libstdc++-v3/include/experimental/bits/shared_ptr.h

   1 // Experimental shared_ptr with array support -*- C++ -*-
   2
   3 // Copyright (C) 2015-2021 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 /** @file experimental/bits/shared_ptr.h
  26  *  This is an internal header file, included by other library headers.
  27  *  Do not attempt to use it directly. @headername{experimental/memory}
  28  */
  29
  30 #ifndef _GLIBCXX_EXPERIMENTAL_SHARED_PTR_H
  31 #define _GLIBCXX_EXPERIMENTAL_SHARED_PTR_H 1
  32
  33 #pragma GCC system_header
  34
  35 #if __cplusplus >= 201402L
  36
  37 #include <memory>
  38 #include <experimental/type_traits>
  39
  40 namespace std _GLIBCXX_VISIBILITY(default)
  41 {
  42 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  43
  44 namespace experimental
  45 {
  46 inline namespace fundamentals_v2
  47 {
  48   // 8.2.1
  49
  50   template<typename _Tp> class shared_ptr;
  51   template<typename _Tp> class weak_ptr;
  52   template<typename _Tp> class enable_shared_from_this;
  53
  54   template<typename _Yp, typename _Tp>
  55     constexpr bool __sp_compatible_v
  56       = std::__sp_compatible_with<_Yp*, _Tp*>::value;
  57
  58   template<typename _Tp, typename _Yp>
  59     constexpr bool __sp_is_constructible_v
  60       = std::__sp_is_constructible<_Tp, _Yp>::value;
  61
  62   template<typename _Tp>
  63     class shared_ptr : public __shared_ptr<_Tp>
  64     {
  65       using _Base_type = __shared_ptr<_Tp>;
  66
  67     public:
  68       using element_type = typename _Base_type::element_type;
  69
  70     private:
  71       // Constraint for construction from a pointer of type _Yp*:
  72       template<typename _Yp>
  73         using _SafeConv = enable_if_t<__sp_is_constructible_v<_Tp, _Yp>>;
  74
  75       template<typename _Tp1, typename _Res = void>
  76         using _Compatible
  77           = enable_if_t<__sp_compatible_v<_Tp1, _Tp>, _Res>;
  78
  79       template<typename _Tp1, typename _Del,
  80                typename _Ptr = typename unique_ptr<_Tp1, _Del>::pointer,
  81                typename _Res = void>
  82         using _UniqCompatible = enable_if_t<
  83           __sp_compatible_v<_Tp1, _Tp>
  84           && experimental::is_convertible_v<_Ptr, element_type*>,
  85           _Res>;
  86
  87     public:
  88
  89       // 8.2.1.1, shared_ptr constructors
  90       constexpr shared_ptr() noexcept = default;
  91
  92       template<typename _Tp1, typename = _SafeConv<_Tp1>>
  93         explicit
  94         shared_ptr(_Tp1* __p) : _Base_type(__p)
  95         { _M_enable_shared_from_this_with(__p); }
  96
  97       template<typename _Tp1, typename _Deleter, typename = _SafeConv<_Tp1>>
  98         shared_ptr(_Tp1* __p, _Deleter __d)
  99         : _Base_type(__p, __d)
 100         { _M_enable_shared_from_this_with(__p); }
 101
 102       template<typename _Tp1, typename _Deleter, typename _Alloc,
 103                typename = _SafeConv<_Tp1>>
 104         shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
 105         : _Base_type(__p, __d, __a)
 106         { _M_enable_shared_from_this_with(__p); }
 107
 108       template<typename _Deleter>
 109         shared_ptr(nullptr_t __p, _Deleter __d)
 110         : _Base_type(__p, __d) { }
 111
 112       template<typename _Deleter, typename _Alloc>
 113         shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
 114         : _Base_type(__p, __d, __a) { }
 115
 116       template<typename _Tp1>
 117         shared_ptr(const shared_ptr<_Tp1>& __r, element_type* __p) noexcept
 118         : _Base_type(__r, __p) { }
 119
 120       shared_ptr(const shared_ptr& __r) noexcept
