1 // shared_ptr and weak_ptr implementation -*- C++ -*-
2
3 // Copyright (C) 2007-2023 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
55 namespace 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 /// @cond undocumented
104
105 // Constraint for overloads taking non-array types.
106 #if __cpp_concepts && __cpp_lib_type_trait_variable_templates
107 template<typename _Tp>
108 requires (!is_array_v<_Tp>)
109 using _NonArray = _Tp;
110 #else
111 template<typename _Tp>
112 using _NonArray = __enable_if_t<!is_array<_Tp>::value, _Tp>;
113 #endif
114
115 #if __cpp_lib_shared_ptr_arrays >= 201707L
116 // Constraint for overloads taking array types with unknown bound, U[].
117 #if __cpp_concepts
118 template<typename _Tp>
119 requires is_array_v<_Tp> && (extent_v<_Tp> == 0)
120 using _UnboundedArray = _Tp;
121 #else
122 template<typename _Tp>
123 using _UnboundedArray
124 = __enable_if_t<__is_array_unknown_bounds<_Tp>::value, _Tp>;
125 #endif
126
127 // Constraint for overloads taking array types with known bound, U[N].
128 #if __cpp_concepts
129 template<typename _Tp>
130 requires (extent_v<_Tp> != 0)
131 using _BoundedArray = _Tp;
132 #else
133 template<typename _Tp>
134 using _BoundedArray
135 = __enable_if_t<__is_array_known_bounds<_Tp>::value, _Tp>;
136 #endif
137
138 #if __cpp_lib_smart_ptr_for_overwrite
139 // Constraint for overloads taking either non-array or bounded array, U[N].
140 #if __cpp_concepts
141 template<typename _Tp>
142 requires (!is_array_v<_Tp>) || (extent_v<_Tp> != 0)
143 using _NotUnboundedArray = _Tp;
144 #else
145 template<typename _Tp>
146 using _NotUnboundedArray
147 = __enable_if_t<!__is_array_unknown_bounds<_Tp>::value, _Tp>;
148 #endif
149 #endif // smart_ptr_for_overwrite
150 #endif // shared_ptr_arrays
151
152 /// @endcond
153
154 /**
155 * @brief A smart pointer with reference-counted copy semantics.
156 * @headerfile memory
157 * @since C++11
158 *
159 * A `shared_ptr` object is either empty or _owns_ a pointer passed
160 * to the constructor. Copies of a `shared_ptr` share ownership of
161 * the same pointer. When the last `shared_ptr` that owns the pointer
162 * is destroyed or reset, the owned pointer is freed (either by `delete`
163 * or by invoking a custom deleter that was passed to the constructor).
164 *
165 * A `shared_ptr` also stores another pointer, which is usually
166 * (but not always) the same pointer as it owns. The stored pointer
167 * can be retrieved by calling the `get()` member function.
168 *
169 * The equality and relational operators for `shared_ptr` only compare
170 * the stored pointer returned by `get()`, not the owned pointer.
171 * To test whether two `shared_ptr` objects share ownership of the same
172 * pointer see `std::shared_ptr::owner_before` and `std::owner_less`.
173 */
174 template<typename _Tp>
175 class shared_ptr : public __shared_ptr<_Tp>
176 {
177 template<typename... _Args>
178 using _Constructible = typename enable_if<
179 is_constructible<__shared_ptr<_Tp>, _Args...>::value
180 >::type;
181
182 template<typename _Arg>
183 using _Assignable = typename enable_if<
184 is_assignable<__shared_ptr<_Tp>&, _Arg>::value, shared_ptr&
185 >::type;
186
187 public:
188
189 /// The type pointed to by the stored pointer, remove_extent_t<_Tp>
190 using element_type = typename __shared_ptr<_Tp>::element_type;
191
192 #if __cplusplus >= 201703L
193 # define __cpp_lib_shared_ptr_weak_type 201606L
194 /// The corresponding weak_ptr type for this shared_ptr
195 /// @since C++17
196 using weak_type = weak_ptr<_Tp>;
197 #endif
198 /**
199 * @brief Construct an empty %shared_ptr.
200 * @post use_count()==0 && get()==0
201 */
202 constexpr shared_ptr() noexcept : __shared_ptr<_Tp>() { }
203
204 shared_ptr(const shared_ptr&) noexcept = default; ///< Copy constructor
205
206 /**
207 * @brief Construct a %shared_ptr that owns the pointer @a __p.
208 * @param __p A pointer that is convertible to element_type*.
209 * @post use_count() == 1 && get() == __p
210 * @throw std::bad_alloc, in which case @c delete @a __p is called.
211 */
212 template<typename _Yp, typename = _Constructible<_Yp*>>
213 explicit
214 shared_ptr(_Yp* __p) : __shared_ptr<_Tp>(__p) { }
215
216 /**
217 * @brief Construct a %shared_ptr that owns the pointer @a __p
218 * and the deleter @a __d.
219 * @param __p A pointer.
220 * @param __d A deleter.
221 * @post use_count() == 1 && get() == __p
222 * @throw std::bad_alloc, in which case @a __d(__p) is called.
223 *
224 * Requirements: _Deleter's copy constructor and destructor must
225 * not throw
226 *
227 * __shared_ptr will release __p by calling __d(__p)
228 */
229 template<typename _Yp, typename _Deleter,
230 typename = _Constructible<_Yp*, _Deleter>>
231 shared_ptr(_Yp* __p, _Deleter __d)
232 : __shared_ptr<_Tp>(__p, std::move(__d)) { }
233
234 /**
235 * @brief Construct a %shared_ptr that owns a null pointer
236 * and the deleter @a __d.
