1 /*
2 * Copyright (C) 2005 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #ifndef ANDROID_STRONG_POINTER_H
18 #define ANDROID_STRONG_POINTER_H
19
20 #include <functional>
21 #include <type_traits> // for common_type.
22
23 // ---------------------------------------------------------------------------
24 namespace android {
25
26 template<typename T> class wp;
27
28 // ---------------------------------------------------------------------------
29
30 // TODO: Maybe remove sp<> ? wp<> comparison? These are dangerous: If the wp<>
31 // was created before the sp<>, and they point to different objects, they may
32 // compare equal even if they are entirely unrelated. E.g. CameraService
33 // currently performa such comparisons.
34
35 #define COMPARE_STRONG(_op_) \
36 template<typename U> \
37 inline bool operator _op_ (const sp<U>& o) const { \
38 return m_ptr _op_ o.m_ptr; \
39 } \
40 template<typename U> \
41 inline bool operator _op_ (const U* o) const { \
42 return m_ptr _op_ o; \
43 } \
44 /* Needed to handle type inference for nullptr: */ \
45 inline bool operator _op_ (const T* o) const { \
46 return m_ptr _op_ o; \
47 }
48
49 template<template<typename C> class comparator, typename T, typename U>
_sp_compare_(T * a,U * b)50 static inline bool _sp_compare_(T* a, U* b) {
51 return comparator<typename std::common_type<T*, U*>::type>()(a, b);
52 }
53
54 // Use std::less and friends to avoid undefined behavior when ordering pointers
55 // to different objects.
56 #define COMPARE_STRONG_FUNCTIONAL(_op_, _compare_) \
57 template<typename U> \
58 inline bool operator _op_ (const sp<U>& o) const { \
59 return _sp_compare_<_compare_>(m_ptr, o.m_ptr); \
60 } \
61 template<typename U> \
62 inline bool operator _op_ (const U* o) const { \
63 return _sp_compare_<_compare_>(m_ptr, o); \
64 }
65 // ---------------------------------------------------------------------------
66
67 template<typename T>
68 class sp {
69 public:
sp()70 inline sp() : m_ptr(nullptr) { }
71
72 sp(T* other); // NOLINT(implicit)
73 sp(const sp<T>& other);
74 sp(sp<T>&& other) noexcept;
75 template<typename U> sp(U* other); // NOLINT(implicit)
76 template<typename U> sp(const sp<U>& other); // NOLINT(implicit)
77 template<typename U> sp(sp<U>&& other); // NOLINT(implicit)
78
79 ~sp();
80
81 // Assignment
82
83 sp& operator = (T* other);
84 sp& operator = (const sp<T>& other);
85 sp& operator=(sp<T>&& other) noexcept;
86
87 template<typename U> sp& operator = (const sp<U>& other);
88 template<typename U> sp& operator = (sp<U>&& other);
89 template<typename U> sp& operator = (U* other);
90
91 //! Special optimization for use by ProcessState (and nobody else).
92 void force_set(T* other);
93
94 // Reset
95
96 void clear();
97
98 // Accessors
99
100 inline T& operator* () const { return *m_ptr; }
101 inline T* operator-> () const { return m_ptr; }
get()102 inline T* get() const { return m_ptr; }
103 inline explicit operator bool () const { return m_ptr != nullptr; }
104
105 // Operators
106
107 COMPARE_STRONG(==)
108 COMPARE_STRONG(!=)
109 COMPARE_STRONG_FUNCTIONAL(>, std::greater)
110 COMPARE_STRONG_FUNCTIONAL(<, std::less)
111 COMPARE_STRONG_FUNCTIONAL(<=, std::less_equal)
112 COMPARE_STRONG_FUNCTIONAL(>=, std::greater_equal)
113
114 // Punt these to the wp<> implementation.
115 template<typename U>
116 inline bool operator == (const wp<U>& o) const {
117 return o == *this;
118 }
119
120 template<typename U>
121 inline bool operator != (const wp<U>& o) const {
122 return o != *this;
123 }
124
125 private:
126 template<typename Y> friend class sp;
127 template<typename Y> friend class wp;
128 void set_pointer(T* ptr);
129 T* m_ptr;
130 };
131
132 // For code size reasons, we do not want this inlined or templated.
