redis源码阅读之ae_evport

evport是redis当中I/O多路复用的首选，，代码如下

#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

具体的evport原理还是得等到彻底结束redis这个部分之后再讲，今天只谈封装部分，redis当中封装evport的结构如下

typedef struct aeApiState {
    int portfd; /* event port */
    int npending; /* # of pending fds */
    int pending_fds[MAX_EVENT_BATCHSZ]; /* pending fds */
    int pending_masks[MAX_EVENT_BATCHSZ]; /* pending fds' masks */
} aeApiState;

其中对于这个结构的常规调用如下：

static int aeApiCreate(aeEventLoop *eventLoop) {
    int i;
    aeApiState *state = zmalloc(sizeof(aeApiState));
    if (!state) return -1;

    state->portfd = port_create();
    if (state->portfd == -1) {
        zfree(state);
        return -1;
    }

    state->npending = 0;

    for (i = 0; i < MAX_EVENT_BATCHSZ; i++) {
        state->pending_fds[i] = -1;
        state->pending_masks[i] = AE_NONE;
    }

    eventLoop->apidata = state;
    return 0;
}

static int aeApiResize(aeEventLoop *eventLoop, int setsize) {
    /* Nothing to resize here. */
    return 0;
}

static void aeApiFree(aeEventLoop *eventLoop) {
    aeApiState *state = eventLoop->apidata;

    close(state->portfd);
    zfree(state);
}

static int aeApiLookupPending(aeApiState *state, int fd) {
    int i;

    for (i = 0; i < state->npending; i++) {
        if (state->pending_fds[i] == fd)
            return (i);
    }

    return (-1);
}

/*
 * Helper function to invoke port_associate for the given fd and mask.
 */
static int aeApiAssociate(const char *where, int portfd, int fd, int mask) {
    int events = 0;
    int rv, err;

    if (mask & AE_READABLE)
        events |= POLLIN;
    if (mask & AE_WRITABLE)
        events |= POLLOUT;

    if (evport_debug)
        fprintf(stderr, "%s: port_associate(%d, 0x%x) = ", where, fd, events);

    rv = port_associate(portfd, PORT_SOURCE_FD, fd, events,
        (void *)(uintptr_t)mask);
    err = errno;

    if (evport_debug)
        fprintf(stderr, "%d (%s)\n", rv, rv == 0 ? "no error" : strerror(err));

    if (rv == -1) {
        fprintf(stderr, "%s: port_associate: %s\n", where, strerror(err));

        if (err == EAGAIN)
            fprintf(stderr, "aeApiAssociate: event port limit exceeded.");
    }

    return rv;
}

static int aeApiAddEvent(aeEventLoop *eventLoop, int fd, int mask) {
    aeApiState *state = eventLoop->apidata;
    int fullmask, pfd;

    if (evport_debug)
        fprintf(stderr, "aeApiAddEvent: fd %d mask 0x%x\n", fd, mask);

    /*
     * Since port_associate's "events" argument replaces any existing events, we
     * must be sure to include whatever events are already associated when
     * we call port_associate() again.
     */
    fullmask = mask | eventLoop->events[fd].mask;
    pfd = aeApiLookupPending(state, fd);

    if (pfd != -1) {
        /*
         * This fd was recently returned from aeApiPoll. It should be safe to
         * assume that the consumer has processed that poll event, but we play
         * it safer by simply updating pending_mask. The fd will be
         * re-associated as usual when aeApiPoll is called again.
         */
        if (evport_debug)
            fprintf(stderr, "aeApiAddEvent: adding to pending fd %d\n", fd);
        state->pending_masks[pfd] |= fullmask;
        return 0;
    }

    return (aeApiAssociate("aeApiAddEvent", state->portfd, fd, fullmask));
}

static void aeApiDelEvent(aeEventLoop *eventLoop, int fd, int mask) {
    aeApiState *state = eventLoop->apidata;
    int fullmask, pfd;

    if (evport_debug)
        fprintf(stderr, "del fd %d mask 0x%x\n", fd, mask);

    pfd = aeApiLookupPending(state, fd);

    if (pfd != -1) {
        if (evport_debug)
            fprintf(stderr, "deleting event from pending fd %d\n", fd);

