1 // shared_ptr and weak_ptr implementation -*- C++ -*- 2 3 // Copyright (C) 2007-2020 Free Software Foundation, Inc. 4 // 5 // This file is part of the GNU ISO C++ Library. This library is free 6 // software; you can redistribute it and/or modify it under the 7 // terms of the GNU General Public License as published by the 8 // Free Software Foundation; either version 3, or (at your option) 9 // any later version. 10 11 // This library is distributed in the hope that it will be useful, 12 // but WITHOUT ANY WARRANTY; without even the implied warranty of 13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 // GNU General Public License for more details. 15 16 // Under Section 7 of GPL version 3, you are granted additional 17 // permissions described in the GCC Runtime Library Exception, version 18 // 3.1, as published by the Free Software Foundation. 19 20 // You should have received a copy of the GNU General Public License and 21 // a copy of the GCC Runtime Library Exception along with this program; 22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23 // <http://www.gnu.org/licenses/>. 24 25 // GCC Note: Based on files from version 1.32.0 of the Boost library. 26 27 // shared_count.hpp 28 // Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd. 29 30 // shared_ptr.hpp 31 // Copyright (C) 1998, 1999 Greg Colvin and Beman Dawes. 32 // Copyright (C) 2001, 2002, 2003 Peter Dimov 33 34 // weak_ptr.hpp 35 // Copyright (C) 2001, 2002, 2003 Peter Dimov 36 37 // enable_shared_from_this.hpp 38 // Copyright (C) 2002 Peter Dimov 39 40 // Distributed under the Boost Software License, Version 1.0. (See 41 // accompanying file LICENSE_1_0.txt or copy at 42 // http://www.boost.org/LICENSE_1_0.txt) 43 44 /** @file 45 * This is an internal header file, included by other library headers. 46 * Do not attempt to use it directly. @headername{memory} 47 */ 48 49 #ifndef _SHARED_PTR_H 50 #define _SHARED_PTR_H 1 51 52 #include <bits/shared_ptr_base.h> 53 54 namespace std _GLIBCXX_VISIBILITY(default) 55 { 56 _GLIBCXX_BEGIN_NAMESPACE_VERSION 57 58 /** 59 * @addtogroup pointer_abstractions 60 * @{ 61 */ 62 63 // 20.7.2.2.11 shared_ptr I/O 64 65 /// Write the stored pointer to an ostream. 66 /// @relates shared_ptr 67 template<typename _Ch, typename _Tr, typename _Tp, _Lock_policy _Lp> 68 inline std::basic_ostream<_Ch, _Tr>& 69 operator<<(std::basic_ostream<_Ch, _Tr>& __os, 70 const __shared_ptr<_Tp, _Lp>& __p) 71 { 72 __os << __p.get(); 73 return __os; 74 } 75 76 template<typename _Del, typename _Tp, _Lock_policy _Lp> 77 inline _Del* 78 get_deleter(const __shared_ptr<_Tp, _Lp>& __p) noexcept 79 { 80 #if __cpp_rtti 81 return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del))); 82 #else 83 return 0; 84 #endif 85 } 86 87 /// 20.7.2.2.10 shared_ptr get_deleter 88 89 /// If `__p` has a deleter of type `_Del`, return a pointer to it. 90 /// @relates shared_ptr 91 template<typename _Del, typename _Tp> 92 inline _Del* 93 get_deleter(const shared_ptr<_Tp>& __p) noexcept 94 { 95 #if __cpp_rtti 96 return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del))); 97 #else 98 return 0; 99 #endif 100 } 101 102 /** 103 * @brief A smart pointer with reference-counted copy semantics. 104 * 105 * A `shared_ptr` object is either empty or _owns_ a pointer passed 106 * to the constructor. Copies of a `shared_ptr` share ownership of 107 * the same pointer. When the last `shared_ptr` that owns the pointer 108 * is destroyed or reset, the owned pointer is freed (either by `delete` 109 * or by invoking a custom deleter that was passed to the constructor). 110 * 111 * A `shared_ptr` also stores another pointer, which is usually 112 * (but not always) the same pointer as it owns. The stored pointer 113 * can be retrieved by calling the `get()` member function. 114 * 115 * The equality and relational operators for `shared_ptr` only compare 116 * the stored pointer returned by `get()`, not the owned pointer. 