diff options
| -rw-r--r-- | src/corelib/global/qglobalstatic.h | 8 | ||||
| -rw-r--r-- | src/corelib/global/qglobalstatic.qdoc | 18 |
2 files changed, 14 insertions, 12 deletions
diff --git a/src/corelib/global/qglobalstatic.h b/src/corelib/global/qglobalstatic.h index 01e06e5234..cf96e5ae8e 100644 --- a/src/corelib/global/qglobalstatic.h +++ b/src/corelib/global/qglobalstatic.h @@ -57,15 +57,17 @@ enum GuardValues { Initializing = 1 }; -template <typename QGS> struct Holder +template <typename QGS> union Holder { using Type = typename QGS::QGS_Type; using PlainType = std::remove_cv_t<Type>; static constexpr bool ConstructionIsNoexcept = noexcept(QGS::innerFunction(nullptr)); - std::aligned_union_t<1, PlainType> storage; static inline QBasicAtomicInteger<qint8> guard = { QtGlobalStatic::Uninitialized }; + // union's sole member + PlainType storage; + Holder() noexcept(ConstructionIsNoexcept) { QGS::innerFunction(pointer()); @@ -81,7 +83,7 @@ template <typename QGS> struct Holder PlainType *pointer() noexcept { - return reinterpret_cast<PlainType *>(&storage); + return &storage; } Q_DISABLE_COPY_MOVE(Holder) diff --git a/src/corelib/global/qglobalstatic.qdoc b/src/corelib/global/qglobalstatic.qdoc index 5aea8fed06..99416ad102 100644 --- a/src/corelib/global/qglobalstatic.qdoc +++ b/src/corelib/global/qglobalstatic.qdoc @@ -234,15 +234,15 @@ new and the variadic arguments. The majority of the work is done by the public \l QGlobalStatic class and - the private \c QtGlobalStatic::Holder class. The \c Holder class has a - non-static, trivial member of suitable size and alignment to hold \a TYPE - (a \c{std::aligned_union_t} or a \c{std::aligned_storage_t}). The - constructor calls the "QGS" type's static member function with a pointer to - this location so it can be initialized and the destructor calls the type's - destructor. The \c{Holder} type is therefore neither trivially - constructible nor trivially destructible. It is used as a function-local \c - static so its initialization is thread-safe due to C++11's requirement that - such variables be thread-safely initialized. + the private \c QtGlobalStatic::Holder class. The \c Holder union has a + single non-static member of type \a TYPE, but because this is a union, its + construction and destruction are explicitly controlled in the Holder's + constructor and destructor. The constructor calls the "QGS" type's static + member function with a pointer to this member so it can be initialized + and the destructor calls the type's destructor. The \c{Holder} type is + therefore neither trivially constructible nor trivially destructible. It is + used as a function-local \c static so its initialization is thread-safe due + to C++11's requirement that such variables be thread-safely initialized. Additionally, both the constructor and destructor modify a guard variable after construction and before destruction, respectively. The guard variable |