Programming

    s = socket(PF_INET, SOCK_STREAM, 0);    //socket
    fcntl(s, F_SETFL, O_NONBLOCK);             //set socket to nonblock

retry_conn:    
    ret = connect(s, (struct sockaddr *)&serv_addr, sizeof(struct sockaddr_in)); // try to connect, for sure there no connection to "serv_addr" 
    printf("connect, status=%d, errno=%d \n", status, errno); 
    
    if (errno == EINPROGRESS) //no connection
    {
        if (poll(fds, 1, delay_time / 1000) > 0)
        {
            ret = getsockopt(s, SOL_SOCKET, SO_ERROR, &error_s, &len_s)
            printf("getsockopt, status: %d, error_s=%d, errno=%d\n", status, error_s, errno);
        }
        
        if (error_s)
        {
            printf("try_connect_again\n");
            goto: try_connect_again;
        }
        else
        {
            connected!!!!!!!!!
        }
    }

    connect, status=-1, errno=150
    getsockopt, status: 0, error_s=146, errno=150
    try_connect_again
    connect, status=-1, errno=150
    getsockopt, status: 0, error_s=0, errno=0