237 * @param __p A null pointer constant.
238 * @param __d A deleter.
239 * @post use_count() == 1 && get() == __p
240 * @throw std::bad_alloc, in which case @a __d(__p) is called.
241 *
242 * Requirements: _Deleter's copy constructor and destructor must
243 * not throw
244 *
245 * The last owner will call __d(__p)
246 */
247 template<typename _Deleter>
248 shared_ptr(nullptr_t __p, _Deleter __d)
249 : __shared_ptr<_Tp>(__p, std::move(__d)) { }
250
251 /**
252 * @brief Construct a %shared_ptr that owns the pointer @a __p
253 * and the deleter @a __d.
254 * @param __p A pointer.
255 * @param __d A deleter.
256 * @param __a An allocator.
257 * @post use_count() == 1 && get() == __p
258 * @throw std::bad_alloc, in which case @a __d(__p) is called.
259 *
260 * Requirements: _Deleter's copy constructor and destructor must
261 * not throw _Alloc's copy constructor and destructor must not
262 * throw.
263 *
264 * __shared_ptr will release __p by calling __d(__p)
265 */
266 template<typename _Yp, typename _Deleter, typename _Alloc,
267 typename = _Constructible<_Yp*, _Deleter, _Alloc>>
268 shared_ptr(_Yp* __p, _Deleter __d, _Alloc __a)
269 : __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
270
271 /**
272 * @brief Construct a %shared_ptr that owns a null pointer
273 * and the deleter @a __d.
274 * @param __p A null pointer constant.
275 * @param __d A deleter.
276 * @param __a An allocator.
277 * @post use_count() == 1 && get() == __p
278 * @throw std::bad_alloc, in which case @a __d(__p) is called.
279 *
280 * Requirements: _Deleter's copy constructor and destructor must
281 * not throw _Alloc's copy constructor and destructor must not
282 * throw.
283 *
284 * The last owner will call __d(__p)
285 */
286 template<typename _Deleter, typename _Alloc>
287 shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
288 : __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
289
290 // Aliasing constructor
291
292 /**
293 * @brief Constructs a `shared_ptr` instance that stores `__p`
294 * and shares ownership with `__r`.
295 * @param __r A `shared_ptr`.
296 * @param __p A pointer that will remain valid while `*__r` is valid.
297 * @post `get() == __p && use_count() == __r.use_count()`
298 *
299 * This can be used to construct a `shared_ptr` to a sub-object
300 * of an object managed by an existing `shared_ptr`. The complete
301 * object will remain valid while any `shared_ptr` owns it, even
302 * if they don't store a pointer to the complete object.
303 *
304 * @code
305 * shared_ptr<pair<int,int>> pii(new pair<int,int>());
306 * shared_ptr<int> pi(pii, &pii->first);
307 * assert(pii.use_count() == 2);
308 * @endcode
309 */
310 template<typename _Yp>
311 shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) noexcept
312 : __shared_ptr<_Tp>(__r, __p) { }
313
314 #if __cplusplus > 201703L
315 // _GLIBCXX_RESOLVE_LIB_DEFECTS
316 // 2996. Missing rvalue overloads for shared_ptr operations
317 /**
318 * @brief Constructs a `shared_ptr` instance that stores `__p`
319 * and shares ownership with `__r`.
320 * @param __r A `shared_ptr`.
321 * @param __p A pointer that will remain valid while `*__r` is valid.
322 * @post `get() == __p && !__r.use_count() && !__r.get()`
323 * @since C++17
324 *
325 * This can be used to construct a `shared_ptr` to a sub-object
326 * of an object managed by an existing `shared_ptr`. The complete
327 * object will remain valid while any `shared_ptr` owns it, even
328 * if they don't store a pointer to the complete object.
329 *
330 * @code
331 * shared_ptr<pair<int,int>> pii(new pair<int,int>());
332 * shared_ptr<int> pi1(pii, &pii->first);
333 * assert(pii.use_count() == 2);
334 * shared_ptr<int> pi2(std::move(pii), &pii->second);
335 * assert(pii.use_count() == 0);
336 * @endcode
337 */
338 template<typename _Yp>
339 shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept
340 : __shared_ptr<_Tp>(std::move(__r), __p) { }
341 #endif
342 /**
343 * @brief If @a __r is empty, constructs an empty %shared_ptr;
344 * otherwise construct a %shared_ptr that shares ownership
345 * with @a __r.
346 * @param __r A %shared_ptr.
347 * @post get() == __r.get() && use_count() == __r.use_count()
348 */
349 template<typename _Yp,
350 typename = _Constructible<const shared_ptr<_Yp>&>>
351 shared_ptr(const shared_ptr<_Yp>& __r) noexcept
352 : __shared_ptr<_Tp>(__r) { }
353
354 /**
355 * @brief Move-constructs a %shared_ptr instance from @a __r.
356 * @param __r A %shared_ptr rvalue.
357 * @post *this contains the old value of @a __r, @a __r is empty.
358 */
359 shared_ptr(shared_ptr&& __r) noexcept
360 : __shared_ptr<_Tp>(std::move(__r)) { }
361
362 /**
363 * @brief Move-constructs a %shared_ptr instance from @a __r.
