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5a4f21c50f
- 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
65 lines
2.0 KiB
C++
65 lines
2.0 KiB
C++
#pragma once
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#include <Access/LDAPClient.h>
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#include <Access/Credentials.h>
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#include <Access/GSSAcceptor.h>
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#include <base/defines.h>
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#include <base/types.h>
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#include <chrono>
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#include <map>
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#include <mutex>
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#include <optional>
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#include <unordered_map>
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namespace Poco
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{
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class Logger;
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namespace Util
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{
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class AbstractConfiguration;
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}
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}
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namespace DB
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{
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class ExternalAuthenticators
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{
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public:
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void reset();
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void setConfiguration(const Poco::Util::AbstractConfiguration & config, Poco::Logger * log);
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// The name and readiness of the credentials must be verified before calling these.
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bool checkLDAPCredentials(const String & server, const BasicCredentials & credentials,
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const LDAPClient::RoleSearchParamsList * role_search_params = nullptr, LDAPClient::SearchResultsList * role_search_results = nullptr) const;
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bool checkKerberosCredentials(const String & realm, const GSSAcceptorContext & credentials) const;
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GSSAcceptorContext::Params getKerberosParams() const;
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private:
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struct LDAPCacheEntry
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{
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std::size_t last_successful_params_hash = 0;
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std::chrono::steady_clock::time_point last_successful_authentication_timestamp;
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LDAPClient::SearchResultsList last_successful_role_search_results;
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};
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using LDAPCache = std::unordered_map<String, LDAPCacheEntry>; // user name -> cache entry
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using LDAPCaches = std::map<String, LDAPCache>; // server name -> cache
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using LDAPParams = std::map<String, LDAPClient::Params>; // server name -> params
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mutable std::mutex mutex;
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LDAPParams ldap_client_params_blueprint TSA_GUARDED_BY(mutex) ;
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mutable LDAPCaches ldap_caches TSA_GUARDED_BY(mutex) ;
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std::optional<GSSAcceptorContext::Params> kerberos_params TSA_GUARDED_BY(mutex) ;
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void resetImpl() TSA_REQUIRES(mutex);
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};
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void parseLDAPRoleSearchParams(LDAPClient::RoleSearchParams & params, const Poco::Util::AbstractConfiguration & config, const String & prefix);
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}
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