openssl ssl_connect永远阻止 - 如何设置超时？

#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
#include<openssl/ssl.h>

int ssl_connect_with_timeout(SSL *ssl, int timeout_seconds) {
    fd_set readfds, writefds;
    struct timeval timeout;
    int ret;

    FD_ZERO(&readfds);
    FD_ZERO(&writefds);
    FD_SET(SSL_get_fd(ssl), &readfds);
    FD_SET(SSL_get_fd(ssl), &writefds);

    timeout.tv_sec = timeout_seconds;
    timeout.tv_usec = 0;

    ret = select(SSL_get_fd(ssl) + 1, &readfds, &writefds, NULL, &timeout);
    if (ret == 0) {
        // 超时
        return -1;
    } else if (ret < 0) {
        // 错误
        return -2;
    }

    // 连接建立
    return ssl_connect(ssl);
}