Fix race conditions in LOG_EVERY_N #492
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A mutex is quite heavy. Would thread-local storage possibly suffice? cc @os12 |
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There is no need for a mutex. These counters just need to become 👎 |
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Glog still uses C++03. There should be atleast a fallback mechanism for pre C++11 compilers. |
src/glog/logging.h.in
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| #define SOME_KIND_OF_LOG_EVERY_N(severity, n, what_to_do) \ | ||
| static int LOG_OCCURRENCES = 0, LOG_OCCURRENCES_MOD_N = 0; \ | ||
| thread_local int LOG_OCCURRENCES = 0, LOG_OCCURRENCES_MOD_N = 0; \ |
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This looks wrong to me. Imagine the same LOG_EVERY_XXX() called from several threads concurrently - every thread will get its own count now...
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I've made the counters std::atomic<int>, and now the only thing left is a fallback mechanism for pre C++11 compilers. Do you have any idea?
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Both GCC and MSVC provide atomic intrinsics. Please see https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html and https://docs.microsoft.com/en-us/windows/win32/api/winnt/nf-winnt-interlockedincrement.
src/glog/logging.h.in
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| // Microsoft Visual Studio 14 (2015) sets __cplusplus==199711 despite | ||
| // reasonably good C++11 support, so we set LANG_CXX for it and | ||
| // newer versions (_MSC_VER >= 1900). | ||
| #define SUPPORT_CPLUSPLUS11 (defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L || \ |
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std::atomic<> availability should be checked in CMakeLists.txt using CheckCXXSymbolExists or CheckCXXSourceCompiles module.
* Use CMakeLists.txt to check the availability of std::atomic<> * Declare the static integer counters as std::atomic<int> instead of int if C++11's atomic is available
aesophor
changed the title
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@aesophor Could you please resolve the conflict? |
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@sergiud I've resolved the conflict and CI has passed successfully. Thanks! |
4 participants
Fixes issue #439
by protecting critical sections with mutexes.Note:
CheckCXXSourceCompilesto check the availability ofstd::atomic<>std::atomic<int>