133 void sp_report_race();
134
135 #undef COMPARE
136
137 // ---------------------------------------------------------------------------
138 // No user serviceable parts below here.
139
140 template<typename T>
sp(T * other)141 sp<T>::sp(T* other)
142 : m_ptr(other) {
143 if (other)
144 other->incStrong(this);
145 }
146
147 template<typename T>
sp(const sp<T> & other)148 sp<T>::sp(const sp<T>& other)
149 : m_ptr(other.m_ptr) {
150 if (m_ptr)
151 m_ptr->incStrong(this);
152 }
153
154 template <typename T>
sp(sp<T> && other)155 sp<T>::sp(sp<T>&& other) noexcept : m_ptr(other.m_ptr) {
156 other.m_ptr = nullptr;
157 }
158
159 template<typename T> template<typename U>
sp(U * other)160 sp<T>::sp(U* other)
161 : m_ptr(other) {
162 if (other)
163 (static_cast<T*>(other))->incStrong(this);
164 }
165
166 template<typename T> template<typename U>
sp(const sp<U> & other)167 sp<T>::sp(const sp<U>& other)
168 : m_ptr(other.m_ptr) {
169 if (m_ptr)
170 m_ptr->incStrong(this);
171 }
172
173 template<typename T> template<typename U>
sp(sp<U> && other)174 sp<T>::sp(sp<U>&& other)
175 : m_ptr(other.m_ptr) {
176 other.m_ptr = nullptr;
177 }
178
179 template<typename T>
~sp()180 sp<T>::~sp() {
181 if (m_ptr)
182 m_ptr->decStrong(this);
183 }
184
185 template<typename T>
186 sp<T>& sp<T>::operator =(const sp<T>& other) {
187 // Force m_ptr to be read twice, to heuristically check for data races.
188 T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
189 T* otherPtr(other.m_ptr);
190 if (otherPtr) otherPtr->incStrong(this);
191 if (oldPtr) oldPtr->decStrong(this);
192 if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
193 m_ptr = otherPtr;
194 return *this;
195 }
196
197 template <typename T>
198 sp<T>& sp<T>::operator=(sp<T>&& other) noexcept {
199 T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
200 if (oldPtr) oldPtr->decStrong(this);
201 if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
202 m_ptr = other.m_ptr;
203 other.m_ptr = nullptr;
204 return *this;
205 }
206
207 template<typename T>
208 sp<T>& sp<T>::operator =(T* other) {
209 T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
210 if (other) other->incStrong(this);
211 if (oldPtr) oldPtr->decStrong(this);
212 if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
213 m_ptr = other;
214 return *this;
215 }
216
217 template<typename T> template<typename U>
218 sp<T>& sp<T>::operator =(const sp<U>& other) {
219 T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
220 T* otherPtr(other.m_ptr);
221 if (otherPtr) otherPtr->incStrong(this);
222 if (oldPtr) oldPtr->decStrong(this);
223 if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
224 m_ptr = otherPtr;
225 return *this;
226 }
227
228 template<typename T> template<typename U>
229 sp<T>& sp<T>::operator =(sp<U>&& other) {
230 T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
231 if (m_ptr) m_ptr->decStrong(this);
232 if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
233 m_ptr = other.m_ptr;
234 other.m_ptr = nullptr;
235 return *this;
236 }
237
238 template<typename T> template<typename U>
239 sp<T>& sp<T>::operator =(U* other) {
240 T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
241 if (other) (static_cast<T*>(other))->incStrong(this);
242 if (oldPtr) oldPtr->decStrong(this);
243 if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
244 m_ptr = other;
245 return *this;
246 }
247
248 template<typename T>
force_set(T * other)249 void sp<T>::force_set(T* other) {
250 other->forceIncStrong(this);
251 m_ptr = other;
252 }
253
254 template<typename T>
clear()255 void sp<T>::clear() {
256 T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
257 if (oldPtr) {
258 oldPtr->decStrong(this);
259 if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
260 m_ptr = nullptr;
261 }
262 }
263
264 template<typename T>
set_pointer(T * ptr)265 void sp<T>::set_pointer(T* ptr) {
266 m_ptr = ptr;
267 }
268
269 } // namespace android
270
271 // ---------------------------------------------------------------------------
272
273 #endif // ANDROID_STRONG_POINTER_H
274