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ICU-20845 UMutex not trivially but constexpr constructible

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This commit is contained in:
Markus Scherer 2019-10-01 16:33:53 -07:00
parent 7f862281da
commit e5381c956b
2 changed files with 16 additions and 14 deletions
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12
icu4c/source/common/umutex.cpp
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@ -36,15 +36,6 @@ U_NAMESPACE_BEGIN
#error U_USER_MUTEX_CPP not supported #error U_USER_MUTEX_CPP not supported
#endif #endif
// Check that UMutex is trivially constructable & destructable, which ensures that
// static instances are not running static constructors or destructors.
#if (defined(__GNUG__) && __GNUC__ < 5) || (defined(__clang__) && __clang_major__ < 5)
// skip
#else
static_assert(std::is_trivially_constructible<UMutex>::value, "UMutex not trivially constructable.");
static_assert(std::is_trivially_destructible<UMutex>::value, "UMutex not trivially destructable.");
#endif
/************************************************************************************************* /*************************************************************************************************
* *
@ -56,7 +47,8 @@ namespace {
std::mutex *initMutex; std::mutex *initMutex;
std::condition_variable *initCondition; std::condition_variable *initCondition;
// The ICU global mutex. Used when ICU implementation code passes NULL for the mutex pointer. // The ICU global mutex.
// Used when ICU implementation code passes nullptr for the mutex pointer.
UMutex globalMutex; UMutex globalMutex;
std::once_flag initFlag; std::once_flag initFlag;

18
icu4c/source/common/umutex.h
View File

@ -184,6 +184,16 @@ template<class T> void umtx_initOnce(UInitOnce &uio, void (U_CALLCONV *fp)(T, UE
} }
} }
// UMutex should be constexpr-constructible, so that no initialization code
// is run during startup.
// This works on all C++ libraries except MS VS before VS2019.
#if (defined(_CPPLIB_VER) && !defined(_MSVC_STL_VERSION)) || \
(defined(_MSVC_STL_VERSION) && _MSVC_STL_VERSION < 142)
// (VS std lib older than VS2017) || (VS std lib version < VS2019)
# define UMUTEX_CONSTEXPR
#else
# define UMUTEX_CONSTEXPR constexpr
#endif
/** /**
* UMutex - ICU Mutex class. * UMutex - ICU Mutex class.
@ -212,7 +222,7 @@ template<class T> void umtx_initOnce(UInitOnce &uio, void (U_CALLCONV *fp)(T, UE
class U_COMMON_API UMutex { class U_COMMON_API UMutex {
public: public:
UMutex() = default; UMUTEX_CONSTEXPR UMutex() {}
~UMutex() = default; ~UMutex() = default;
UMutex(const UMutex &other) = delete; UMutex(const UMutex &other) = delete;
@ -230,13 +240,13 @@ public:
static void cleanup(); static void cleanup();
private: private:
alignas(std::mutex) char fStorage[sizeof(std::mutex)]; alignas(std::mutex) char fStorage[sizeof(std::mutex)] {};
std::atomic<std::mutex *> fMutex; std::atomic<std::mutex *> fMutex { nullptr };
/** All initialized UMutexes are kept in a linked list, so that they can be found, /** All initialized UMutexes are kept in a linked list, so that they can be found,
* and the underlying std::mutex destructed, by u_cleanup(). * and the underlying std::mutex destructed, by u_cleanup().
*/ */
UMutex *fListLink; UMutex *fListLink { nullptr };
static UMutex *gListHead; static UMutex *gListHead;
/** Out-of-line function to lazily initialize a UMutex on first use. /** Out-of-line function to lazily initialize a UMutex on first use.