117 * To test whether two `shared_ptr` objects share ownership of the same 118 * pointer see `std::shared_ptr::owner_before` and `std::owner_less`. 119 */ 120 template<typename _Tp> 121 class shared_ptr : public __shared_ptr<_Tp> 122 { 123 template<typename... _Args> 124 using _Constructible = typename enable_if< 125 is_constructible<__shared_ptr<_Tp>, _Args...>::value 126 >::type; 127 128 template<typename _Arg> 129 using _Assignable = typename enable_if< 130 is_assignable<__shared_ptr<_Tp>&, _Arg>::value, shared_ptr& 131 >::type; 132 133 public: 134 135 /// The type pointed to by the stored pointer, remove_extent_t<_Tp> 136 using element_type = typename __shared_ptr<_Tp>::element_type; 137 138 #if __cplusplus >= 201703L 139 # define __cpp_lib_shared_ptr_weak_type 201606 140 /// The corresponding weak_ptr type for this shared_ptr 141 using weak_type = weak_ptr<_Tp>; 142 #endif 143 /** 144 * @brief Construct an empty %shared_ptr. 145 * @post use_count()==0 && get()==0 146 */ 147 constexpr shared_ptr() noexcept : __shared_ptr<_Tp>() { } 148 149 shared_ptr(const shared_ptr&) noexcept = default; ///< Copy constructor 150 151 /** 152 * @brief Construct a %shared_ptr that owns the pointer @a __p. 153 * @param __p A pointer that is convertible to element_type*. 154 * @post use_count() == 1 && get() == __p 155 * @throw std::bad_alloc, in which case @c delete @a __p is called. 156 */ 157 template<typename _Yp, typename = _Constructible<_Yp*>> 158 explicit 159 shared_ptr(_Yp* __p) : __shared_ptr<_Tp>(__p) { } 160 161 /** 162 * @brief Construct a %shared_ptr that owns the pointer @a __p 163 * and the deleter @a __d. 164 * @param __p A pointer. 165 * @param __d A deleter. 166 * @post use_count() == 1 && get() == __p 167 * @throw std::bad_alloc, in which case @a __d(__p) is called. 168 * 169 * Requirements: _Deleter's copy constructor and destructor must 170 * not throw 171 * 172 * __shared_ptr will release __p by calling __d(__p) 173 */ 174 template<typename _Yp, typename _Deleter, 175 typename = _Constructible<_Yp*, _Deleter>> 176 shared_ptr(_Yp* __p, _Deleter __d) 177 : __shared_ptr<_Tp>(__p, std::move(__d)) { } 178 179 /** 180 * @brief Construct a %shared_ptr that owns a null pointer 181 * and the deleter @a __d. 182 * @param __p A null pointer constant. 183 * @param __d A deleter. 184 * @post use_count() == 1 && get() == __p 185 * @throw std::bad_alloc, in which case @a __d(__p) is called. 186 * 187 * Requirements: _Deleter's copy constructor and destructor must 188 * not throw 189 * 190 * The last owner will call __d(__p) 191 */ 192 template<typename _Deleter> 193 shared_ptr(nullptr_t __p, _Deleter __d) 194 : __shared_ptr<_Tp>(__p, std::move(__d)) { } 195 196 /** 197 * @brief Construct a %shared_ptr that owns the pointer @a __p 198 * and the deleter @a __d. 199 * @param __p A pointer. 200 * @param __d A deleter. 201 * @param __a An allocator. 202 * @post use_count() == 1 && get() == __p 203 * @throw std::bad_alloc, in which case @a __d(__p) is called. 204 * 205 * Requirements: _Deleter's copy constructor and destructor must 206 * not throw _Alloc's copy constructor and destructor must not 207 * throw. 208 * 209 * __shared_ptr will release __p by calling __d(__p) 210 */ 211 template<typename _Yp, typename _Deleter, typename _Alloc, 212 typename = _Constructible<_Yp*, _Deleter, _Alloc>> 213 shared_ptr(_Yp* __p, _Deleter __d, _Alloc __a) 214 : __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { } 215 216 /** 217 * @brief Construct a %shared_ptr that owns a null pointer 218 * and the deleter @a __d. 219 * @param __p A null pointer constant. 220 * @param __d A deleter. 221 * @param __a An allocator. 222 * @post use_count() == 1 && get() == __p 223 * @throw std::bad_alloc, in which case @a __d(__p) is called. 