        /*
         * This fd was just returned from aeApiPoll, so it's not currently
         * associated with the port. All we need to do is update
         * pending_mask appropriately.
         */
        state->pending_masks[pfd] &= ~mask;

        if (state->pending_masks[pfd] == AE_NONE)
            state->pending_fds[pfd] = -1;

        return;
    }

    /*
     * The fd is currently associated with the port. Like with the add case
     * above, we must look at the full mask for the file descriptor before
     * updating that association. We don't have a good way of knowing what the
     * events are without looking into the eventLoop state directly. We rely on
     * the fact that our caller has already updated the mask in the eventLoop.
     */

    fullmask = eventLoop->events[fd].mask;
    if (fullmask == AE_NONE) {
        /*
         * We're removing *all* events, so use port_dissociate to remove the
         * association completely. Failure here indicates a bug.
         */
        if (evport_debug)
            fprintf(stderr, "aeApiDelEvent: port_dissociate(%d)\n", fd);

        if (port_dissociate(state->portfd, PORT_SOURCE_FD, fd) != 0) {
            perror("aeApiDelEvent: port_dissociate");
            abort(); /* will not return */
        }
    } else if (aeApiAssociate("aeApiDelEvent", state->portfd, fd,
        fullmask) != 0) {
        /*
         * ENOMEM is a potentially transient condition, but the kernel won't
         * generally return it unless things are really bad. EAGAIN indicates
         * we've reached an resource limit, for which it doesn't make sense to
         * retry (counter-intuitively). All other errors indicate a bug. In any
         * of these cases, the best we can do is to abort.
         */
        abort(); /* will not return */
    }
}
static char *aeApiName(void) {
    return "evport";
}

关键调用api如下：

static int aeApiPoll(aeEventLoop *eventLoop, struct timeval *tvp) {
    aeApiState *state = eventLoop->apidata;
    struct timespec timeout, *tsp;
    int mask, i;
    uint_t nevents;
    port_event_t event[MAX_EVENT_BATCHSZ];

    /*
     * If we've returned fd events before, we must re-associate them with the
     * port now, before calling port_get(). See the block comment at the top of
     * this file for an explanation of why.
     */
    for (i = 0; i < state->npending; i++) {
        if (state->pending_fds[i] == -1)
            /* This fd has since been deleted. */
            continue;

        if (aeApiAssociate("aeApiPoll", state->portfd,
            state->pending_fds[i], state->pending_masks[i]) != 0) {
            /* See aeApiDelEvent for why this case is fatal. */
            abort();
        }

        state->pending_masks[i] = AE_NONE;
        state->pending_fds[i] = -1;
    }

    state->npending = 0;

    if (tvp != NULL) {
        timeout.tv_sec = tvp->tv_sec;
        timeout.tv_nsec = tvp->tv_usec * 1000;
        tsp = &timeout;
    } else {
        tsp = NULL;
    }

    /*
     * port_getn can return with errno == ETIME having returned some events (!).
     * So if we get ETIME, we check nevents, too.
     */
    nevents = 1;
    if (port_getn(state->portfd, event, MAX_EVENT_BATCHSZ, &nevents,
        tsp) == -1 && (errno != ETIME || nevents == 0)) {
        if (errno == ETIME || errno == EINTR)
            return 0;

        /* Any other error indicates a bug. */
        perror("aeApiPoll: port_get");
        abort();
    }

    state->npending = nevents;

    for (i = 0; i < nevents; i++) {
            mask = 0;
            if (event[i].portev_events & POLLIN)
                mask |= AE_READABLE;
            if (event[i].portev_events & POLLOUT)
                mask |= AE_WRITABLE;

            eventLoop->fired[i].fd = event[i].portev_object;
            eventLoop->fired[i].mask = mask;

            if (evport_debug)
                fprintf(stderr, "aeApiPoll: fd %d mask 0x%x\n",
                    (int)event[i].portev_object, mask);

            state->pending_fds[i] = event[i].portev_object;
            state->pending_masks[i] = (uintptr_t)event[i].portev_user;
    }

    return nevents;
}

redis当中的I/O多路复用就暂时讲到这里了，还请各位看官老爷多提宝贵意见~~~