Line data Source code
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.
92 100 : void join_new() {
93 100 : next_ = this;
94 100 : }
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.
108 160 : void join(linked_ptr_internal const* ptr)
109 : GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) {
110 160 : MutexLock lock(&g_linked_ptr_mutex);
111 :
112 160 : linked_ptr_internal const* p = ptr;
113 160 : while (p->next_ != ptr) p = p->next_;
114 160 : p->next_ = this;
115 160 : next_ = ptr;
116 160 : }
117 :
118 : // Leave whatever circle we're part of. Returns true if we were the
119 : // last member of the circle. Once this is done, you can join() another.
120 210 : bool depart()
121 : GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) {
122 210 : MutexLock lock(&g_linked_ptr_mutex);
123 :
124 210 : if (next_ == this) return true;
125 160 : linked_ptr_internal const* p = next_;
126 160 : while (p->next_ != this) p = p->next_;
127 160 : p->next_ = next_;
128 160 : return false;
129 : }
130 :
131 : private:
132 : mutable linked_ptr_internal const* next_;
133 : };
134 :
135 : template <typename T>
136 : class linked_ptr {
137 : public:
138 : typedef T element_type;
139 :
140 : // Take over ownership of a raw pointer. This should happen as soon as
141 : // possible after the object is created.
142 100 : explicit linked_ptr(T* ptr = NULL) { capture(ptr); }
143 210 : ~linked_ptr() { depart(); }
144 :
145 : // Copy an existing linked_ptr<>, adding ourselves to the list of references.
146 : template <typename U> linked_ptr(linked_ptr<U> const& ptr) { copy(&ptr); }
147 160 : linked_ptr(linked_ptr const& ptr) { // NOLINT
148 160 : assert(&ptr != this);
149 160 : copy(&ptr);
150 160 : }
151 :
152 : // Assignment releases the old value and acquires the new.
153 : template <typename U> linked_ptr& operator=(linked_ptr<U> const& ptr) {
154 : depart();
155 : copy(&ptr);
156 : return *this;
157 : }
158 :
159 : linked_ptr& operator=(linked_ptr const& ptr) {
160 : if (&ptr != this) {
161 : depart();
162 : copy(&ptr);
163 : }
164 : return *this;
165 : }
166 :
167 : // Smart pointer members.
168 : void reset(T* ptr = NULL) {
169 : depart();
170 : capture(ptr);
171 : }
172 160 : T* get() const { return value_; }
173 480 : T* operator->() const { return value_; }
174 : T& operator*() const { return *value_; }
175 :
176 : bool operator==(T* p) const { return value_ == p; }
177 : bool operator!=(T* p) const { return value_ != p; }
178 : template <typename U>
179 : bool operator==(linked_ptr<U> const& ptr) const {
180 : return value_ == ptr.get();
181 : }
182 : template <typename U>
183 : bool operator!=(linked_ptr<U> const& ptr) const {
184 : return value_ != ptr.get();
185 : }
186 :
187 : private:
188 : template <typename U>
189 : friend class linked_ptr;
190 :
191 : T* value_;
192 : linked_ptr_internal link_;
193 :
194 210 : void depart() {
195 210 : if (link_.depart()) delete value_;
196 210 : }
197 :
198 100 : void capture(T* ptr) {
199 100 : value_ = ptr;
200 100 : link_.join_new();
201 100 : }
202 :
203 160 : template <typename U> void copy(linked_ptr<U> const* ptr) {
204 160 : value_ = ptr->get();
205 160 : if (value_)
206 160 : link_.join(&ptr->link_);
207 : else
208 0 : link_.join_new();
209 160 : }
210 : };
211 :
212 : template<typename T> inline
213 : bool operator==(T* ptr, const linked_ptr<T>& x) {
214 : return ptr == x.get();
215 : }
216 :
217 : template<typename T> inline
218 : bool operator!=(T* ptr, const linked_ptr<T>& x) {
219 : return ptr != x.get();
220 : }
221 :
222 : // A function to convert T* into linked_ptr<T>
223 : // Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation
224 : // for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg))
225 : template <typename T>
226 : linked_ptr<T> make_linked_ptr(T* ptr) {
227 : return linked_ptr<T>(ptr);
228 : }
229 :
230 : } // namespace internal
231 : } // namespace testing
232 :
233 : #endif // GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_
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