId-1; // 獲取最大的定時器ID
    while(te) {
        long now_sec, now_ms;
        long long id;

        /* Remove events scheduled for deletion. */
        // 刪除已經標記失效的定時器
        if (te->id == AE_DELETED_EVENT_ID) {
            aeTimeEvent *next = te->next;
            if (te->prev)
                te->prev->next = te->next;
            else
                eventLoop->timeEventHead = te->next;
            if (te->next)
                te->next->prev = te->prev;
            if (te->finalizerProc)
                te->finalizerProc(eventLoop, te->clientData);
            zfree(te);
            te = next;
            continue;
        }

        /* Make sure we don't process time events created by time events in
         * this iteration. Note that this check is currently useless: we always
         * add new timers on the head, however if we change the implementation
         * detail, this check may be useful again: we keep it here for future
         * defense. */
        // 保證不處理定時器處理過程中建立的定時器事件，暫時沒用，因為新增定時器事件總是在頭部新增
        if (te->id > maxId) {
            te = te->next;
            continue;
        }
        aeGetTime(&now_sec, &now_ms);
        if (now_sec > te->when_sec ||
            (now_sec == te->when_sec && now_ms >= te->when_ms))
        {
            int retval;

            id = te->id;
            // 回撥定時器事件處理函式
            retval = te->timeProc(eventLoop, id, te->clientData);
            processed++;
            if (retval != AE_NOMORE) { // 如果定時器還需要重複使用
                aeAddMillisecondsToNow(retval,&te->when_sec,&te->when_ms); // 設定新的觸發時間
            } else { // 否則，標記定時器失效
                te->id = AE_DELETED_EVENT_ID; 
            }
        }
        te = te->next;
    }
    return processed;
}

建立File事件

int aeCreateFileEvent(aeEventLoop *eventLoop, int fd, int mask,
        aeFileProc *proc, void *clientData)
{
    // 檔案描述符不能大於setsize，否則eventLoop->events會溢位
    if (fd >= eventLoop->setsize) {
        errno = ERANGE;
        return AE_ERR;
    }
    // 這裡以描述作為下標記錄事件，可以避免迴圈查詢
    aeFileEvent *fe = &eventLoop->events[fd];
    // 呼叫底層封裝的多路複用介面新增事件監控
    if (aeApiAddEvent(eventLoop, fd, mask) == -1)
        return AE_ERR;
    // 更新描述符監控的事件資訊和處理函式以及客戶端資訊
    fe->mask |= mask;
    if (mask & AE_READABLE) fe->rfileProc = proc;
    if (mask & AE_WRITABLE) fe->wfileProc = proc;
    fe->clientData = clientData;
    // 記錄當前最大的檔案描述符
    if (fd > eventLoop->maxfd)
        eventLoop->maxfd = fd;
    return AE_OK;
}

還有一些其他的介面函式比較簡單，就沒必要一一分析了

void aeDeleteFileEvent(aeEventLoop *eventLoop, int fd, int mask)  // 刪除FileEvent

long long aeCreateTimeEvent(aeEventLoop *eventLoop, long long milliseconds, aeTimeProc *proc, void *clientData, aeEventFinalizerProc *finalizerProc)  // 新增定時器事件

int aeDeleteTimeEvent(aeEventLoop *eventLoop, long long id) //刪除定時器事件

static aeTimeEvent *aeSearchNearestTimer(aeEventLoop *eventLoop) //獲取最接近的定時器事件