1 // shared_ptr and weak_ptr implementation -*- C++ -*-
2
3 // Copyright (C) 2007-2020 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
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24
25 // GCC Note: Based on files from version 1.32.0 of the Boost library.
26
27 // shared_count.hpp
28 // Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
29
30 // shared_ptr.hpp
31 // Copyright (C) 1998, 1999 Greg Colvin and Beman Dawes.
32 // Copyright (C) 2001, 2002, 2003 Peter Dimov
33
34 // weak_ptr.hpp
35 // Copyright (C) 2001, 2002, 2003 Peter Dimov
36
37 // enable_shared_from_this.hpp
38 // Copyright (C) 2002 Peter Dimov
39
40 // Distributed under the Boost Software License, Version 1.0. (See
41 // accompanying file LICENSE_1_0.txt or copy at
42 // http://www.boost.org/LICENSE_1_0.txt)
43
44 /** @file
45 * This is an internal header file, included by other library headers.
46 * Do not attempt to use it directly. @headername{memory}
47 */
48
49 #ifndef _SHARED_PTR_H
50 #define _SHARED_PTR_H 1
51
52 #include <bits/shared_ptr_base.h>
53
_GLIBCXX_VISIBILITY(default)54 namespace std _GLIBCXX_VISIBILITY(default)
55 {
56 _GLIBCXX_BEGIN_NAMESPACE_VERSION
57
58 /**
59 * @addtogroup pointer_abstractions
60 * @{
61 */
62
63 // 20.7.2.2.11 shared_ptr I/O
64
65 /// Write the stored pointer to an ostream.
66 /// @relates shared_ptr
67 template<typename _Ch, typename _Tr, typename _Tp, _Lock_policy _Lp>
68 inline std::basic_ostream<_Ch, _Tr>&
69 operator<<(std::basic_ostream<_Ch, _Tr>& __os,
70 const __shared_ptr<_Tp, _Lp>& __p)
71 {
72 __os << __p.get();
73 return __os;
74 }
75
76 template<typename _Del, typename _Tp, _Lock_policy _Lp>
77 inline _Del*
78 get_deleter(const __shared_ptr<_Tp, _Lp>& __p) noexcept
79 {
80 #if __cpp_rtti
81 return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del)));
82 #else
83 return 0;
84 #endif
85 }
86
87 /// 20.7.2.2.10 shared_ptr get_deleter
88
89 /// If `__p` has a deleter of type `_Del`, return a pointer to it.
90 /// @relates shared_ptr
91 template<typename _Del, typename _Tp>
92 inline _Del*
93 get_deleter(const shared_ptr<_Tp>& __p) noexcept
94 {
95 #if __cpp_rtti
96 return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del)));
97 #else
98 return 0;
99 #endif
100 }
101
102 /**
103 * @brief A smart pointer with reference-counted copy semantics.
104 *
105 * A `shared_ptr` object is either empty or _owns_ a pointer passed
106 * to the constructor. Copies of a `shared_ptr` share ownership of
107 * the same pointer. When the last `shared_ptr` that owns the pointer
108 * is destroyed or reset, the owned pointer is freed (either by `delete`
109 * or by invoking a custom deleter that was passed to the constructor).
110 *
111 * A `shared_ptr` also stores another pointer, which is usually
112 * (but not always) the same pointer as it owns. The stored pointer
113 * can be retrieved by calling the `get()` member function.
114 *
115 * The equality and relational operators for `shared_ptr` only compare
116 * the stored pointer returned by `get()`, not the owned pointer.
117 * To test whether two `shared_ptr` objects share ownership of the same
118 * pointer see `std::shared_ptr::owner_before` and `std::owner_less`.
119 */
120 template<typename _Tp>
121 class shared_ptr : public __shared_ptr<_Tp>
122 {
123 template<typename... _Args>
124 using _Constructible = typename enable_if<
125 is_constructible<__shared_ptr<_Tp>, _Args...>::value
126 >::type;
127
128 template<typename _Arg>
129 using _Assignable = typename enable_if<
130 is_assignable<__shared_ptr<_Tp>&, _Arg>::value, shared_ptr&
131 >::type;
132
133 public:
134
135 /// The type pointed to by the stored pointer, remove_extent_t<_Tp>
136 using element_type = typename __shared_ptr<_Tp>::element_type;
137
138 #if __cplusplus >= 201703L
139 # define __cpp_lib_shared_ptr_weak_type 201606
140 /// The corresponding weak_ptr type for this shared_ptr
141 using weak_type = weak_ptr<_Tp>;
142 #endif
143 /**
144 * @brief Construct an empty %shared_ptr.