364 * @param __r A %shared_ptr rvalue.
365 * @post *this contains the old value of @a __r, @a __r is empty.
366 */
367 template<typename _Yp, typename = _Constructible<shared_ptr<_Yp>>>
368 shared_ptr(shared_ptr<_Yp>&& __r) noexcept
369 : __shared_ptr<_Tp>(std::move(__r)) { }
370
371 /**
372 * @brief Constructs a %shared_ptr that shares ownership with @a __r
373 * and stores a copy of the pointer stored in @a __r.
374 * @param __r A weak_ptr.
375 * @post use_count() == __r.use_count()
376 * @throw bad_weak_ptr when __r.expired(),
377 * in which case the constructor has no effect.
378 */
379 template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
380 explicit shared_ptr(const weak_ptr<_Yp>& __r)
381 : __shared_ptr<_Tp>(__r) { }
382
383 #if _GLIBCXX_USE_DEPRECATED
384 #pragma GCC diagnostic push
385 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
386 template<typename _Yp, typename = _Constructible<auto_ptr<_Yp>>>
387 shared_ptr(auto_ptr<_Yp>&& __r);
388 #pragma GCC diagnostic pop
389 #endif
390
391 // _GLIBCXX_RESOLVE_LIB_DEFECTS
392 // 2399. shared_ptr's constructor from unique_ptr should be constrained
393 template<typename _Yp, typename _Del,
394 typename = _Constructible<unique_ptr<_Yp, _Del>>>
395 shared_ptr(unique_ptr<_Yp, _Del>&& __r)
396 : __shared_ptr<_Tp>(std::move(__r)) { }
397
398 #if __cplusplus <= 201402L && _GLIBCXX_USE_DEPRECATED
399 // This non-standard constructor exists to support conversions that
400 // were possible in C++11 and C++14 but are ill-formed in C++17.
401 // If an exception is thrown this constructor has no effect.
402 template<typename _Yp, typename _Del,
403 _Constructible<unique_ptr<_Yp, _Del>, __sp_array_delete>* = 0>
404 shared_ptr(unique_ptr<_Yp, _Del>&& __r)
405 : __shared_ptr<_Tp>(std::move(__r), __sp_array_delete()) { }
406 #endif
407
408 /**
409 * @brief Construct an empty %shared_ptr.
410 * @post use_count() == 0 && get() == nullptr
411 */
412 constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
413
414 shared_ptr& operator=(const shared_ptr&) noexcept = default;
415
416 template<typename _Yp>
417 _Assignable<const shared_ptr<_Yp>&>
418 operator=(const shared_ptr<_Yp>& __r) noexcept
419 {
420 this->__shared_ptr<_Tp>::operator=(__r);
421 return *this;
422 }
423
424 #if _GLIBCXX_USE_DEPRECATED
425 #pragma GCC diagnostic push
426 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
427 template<typename _Yp>
428 _Assignable<auto_ptr<_Yp>>
429 operator=(auto_ptr<_Yp>&& __r)
430 {
431 this->__shared_ptr<_Tp>::operator=(std::move(__r));
432 return *this;
433 }
434 #pragma GCC diagnostic pop
435 #endif
436
437 shared_ptr&
438 operator=(shared_ptr&& __r) noexcept
439 {
440 this->__shared_ptr<_Tp>::operator=(std::move(__r));
441 return *this;
442 }
443
444 template<class _Yp>
445 _Assignable<shared_ptr<_Yp>>
446 operator=(shared_ptr<_Yp>&& __r) noexcept
447 {
448 this->__shared_ptr<_Tp>::operator=(std::move(__r));
449 return *this;
450 }
451
452 template<typename _Yp, typename _Del>
453 _Assignable<unique_ptr<_Yp, _Del>>
454 operator=(unique_ptr<_Yp, _Del>&& __r)
455 {
456 this->__shared_ptr<_Tp>::operator=(std::move(__r));
457 return *this;
458 }
459
460 private:
461 // This constructor is non-standard, it is used by allocate_shared.
462 template<typename _Alloc, typename... _Args>
463 shared_ptr(_Sp_alloc_shared_tag<_Alloc> __tag, _Args&&... __args)
464 : __shared_ptr<_Tp>(__tag, std::forward<_Args>(__args)...)
465 { }
466
467 template<typename _Yp, typename _Alloc, typename... _Args>
468 friend shared_ptr<_NonArray<_Yp>>
469 allocate_shared(const _Alloc&, _Args&&...);
470
471 template<typename _Yp, typename... _Args>
472 friend shared_ptr<_NonArray<_Yp>>
473 make_shared(_Args&&...);
474
475 #if __cpp_lib_shared_ptr_arrays >= 201707L
476 // This constructor is non-standard, it is used by allocate_shared<T[]>.
