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QRandomGenerator: port away from std::aligned_storage

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It's deprecated in C++23. Just use an explicitly-aligned char array
directly, wrapped in a struct to avoid decays to char*.

Task-number: QTBUG-99122
Pick-to: 6.3 6.2
Change-Id: Ic5807f0161cd9f360baa07464988bc48b9679f64
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Marc Mutz 2022-05-07 12:53:23 +02:00
parent d8e03bb02d
commit 32f1847e1e
1 changed files with 5 additions and 4 deletions
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9
src/corelib/global/qrandom.cpp
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@ -353,16 +353,17 @@ struct QRandomGenerator::SystemAndGlobalGenerators
// the state in case another thread tries to lock the mutex. It's not // the state in case another thread tries to lock the mutex. It's not
// a common scenario, but since sizeof(QRandomGenerator) >= 2560, the // a common scenario, but since sizeof(QRandomGenerator) >= 2560, the
// overhead is actually acceptable. // overhead is actually acceptable.
// 2) We use both alignas and std::aligned_storage<..., 64> because // 2) We use both alignas(T) and alignas(64) because some implementations
// some implementations of std::aligned_storage can't align to more // can't align to more than a primitive type's alignment.
// than a primitive type's alignment.
// 3) We don't store the entire system QRandomGenerator, only the space // 3) We don't store the entire system QRandomGenerator, only the space
// used by the QRandomGenerator::type member. This is fine because we // used by the QRandomGenerator::type member. This is fine because we
// (ab)use the common initial sequence exclusion to aliasing rules. // (ab)use the common initial sequence exclusion to aliasing rules.
QBasicMutex globalPRNGMutex; QBasicMutex globalPRNGMutex;
struct ShortenedSystem { uint type; } system_; struct ShortenedSystem { uint type; } system_;
SystemGenerator sys; SystemGenerator sys;
alignas(64) std::aligned_storage<sizeof(QRandomGenerator64), 64>::type global_; alignas(64) struct {
alignas(QRandomGenerator64) uchar data[sizeof(QRandomGenerator64)];
} global_;
constexpr SystemAndGlobalGenerators() constexpr SystemAndGlobalGenerators()
: globalPRNGMutex{}, system_{0}, sys{}, global_{} : globalPRNGMutex{}, system_{0}, sys{}, global_{}