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/****************************************************************************
**
** Copyright (C) 2021 Intel Corporation.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the QtCore module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 3 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL3 included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 3 requirements
** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 2.0 or (at your option) the GNU General
** Public license version 3 or any later version approved by the KDE Free
** Qt Foundation. The licenses are as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
** included in the packaging of this file. Please review the following
** information to ensure the GNU General Public License requirements will
** be met: https://www.gnu.org/licenses/gpl-2.0.html and
** https://www.gnu.org/licenses/gpl-3.0.html.
**
** $QT_END_LICENSE$
**
****************************************************************************/
#include <QtCore/qglobal.h>
#ifndef QGLOBALSTATIC_H
#define QGLOBALSTATIC_H
#include <QtCore/qatomic.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()
{
pointer()->~PlainType();
std::atomic_thread_fence(std::memory_order_acquire); // avoid mixing stores to guard and *pointer()
guard.storeRelaxed(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_GLOBAL_STATIC",
"The global static was used after being destroyed");
return instance();
}
Type &operator*()
{
Q_ASSERT_X(!isDestroyed(), "Q_GLOBAL_STATIC",
"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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