477 template<typename _Alloc, typename _Init = const remove_extent_t<_Tp>*>
478 shared_ptr(const _Sp_counted_array_base<_Alloc>& __a,
479 _Init __init = nullptr)
480 : __shared_ptr<_Tp>(__a, __init)
481 { }
482
483 template<typename _Yp, typename _Alloc>
484 friend shared_ptr<_UnboundedArray<_Yp>>
485 allocate_shared(const _Alloc&, size_t);
486
487 template<typename _Yp>
488 friend shared_ptr<_UnboundedArray<_Yp>>
489 make_shared(size_t);
490
491 template<typename _Yp, typename _Alloc>
492 friend shared_ptr<_UnboundedArray<_Yp>>
493 allocate_shared(const _Alloc&, size_t, const remove_extent_t<_Yp>&);
494
495 template<typename _Yp>
496 friend shared_ptr<_UnboundedArray<_Yp>>
497 make_shared(size_t, const remove_extent_t<_Yp>&);
498
499 template<typename _Yp, typename _Alloc>
500 friend shared_ptr<_BoundedArray<_Yp>>
501 allocate_shared(const _Alloc&);
502
503 template<typename _Yp>
504 friend shared_ptr<_BoundedArray<_Yp>>
505 make_shared();
506
507 template<typename _Yp, typename _Alloc>
508 friend shared_ptr<_BoundedArray<_Yp>>
509 allocate_shared(const _Alloc&, const remove_extent_t<_Yp>&);
510
511 template<typename _Yp>
512 friend shared_ptr<_BoundedArray<_Yp>>
513 make_shared(const remove_extent_t<_Yp>&);
514
515 #if __cpp_lib_smart_ptr_for_overwrite
516 template<typename _Yp, typename _Alloc>
517 friend shared_ptr<_NotUnboundedArray<_Yp>>
518 allocate_shared_for_overwrite(const _Alloc&);
519
520 template<typename _Yp>
521 friend shared_ptr<_NotUnboundedArray<_Yp>>
522 make_shared_for_overwrite();
523
524 template<typename _Yp, typename _Alloc>
525 friend shared_ptr<_UnboundedArray<_Yp>>
526 allocate_shared_for_overwrite(const _Alloc&, size_t);
527
528 template<typename _Yp>
529 friend shared_ptr<_UnboundedArray<_Yp>>
530 make_shared_for_overwrite(size_t);
531 #endif
532 #endif
533
534 // This constructor is non-standard, it is used by weak_ptr::lock().
535 shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t) noexcept
536 : __shared_ptr<_Tp>(__r, std::nothrow) { }
537
538 friend class weak_ptr<_Tp>;
539 };
540
541 #if __cpp_deduction_guides >= 201606
542 template<typename _Tp>
543 shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
544 template<typename _Tp, typename _Del>
545 shared_ptr(unique_ptr<_Tp, _Del>) -> shared_ptr<_Tp>;
546 #endif
547
548 // 20.7.2.2.7 shared_ptr comparisons
549
550 /// @relates shared_ptr @{
551
552 /// Equality operator for shared_ptr objects, compares the stored pointers
553 template<typename _Tp, typename _Up>
554 _GLIBCXX_NODISCARD inline bool
555 operator==(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
556 { return __a.get() == __b.get(); }
557
558 /// shared_ptr comparison with nullptr
559 template<typename _Tp>
560 _GLIBCXX_NODISCARD inline bool
561 operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
562 { return !__a; }
563
564 #ifdef __cpp_lib_three_way_comparison
565 template<typename _Tp, typename _Up>
566 inline strong_ordering
567 operator<=>(const shared_ptr<_Tp>& __a,
568 const shared_ptr<_Up>& __b) noexcept
569 { return compare_three_way()(__a.get(), __b.get()); }
570
571 template<typename _Tp>
572 inline strong_ordering
573 operator<=>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
574 {
575 using pointer = typename shared_ptr<_Tp>::element_type*;
576 return compare_three_way()(__a.get(), static_cast<pointer>(nullptr));
577 }
578 #else
579 /// shared_ptr comparison with nullptr
580 template<typename _Tp>
581 _GLIBCXX_NODISCARD inline bool
582 operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
583 { return !__a; }
584
585 /// Inequality operator for shared_ptr objects, compares the stored pointers
586 template<typename _Tp, typename _Up>
587 _GLIBCXX_NODISCARD inline bool
588 operator!=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
589 { return __a.get() != __b.get(); }
590
591 /// shared_ptr comparison with nullptr
592 template<typename _Tp>
593 _GLIBCXX_NODISCARD inline bool
594 operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
595 { return (bool)__a; }
596
597 /// shared_ptr comparison with nullptr
598 template<typename _Tp>
599 _GLIBCXX_NODISCARD inline bool
600 operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
601 { return (bool)__a; }
602
603 /// Relational operator for shared_ptr objects, compares the stored pointers
604 template<typename _Tp, typename _Up>
605 _GLIBCXX_NODISCARD inline bool
606 operator<(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
607 {
608 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
609 using _Up_elt = typename shared_ptr<_Up>::element_type;
610 using _Vp = typename common_type<_Tp_elt*, _Up_elt*>::type;
611 return less<_Vp>()(__a.get(), __b.get());
612 }
613
614 /// shared_ptr comparison with nullptr
615 template<typename _Tp>
616 _GLIBCXX_NODISCARD inline bool
617 operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
618 {
619 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
620 return less<_Tp_elt*>()(__a.get(), nullptr);
621 }
622
623 /// shared_ptr comparison with nullptr
624 template<typename _Tp>
625 _GLIBCXX_NODISCARD inline bool
626 operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
627 {
628 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
629 return less<_Tp_elt*>()(nullptr, __a.get());
630 }
631
632 /// Relational operator for shared_ptr objects, compares the stored pointers
633 template<typename _Tp, typename _Up>
