1 // shared_ptr and weak_ptr implementation -*- C++ -*-
2
3 // Copyright (C) 2007-2017 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24
25 // GCC Note: Based on files from version 1.32.0 of the Boost library.
26
27 // shared_count.hpp
28 // Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
29
30 // shared_ptr.hpp
31 // Copyright (C) 1998, 1999 Greg Colvin and Beman Dawes.
32 // Copyright (C) 2001, 2002, 2003 Peter Dimov
33
34 // weak_ptr.hpp
35 // Copyright (C) 2001, 2002, 2003 Peter Dimov
36
37 // enable_shared_from_this.hpp
38 // Copyright (C) 2002 Peter Dimov
39
40 // Distributed under the Boost Software License, Version 1.0. (See
41 // accompanying file LICENSE_1_0.txt or copy at
42 // http://www.boost.org/LICENSE_1_0.txt)
43
44 /** @file
45 * This is an internal header file, included by other library headers.
46 * Do not attempt to use it directly. @headername{memory}
47 */
48
49 #ifndef _SHARED_PTR_H
50 #define _SHARED_PTR_H 1
51
52 #include <bits/shared_ptr_base.h>
53
_GLIBCXX_VISIBILITY(default)54 namespace std _GLIBCXX_VISIBILITY(default)
55 {
56 _GLIBCXX_BEGIN_NAMESPACE_VERSION
57
58 /**
59 * @addtogroup pointer_abstractions
60 * @{
61 */
62
63 /// 20.7.2.2.11 shared_ptr I/O
64 template<typename _Ch, typename _Tr, typename _Tp, _Lock_policy _Lp>
65 inline std::basic_ostream<_Ch, _Tr>&
66 operator<<(std::basic_ostream<_Ch, _Tr>& __os,
67 const __shared_ptr<_Tp, _Lp>& __p)
68 {
69 __os << __p.get();
70 return __os;
71 }
72
73 /// 20.7.2.2.10 shared_ptr get_deleter
74 template<typename _Del, typename _Tp, _Lock_policy _Lp>
75 inline _Del*
76 get_deleter(const __shared_ptr<_Tp, _Lp>& __p) noexcept
77 {
78 #if __cpp_rtti
79 return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del)));
80 #else
81 return 0;
82 #endif
83 }
84
85
86 /**
87 * @brief A smart pointer with reference-counted copy semantics.
88 *
89 * The object pointed to is deleted when the last shared_ptr pointing to
90 * it is destroyed or reset.
91 */
92 template<typename _Tp>
93 class shared_ptr : public __shared_ptr<_Tp>
94 {
95 template<typename... _Args>
96 using _Constructible = typename enable_if<
97 is_constructible<__shared_ptr<_Tp>, _Args...>::value
98 >::type;
99
100 template<typename _Arg>
101 using _Assignable = typename enable_if<
102 is_assignable<__shared_ptr<_Tp>&, _Arg>::value, shared_ptr&
103 >::type;
104
105 public:
106
107 using element_type = typename __shared_ptr<_Tp>::element_type;
108
109 #if __cplusplus > 201402L
110 # define __cpp_lib_shared_ptr_weak_type 201606
111 using weak_type = weak_ptr<_Tp>;
112 #endif
113 /**
114 * @brief Construct an empty %shared_ptr.
115 * @post use_count()==0 && get()==0
116 */
117 constexpr shared_ptr() noexcept : __shared_ptr<_Tp>() { }
118
119 shared_ptr(const shared_ptr&) noexcept = default;
120
121 /**
122 * @brief Construct a %shared_ptr that owns the pointer @a __p.
123 * @param __p A pointer that is convertible to element_type*.
124 * @post use_count() == 1 && get() == __p
125 * @throw std::bad_alloc, in which case @c delete @a __p is called.
126 */
127 template<typename _Yp, typename = _Constructible<_Yp*>>
128 explicit
129 shared_ptr(_Yp* __p) : __shared_ptr<_Tp>(__p) { }
130
131 /**
132 * @brief Construct a %shared_ptr that owns the pointer @a __p
133 * and the deleter @a __d.
134 * @param __p A pointer.
135 * @param __d A deleter.
