1// shared_ptr and weak_ptr implementation -*- C++ -*-
2
3// Copyright (C) 2007-2021 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
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 <iosfwd> // std::basic_ostream
53#include <bits/shared_ptr_base.h>
54
55namespace std _GLIBCXX_VISIBILITY(default)
56{
57_GLIBCXX_BEGIN_NAMESPACE_VERSION
58
59 /**
60 * @addtogroup pointer_abstractions
61 * @{
62 */
63
64 // 20.7.2.2.11 shared_ptr I/O
65
66 /// Write the stored pointer to an ostream.
67 /// @relates shared_ptr
68 template<typename _Ch, typename _Tr, typename _Tp, _Lock_policy _Lp>
69 inline std::basic_ostream<_Ch, _Tr>&
70 operator<<(std::basic_ostream<_Ch, _Tr>& __os,
71 const __shared_ptr<_Tp, _Lp>& __p)
72 {
73 __os << __p.get();
74 return __os;
75 }
76
77 template<typename _Del, typename _Tp, _Lock_policy _Lp>
78 inline _Del*
79 get_deleter(const __shared_ptr<_Tp, _Lp>& __p) noexcept
80 {
81#if __cpp_rtti
82 return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del)));
83#else
84 return 0;
85#endif
86 }
87
88 /// 20.7.2.2.10 shared_ptr get_deleter
89
90 /// If `__p` has a deleter of type `_Del`, return a pointer to it.
91 /// @relates shared_ptr
92 template<typename _Del, typename _Tp>
93 inline _Del*
94 get_deleter(const shared_ptr<_Tp>& __p) noexcept
95 {
96#if __cpp_rtti
97 return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del)));
98#else
99 return 0;
100#endif
101 }
102
103 /**
104 * @brief A smart pointer with reference-counted copy semantics.
105 *
106 * A `shared_ptr` object is either empty or _owns_ a pointer passed
107 * to the constructor. Copies of a `shared_ptr` share ownership of
108 * the same pointer. When the last `shared_ptr` that owns the pointer
109 * is destroyed or reset, the owned pointer is freed (either by `delete`
110 * or by invoking a custom deleter that was passed to the constructor).
111 *
112 * A `shared_ptr` also stores another pointer, which is usually
113 * (but not always) the same pointer as it owns. The stored pointer
114 * can be retrieved by calling the `get()` member function.
115 *
116 * The equality and relational operators for `shared_ptr` only compare
117 * the stored pointer returned by `get()`, not the owned pointer.
118 * To test whether two `shared_ptr` objects share ownership of the same
119 * pointer see `std::shared_ptr::owner_before` and `std::owner_less`.
120 */
121 template<typename _Tp>
122 class shared_ptr : public __shared_ptr<_Tp>
123 {
124 template<typename... _Args>
125 using _Constructible = typename enable_if<
126 is_constructible<__shared_ptr<_Tp>, _Args...>::value
127 >::type;
128
129 template<typename _Arg>
130 using _Assignable = typename enable_if<
131 is_assignable<__shared_ptr<_Tp>&, _Arg>::value, shared_ptr&
132 >::type;
133
134 public:
135
136 /// The type pointed to by the stored pointer, remove_extent_t<_Tp>
137 using element_type = typename __shared_ptr<_Tp>::element_type;
138
139#if __cplusplus >= 201703L
140# define __cpp_lib_shared_ptr_weak_type 201606
141 /// The corresponding weak_ptr type for this shared_ptr
142 using weak_type = weak_ptr<_Tp>;
143#endif
144 /**
145 * @brief Construct an empty %shared_ptr.
146 * @post use_count()==0 && get()==0
147 */
148 constexpr shared_ptr() noexcept : __shared_ptr<_Tp>() { }
149
150 shared_ptr(const shared_ptr&) noexcept = default; ///< Copy constructor
151
152 /**
153 * @brief Construct a %shared_ptr that owns the pointer @a __p.
154 * @param __p A pointer that is convertible to element_type*.
155 * @post use_count() == 1 && get() == __p
156 * @throw std::bad_alloc, in which case @c delete @a __p is called.
