1// Copyright (C) 2020 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz <marc.mutz@kdab.com>
2// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
3#ifndef QDUPLICATETRACKER_P_H
4#define QDUPLICATETRACKER_P_H
5
6//
7// W A R N I N G
8// -------------
9//
10// This file is not part of the Qt API. It exists purely as an
11// implementation detail. This header file may change from version to
12// version without notice, or even be removed.
13//
14// We mean it.
15//
16
17#include <private/qglobal_p.h>
18
19#ifdef __cpp_lib_memory_resource
20# include <unordered_set>
21# include <memory_resource>
22# include <qhash.h> // for the hashing helpers
23#else
24# include <qset.h>
25#endif
26
27QT_BEGIN_NAMESPACE
28
29template <typename T, size_t Prealloc = 32>
30class QDuplicateTracker {
31#ifdef __cpp_lib_memory_resource
32 template <typename HT>
33 struct QHasher {
34 size_t storedSeed = QHashSeed::globalSeed();
35 size_t operator()(const HT &t) const {
36 return QHashPrivate::calculateHash(t, storedSeed);
37 }
38 };
39
40 struct node_guesstimate { void *next; size_t hash; T value; };
41 static constexpr size_t bufferSize(size_t N) {
42 return N * sizeof(void*) // bucket list
43 + N * sizeof(node_guesstimate); // nodes
44 }
45
46 char buffer[bufferSize(N: Prealloc)];
47 std::pmr::monotonic_buffer_resource res{buffer, sizeof buffer};
48 using Set = std::pmr::unordered_set<T, QHasher<T>>;
49 Set set{Prealloc, &res};
50#else
51 class Set : public QSet<T> {
52 qsizetype setSize = 0;
53 public:
54 explicit Set(qsizetype n) : QSet<T>{}
55 { this->reserve(n); }
56
57 auto insert(const T &e) {
58 auto it = QSet<T>::insert(e);
59 const auto n = this->size();
60 return std::pair{it, std::exchange(setSize, n) != n};
61 }
62
63 auto insert(T &&e) {
64 auto it = QSet<T>::insert(std::move(e));
65 const auto n = this->size();
66 return std::pair{it, std::exchange(setSize, n) != n};
67 }
68 };
69 Set set{Prealloc};
70#endif
71 Q_DISABLE_COPY_MOVE(QDuplicateTracker)
72public:
73 static constexpr inline bool uses_pmr =
74 #ifdef __cpp_lib_memory_resource
75 true
76 #else
77 false
78 #endif
79 ;
80 QDuplicateTracker() {} // don't `= default`, lest we value-initialize `buffer`
81 explicit QDuplicateTracker(qsizetype n)
82#ifdef __cpp_lib_memory_resource
83 : set{size_t(n), &res}
84#else
85 : set{n}
86#endif
87 {}
88 Q_DECL_DEPRECATED_X("Pass the capacity to reserve() to the ctor instead.")
89 void reserve(qsizetype n) { set.reserve(n); }
90 [[nodiscard]] bool hasSeen(const T &s)
91 {
92 return !set.insert(s).second;
93 }
94 [[nodiscard]] bool hasSeen(T &&s)
95 {
96 return !set.insert(std::move(s)).second;
97 }
98 // For when you want to know, but aren't *yet* sure you'll add it:
99 [[nodiscard]] bool contains(const T &s) const
100 {
101 return set.find(s) != set.end(); // TODO C++20: can use set.contains()
102 }
103
104 template <typename C>
105 void appendTo(C &c) const &
106 {
107 for (const auto &e : set)
108 c.push_back(e);
109 }
110
111 template <typename C>
112 void appendTo(C &c) &&
113 {
114 if constexpr (uses_pmr) {
115 while (!set.empty())
116 c.push_back(std::move(set.extract(set.begin()).value()));
117 } else {
118 return appendTo(c); // lvalue version
119 }
120 }
121
122 void clear()
123 {
124#ifdef __cpp_lib_memory_resource
125 // The birth defect of std::unordered_set is that both the nodes as
126 // well as the bucket array are allocated from the same allocator, so
127 // if we want to reclaim memory from the freed nodes, we also need to
128 // reclaim the memory for the bucket array.
129
130 set = Set(); // release all memory in `res` (clear() doesn't, and swap() is UB!)
131 res.release(); // restore to initial state (buffer, sizeof buffer)
132 // m_b_r can't reuse buffers, anyway
133 // now that `res` is reset to the initial state, also reset `set`:
134 set = Set{Prealloc, &res};
135#else
136 set.clear();
137#endif // __cpp_lib_memory_resource
138 }
139};
140
141QT_END_NAMESPACE
142
143#endif /* QDUPLICATETRACKER_P_H */
144

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