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// Copyright (C) 2025 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 QCACHEDVALUE_P_H
#define QCACHEDVALUE_P_H
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
#include <QReadWriteLock>
#include <optional>
#include <unordered_map>
QT_BEGIN_NAMESPACE
template <typename T>
class QCachedValue
{
public:
QCachedValue() = default;
Q_DISABLE_COPY(QCachedValue)
template <typename Creator>
T ensure(Creator &&creator)
{
{
QReadLocker locker(&m_lock);
if (m_cached)
return *m_cached;
}
{
QWriteLocker locker(&m_lock);
if (!m_cached)
m_cached = creator();
return *m_cached;
}
}
bool update(T value)
{
QWriteLocker locker(&m_lock);
if (value == m_cached)
return false;
auto temp = std::exchange(m_cached, std::move(value));
locker.unlock();
return true;
}
void reset()
{
QWriteLocker locker(&m_lock);
auto temp = std::exchange(m_cached, std::nullopt);
locker.unlock();
}
private:
QReadWriteLock m_lock;
std::optional<T> m_cached;
};
template <typename Key, typename Value>
class QCachedValueMap
{
public:
QCachedValueMap() = default;
Q_DISABLE_COPY(QCachedValueMap)
template <typename Creator>
Value ensure(const Key &key, Creator &&creator)
{
{
QReadLocker locker(&m_lock);
auto it = m_map.find(key);
if (it != m_map.end())
return it->second;
}
{
QWriteLocker locker(&m_lock);
auto emplaceRes = m_map.try_emplace(key, creator());
return emplaceRes.first->second;
}
}
private:
QReadWriteLock m_lock;
std::unordered_map<Key, Value> m_map;
};
QT_END_NAMESPACE
#endif // QCACHEDVALUE_P_H
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