157 */
158 template<typename _Yp, typename = _Constructible<_Yp*>>
159 explicit
160 shared_ptr(_Yp* __p) : __shared_ptr<_Tp>(__p) { }
161
162 /**
163 * @brief Construct a %shared_ptr that owns the pointer @a __p
164 * and the deleter @a __d.
165 * @param __p A pointer.
166 * @param __d A deleter.
167 * @post use_count() == 1 && get() == __p
168 * @throw std::bad_alloc, in which case @a __d(__p) is called.
169 *
170 * Requirements: _Deleter's copy constructor and destructor must
171 * not throw
172 *
173 * __shared_ptr will release __p by calling __d(__p)
174 */
175 template<typename _Yp, typename _Deleter,
176 typename = _Constructible<_Yp*, _Deleter>>
177 shared_ptr(_Yp* __p, _Deleter __d)
178 : __shared_ptr<_Tp>(__p, std::move(__d)) { }
179
180 /**
181 * @brief Construct a %shared_ptr that owns a null pointer
182 * and the deleter @a __d.
183 * @param __p A null pointer constant.
184 * @param __d A deleter.
185 * @post use_count() == 1 && get() == __p
186 * @throw std::bad_alloc, in which case @a __d(__p) is called.
187 *
188 * Requirements: _Deleter's copy constructor and destructor must
189 * not throw
190 *
191 * The last owner will call __d(__p)
192 */
193 template<typename _Deleter>
194 shared_ptr(nullptr_t __p, _Deleter __d)
195 : __shared_ptr<_Tp>(__p, std::move(__d)) { }
196
197 /**
198 * @brief Construct a %shared_ptr that owns the pointer @a __p
199 * and the deleter @a __d.
200 * @param __p A pointer.
201 * @param __d A deleter.
202 * @param __a An allocator.
203 * @post use_count() == 1 && get() == __p
204 * @throw std::bad_alloc, in which case @a __d(__p) is called.
205 *
206 * Requirements: _Deleter's copy constructor and destructor must
207 * not throw _Alloc's copy constructor and destructor must not
208 * throw.
209 *
210 * __shared_ptr will release __p by calling __d(__p)
211 */
212 template<typename _Yp, typename _Deleter, typename _Alloc,
213 typename = _Constructible<_Yp*, _Deleter, _Alloc>>
214 shared_ptr(_Yp* __p, _Deleter __d, _Alloc __a)
215 : __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
216
217 /**
218 * @brief Construct a %shared_ptr that owns a null pointer
219 * and the deleter @a __d.
220 * @param __p A null pointer constant.
221 * @param __d A deleter.
222 * @param __a An allocator.
223 * @post use_count() == 1 && get() == __p
224 * @throw std::bad_alloc, in which case @a __d(__p) is called.
225 *
226 * Requirements: _Deleter's copy constructor and destructor must
227 * not throw _Alloc's copy constructor and destructor must not
228 * throw.
229 *
230 * The last owner will call __d(__p)
231 */
232 template<typename _Deleter, typename _Alloc>
233 shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
234 : __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
235
236 // Aliasing constructor
237
238 /**
239 * @brief Constructs a `shared_ptr` instance that stores `__p`
240 * and shares ownership with `__r`.
241 * @param __r A `shared_ptr`.
242 * @param __p A pointer that will remain valid while `*__r` is valid.
243 * @post `get() == __p && use_count() == __r.use_count()`
244 *
245 * This can be used to construct a `shared_ptr` to a sub-object
246 * of an object managed by an existing `shared_ptr`. The complete
247 * object will remain valid while any `shared_ptr` owns it, even
248 * if they don't store a pointer to the complete object.
249 *
250 * @code
251 * shared_ptr<pair<int,int>> pii(new pair<int,int>());
252 * shared_ptr<int> pi(pii, &pii->first);
253 * assert(pii.use_count() == 2);
254 * @endcode
255 */
256 template<typename _Yp>
257 shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) noexcept
258 : __shared_ptr<_Tp>(__r, __p) { }
259
260#if __cplusplus > 201703L
261 // _GLIBCXX_RESOLVE_LIB_DEFECTS
262 // 2996. Missing rvalue overloads for shared_ptr operations
263 /**
264 * @brief Constructs a `shared_ptr` instance that stores `__p`
265 * and shares ownership with `__r`.