136 * @post use_count() == 1 && get() == __p
137 * @throw std::bad_alloc, in which case @a __d(__p) is called.
138 *
139 * Requirements: _Deleter's copy constructor and destructor must
140 * not throw
141 *
142 * __shared_ptr will release __p by calling __d(__p)
143 */
144 template<typename _Yp, typename _Deleter,
145 typename = _Constructible<_Yp*, _Deleter>>
146 shared_ptr(_Yp* __p, _Deleter __d)
147 : __shared_ptr<_Tp>(__p, std::move(__d)) { }
148
149 /**
150 * @brief Construct a %shared_ptr that owns a null pointer
151 * and the deleter @a __d.
152 * @param __p A null pointer constant.
153 * @param __d A deleter.
154 * @post use_count() == 1 && get() == __p
155 * @throw std::bad_alloc, in which case @a __d(__p) is called.
156 *
157 * Requirements: _Deleter's copy constructor and destructor must
158 * not throw
159 *
160 * The last owner will call __d(__p)
161 */
162 template<typename _Deleter>
163 shared_ptr(nullptr_t __p, _Deleter __d)
164 : __shared_ptr<_Tp>(__p, std::move(__d)) { }
165
166 /**
167 * @brief Construct a %shared_ptr that owns the pointer @a __p
168 * and the deleter @a __d.
169 * @param __p A pointer.
170 * @param __d A deleter.
171 * @param __a An allocator.
172 * @post use_count() == 1 && get() == __p
173 * @throw std::bad_alloc, in which case @a __d(__p) is called.
174 *
175 * Requirements: _Deleter's copy constructor and destructor must
176 * not throw _Alloc's copy constructor and destructor must not
177 * throw.
178 *
179 * __shared_ptr will release __p by calling __d(__p)
180 */
181 template<typename _Yp, typename _Deleter, typename _Alloc,
182 typename = _Constructible<_Yp*, _Deleter, _Alloc>>
183 shared_ptr(_Yp* __p, _Deleter __d, _Alloc __a)
184 : __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
185
186 /**
187 * @brief Construct a %shared_ptr that owns a null pointer
188 * and the deleter @a __d.
189 * @param __p A null pointer constant.
190 * @param __d A deleter.
191 * @param __a An allocator.
192 * @post use_count() == 1 && get() == __p
193 * @throw std::bad_alloc, in which case @a __d(__p) is called.
194 *
195 * Requirements: _Deleter's copy constructor and destructor must
196 * not throw _Alloc's copy constructor and destructor must not
197 * throw.
198 *
199 * The last owner will call __d(__p)
200 */
201 template<typename _Deleter, typename _Alloc>
202 shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
203 : __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
204
205 // Aliasing constructor
206
207 /**
208 * @brief Constructs a %shared_ptr instance that stores @a __p
209 * and shares ownership with @a __r.
210 * @param __r A %shared_ptr.
211 * @param __p A pointer that will remain valid while @a *__r is valid.
212 * @post get() == __p && use_count() == __r.use_count()
213 *
214 * This can be used to construct a @c shared_ptr to a sub-object
215 * of an object managed by an existing @c shared_ptr.
216 *
217 * @code
218 * shared_ptr< pair<int,int> > pii(new pair<int,int>());
219 * shared_ptr<int> pi(pii, &pii->first);
220 * assert(pii.use_count() == 2);
221 * @endcode
222 */
223 template<typename _Yp>
224 shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) noexcept
225 : __shared_ptr<_Tp>(__r, __p) { }
226
227 /**
228 * @brief If @a __r is empty, constructs an empty %shared_ptr;
229 * otherwise construct a %shared_ptr that shares ownership
230 * with @a __r.
231 * @param __r A %shared_ptr.
232 * @post get() == __r.get() && use_count() == __r.use_count()
233 */
234 template<typename _Yp,
235 typename = _Constructible<const shared_ptr<_Yp>&>>
236 shared_ptr(const shared_ptr<_Yp>& __r) noexcept
237 : __shared_ptr<_Tp>(__r) { }
238
239 /**
240 * @brief Move-constructs a %shared_ptr instance from @a __r.
241 * @param __r A %shared_ptr rvalue.
242 * @post *this contains the old value of @a __r, @a __r is empty.