 121         : _Base_type(__r) { }
 122
 123       template<typename _Tp1, typename = _Compatible<_Tp1>>
 124         shared_ptr(const shared_ptr<_Tp1>& __r) noexcept
 125         : _Base_type(__r) { }
 126
 127       shared_ptr(shared_ptr&& __r) noexcept
 128       : _Base_type(std::move(__r)) { }
 129
 130       template<typename _Tp1, typename = _Compatible<_Tp1>>
 131         shared_ptr(shared_ptr<_Tp1>&& __r) noexcept
 132         : _Base_type(std::move(__r)) { }
 133
 134       template<typename _Tp1, typename = _Compatible<_Tp1>>
 135         explicit
 136         shared_ptr(const weak_ptr<_Tp1>& __r)
 137         : _Base_type(__r) { }
 138
 139 #if _GLIBCXX_USE_DEPRECATED
 140 #pragma GCC diagnostic push
 141 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 142       template<typename _Tp1, typename = _Compatible<_Tp1>>
 143         shared_ptr(std::auto_ptr<_Tp1>&& __r)
 144         : _Base_type(std::move(__r))
 145         { _M_enable_shared_from_this_with(static_cast<_Tp1*>(this->get())); }
 146 #pragma GCC diagnostic pop
 147 #endif
 148
 149       template<typename _Tp1, typename _Del,
 150                typename = _UniqCompatible<_Tp1, _Del>>
 151         shared_ptr(unique_ptr<_Tp1, _Del>&& __r)
 152         : _Base_type(std::move(__r))
 153         {
 154           // XXX assume conversion from __r.get() to this->get() to __elem_t*
 155           // is a round trip, which might not be true in all cases.
 156           using __elem_t = typename unique_ptr<_Tp1, _Del>::element_type;
 157           _M_enable_shared_from_this_with(static_cast<__elem_t*>(this->get()));
 158         }
 159
 160       constexpr shared_ptr(nullptr_t __p)
 161       : _Base_type(__p) { }
 162
 163       // C++14 20.8.2.2
 164       ~shared_ptr() = default;
 165
 166       // C++14 20.8.2.3
 167       shared_ptr& operator=(const shared_ptr&) noexcept = default;
 168
 169       template <typename _Tp1>
 170         _Compatible<_Tp1, shared_ptr&>
 171         operator=(const shared_ptr<_Tp1>& __r) noexcept
 172         {
 173           _Base_type::operator=(__r);
 174           return *this;
 175         }
 176
 177       shared_ptr&
 178       operator=(shared_ptr&& __r) noexcept
 179       {
 180         _Base_type::operator=(std::move(__r));
 181         return *this;
 182       }
 183
 184       template <typename _Tp1>
 185         _Compatible<_Tp1, shared_ptr&>
 186         operator=(shared_ptr<_Tp1>&& __r) noexcept
 187         {
 188           _Base_type::operator=(std::move(__r));
 189           return *this;
 190         }
 191
 192 #if _GLIBCXX_USE_DEPRECATED
 193 #pragma GCC diagnostic push
 194 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 195       template<typename _Tp1>
 196         _Compatible<_Tp1, shared_ptr&>
 197         operator=(std::auto_ptr<_Tp1>&& __r)
 198         {
 199           __shared_ptr<_Tp>::operator=(std::move(__r));
 200           return *this;
 201         }
 202 #pragma GCC diagnostic pop
 203 #endif
 204
 205       template <typename _Tp1, typename _Del>
 206         _UniqCompatible<_Tp1, _Del, shared_ptr&>
 207         operator=(unique_ptr<_Tp1, _Del>&& __r)
 208         {
 209           _Base_type::operator=(std::move(__r));
 210           return *this;
 211         }
 212
 213       // C++14 20.8.2.2.4
 214       // swap & reset
 215       // 8.2.1.2 shared_ptr observers
 216       // in __shared_ptr
 217
 218     private:
 219       template<typename _Alloc, typename... _Args>
 220         shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
 221                    _Args&&... __args)
 222         : _Base_type(__tag, __a, std::forward<_Args>(__args)...)
