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1 | /* |
2 | * This file is open source software, licensed to you under the terms | |
3 | * of the Apache License, Version 2.0 (the "License"). See the NOTICE file | |
4 | * distributed with this work for additional information regarding copyright | |
5 | * ownership. You may not use this file except in compliance with the License. | |
6 | * | |
7 | * You may obtain a copy of the License at | |
8 | * | |
9 | * http://www.apache.org/licenses/LICENSE-2.0 | |
10 | * | |
11 | * Unless required by applicable law or agreed to in writing, | |
12 | * software distributed under the License is distributed on an | |
13 | * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | |
14 | * KIND, either express or implied. See the License for the | |
15 | * specific language governing permissions and limitations | |
16 | * under the License. | |
17 | */ | |
18 | /* | |
19 | * Copyright (C) 2014 Cloudius Systems, Ltd. | |
20 | */ | |
21 | ||
22 | #ifndef CEPH_COMMON_DELETER_H | |
23 | #define CEPH_COMMON_DELETER_H | |
24 | ||
25 | #include <atomic> | |
7c673cae FG |
26 | |
27 | /// \addtogroup memory-module | |
28 | /// @{ | |
29 | ||
30 | /// Provides a mechanism for managing the lifetime of a buffer. | |
31 | /// | |
32 | /// A \c deleter is an object that is used to inform the consumer | |
33 | /// of some buffer (not referenced by the deleter itself) how to | |
34 | /// delete the buffer. This can be by calling an arbitrary function | |
35 | /// or destroying an object carried by the deleter. Examples of | |
36 | /// a deleter's encapsulated actions are: | |
37 | /// | |
38 | /// - calling \c std::free(p) on some captured pointer, p | |
39 | /// - calling \c delete \c p on some captured pointer, p | |
40 | /// - decrementing a reference count somewhere | |
41 | /// | |
42 | /// A deleter performs its action from its destructor. | |
43 | class deleter final { | |
44 | public: | |
45 | /// \cond internal | |
46 | struct impl; | |
47 | struct raw_object_tag {}; | |
48 | /// \endcond | |
49 | private: | |
50 | // if bit 0 set, point to object to be freed directly. | |
51 | impl* _impl = nullptr; | |
52 | public: | |
53 | /// Constructs an empty deleter that does nothing in its destructor. | |
54 | deleter() = default; | |
55 | deleter(const deleter&) = delete; | |
56 | /// Moves a deleter. | |
57 | deleter(deleter&& x) noexcept : _impl(x._impl) { x._impl = nullptr; } | |
58 | /// \cond internal | |
59 | explicit deleter(impl* i) : _impl(i) {} | |
60 | deleter(raw_object_tag tag, void* object) | |
61 | : _impl(from_raw_object(object)) {} | |
62 | /// \endcond | |
63 | /// Destroys the deleter and carries out the encapsulated action. | |
64 | ~deleter(); | |
65 | deleter& operator=(deleter&& x); | |
66 | deleter& operator=(deleter&) = delete; | |
67 | /// Performs a sharing operation. The encapsulated action will only | |
68 | /// be carried out after both the original deleter and the returned | |
69 | /// deleter are both destroyed. | |
70 | /// | |
71 | /// \return a deleter with the same encapsulated action as this one. | |
72 | deleter share(); | |
73 | /// Checks whether the deleter has an associated action. | |
74 | explicit operator bool() const { return bool(_impl); } | |
75 | /// \cond internal | |
76 | void reset(impl* i) { | |
77 | this->~deleter(); | |
78 | new (this) deleter(i); | |
79 | } | |
80 | /// \endcond | |
81 | /// Appends another deleter to this deleter. When this deleter is | |
82 | /// destroyed, both encapsulated actions will be carried out. | |
83 | void append(deleter d); | |
84 | private: | |
85 | static bool is_raw_object(impl* i) { | |
86 | auto x = reinterpret_cast<uintptr_t>(i); | |
87 | return x & 1; | |
88 | } | |
89 | bool is_raw_object() const { | |
90 | return is_raw_object(_impl); | |
91 | } | |
92 | static void* to_raw_object(impl* i) { | |
93 | auto x = reinterpret_cast<uintptr_t>(i); | |
94 | return reinterpret_cast<void*>(x & ~uintptr_t(1)); | |
95 | } | |
96 | void* to_raw_object() const { | |
97 | return to_raw_object(_impl); | |
98 | } | |
99 | impl* from_raw_object(void* object) { | |
100 | auto x = reinterpret_cast<uintptr_t>(object); | |
101 | return reinterpret_cast<impl*>(x | 1); | |
102 | } | |
103 | }; | |
104 | ||
105 | /// \cond internal | |
106 | struct deleter::impl { | |
107 | std::atomic_uint refs; | |
108 | deleter next; | |
109 | impl(deleter next) : refs(1), next(std::move(next)) {} | |
110 | virtual ~impl() {} | |
111 | }; | |
112 | /// \endcond | |
113 | ||
114 | inline deleter::~deleter() { | |
115 | if (is_raw_object()) { | |
116 | std::free(to_raw_object()); | |
117 | return; | |
118 | } | |
119 | if (_impl && --_impl->refs == 0) { | |
120 | delete _impl; | |
121 | } | |
122 | } | |
123 | ||
124 | inline deleter& deleter::operator=(deleter&& x) { | |
125 | if (this != &x) { | |
126 | this->~deleter(); | |
127 | new (this) deleter(std::move(x)); | |
128 | } | |
129 | return *this; | |
130 | } | |
