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// 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 QGLOBALSTATIC_H
#define QGLOBALSTATIC_H
#include <QtCore/qassert.h>
#include <QtCore/qatomic.h>
#include <QtCore/qtclasshelpermacros.h>
#include <atomic> // for bootstrapped (no thread) builds
#include <type_traits>
QT_BEGIN_NAMESPACE
namespace QtGlobalStatic {
enum GuardValues {
Destroyed = -2,
Initialized = -1,
Uninitialized = 0,
Initializing = 1
};
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));
Q_CONSTINIT static inline QBasicAtomicInteger<qint8> guard = { QtGlobalStatic::Uninitialized };
// union's sole member
PlainType storage;
Holder() noexcept(ConstructionIsNoexcept)
{
QGS::innerFunction(pointer());
guard.storeRelaxed(QtGlobalStatic::Initialized);
}
~Holder()
{
// TSAN does not support atomic_thread_fence and GCC complains:
// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97868
// https://github.com/google/sanitizers/issues/1352
QT_WARNING_PUSH
#if defined(Q_CC_GNU_ONLY) && Q_CC_GNU >= 1100
QT_WARNING_DISABLE_GCC("-Wtsan")
#endif
// import changes to *pointer() by other threads before running ~PlainType():
std::atomic_thread_fence(std::memory_order_acquire);
QT_WARNING_POP
pointer()->~PlainType();
guard.storeRelease(QtGlobalStatic::Destroyed);
}
PlainType *pointer() noexcept
{
return &storage;
}
Q_DISABLE_COPY_MOVE(Holder)
};
}
template <typename Holder> struct QGlobalStatic
{
using Type = typename Holder::Type;
bool isDestroyed() const noexcept { return guardValue() <= QtGlobalStatic::Destroyed; }
bool exists() const noexcept { return guardValue() == QtGlobalStatic::Initialized; }
operator Type *()
{
if (isDestroyed())
return nullptr;
return instance();
}
Type *operator()()
{
if (isDestroyed())
return nullptr;
return instance();
}
Type *operator->()
{
Q_ASSERT_X(!isDestroyed(), Q_FUNC_INFO,
"The global static was used after being destroyed");
return instance();
}
Type &operator*()
{
Q_ASSERT_X(!isDestroyed(), Q_FUNC_INFO,
"The global static was used after being destroyed");
return *instance();
}
protected:
static Type *instance() noexcept(Holder::ConstructionIsNoexcept)
{
static Holder holder;
return holder.pointer();
}
static QtGlobalStatic::GuardValues guardValue() noexcept
{
return QtGlobalStatic::GuardValues(Holder::guard.loadAcquire());
}
};
#define Q_GLOBAL_STATIC_WITH_ARGS(TYPE, NAME, ARGS) \
QT_WARNING_PUSH \
QT_WARNING_DISABLE_CLANG("-Wunevaluated-expression") \
namespace { struct Q_QGS_ ## NAME { \
typedef TYPE QGS_Type; \
static void innerFunction(void *pointer) \
noexcept(noexcept(std::remove_cv_t<QGS_Type> ARGS)) \
{ \
new (pointer) QGS_Type ARGS; \
} \
}; } \
Q_CONSTINIT static QGlobalStatic<QtGlobalStatic::Holder<Q_QGS_ ## NAME>> NAME; \
QT_WARNING_POP
/**/
#define Q_GLOBAL_STATIC(TYPE, NAME, ...) \
Q_GLOBAL_STATIC_WITH_ARGS(TYPE, NAME, (__VA_ARGS__))
QT_END_NAMESPACE
#endif // QGLOBALSTATIC_H
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