 223         { _M_enable_shared_from_this_with(this->get()); }
 224
 225       template<typename _Tp1, typename _Alloc, typename... _Args>
 226         friend shared_ptr<_Tp1>
 227         allocate_shared(const _Alloc& __a, _Args&&...  __args);
 228
 229       shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t)
 230       : _Base_type(__r, std::nothrow) { }
 231
 232       friend class weak_ptr<_Tp>;
 233
 234       template<typename _Yp>
 235         using __esft_base_t =
 236           decltype(__expt_enable_shared_from_this_base(std::declval<_Yp*>()));
 237
 238       // Detect an accessible and unambiguous enable_shared_from_this base.
 239       template<typename _Yp, typename = void>
 240         struct __has_esft_base
 241         : false_type { };
 242
 243       template<typename _Yp>
 244         struct __has_esft_base<_Yp, __void_t<__esft_base_t<_Yp>>>
 245         : __bool_constant<!is_array_v<_Tp>> { };  // ignore base for arrays
 246
 247       template<typename _Yp>
 248         typename enable_if<__has_esft_base<_Yp>::value>::type
 249         _M_enable_shared_from_this_with(const _Yp* __p) noexcept
 250         {
 251           if (auto __base = __expt_enable_shared_from_this_base(__p))
 252             {
 253               __base->_M_weak_this
 254                 = shared_ptr<_Yp>(*this, const_cast<_Yp*>(__p));
 255             }
 256         }
 257
 258       template<typename _Yp>
 259         typename enable_if<!__has_esft_base<_Yp>::value>::type
 260         _M_enable_shared_from_this_with(const _Yp*) noexcept
 261         { }
 262     };
 263
 264   // C++14 20.8.2.2.7
 265   template<typename _Tp1, typename _Tp2>
 266     bool operator==(const shared_ptr<_Tp1>& __a,
 267                     const shared_ptr<_Tp2>& __b) noexcept
 268     { return __a.get() == __b.get(); }
 269
 270   template<typename _Tp>
 271     inline bool
 272     operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
 273     { return !__a; }
 274
 275   template<typename _Tp>
 276     inline bool
 277     operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
 278     { return !__a; }
 279
 280   template<typename _Tp1, typename _Tp2>
 281     inline bool
 282     operator!=(const shared_ptr<_Tp1>& __a,
 283                const shared_ptr<_Tp2>& __b) noexcept
 284     { return __a.get() != __b.get(); }
 285
 286   template<typename _Tp>
 287     inline bool
 288     operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
 289     { return (bool)__a; }
 290
 291   template<typename _Tp>
 292     inline bool
 293     operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
 294     { return (bool)__a; }
 295
 296   template<typename _Tp1, typename _Tp2>
 297     inline bool
 298     operator<(const shared_ptr<_Tp1>& __a,
 299               const shared_ptr<_Tp2>& __b) noexcept
 300     {
 301       using __elem_t1 = typename shared_ptr<_Tp1>::element_type;
 302       using __elem_t2 = typename shared_ptr<_Tp2>::element_type;
 303       using _CT = common_type_t<__elem_t1*, __elem_t2*>;
 304       return std::less<_CT>()(__a.get(), __b.get());
 305     }
 306
 307   template<typename _Tp>
 308     inline bool
 309     operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
 310     {
 311       using __elem_t = typename shared_ptr<_Tp>::element_type;
 312       return std::less<__elem_t*>()(__a.get(), nullptr);
 313     }
 314
 315   template<typename _Tp>
 316     inline bool
 317     operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
 318     {
 319       using __elem_t = typename shared_ptr<_Tp>::element_type;
 320       return std::less<__elem_t*>()(nullptr, __a.get());
 321     }
 322
 323   template<typename _Tp1, typename _Tp2>
 324     inline bool
 325     operator<=(const shared_ptr<_Tp1>& __a,
 326                const shared_ptr<_Tp2>& __b) noexcept
 327     { return !(__b < __a); }
 328
 329   template<typename _Tp>
 330     inline bool
 331     operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
 332     { return !(nullptr < __a); }
 333
 334   template<typename _Tp>