266 * @param __r A `shared_ptr`.
267 * @param __p A pointer that will remain valid while `*__r` is valid.
268 * @post `get() == __p && !__r.use_count() && !__r.get()`
269 *
270 * This can be used to construct a `shared_ptr` to a sub-object
271 * of an object managed by an existing `shared_ptr`. The complete
272 * object will remain valid while any `shared_ptr` owns it, even
273 * if they don't store a pointer to the complete object.
274 *
275 * @code
276 * shared_ptr<pair<int,int>> pii(new pair<int,int>());
277 * shared_ptr<int> pi1(pii, &pii->first);
278 * assert(pii.use_count() == 2);
279 * shared_ptr<int> pi2(std::move(pii), &pii->second);
280 * assert(pii.use_count() == 0);
281 * @endcode
282 */
283 template<typename _Yp>
284 shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept
285 : __shared_ptr<_Tp>(std::move(__r), __p) { }
286#endif
287 /**
288 * @brief If @a __r is empty, constructs an empty %shared_ptr;
289 * otherwise construct a %shared_ptr that shares ownership
290 * with @a __r.
291 * @param __r A %shared_ptr.
292 * @post get() == __r.get() && use_count() == __r.use_count()
293 */
294 template<typename _Yp,
295 typename = _Constructible<const shared_ptr<_Yp>&>>
296 shared_ptr(const shared_ptr<_Yp>& __r) noexcept
297 : __shared_ptr<_Tp>(__r) { }
298
299 /**
300 * @brief Move-constructs a %shared_ptr instance from @a __r.
301 * @param __r A %shared_ptr rvalue.
302 * @post *this contains the old value of @a __r, @a __r is empty.
303 */
304 shared_ptr(shared_ptr&& __r) noexcept
305 : __shared_ptr<_Tp>(std::move(__r)) { }
306
307 /**
308 * @brief Move-constructs a %shared_ptr instance from @a __r.
309 * @param __r A %shared_ptr rvalue.
310 * @post *this contains the old value of @a __r, @a __r is empty.
311 */
312 template<typename _Yp, typename = _Constructible<shared_ptr<_Yp>>>
313 shared_ptr(shared_ptr<_Yp>&& __r) noexcept
314 : __shared_ptr<_Tp>(std::move(__r)) { }
315
316 /**
317 * @brief Constructs a %shared_ptr that shares ownership with @a __r
318 * and stores a copy of the pointer stored in @a __r.
319 * @param __r A weak_ptr.
320 * @post use_count() == __r.use_count()
321 * @throw bad_weak_ptr when __r.expired(),
322 * in which case the constructor has no effect.
323 */
324 template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
325 explicit shared_ptr(const weak_ptr<_Yp>& __r)
326 : __shared_ptr<_Tp>(__r) { }
327
328#if _GLIBCXX_USE_DEPRECATED
329#pragma GCC diagnostic push
330#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
331 template<typename _Yp, typename = _Constructible<auto_ptr<_Yp>>>
332 shared_ptr(auto_ptr<_Yp>&& __r);
333#pragma GCC diagnostic pop
334#endif
335
336 // _GLIBCXX_RESOLVE_LIB_DEFECTS
337 // 2399. shared_ptr's constructor from unique_ptr should be constrained
338 template<typename _Yp, typename _Del,
339 typename = _Constructible<unique_ptr<_Yp, _Del>>>
340 shared_ptr(unique_ptr<_Yp, _Del>&& __r)
341 : __shared_ptr<_Tp>(std::move(__r)) { }
342
343#if __cplusplus <= 201402L && _GLIBCXX_USE_DEPRECATED
344 // This non-standard constructor exists to support conversions that
345 // were possible in C++11 and C++14 but are ill-formed in C++17.
346 // If an exception is thrown this constructor has no effect.
347 template<typename _Yp, typename _Del,
348 _Constructible<unique_ptr<_Yp, _Del>, __sp_array_delete>* = 0>
349 shared_ptr(unique_ptr<_Yp, _Del>&& __r)
350 : __shared_ptr<_Tp>(std::move(__r), __sp_array_delete()) { }
351#endif
352
353 /**
354 * @brief Construct an empty %shared_ptr.