145 * @post use_count()==0 && get()==0
146 */
147 constexpr shared_ptr() noexcept : __shared_ptr<_Tp>() { }
148
149 shared_ptr(const shared_ptr&) noexcept = default; ///< Copy constructor
150
151 /**
152 * @brief Construct a %shared_ptr that owns the pointer @a __p.
153 * @param __p A pointer that is convertible to element_type*.
154 * @post use_count() == 1 && get() == __p
155 * @throw std::bad_alloc, in which case @c delete @a __p is called.
156 */
157 template<typename _Yp, typename = _Constructible<_Yp*>>
158 explicit
159 shared_ptr(_Yp* __p) : __shared_ptr<_Tp>(__p) { }
160
161 /**
162 * @brief Construct a %shared_ptr that owns the pointer @a __p
163 * and the deleter @a __d.
164 * @param __p A pointer.
165 * @param __d A deleter.
166 * @post use_count() == 1 && get() == __p
167 * @throw std::bad_alloc, in which case @a __d(__p) is called.
168 *
169 * Requirements: _Deleter's copy constructor and destructor must
170 * not throw
171 *
172 * __shared_ptr will release __p by calling __d(__p)
173 */
174 template<typename _Yp, typename _Deleter,
175 typename = _Constructible<_Yp*, _Deleter>>
176 shared_ptr(_Yp* __p, _Deleter __d)
177 : __shared_ptr<_Tp>(__p, std::move(__d)) { }
178
179 /**
180 * @brief Construct a %shared_ptr that owns a null pointer
181 * and the deleter @a __d.
182 * @param __p A null pointer constant.
183 * @param __d A deleter.
184 * @post use_count() == 1 && get() == __p
185 * @throw std::bad_alloc, in which case @a __d(__p) is called.
186 *
187 * Requirements: _Deleter's copy constructor and destructor must
188 * not throw
189 *
190 * The last owner will call __d(__p)
191 */
192 template<typename _Deleter>
193 shared_ptr(nullptr_t __p, _Deleter __d)
194 : __shared_ptr<_Tp>(__p, std::move(__d)) { }
195
196 /**
197 * @brief Construct a %shared_ptr that owns the pointer @a __p
198 * and the deleter @a __d.
199 * @param __p A pointer.
200 * @param __d A deleter.
201 * @param __a An allocator.
202 * @post use_count() == 1 && get() == __p
203 * @throw std::bad_alloc, in which case @a __d(__p) is called.
204 *
205 * Requirements: _Deleter's copy constructor and destructor must
206 * not throw _Alloc's copy constructor and destructor must not
207 * throw.
208 *
209 * __shared_ptr will release __p by calling __d(__p)
210 */
211 template<typename _Yp, typename _Deleter, typename _Alloc,
212 typename = _Constructible<_Yp*, _Deleter, _Alloc>>
213 shared_ptr(_Yp* __p, _Deleter __d, _Alloc __a)
214 : __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
215
216 /**
217 * @brief Construct a %shared_ptr that owns a null pointer
218 * and the deleter @a __d.
219 * @param __p A null pointer constant.
220 * @param __d A deleter.
221 * @param __a An allocator.
222 * @post use_count() == 1 && get() == __p
223 * @throw std::bad_alloc, in which case @a __d(__p) is called.
224 *
225 * Requirements: _Deleter's copy constructor and destructor must
226 * not throw _Alloc's copy constructor and destructor must not
227 * throw.
228 *
229 * The last owner will call __d(__p)
230 */
231 template<typename _Deleter, typename _Alloc>
232 shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
233 : __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
234
235 // Aliasing constructor
236
237 /**
238 * @brief Constructs a `shared_ptr` instance that stores `__p`
239 * and shares ownership with `__r`.
240 * @param __r A `shared_ptr`.
241 * @param __p A pointer that will remain valid while `*__r` is valid.