224 * 225 * Requirements: _Deleter's copy constructor and destructor must 226 * not throw _Alloc's copy constructor and destructor must not 227 * throw. 228 * 229 * The last owner will call __d(__p) 230 */ 231 template<typename _Deleter, typename _Alloc> 232 shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a) 233 : __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { } 234 235 // Aliasing constructor 236 237 /** 238 * @brief Constructs a `shared_ptr` instance that stores `__p` 239 * and shares ownership with `__r`. 240 * @param __r A `shared_ptr`. 241 * @param __p A pointer that will remain valid while `*__r` is valid. 242 * @post `get() == __p && use_count() == __r.use_count()` 243 * 244 * This can be used to construct a `shared_ptr` to a sub-object 245 * of an object managed by an existing `shared_ptr`. The complete 246 * object will remain valid while any `shared_ptr` owns it, even 247 * if they don't store a pointer to the complete object. 248 * 249 * @code 250 * shared_ptr<pair<int,int>> pii(new pair<int,int>()); 251 * shared_ptr<int> pi(pii, &pii->first); 252 * assert(pii.use_count() == 2); 253 * @endcode 254 */ 255 template<typename _Yp> 256 shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) noexcept 257 : __shared_ptr<_Tp>(__r, __p) { } 258 259 #if __cplusplus > 201703L 260 // _GLIBCXX_RESOLVE_LIB_DEFECTS 261 // 2996. Missing rvalue overloads for shared_ptr operations 262 /** 263 * @brief Constructs a `shared_ptr` instance that stores `__p` 264 * and shares ownership with `__r`. 265 * @param __r A `shared_ptr`. 266 * @param __p A pointer that will remain valid while `*__r` is valid. 267 * @post `get() == __p && !__r.use_count() && !__r.get()` 268 * 269 * This can be used to construct a `shared_ptr` to a sub-object 270 * of an object managed by an existing `shared_ptr`. The complete 271 * object will remain valid while any `shared_ptr` owns it, even 272 * if they don't store a pointer to the complete object. 273 * 274 * @code 275 * shared_ptr<pair<int,int>> pii(new pair<int,int>()); 276 * shared_ptr<int> pi1(pii, &pii->first); 277 * assert(pii.use_count() == 2); 278 * shared_ptr<int> pi2(std::move(pii), &pii->second); 279 * assert(pii.use_count() == 0); 280 * @endcode 281 */ 282 template<typename _Yp> 283 shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept 284 : __shared_ptr<_Tp>(std::move(__r), __p) { } 285 #endif 286 /** 287 * @brief If @a __r is empty, constructs an empty %shared_ptr; 288 * otherwise construct a %shared_ptr that shares ownership 289 * with @a __r. 290 * @param __r A %shared_ptr. 291 * @post get() == __r.get() && use_count() == __r.use_count() 292 */ 293 template<typename _Yp, 294 typename = _Constructible<const shared_ptr<_Yp>&>> 295 shared_ptr(const shared_ptr<_Yp>& __r) noexcept 296 : __shared_ptr<_Tp>(__r) { } 297 298 /** 299 * @brief Move-constructs a %shared_ptr instance from @a __r. 300 * @param __r A %shared_ptr rvalue. 301 * @post *this contains the old value of @a __r, @a __r is empty. 302 */ 303 shared_ptr(shared_ptr&& __r) noexcept 304 : __shared_ptr<_Tp>(std::move(__r)) { } 305 306 /** 307 * @brief Move-constructs a %shared_ptr instance from @a __r. 308 * @param __r A %shared_ptr rvalue. 309 * @post *this contains the old value of @a __r, @a __r is empty. 310 */ 311 template<typename _Yp, typename = _Constructible<shared_ptr<_Yp>>> 312 shared_ptr(shared_ptr<_Yp>&& __r) noexcept 313 : __shared_ptr<_Tp>(std::move(__r)) { } 314 315 /** 316 * @brief Constructs a %shared_ptr that shares ownership with @a __r 317 * and stores a copy of the pointer stored in @a __r. 318 * @param __r A weak_ptr. 319 * @post use_count() == __r.use_count() 320 * @throw bad_weak_ptr when __r.expired(), 321 * in which case the constructor has no effect. 