If you will execute 'SYSTEM RELOAD CONFIG' via, i.e., TCP protocol, then
reload on port change will endlessly wait for connection from which this
query had been issued, and you will see the following message in the
logs:
2022.04.28 03:34:57.552513 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Debug> executeQuery: (from 127.0.0.1:11774) system reload config
...
2022.04.28 03:34:57.710640 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Information> Application: Stopped listening for http://127.0.0.1:18123
2022.04.28 03:34:57.798774 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Information> Application: Stopped listening for native protocol (tcp): 127.0.0.1:19000
...
2022.04.28 03:34:57.901375 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Debug> Application: Server finished: http://127.0.0.1:18123
2022.04.28 03:34:57.901455 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Trace> Application: Waiting server to finish: native protocol (tcp): 127.0.0.1:19000
2022.04.28 03:34:58.001717 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Trace> Application: Waiting server to finish: native protocol (tcp): 127.0.0.1:19000
2022.04.28 03:34:58.101881 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Trace> Application: Waiting server to finish: native protocol (tcp): 127.0.0.1:19000
...
2022.04.28 03:35:01.707951 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Trace> Application: Waiting server to finish: native protocol (tcp): 127.0.0.1:19000
But waiting for the current connection will never ends.
So instead of waiting directly from the query context (SYSTEM RELOAD
CONFIG) do this in background (actually not even in background, but
check on server reload and on exit).
v0: just don't wait for the servers
v2: fix use-after-free by removing dependency from server in handlers
v3: wait servers in background to avoid use-after-free of the context
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
Official docs:
Some headers from C library were deprecated in C++ and are no longer
welcome in C++ codebases. Some have no effect in C++. For more details
refer to the C++ 14 Standard [depr.c.headers] section. This check
replaces C standard library headers with their C++ alternatives and
removes redundant ones.
