linux c 套接字连接非阻塞轮询

Question

我正在使用以下代码在某些通过 WiFi 连接互联网的物联网设备上实现非阻塞 connect() 。有时，WiFi 会掉线，在 99% 的情况下，代码会以 rc != 1 退出，这意味着 connect() 失败。

但是，由于某种原因，即使没有连接互联网，有时我也会收到 poll() 成功执行 POLLOUT 事件和 SO_ERROR说没有错误。这是 poll() 中的错误，还是我检查错误？为什么我会获得 connect() 成功，这是不可能的？

sockfd = socket(AF_INET, SOCK_STREAM, 0);

addr = (struct sockaddr*)&address;
addrlen = sizeof(struct sockaddr_in);
int rc = -1;
// Set O_NONBLOCK
int sockfd_flags_before;
if ((sockfd_flags_before = fcntl(sockfd, F_GETFL, 0) < 0)) return -1;
if (fcntl(sockfd, F_SETFL, sockfd_flags_before | O_NONBLOCK) < 0) return -1;
// Start connecting (asynchronously)
struct timespec start;
struct timespec now;
if (clock_gettime(CLOCK_REALTIME, &start) < 0) { LOG_ERROR("Cannot get time"); return false; }
do {
    if (connect(sockfd, addr, addrlen) < 0) {
        // Did connect return an error? If so, we'll fail.
        int err = errno;
        if ((err != EWOULDBLOCK) && (err != EINPROGRESS)) {
            rc = -1;
        }
        // Otherwise, we'll wait for it to complete.
        else {
            // Wait for the connection to complete.
            do {
                // Calculate how long until the deadline
                if (clock_gettime(CLOCK_REALTIME, &now) < 0)
                {
                    rc = -1; break;
                }
                int elapsed = Util::TimespecDiffMs(&now, &start);
                int remaining = timeout_ms - elapsed;
                if (remaining <= 0) { rc = 0; break; }
                // Wait for connect to complete (or for the timeout deadline)
                struct pollfd pfds[] = { {sockfd, POLLOUT,NULL } };
                rc = poll(pfds, 1, remaining);
                // If poll 'succeeded', make sure it *really* succeeded
                if (rc > 0) {


                    int error = -1; socklen_t len = sizeof(error);
                    int retval = getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &error, &len);
                    if (retval == 0) errno = error;
                    if (error != 0) rc = -1;
                }
            }
            // If poll was interrupted, try again.
            while (rc == -1 && errno == EINTR);
            // Did poll timeout? If so, fail.
            if (rc == 0) {

                errno = ETIMEDOUT;
                rc = -1;
            }
        }
    }
} while (0);