Question

我正在阅读redis源代码并在ae_epoll.c中找到以下代码：

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？我已经阅读了关于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

那么为什么在EPOLLERR或EPOLLHUP事件发生时设置AE_WRITABE？

这可能是为了简化调用aeApiPoll()的代码，例如： G。在ae.c :aeProcessEvents()中：

        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++;
        }

fe->wfileProc()无论如何都必须处理挂起和错误情况，因为它们可以随时发生，也可以在处理AE_WRITABLE事件时发生;由于没有针对异常条件的单独事件标志，处理循环不需要对它们进行特殊处理。

EPOLLERR和EPOLLHUP真正意味着什么以及如何处理它们？

1 个答案: