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1 | // Copyright 2003 Google Inc. |
2 | // All rights reserved. | |
3 | // | |
4 | // Redistribution and use in source and binary forms, with or without | |
5 | // modification, are permitted provided that the following conditions are | |
6 | // met: | |
7 | // | |
8 | // * Redistributions of source code must retain the above copyright | |
9 | // notice, this list of conditions and the following disclaimer. | |
10 | // * Redistributions in binary form must reproduce the above | |
11 | // copyright notice, this list of conditions and the following disclaimer | |
12 | // in the documentation and/or other materials provided with the | |
13 | // distribution. | |
14 | // * Neither the name of Google Inc. nor the names of its | |
15 | // contributors may be used to endorse or promote products derived from | |
16 | // this software without specific prior written permission. | |
17 | // | |
18 | // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |
19 | // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |
20 | // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR | |
21 | // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT | |
22 | // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, | |
23 | // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT | |
24 | // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
25 | // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
26 | // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
27 | // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE | |
28 | // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
29 | // | |
30 | // Authors: Dan Egnor (egnor@google.com) | |
31 | // | |
32 | // A "smart" pointer type with reference tracking. Every pointer to a | |
33 | // particular object is kept on a circular linked list. When the last pointer | |
34 | // to an object is destroyed or reassigned, the object is deleted. | |
35 | // | |
36 | // Used properly, this deletes the object when the last reference goes away. | |
37 | // There are several caveats: | |
38 | // - Like all reference counting schemes, cycles lead to leaks. | |
39 | // - Each smart pointer is actually two pointers (8 bytes instead of 4). | |
40 | // - Every time a pointer is assigned, the entire list of pointers to that | |
41 | // object is traversed. This class is therefore NOT SUITABLE when there | |
42 | // will often be more than two or three pointers to a particular object. | |
43 | // - References are only tracked as long as linked_ptr<> objects are copied. | |
44 | // If a linked_ptr<> is converted to a raw pointer and back, BAD THINGS | |
45 | // will happen (double deletion). | |
46 | // | |
47 | // A good use of this class is storing object references in STL containers. | |
48 | // You can safely put linked_ptr<> in a vector<>. | |
49 | // Other uses may not be as good. | |
50 | // | |
51 | // Note: If you use an incomplete type with linked_ptr<>, the class | |
52 | // *containing* linked_ptr<> must have a constructor and destructor (even | |
53 | // if they do nothing!). | |
54 | // | |
55 | // Bill Gibbons suggested we use something like this. | |
56 | // | |
57 | // Thread Safety: | |
58 | // Unlike other linked_ptr implementations, in this implementation | |
59 | // a linked_ptr object is thread-safe in the sense that: | |
60 | // - it's safe to copy linked_ptr objects concurrently, | |
61 | // - it's safe to copy *from* a linked_ptr and read its underlying | |
62 | // raw pointer (e.g. via get()) concurrently, and | |
63 | // - it's safe to write to two linked_ptrs that point to the same | |
64 | // shared object concurrently. | |
65 | // TODO(wan@google.com): rename this to safe_linked_ptr to avoid | |
66 | // confusion with normal linked_ptr. | |
67 | ||
68 | #ifndef GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_ | |
69 | #define GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_ | |
70 | ||
71 | #include <stdlib.h> | |
72 | #include <assert.h> | |
73 | ||
74 | #include "gtest/internal/gtest-port.h" | |
75 | ||
76 | namespace testing { | |
77 | namespace internal { | |
78 | ||
79 | // Protects copying of all linked_ptr objects. | |
80 | GTEST_API_ GTEST_DECLARE_STATIC_MUTEX_(g_linked_ptr_mutex); | |
81 | ||
82 | // This is used internally by all instances of linked_ptr<>. It needs to be | |
83 | // a non-template class because different types of linked_ptr<> can refer to | |
84 | // the same object (linked_ptr<Superclass>(obj) vs linked_ptr<Subclass>(obj)). | |
85 | // So, it needs to be possible for different types of linked_ptr to participate | |
86 | // in the same circular linked list, so we need a single class type here. | |
87 | // | |
88 | // DO NOT USE THIS CLASS DIRECTLY YOURSELF. Use linked_ptr<T>. | |
89 | class linked_ptr_internal { | |
90 | public: | |
91 | // Create a new circle that includes only this instance. | |
92 | void join_new() { | |
93 | next_ = this; | |
94 | } | |
95 | ||
96 | // Many linked_ptr operations may change p.link_ for some linked_ptr | |
