libstdc++
shared_ptr_atomic.h
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1 // shared_ptr atomic access -*- C++ -*-
2 
3 // Copyright (C) 2014-2021 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
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22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file bits/shared_ptr_atomic.h
26  * This is an internal header file, included by other library headers.
27  * Do not attempt to use it directly. @headername{memory}
28  */
29 
30 #ifndef _SHARED_PTR_ATOMIC_H
31 #define _SHARED_PTR_ATOMIC_H 1
32 
33 #include <bits/atomic_base.h>
34 
35 namespace std _GLIBCXX_VISIBILITY(default)
36 {
37 _GLIBCXX_BEGIN_NAMESPACE_VERSION
38 
39  /**
40  * @addtogroup pointer_abstractions
41  * @{
42  */
43  /// @relates shared_ptr @{
44 
45  /// @cond undocumented
46 
47  struct _Sp_locker
48  {
49  _Sp_locker(const _Sp_locker&) = delete;
50  _Sp_locker& operator=(const _Sp_locker&) = delete;
51 
52 #ifdef __GTHREADS
53  explicit
54  _Sp_locker(const void*) noexcept;
55  _Sp_locker(const void*, const void*) noexcept;
56  ~_Sp_locker();
57 
58  private:
59  unsigned char _M_key1;
60  unsigned char _M_key2;
61 #else
62  explicit _Sp_locker(const void*, const void* = nullptr) { }
63 #endif
64  };
65 
66  /// @endcond
67 
68  /**
69  * @brief Report whether shared_ptr atomic operations are lock-free.
70  * @param __p A non-null pointer to a shared_ptr object.
71  * @return True if atomic access to @c *__p is lock-free, false otherwise.
72  * @{
73  */
74  template<typename _Tp, _Lock_policy _Lp>
75  inline bool
76  atomic_is_lock_free(const __shared_ptr<_Tp, _Lp>* __p)
77  {
78 #ifdef __GTHREADS
79  return __gthread_active_p() == 0;
80 #else
81  return true;
82 #endif
83  }
84 
85  template<typename _Tp>
86  inline bool
87  atomic_is_lock_free(const shared_ptr<_Tp>* __p)
88  { return std::atomic_is_lock_free<_Tp, __default_lock_policy>(__p); }
89 
90  /// @}
91 
92  /**
93  * @brief Atomic load for shared_ptr objects.
94  * @param __p A non-null pointer to a shared_ptr object.
95  * @return @c *__p
96  *
97  * The memory order shall not be @c memory_order_release or
98  * @c memory_order_acq_rel.
99  * @{
100  */
101  template<typename _Tp>
102  inline shared_ptr<_Tp>
104  {
105  _Sp_locker __lock{__p};
106  return *__p;
107  }
108 
109  template<typename _Tp>
110  inline shared_ptr<_Tp>
111  atomic_load(const shared_ptr<_Tp>* __p)
112  { return std::atomic_load_explicit(__p, memory_order_seq_cst); }
113 
114  template<typename _Tp, _Lock_policy _Lp>
115  inline __shared_ptr<_Tp, _Lp>
116  atomic_load_explicit(const __shared_ptr<_Tp, _Lp>* __p, memory_order)
117  {
118  _Sp_locker __lock{__p};
119  return *__p;
120  }
121 
122  template<typename _Tp, _Lock_policy _Lp>
123  inline __shared_ptr<_Tp, _Lp>
124  atomic_load(const __shared_ptr<_Tp, _Lp>* __p)
125  { return std::atomic_load_explicit(__p, memory_order_seq_cst); }
126  /// @}
127 
128  /**
129  * @brief Atomic store for shared_ptr objects.
130  * @param __p A non-null pointer to a shared_ptr object.
131  * @param __r The value to store.
132  *
133  * The memory order shall not be @c memory_order_acquire or
134  * @c memory_order_acq_rel.
