redis源码笔记ae.c

ae.c是redis事件框架的具体实现，这篇blog对这份源码进行简单说明。其中谈到了作者已经标记的一些未来可能做的改进。

ae.c

#include <stdio.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>

#include "ae.h"
#include "zmalloc.h"
#include "config.h"

/* Include the best multiplexing layer supported by this system.
 * The following should be ordered by performances, descending. */
    //为了支持不同的平台，redis用相同的接口封装了系统提供的多路复用层代码。接口共提供如下函数：aeApiCreate\aeApiFree\aeApiAddEvent\aeApiDelEvent\aeApiPoll\aeApiName函数，以及一个struct aeApiState
    //通过包含不同的头文件，选择不同的底层实现
    //按如下顺序，效率递减： epoll > kqueue > select
#ifdef HAVE_EPOLL
#include "ae_epoll.c"
#else
    #ifdef HAVE_KQUEUE
    #include "ae_kqueue.c"
    #else
    #include "ae_select.c"
    #endif
#endif

    //初始化函数，创建事件循环，函数内部alloc一个结构，用于表示事件状态，供后续其他函数作为参数使用
aeEventLoop *aeCreateEventLoop(void) {
    aeEventLoop *eventLoop;
    int i;

    eventLoop = zmalloc(sizeof(*eventLoop));
    if (!eventLoop) return NULL;
        //时间event用链表存储
    eventLoop->timeEventHead = NULL;
    eventLoop->timeEventNextId = 0;
        //表示是否停止事件循环
    eventLoop->stop = 0;
        //maxfd只由ae_select.c使用，后续有些相关的处理，如果使用epoll的话，其实可以进行简化
    eventLoop->maxfd = -1;
        //每次调用epoll\select前调用的函数，由框架使用者注册
    eventLoop->beforesleep = NULL;
    if (aeApiCreate(eventLoop) == -1) {
        zfree(eventLoop);
        return NULL;
    }
    /* Events with mask == AE_NONE are not set. So let's initialize the
     * vector with it. */
        
        //将所有的文件描述符的mask设置为无效值，作为初始化
    for (i = 0; i < AE_SETSIZE; i++)
        eventLoop->events[i].mask = AE_NONE;
    return eventLoop;
}

    //底层实现执行释放操作后，释放state的内存
void aeDeleteEventLoop(aeEventLoop *eventLoop) {
    aeApiFree(eventLoop);
    zfree(eventLoop);
}

    //停止事件循环,redis作为一个无限循环的server，在redis.c中并没有任何一处调用此函数
void aeStop(aeEventLoop *eventLoop) {
    eventLoop->stop = 1;
}

    //创建文件fd事件，加入事件循环监控列表，使得后续epoll\select时将会测试这个文件描述符的可读性（可写性）
int aeCreateFileEvent(aeEventLoop *eventLoop, int fd, int mask,
        aeFileProc *proc, void *clientData)
{
    if (fd >= AE_SETSIZE) return AE_ERR;
    aeFileEvent *fe = &eventLoop->events[fd];

    if (aeApiAddEvent(eventLoop, fd, mask) == -1)
        return AE_ERR;
    fe->mask |= mask;
        //注册函数
    if (mask & AE_READABLE) fe->rfileProc = proc;
    if (mask & AE_WRITABLE) fe->wfileProc = proc;
    fe->clientData = clientData;
        //更新maxfd
    if (fd > eventLoop->maxfd)
        eventLoop->maxfd = fd;
    return AE_OK;
}

void aeDeleteFileEvent(aeEventLoop *eventLoop, int fd, int mask)
{
    if (fd >= AE_SETSIZE) return;
    aeFileEvent *fe = &eventLoop->events[fd];

    if (fe->mask == AE_NONE) return;
    fe->mask = fe->mask & (~mask);
    if (fd == eventLoop->maxfd && fe->mask == AE_NONE) {
        /* Update the max fd */
        int j;

        for (j = eventLoop->maxfd-1; j >= 0; j--)
            if (eventLoop->events[j].mask != AE_NONE) break;
        eventLoop->maxfd = j;
    }
    aeApiDelEvent(eventLoop, fd, mask);
}

