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