source: gtest-1.7.0/include/gtest/internal/gtest-linked_ptr.h@ 12748

Last change on this file since 12748 was 12746, checked in by hock@…, 11 years ago

integrated the Google Testing Framework (gtest)

and wrote an Hello World test, to ensure the framework is working..

File size: 7.9 KB
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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
76namespace testing {
77namespace internal {
78
79// Protects copying of all linked_ptr objects.
80GTEST_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>.
89class 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) p = p->next_;
114 p->next_ = this;
115 next_ = ptr;
116 }
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 bool depart()
121 GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) {
122 MutexLock lock(&g_linked_ptr_mutex);
123
124 if (next_ == this) return true;
125 linked_ptr_internal const* p = next_;
126 while (p->next_ != this) p = p->next_;
127 p->next_ = next_;
128 return false;
129 }
130
131 private:
132 mutable linked_ptr_internal const* next_;
133};
134
135template <typename T>
136class 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 explicit linked_ptr(T* ptr = NULL) { capture(ptr); }
143 ~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 linked_ptr(linked_ptr const& ptr) { // NOLINT
148 assert(&ptr != this);
149 copy(&ptr);
150 }
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 T* get() const { return value_; }
173 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 void depart() {
195 if (link_.depart()) delete value_;
196 }
197
198 void capture(T* ptr) {
199 value_ = ptr;
200 link_.join_new();
201 }
202
203 template <typename U> void copy(linked_ptr<U> const* ptr) {
204 value_ = ptr->get();
205 if (value_)
206 link_.join(&ptr->link_);
207 else
208 link_.join_new();
209 }
210};
211
212template<typename T> inline
213bool operator==(T* ptr, const linked_ptr<T>& x) {
214 return ptr == x.get();
215}
216
217template<typename T> inline
218bool 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))
225template <typename T>
226linked_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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