322 */ 323 template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>> 324 explicit shared_ptr(const weak_ptr<_Yp>& __r) 325 : __shared_ptr<_Tp>(__r) { } 326 327 #if _GLIBCXX_USE_DEPRECATED 328 #pragma GCC diagnostic push 329 #pragma GCC diagnostic ignored "-Wdeprecated-declarations" 330 template<typename _Yp, typename = _Constructible<auto_ptr<_Yp>>> 331 shared_ptr(auto_ptr<_Yp>&& __r); 332 #pragma GCC diagnostic pop 333 #endif 334 335 // _GLIBCXX_RESOLVE_LIB_DEFECTS 336 // 2399. shared_ptr's constructor from unique_ptr should be constrained 337 template<typename _Yp, typename _Del, 338 typename = _Constructible<unique_ptr<_Yp, _Del>>> 339 shared_ptr(unique_ptr<_Yp, _Del>&& __r) 340 : __shared_ptr<_Tp>(std::move(__r)) { } 341 342 #if __cplusplus <= 201402L && _GLIBCXX_USE_DEPRECATED 343 // This non-standard constructor exists to support conversions that 344 // were possible in C++11 and C++14 but are ill-formed in C++17. 345 // If an exception is thrown this constructor has no effect. 346 template<typename _Yp, typename _Del, 347 _Constructible<unique_ptr<_Yp, _Del>, __sp_array_delete>* = 0> 348 shared_ptr(unique_ptr<_Yp, _Del>&& __r) 349 : __shared_ptr<_Tp>(std::move(__r), __sp_array_delete()) { } 350 #endif 351 352 /** 353 * @brief Construct an empty %shared_ptr. 354 * @post use_count() == 0 && get() == nullptr 355 */ 356 constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { } 357 358 shared_ptr& operator=(const shared_ptr&) noexcept = default; 359 360 template<typename _Yp> 361 _Assignable<const shared_ptr<_Yp>&> 362 operator=(const shared_ptr<_Yp>& __r) noexcept 363 { 364 this->__shared_ptr<_Tp>::operator=(__r); 365 return *this; 366 } 367 368 #if _GLIBCXX_USE_DEPRECATED 369 #pragma GCC diagnostic push 370 #pragma GCC diagnostic ignored "-Wdeprecated-declarations" 371 template<typename _Yp> 372 _Assignable<auto_ptr<_Yp>> 373 operator=(auto_ptr<_Yp>&& __r) 374 { 375 this->__shared_ptr<_Tp>::operator=(std::move(__r)); 376 return *this; 377 } 378 #pragma GCC diagnostic pop 379 #endif 380 381 shared_ptr& 382 operator=(shared_ptr&& __r) noexcept 383 { 384 this->__shared_ptr<_Tp>::operator=(std::move(__r)); 385 return *this; 386 } 387 388 template<class _Yp> 389 _Assignable<shared_ptr<_Yp>> 390 operator=(shared_ptr<_Yp>&& __r) noexcept 391 { 392 this->__shared_ptr<_Tp>::operator=(std::move(__r)); 393 return *this; 394 } 395 396 template<typename _Yp, typename _Del> 397 _Assignable<unique_ptr<_Yp, _Del>> 398 operator=(unique_ptr<_Yp, _Del>&& __r) 399 { 400 this->__shared_ptr<_Tp>::operator=(std::move(__r)); 401 return *this; 402 } 403 404 private: 405 // This constructor is non-standard, it is used by allocate_shared. 406 template<typename _Alloc, typename... _Args> 407 shared_ptr(_Sp_alloc_shared_tag<_Alloc> __tag, _Args&&... __args) 408 : __shared_ptr<_Tp>(__tag, std::forward<_Args>(__args)...) 409 { } 410 411 template<typename _Yp, typename _Alloc, typename... _Args> 412 friend shared_ptr<_Yp> 413 allocate_shared(const _Alloc& __a, _Args&&... __args); 414 415 // This constructor is non-standard, it is used by weak_ptr::lock(). 416 shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t) 417 : __shared_ptr<_Tp>(__r, std::nothrow) { } 418 419 friend class weak_ptr<_Tp>; 420 }; 421 422 #if __cpp_deduction_guides >= 201606 423 template<typename _Tp> 424 shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>; 425 template<typename _Tp, typename _Del> 426 shared_ptr(unique_ptr<_Tp, _Del>) -> shared_ptr<_Tp>; 427 #endif 428 429 // 20.7.2.2.7 shared_ptr comparisons 430 431 /// @relates shared_ptr @{ 432 433 /// Equality operator for shared_ptr objects, compares the stored pointers 434 template<typename _Tp, typename _Up> 435 _GLIBCXX_NODISCARD inline bool 436 operator==(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept 437 { return __a.get() == __b.get(); } 438 439 /// shared_ptr comparison with nullptr 440 template<typename _Tp> 441 _GLIBCXX_NODISCARD inline bool 442 operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept 443 { return !