Function anetKeepAlive

app/redis-6.2.6/src/anet.c:133–177

Set TCP keep alive option to detect dead peers. The interval option * is only used for Linux as we are using Linux-specific APIs to set * the probe send time, interval, and count. */

 * is only used for Linux as we are using Linux-specific APIs to set
 * the probe send time, interval, and count. */
int anetKeepAlive(char *err, int fd, int interval)
{
    int val = 1;

    if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &val, sizeof(val)) == -1)
    {
        anetSetError(err, "setsockopt SO_KEEPALIVE: %s", strerror(errno));
        return ANET_ERR;
    }

#ifdef __linux__
    /* Default settings are more or less garbage, with the keepalive time
     * set to 7200 by default on Linux. Modify settings to make the feature
     * actually useful. */

    /* Send first probe after interval. */
    val = interval;
    if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPIDLE, &val, sizeof(val)) < 0) {
        anetSetError(err, "setsockopt TCP_KEEPIDLE: %s\n", strerror(errno));
        return ANET_ERR;
    }

    /* Send next probes after the specified interval. Note that we set the
     * delay as interval / 3, as we send three probes before detecting
     * an error (see the next setsockopt call). */
    val = interval/3;
    if (val == 0) val = 1;
    if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPINTVL, &val, sizeof(val)) < 0) {
        anetSetError(err, "setsockopt TCP_KEEPINTVL: %s\n", strerror(errno));
        return ANET_ERR;
    }

    /* Consider the socket in error state after three we send three ACK
     * probes without getting a reply. */
    val = 3;
    if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPCNT, &val, sizeof(val)) < 0) {
        anetSetError(err, "setsockopt TCP_KEEPCNT: %s\n", strerror(errno));
        return ANET_ERR;
    }
#else
    ((void) interval); /* Avoid unused var warning for non Linux systems. */
#endif

    return ANET_OK;
}

static int anetSetTcpNoDelay(char *err, int fd, int val)
{