97 | // variable p in the same circle as this object. Therefore we need | |
98 | // to prevent two such operations from occurring concurrently. | |
99 | // | |
100 | // Note that different types of linked_ptr objects can coexist in a | |
101 | // circle (e.g. linked_ptr<Base>, linked_ptr<Derived1>, and | |
102 | // linked_ptr<Derived2>). Therefore we must use a single mutex to | |
103 | // protect all linked_ptr objects. This can create serious | |
104 | // contention in production code, but is acceptable in a testing | |
105 | // framework. | |
106 | ||
107 | // Join an existing circle. | |
108 | void join(linked_ptr_internal const* ptr) | |
109 | GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) { | |
110 | MutexLock lock(&g_linked_ptr_mutex); | |
111 | ||
112 | linked_ptr_internal const* p = ptr; | |
113 | while (p->next_ != ptr) { | |
114 | assert(p->next_ != this && | |
115 | "Trying to join() a linked ring we are already in. " | |
116 | "Is GMock thread safety enabled?"); | |
117 | p = p->next_; | |
118 | } | |
119 | p->next_ = this; | |
120 | next_ = ptr; | |
121 | } | |
122 | ||
123 | // Leave whatever circle we're part of. Returns true if we were the | |
124 | // last member of the circle. Once this is done, you can join() another. | |
125 | bool depart() | |
126 | GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) { | |
127 | MutexLock lock(&g_linked_ptr_mutex); | |
128 | ||
129 | if (next_ == this) return true; | |
130 | linked_ptr_internal const* p = next_; | |
131 | while (p->next_ != this) { | |
132 | assert(p->next_ != next_ && | |
133 | "Trying to depart() a linked ring we are not in. " | |
134 | "Is GMock thread safety enabled?"); | |
135 | p = p->next_; | |
136 | } | |
137 | p->next_ = next_; | |
138 | return false; | |
139 | } | |
140 | ||
141 | private: | |
142 | mutable linked_ptr_internal const* next_; | |
143 | }; | |
144 | ||
145 | template <typename T> | |
146 | class linked_ptr { | |
147 | public: | |
148 | typedef T element_type; | |
149 | ||
150 | // Take over ownership of a raw pointer. This should happen as soon as | |
151 | // possible after the object is created. | |
152 | explicit linked_ptr(T* ptr = NULL) { capture(ptr); } | |
153 | ~linked_ptr() { depart(); } | |
154 | ||
155 | // Copy an existing linked_ptr<>, adding ourselves to the list of references. | |
156 | template <typename U> linked_ptr(linked_ptr<U> const& ptr) { copy(&ptr); } | |
157 | linked_ptr(linked_ptr const& ptr) { // NOLINT | |
158 | assert(&ptr != this); | |
159 | copy(&ptr); | |
160 | } | |
161 | ||
162 | // Assignment releases the old value and acquires the new. | |
163 | template <typename U> linked_ptr& operator=(linked_ptr<U> const& ptr) { | |
164 | depart(); | |
165 | copy(&ptr); | |
166 | return *this; | |
167 | } | |
168 | ||
169 | linked_ptr& operator=(linked_ptr const& ptr) { | |
170 | if (&ptr != this) { | |
171 | depart(); | |
172 | copy(&ptr); | |
173 | } | |
174 | return *this; | |
175 | } | |
176 | ||
177 | // Smart pointer members. | |
178 | void reset(T* ptr = NULL) { | |
179 | depart(); | |
180 | capture(ptr); | |
181 | } | |
182 | T* get() const { return value_; } | |
183 | T* operator->() const { return value_; } | |
184 | T& operator*() const { return *value_; } | |
185 | ||
186 | bool operator==(T* p) const { return value_ == p; } | |
187 | bool operator!=(T* p) const { return value_ != p; } | |
188 | template <typename U> | |
189 | bool operator==(linked_ptr<U> const& ptr) const { | |
190 | return value_ == ptr.get(); | |
191 | } | |
192 | template <typename U> | |
193 | bool operator!=(linked_ptr<U> const& ptr) const { | |
194 | return value_ != ptr.get(); | |
195 | } | |
196 | ||
197 | private: | |
198 | template <typename U> | |
199 | friend class linked_ptr; | |
200 | ||
201 | T* value_; | |
202 | linked_ptr_internal link_; | |
203 | ||
204 | void depart() { | |
205 | if (link_.depart()) delete value_; | |
206 | } | |
207 | ||
208 | void capture(T* ptr) { | |
209 | value_ = ptr; | |
210 | link_.join_new(); | |
211 | } | |
212 | ||
213 | template <typename U> void copy(linked_ptr<U> const* ptr) { | |
214 | value_ = ptr->get(); | |
215 | if (value_) | |
216 | link_.join(&ptr->link_); | |
217 | else | |
218 | link_.join_new(); | |
219 | } | |
220 | }; | |
221 | ||
222 | template<typename T> inline | |
223 | bool operator==(T* ptr, const linked_ptr<T>& x) { | |
224 | return ptr == x.get(); | |
225 | } | |
226 | ||
227 | template<typename T> inline | |
228 | bool operator!=(T* ptr, const linked_ptr<T>& x) { | |
229 | return ptr != x.get(); | |
230 | } | |
231 | ||
232 | // A function to convert T* into linked_ptr<T> | |
233 | // Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation | |
234 | // for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg)) | |
235 | template <typename T> | |
236 | linked_ptr<T> make_linked_ptr(T* ptr) { | |
237 | return linked_ptr<T>(ptr); | |
238 | } | |
239 | ||
240 | } // namespace internal | |
241 | } // namespace testing | |
242 | ||
243 | #endif // GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_ |