1 // Copyright 2003 Google Inc.
2 // All rights reserved.
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5 // modification, are permitted provided that the following conditions are
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9 // notice, this list of conditions and the following disclaimer.
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11 // copyright notice, this list of conditions and the following disclaimer
12 // in the documentation and/or other materials provided with the
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15 // contributors may be used to endorse or promote products derived from
16 // this software without specific prior written permission.
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.
30 // Authors: Dan Egnor (egnor@google.com)
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.
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).
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.
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!).
55 // Bill Gibbons suggested we use something like this.
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.
68 #ifndef GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_
69 #define GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_
74 #include <gtest/internal/gtest-port.h>
79 // Protects copying of all linked_ptr objects.
80 extern Mutex g_linked_ptr_mutex
;
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.
88 // DO NOT USE THIS CLASS DIRECTLY YOURSELF. Use linked_ptr<T>.
89 class linked_ptr_internal
{
91 // Create a new circle that includes only this instance.
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.
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
107 // Join an existing circle.
108 // L < g_linked_ptr_mutex
109 void join(linked_ptr_internal
const* ptr
) {
110 MutexLock
lock(&g_linked_ptr_mutex
);
112 linked_ptr_internal
const* p
= ptr
;
113 while (p
->next_
!= ptr
) p
= p
->next_
;
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 // L < g_linked_ptr_mutex
122 MutexLock
lock(&g_linked_ptr_mutex
);
124 if (next_
== this) return true;
125 linked_ptr_internal
const* p
= next_
;
126 while (p
->next_
!= this) p
= p
->next_
;
132 mutable linked_ptr_internal
const* next_
;
135 template <typename T
>
138 typedef T element_type
;
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(); }
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);
152 // Assignment releases the old value and acquires the new.
153 template <typename U
> linked_ptr
& operator=(linked_ptr
<U
> const& ptr
) {
159 linked_ptr
& operator=(linked_ptr
const& ptr
) {
167 // Smart pointer members.
168 void reset(T
* ptr
= NULL
) {
172 T
* get() const { return value_
; }
173 T
* operator->() const { return value_
; }
174 T
& operator*() const { return *value_
; }
175 // Release ownership of the pointed object and returns it.
176 // Sole ownership by this linked_ptr object is required.
178 bool last
= link_
.depart();
185 bool operator==(T
* p
) const { return value_
== p
; }
186 bool operator!=(T
* p
) const { return value_
!= p
; }
187 template <typename U
>
188 bool operator==(linked_ptr
<U
> const& ptr
) const {
189 return value_
== ptr
.get();
191 template <typename U
>
192 bool operator!=(linked_ptr
<U
> const& ptr
) const {
193 return value_
!= ptr
.get();
197 template <typename U
>
198 friend class linked_ptr
;
201 linked_ptr_internal link_
;
204 if (link_
.depart()) delete value_
;
207 void capture(T
* ptr
) {
212 template <typename U
> void copy(linked_ptr
<U
> const* ptr
) {
215 link_
.join(&ptr
->link_
);
221 template<typename T
> inline
222 bool operator==(T
* ptr
, const linked_ptr
<T
>& x
) {
223 return ptr
== x
.get();
226 template<typename T
> inline
227 bool operator!=(T
* ptr
, const linked_ptr
<T
>& x
) {
228 return ptr
!= x
.get();
231 // A function to convert T* into linked_ptr<T>
232 // Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation
233 // for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg))
234 template <typename T
>
235 linked_ptr
<T
> make_linked_ptr(T
* ptr
) {
236 return linked_ptr
<T
>(ptr
);
239 } // namespace internal
240 } // namespace testing
242 #endif // GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_