    //返回值为该文件描述符关注的事件类型（可读、可写）
int aeGetFileEvents(aeEventLoop *eventLoop, int fd) {
    if (fd >= AE_SETSIZE) return 0;
    aeFileEvent *fe = &eventLoop->events[fd];

    return fe->mask;
}

static void aeGetTime(long *seconds, long *milliseconds)
{
    struct timeval tv;

    gettimeofday(&tv, NULL);
    *seconds = tv.tv_sec;
    *milliseconds = tv.tv_usec/1000;
}

static void aeAddMillisecondsToNow(long long milliseconds, long *sec, long *ms) {
    long cur_sec, cur_ms, when_sec, when_ms;

    aeGetTime(&cur_sec, &cur_ms);
    when_sec = cur_sec + milliseconds/1000;
    when_ms = cur_ms + milliseconds%1000;
    if (when_ms >= 1000) {
        when_sec ++;
        when_ms -= 1000;
    }
    *sec = when_sec;
    *ms = when_ms;
}

long long aeCreateTimeEvent(aeEventLoop *eventLoop, long long milliseconds,
        aeTimeProc *proc, void *clientData,
        aeEventFinalizerProc *finalizerProc)
{
    long long id = eventLoop->timeEventNextId++;
    aeTimeEvent *te;

    te = zmalloc(sizeof(*te));
    if (te == NULL) return AE_ERR;
    te->id = id;
        //time event执行时间为绝对时间点
    aeAddMillisecondsToNow(milliseconds,&te->when_sec,&te->when_ms);
    te->timeProc = proc;
    te->finalizerProc = finalizerProc;
    te->clientData = clientData;
        //time event链表为无序表，直接插入到链表头
    te->next = eventLoop->timeEventHead;
    eventLoop->timeEventHead = te;
    return id;
}

    //从链表中删除，是以id作为key查找的（顺序遍历）
int aeDeleteTimeEvent(aeEventLoop *eventLoop, long long id)
{
    aeTimeEvent *te, *prev = NULL;

    te = eventLoop->timeEventHead;
    while(te) {
        if (te->id == id) {
            if (prev == NULL)
                eventLoop->timeEventHead = te->next;
            else
                prev->next = te->next;
            if (te->finalizerProc)
                te->finalizerProc(eventLoop, te->clientData);
            zfree(te);
            return AE_OK;
        }
        prev = te;
        te = te->next;
    }
    return AE_ERR; /* NO event with the specified ID found */
}

/* Search the first timer to fire.
161  * This operation is useful to know how many time the select can be
162  * put in sleep without to delay any event. （没大看懂）,也许是给一个阻塞时间的上限值
 * If there are no timers NULL is returned.
 *
 * Note that's O(N) since time events are unsorted.
 * Possible optimizations (not needed by Redis so far, but...):
 * 1) Insert the event in order, so that the nearest is just the head.
 *    Much better but still insertion or deletion of timers is O(N).
 * 2) Use a skiplist to have this operation as O(1) and insertion as O(log(N)).
 */
static aeTimeEvent *aeSearchNearestTimer(aeEventLoop *eventLoop)
{
    aeTimeEvent *te = eventLoop->timeEventHead;
    aeTimeEvent *nearest = NULL;

    while(te) {
        if (!nearest || te->when_sec < nearest->when_sec ||
                (te->when_sec == nearest->when_sec &&
                 te->when_ms < nearest->when_ms))
            nearest = te;
        te = te->next;
    }
    return nearest;
}

    //对time event进行处理
/* Process time events */
static int processTimeEvents(aeEventLoop *eventLoop) {

        //处理的事件数
    int processed = 0;
    aeTimeEvent *te;
    long long maxId;

    te = eventLoop->timeEventHead;
    maxId = eventLoop->timeEventNextId-1;
    while(te) {
        long now_sec, now_ms;
        long long id;

        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;
                //如果执行时间到或已超出，则执行对应的时间处理函数
            retval = te->timeProc(eventLoop, id, te->clientData);
            processed++;
            /* After an event is processed our time event list may
             * no longer be the same, so we restart from head. //因为时间处理函数timeProc可能改变此链表
213              * Still we make sure to don't process events registered
214              * by event handlers itself in order to don't loop forever.？
             * To do so we saved the max ID we want to handle.
             *
             * FUTURE OPTIMIZATIONS:
             * Note that this is NOT great algorithmically. Redis uses
             * a single time event so it's not a problem but the right
             * way to do this is to add the new elements on head, and
             * to flag deleted elements in a special way for later
             * deletion (putting references to the nodes to delete into
             * another linked list). */
           
                //如果这个时间处理函数不再继续执行，则从time event的链表中删除事件；否则，retval为继续执行的时间间隔（单位为ms），在当前的timeevent struct的时间值上进行增加
            if (retval != AE_NOMORE) {
                aeAddMillisecondsToNow(retval,&te->when_sec,&te->when_ms);
            } else {
                aeDeleteTimeEvent(eventLoop, id);
            }
            te = eventLoop->timeEventHead;
        } else {
            te = te->next;
        }
    }
    return processed;
}

