c - EPOLLERR 和 EPOLLHUP 的真正含义是什么以及如何处理它们？

Question

我正在阅读 redis 源代码，在 ae_epoll.c 中我发现了以下代码:

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;

            /* so why set AE_WRITABE when EPOLLERR or EPOLLHUP happend? */
            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;
}

那么为什么在 EPOLLERR 或 EPOLLHUP 事件发生时设置 AE_WRITABE？我已经阅读了有关 EPOLLERR 和 EPOLLHUP 的手册页，但我无法理解。

EPOLLERR
        Error condition happened on the  associated  file  descriptor.   epoll_wait(2)
        will always wait for this event; it is not necessary to set it in events.

EPOLLHUP
        Hang up happened on the associated file descriptor.  epoll_wait(2) will always
        wait for this event; it is not necessary to set it in events.

Answer 1

so why set AE_WRITABE when EPOLLERR or EPOLLHUP event happened?

这大概是为了简化调用 aeApiPoll() 的代码，例如。 G。在 ae.c :aeProcessEvents():

        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);
            }
            if (fe->mask & mask & AE_WRITABLE) {
                if (!rfired || fe->wfileProc != fe->rfileProc)
                    fe->wfileProc(eventLoop,fd,fe->clientData,mask);
            }
            processed++;
        }

无论如何，fe->wfileProc() 必须处理挂起和错误情况，因为它们随时可能发生，在处理 AE_WRITABLE 事件时也是如此；由于没有针对异常情况的单独事件标志，处理循环不需要对它们进行特殊处理。