In PR #37300, Alexej asked why we the compiler does not warn about
unnecessary semicolons, e.g.
f()
{
}; // <-- here
The answer is surprising: In C++98, above syntax was disallowed but by
most compilers accepted it regardless. C++>11 introduced "empty
declarations" which made the syntax legal.
The previous behavior can be restored using flag
-Wc++98-compat-extra-semi. This finds many useless semicolons which were
removed in this change. Unfortunately, there are also false positives
which would require #pragma-s and HAS_* logic (--> check_flags.cmake) to
suppress. In the end, -Wc++98-compat-extra-semi comes with extra effort
for little benefit. Therefore, this change only fixes some semicolons
but does not enable the flag.
In case of ECONNRESET (Connection reset by peer) the "cancelled" will
not be set, and so drain() will fail with LOGICAL_ERROR:
<details>
2021.10.16 04:10:55.054771 [ 7635 ] {882164e0-ca26-4955-8759-708ba1f6e85c} <Error> PullingAsyncPipelineExecutor: Code: 210. DB::NetException: Connection reset by peer, while writing to socket (127.0.0.2:9000). (NETWORK_ERROR), Stack trace (when copying this message, always include the lines below):
...
4. ./obj-x86_64-linux-gnu/../src/Common/NetException.h:12: DB::NetException::NetException(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, int) @ 0x20db5749 in /usr/bin/clickhouse
5. ./obj-x86_64-linux-gnu/../src/IO/WriteBufferFromPocoSocket.cpp:56: DB::WriteBufferFromPocoSocket::nextImpl() @ 0x211d56bb in /usr/bin/clickhouse
6. ./obj-x86_64-linux-gnu/../src/IO/WriteBuffer.h:47: DB::WriteBuffer::next() @ 0x14e4c874 in /usr/bin/clickhouse
7. ./obj-x86_64-linux-gnu/../src/Client/Connection.cpp:560: DB::Connection::sendCancel() @ 0x227c0c22 in /usr/bin/clickhouse
8. ./obj-x86_64-linux-gnu/../src/Client/HedgedConnections.cpp:242: DB::HedgedConnections::sendCancel() @ 0x227f1b53 in /usr/bin/clickhouse
...
2021.10.16 04:12:35.555530 [ 5575 ] {} <Fatal> : Logical error: 'Cannot drain connections: cancel first.'.
</details>
Found by stress tests on CI [1].
[1]: https://clickhouse-test-reports.s3.yandex.net/0/d3cb99701d4aaec384fd183168d10e0f650ecc1d/stress_test_(debug).html#fail1