__a; } 444 445 #ifdef __cpp_lib_three_way_comparison 446 template<typename _Tp, typename _Up> 447 inline strong_ordering 448 operator<=>(const shared_ptr<_Tp>& __a, 449 const shared_ptr<_Up>& __b) noexcept 450 { return compare_three_way()(__a.get(), __b.get()); } 451 452 template<typename _Tp> 453 inline strong_ordering 454 operator<=>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept 455 { 456 using pointer = typename shared_ptr<_Tp>::element_type*; 457 return compare_three_way()(__a.get(), static_cast<pointer>(nullptr)); 458 } 459 #else 460 /// shared_ptr comparison with nullptr 461 template<typename _Tp> 462 _GLIBCXX_NODISCARD inline bool 463 operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept 464 { return !__a; } 465 466 /// Inequality operator for shared_ptr objects, compares the stored pointers 467 template<typename _Tp, typename _Up> 468 _GLIBCXX_NODISCARD inline bool 469 operator!=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept 470 { return __a.get() != __b.get(); } 471 472 /// shared_ptr comparison with nullptr 473 template<typename _Tp> 474 _GLIBCXX_NODISCARD inline bool 475 operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept 476 { return (bool)__a; } 477 478 /// shared_ptr comparison with nullptr 479 template<typename _Tp> 480 _GLIBCXX_NODISCARD inline bool 481 operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept 482 { return (bool)__a; } 483 484 /// Relational operator for shared_ptr objects, compares the stored pointers 485 template<typename _Tp, typename _Up> 486 _GLIBCXX_NODISCARD inline bool 487 operator<(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept 488 { 489 using _Tp_elt = typename shared_ptr<_Tp>::element_type; 490 using _Up_elt = typename shared_ptr<_Up>::element_type; 491 using _Vp = typename common_type<_Tp_elt*, _Up_elt*>::type; 492 return less<_Vp>()(__a.get(), __b.get()); 493 } 494 495 /// shared_ptr comparison with nullptr 496 template<typename _Tp> 497 _GLIBCXX_NODISCARD inline bool 498 operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept 499 { 500 using _Tp_elt = typename shared_ptr<_Tp>::element_type; 501 return less<_Tp_elt*>()(__a.get(), nullptr); 502 } 503 504 /// shared_ptr comparison with nullptr 505 template<typename _Tp> 506 _GLIBCXX_NODISCARD inline bool 507 operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept 508 { 509 using _Tp_elt = typename shared_ptr<_Tp>::element_type; 510 return less<_Tp_elt*>()(nullptr, __a.get()); 511 } 512 513 /// Relational operator for shared_ptr objects, compares the stored pointers 514 template<typename _Tp, typename _Up> 515 _GLIBCXX_NODISCARD inline bool 516 operator<=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept 517 { return !(__b < __a); } 518 519 /// shared_ptr comparison with nullptr 520 template<typename _Tp> 521 _GLIBCXX_NODISCARD inline bool 522 operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept 523 { return !(nullptr < __a); } 524 525 /// shared_ptr comparison with nullptr 526 template<typename _Tp> 527 _GLIBCXX_NODISCARD inline bool 528 operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept 529 { return !(__a < nullptr); } 530 531 /// Relational operator for shared_ptr objects, compares the stored pointers 532 template<typename _Tp, typename _Up> 533 _GLIBCXX_NODISCARD inline bool 534 operator>(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept 535 { return (__b < __a); } 536 537 /// shared_ptr comparison with nullptr 538 template<typename _Tp> 539 _GLIBCXX_NODISCARD inline bool 540 operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept 541 { return nullptr < __a; } 542 543 /// shared_ptr comparison with nullptr 544 template<typename _Tp> 545 _GLIBCXX_NODISCARD inline bool 546 operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept 547 { return __a < nullptr; } 548 549 /// Relational operator for shared_ptr objects, compares the stored pointers 550 template<typename _Tp, typename _Up> 551 _GLIBCXX_NODISCARD inline bool 552 operator>=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept 553 { return !