634 _GLIBCXX_NODISCARD inline bool
635 operator<=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
636 { return !(__b < __a); }
637
638 /// shared_ptr comparison with nullptr
639 template<typename _Tp>
640 _GLIBCXX_NODISCARD inline bool
641 operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
642 { return !(nullptr < __a); }
643
644 /// shared_ptr comparison with nullptr
645 template<typename _Tp>
646 _GLIBCXX_NODISCARD inline bool
647 operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
648 { return !(__a < nullptr); }
649
650 /// Relational operator for shared_ptr objects, compares the stored pointers
651 template<typename _Tp, typename _Up>
652 _GLIBCXX_NODISCARD inline bool
653 operator>(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
654 { return (__b < __a); }
655
656 /// shared_ptr comparison with nullptr
657 template<typename _Tp>
658 _GLIBCXX_NODISCARD inline bool
659 operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
660 { return nullptr < __a; }
661
662 /// shared_ptr comparison with nullptr
663 template<typename _Tp>
664 _GLIBCXX_NODISCARD inline bool
665 operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
666 { return __a < nullptr; }
667
668 /// Relational operator for shared_ptr objects, compares the stored pointers
669 template<typename _Tp, typename _Up>
670 _GLIBCXX_NODISCARD inline bool
671 operator>=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
672 { return !(__a < __b); }
673
674 /// shared_ptr comparison with nullptr
675 template<typename _Tp>
676 _GLIBCXX_NODISCARD inline bool
677 operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
678 { return !(__a < nullptr); }
679
680 /// shared_ptr comparison with nullptr
681 template<typename _Tp>
682 _GLIBCXX_NODISCARD inline bool
683 operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
684 { return !(nullptr < __a); }
685 #endif
686
687 // 20.7.2.2.8 shared_ptr specialized algorithms.
688
689 /// Swap overload for shared_ptr
690 template<typename _Tp>
691 inline void
692 swap(shared_ptr<_Tp>& __a, shared_ptr<_Tp>& __b) noexcept
693 { __a.swap(__b); }
694
695 // 20.7.2.2.9 shared_ptr casts.
696
697 /// Convert type of `shared_ptr`, via `static_cast`
698 template<typename _Tp, typename _Up>
699 inline shared_ptr<_Tp>
700 static_pointer_cast(const shared_ptr<_Up>& __r) noexcept
701 {
702 using _Sp = shared_ptr<_Tp>;
703 return _Sp(__r, static_cast<typename _Sp::element_type*>(__r.get()));
704 }
705
706 /// Convert type of `shared_ptr`, via `const_cast`
707 template<typename _Tp, typename _Up>
708 inline shared_ptr<_Tp>
709 const_pointer_cast(const shared_ptr<_Up>& __r) noexcept
710 {
711 using _Sp = shared_ptr<_Tp>;
712 return _Sp(__r, const_cast<typename _Sp::element_type*>(__r.get()));
713 }
714
715 /// Convert type of `shared_ptr`, via `dynamic_cast`
716 template<typename _Tp, typename _Up>
717 inline shared_ptr<_Tp>
718 dynamic_pointer_cast(const shared_ptr<_Up>& __r) noexcept
719 {
720 using _Sp = shared_ptr<_Tp>;
721 if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
722 return _Sp(__r, __p);
723 return _Sp();
724 }
725
726 #if __cplusplus >= 201703L
727 /// Convert type of `shared_ptr`, via `reinterpret_cast`
728 /// @since C++17
729 template<typename _Tp, typename _Up>
730 inline shared_ptr<_Tp>
731 reinterpret_pointer_cast(const shared_ptr<_Up>& __r) noexcept
732 {
733 using _Sp = shared_ptr<_Tp>;
734 return _Sp(__r, reinterpret_cast<typename _Sp::element_type*>(__r.get()));
735 }
736
737 #if __cplusplus > 201703L
738 // _GLIBCXX_RESOLVE_LIB_DEFECTS
739 // 2996. Missing rvalue overloads for shared_ptr operations
740
741 /// Convert type of `shared_ptr` rvalue, via `static_cast`
742 /// @since C++20
743 template<typename _Tp, typename _Up>
744 inline shared_ptr<_Tp>
745 static_pointer_cast(shared_ptr<_Up>&& __r) noexcept
746 {
747 using _Sp = shared_ptr<_Tp>;
748 return _Sp(std::move(__r),
749 static_cast<typename _Sp::element_type*>(__r.get()));
750 }
751
752 /// Convert type of `shared_ptr` rvalue, via `const_cast`
753 /// @since C++20
754 template<typename _Tp, typename _Up>
755 inline shared_ptr<_Tp>
756 const_pointer_cast(shared_ptr<_Up>&& __r) noexcept
757 {
758 using _Sp = shared_ptr<_Tp>;
759 return _Sp(std::move(__r),
760 const_cast<typename _Sp::element_type*>(__r.get()));
761 }
762
763 /// Convert type of `shared_ptr` rvalue, via `dynamic_cast`
764 /// @since C++20
765 template<typename _Tp, typename _Up>
766 inline shared_ptr<_Tp>
767 dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept
768 {
769 using _Sp = shared_ptr<_Tp>;
770 if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
771 return _Sp(std::move(__r), __p);
772 return _Sp();
773 }
774
775 /// Convert type of `shared_ptr` rvalue, via `reinterpret_cast`
776 /// @since C++20
777 template<typename _Tp, typename _Up>
778 inline shared_ptr<_Tp>
779 reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept
780 {
781 using _Sp = shared_ptr<_Tp>;
782 return _Sp(std::move(__r),
783 reinterpret_cast<typename _Sp::element_type*>(__r.get()));
784 }
785 #endif // C++20
786 #endif // C++17
787
788 /// @}
789
790 /**
791 * @brief A non-owning observer for a pointer owned by a shared_ptr
792 * @headerfile memory
793 * @since C++11
794 *
795 * A weak_ptr provides a safe alternative to a raw pointer when you want
796 * a non-owning reference to an object that is managed by a shared_ptr.