242 * @post `get() == __p && use_count() == __r.use_count()`
243 *
244 * This can be used to construct a `shared_ptr` to a sub-object
245 * of an object managed by an existing `shared_ptr`. The complete
246 * object will remain valid while any `shared_ptr` owns it, even
247 * if they don't store a pointer to the complete object.
248 *
249 * @code
250 * shared_ptr<pair<int,int>> pii(new pair<int,int>());
251 * shared_ptr<int> pi(pii, &pii->first);
252 * assert(pii.use_count() == 2);
253 * @endcode
254 */
255 template<typename _Yp>
256 shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) noexcept
257 : __shared_ptr<_Tp>(__r, __p) { }
258
259 #if __cplusplus > 201703L
260 // _GLIBCXX_RESOLVE_LIB_DEFECTS
261 // 2996. Missing rvalue overloads for shared_ptr operations
262 /**
263 * @brief Constructs a `shared_ptr` instance that stores `__p`
264 * and shares ownership with `__r`.
265 * @param __r A `shared_ptr`.
266 * @param __p A pointer that will remain valid while `*__r` is valid.
267 * @post `get() == __p && !__r.use_count() && !__r.get()`
268 *
269 * This can be used to construct a `shared_ptr` to a sub-object
270 * of an object managed by an existing `shared_ptr`. The complete
271 * object will remain valid while any `shared_ptr` owns it, even
272 * if they don't store a pointer to the complete object.
273 *
274 * @code
275 * shared_ptr<pair<int,int>> pii(new pair<int,int>());
276 * shared_ptr<int> pi1(pii, &pii->first);
277 * assert(pii.use_count() == 2);
278 * shared_ptr<int> pi2(std::move(pii), &pii->second);
279 * assert(pii.use_count() == 0);
280 * @endcode
281 */
282 template<typename _Yp>
283 shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept
284 : __shared_ptr<_Tp>(std::move(__r), __p) { }
285 #endif
286 /**
287 * @brief If @a __r is empty, constructs an empty %shared_ptr;
288 * otherwise construct a %shared_ptr that shares ownership
289 * with @a __r.
290 * @param __r A %shared_ptr.
291 * @post get() == __r.get() && use_count() == __r.use_count()
292 */
293 template<typename _Yp,
294 typename = _Constructible<const shared_ptr<_Yp>&>>
295 shared_ptr(const shared_ptr<_Yp>& __r) noexcept
296 : __shared_ptr<_Tp>(__r) { }
297
298 /**
299 * @brief Move-constructs a %shared_ptr instance from @a __r.
300 * @param __r A %shared_ptr rvalue.
301 * @post *this contains the old value of @a __r, @a __r is empty.
302 */
303 shared_ptr(shared_ptr&& __r) noexcept
304 : __shared_ptr<_Tp>(std::move(__r)) { }
305
306 /**
307 * @brief Move-constructs a %shared_ptr instance from @a __r.
308 * @param __r A %shared_ptr rvalue.
309 * @post *this contains the old value of @a __r, @a __r is empty.
310 */
311 template<typename _Yp, typename = _Constructible<shared_ptr<_Yp>>>
312 shared_ptr(shared_ptr<_Yp>&& __r) noexcept
313 : __shared_ptr<_Tp>(std::move(__r)) { }
314
315 /**
316 * @brief Constructs a %shared_ptr that shares ownership with @a __r
317 * and stores a copy of the pointer stored in @a __r.
318 * @param __r A weak_ptr.
319 * @post use_count() == __r.use_count()
320 * @throw bad_weak_ptr when __r.expired(),
321 * in which case the constructor has no effect.
322 */
323 template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
324 explicit shared_ptr(const weak_ptr<_Yp>& __r)
325 : __shared_ptr<_Tp>(__r) { }
326
327 #if _GLIBCXX_USE_DEPRECATED
328 #pragma GCC diagnostic push
329 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
330 template<typename _Yp, typename = _Constructible<auto_ptr<_Yp>>>
331 shared_ptr(auto_ptr<_Yp>&& __r);
332 #pragma GCC diagnostic pop
333 #endif
334
335 // _GLIBCXX_RESOLVE_LIB_DEFECTS
336 // 2399. shared_ptr's constructor from unique_ptr should be constrained
337 template<typename _Yp, typename _Del,
338 typename = _Constructible<unique_ptr<_Yp, _Del>>>
339 shared_ptr(unique_ptr<_Yp, _Del>&& __r)
340 : __shared_ptr<_Tp>(std::move(__r)) { }
341
342 #if __cplusplus <= 201402L && _GLIBCXX_USE_DEPRECATED
343 // This non-standard constructor exists to support conversions that
344 // were possible in C++11 and C++14 but are ill-formed in C++17.