 335     inline bool
 336     operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
 337     { return !(__a < nullptr); }
 338
 339   template<typename _Tp1, typename _Tp2>
 340     inline bool
 341     operator>(const shared_ptr<_Tp1>& __a,
 342               const shared_ptr<_Tp2>& __b) noexcept
 343     { return (__b < __a); }
 344
 345   template<typename _Tp>
 346     inline bool
 347     operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
 348     {
 349       using __elem_t = typename shared_ptr<_Tp>::element_type;
 350       return std::less<__elem_t*>()(nullptr, __a.get());
 351     }
 352
 353   template<typename _Tp>
 354     inline bool
 355     operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
 356     {
 357       using __elem_t = typename shared_ptr<_Tp>::element_type;
 358       return std::less<__elem_t*>()(__a.get(), nullptr);
 359     }
 360
 361   template<typename _Tp1, typename _Tp2>
 362     inline bool
 363     operator>=(const shared_ptr<_Tp1>& __a,
 364                const shared_ptr<_Tp2>& __b) noexcept
 365     { return !(__a < __b); }
 366
 367   template<typename _Tp>
 368     inline bool
 369     operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
 370     { return !(__a < nullptr); }
 371
 372   template<typename _Tp>
 373     inline bool
 374     operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
 375     { return !(nullptr < __a); }
 376
 377   // C++14 20.8.2.2.8
 378   template<typename _Tp>
 379     inline void
 380     swap(shared_ptr<_Tp>& __a, shared_ptr<_Tp>& __b) noexcept
 381     { __a.swap(__b); }
 382
 383   // 8.2.1.3, shared_ptr casts
 384   template<typename _Tp, typename _Tp1>
 385     inline shared_ptr<_Tp>
 386     static_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
 387     {
 388       using __elem_t = typename shared_ptr<_Tp>::element_type;
 389       return shared_ptr<_Tp>(__r, static_cast<__elem_t*>(__r.get()));
 390     }
 391
 392   template<typename _Tp, typename _Tp1>
 393     inline shared_ptr<_Tp>
 394     dynamic_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
 395     {
 396       using __elem_t = typename shared_ptr<_Tp>::element_type;
 397       if (_Tp* __p = dynamic_cast<__elem_t*>(__r.get()))
 398         return shared_ptr<_Tp>(__r, __p);
 399       return shared_ptr<_Tp>();
 400     }
 401
 402   template<typename _Tp, typename _Tp1>
 403     inline shared_ptr<_Tp>
 404     const_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
 405     {
 406       using __elem_t = typename shared_ptr<_Tp>::element_type;
 407       return shared_ptr<_Tp>(__r, const_cast<__elem_t*>(__r.get()));
 408     }
 409
 410   template<typename _Tp, typename _Tp1>
 411     inline shared_ptr<_Tp>
 412     reinterpret_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
 413     {
 414       using __elem_t = typename shared_ptr<_Tp>::element_type;
 415       return shared_ptr<_Tp>(__r, reinterpret_cast<__elem_t*>(__r.get()));
 416     }
 417
 418   // C++14 20.8.2.3
 419   template<typename _Tp>
 420     class weak_ptr : public __weak_ptr<_Tp>
 421     {
 422       template<typename _Tp1, typename _Res = void>
 423         using _Compatible = enable_if_t<__sp_compatible_v<_Tp1, _Tp>, _Res>;
 424
 425       using _Base_type = __weak_ptr<_Tp>;
 426
 427      public:
 428        constexpr weak_ptr() noexcept = default;
 429
 430        template<typename _Tp1, typename = _Compatible<_Tp1>>
 431          weak_ptr(const shared_ptr<_Tp1>& __r) noexcept
 432          : _Base_type(__r) { }
 433
 434        weak_ptr(const weak_ptr&) noexcept = default;
 435
 436        template<typename _Tp1, typename = _Compatible<_Tp1>>
 437          weak_ptr(const weak_ptr<_Tp1>& __r) noexcept
 438          : _Base_type(__r) { }
 439
 440        weak_ptr(weak_ptr&&) noexcept = default;
 441
 442        template<typename _Tp1, typename = _Compatible<_Tp1>>
 443          weak_ptr(weak_ptr<_Tp1>&& __r) noexcept
 444          : _Base_type(std::move(__r)) { }
 445
 446        weak_ptr&
 447        operator=(const weak_ptr& __r) noexcept = default;