131 | ||
132 | /// \cond internal | |
133 | template <typename Deleter> | |
134 | struct lambda_deleter_impl final : deleter::impl { | |
135 | Deleter del; | |
136 | lambda_deleter_impl(deleter next, Deleter&& del) | |
137 | : impl(std::move(next)), del(std::move(del)) {} | |
138 | ~lambda_deleter_impl() override { del(); } | |
139 | }; | |
140 | ||
141 | template <typename Object> | |
142 | struct object_deleter_impl final : deleter::impl { | |
143 | Object obj; | |
144 | object_deleter_impl(deleter next, Object&& obj) | |
145 | : impl(std::move(next)), obj(std::move(obj)) {} | |
146 | }; | |
147 | ||
148 | template <typename Object> | |
149 | inline | |
150 | object_deleter_impl<Object>* make_object_deleter_impl(deleter next, Object obj) { | |
151 | return new object_deleter_impl<Object>(std::move(next), std::move(obj)); | |
152 | } | |
153 | /// \endcond | |
154 | ||
155 | /// Makes a \ref deleter that encapsulates the action of | |
156 | /// destroying an object, as well as running another deleter. The input | |
157 | /// object is moved to the deleter, and destroyed when the deleter is destroyed. | |
158 | /// | |
159 | /// \param d deleter that will become part of the new deleter's encapsulated action | |
160 | /// \param o object whose destructor becomes part of the new deleter's encapsulated action | |
161 | /// \related deleter | |
162 | template <typename Object> | |
163 | deleter make_deleter(deleter next, Object o) { | |
164 | return deleter(new lambda_deleter_impl<Object>(std::move(next), std::move(o))); | |
165 | } | |
166 | ||
167 | /// Makes a \ref deleter that encapsulates the action of destroying an object. The input | |
168 | /// object is moved to the deleter, and destroyed when the deleter is destroyed. | |
169 | /// | |
170 | /// \param o object whose destructor becomes the new deleter's encapsulated action | |
171 | /// \related deleter | |
172 | template <typename Object> | |
173 | deleter make_deleter(Object o) { | |
174 | return make_deleter(deleter(), std::move(o)); | |
175 | } | |
176 | ||
177 | /// \cond internal | |
178 | struct free_deleter_impl final : deleter::impl { | |
179 | void* obj; | |
180 | free_deleter_impl(void* obj) : impl(deleter()), obj(obj) {} | |
181 | ~free_deleter_impl() override { std::free(obj); } | |
182 | }; | |
183 | /// \endcond | |
184 | ||
185 | inline deleter deleter::share() { | |
186 | if (!_impl) { | |
187 | return deleter(); | |
188 | } | |
189 | if (is_raw_object()) { | |
190 | _impl = new free_deleter_impl(to_raw_object()); | |
191 | } | |
192 | ++_impl->refs; | |
193 | return deleter(_impl); | |
194 | } | |
195 | ||
196 | // Appends 'd' to the chain of deleters. Avoids allocation if possible. For | |
197 | // performance reasons the current chain should be shorter and 'd' should be | |
198 | // longer. | |
199 | inline void deleter::append(deleter d) { | |
200 | if (!d._impl) { | |
201 | return; | |
202 | } | |
203 | impl* next_impl = _impl; | |
204 | deleter* next_d = this; | |
205 | while (next_impl) { | |
206 | if (next_impl == d._impl) | |
207 | return ; | |
208 | if (is_raw_object(next_impl)) { | |
209 | next_d->_impl = next_impl = new free_deleter_impl(to_raw_object(next_impl)); | |
210 | } | |
211 | if (next_impl->refs != 1) { | |
212 | next_d->_impl = next_impl = make_object_deleter_impl(std::move(next_impl->next), deleter(next_impl)); | |
213 | } | |
214 | next_d = &next_impl->next; | |
215 | next_impl = next_d->_impl; | |
216 | } | |
217 | next_d->_impl = d._impl; | |
218 | d._impl = nullptr; | |
219 | } | |
220 | ||
221 | /// Makes a deleter that calls \c std::free() when it is destroyed. | |
222 | /// | |
223 | /// \param obj object to free. | |
224 | /// \related deleter | |
225 | inline deleter make_free_deleter(void* obj) { | |
226 | if (!obj) { | |
227 | return deleter(); | |
228 | } | |
229 | return deleter(deleter::raw_object_tag(), obj); | |
230 | } | |
231 | ||
232 | /// Makes a deleter that calls \c std::free() when it is destroyed, as well | |
233 | /// as invoking the encapsulated action of another deleter. | |
234 | /// | |
235 | /// \param d deleter to invoke. | |
236 | /// \param obj object to free. | |
237 | /// \related deleter | |
238 | inline deleter make_free_deleter(deleter next, void* obj) { | |
239 | return make_deleter(std::move(next), [obj] () mutable { std::free(obj); }); | |
240 | } | |
241 | ||
242 | /// \see make_deleter(Object) | |
243 | /// \related deleter | |
244 | template <typename T> | |
245 | inline deleter make_object_deleter(T&& obj) { | |
246 | return deleter{make_object_deleter_impl(deleter(), std::move(obj))}; | |
247 | } | |
248 | ||
249 | /// \see make_deleter(deleter, Object) | |
250 | /// \related deleter | |
251 | template <typename T> | |
252 | inline deleter make_object_deleter(deleter d, T&& obj) { | |
253 | return deleter{make_object_deleter_impl(std::move(d), std::move(obj))}; | |
254 | } | |
255 | ||
256 | /// @} | |
257 | ||
258 | #endif /* CEPH_COMMON_DELETER_H */ |