select版的sendn函数

int sendn_select(int fd, const char *buf, unsigned int len)
{
        fd_set wset;
        int ok = 0;
        int send_len = 0;
        int tmp_len = 0;
        struct timeval t;
        int maxfd;

        if(fd < 0 || !buf || !len)
        {
                return -1;
        }

        FD_ZERO(&wset);
        maxfd = fd + 1;

        while (!ok)
        {
                t.tv_sec = 0;
                t.tv_usec = 100;

                FD_SET(fd,&wset);
                if(select(maxfd,NULL,&wset,NULL,&t) < 0)
                {
                        if(errno == EINTR)
                        {
                                continue;
                        }
                        else
                        {
                                return -1;
                        }
                }
                tmp_len = send(fd, buf + send_len, len - (unsigned int)send_len, 0);
                if (!tmp_len)
                {
                        continue;
                }
                else if (tmp_len < 0)
                {
                        if (errno != EINTR && errno != EAGAIN && errno != EWOULDBLOCK)
                        {
                                return -1;
                        }
                }
                else if (tmp_len < (int)len - send_len)
                {
                        send_len += tmp_len;
                }
                else {
                        ok = 1;
                }
        }
        return 0;
}