345 // If an exception is thrown this constructor has no effect.
346 template<typename _Yp, typename _Del,
347 _Constructible<unique_ptr<_Yp, _Del>, __sp_array_delete>* = 0>
348 shared_ptr(unique_ptr<_Yp, _Del>&& __r)
349 : __shared_ptr<_Tp>(std::move(__r), __sp_array_delete()) { }
350 #endif
351
352 /**
353 * @brief Construct an empty %shared_ptr.
354 * @post use_count() == 0 && get() == nullptr
355 */
356 constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
357
358 shared_ptr& operator=(const shared_ptr&) noexcept = default;
359
360 template<typename _Yp>
361 _Assignable<const shared_ptr<_Yp>&>
362 operator=(const shared_ptr<_Yp>& __r) noexcept
363 {
364 this->__shared_ptr<_Tp>::operator=(__r);
365 return *this;
366 }
367
368 #if _GLIBCXX_USE_DEPRECATED
369 #pragma GCC diagnostic push
370 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
371 template<typename _Yp>
372 _Assignable<auto_ptr<_Yp>>
373 operator=(auto_ptr<_Yp>&& __r)
374 {
375 this->__shared_ptr<_Tp>::operator=(std::move(__r));
376 return *this;
377 }
378 #pragma GCC diagnostic pop
379 #endif
380
381 shared_ptr&
382 operator=(shared_ptr&& __r) noexcept
383 {
384 this->__shared_ptr<_Tp>::operator=(std::move(__r));
385 return *this;
386 }
387
388 template<class _Yp>
389 _Assignable<shared_ptr<_Yp>>
390 operator=(shared_ptr<_Yp>&& __r) noexcept
391 {
392 this->__shared_ptr<_Tp>::operator=(std::move(__r));
393 return *this;
394 }
395
396 template<typename _Yp, typename _Del>
397 _Assignable<unique_ptr<_Yp, _Del>>
398 operator=(unique_ptr<_Yp, _Del>&& __r)
399 {
400 this->__shared_ptr<_Tp>::operator=(std::move(__r));
401 return *this;
402 }
403
404 private:
405 // This constructor is non-standard, it is used by allocate_shared.
406 template<typename _Alloc, typename... _Args>
407 shared_ptr(_Sp_alloc_shared_tag<_Alloc> __tag, _Args&&... __args)
408 : __shared_ptr<_Tp>(__tag, std::forward<_Args>(__args)...)
409 { }
410
411 template<typename _Yp, typename _Alloc, typename... _Args>
412 friend shared_ptr<_Yp>
413 allocate_shared(const _Alloc& __a, _Args&&... __args);
414
415 // This constructor is non-standard, it is used by weak_ptr::lock().