243 */
244 shared_ptr(shared_ptr&& __r) noexcept
245 : __shared_ptr<_Tp>(std::move(__r)) { }
246
247 /**
248 * @brief Move-constructs a %shared_ptr instance from @a __r.
249 * @param __r A %shared_ptr rvalue.
250 * @post *this contains the old value of @a __r, @a __r is empty.
251 */
252 template<typename _Yp, typename = _Constructible<shared_ptr<_Yp>>>
253 shared_ptr(shared_ptr<_Yp>&& __r) noexcept
254 : __shared_ptr<_Tp>(std::move(__r)) { }
255
256 /**
257 * @brief Constructs a %shared_ptr that shares ownership with @a __r
258 * and stores a copy of the pointer stored in @a __r.
259 * @param __r A weak_ptr.
260 * @post use_count() == __r.use_count()
261 * @throw bad_weak_ptr when __r.expired(),
262 * in which case the constructor has no effect.
263 */
264 template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
265 explicit shared_ptr(const weak_ptr<_Yp>& __r)
266 : __shared_ptr<_Tp>(__r) { }
267
268 #if _GLIBCXX_USE_DEPRECATED
269 template<typename _Yp, typename = _Constructible<auto_ptr<_Yp>>>
270 shared_ptr(auto_ptr<_Yp>&& __r);
271 #endif
272
273 // _GLIBCXX_RESOLVE_LIB_DEFECTS
274 // 2399. shared_ptr's constructor from unique_ptr should be constrained
275 template<typename _Yp, typename _Del,
276 typename = _Constructible<unique_ptr<_Yp, _Del>>>
277 shared_ptr(unique_ptr<_Yp, _Del>&& __r)
278 : __shared_ptr<_Tp>(std::move(__r)) { }
279
280 #if __cplusplus <= 201402L && _GLIBCXX_USE_DEPRECATED
281 // This non-standard constructor exists to support conversions that
282 // were possible in C++11 and C++14 but are ill-formed in C++17.
283 // If an exception is thrown this constructor has no effect.
284 template<typename _Yp, typename _Del,
285 _Constructible<unique_ptr<_Yp, _Del>, __sp_array_delete>* = 0>
286 shared_ptr(unique_ptr<_Yp, _Del>&& __r)
287 : __shared_ptr<_Tp>(std::move(__r), __sp_array_delete()) { }
288 #endif
289
290 /**
291 * @brief Construct an empty %shared_ptr.
292 * @post use_count() == 0 && get() == nullptr
293 */
294 constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
295
296 shared_ptr& operator=(const shared_ptr&) noexcept = default;
297
298 template<typename _Yp>
299 _Assignable<const shared_ptr<_Yp>&>
300 operator=(const shared_ptr<_Yp>& __r) noexcept
301 {
302 this->__shared_ptr<_Tp>::operator=(__r);
303 return *this;
304 }
305
306 #if _GLIBCXX_USE_DEPRECATED
307 template<typename _Yp>
308 _Assignable<auto_ptr<_Yp>>
309 operator=(auto_ptr<_Yp>&& __r)
310 {
311 this->__shared_ptr<_Tp>::operator=(std::move(__r));
312 return *this;
313 }
314 #endif
315
316 shared_ptr&
317 operator=(shared_ptr&& __r) noexcept
318 {
319 this->__shared_ptr<_Tp>::operator=(std::move(__r));
320 return *this;
321 }
322
323 template<class _Yp>
324 _Assignable<shared_ptr<_Yp>>
325 operator=(shared_ptr<_Yp>&& __r) noexcept
326 {
327 this->__shared_ptr<_Tp>::operator=(std::move(__r));
328 return *this;
329 }
330
331 template<typename _Yp, typename _Del>
332 _Assignable<unique_ptr<_Yp, _Del>>
333 operator=(unique_ptr<_Yp, _Del>&& __r)
334 {
335 this->__shared_ptr<_Tp>::operator=(std::move(__r));
336 return *this;
337 }
338
339 private:
340 // This constructor is non-standard, it is used by allocate_shared.
341 template<typename _Alloc, typename... _Args>
342 shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
343 _Args&&... __args)
344 : __shared_ptr<_Tp>(__tag, __a, std::forward<_Args>(__args)...)
