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// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#ifndef QATOMICSCOPEDVALUEROLLBACK_P_H
#define QATOMICSCOPEDVALUEROLLBACK_P_H
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists for the convenience
// of qapplication_*.cpp, qwidget*.cpp and qfiledialog.cpp. This header
// file may change from version to version without notice, or even be removed.
//
// We mean it.
//
#include <QtCore/qglobal.h>
#include <QtCore/qatomic.h>
#include <atomic>
QT_BEGIN_NAMESPACE
template <typename T>
class [[nodiscard]] QAtomicScopedValueRollback
{
std::atomic<T> &m_atomic;
T m_value;
std::memory_order m_mo;
Q_DISABLE_COPY_MOVE(QAtomicScopedValueRollback)
constexpr std::memory_order store_part(std::memory_order mo) noexcept
{
switch (mo) {
case std::memory_order_relaxed:
case std::memory_order_consume:
case std::memory_order_acquire: return std::memory_order_relaxed;
case std::memory_order_release:
case std::memory_order_acq_rel: return std::memory_order_release;
case std::memory_order_seq_cst: return std::memory_order_seq_cst;
}
// GCC 8.x does not tread __builtin_unreachable() as constexpr
#if !defined(Q_CC_GNU_ONLY) || (Q_CC_GNU >= 900)
// NOLINTNEXTLINE(qt-use-unreachable-return): Triggers on Clang, breaking GCC 8
Q_UNREACHABLE();
#endif
return std::memory_order_seq_cst;
}
public:
//
// std::atomic:
//
explicit constexpr
QAtomicScopedValueRollback(std::atomic<T> &var,
std::memory_order mo = std::memory_order_seq_cst)
: m_atomic(var), m_value(var.load(mo)), m_mo(mo) {}
explicit constexpr
QAtomicScopedValueRollback(std::atomic<T> &var, T value,
std::memory_order mo = std::memory_order_seq_cst)
: m_atomic(var), m_value(var.exchange(value, mo)), m_mo(mo) {}
//
// Q(Basic)AtomicInteger:
//
explicit constexpr
QAtomicScopedValueRollback(QBasicAtomicInteger<T> &var,
std::memory_order mo = std::memory_order_seq_cst)
: QAtomicScopedValueRollback(var._q_value, mo) {}
explicit constexpr
QAtomicScopedValueRollback(QBasicAtomicInteger<T> &var, T value,
std::memory_order mo = std::memory_order_seq_cst)
: QAtomicScopedValueRollback(var._q_value, value, mo) {}
//
// Q(Basic)AtomicPointer:
//
explicit constexpr
QAtomicScopedValueRollback(QBasicAtomicPointer<std::remove_pointer_t<T>> &var,
std::memory_order mo = std::memory_order_seq_cst)
: QAtomicScopedValueRollback(var._q_value, mo) {}
explicit constexpr
QAtomicScopedValueRollback(QBasicAtomicPointer<std::remove_pointer_t<T>> &var, T value,
std::memory_order mo = std::memory_order_seq_cst)
: QAtomicScopedValueRollback(var._q_value, value, mo) {}
#if __cpp_constexpr >= 201907L
constexpr
#endif
~QAtomicScopedValueRollback()
{
m_atomic.store(m_value, store_part(m_mo));
}
constexpr void commit()
{
m_value = m_atomic.load(m_mo);
}
};
QT_END_NAMESPACE
#endif // QATOMICASCOPEDVALUEROLLBACK_P_H
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