416 shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t)
417 : __shared_ptr<_Tp>(__r, std::nothrow) { }
418
419 friend class weak_ptr<_Tp>;
420 };
421
422 #if __cpp_deduction_guides >= 201606
423 template<typename _Tp>
424 shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
425 template<typename _Tp, typename _Del>
426 shared_ptr(unique_ptr<_Tp, _Del>) -> shared_ptr<_Tp>;
427 #endif
428
429 // 20.7.2.2.7 shared_ptr comparisons
430
431 /// @relates shared_ptr @{
432
433 /// Equality operator for shared_ptr objects, compares the stored pointers
434 template<typename _Tp, typename _Up>
435 _GLIBCXX_NODISCARD inline bool
436 operator==(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
437 { return __a.get() == __b.get(); }
438
439 /// shared_ptr comparison with nullptr
440 template<typename _Tp>
441 _GLIBCXX_NODISCARD inline bool
442 operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
443 { return !__a; }
444
445 #ifdef __cpp_lib_three_way_comparison
446 template<typename _Tp, typename _Up>
447 inline strong_ordering
448 operator<=>(const shared_ptr<_Tp>& __a,
449 const shared_ptr<_Up>& __b) noexcept
450 { return compare_three_way()(__a.get(), __b.get()); }
451
452 template<typename _Tp>
453 inline strong_ordering
454 operator<=>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
455 {
456 using pointer = typename shared_ptr<_Tp>::element_type*;
457 return compare_three_way()(__a.get(), static_cast<pointer>(nullptr));
458 }
459 #else
460 /// shared_ptr comparison with nullptr
461 template<typename _Tp>
462 _GLIBCXX_NODISCARD inline bool
463 operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
464 { return !__a; }
465
466 /// Inequality operator for shared_ptr objects, compares the stored pointers
467 template<typename _Tp, typename _Up>
468 _GLIBCXX_NODISCARD inline bool
469 operator!=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
470 { return __a.get() != __b.get(); }
471
472 /// shared_ptr comparison with nullptr
473 template<typename _Tp>
474 _GLIBCXX_NODISCARD inline bool
475 operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
476 { return (bool)__a; }
477
478 /// shared_ptr comparison with nullptr
479 template<typename _Tp>
480 _GLIBCXX_NODISCARD inline bool
481 operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
482 { return (bool)__a; }
483
484 /// Relational operator for shared_ptr objects, compares the stored pointers
485 template<typename _Tp, typename _Up>
486 _GLIBCXX_NODISCARD inline bool
487 operator<(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
488 {
489 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
490 using _Up_elt = typename shared_ptr<_Up>::element_type;
491 using _Vp = typename common_type<_Tp_elt*, _Up_elt*>::type;
492 return less<_Vp>()(__a.get(), __b.get());
493 }
494
495 /// shared_ptr comparison with nullptr
496 template<typename _Tp>
497 _GLIBCXX_NODISCARD inline bool
498 operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
499 {
500 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
501 return less<_Tp_elt*>()(__a.get(), nullptr);
502 }
503
504 /// shared_ptr comparison with nullptr
505 template<typename _Tp>
506 _GLIBCXX_NODISCARD inline bool
507 operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
508 {
509 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
510 return less<_Tp_elt*>()(nullptr, __a.get());
511 }
512
513 /// Relational operator for shared_ptr objects, compares the stored pointers
514 template<typename _Tp, typename _Up>
515 _GLIBCXX_NODISCARD inline bool
516 operator<=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
517 { return !(__b < __a); }
518
519 /// shared_ptr comparison with nullptr
520 template<typename _Tp>
521 _GLIBCXX_NODISCARD inline bool
522 operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
523 { return !(nullptr < __a); }
524
525 /// shared_ptr comparison with nullptr
526 template<typename _Tp>
527 _GLIBCXX_NODISCARD inline bool
528 operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
529 { return !(__a < nullptr); }
530
531 /// Relational operator for shared_ptr objects, compares the stored pointers
532 template<typename _Tp, typename _Up>
533 _GLIBCXX_NODISCARD inline bool
534 operator>(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
535 { return (__b < __a); }
536
537 /// shared_ptr comparison with nullptr
538 template<typename _Tp>
539 _GLIBCXX_NODISCARD inline bool
540 operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
541 { return nullptr < __a; }
542
543 /// shared_ptr comparison with nullptr
544 template<typename _Tp>
545 _GLIBCXX_NODISCARD inline bool
546 operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
547 { return __a < nullptr; }
548
549 /// Relational operator for shared_ptr objects, compares the stored pointers
550 template<typename _Tp, typename _Up>
551 _GLIBCXX_NODISCARD inline bool
552 operator>=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
553 { return !(__a < __b); }
554
555 /// shared_ptr comparison with nullptr
556 template<typename _Tp>
557 _GLIBCXX_NODISCARD inline bool
558 operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
559 { return !(__a < nullptr); }
560
561 /// shared_ptr comparison with nullptr
562 template<typename _Tp>
563 _GLIBCXX_NODISCARD inline bool
564 operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
565 { return !(nullptr < __a); }
566 #endif
567
568 // 20.7.2.2.8 shared_ptr specialized algorithms.
569
570 /// Swap overload for shared_ptr
571 template<typename _Tp>
572 inline void
573 swap(shared_ptr<_Tp>& __a, shared_ptr<_Tp>& __b) noexcept
574 { __a.swap(__b); }
575
576 // 20.7.2.2.9 shared_ptr casts.