345 { }
346
347 template<typename _Yp, typename _Alloc, typename... _Args>
348 friend shared_ptr<_Yp>
349 allocate_shared(const _Alloc& __a, _Args&&... __args);
350
351 // This constructor is non-standard, it is used by weak_ptr::lock().
352 shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t)
353 : __shared_ptr<_Tp>(__r, std::nothrow) { }
354
355 friend class weak_ptr<_Tp>;
356 };
357
358 #if __cpp_deduction_guides >= 201606
359 template<typename _Tp>
360 shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
361 template<typename _Tp, typename _Del>
362 shared_ptr(unique_ptr<_Tp, _Del>) -> shared_ptr<_Tp>;
363 #endif
364
365 // 20.7.2.2.7 shared_ptr comparisons
366 template<typename _Tp, typename _Up>
367 inline bool
368 operator==(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
369 { return __a.get() == __b.get(); }
370
371 template<typename _Tp>
372 inline bool
373 operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
374 { return !__a; }
375
376 template<typename _Tp>
377 inline bool
378 operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
379 { return !__a; }
380
381 template<typename _Tp, typename _Up>
382 inline bool
383 operator!=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
384 { return __a.get() != __b.get(); }
385
386 template<typename _Tp>
387 inline bool
388 operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
389 { return (bool)__a; }
390
391 template<typename _Tp>
392 inline bool
393 operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
394 { return (bool)__a; }
395
396 template<typename _Tp, typename _Up>
397 inline bool
398 operator<(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
399 {
400 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
401 using _Up_elt = typename shared_ptr<_Up>::element_type;
402 using _Vp = typename common_type<_Tp_elt*, _Up_elt*>::type;
403 return less<_Vp>()(__a.get(), __b.get());
404 }
405
406 template<typename _Tp>
407 inline bool
408 operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
409 {
410 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
411 return less<_Tp_elt*>()(__a.get(), nullptr);
412 }
413
414 template<typename _Tp>
415 inline bool
416 operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
417 {
418 using _Tp_elt = typename shared_ptr<_Tp>::element_type;
419 return less<_Tp_elt*>()(nullptr, __a.get());
420 }
421
422 template<typename _Tp, typename _Up>
423 inline bool
424 operator<=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
425 { return !(__b < __a); }
426
427 template<typename _Tp>
428 inline bool
429 operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
430 { return !(nullptr < __a); }
431
432 template<typename _Tp>
433 inline bool
434 operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
435 { return !(__a < nullptr); }
436
437 template<typename _Tp, typename _Up>
438 inline bool
439 operator>(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
440 { return (__b < __a); }
441
442 template<typename _Tp>
443 inline bool
444 operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
445 { return nullptr < __a; }
446
447 template<typename _Tp>
448 inline bool
449 operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
450 { return __a < nullptr; }
451
452 template<typename _Tp, typename _Up>
453 inline bool
454 operator>=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
455 { return !(__a < __b); }
456
457 template<typename _Tp>
458 inline bool
459 operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
460 { return !(__a < nullptr); }
461
462 template<typename _Tp>
463 inline bool
464 operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
465 { return !(nullptr < __a); }
466
467 template<typename _Tp>
468 struct less<shared_ptr<_Tp>> : public _Sp_less<shared_ptr<_Tp>>
469 { };
470
471 // 20.7.2.2.8 shared_ptr specialized algorithms.
472 template<typename _Tp>
473 inline void
474 swap(shared_ptr<_Tp>& __a, shared_ptr<_Tp>& __b) noexcept
475 { __a.swap(__b); }
476
477 // 20.7.2.2.9 shared_ptr casts.
