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