1// Copyright (C) 2022 The Qt Company Ltd.
2// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
3
4#ifndef QATOMICSCOPEDVALUEROLLBACK_H
5#define QATOMICSCOPEDVALUEROLLBACK_H
6
7#include <QtCore/qassert.h>
8#include <QtCore/qatomic.h>
9#include <QtCore/qcompilerdetection.h>
10#include <QtCore/qtclasshelpermacros.h>
11#include <QtCore/qtconfigmacros.h>
12
13#include <atomic>
14#include <type_traits>
15
16QT_BEGIN_NAMESPACE
17
18template <typename T>
19class QAtomicScopedValueRollback
20{
21 std::atomic<T> &m_atomic;
22 T m_value;
23 std::memory_order m_mo;
24
25 Q_DISABLE_COPY_MOVE(QAtomicScopedValueRollback)
26
27 static constexpr std::memory_order store_part(std::memory_order mo) noexcept
28 {
29 switch (mo) {
30 case std::memory_order_relaxed:
31 case std::memory_order_consume:
32 case std::memory_order_acquire: return std::memory_order_relaxed;
33 case std::memory_order_release:
34 case std::memory_order_acq_rel: return std::memory_order_release;
35 case std::memory_order_seq_cst: return std::memory_order_seq_cst;
36 }
37 // GCC 8.x does not treat __builtin_unreachable() as constexpr
38#if !defined(Q_CC_GNU_ONLY) || (Q_CC_GNU >= 900)
39 // NOLINTNEXTLINE(qt-use-unreachable-return): Triggers on Clang, breaking GCC 8
40 Q_UNREACHABLE();
41#endif
42 return std::memory_order_seq_cst;
43 }
44
45 static constexpr std::memory_order load_part(std::memory_order mo) noexcept
46 {
47 switch (mo) {
48 case std::memory_order_relaxed:
49 case std::memory_order_release: return std::memory_order_relaxed;
50 case std::memory_order_consume: return std::memory_order_consume;
51 case std::memory_order_acquire:
52 case std::memory_order_acq_rel: return std::memory_order_acquire;
53 case std::memory_order_seq_cst: return std::memory_order_seq_cst;
54 }
55 // GCC 8.x does not treat __builtin_unreachable() as constexpr
56#if !defined(Q_CC_GNU_ONLY) || (Q_CC_GNU >= 900)
57 // NOLINTNEXTLINE(qt-use-unreachable-return): Triggers on Clang, breaking GCC 8
58 Q_UNREACHABLE();
59#endif
60 return std::memory_order_seq_cst;
61 }
62public:
63 //
64 // std::atomic:
65 //
66 Q_NODISCARD_CTOR
67 explicit constexpr
68 QAtomicScopedValueRollback(std::atomic<T> &var,
69 std::memory_order mo = std::memory_order_seq_cst)
70 : m_atomic(var), m_value(var.load(load_part(mo))), m_mo(mo) {}
71
72 Q_NODISCARD_CTOR
73 explicit constexpr
74 QAtomicScopedValueRollback(std::atomic<T> &var, T value,
75 std::memory_order mo = std::memory_order_seq_cst)
76 : m_atomic(var), m_value(var.exchange(value, mo)), m_mo(mo) {}
77
78 //
79 // Q(Basic)AtomicInteger:
80 //
81 Q_NODISCARD_CTOR
82 explicit constexpr
83 QAtomicScopedValueRollback(QBasicAtomicInteger<T> &var,
84 std::memory_order mo = std::memory_order_seq_cst)
85 : QAtomicScopedValueRollback(var._q_value, mo) {}
86
87 Q_NODISCARD_CTOR
88 explicit constexpr
89 QAtomicScopedValueRollback(QBasicAtomicInteger<T> &var, T value,
90 std::memory_order mo = std::memory_order_seq_cst)
91 : QAtomicScopedValueRollback(var._q_value, value, mo) {}
92
93 //
94 // Q(Basic)AtomicPointer:
95 //
96 Q_NODISCARD_CTOR
97 explicit constexpr
98 QAtomicScopedValueRollback(QBasicAtomicPointer<std::remove_pointer_t<T>> &var,
99 std::memory_order mo = std::memory_order_seq_cst)
100 : QAtomicScopedValueRollback(var._q_value, mo) {}
101
102 Q_NODISCARD_CTOR
103 explicit constexpr
104 QAtomicScopedValueRollback(QBasicAtomicPointer<std::remove_pointer_t<T>> &var, T value,
105 std::memory_order mo = std::memory_order_seq_cst)
106 : QAtomicScopedValueRollback(var._q_value, value, mo) {}
107
108 ~QAtomicScopedValueRollback()
109 {
110 m_atomic.store(m_value, store_part(mo: m_mo));
111 }
112
113 void commit()
114 {
115 m_value = m_atomic.load(load_part(mo: m_mo));
116 }
117};
118
119template <typename T>
120QAtomicScopedValueRollback(QBasicAtomicPointer<T> &)
121 -> QAtomicScopedValueRollback<T*>;
122template <typename T>
123QAtomicScopedValueRollback(QBasicAtomicPointer<T> &, std::memory_order)
124 -> QAtomicScopedValueRollback<T*>;
125
126template <typename T, typename V,
127 std::enable_if_t<std::is_convertible_v<V, T>, bool> = true>
128QAtomicScopedValueRollback(std::atomic<T>&, V)
129 -> QAtomicScopedValueRollback<T>;
130template <typename T, typename V,
131 std::enable_if_t<std::is_convertible_v<V, T>, bool> = true>
132QAtomicScopedValueRollback(std::atomic<T>&, V, std::memory_order)
133 -> QAtomicScopedValueRollback<T>;
134
135template <typename T, typename V,
136 std::enable_if_t<std::is_convertible_v<V, T>, bool> = true>
137QAtomicScopedValueRollback(QBasicAtomicInteger<T>&, V)
138 -> QAtomicScopedValueRollback<T>;
139template <typename T, typename V,
140 std::enable_if_t<std::is_convertible_v<V, T>, bool> = true>
141QAtomicScopedValueRollback(QBasicAtomicInteger<T>&, V, std::memory_order)
142 -> QAtomicScopedValueRollback<T>;
143
144template <typename T, typename V,
145 std::enable_if_t<std::is_convertible_v<V, T*>, bool> = true>
146QAtomicScopedValueRollback(QBasicAtomicPointer<T>&, V)
147 -> QAtomicScopedValueRollback<T*>;
148template <typename T, typename V,
149 std::enable_if_t<std::is_convertible_v<V, T*>, bool> = true>
150QAtomicScopedValueRollback(QBasicAtomicPointer<T>&, V, std::memory_order)
151 -> QAtomicScopedValueRollback<T*>;
152
153QT_END_NAMESPACE
154
155#endif // QATOMICASCOPEDVALUEROLLBACK_H
156

source code of qtbase/src/corelib/tools/qatomicscopedvaluerollback.h