797 *
798 * Unlike a raw pointer, a weak_ptr can be converted to a new shared_ptr
799 * that shares ownership with every other shared_ptr that already owns
800 * the pointer. In other words you can upgrade from a non-owning "weak"
801 * reference to an owning shared_ptr, without having access to any of
802 * the existing shared_ptr objects.
803 *
804 * Also unlike a raw pointer, a weak_ptr does not become "dangling" after
805 * the object it points to has been destroyed. Instead, a weak_ptr
806 * becomes _expired_ and can no longer be converted to a shared_ptr that
807 * owns the freed pointer, so you cannot accidentally access the pointed-to
808 * object after it has been destroyed.
809 */
810 template<typename _Tp>
811 class weak_ptr : public __weak_ptr<_Tp>
812 {
813 template<typename _Arg>
814 using _Constructible = typename enable_if<
815 is_constructible<__weak_ptr<_Tp>, _Arg>::value
816 >::type;
817
818 template<typename _Arg>
819 using _Assignable = typename enable_if<
820 is_assignable<__weak_ptr<_Tp>&, _Arg>::value, weak_ptr&
821 >::type;
822
823 public:
824 constexpr weak_ptr() noexcept = default;
825
826 template<typename _Yp,
827 typename = _Constructible<const shared_ptr<_Yp>&>>
828 weak_ptr(const shared_ptr<_Yp>& __r) noexcept
829 : __weak_ptr<_Tp>(__r) { }
830
831 weak_ptr(const weak_ptr&) noexcept = default;
832
833 template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
834 weak_ptr(const weak_ptr<_Yp>& __r) noexcept
835 : __weak_ptr<_Tp>(__r) { }
836
837 weak_ptr(weak_ptr&&) noexcept = default;
838
839 template<typename _Yp, typename = _Constructible<weak_ptr<_Yp>>>
840 weak_ptr(weak_ptr<_Yp>&& __r) noexcept
841 : __weak_ptr<_Tp>(std::move(__r)) { }
842
843 weak_ptr&
844 operator=(const weak_ptr& __r) noexcept = default;
845
846 template<typename _Yp>
847 _Assignable<const weak_ptr<_Yp>&>
848 operator=(const weak_ptr<_Yp>& __r) noexcept
849 {
850 this->__weak_ptr<_Tp>::operator=(__r);
851 return *this;
852 }
853
854 template<typename _Yp>
855 _Assignable<const shared_ptr<_Yp>&>
856 operator=(const shared_ptr<_Yp>& __r) noexcept
857 {
858 this->__weak_ptr<_Tp>::operator=(__r);
859 return *this;
860 }
861
862 weak_ptr&
863 operator=(weak_ptr&& __r) noexcept = default;
864
865 template<typename _Yp>
866 _Assignable<weak_ptr<_Yp>>
867 operator=(weak_ptr<_Yp>&& __r) noexcept
868 {
869 this->__weak_ptr<_Tp>::operator=(std::move(__r));
870 return *this;
871 }
872
873 shared_ptr<_Tp>
874 lock() const noexcept
875 { return shared_ptr<_Tp>(*this, std::nothrow); }
876 };
877
878 #if __cpp_deduction_guides >= 201606
879 template<typename _Tp>
880 weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
881 #endif
882
883 // 20.7.2.3.6 weak_ptr specialized algorithms.
884 /// Swap overload for weak_ptr
885 /// @relates weak_ptr
886 template<typename _Tp>
887 inline void
888 swap(weak_ptr<_Tp>& __a, weak_ptr<_Tp>& __b) noexcept
889 { __a.swap(__b); }
890
891
892 /// Primary template owner_less
893 template<typename _Tp = void>
894 struct owner_less;
895
896 /// Void specialization of owner_less compares either shared_ptr or weak_ptr
897 template<>
898 struct owner_less<void> : _Sp_owner_less<void, void>
899 { };
900
901 /// Partial specialization of owner_less for shared_ptr.
902 template<typename _Tp>
903 struct owner_less<shared_ptr<_Tp>>
904 : public _Sp_owner_less<shared_ptr<_Tp>, weak_ptr<_Tp>>
905 { };
906
907 /// Partial specialization of owner_less for weak_ptr.
908 template<typename _Tp>
909 struct owner_less<weak_ptr<_Tp>>
910 : public _Sp_owner_less<weak_ptr<_Tp>, shared_ptr<_Tp>>
911 { };
912
913 /**
914 * @brief Base class allowing use of the member function `shared_from_this`.