355 * @post use_count() == 0 && get() == nullptr
356 */
357 constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
358
359 shared_ptr& operator=(const shared_ptr&) noexcept = default;
360
361 template<typename _Yp>
362 _Assignable<const shared_ptr<_Yp>&>
363 operator=(const shared_ptr<_Yp>& __r) noexcept
364 {
365 this->__shared_ptr<_Tp>::operator=(__r);
366 return *this;
367 }
368
369#if _GLIBCXX_USE_DEPRECATED
370#pragma GCC diagnostic push
371#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
372 template<typename _Yp>
373 _Assignable<auto_ptr<_Yp>>
374 operator=(auto_ptr<_Yp>&& __r)
375 {
376 this->__shared_ptr<_Tp>::operator=(std::move(__r));
377 return *this;
378 }
379#pragma GCC diagnostic pop
380#endif
381
382 shared_ptr&
383 operator=(shared_ptr&& __r) noexcept
384 {
385 this->__shared_ptr<_Tp>::operator=(std::move(__r));
386 return *this;
387 }
388
389 template<class _Yp>
390 _Assignable<shared_ptr<_Yp>>
391 operator=(shared_ptr<_Yp>&& __r) noexcept
392 {
393 this->__shared_ptr<_Tp>::operator=(std::move(__r));
394 return *this;
395 }
396
397 template<typename _Yp, typename _Del>
398 _Assignable<unique_ptr<_Yp, _Del>>
399 operator=(unique_ptr<_Yp, _Del>&& __r)
400 {
401 this->__shared_ptr<_Tp>::operator=(std::move(__r));
402 return *this;
403 }
404
405 private:
406 // This constructor is non-standard, it is used by allocate_shared.
407 template<typename _Alloc, typename... _Args>
408 shared_ptr(_Sp_alloc_shared_tag<_Alloc> __tag, _Args&&... __args)
409 : __shared_ptr<_Tp>(__tag, std::forward<_Args>(__args)...)
410 { }
411
412 template<typename _Yp, typename _Alloc, typename... _Args>
413 friend shared_ptr<_Yp>
414 allocate_shared(const _Alloc& __a, _Args&&... __args);
415
416 // This constructor is non-standard, it is used by weak_ptr::lock().
417 shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t) noexcept
418 : __shared_ptr<_Tp>(__r, std::nothrow) { }
419
420 friend class weak_ptr<_Tp>;
421 };
422
423#if __cpp_deduction_guides >= 201606
424 template<typename _Tp>
425 shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
426 template<typename _Tp, typename _Del>
427 shared_ptr(unique_ptr<_Tp, _Del>) -> shared_ptr<_Tp>;
428#endif
429
430 // 20.7.2.2.7 shared_ptr comparisons
431
432 /// @relates shared_ptr @{
433
434 /// Equality operator for shared_ptr objects, compares the stored pointers
435 template<typename _Tp, typename _Up>
436 _GLIBCXX_NODISCARD inline bool
437 operator==(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
438 { return __a.get() == __b.get(); }
439
440 /// shared_ptr comparison with nullptr
441 template<typename _Tp>
442 _GLIBCXX_NODISCARD inline bool
443 operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
444 { return !__a; }
445
446#ifdef __cpp_lib_three_way_comparison
447 template<typename _Tp, typename _Up>
448 inline strong_ordering
449 operator<=>(const shared_ptr<_Tp>& __a,
450 const shared_ptr<_Up>& __b) noexcept
451 { return compare_three_way()(__a.get(), __b.get()); }
452
453 template<typename _Tp>
454 inline strong_ordering
455 operator<=>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
456 {
457 using pointer = typename shared_ptr<_Tp>::element_type*;
458 return compare_three_way()(__a.get(), static_cast<pointer>(nullptr));
459 }
460#else
461 /// shared_ptr comparison with nullptr
462 template<typename _Tp>
463 _GLIBCXX_NODISCARD inline bool
464 operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
465 { return !__a; }
466
467 /// Inequality operator for shared_ptr objects, compares the stored pointers
468 template<typename _Tp, typename _Up>
469 _GLIBCXX_NODISCARD inline bool
470 operator!=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
471 { return __a.get() != __b.get(); }