577
578 /// Convert type of `shared_ptr`, via `static_cast`
579 template<typename _Tp, typename _Up>
580 inline shared_ptr<_Tp>
581 static_pointer_cast(const shared_ptr<_Up>& __r) noexcept
582 {
583 using _Sp = shared_ptr<_Tp>;
584 return _Sp(__r, static_cast<typename _Sp::element_type*>(__r.get()));
585 }
586
587 /// Convert type of `shared_ptr`, via `const_cast`
588 template<typename _Tp, typename _Up>
589 inline shared_ptr<_Tp>
590 const_pointer_cast(const shared_ptr<_Up>& __r) noexcept
591 {
592 using _Sp = shared_ptr<_Tp>;
593 return _Sp(__r, const_cast<typename _Sp::element_type*>(__r.get()));
594 }
595
596 /// Convert type of `shared_ptr`, via `dynamic_cast`
597 template<typename _Tp, typename _Up>
598 inline shared_ptr<_Tp>
599 dynamic_pointer_cast(const shared_ptr<_Up>& __r) noexcept
600 {
601 using _Sp = shared_ptr<_Tp>;
602 if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
603 return _Sp(__r, __p);
604 return _Sp();
605 }
606
607 #if __cplusplus >= 201703L
608 /// Convert type of `shared_ptr`, via `reinterpret_cast`
609 template<typename _Tp, typename _Up>
610 inline shared_ptr<_Tp>
611 reinterpret_pointer_cast(const shared_ptr<_Up>& __r) noexcept
612 {
613 using _Sp = shared_ptr<_Tp>;
614 return _Sp(__r, reinterpret_cast<typename _Sp::element_type*>(__r.get()));
615 }
616
617 #if __cplusplus > 201703L
618 // _GLIBCXX_RESOLVE_LIB_DEFECTS
619 // 2996. Missing rvalue overloads for shared_ptr operations
620
621 /// Convert type of `shared_ptr` rvalue, via `static_cast`
622 template<typename _Tp, typename _Up>
623 inline shared_ptr<_Tp>
624 static_pointer_cast(shared_ptr<_Up>&& __r) noexcept
625 {
626 using _Sp = shared_ptr<_Tp>;
627 return _Sp(std::move(__r),
628 static_cast<typename _Sp::element_type*>(__r.get()));
629 }
630
631 /// Convert type of `shared_ptr` rvalue, via `const_cast`
632 template<typename _Tp, typename _Up>
633 inline shared_ptr<_Tp>
634 const_pointer_cast(shared_ptr<_Up>&& __r) noexcept
635 {
636 using _Sp = shared_ptr<_Tp>;
637 return _Sp(std::move(__r),
638 const_cast<typename _Sp::element_type*>(__r.get()));
639 }
640
641 /// Convert type of `shared_ptr` rvalue, via `dynamic_cast`
642 template<typename _Tp, typename _Up>
643 inline shared_ptr<_Tp>
644 dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept
645 {
646 using _Sp = shared_ptr<_Tp>;
647 if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
648 return _Sp(std::move(__r), __p);
649 return _Sp();
650 }
651
652 /// Convert type of `shared_ptr` rvalue, via `reinterpret_cast`
653 template<typename _Tp, typename _Up>
654 inline shared_ptr<_Tp>
655 reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept
656 {
657 using _Sp = shared_ptr<_Tp>;
658 return _Sp(std::move(__r),
659 reinterpret_cast<typename _Sp::element_type*>(__r.get()));
660 }
661 #endif // C++20
662 #endif // C++17
663
664 /// @}
665
666 /**
667 * @brief A non-owning observer for a pointer owned by a shared_ptr
668 *
669 * A weak_ptr provides a safe alternative to a raw pointer when you want
670 * a non-owning reference to an object that is managed by a shared_ptr.
671 *
672 * Unlike a raw pointer, a weak_ptr can be converted to a new shared_ptr
673 * that shares ownership with every other shared_ptr that already owns
674 * the pointer. In other words you can upgrade from a non-owning "weak"
675 * reference to an owning shared_ptr, without having access to any of
676 * the existing shared_ptr objects.
