| 1 | // Copyright (C) 2025 The Qt Company Ltd. |
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| 2 | // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only |
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| 3 | |
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| 4 | #ifndef QCACHEDVALUE_P_H |
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| 5 | #define QCACHEDVALUE_P_H |
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| 6 | |
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| 7 | // |
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| 8 | // W A R N I N G |
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| 9 | // ------------- |
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| 10 | // |
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| 11 | // This file is not part of the Qt API. It exists purely as an |
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| 12 | // implementation detail. This header file may change from version to |
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| 13 | // version without notice, or even be removed. |
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| 14 | // |
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| 15 | // We mean it. |
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| 16 | // |
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| 17 | |
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| 18 | #include <QReadWriteLock> |
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| 19 | |
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| 20 | #include <optional> |
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| 21 | #include <unordered_map> |
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| 22 | |
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| 23 | QT_BEGIN_NAMESPACE |
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| 24 | |
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| 25 | template <typename T> |
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| 26 | class QCachedValue |
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| 27 | { |
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| 28 | public: |
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| 29 | QCachedValue() = default; |
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| 30 | |
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| 31 | Q_DISABLE_COPY(QCachedValue) |
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| 32 | |
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| 33 | template <typename Creator> |
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| 34 | T ensure(Creator &&creator) |
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| 35 | { |
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| 36 | { |
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| 37 | QReadLocker locker(&m_lock); |
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| 38 | if (m_cached) |
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| 39 | return *m_cached; |
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| 40 | } |
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| 41 | |
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| 42 | { |
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| 43 | QWriteLocker locker(&m_lock); |
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| 44 | if (!m_cached) |
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| 45 | m_cached = creator(); |
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| 46 | return *m_cached; |
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| 47 | } |
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| 48 | } |
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| 49 | |
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| 50 | bool update(T value) |
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| 51 | { |
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| 52 | QWriteLocker locker(&m_lock); |
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| 53 | if (value == m_cached) |
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| 54 | return false; |
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| 55 | auto temp = std::exchange(m_cached, std::move(value)); |
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| 56 | locker.unlock(); |
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| 57 | return true; |
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| 58 | } |
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| 59 | |
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| 60 | void reset() |
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| 61 | { |
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| 62 | QWriteLocker locker(&m_lock); |
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| 63 | auto temp = std::exchange(m_cached, std::nullopt); |
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| 64 | locker.unlock(); |
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| 65 | } |
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| 66 | |
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| 67 | private: |
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| 68 | QReadWriteLock m_lock; |
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| 69 | std::optional<T> m_cached; |
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| 70 | }; |
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| 71 | |
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| 72 | template <typename Key, typename Value> |
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| 73 | class QCachedValueMap |
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| 74 | { |
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| 75 | public: |
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| 76 | QCachedValueMap() = default; |
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| 77 | |
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| 78 | Q_DISABLE_COPY(QCachedValueMap) |
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| 79 | |
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| 80 | template <typename Creator> |
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| 81 | Value ensure(const Key &key, Creator &&creator) |
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| 82 | { |
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| 83 | { |
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| 84 | QReadLocker locker(&m_lock); |
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| 85 | auto it = m_map.find(key); |
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| 86 | if (it != m_map.end()) |
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| 87 | return it->second; |
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| 88 | } |
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| 89 | |
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| 90 | { |
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| 91 | QWriteLocker locker(&m_lock); |
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| 92 | auto emplaceRes = m_map.try_emplace(key, creator()); |
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| 93 | return emplaceRes.first->second; |
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| 94 | } |
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| 95 | } |
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| 96 | |
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| 97 | private: |
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| 98 | QReadWriteLock m_lock; |
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| 99 | std::unordered_map<Key, Value> m_map; |
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| 100 | }; |
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| 101 | |
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| 102 | QT_END_NAMESPACE |
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| 103 | |
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| 104 | #endif // QCACHEDVALUE_P_H |
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| 105 | |
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