This is like Alt-# in readline, it is useful when you need to look
something else, and need to save current query/command somewhere, and
commented lin the history is a good option.
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
* Remove strange code
* Even more code removal
* Fix style
* Remove even more code
* Simplify code by making it slower
* Attempt to do something
* Attempt to do something
* Well do something with this horrible trash
* Add a test
clang-tidy now also checks code in header files. Because the analyzer
finds tons of issues, activate the check only for directory "base/" (see
file ".clang-tidy"). All other directories, in particular "src/" are
left to future work.
While many findings were fixed, some were not (and suppressed instead).
Reasons for this include: a) the file is 1:1 copypaste of a 3rd-party
lib (e.g. pcg_extras.h) and fixing stuff would make upgrades/fixes more
difficult b) a fix would have broken lots of using code
getauxval() from glibc-compatibility did not work always correctly:
- It does not work after setenv(), and this breaks vsyscalls,
like sched_getcpu() [1] (and BaseDaemon.cpp always set TZ if timezone
is defined, which is true for CI [2]).
Also note, that fixing setenv() will not fix LSan,
since the culprit is getauxval()
[1]: https://bugzilla.redhat.com/show_bug.cgi?id=1163404
[2]: ClickHouse#32928 (comment)
- Another think that is definitely broken is LSan (Leak Sanitizer), it
relies on worked getauxval() but it does not work if __environ is not
initialized yet (there is even a commit about this).
And because of, at least, one leak had been introduced [3]:
[3]: ClickHouse#33840
Fix this by using /proc/self/auxv with fallback to environ solution to
make it compatible with environment that does not allow reading from
auxv (or no procfs).
v2: add fallback to environ solution
v3: fix return value for __auxv_init_procfs()
(cherry picked from commit f187c3499a)
v4: more verbose message on errors, CI founds [1]:
AUXV already has value (529267711)
[1]: https://s3.amazonaws.com/clickhouse-test-reports/39103/2325f7e8442d1672ce5fb43b11039b6a8937e298/stress_test__memory__actions_.html
v5: break at AT_NULL
v6: ignore AT_IGNORE
v7: suppress TSan and remove superior check to avoid abort() in case of race
v8: proper suppressions (not inner function but itself)
Refs: #33957
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
getauxval() from glibc-compatibility did not work always correctly:
- It does not work after setenv(), and this breaks vsyscalls,
like sched_getcpu() [1] (and BaseDaemon.cpp always set TZ if timezone
is defined, which is true for CI [2]).
Also note, that fixing setenv() will not fix LSan,
since the culprit is getauxval()
[1]: https://bugzilla.redhat.com/show_bug.cgi?id=1163404
[2]: ClickHouse#32928 (comment)
- Another think that is definitely broken is LSan (Leak Sanitizer), it
relies on worked getauxval() but it does not work if __environ is not
initialized yet (there is even a commit about this).
And because of, at least, one leak had been introduced [3]:
[3]: ClickHouse#33840
Fix this by using /proc/self/auxv with fallback to environ solution to
make it compatible with environment that does not allow reading from
auxv (or no procfs).
v2: add fallback to environ solution
v3: fix return value for __auxv_init_procfs()
Refs: #33957
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
A simple HelloWorld program with zero includes except iostream triggers
a build of ca. 2000 source files. The reason is that ClickHouse's
top-level CMakeLists.txt overrides "add_executable()" to link all
binaries against "clickhouse_new_delete". This links against
"clickhouse_common_io", which in turn has lots of 3rd party library
dependencies ... Without linking "clickhouse_new_delete", the number of
compiled files for "HelloWorld" goes down to ca. 70.
As an example, the self-extracting-executable needs none of its current
dependencies but other programs may also benefit.
In order to restore access to the original "add_executable()", the
overriding version is now prefixed. There is precedence for a
"clickhouse_" prefix (as opposed to "ch_"), for example
"clickhouse_split_debug_symbols". In general prefixing makes sense also
because overriding CMake commands relies on undocumented behavior and is
considered not-so-great practice (*).
(*) https://crascit.com/2018/09/14/do-not-redefine-cmake-commands/
- TSA is a static analyzer build by Google which finds race conditions
and deadlocks at compile time.
- It works by associating a shared member variable with a
synchronization primitive that protects it. The compiler can then
check at each access if proper locking happened before. A good
introduction are [0] and [1].
- TSA requires some help by the programmer via annotations. Luckily,
LLVM's libcxx already has annotations for std::mutex, std::lock_guard,
std::shared_mutex and std::scoped_lock. This commit enables them
(--> contrib/libcxx-cmake/CMakeLists.txt).
- Further, this commit adds convenience macros for the low-level
annotations for use in ClickHouse (--> base/defines.h). For
demonstration, they are leveraged in a few places.
- As we compile with "-Wall -Wextra -Weverything", the required compiler
flag "-Wthread-safety-analysis" was already enabled. Negative checks
are an experimental feature of TSA and disabled
(--> cmake/warnings.cmake). Compile times did not increase noticeably.
- TSA is used in a few places with simple locking. I tried TSA also
where locking is more complex. The problem was usually that it is
unclear which data is protected by which lock :-(. But there was
definitely some weird code where locking looked broken. So there is
some potential to find bugs.
*** Limitations of TSA besides the ones listed in [1]:
- The programmer needs to know which lock protects which piece of shared
data. This is not always easy for large classes.
- Two synchronization primitives used in ClickHouse are not annotated in
libcxx:
(1) std::unique_lock: A releaseable lock handle often together with
std::condition_variable, e.g. in solve producer-consumer problems.
(2) std::recursive_mutex: A re-entrant mutex variant. Its usage can be
considered a design flaw + typically it is slower than a standard
mutex. In this commit, one std::recursive_mutex was converted to
std::mutex and annotated with TSA.
- For free-standing functions (e.g. helper functions) which are passed
shared data members, it can be tricky to specify the associated lock.
This is because the annotations use the normal C++ rules for symbol
resolution.
[0] https://clang.llvm.org/docs/ThreadSafetyAnalysis.html
[1] https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/42958.pdf