677 *
678 * Also unlike a raw pointer, a weak_ptr does not become "dangling" after
679 * the object it points to has been destroyed. Instead, a weak_ptr
680 * becomes _expired_ and can no longer be converted to a shared_ptr that
681 * owns the freed pointer, so you cannot accidentally access the pointed-to
682 * object after it has been destroyed.
683 */
684 template<typename _Tp>
685 class weak_ptr : public __weak_ptr<_Tp>
686 {
687 template<typename _Arg>
688 using _Constructible = typename enable_if<
689 is_constructible<__weak_ptr<_Tp>, _Arg>::value
690 >::type;
691
692 template<typename _Arg>
693 using _Assignable = typename enable_if<
694 is_assignable<__weak_ptr<_Tp>&, _Arg>::value, weak_ptr&
695 >::type;
696
697 public:
698 constexpr weak_ptr() noexcept = default;
699
700 template<typename _Yp,
701 typename = _Constructible<const shared_ptr<_Yp>&>>
702 weak_ptr(const shared_ptr<_Yp>& __r) noexcept
703 : __weak_ptr<_Tp>(__r) { }
704
705 weak_ptr(const weak_ptr&) noexcept = default;
706
707 template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
708 weak_ptr(const weak_ptr<_Yp>& __r) noexcept
709 : __weak_ptr<_Tp>(__r) { }
710
711 weak_ptr(weak_ptr&&) noexcept = default;
712
713 template<typename _Yp, typename = _Constructible<weak_ptr<_Yp>>>
714 weak_ptr(weak_ptr<_Yp>&& __r) noexcept
715 : __weak_ptr<_Tp>(std::move(__r)) { }
716
717 weak_ptr&
718 operator=(const weak_ptr& __r) noexcept = default;
719
720 template<typename _Yp>
721 _Assignable<const weak_ptr<_Yp>&>
722 operator=(const weak_ptr<_Yp>& __r) noexcept
723 {
724 this->__weak_ptr<_Tp>::operator=(__r);
725 return *this;
726 }
727
728 template<typename _Yp>
729 _Assignable<const shared_ptr<_Yp>&>
730 operator=(const shared_ptr<_Yp>& __r) noexcept
731 {
732 this->__weak_ptr<_Tp>::operator=(__r);
733 return *this;
734 }
735
736 weak_ptr&
737 operator=(weak_ptr&& __r) noexcept = default;
738
739 template<typename _Yp>
740 _Assignable<weak_ptr<_Yp>>
741 operator=(weak_ptr<_Yp>&& __r) noexcept
742 {
743 this->__weak_ptr<_Tp>::operator=(std::move(__r));
744 return *this;
745 }
746
747 shared_ptr<_Tp>
748 lock() const noexcept
749 { return shared_ptr<_Tp>(*this, std::nothrow); }
750 };
751
752 #if __cpp_deduction_guides >= 201606
753 template<typename _Tp>
754 weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
755 #endif
756
757 // 20.7.2.3.6 weak_ptr specialized algorithms.
758 /// Swap overload for weak_ptr
759 /// @relates weak_ptr
760 template<typename _Tp>
761 inline void
762 swap(weak_ptr<_Tp>& __a, weak_ptr<_Tp>& __b) noexcept
763 { __a.swap(__b); }
764
765
766 /// Primary template owner_less
767 template<typename _Tp = void>
768 struct owner_less;
769
770 /// Void specialization of owner_less compares either shared_ptr or weak_ptr
771 template<>
772 struct owner_less<void> : _Sp_owner_less<void, void>
773 { };
774
775 /// Partial specialization of owner_less for shared_ptr.
776 template<typename _Tp>
777 struct owner_less<shared_ptr<_Tp>>
778 : public _Sp_owner_less<shared_ptr<_Tp>, weak_ptr<_Tp>>
779 { };
780
781 /// Partial specialization of owner_less for weak_ptr.
782 template<typename _Tp>
783 struct owner_less<weak_ptr<_Tp>>
784 : public _Sp_owner_less<weak_ptr<_Tp>, shared_ptr<_Tp>>
785 { };
786
787 /**
788 * @brief Base class allowing use of member function shared_from_this.
