c++ - 套接字保活不工作

Question

我有一个客户端 connect() 到服务器，当空闲时，它会在几个小时后超时。 我加了 setsockopt(socket, SOL_SOCKET, SO_KEEPALIVE...) 1 秒 但这并没有什么不同。 关于为什么 keepalive 不起作用的任何线索？ 如果我使用 SOL_TCP 而不是 SOL_SOCKET，会有什么不同吗？ 这是在 Linux 上。

Answer 1

int val = 1;
setsockopt(socket, SOL_SOCKET, SO_KEEPALIVE, &val, sizeof val)

只启用keepalive。您将获得 keepalive 探测的默认计时器，您可以使用以下命令查看:

sysctl net.ipv4.tcp_keepalive_time

通常默认为几个小时。

如果你想改变默认定时器，你可以使用这个:

struct KeepConfig cfg = { 60, 5, 5};
set_tcp_keepalive_cfg(fd, &cfg);

在这里使用辅助函数:

struct KeepConfig {
    /** The time (in seconds) the connection needs to remain 
     * idle before TCP starts sending keepalive probes (TCP_KEEPIDLE socket option)
     */
    int keepidle;
    /** The maximum number of keepalive probes TCP should 
     * send before dropping the connection. (TCP_KEEPCNT socket option)
     */
    int keepcnt;

    /** The time (in seconds) between individual keepalive probes.
     *  (TCP_KEEPINTVL socket option)
     */
    int keepintvl;
};

/**
* enable TCP keepalive on the socket
* @param fd file descriptor
* @return 0 on success -1 on failure
*/
int set_tcp_keepalive(int sockfd)
{
    int optval = 1;

    return setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &optval, sizeof(optval));
}

/** Set the keepalive options on the socket
* This also enables TCP keepalive on the socket
*
* @param fd file descriptor
* @param fd file descriptor
* @return 0 on success -1 on failure
*/
int set_tcp_keepalive_cfg(int sockfd, const struct KeepConfig *cfg)
{
    int rc;

    //first turn on keepalive
    rc = set_tcp_keepalive(sockfd);
    if (rc != 0) {
        return rc;
    }

    //set the keepalive options
    rc = setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPCNT, &cfg->keepcnt, sizeof cfg->keepcnt);
    if (rc != 0) {
        return rc;
    }

    rc = setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPIDLE, &cfg->keepidle, sizeof cfg->keepidle);
    if (rc != 0) {
        return rc;
    }

    rc = setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPINTVL, &cfg->keepintvl, sizeof cfg->keepintvl);
    if (rc != 0) {
        return rc;
    }

    return 0;
}