gtest-linked_ptr.h
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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 
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>.
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 
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  explicit linked_ptr(T* ptr = NULL) { capture(ptr); }
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 
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_;
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 
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>
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_
testing
Definition: gtest-death-test.h:43
testing::internal::linked_ptr::depart
void depart()
Definition: gtest-linked_ptr.h:194
testing::internal::linked_ptr::operator==
bool operator==(T *p) const
Definition: gtest-linked_ptr.h:176
testing::internal::operator==
bool operator==(T *ptr, const linked_ptr< T > &x)
Definition: gtest-linked_ptr.h:213
testing::internal::linked_ptr::linked_ptr
linked_ptr(T *ptr=NULL)
Definition: gtest-linked_ptr.h:142
testing::internal::linked_ptr
Definition: gtest-linked_ptr.h:136
testing::internal::linked_ptr::get
T * get() const
Definition: gtest-linked_ptr.h:172
testing::internal::linked_ptr_internal::join
void join(linked_ptr_internal const *ptr) GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex)
Definition: gtest-linked_ptr.h:108
testing::internal::linked_ptr_internal::join_new
void join_new()
Definition: gtest-linked_ptr.h:92
testing::internal::linked_ptr::operator==
bool operator==(linked_ptr< U > const &ptr) const
Definition: gtest-linked_ptr.h:179
GTEST_LOCK_EXCLUDED_
#define GTEST_LOCK_EXCLUDED_(locks)
Definition: gtest-port.h:1931
testing::internal::linked_ptr::operator->
T * operator->() const
Definition: gtest-linked_ptr.h:173
testing::internal::linked_ptr_internal::next_
linked_ptr_internal const * next_
Definition: gtest-linked_ptr.h:132
gtest-port.h
GTEST_API_
#define GTEST_API_
Definition: gtest-port.h:771
testing::internal::linked_ptr::operator=
linked_ptr & operator=(linked_ptr const &ptr)
Definition: gtest-linked_ptr.h:159
testing::internal::linked_ptr::operator!=
bool operator!=(T *p) const
Definition: gtest-linked_ptr.h:177
testing::internal::linked_ptr::operator!=
bool operator!=(linked_ptr< U > const &ptr) const
Definition: gtest-linked_ptr.h:183
testing::internal::linked_ptr_internal::depart
bool depart() GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex)
Definition: gtest-linked_ptr.h:120
testing::internal::linked_ptr::element_type
T element_type
Definition: gtest-linked_ptr.h:138
testing::internal::make_linked_ptr
linked_ptr< T > make_linked_ptr(T *ptr)
Definition: gtest-linked_ptr.h:226
testing::internal::linked_ptr::linked_ptr
linked_ptr(linked_ptr< U > const &ptr)
Definition: gtest-linked_ptr.h:146
testing::internal::linked_ptr::capture
void capture(T *ptr)
Definition: gtest-linked_ptr.h:198
testing::internal::linked_ptr::operator*
T & operator*() const
Definition: gtest-linked_ptr.h:174
testing::internal::linked_ptr::linked_ptr
linked_ptr(linked_ptr const &ptr)
Definition: gtest-linked_ptr.h:147
testing::internal::linked_ptr::link_
linked_ptr_internal link_
Definition: gtest-linked_ptr.h:192
testing::internal::GTestMutexLock
Definition: gtest-port.h:1561
testing::internal::linked_ptr::operator=
linked_ptr & operator=(linked_ptr< U > const &ptr)
Definition: gtest-linked_ptr.h:153
testing::internal::linked_ptr::~linked_ptr
~linked_ptr()
Definition: gtest-linked_ptr.h:143
testing::internal::operator!=
bool operator!=(T *ptr, const linked_ptr< T > &x)
Definition: gtest-linked_ptr.h:218
testing::internal::linked_ptr::reset
void reset(T *ptr=NULL)
Definition: gtest-linked_ptr.h:168
testing::internal::linked_ptr::copy
void copy(linked_ptr< U > const *ptr)
Definition: gtest-linked_ptr.h:203
testing::internal::linked_ptr_internal
Definition: gtest-linked_ptr.h:89
testing::internal::GTEST_DECLARE_STATIC_MUTEX_
GTEST_API_ GTEST_DECLARE_STATIC_MUTEX_(g_linked_ptr_mutex)
testing::internal::linked_ptr::value_
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Definition: gtest-linked_ptr.h:191


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