(__a < __b); } 554 555 /// shared_ptr comparison with nullptr 556 template<typename _Tp> 557 _GLIBCXX_NODISCARD inline bool 558 operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept 559 { return !(__a < nullptr); } 560 561 /// shared_ptr comparison with nullptr 562 template<typename _Tp> 563 _GLIBCXX_NODISCARD inline bool 564 operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept 565 { return !(nullptr < __a); } 566 #endif 567 568 // 20.7.2.2.8 shared_ptr specialized algorithms. 569 570 /// Swap overload for shared_ptr 571 template<typename _Tp> 572 inline void 573 swap(shared_ptr<_Tp>& __a, shared_ptr<_Tp>& __b) noexcept 574 { __a.swap(__b); } 575 576 // 20.7.2.2.9 shared_ptr casts. 577 578 /// Convert type of `shared_ptr`, via `static_cast` 579 template<typename _Tp, typename _Up> 580 inline shared_ptr<_Tp> 581 static_pointer_cast(const shared_ptr<_Up>& __r) noexcept 582 { 583 using _Sp = shared_ptr<_Tp>; 584 return _Sp(__r, static_cast<typename _Sp::element_type*>(__r.get())); 585 } 586 587 /// Convert type of `shared_ptr`, via `const_cast` 588 template<typename _Tp, typename _Up> 589 inline shared_ptr<_Tp> 590 const_pointer_cast(const shared_ptr<_Up>& __r) noexcept 591 { 592 using _Sp = shared_ptr<_Tp>; 593 return _Sp(__r, const_cast<typename _Sp::element_type*>(__r.get())); 594 } 595 596 /// Convert type of `shared_ptr`, via `dynamic_cast` 597 template<typename _Tp, typename _Up> 598 inline shared_ptr<_Tp> 599 dynamic_pointer_cast(const shared_ptr<_Up>& __r) noexcept 600 { 601 using _Sp = shared_ptr<_Tp>; 602 if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get())) 603 return _Sp(__r, __p); 604 return _Sp(); 605 } 606 607 #if __cplusplus >= 201703L 608 /// Convert type of `shared_ptr`, via `reinterpret_cast` 609 template<typename _Tp, typename _Up> 610 inline shared_ptr<_Tp> 611 reinterpret_pointer_cast(const shared_ptr<_Up>& __r) noexcept 612 { 613 using _Sp = shared_ptr<_Tp>; 614 return _Sp(__r, reinterpret_cast<typename _Sp::element_type*>(__r.get())); 615 } 616 617 #if __cplusplus > 201703L 618 // _GLIBCXX_RESOLVE_LIB_DEFECTS 619 // 2996. Missing rvalue overloads for shared_ptr operations 620 621 /// Convert type of `shared_ptr` rvalue, via `static_cast` 622 template<typename _Tp, typename _Up> 623 inline shared_ptr<_Tp> 624 static_pointer_cast(shared_ptr<_Up>&& __r) noexcept 625 { 626 using _Sp = shared_ptr<_Tp>; 627 return _Sp(std::move(__r), 628 static_cast<typename _Sp::element_type*>(__r.get())); 629 } 630 631 /// Convert type of `shared_ptr` rvalue, via `const_cast` 632 template<typename _Tp, typename _Up> 633 inline shared_ptr<_Tp> 634 const_pointer_cast(shared_ptr<_Up>&& __r) noexcept 635 { 636 using _Sp = shared_ptr<_Tp>; 637 return _Sp(std::move(__r), 638 const_cast<typename _Sp::element_type*>(__r.get())); 639 } 640 641 /// Convert type of `shared_ptr` rvalue, via `dynamic_cast` 642 template<typename _Tp, typename _Up> 643 inline shared_ptr<_Tp> 644 dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept 645 { 646 using _Sp = shared_ptr<_Tp>; 647 if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get())) 648 return _Sp(std::move(__r), __p); 649 return _Sp(); 650 } 651 652 /// Convert type of `shared_ptr` rvalue, via `reinterpret_cast` 653 template<typename _Tp, typename _Up> 654 inline shared_ptr<_Tp> 655 reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept 656 { 657 using _Sp = shared_ptr<_Tp>; 658 return _Sp(std::move(__r), 659 reinterpret_cast<typename _Sp::element_type*>(__r.get())); 660 } 661 #endif // C++20 662 #endif // C++17 663 664 /// @} 665 666 /** 667 * @brief A non-owning observer for a pointer owned by a shared_ptr 668 * 669 * A weak_ptr provides a safe alternative to a raw pointer when you want 670 * a non-owning reference to an object that is managed by a shared_ptr. 671 * 672 * Unlike a raw pointer, a weak_ptr can be converted to a new shared_ptr 673 * that shares ownership with every other shared_ptr that already owns 674 * the pointer. In other words you can upgrade from a non-owning "weak" 675 * reference to an owning shared_ptr, without having access to any of 676 * the existing shared_ptr objects. 