472
473 /// shared_ptr comparison with nullptr
474 template<typename _Tp>
475 _GLIBCXX_NODISCARD inline bool
476 operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
477 { return (bool)__a; }
478
479 /// shared_ptr comparison with nullptr
480 template<typename _Tp>
481 _GLIBCXX_NODISCARD inline bool
482 operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
483 { return (bool)__a; }
484
485 /// Relational operator for shared_ptr objects, compares the stored pointers
486 template<typename _Tp, typename _Up>
487 _GLIBCXX_NODISCARD inline bool
488 operator<(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
489 {
490 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
491 using _Up_elt = typename shared_ptr<_Up>::element_type;
492 using _Vp = typename common_type<_Tp_elt*, _Up_elt*>::type;
493 return less<_Vp>()(__a.get(), __b.get());
494 }
495
496 /// shared_ptr comparison with nullptr
497 template<typename _Tp>
498 _GLIBCXX_NODISCARD inline bool
499 operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
500 {
501 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
502 return less<_Tp_elt*>()(__a.get(), nullptr);
503 }
504
505 /// shared_ptr comparison with nullptr
506 template<typename _Tp>
507 _GLIBCXX_NODISCARD inline bool
508 operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
509 {
510 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
511 return less<_Tp_elt*>()(nullptr, __a.get());
512 }
513
514 /// Relational operator for shared_ptr objects, compares the stored pointers
515 template<typename _Tp, typename _Up>
516 _GLIBCXX_NODISCARD inline bool
517 operator<=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
518 { return !(__b < __a); }
519
520 /// shared_ptr comparison with nullptr
521 template<typename _Tp>
522 _GLIBCXX_NODISCARD inline bool
523 operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
524 { return !(nullptr < __a); }
525
526 /// shared_ptr comparison with nullptr
527 template<typename _Tp>
528 _GLIBCXX_NODISCARD inline bool
529 operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
530 { return !(__a < nullptr); }
531
532 /// Relational operator for shared_ptr objects, compares the stored pointers
533 template<typename _Tp, typename _Up>
534 _GLIBCXX_NODISCARD inline bool
535 operator>(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
536 { return (__b < __a); }
537
538 /// shared_ptr comparison with nullptr
539 template<typename _Tp>
540 _GLIBCXX_NODISCARD inline bool
541 operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
542 { return nullptr < __a; }
543
544 /// shared_ptr comparison with nullptr
545 template<typename _Tp>
546 _GLIBCXX_NODISCARD inline bool
547 operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
548 { return __a < nullptr; }
549
550 /// Relational operator for shared_ptr objects, compares the stored pointers
551 template<typename _Tp, typename _Up>
552 _GLIBCXX_NODISCARD inline bool
553 operator>=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
554 { return !(__a < __b); }
555
556 /// shared_ptr comparison with nullptr
557 template<typename _Tp>
558 _GLIBCXX_NODISCARD inline bool
559 operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
560 { return !(__a < nullptr); }
561
562 /// shared_ptr comparison with nullptr
563 template<typename _Tp>
564 _GLIBCXX_NODISCARD inline bool
565 operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
566 { return !(nullptr < __a); }
567#endif
568
569 // 20.7.2.2.8 shared_ptr specialized algorithms.
570
571 /// Swap overload for shared_ptr
572 template<typename _Tp>
573 inline void
574 swap(shared_ptr<_Tp>& __a, shared_ptr<_Tp>& __b) noexcept
575 { __a.swap(__b); }
576
577 // 20.7.2.2.9 shared_ptr casts.
