使用SO_REVTIMEO套接字选项为recvfrom设置超时

void dg_cli(FILE *fp, int sockfd, const SA *pservaddr, socklen_t servlen)
{
    int                n;
    char            sendline[MAXLINE], recvline[MAXLINE + 1];
    struct timeval    tv;

    tv.tv_sec = 5;
    tv.tv_usec = 0;
    setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));

    while (fgets(sendline, MAXLINE, fp) != NULL) {

        sendto(sockfd, sendline, strlen(sendline), 0, pservaddr, servlen);

        n = recvfrom(sockfd, recvline, MAXLINE, 0, NULL, NULL);
        if (n < 0) {
            if (errno == EWOULDBLOCK) {
                fprintf(stderr, "socket timeout\n");
                continue;
            } else
                err_sys("recvfrom error");
        }

        recvline[n] = 0;    /* null terminate */
        fputs(recvline, stdout);
    }
}