478 template<typename _Tp, typename _Up>
479 inline shared_ptr<_Tp>
480 static_pointer_cast(const shared_ptr<_Up>& __r) noexcept
481 {
482 using _Sp = shared_ptr<_Tp>;
483 return _Sp(__r, static_cast<typename _Sp::element_type*>(__r.get()));
484 }
485
486 template<typename _Tp, typename _Up>
487 inline shared_ptr<_Tp>
488 const_pointer_cast(const shared_ptr<_Up>& __r) noexcept
489 {
490 using _Sp = shared_ptr<_Tp>;
491 return _Sp(__r, const_cast<typename _Sp::element_type*>(__r.get()));
492 }
493
494 template<typename _Tp, typename _Up>
495 inline shared_ptr<_Tp>
496 dynamic_pointer_cast(const shared_ptr<_Up>& __r) noexcept
497 {
498 using _Sp = shared_ptr<_Tp>;
499 if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
500 return _Sp(__r, __p);
501 return _Sp();
502 }
503
504 #if __cplusplus > 201402L
505 template<typename _Tp, typename _Up>
506 inline shared_ptr<_Tp>
507 reinterpret_pointer_cast(const shared_ptr<_Up>& __r) noexcept
508 {
509 using _Sp = shared_ptr<_Tp>;
510 return _Sp(__r, reinterpret_cast<typename _Sp::element_type*>(__r.get()));
511 }
512 #endif
513
514 /**
515 * @brief A smart pointer with weak semantics.
516 *
517 * With forwarding constructors and assignment operators.
518 */
519 template<typename _Tp>
520 class weak_ptr : public __weak_ptr<_Tp>
521 {
522 template<typename _Arg>
523 using _Constructible = typename enable_if<
524 is_constructible<__weak_ptr<_Tp>, _Arg>::value
525 >::type;
526
527 template<typename _Arg>
528 using _Assignable = typename enable_if<
529 is_assignable<__weak_ptr<_Tp>&, _Arg>::value, weak_ptr&
530 >::type;
531
532 public:
533 constexpr weak_ptr() noexcept = default;
534
535 template<typename _Yp,
536 typename = _Constructible<const shared_ptr<_Yp>&>>
537 weak_ptr(const shared_ptr<_Yp>& __r) noexcept
538 : __weak_ptr<_Tp>(__r) { }
539
540 weak_ptr(const weak_ptr&) noexcept = default;
541
542 template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
543 weak_ptr(const weak_ptr<_Yp>& __r) noexcept
544 : __weak_ptr<_Tp>(__r) { }
545
546 weak_ptr(weak_ptr&&) noexcept = default;
547
548 template<typename _Yp, typename = _Constructible<weak_ptr<_Yp>>>
549 weak_ptr(weak_ptr<_Yp>&& __r) noexcept
550 : __weak_ptr<_Tp>(std::move(__r)) { }
551
552 weak_ptr&
553 operator=(const weak_ptr& __r) noexcept = default;
554
555 template<typename _Yp>
556 _Assignable<const weak_ptr<_Yp>&>
557 operator=(const weak_ptr<_Yp>& __r) noexcept
558 {
559 this->__weak_ptr<_Tp>::operator=(__r);
560 return *this;
561 }
562
563 template<typename _Yp>
564 _Assignable<const shared_ptr<_Yp>&>
565 operator=(const shared_ptr<_Yp>& __r) noexcept
566 {
567 this->__weak_ptr<_Tp>::operator=(__r);
568 return *this;
569 }
570
571 weak_ptr&
572 operator=(weak_ptr&& __r) noexcept = default;
573
574 template<typename _Yp>
575 _Assignable<weak_ptr<_Yp>>
576 operator=(weak_ptr<_Yp>&& __r) noexcept
577 {
578 this->__weak_ptr<_Tp>::operator=(std::move(__r));
579 return *this;
580 }
581
582 shared_ptr<_Tp>
583 lock() const noexcept
584 { return shared_ptr<_Tp>(*this, std::nothrow); }
585 };
586
587 #if __cpp_deduction_guides >= 201606
588 template<typename _Tp>
589 weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
590 #endif
591
592 // 20.7.2.3.6 weak_ptr specialized algorithms.
593 template<typename _Tp>
594 inline void
595 swap(weak_ptr<_Tp>& __a, weak_ptr<_Tp>& __b) noexcept
596 { __a.swap(__b); }
597
598
599 /// Primary template owner_less
600 template<typename _Tp = void>
601 struct owner_less;
602
603 /// Void specialization of owner_less
604 template<>
605 struct owner_less<void> : _Sp_owner_less<void, void>
606 { };
607
608 /// Partial specialization of owner_less for shared_ptr.