578
579 /// Convert type of `shared_ptr`, via `static_cast`
580 template<typename _Tp, typename _Up>
581 inline shared_ptr<_Tp>
582 static_pointer_cast(const shared_ptr<_Up>& __r) noexcept
583 {
584 using _Sp = shared_ptr<_Tp>;
585 return _Sp(__r, static_cast<typename _Sp::element_type*>(__r.get()));
586 }
587
588 /// Convert type of `shared_ptr`, via `const_cast`
589 template<typename _Tp, typename _Up>
590 inline shared_ptr<_Tp>
591 const_pointer_cast(const shared_ptr<_Up>& __r) noexcept
592 {
593 using _Sp = shared_ptr<_Tp>;
594 return _Sp(__r, const_cast<typename _Sp::element_type*>(__r.get()));
595 }
596
597 /// Convert type of `shared_ptr`, via `dynamic_cast`
598 template<typename _Tp, typename _Up>
599 inline shared_ptr<_Tp>
600 dynamic_pointer_cast(const shared_ptr<_Up>& __r) noexcept
601 {
602 using _Sp = shared_ptr<_Tp>;
603 if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
604 return _Sp(__r, __p);
605 return _Sp();
606 }
607
608#if __cplusplus >= 201703L
609 /// Convert type of `shared_ptr`, via `reinterpret_cast`
610 template<typename _Tp, typename _Up>
611 inline shared_ptr<_Tp>
612 reinterpret_pointer_cast(const shared_ptr<_Up>& __r) noexcept
613 {
614 using _Sp = shared_ptr<_Tp>;
615 return _Sp(__r, reinterpret_cast<typename _Sp::element_type*>(__r.get()));
616 }
617
618#if __cplusplus > 201703L
619 // _GLIBCXX_RESOLVE_LIB_DEFECTS
620 // 2996. Missing rvalue overloads for shared_ptr operations
621
622 /// Convert type of `shared_ptr` rvalue, via `static_cast`
623 template<typename _Tp, typename _Up>
624 inline shared_ptr<_Tp>
625 static_pointer_cast(shared_ptr<_Up>&& __r) noexcept
626 {
627 using _Sp = shared_ptr<_Tp>;
628 return _Sp(std::move(__r),
629 static_cast<typename _Sp::element_type*>(__r.get()));
630 }
631
632 /// Convert type of `shared_ptr` rvalue, via `const_cast`
633 template<typename _Tp, typename _Up>
634 inline shared_ptr<_Tp>
635 const_pointer_cast(shared_ptr<_Up>&& __r) noexcept
636 {
637 using _Sp = shared_ptr<_Tp>;
638 return _Sp(std::move(__r),
639 const_cast<typename _Sp::element_type*>(__r.get()));
640 }
641
642 /// Convert type of `shared_ptr` rvalue, via `dynamic_cast`
643 template<typename _Tp, typename _Up>
644 inline shared_ptr<_Tp>
645 dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept
646 {
647 using _Sp = shared_ptr<_Tp>;
648 if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
649 return _Sp(std::move(__r), __p);
650 return _Sp();
651 }
652
653 /// Convert type of `shared_ptr` rvalue, via `reinterpret_cast`
654 template<typename _Tp, typename _Up>
655 inline shared_ptr<_Tp>
656 reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept
657 {
658 using _Sp = shared_ptr<_Tp>;
659 return _Sp(std::move(__r),
660 reinterpret_cast<typename _Sp::element_type*>(__r.get()));
661 }
662#endif // C++20
663#endif // C++17
664
665 /// @}
666
667 /**
668 * @brief A non-owning observer for a pointer owned by a shared_ptr
669 *
670 * A weak_ptr provides a safe alternative to a raw pointer when you want
671 * a non-owning reference to an object that is managed by a shared_ptr.
672 *
673 * Unlike a raw pointer, a weak_ptr can be converted to a new shared_ptr
674 * that shares ownership with every other shared_ptr that already owns
675 * the pointer. In other words you can upgrade from a non-owning "weak"
676 * reference to an owning shared_ptr, without having access to any of
677 * the existing shared_ptr objects.
678 *
679 * Also unlike a raw pointer, a weak_ptr does not become "dangling" after
680 * the object it points to has been destroyed. Instead, a weak_ptr
681 * becomes _expired_ and can no longer be converted to a shared_ptr that
682 * owns the freed pointer, so you cannot accidentally access the pointed-to
683 * object after it has been destroyed.
