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 // A "smart" pointer type with reference tracking. Every pointer to a
31 // particular object is kept on a circular linked list. When the last pointer
32 // to an object is destroyed or reassigned, the object is deleted.
33 //
34 // Used properly, this deletes the object when the last reference goes away.
35 // There are several caveats:
36 // - Like all reference counting schemes, cycles lead to leaks.
37 // - Each smart pointer is actually two pointers (8 bytes instead of 4).
38 // - Every time a pointer is assigned, the entire list of pointers to that
39 // object is traversed. This class is therefore NOT SUITABLE when there
40 // will often be more than two or three pointers to a particular object.
41 // - References are only tracked as long as linked_ptr<> objects are copied.
42 // If a linked_ptr<> is converted to a raw pointer and back, BAD THINGS
43 // will happen (double deletion).
44 //
45 // A good use of this class is storing object references in STL containers.
46 // You can safely put linked_ptr<> in a vector<>.
47 // Other uses may not be as good.
48 //
49 // Note: If you use an incomplete type with linked_ptr<>, the class
50 // *containing* linked_ptr<> must have a constructor and destructor (even
51 // if they do nothing!).
52 //
53 // Bill Gibbons suggested we use something like this.
54 //
55 // Thread Safety:
56 // Unlike other linked_ptr implementations, in this implementation
57 // a linked_ptr object is thread-safe in the sense that:
58 // - it's safe to copy linked_ptr objects concurrently,
59 // - it's safe to copy *from* a linked_ptr and read its underlying
60 // raw pointer (e.g. via get()) concurrently, and
61 // - it's safe to write to two linked_ptrs that point to the same
62 // shared object concurrently.
63 // FIXME: rename this to safe_linked_ptr to avoid
64 // confusion with normal linked_ptr.
65
66 // GOOGLETEST_CM0001 DO NOT DELETE
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_