Public suffix list may contain special characters (you may find format
here - [1]):
- asterisk (*)
- exclamation mark (!)
[1]: https://github.com/publicsuffix/list/wiki/Format
It is easier to describe how it should be interpreted with an examples.
Consider the following part of the list:
*.sch.uk
*.kawasaki.jp
!city.kawasaki.jp
And here are the results for `cutToFirstSignificantSubdomainCustom()`:
If you have only asterisk (*):
foo.something.sheffield.sch.uk -> something.sheffield.sch.uk
sheffield.sch.uk -> sheffield.sch.uk
If you have exclamation mark (!) too:
foo.kawasaki.jp -> foo.kawasaki.jp
foo.foo.kawasaki.jp -> foo.foo.kawasaki.jp
city.kawasaki.jp -> city.kawasaki.jp
some.city.kawasaki.jp -> city.kawasaki.jp
TLDs had been verified wit the following script [2], to match with
python publicsuffix2 module.
[2]: https://gist.github.com/azat/c1a7a9f1e3519793134ef4b1df5461a6
v2: fix StringHashTable padding requirements
Fixes: #39468
Follow-up for: #17748
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
- 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
v2: Add a note that top_level_domains_lists aren not applied w/o restart
v3: Remove ExtractFirstSignificantSubdomain{Default,Custom}Lookup.h headers
v4: TLDListsHolder: remove FIXME for dense_hash_map (this is not significant)