135  * @{
136  */
137  template<typename _Tp>
138  inline void
140  memory_order)
141  {
142  _Sp_locker __lock{__p};
143  __p->swap(__r); // use swap so that **__p not destroyed while lock held
144  }
145 
146  template<typename _Tp>
147  inline void
148  atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
149  { std::atomic_store_explicit(__p, std::move(__r), memory_order_seq_cst); }
150 
151  template<typename _Tp, _Lock_policy _Lp>
152  inline void
153  atomic_store_explicit(__shared_ptr<_Tp, _Lp>* __p,
154  __shared_ptr<_Tp, _Lp> __r,
155  memory_order)
156  {
157  _Sp_locker __lock{__p};
158  __p->swap(__r); // use swap so that **__p not destroyed while lock held
159  }
160 
161  template<typename _Tp, _Lock_policy _Lp>
162  inline void
163  atomic_store(__shared_ptr<_Tp, _Lp>* __p, __shared_ptr<_Tp, _Lp> __r)
164  { std::atomic_store_explicit(__p, std::move(__r), memory_order_seq_cst); }
165  /// @}
166 
167  /**
168  * @brief Atomic exchange for shared_ptr objects.
169  * @param __p A non-null pointer to a shared_ptr object.
170  * @param __r New value to store in @c *__p.
171  * @return The original value of @c *__p
172  * @{
173  */
174  template<typename _Tp>
175  inline shared_ptr<_Tp>
177  memory_order)
178  {
179  _Sp_locker __lock{__p};
180  __p->swap(__r);
181  return __r;
182  }
183 
184  template<typename _Tp>
185  inline shared_ptr<_Tp>
186  atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
187  {
188  return std::atomic_exchange_explicit(__p, std::move(__r),
189  memory_order_seq_cst);
190  }
191 
192  template<typename _Tp, _Lock_policy _Lp>
193  inline __shared_ptr<_Tp, _Lp>
194  atomic_exchange_explicit(__shared_ptr<_Tp, _Lp>* __p,
195  __shared_ptr<_Tp, _Lp> __r,
196  memory_order)
197  {
198  _Sp_locker __lock{__p};
199  __p->swap(__r);
200  return __r;
201  }
202 
203  template<typename _Tp, _Lock_policy _Lp>
204  inline __shared_ptr<_Tp, _Lp>
205  atomic_exchange(__shared_ptr<_Tp, _Lp>* __p, __shared_ptr<_Tp, _Lp> __r)
206  {
207  return std::atomic_exchange_explicit(__p, std::move(__r),
208  memory_order_seq_cst);
209  }
210  /// @}
211 
212  /**
213  * @brief Atomic compare-and-swap for shared_ptr objects.
214  * @param __p A non-null pointer to a shared_ptr object.
215  * @param __v A non-null pointer to a shared_ptr object.
216  * @param __w A non-null pointer to a shared_ptr object.
217  * @return True if @c *__p was equivalent to @c *__v, false otherwise.
218  *
219  * The memory order for failure shall not be @c memory_order_release or
220  * @c memory_order_acq_rel, or stronger than the memory order for success.
221  * @{
222  */
223  template<typename _Tp>
224  bool
226  shared_ptr<_Tp>* __v,
227  shared_ptr<_Tp> __w,
228  memory_order,
229  memory_order)
230  {
231  shared_ptr<_Tp> __x; // goes out of scope after __lock
232  _Sp_locker __lock{__p, __v};
234  if (*__p == *__v && !__less(*__p, *__v) && !__less(*__v, *__p))
235  {
236  __x = std::move(*__p);
237  *__p = std::move(__w);
238  return true;
239  }
240  __x = std::move(*__v);
241  *__v = *__p;
242  return false;
243  }
244 
245  template<typename _Tp>
246  inline bool
247  atomic_compare_exchange_strong(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v,
248  shared_ptr<_Tp> __w)
249  {
250  return std::atomic_compare_exchange_strong_explicit(__p, __v,
251  std::move(__w), memory_order_seq_cst, memory_order_seq_cst);
252  }
253 
254  template<typename _Tp>
255  inline bool
256  atomic_compare_exchange_weak_explicit(shared_ptr<_Tp>* __p,