 448
 449        template<typename _Tp1>
 450          _Compatible<_Tp1, weak_ptr&>
 451          operator=(const weak_ptr<_Tp1>& __r) noexcept
 452          {
 453            this->_Base_type::operator=(__r);
 454            return *this;
 455          }
 456
 457        template<typename _Tp1>
 458          _Compatible<_Tp1, weak_ptr&>
 459          operator=(const shared_ptr<_Tp1>& __r) noexcept
 460          {
 461            this->_Base_type::operator=(__r);
 462            return *this;
 463          }
 464
 465        weak_ptr&
 466        operator=(weak_ptr&& __r) noexcept = default;
 467
 468        template<typename _Tp1>
 469          _Compatible<_Tp1, weak_ptr&>
 470          operator=(weak_ptr<_Tp1>&& __r) noexcept
 471          {
 472            this->_Base_type::operator=(std::move(__r));
 473            return *this;
 474          }
 475
 476        shared_ptr<_Tp>
 477        lock() const noexcept
 478        { return shared_ptr<_Tp>(*this, std::nothrow); }
 479
 480        friend class enable_shared_from_this<_Tp>;
 481     };
 482
 483   // C++14 20.8.2.3.6
 484   template<typename _Tp>
 485     inline void
 486     swap(weak_ptr<_Tp>& __a, weak_ptr<_Tp>& __b) noexcept
 487     { __a.swap(__b); }
 488
 489   /// C++14 20.8.2.2.10
 490   template<typename _Del, typename _Tp>
 491     inline _Del*
 492     get_deleter(const shared_ptr<_Tp>& __p) noexcept
 493     { return std::get_deleter<_Del>(__p); }
 494
 495   // C++14 20.8.2.2.11
 496   template<typename _Ch, typename _Tr, typename _Tp>
 497     inline std::basic_ostream<_Ch, _Tr>&
 498     operator<<(std::basic_ostream<_Ch, _Tr>& __os, const shared_ptr<_Tp>& __p)
 499     {
 500       __os << __p.get();
 501       return __os;
 502     }
 503
 504   // C++14 20.8.2.4
 505   template<typename _Tp = void> class owner_less;
 506
 507    /// Partial specialization of owner_less for shared_ptr.
 508   template<typename _Tp>
 509     struct owner_less<shared_ptr<_Tp>>
 510     : public _Sp_owner_less<shared_ptr<_Tp>, weak_ptr<_Tp>>
 511     { };
 512
 513   /// Partial specialization of owner_less for weak_ptr.
 514   template<typename _Tp>
 515     struct owner_less<weak_ptr<_Tp>>
 516     : public _Sp_owner_less<weak_ptr<_Tp>, shared_ptr<_Tp>>
 517     { };
 518
 519   template<>
 520     class owner_less<void>
 521     {
 522       template<typename _Tp, typename _Up>
 523         bool
 524         operator()(shared_ptr<_Tp> const& __lhs,
 525                    shared_ptr<_Up> const& __rhs) const
 526         { return __lhs.owner_before(__rhs); }
 527
 528       template<typename _Tp, typename _Up>
 529         bool
 530         operator()(shared_ptr<_Tp> const& __lhs,
 531                    weak_ptr<_Up> const& __rhs) const
 532         { return __lhs.owner_before(__rhs); }
 533
 534       template<typename _Tp, typename _Up>
 535         bool
 536         operator()(weak_ptr<_Tp> const& __lhs,
 537                    shared_ptr<_Up> const& __rhs) const
 538         { return __lhs.owner_before(__rhs); }
 539
 540       template<typename _Tp, typename _Up>
 541         bool
 542         operator()(weak_ptr<_Tp> const& __lhs,
 543                    weak_ptr<_Up> const& __rhs) const
 544         { return __lhs.owner_before(__rhs); }
 545
 546       typedef void is_transparent;
 547     };
 548
 549    // C++14 20.8.2.6
 550    template<typename _Tp>
 551      inline bool
 552      atomic_is_lock_free(const shared_ptr<_Tp>* __p)
 553      { return std::atomic_is_lock_free<_Tp, __default_lock_policy>(__p); }
 554
 555    template<typename _Tp>
 556      shared_ptr<_Tp> atomic_load(const shared_ptr<_Tp>* __p)
 557      { return std::atomic_load<_Tp>(__p); }
 558
 559    template<typename _Tp>
 560      shared_ptr<_Tp>
 561      atomic_load_explicit(const shared_ptr<_Tp>* __p, memory_order __mo)
 562      { return std::atomic_load_explicit<_Tp>(__p, __mo); }
 563
 564    template<typename _Tp>
 565      void atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
 566      { return std::atomic_store<_Tp>(__p, __r); }