677 * 678 * Also unlike a raw pointer, a weak_ptr does not become "dangling" after 679 * the object it points to has been destroyed. Instead, a weak_ptr 680 * becomes _expired_ and can no longer be converted to a shared_ptr that 681 * owns the freed pointer, so you cannot accidentally access the pointed-to 682 * object after it has been destroyed. 683 */ 684 template<typename _Tp> 685 class weak_ptr : public __weak_ptr<_Tp> 686 { 687 template<typename _Arg> 688 using _Constructible = typename enable_if< 689 is_constructible<__weak_ptr<_Tp>, _Arg>::value 690 >::type; 691 692 template<typename _Arg> 693 using _Assignable = typename enable_if< 694 is_assignable<__weak_ptr<_Tp>&, _Arg>::value, weak_ptr& 695 >::type; 696 697 public: 698 constexpr weak_ptr() noexcept = default; 699 700 template<typename _Yp, 701 typename = _Constructible<const shared_ptr<_Yp>&>> 702 weak_ptr(const shared_ptr<_Yp>& __r) noexcept 703 : __weak_ptr<_Tp>(__r) { } 704 705 weak_ptr(const weak_ptr&) noexcept = default; 706 707 template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>> 708 weak_ptr(const weak_ptr<_Yp>& __r) noexcept 709 : __weak_ptr<_Tp>(__r) { } 710 711 weak_ptr(weak_ptr&&) noexcept = default; 712 713 template<typename _Yp, typename = _Constructible<weak_ptr<_Yp>>> 714 weak_ptr(weak_ptr<_Yp>&& __r) noexcept 715 : __weak_ptr<_Tp>(std::move(__r)) { } 716 717 weak_ptr& 718 operator=(const weak_ptr& __r) noexcept = default; 719 720 template<typename _Yp> 721 _Assignable<const weak_ptr<_Yp>&> 722 operator=(const weak_ptr<_Yp>& __r) noexcept 723 { 724 this->__weak_ptr<_Tp>::operator=(__r); 725 return *this; 726 } 727 728 template<typename _Yp> 729 _Assignable<const shared_ptr<_Yp>&> 730 operator=(const shared_ptr<_Yp>& __r) noexcept 731 { 732 this->__weak_ptr<_Tp>::operator=(__r); 733 return *this; 734 } 735 736 weak_ptr& 737 operator=(weak_ptr&& __r) noexcept = default; 738 739 template<typename _Yp> 740 _Assignable<weak_ptr<_Yp>> 741 operator=(weak_ptr<_Yp>&& __r) noexcept 742 { 743 this->__weak_ptr<_Tp>::operator=(std::move(__r)); 744 return *this; 745 } 746 747 shared_ptr<_Tp> 748 lock() const noexcept 749 { return shared_ptr<_Tp>(*this, std::nothrow); } 750 }; 751 752 #if __cpp_deduction_guides >= 201606 753 template<typename _Tp> 754 weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>; 755 #endif 756 757 // 20.7.2.3.6 weak_ptr specialized algorithms. 758 /// Swap overload for weak_ptr 759 /// @relates weak_ptr 760 template<typename _Tp> 761 inline void 762 swap(weak_ptr<_Tp>& __a, weak_ptr<_Tp>& __b) noexcept 763 { __a.swap(__b); } 764 765 766 /// Primary template owner_less 767 template<typename _Tp = void> 768 struct owner_less; 769 770 /// Void specialization of owner_less compares either shared_ptr or weak_ptr 771 template<> 772 struct owner_less<void> : _Sp_owner_less<void, void> 773 { }; 774 775 /// Partial specialization of owner_less for shared_ptr. 776 template<typename _Tp> 777 struct owner_less<shared_ptr<_Tp>> 778 : public _Sp_owner_less<shared_ptr<_Tp>, weak_ptr<_Tp>> 779 { }; 780 781 /// Partial specialization of owner_less for weak_ptr. 782 template<typename _Tp> 783 struct owner_less<weak_ptr<_Tp>> 784 : public _Sp_owner_less<weak_ptr<_Tp>, shared_ptr<_Tp>> 785 { }; 786 787 /** 788 * @brief Base class allowing use of member function shared_from_this. 789 */ 790 template<typename _Tp> 791 class enable_shared_from_this 