915 * @headerfile memory
916 * @since C++11
917 */
918 template<typename _Tp>
919 class enable_shared_from_this
920 {
921 protected:
922 constexpr enable_shared_from_this() noexcept { }
923
924 enable_shared_from_this(const enable_shared_from_this&) noexcept { }
925
926 enable_shared_from_this&
927 operator=(const enable_shared_from_this&) noexcept
928 { return *this; }
929
930 ~enable_shared_from_this() { }
931
932 public:
933 shared_ptr<_Tp>
934 shared_from_this()
935 { return shared_ptr<_Tp>(this->_M_weak_this); }
936
937 shared_ptr<const _Tp>
938 shared_from_this() const
939 { return shared_ptr<const _Tp>(this->_M_weak_this); }
940
941 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
942 #define __cpp_lib_enable_shared_from_this 201603L
943 /** @{
944 * Get a `weak_ptr` referring to the object that has `*this` as its base.
945 * @since C++17
946 */
947 weak_ptr<_Tp>
948 weak_from_this() noexcept
949 { return this->_M_weak_this; }
950
951 weak_ptr<const _Tp>
952 weak_from_this() const noexcept
953 { return this->_M_weak_this; }
954 /// @}
955 #endif
956
957 private:
958 template<typename _Tp1>
959 void
960 _M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
961 { _M_weak_this._M_assign(__p, __n); }
962
963 // Found by ADL when this is an associated class.
964 friend const enable_shared_from_this*
965 __enable_shared_from_this_base(const __shared_count<>&,
966 const enable_shared_from_this* __p)
967 { return __p; }
968
969 template<typename, _Lock_policy>
970 friend class __shared_ptr;
971
972 mutable weak_ptr<_Tp> _M_weak_this;
973 };
974
975 /// @relates shared_ptr @{
976
977 /**
978 * @brief Create an object that is owned by a shared_ptr.
979 * @param __a An allocator.
980 * @param __args Arguments for the @a _Tp object's constructor.
981 * @return A shared_ptr that owns the newly created object.
982 * @throw An exception thrown from @a _Alloc::allocate or from the
983 * constructor of @a _Tp.
984 *
985 * A copy of @a __a will be used to allocate memory for the shared_ptr
986 * and the new object.
987 */
988 template<typename _Tp, typename _Alloc, typename... _Args>
989 inline shared_ptr<_NonArray<_Tp>>
990 allocate_shared(const _Alloc& __a, _Args&&... __args)
991 {
992 return shared_ptr<_Tp>(_Sp_alloc_shared_tag<_Alloc>{__a},
993 std::forward<_Args>(__args)...);
994 }
995
996 /**
997 * @brief Create an object that is owned by a shared_ptr.
998 * @param __args Arguments for the @a _Tp object's constructor.
999 * @return A shared_ptr that owns the newly created object.
1000 * @throw std::bad_alloc, or an exception thrown from the
1001 * constructor of @a _Tp.
1002 */
1003 template<typename _Tp, typename... _Args>
1004 inline shared_ptr<_NonArray<_Tp>>
1005 make_shared(_Args&&... __args)
1006 {
1007 using _Alloc = allocator<void>;
1008 _Alloc __a;
1009 return shared_ptr<_Tp>(_Sp_alloc_shared_tag<_Alloc>{__a},
1010 std::forward<_Args>(__args)...);
1011 }
1012
1013 #if __cpp_lib_shared_ptr_arrays >= 201707L
1014 /// @cond undocumented
1015 template<typename _Tp, typename _Alloc = allocator<void>>
1016 auto
1017 __make_shared_arr_tag(size_t __n, const _Alloc& __a = _Alloc()) noexcept
1018 {
1019 using _Up = remove_all_extents_t<_Tp>;
1020 using _UpAlloc = __alloc_rebind<_Alloc, _Up>;
1021 size_t __s = sizeof(remove_extent_t<_Tp>) / sizeof(_Up);
1022 if (__builtin_mul_overflow(__s, __n, &__n))
1023 std::__throw_bad_array_new_length();
1024 return _Sp_counted_array_base<_UpAlloc>{_UpAlloc(__a), __n};
1025 }
1026 /// @endcond
1027
1028 template<typename _Tp, typename _Alloc>
1029 inline shared_ptr<_UnboundedArray<_Tp>>
1030 allocate_shared(const _Alloc& __a, size_t __n)
1031 {
1032 return shared_ptr<_Tp>(std::__make_shared_arr_tag<_Tp>(__n, __a));
1033 }
1034
1035 template<typename _Tp>
1036 inline shared_ptr<_UnboundedArray<_Tp>>
1037 make_shared(size_t __n)
1038 {
1039 return shared_ptr<_Tp>(std::__make_shared_arr_tag<_Tp>(__n));
1040 }
1041
1042 template<typename _Tp, typename _Alloc>
1043 inline shared_ptr<_UnboundedArray<_Tp>>
1044 allocate_shared(const _Alloc& __a, size_t __n,
1045 const remove_extent_t<_Tp>& __u)
1046 {
1047 return shared_ptr<_Tp>(std::__make_shared_arr_tag<_Tp>(__n, __a),
1048 std::__addressof(__u));
1049 }
1050
1051 template<typename _Tp>
1052 inline shared_ptr<_UnboundedArray<_Tp>>