257  shared_ptr<_Tp>* __v,
258  shared_ptr<_Tp> __w,
259  memory_order __success,
260  memory_order __failure)
261  {
262  return std::atomic_compare_exchange_strong_explicit(__p, __v,
263  std::move(__w), __success, __failure);
264  }
265 
266  template<typename _Tp>
267  inline bool
268  atomic_compare_exchange_weak(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v,
269  shared_ptr<_Tp> __w)
270  {
271  return std::atomic_compare_exchange_weak_explicit(__p, __v,
272  std::move(__w), memory_order_seq_cst, memory_order_seq_cst);
273  }
274 
275  template<typename _Tp, _Lock_policy _Lp>
276  bool
277  atomic_compare_exchange_strong_explicit(__shared_ptr<_Tp, _Lp>* __p,
278  __shared_ptr<_Tp, _Lp>* __v,
279  __shared_ptr<_Tp, _Lp> __w,
280  memory_order,
281  memory_order)
282  {
283  __shared_ptr<_Tp, _Lp> __x; // goes out of scope after __lock
284  _Sp_locker __lock{__p, __v};
285  owner_less<__shared_ptr<_Tp, _Lp>> __less;
286  if (*__p == *__v && !__less(*__p, *__v) && !__less(*__v, *__p))
287  {
288  __x = std::move(*__p);
289  *__p = std::move(__w);
290  return true;
291  }
292  __x = std::move(*__v);
293  *__v = *__p;
294  return false;
295  }
296 
297  template<typename _Tp, _Lock_policy _Lp>
298  inline bool
299  atomic_compare_exchange_strong(__shared_ptr<_Tp, _Lp>* __p,
300  __shared_ptr<_Tp, _Lp>* __v,
301  __shared_ptr<_Tp, _Lp> __w)
302  {
303  return std::atomic_compare_exchange_strong_explicit(__p, __v,
304  std::move(__w), memory_order_seq_cst, memory_order_seq_cst);
305  }
306 
307  template<typename _Tp, _Lock_policy _Lp>
308  inline bool
309  atomic_compare_exchange_weak_explicit(__shared_ptr<_Tp, _Lp>* __p,
310  __shared_ptr<_Tp, _Lp>* __v,
311  __shared_ptr<_Tp, _Lp> __w,
312  memory_order __success,
313  memory_order __failure)
314  {
315  return std::atomic_compare_exchange_strong_explicit(__p, __v,
316  std::move(__w), __success, __failure);
317  }
318 
319  template<typename _Tp, _Lock_policy _Lp>
320  inline bool
321  atomic_compare_exchange_weak(__shared_ptr<_Tp, _Lp>* __p,
322  __shared_ptr<_Tp, _Lp>* __v,
323  __shared_ptr<_Tp, _Lp> __w)
324  {
325  return std::atomic_compare_exchange_weak_explicit(__p, __v,
326  std::move(__w), memory_order_seq_cst, memory_order_seq_cst);
327  }
328  /// @}
329 
330  /// @} relates shared_ptr
331  /// @} group pointer_abstractions
332 
333 _GLIBCXX_END_NAMESPACE_VERSION
334 } // namespace
335 
336 #endif // _SHARED_PTR_ATOMIC_H
shared_ptr< _Tp > atomic_exchange_explicit(shared_ptr< _Tp > *__p, shared_ptr< _Tp > __r, memory_order)
Atomic exchange for shared_ptr objects.
bool atomic_compare_exchange_strong_explicit(shared_ptr< _Tp > *__p, shared_ptr< _Tp > *__v, shared_ptr< _Tp > __w, memory_order, memory_order)
Atomic compare-and-swap for shared_ptr objects.
void atomic_store_explicit(shared_ptr< _Tp > *__p, shared_ptr< _Tp > __r, memory_order)
Atomic store for shared_ptr objects.
bool atomic_is_lock_free(const __shared_ptr< _Tp, _Lp > *__p)
Report whether shared_ptr atomic operations are lock-free.
void swap(shared_ptr< _Tp > &__a, shared_ptr< _Tp > &__b) noexcept
Swap overload for shared_ptr.
shared_ptr< _Tp > atomic_load_explicit(const shared_ptr< _Tp > *__p, memory_order)
Atomic load for shared_ptr objects.
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:104
memory_order
Enumeration for memory_order.
Definition: atomic_base.h:79
ISO C++ entities toplevel namespace is std.
A smart pointer with reference-counted copy semantics.
Primary template owner_less.