Implement TCP Keep-Alives across most Unix-like systems (#12782)
## TCP Keep-Alives [TCP Keep-Alives](https://datatracker.ietf.org/doc/html/rfc9293#name-tcp-keep-alives) provides a way to detect whether a TCP connection is alive or dead, which can be useful for reducing system resources by cleaning up dead connections. There is full support of TCP Keep-Alives on Linux and partial support on macOS in `redis` at present. This PR intends to complete the rest. ## Unix-like OS's support `TCP_KEEPIDLE`, `TCP_KEEPINTVL`, and `TCP_KEEPCNT` are not included in the POSIX standard for `setsockopts`, while these three socket options are widely available on most Unix-like systems and Windows. ### References - [AIX](https://www.ibm.com/support/pages/ibm-aix-tcp-keepalive-probes) - [DragonflyBSD](https://man.dragonflybsd.org/?command=tcp§ion=4) - [FreeBSD](https://www.freebsd.org/cgi/man.cgi?query=tcp) - [HP-UX](https://docstore.mik.ua/manuals/hp-ux/en/B2355-60130/TCP.7P.html) - [illumos](https://illumos.org/man/4P/tcp) - [Linux](https://man7.org/linux/man-pages/man7/tcp.7.html) - [NetBSD](https://man.netbsd.org/NetBSD-8.0/tcp.4) - [Windows](https://learn.microsoft.com/en-us/windows/win32/winsock/ipproto-tcp-socket-options) ### Mac OS In earlier versions, macOS only supported setting `TCP_KEEPALIVE` (the equivalent of `TCP_KEEPIDLE` on other platforms), but since macOS 10.8 it has supported `TCP_KEEPINTVL` and `TCP_KEEPCNT`. Check out [this mailing list](https://lists.apple.com/archives/macnetworkprog/2012/Jul/msg00005.html) and [the source code](https://github.com/apple/darwin-xnu/blob/main/bsd/netinet/tcp.h#L215-L230) for more details. ### Solaris Solaris claimed it supported the TCP-Alives mechanism, but `TCP_KEEPIDLE`, `TCP_KEEPINTVL`, and `TCP_KEEPCNT` were not available on Solaris until the latest version 11.4. Therefore, we need to simulate the TCP-Alives mechanism on other platforms via `TCP_KEEPALIVE_THRESHOLD` + `TCP_KEEPALIVE_ABORT_THRESHOLD`. - [Solaris 11.3](https://docs.oracle.com/cd/E86824_01/html/E54777/tcp-7p.html) - [Solaris 11.4](https://docs.oracle.com/cd/E88353_01/html/E37851/tcp-4p.html) --------- Co-authored-by: Oran Agra <oran@redislabs.com>
This commit is contained in:
Andy Pan
GitHub
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commit
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149
src/anet.c
149
src/anet.c
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@ -130,57 +130,142 @@ int anetCloexec(int fd) {
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return r;
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}
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/* Set TCP keep alive option to detect dead peers. The interval option
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* is only used for Linux as we are using Linux-specific APIs to set
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* the probe send time, interval, and count. */
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/* Enable TCP keep-alive mechanism to detect dead peers,
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* TCP_KEEPIDLE, TCP_KEEPINTVL and TCP_KEEPCNT will be set accordingly. */
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int anetKeepAlive(char *err, int fd, int interval)
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{
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int val = 1;
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if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &val, sizeof(val)) == -1)
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int enabled = 1;
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if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &enabled, sizeof(enabled)))
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{
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anetSetError(err, "setsockopt SO_KEEPALIVE: %s", strerror(errno));
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return ANET_ERR;
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}
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#ifdef __linux__
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/* Default settings are more or less garbage, with the keepalive time
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* set to 7200 by default on Linux. Modify settings to make the feature
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* actually useful. */
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int idle;
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int intvl;
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int cnt;
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/* Send first probe after interval. */
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val = interval;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPIDLE, &val, sizeof(val)) < 0) {
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anetSetError(err, "setsockopt TCP_KEEPIDLE: %s\n", strerror(errno));
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return ANET_ERR;
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}
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/* There are platforms that are expected to support the full mechanism of TCP keep-alive,
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* we want the compiler to emit warnings of unused variables if the preprocessor directives
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* somehow fail, and other than those platforms, just omit these warnings if they happen.
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*/
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#if !(defined(_AIX) || defined(__APPLE__) || defined(__DragonFly__) || \
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defined(__FreeBSD__) || defined(__illumos__) || defined(__linux__) || \
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defined(__NetBSD__) || defined(__sun))
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UNUSED(interval);
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UNUSED(idle);
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UNUSED(intvl);
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UNUSED(cnt);
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#endif
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/* Send next probes after the specified interval. Note that we set the
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* delay as interval / 3, as we send three probes before detecting
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* an error (see the next setsockopt call). */
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val = interval/3;
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if (val == 0) val = 1;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPINTVL, &val, sizeof(val)) < 0) {
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/* The implementation of TCP keep-alive on Solaris/SmartOS is a bit unusual
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* compared to other Unix-like systems.
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* Thus, we need to specialize it on Solaris. */
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#ifdef __sun
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/* There are two keep-alive mechanisms on Solaris:
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* - By default, the first keep-alive probe is sent out after a TCP connection is idle for two hours.
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* If the peer does not respond to the probe within eight minutes, the TCP connection is aborted.