789 */
790 template<typename _Tp>
791 class enable_shared_from_this
792 {
793 protected:
794 constexpr enable_shared_from_this() noexcept { }
795
796 enable_shared_from_this(const enable_shared_from_this&) noexcept { }
797
798 enable_shared_from_this&
799 operator=(const enable_shared_from_this&) noexcept
800 { return *this; }
801
802 ~enable_shared_from_this() { }
803
804 public:
805 shared_ptr<_Tp>
806 shared_from_this()
807 { return shared_ptr<_Tp>(this->_M_weak_this); }
808
809 shared_ptr<const _Tp>
810 shared_from_this() const
811 { return shared_ptr<const _Tp>(this->_M_weak_this); }
812
813 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
814 #define __cpp_lib_enable_shared_from_this 201603
815 weak_ptr<_Tp>
816 weak_from_this() noexcept
817 { return this->_M_weak_this; }
818
819 weak_ptr<const _Tp>
820 weak_from_this() const noexcept
821 { return this->_M_weak_this; }
822 #endif
823
824 private:
825 template<typename _Tp1>
826 void
827 _M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
828 { _M_weak_this._M_assign(__p, __n); }
829
830 // Found by ADL when this is an associated class.
831 friend const enable_shared_from_this*
832 __enable_shared_from_this_base(const __shared_count<>&,
833 const enable_shared_from_this* __p)
834 { return __p; }
835
836 template<typename, _Lock_policy>
837 friend class __shared_ptr;
838
839 mutable weak_ptr<_Tp> _M_weak_this;
840 };
841
842 /// @relates shared_ptr @{
843
844 /**
845 * @brief Create an object that is owned by a shared_ptr.
846 * @param __a An allocator.
847 * @param __args Arguments for the @a _Tp object's constructor.
848 * @return A shared_ptr that owns the newly created object.
849 * @throw An exception thrown from @a _Alloc::allocate or from the
850 * constructor of @a _Tp.
851 *
852 * A copy of @a __a will be used to allocate memory for the shared_ptr
853 * and the new object.
854 */
855 template<typename _Tp, typename _Alloc, typename... _Args>
856 inline shared_ptr<_Tp>
857 allocate_shared(const _Alloc& __a, _Args&&... __args)
858 {
859 static_assert(!is_array<_Tp>::value, "make_shared<T[]> not supported");
860
861 return shared_ptr<_Tp>(_Sp_alloc_shared_tag<_Alloc>{__a},
862 std::forward<_Args>(__args)...);
863 }
864
865 /**
866 * @brief Create an object that is owned by a shared_ptr.
867 * @param __args Arguments for the @a _Tp object's constructor.
868 * @return A shared_ptr that owns the newly created object.
869 * @throw std::bad_alloc, or an exception thrown from the
870 * constructor of @a _Tp.
871 */
872 template<typename _Tp, typename... _Args>
873 inline shared_ptr<_Tp>
874 make_shared(_Args&&... __args)
875 {
876 typedef typename std::remove_cv<_Tp>::type _Tp_nc;
877 return std::allocate_shared<_Tp>(std::allocator<_Tp_nc>(),
878 std::forward<_Args>(__args)...);
879 }
880
881 /// std::hash specialization for shared_ptr.
882 template<typename _Tp>
883 struct hash<shared_ptr<_Tp>>
884 : public __hash_base<size_t, shared_ptr<_Tp>>
885 {
886 size_t
887 operator()(const shared_ptr<_Tp>& __s) const noexcept
888 {
889 return std::hash<typename shared_ptr<_Tp>::element_type*>()(__s.get());
890 }
891 };
892
893 /// @} relates shared_ptr
894 /// @} group pointer_abstractions
895
896 #if __cplusplus >= 201703L
897 namespace __detail::__variant
898 {
899 template<typename> struct _Never_valueless_alt; // see <variant>
900
901 // Provide the strong exception-safety guarantee when emplacing a
902 // shared_ptr into a variant.
903 template<typename _Tp>
904 struct _Never_valueless_alt<std::shared_ptr<_Tp>>
905 : std::true_type
906 { };
907
908 // Provide the strong exception-safety guarantee when emplacing a
909 // weak_ptr into a variant.
910 template<typename _Tp>
911 struct _Never_valueless_alt<std::weak_ptr<_Tp>>
912 : std::true_type
913 { };
914 } // namespace __detail::__variant
915 #endif // C++17
916
917 _GLIBCXX_END_NAMESPACE_VERSION
918 } // namespace
919
920 #endif // _SHARED_PTR_H
921