684 */
685 template<typename _Tp>
686 class weak_ptr : public __weak_ptr<_Tp>
687 {
688 template<typename _Arg>
689 using _Constructible = typename enable_if<
690 is_constructible<__weak_ptr<_Tp>, _Arg>::value
691 >::type;
692
693 template<typename _Arg>
694 using _Assignable = typename enable_if<
695 is_assignable<__weak_ptr<_Tp>&, _Arg>::value, weak_ptr&
696 >::type;
697
698 public:
699 constexpr weak_ptr() noexcept = default;
700
701 template<typename _Yp,
702 typename = _Constructible<const shared_ptr<_Yp>&>>
703 weak_ptr(const shared_ptr<_Yp>& __r) noexcept
704 : __weak_ptr<_Tp>(__r) { }
705
706 weak_ptr(const weak_ptr&) noexcept = default;
707
708 template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
709 weak_ptr(const weak_ptr<_Yp>& __r) noexcept
710 : __weak_ptr<_Tp>(__r) { }
711
712 weak_ptr(weak_ptr&&) noexcept = default;
713
714 template<typename _Yp, typename = _Constructible<weak_ptr<_Yp>>>
715 weak_ptr(weak_ptr<_Yp>&& __r) noexcept
716 : __weak_ptr<_Tp>(std::move(__r)) { }
717
718 weak_ptr&
719 operator=(const weak_ptr& __r) noexcept = default;
720
721 template<typename _Yp>
722 _Assignable<const weak_ptr<_Yp>&>
723 operator=(const weak_ptr<_Yp>& __r) noexcept
724 {
725 this->__weak_ptr<_Tp>::operator=(__r);
726 return *this;
727 }
728
729 template<typename _Yp>
730 _Assignable<const shared_ptr<_Yp>&>
731 operator=(const shared_ptr<_Yp>& __r) noexcept
732 {
733 this->__weak_ptr<_Tp>::operator=(__r);
734 return *this;
735 }
736
737 weak_ptr&
738 operator=(weak_ptr&& __r) noexcept = default;
739
740 template<typename _Yp>
741 _Assignable<weak_ptr<_Yp>>
742 operator=(weak_ptr<_Yp>&& __r) noexcept
743 {
744 this->__weak_ptr<_Tp>::operator=(std::move(__r));
745 return *this;
746 }
747
748 shared_ptr<_Tp>
749 lock() const noexcept
750 { return shared_ptr<_Tp>(*this, std::nothrow); }
751 };
752
753#if __cpp_deduction_guides >= 201606
754 template<typename _Tp>
755 weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
756#endif
757
758 // 20.7.2.3.6 weak_ptr specialized algorithms.
759 /// Swap overload for weak_ptr
760 /// @relates weak_ptr
761 template<typename _Tp>
762 inline void
763 swap(weak_ptr<_Tp>& __a, weak_ptr<_Tp>& __b) noexcept
764 { __a.swap(__b); }
765
766
767 /// Primary template owner_less
768 template<typename _Tp = void>
769 struct owner_less;
770
771 /// Void specialization of owner_less compares either shared_ptr or weak_ptr
772 template<>
773 struct owner_less<void> : _Sp_owner_less<void, void>
774 { };
775
776 /// Partial specialization of owner_less for shared_ptr.
777 template<typename _Tp>
778 struct owner_less<shared_ptr<_Tp>>
779 : public _Sp_owner_less<shared_ptr<_Tp>, weak_ptr<_Tp>>
780 { };
781
782 /// Partial specialization of owner_less for weak_ptr.
783 template<typename _Tp>
784 struct owner_less<weak_ptr<_Tp>>
785 : public _Sp_owner_less<weak_ptr<_Tp>, shared_ptr<_Tp>>
786 { };
787
788 /**
789 * @brief Base class allowing use of member function shared_from_this.