609 template<typename _Tp>
610 struct owner_less<shared_ptr<_Tp>>
611 : public _Sp_owner_less<shared_ptr<_Tp>, weak_ptr<_Tp>>
612 { };
613
614 /// Partial specialization of owner_less for weak_ptr.
615 template<typename _Tp>
616 struct owner_less<weak_ptr<_Tp>>
617 : public _Sp_owner_less<weak_ptr<_Tp>, shared_ptr<_Tp>>
618 { };
619
620 /**
621 * @brief Base class allowing use of member function shared_from_this.
622 */
623 template<typename _Tp>
624 class enable_shared_from_this
625 {
626 protected:
627 constexpr enable_shared_from_this() noexcept { }
628
629 enable_shared_from_this(const enable_shared_from_this&) noexcept { }
630
631 enable_shared_from_this&
632 operator=(const enable_shared_from_this&) noexcept
633 { return *this; }
634
635 ~enable_shared_from_this() { }
636
637 public:
638 shared_ptr<_Tp>
639 shared_from_this()
640 { return shared_ptr<_Tp>(this->_M_weak_this); }
641
642 shared_ptr<const _Tp>
643 shared_from_this() const
644 { return shared_ptr<const _Tp>(this->_M_weak_this); }
645
646 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
647 #define __cpp_lib_enable_shared_from_this 201603
648 weak_ptr<_Tp>
649 weak_from_this() noexcept
650 { return this->_M_weak_this; }
651
652 weak_ptr<const _Tp>
653 weak_from_this() const noexcept
654 { return this->_M_weak_this; }
655 #endif
656
657 private:
658 template<typename _Tp1>
659 void
660 _M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
661 { _M_weak_this._M_assign(__p, __n); }
662
663 // Found by ADL when this is an associated class.
664 friend const enable_shared_from_this*
665 __enable_shared_from_this_base(const __shared_count<>&,
666 const enable_shared_from_this* __p)
667 { return __p; }
668
669 template<typename, _Lock_policy>
670 friend class __shared_ptr;
671
672 mutable weak_ptr<_Tp> _M_weak_this;
673 };
674
675 /**
676 * @brief Create an object that is owned by a shared_ptr.
677 * @param __a An allocator.
678 * @param __args Arguments for the @a _Tp object's constructor.
679 * @return A shared_ptr that owns the newly created object.
680 * @throw An exception thrown from @a _Alloc::allocate or from the
681 * constructor of @a _Tp.
682 *
683 * A copy of @a __a will be used to allocate memory for the shared_ptr
684 * and the new object.
685 */
686 template<typename _Tp, typename _Alloc, typename... _Args>
687 inline shared_ptr<_Tp>
688 allocate_shared(const _Alloc& __a, _Args&&... __args)
689 {
690 return shared_ptr<_Tp>(_Sp_make_shared_tag(), __a,
691 std::forward<_Args>(__args)...);
692 }
693
694 /**
695 * @brief Create an object that is owned by a shared_ptr.
696 * @param __args Arguments for the @a _Tp object's constructor.
697 * @return A shared_ptr that owns the newly created object.
698 * @throw std::bad_alloc, or an exception thrown from the
699 * constructor of @a _Tp.
700 */
701 template<typename _Tp, typename... _Args>
702 inline shared_ptr<_Tp>
703 make_shared(_Args&&... __args)
704 {
705 typedef typename std::remove_const<_Tp>::type _Tp_nc;
706 return std::allocate_shared<_Tp>(std::allocator<_Tp_nc>(),
707 std::forward<_Args>(__args)...);
708 }
709
710 /// std::hash specialization for shared_ptr.
711 template<typename _Tp>
712 struct hash<shared_ptr<_Tp>>
713 : public __hash_base<size_t, shared_ptr<_Tp>>
714 {
715 size_t
716 operator()(const shared_ptr<_Tp>& __s) const noexcept
717 {
718 return std::hash<typename shared_ptr<_Tp>::element_type*>()(__s.get());
719 }
720 };
721
722 // @} group pointer_abstractions
723
724 _GLIBCXX_END_NAMESPACE_VERSION
725 } // namespace
726
727 #endif // _SHARED_PTR_H
728