1053 make_shared(size_t __n, const remove_extent_t<_Tp>& __u)
1054 {
1055 return shared_ptr<_Tp>(std::__make_shared_arr_tag<_Tp>(__n),
1056 std::__addressof(__u));
1057 }
1058
1059 /// @cond undocumented
1060 template<typename _Tp, typename _Alloc = allocator<void>>
1061 auto
1062 __make_shared_arrN_tag(const _Alloc& __a = _Alloc()) noexcept
1063 {
1064 using _Up = remove_all_extents_t<_Tp>;
1065 using _UpAlloc = __alloc_rebind<_Alloc, _Up>;
1066 size_t __n = sizeof(_Tp) / sizeof(_Up);
1067 return _Sp_counted_array_base<_UpAlloc>{_UpAlloc(__a), __n};
1068 }
1069 /// @endcond
1070
1071 template<typename _Tp, typename _Alloc>
1072 inline shared_ptr<_BoundedArray<_Tp>>
1073 allocate_shared(const _Alloc& __a)
1074 {
1075 return shared_ptr<_Tp>(std::__make_shared_arrN_tag<_Tp>(__a));
1076 }
1077
1078 template<typename _Tp>
1079 inline shared_ptr<_BoundedArray<_Tp>>
1080 make_shared()
1081 {
1082 return shared_ptr<_Tp>(std::__make_shared_arrN_tag<_Tp>());
1083 }
1084
1085 template<typename _Tp, typename _Alloc>
1086 inline shared_ptr<_BoundedArray<_Tp>>
1087 allocate_shared(const _Alloc& __a, const remove_extent_t<_Tp>& __u)
1088 {
1089 return shared_ptr<_Tp>(std::__make_shared_arrN_tag<_Tp>(__a),
1090 std::__addressof(__u));
1091 }
1092
1093 template<typename _Tp>
1094 inline shared_ptr<_BoundedArray<_Tp>>
1095 make_shared(const remove_extent_t<_Tp>& __u)
1096 {
1097 return shared_ptr<_Tp>(std::__make_shared_arrN_tag<_Tp>(),
1098 std::__addressof(__u));
1099 }
1100
1101 #if __cpp_lib_smart_ptr_for_overwrite
1102 template<typename _Tp, typename _Alloc>
1103 inline shared_ptr<_NotUnboundedArray<_Tp>>
1104 allocate_shared_for_overwrite(const _Alloc& __a)
1105 {
1106 if constexpr (is_array_v<_Tp>)
1107 return shared_ptr<_Tp>(std::__make_shared_arrN_tag<_Tp>(__a),
1108 _Sp_overwrite_tag{});
1109 else
1110 {
1111 // Rebind the allocator to _Sp_overwrite_tag, so that the
1112 // relevant _Sp_counted_ptr_inplace specialization is used.
1113 using _Alloc2 = __alloc_rebind<_Alloc, _Sp_overwrite_tag>;
1114 _Alloc2 __a2 = __a;
1115 return shared_ptr<_Tp>(_Sp_alloc_shared_tag<_Alloc2>{__a2});
1116 }
1117 }
1118
1119 template<typename _Tp>
1120 inline shared_ptr<_NotUnboundedArray<_Tp>>
1121 make_shared_for_overwrite()
1122 {
1123 if constexpr (is_array_v<_Tp>)
1124 return shared_ptr<_Tp>(std::__make_shared_arrN_tag<_Tp>(),
1125 _Sp_overwrite_tag{});
1126 else
1127 {
1128 using _Alloc = allocator<_Sp_overwrite_tag>;
1129 return shared_ptr<_Tp>(_Sp_alloc_shared_tag<_Alloc>{{}});
1130 }
1131 }
1132
1133 template<typename _Tp, typename _Alloc>
1134 inline shared_ptr<_UnboundedArray<_Tp>>
1135 allocate_shared_for_overwrite(const _Alloc& __a, size_t __n)
1136 {
1137 return shared_ptr<_Tp>(std::__make_shared_arr_tag<_Tp>(__n, __a),
1138 _Sp_overwrite_tag{});
1139 }
1140
1141 template<typename _Tp>
1142 inline shared_ptr<_UnboundedArray<_Tp>>
1143 make_shared_for_overwrite(size_t __n)
1144 {
1145 return shared_ptr<_Tp>(std::__make_shared_arr_tag<_Tp>(__n),
1146 _Sp_overwrite_tag{});
1147 }
1148 #endif // smart_ptr_for_overwrite
1149 #endif // shared_ptr_arrays
1150
1151 /// std::hash specialization for shared_ptr.
1152 template<typename _Tp>
1153 struct hash<shared_ptr<_Tp>>
1154 : public __hash_base<size_t, shared_ptr<_Tp>>
1155 {
1156 size_t
1157 operator()(const shared_ptr<_Tp>& __s) const noexcept
1158 {
1159 return std::hash<typename shared_ptr<_Tp>::element_type*>()(__s.get());
1160 }
1161 };
1162
1163 /// @} relates shared_ptr
1164 /// @} group pointer_abstractions
1165
1166 #if __cplusplus >= 201703L
1167 namespace __detail::__variant
1168 {
1169 template<typename> struct _Never_valueless_alt; // see <variant>
1170
1171 // Provide the strong exception-safety guarantee when emplacing a
1172 // shared_ptr into a variant.
1173 template<typename _Tp>
1174 struct _Never_valueless_alt<std::shared_ptr<_Tp>>
1175 : std::true_type
1176 { };
1177
1178 // Provide the strong exception-safety guarantee when emplacing a
1179 // weak_ptr into a variant.
1180 template<typename _Tp>
1181 struct _Never_valueless_alt<std::weak_ptr<_Tp>>
1182 : std::true_type
1183 { };
1184 } // namespace __detail::__variant
1185 #endif // C++17
1186
1187 _GLIBCXX_END_NAMESPACE_VERSION
1188 } // namespace
1189
1190 #endif // _SHARED_PTR_H