790 */
791 template<typename _Tp>
792 class enable_shared_from_this
793 {
794 protected:
795 constexpr enable_shared_from_this() noexcept { }
796
797 enable_shared_from_this(const enable_shared_from_this&) noexcept { }
798
799 enable_shared_from_this&
800 operator=(const enable_shared_from_this&) noexcept
801 { return *this; }
802
803 ~enable_shared_from_this() { }
804
805 public:
806 shared_ptr<_Tp>
807 shared_from_this()
808 { return shared_ptr<_Tp>(this->_M_weak_this); }
809
810 shared_ptr<const _Tp>
811 shared_from_this() const
812 { return shared_ptr<const _Tp>(this->_M_weak_this); }
813
814#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
815#define __cpp_lib_enable_shared_from_this 201603
816 weak_ptr<_Tp>
817 weak_from_this() noexcept
818 { return this->_M_weak_this; }
819
820 weak_ptr<const _Tp>
821 weak_from_this() const noexcept
822 { return this->_M_weak_this; }
823#endif
824
825 private:
826 template<typename _Tp1>
827 void
828 _M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
829 { _M_weak_this._M_assign(__p, __n); }
830
831 // Found by ADL when this is an associated class.
832 friend const enable_shared_from_this*
833 __enable_shared_from_this_base(const __shared_count<>&,
834 const enable_shared_from_this* __p)
835 { return __p; }
836
837 template<typename, _Lock_policy>
838 friend class __shared_ptr;
839
840 mutable weak_ptr<_Tp> _M_weak_this;
841 };
842
843 /// @relates shared_ptr @{
844
845 /**
846 * @brief Create an object that is owned by a shared_ptr.
847 * @param __a An allocator.
848 * @param __args Arguments for the @a _Tp object's constructor.
849 * @return A shared_ptr that owns the newly created object.
850 * @throw An exception thrown from @a _Alloc::allocate or from the
851 * constructor of @a _Tp.
852 *
853 * A copy of @a __a will be used to allocate memory for the shared_ptr
854 * and the new object.
855 */
856 template<typename _Tp, typename _Alloc, typename... _Args>
857 inline shared_ptr<_Tp>
858 allocate_shared(const _Alloc& __a, _Args&&... __args)
859 {
860 static_assert(!is_array<_Tp>::value, "make_shared<T[]> not supported");
861
862 return shared_ptr<_Tp>(_Sp_alloc_shared_tag<_Alloc>{__a},
863 std::forward<_Args>(__args)...);
864 }
865
866 /**
867 * @brief Create an object that is owned by a shared_ptr.
868 * @param __args Arguments for the @a _Tp object's constructor.
869 * @return A shared_ptr that owns the newly created object.
870 * @throw std::bad_alloc, or an exception thrown from the
871 * constructor of @a _Tp.
872 */
873 template<typename _Tp, typename... _Args>
874 inline shared_ptr<_Tp>
875 make_shared(_Args&&... __args)
876 {
877 typedef typename std::remove_cv<_Tp>::type _Tp_nc;
878 return std::allocate_shared<_Tp>(std::allocator<_Tp_nc>(),
879 std::forward<_Args>(__args)...);
880 }
881
882 /// std::hash specialization for shared_ptr.
883 template<typename _Tp>
884 struct hash<shared_ptr<_Tp>>
885 : public __hash_base<size_t, shared_ptr<_Tp>>
886 {
887 size_t
888 operator()(const shared_ptr<_Tp>& __s) const noexcept
889 {
890 return std::hash<typename shared_ptr<_Tp>::element_type*>()(__s.get());
891 }
892 };
893
894 /// @} relates shared_ptr
895 /// @} group pointer_abstractions
896
897#if __cplusplus >= 201703L
898 namespace __detail::__variant
899 {
900 template<typename> struct _Never_valueless_alt; // see <variant>
901
902 // Provide the strong exception-safety guarantee when emplacing a
903 // shared_ptr into a variant.
904 template<typename _Tp>
905 struct _Never_valueless_alt<std::shared_ptr<_Tp>>
906 : std::true_type
907 { };
908
909 // Provide the strong exception-safety guarantee when emplacing a
910 // weak_ptr into a variant.
911 template<typename _Tp>
912 struct _Never_valueless_alt<std::weak_ptr<_Tp>>
913 : std::true_type
914 { };
915 } // namespace __detail::__variant
916#endif // C++17
917
918_GLIBCXX_END_NAMESPACE_VERSION
919} // namespace
920
921#endif // _SHARED_PTR_H
922

source code of include/c++/11/bits/shared_ptr.h