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// Copyright (C) 2021 The Qt Company Ltd.
// Copyright (C) 2021 Intel Corporation.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#ifndef QAPPLICATIONSTATIC_H
#define QAPPLICATIONSTATIC_H
#include <QtCore/QMutex>
#include <QtCore/qcoreapplication.h>
#include <QtCore/qglobalstatic.h>
#include <new>
QT_BEGIN_NAMESPACE
namespace QtGlobalStatic {
template <typename QAS> struct ApplicationHolder
{
using Type = typename QAS::QAS_Type;
using PlainType = std::remove_cv_t<Type>;
Q_CONSTINIT static inline struct { alignas(Type) unsigned char data[sizeof(Type)]; } storage = {};
Q_CONSTINIT static inline QBasicAtomicInteger<qint8> guard = { QtGlobalStatic::Uninitialized };
Q_CONSTINIT static inline QBasicMutex mutex {};
static constexpr bool MutexLockIsNoexcept = noexcept(mutex.lock());
static constexpr bool ConstructionIsNoexcept = noexcept(QAS::innerFunction(nullptr));
ApplicationHolder() = default;
Q_DISABLE_COPY_MOVE(ApplicationHolder)
~ApplicationHolder()
{
if (guard.loadAcquire() == QtGlobalStatic::Initialized) {
// No mutex! Up to external code to ensure no race happens.
guard.storeRelease(QtGlobalStatic::Destroyed);
realPointer()->~PlainType();
}
}
static PlainType *realPointer()
{
return std::launder(reinterpret_cast<PlainType *>(&storage));
}
// called from QGlobalStatic::instance()
PlainType *pointer() noexcept(MutexLockIsNoexcept && ConstructionIsNoexcept)
{
if (guard.loadAcquire() == QtGlobalStatic::Initialized)
return realPointer();
QMutexLocker locker(&mutex);
if (guard.loadRelaxed() == QtGlobalStatic::Uninitialized) {
QAS::innerFunction(&storage);
const auto *app = QCoreApplication::instance();
Q_ASSERT_X(app, Q_FUNC_INFO,
"The application static was used without a QCoreApplication instance");
QObject::connect(app, &QObject::destroyed, app, reset, Qt::DirectConnection);
guard.storeRelease(QtGlobalStatic::Initialized);
}
return realPointer();
}
static void reset()
{
// we only synchronize using the mutex here, not the guard
QMutexLocker locker(&mutex);
realPointer()->~PlainType();
guard.storeRelaxed(QtGlobalStatic::Uninitialized);
}
};
} // namespace QtGlobalStatic
#define Q_APPLICATION_STATIC(TYPE, NAME, ...) \
namespace { struct Q_QAS_ ## NAME { \
typedef TYPE QAS_Type; \
static void innerFunction(void *pointer) \
noexcept(noexcept(std::remove_cv_t<QAS_Type>(__VA_ARGS__))) \
{ \
new (pointer) QAS_Type(__VA_ARGS__); \
} \
}; } \
static QGlobalStatic<QtGlobalStatic::ApplicationHolder<Q_QAS_ ## NAME>> NAME;\
/**/
QT_END_NAMESPACE
#endif // QAPPLICATIONSTATIC_H
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