/* Process every pending(悬而未决) time event, then every pending file event
 * (that may be registered by time event callbacks just processed).
 * Without special flags the function sleeps until some file event
 * fires, or when the next time event occurrs (if any).
 *
 * If flags is 0, the function does nothing and returns.
 * if flags has AE_ALL_EVENTS set, all the kind of events are processed.
 * if flags has AE_FILE_EVENTS set, file events are processed.
 * if flags has AE_TIME_EVENTS set, time events are processed.
 * if flags has AE_DONT_WAIT set the function returns ASAP until all
 * the events that's possible to process without to wait are processed.
 *
 * The function returns the number of events processed. */
int aeProcessEvents(aeEventLoop *eventLoop, int flags)
{
    int processed = 0, numevents;

    /* Nothing to do? return ASAP */
    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. */
    if (eventLoop->maxfd != -1 ||
        ((flags & AE_TIME_EVENTS) && !(flags & AE_DONT_WAIT))) {
        int j;
        aeTimeEvent *shortest = NULL;
        struct timeval tv, *tvp;

        if (flags & AE_TIME_EVENTS && !(flags & AE_DONT_WAIT))
            shortest = aeSearchNearestTimer(eventLoop);
        if (shortest) {
            long now_sec, now_ms;

            /* Calculate the time missing for the nearest
             * timer to fire. */
            aeGetTime(&now_sec, &now_ms);
            tvp = &tv;
            tvp->tv_sec = shortest->when_sec - now_sec;
277             if (shortest->when_ms < now_ms) {
278                 tvp->tv_usec = ((shortest->when_ms+1000) - now_ms)*1000;
279                 tvp->tv_sec --;
280             } else {
281                 tvp->tv_usec = (shortest->when_ms - now_ms)*1000;
282             }
283             if (tvp->tv_sec < 0) tvp->tv_sec = 0;
284             if (tvp->tv_usec < 0) tvp->tv_usec = 0;  疑似有bug，比如当前时间为 1s +2ms  ，shortest时间为0s+1ms的case
        } else {
            /* If we have to check for events but need to return
             * ASAP because of AE_DONT_WAIT we need to se the timeout
             * to zero */
            if (flags & AE_DONT_WAIT) {
                tv.tv_sec = tv.tv_usec = 0;
                tvp = &tv;
            } else {
                /* Otherwise we can block */
                tvp = NULL; /* wait forever */
            }
        }

            //指定这个tvp是说这个tvp到期时，至少由time event可以执行
        numevents = aeApiPoll(eventLoop, tvp);
        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 rfired = 0;

        /* 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. */
            if (fe->mask & mask & AE_READABLE) {
                rfired = 1;
                fe->rfileProc(eventLoop,fd,fe->clientData,mask);
            }
                //避免同一个注册函数被调用两次
            if (fe->mask & mask & AE_WRITABLE) {
                if (!rfired || fe->wfileProc != fe->rfileProc)
                    fe->wfileProc(eventLoop,fd,fe->clientData,mask);
            }
            processed++;
        }
    }
    /* Check time events */
    if (flags & AE_TIME_EVENTS)
        processed += processTimeEvents(eventLoop);

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

    //对select的一个简单封装，没有太大意义
/* Wait for millseconds until the given file descriptor becomes
 * writable/readable/exception */
int aeWait(int fd, int mask, long long milliseconds) {
    struct timeval tv;
    fd_set rfds, wfds, efds;
    int retmask = 0, retval;

    tv.tv_sec = milliseconds/1000;
    tv.tv_usec = (milliseconds%1000)*1000;
    FD_ZERO(&rfds);
    FD_ZERO(&wfds);
    FD_ZERO(&efds);

    if (mask & AE_READABLE) FD_SET(fd,&rfds);
    if (mask & AE_WRITABLE) FD_SET(fd,&wfds);
    if ((retval = select(fd+1, &rfds, &wfds, &efds, &tv)) > 0) {
        if (FD_ISSET(fd,&rfds)) retmask |= AE_READABLE;
        if (FD_ISSET(fd,&wfds)) retmask |= AE_WRITABLE;
        return retmask;
    } else {
        return retval;
    }
}

void aeMain(aeEventLoop *eventLoop) {
    eventLoop->stop = 0;
    while (!eventLoop->stop) {
        if (eventLoop->beforesleep != NULL)
            eventLoop->beforesleep(eventLoop);
        aeProcessEvents(eventLoop, AE_ALL_EVENTS);
    }
}

char *aeGetApiName(void) {
    return aeApiName();
}

void aeSetBeforeSleepProc(aeEventLoop *eventLoop, aeBeforeSleepProc *beforesleep) {
    eventLoop->beforesleep = beforesleep;
}