792 { 793 protected: 794 constexpr enable_shared_from_this() noexcept { } 795 796 enable_shared_from_this(const enable_shared_from_this&) noexcept { } 797 798 enable_shared_from_this& 799 operator=(const enable_shared_from_this&) noexcept 800 { return *this; } 801 802 ~enable_shared_from_this() { } 803 804 public: 805 shared_ptr<_Tp> 806 shared_from_this() 807 { return shared_ptr<_Tp>(this->_M_weak_this); } 808 809 shared_ptr<const _Tp> 810 shared_from_this() const 811 { return shared_ptr<const _Tp>(this->_M_weak_this); } 812 813 #if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11 814 #define __cpp_lib_enable_shared_from_this 201603 815 weak_ptr<_Tp> 816 weak_from_this() noexcept 817 { return this->_M_weak_this; } 818 819 weak_ptr<const _Tp> 820 weak_from_this() const noexcept 821 { return this->_M_weak_this; } 822 #endif 823 824 private: 825 template<typename _Tp1> 826 void 827 _M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept 828 { _M_weak_this._M_assign(__p, __n); } 829 830 // Found by ADL when this is an associated class. 831 friend const enable_shared_from_this* 832 __enable_shared_from_this_base(const __shared_count<>&, 833 const enable_shared_from_this* __p) 834 { return __p; } 835 836 template<typename, _Lock_policy> 837 friend class __shared_ptr; 838 839 mutable weak_ptr<_Tp> _M_weak_this; 840 }; 841 842 /// @relates shared_ptr @{ 843 844 /** 845 * @brief Create an object that is owned by a shared_ptr. 846 * @param __a An allocator. 847 * @param __args Arguments for the @a _Tp object's constructor. 848 * @return A shared_ptr that owns the newly created object. 849 * @throw An exception thrown from @a _Alloc::allocate or from the 850 * constructor of @a _Tp. 851 * 852 * A copy of @a __a will be used to allocate memory for the shared_ptr 853 * and the new object. 854 */ 855 template<typename _Tp, typename _Alloc, typename... _Args> 856 inline shared_ptr<_Tp> 857 allocate_shared(const _Alloc& __a, _Args&&... __args) 858 { 859 static_assert(!is_array<_Tp>::value, "make_shared<T[]> not supported"); 860 861 return shared_ptr<_Tp>(_Sp_alloc_shared_tag<_Alloc>{__a}, 862 std::forward<_Args>(__args)...); 863 } 864 865 /** 866 * @brief Create an object that is owned by a shared_ptr. 867 * @param __args Arguments for the @a _Tp object's constructor. 868 * @return A shared_ptr that owns the newly created object. 869 * @throw std::bad_alloc, or an exception thrown from the 870 * constructor of @a _Tp. 871 */ 872 template<typename _Tp, typename... _Args> 873 inline shared_ptr<_Tp> 874 make_shared(_Args&&... __args) 875 { 876 typedef typename std::remove_cv<_Tp>::type _Tp_nc; 877 return std::allocate_shared<_Tp>(std::allocator<_Tp_nc>(), 878 std::forward<_Args>(__args)...); 879 } 880 881 /// std::hash specialization for shared_ptr. 882 template<typename _Tp> 883 struct hash<shared_ptr<_Tp>> 884 : public __hash_base<size_t, shared_ptr<_Tp>> 885 { 886 size_t 887 operator()(const shared_ptr<_Tp>& __s) const noexcept 888 { 889 return std::hash<typename shared_ptr<_Tp>::element_type*>()(__s.get()); 890 } 891 }; 892 893 /// @} relates shared_ptr 894 /// @} group pointer_abstractions 895 896 #if __cplusplus >= 201703L 897 namespace __detail::__variant 898 { 899 template<typename> struct _Never_valueless_alt; // see <variant> 900 901 // Provide the strong exception-safety guarantee when emplacing a 902 // shared_ptr into a variant. 903 template<typename _Tp> 904 struct _Never_valueless_alt<std::shared_ptr<_Tp>> 905 : std::true_type 906 { }; 907 908 // Provide the strong exception-safety guarantee when emplacing a 909 // weak_ptr into a variant. 910 template<typename _Tp> 911 struct _Never_valueless_alt<std::weak_ptr<_Tp>> 912 : std::true_type 913 { }; 914 } // namespace __detail::__variant 915 #endif // C++17 916 917 _GLIBCXX_END_NAMESPACE_VERSION 918 } // namespace 919 920 #endif // _SHARED_PTR_H 921