redis的文件事件

redis的文件事件：即与io相关的事件。

/* File event structure */
typedef struct aeFileEvent {
    int mask; /* one of AE_(READABLE|WRITABLE) */
    aeFileProc *rfileProc; //读网络数据处理函数
    aeFileProc *wfileProc; //写网络数据处理函数
    void *clientData;
} aeFileEvent;

所有的文件事件放在aeEventLoop的数组中：

/* State of an event based program */
typedef struct aeEventLoop {
    int maxfd;   /* highest file descriptor currently registered */
    int setsize; /* max number of file descriptors tracked */
    long long timeEventNextId;
    time_t lastTime;     /* Used to detect system clock skew */
    aeFileEvent *events; /* Registered events */
    aeFiredEvent *fired; /* Fired events */
    aeTimeEvent *timeEventHead;
    int stop;
    void *apidata; /* This is used for polling API specific data */
    aeBeforeSleepProc *beforesleep;
    aeBeforeSleepProc *aftersleep;
} aeEventLoop;

重点关注 events数组和fired数组，在(server.c) initServer中创建事件循环，

server.el = aeCreateEventLoop(server.maxclients+CONFIG_FDSET_INCR);

在(ae.c) aeCreateEventLoop中，为events数组和fired数组分配内存：

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;
}

在aeCreateFileEvent中为events的具体元素赋值，由创建客户端连接进入aeCreateFileEvent方法的调用栈如下：

// 省略其他代码
client *createClient(int fd) {
    client *c = zmalloc(sizeof(client));

    /* passing -1 as fd it is possible to create a non connected client.
     * This is useful since all the commands needs to be executed
     * in the context of a client. When commands are executed in other
     * contexts (for instance a Lua script) we need a non connected client. */
    if (fd != -1) {
        anetNonBlock(NULL,fd);
        anetEnableTcpNoDelay(NULL,fd);
        if (server.tcpkeepalive)
            anetKeepAlive(NULL,fd,server.tcpkeepalive);
        if (aeCreateFileEvent(server.el,fd,AE_READABLE,
            readQueryFromClient, c) == AE_ERR)
        {
            close(fd);
            zfree(c);
            return NULL;
        }
    }

    ...
    return c;
}

把rfileProc和wfileProc的值设为readQueryFromClient函数

int aeCreateFileEvent(aeEventLoop *eventLoop, int fd, int mask,
        aeFileProc *proc, void *clientData)
{
    if (fd >= eventLoop->setsize) {
        errno = ERANGE;
        return AE_ERR;
    }
    aeFileEvent *fe = &eventLoop->events[fd];

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

当客户端发生网络IO时：

调用epoll_wait，获取发生事件的文件描述符，设置在fired元素中：

static int aeApiPoll(aeEventLoop *eventLoop, struct timeval *tvp) {
    aeApiState *state = eventLoop->apidata;
    int retval, numevents = 0;

    retval = epoll_wait(state->epfd,state->events,eventLoop->setsize,
            tvp ? (tvp->tv_sec*1000 + tvp->tv_usec/1000) : -1);
    if (retval > 0) {
        int j;

        numevents = retval;
        for (j = 0; j < numevents; j++) {
            int mask = 0;
            struct epoll_event *e = state->events+j;

            if (e->events & EPOLLIN) mask |= AE_READABLE;
            if (e->events & EPOLLOUT) mask |= AE_WRITABLE;
            if (e->events & EPOLLERR) mask |= AE_WRITABLE;
            if (e->events & EPOLLHUP) mask |= AE_WRITABLE;
            eventLoop->fired[j].fd = e->data.fd;
            eventLoop->fired[j].mask = mask;
        }
    }
    return numevents;
}

在aeProcessEvents方法中，根据fired元素中的fd，处理IO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 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);
    }
    if (fe->mask & mask & AE_WRITABLE) {
        if (!rfired || fe->wfileProc != fe->rfileProc)
            fe->wfileProc(eventLoop,fd,fe->clientData,mask);
    }
    processed++;
}