Function fd_wait

src/bthread/fd.cpp:206–276

    }

    int fd_wait(int fd, unsigned events, const timespec* abstime) {
        butil::atomic<EpollButex*>* p = fd_butexes.get_or_new(fd);
        if (NULL == p) {
            errno = ENOMEM;
            return -1;
        }

        EpollButex* butex = p->load(butil::memory_order_consume);
        if (NULL == butex) {
            // It is rare to wait on one file descriptor from multiple threads
            // simultaneously. Creating singleton by optimistic locking here
            // saves mutexes for each butex.
            butex = butex_create_checked<EpollButex>();
            butex->store(0, butil::memory_order_relaxed);
            EpollButex* expected = NULL;
            if (!p->compare_exchange_strong(expected, butex,
                                            butil::memory_order_release,
                                            butil::memory_order_consume)) {
                butex_destroy(butex);
                butex = expected;
            }
        }
        
        while (butex == CLOSING_GUARD) {  // bthread_close() is running.
            if (sched_yield() < 0) {
                return -1;
            }
            butex = p->load(butil::memory_order_consume);
        }
        // Save value of butex before adding to epoll because the butex may
        // be changed before butex_wait. No memory fence because EPOLL_CTL_MOD
        // and EPOLL_CTL_ADD shall have release fence.
        const int expected_val = butex->load(butil::memory_order_relaxed);

#if defined(OS_LINUX)
# ifdef BAIDU_KERNEL_FIXED_EPOLLONESHOT_BUG
        epoll_event evt = { events | EPOLLONESHOT, { butex } };
        if (epoll_ctl(_epfd, EPOLL_CTL_MOD, fd, &evt) < 0) {
            if (epoll_ctl(_epfd, EPOLL_CTL_ADD, fd, &evt) < 0 &&
                    errno != EEXIST) {
                PLOG(FATAL) << "Fail to add fd=" << fd << " into epfd=" << _epfd;
                return -1;
            }
        }
# else
        epoll_event evt;
        evt.events = events;
        evt.data.fd = fd;
        if (epoll_ctl(_epfd, EPOLL_CTL_ADD, fd, &evt) < 0 &&
            errno != EEXIST) {
            PLOG(FATAL) << "Fail to add fd=" << fd << " into epfd=" << _epfd;
            return -1;
        }
# endif
#elif defined(OS_MACOSX)
        struct kevent kqueue_event;
        EV_SET(&kqueue_event, fd, events, EV_ADD | EV_ENABLE | EV_ONESHOT,
                0, 0, butex);