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* You can alter the interval for sending out the first probe using the socket option TCP_KEEPALIVE_THRESHOLD
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* in milliseconds or TCP_KEEPIDLE in seconds.
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* The system default is controlled by the TCP ndd parameter tcp_keepalive_interval. The minimum value is ten seconds.
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* The maximum is ten days, while the default is two hours. If you receive no response to the probe,
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* you can use the TCP_KEEPALIVE_ABORT_THRESHOLD socket option to change the time threshold for aborting a TCP connection.
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* The option value is an unsigned integer in milliseconds. The value zero indicates that TCP should never time out and
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* abort the connection when probing. The system default is controlled by the TCP ndd parameter tcp_keepalive_abort_interval.
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* The default is eight minutes.
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* - The second implementation is activated if socket option TCP_KEEPINTVL and/or TCP_KEEPCNT are set.
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* The time between each consequent probes is set by TCP_KEEPINTVL in seconds.
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* The minimum value is ten seconds. The maximum is ten days, while the default is two hours.
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* The TCP connection will be aborted after certain amount of probes, which is set by TCP_KEEPCNT, without receiving response.
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*/
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idle = interval;
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if (idle < 10) idle = 10; // kernel expects at least 10 seconds
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if (idle > 10*24*60*60) idle = 10*24*60*60; // kernel expects at most 10 days
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/* `TCP_KEEPIDLE`, `TCP_KEEPINTVL`, and `TCP_KEEPCNT` were not available on Solaris
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* until version 11.4, but let's take a chance here. */
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#if defined(TCP_KEEPIDLE) && defined(TCP_KEEPINTVL) && defined(TCP_KEEPCNT)
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPIDLE, &idle, sizeof(idle))) {
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anetSetError(err, "setsockopt TCP_KEEPIDLE: %s\n", strerror(errno));
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return ANET_ERR;
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}
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intvl = idle/3;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPINTVL, &intvl, sizeof(intvl))) {
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anetSetError(err, "setsockopt TCP_KEEPINTVL: %s\n", strerror(errno));
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return ANET_ERR;
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}
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cnt = 3;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPCNT, &cnt, sizeof(cnt))) {
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anetSetError(err, "setsockopt TCP_KEEPCNT: %s\n", strerror(errno));
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return ANET_ERR;
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}
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return ANET_OK;
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#endif
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/* Fall back to the first implementation of tcp-alive mechanism for older Solaris,
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* simulate the tcp-alive mechanism on other platforms via `TCP_KEEPALIVE_THRESHOLD` + `TCP_KEEPALIVE_ABORT_THRESHOLD`.
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*/
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idle *= 1000; // kernel expects milliseconds
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPALIVE_THRESHOLD, &idle, sizeof(idle))) {
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anetSetError(err, "setsockopt TCP_KEEPINTVL: %s\n", strerror(errno));
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return ANET_ERR;
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}
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/* Consider the socket in error state after three we send three ACK
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* probes without getting a reply. */
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val = 3;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPCNT, &val, sizeof(val)) < 0) {
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/* Note that the consequent probes will not be sent at equal intervals on Solaris,
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* but will be sent using the exponential backoff algorithm. */
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intvl = idle/3;
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cnt = 3;
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int time_to_abort = intvl * cnt;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPALIVE_ABORT_THRESHOLD, &time_to_abort, sizeof(time_to_abort))) {
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anetSetError(err, "setsockopt TCP_KEEPCNT: %s\n", strerror(errno));
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return ANET_ERR;
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}
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#elif defined(__APPLE__)
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/* Set idle time with interval */
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val = interval;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPALIVE, &val, sizeof(val)) < 0) {
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return ANET_OK;
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#endif
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#ifdef TCP_KEEPIDLE
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/* Default settings are more or less garbage, with the keepalive time
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* set to 7200 by default on Linux and other Unix-like systems.
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* Modify settings to make the feature actually useful. */
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/* Send first probe after interval. */
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idle = interval;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPIDLE, &idle, sizeof(idle))) {
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anetSetError(err, "setsockopt TCP_KEEPIDLE: %s\n", strerror(errno));
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return ANET_ERR;
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}
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#elif defined(TCP_KEEPALIVE)
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/* Darwin/macOS uses TCP_KEEPALIVE in place of TCP_KEEPIDLE. */
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idle = interval;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPALIVE, &idle, sizeof(idle))) {
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anetSetError(err, "setsockopt TCP_KEEPALIVE: %s\n", strerror(errno));
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return ANET_ERR;
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}
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#else
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((void) interval); /* Avoid unused var warning for non Linux systems. */
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#endif
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#ifdef TCP_KEEPINTVL
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/* Send next probes after the specified interval. Note that we set the
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* delay as interval / 3, as we send three probes before detecting
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* an error (see the next setsockopt call). */
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intvl = interval/3;
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if (intvl == 0) intvl = 1;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPINTVL, &intvl, sizeof(intvl))) {
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anetSetError(err, "setsockopt TCP_KEEPINTVL: %s\n", strerror(errno));
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return ANET_ERR;
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}
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#endif
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#ifdef TCP_KEEPCNT
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/* Consider the socket in error state after three we send three ACK
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* probes without getting a reply. */
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cnt = 3;
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if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPCNT, &cnt, sizeof(cnt))) {
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anetSetError(err, "setsockopt TCP_KEEPCNT: %s\n", strerror(errno));
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return ANET_ERR;
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}
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#endif
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return ANET_OK;
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