 567
 568    template<typename _Tp>
 569      shared_ptr<_Tp>
 570      atomic_store_explicit(const shared_ptr<_Tp>* __p,
 571                            shared_ptr<_Tp> __r,
 572                            memory_order __mo)
 573      { return std::atomic_store_explicit<_Tp>(__p, __r, __mo); }
 574
 575    template<typename _Tp>
 576      void atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
 577      { return std::atomic_exchange<_Tp>(__p, __r); }
 578
 579    template<typename _Tp>
 580      shared_ptr<_Tp>
 581      atomic_exchange_explicit(const shared_ptr<_Tp>* __p,
 582                               shared_ptr<_Tp> __r,
 583                               memory_order __mo)
 584      { return std::atomic_exchange_explicit<_Tp>(__p, __r, __mo); }
 585
 586    template<typename _Tp>
 587      bool atomic_compare_exchange_weak(shared_ptr<_Tp>* __p,
 588                                        shared_ptr<_Tp>* __v,
 589                                        shared_ptr<_Tp> __w)
 590      { return std::atomic_compare_exchange_weak<_Tp>(__p, __v, __w); }
 591
 592    template<typename _Tp>
 593      bool atomic_compare_exchange_strong(shared_ptr<_Tp>* __p,
 594                                          shared_ptr<_Tp>* __v,
 595                                          shared_ptr<_Tp> __w)
 596      { return std::atomic_compare_exchange_strong<_Tp>(__p, __v, __w); }
 597
 598    template<typename _Tp>
 599      bool atomic_compare_exchange_weak_explicit(shared_ptr<_Tp>* __p,
 600                                                 shared_ptr<_Tp>* __v,
 601                                                 shared_ptr<_Tp> __w,
 602                                                 memory_order __success,
 603                                                 memory_order __failure)
 604      { return std::atomic_compare_exchange_weak_explicit<_Tp>(__p, __v, __w,
 605                                                               __success,
 606                                                               __failure); }
 607
 608    template<typename _Tp>
 609      bool atomic_compare_exchange_strong_explicit(shared_ptr<_Tp>* __p,
 610                                                   shared_ptr<_Tp>* __v,
 611                                                   shared_ptr<_Tp> __w,
 612                                                   memory_order __success,
 613                                                   memory_order __failure)
 614      { return std::atomic_compare_exchange_strong_explicit<_Tp>(__p, __v, __w,
 615                                                                 __success,
 616                                                                 __failure); }
 617
 618   //enable_shared_from_this
 619   template<typename _Tp>
 620     class enable_shared_from_this
 621     {
 622     protected:
 623       constexpr enable_shared_from_this() noexcept { }
 624
 625       enable_shared_from_this(const enable_shared_from_this&) noexcept { }
 626
 627       enable_shared_from_this&
 628       operator=(const enable_shared_from_this&) noexcept
 629       { return *this; }
 630
 631       ~enable_shared_from_this() { }
 632
 633     public:
 634       shared_ptr<_Tp>
 635       shared_from_this()
 636       { return shared_ptr<_Tp>(this->_M_weak_this); }
 637
 638       shared_ptr<const _Tp>
 639       shared_from_this() const
 640       { return shared_ptr<const _Tp>(this->_M_weak_this); }
 641
 642       weak_ptr<_Tp>
 643       weak_from_this() noexcept
 644       { return _M_weak_this; }
 645
 646       weak_ptr<const _Tp>
 647       weak_from_this() const noexcept
 648       { return _M_weak_this; }
 649
 650     private:
 651       template<typename _Tp1>
 652         void
 653         _M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
 654         { _M_weak_this._M_assign(__p, __n); }
 655
 656       // Found by ADL when this is an associated class.
 657       friend const enable_shared_from_this*
 658       __expt_enable_shared_from_this_base(const enable_shared_from_this* __p)
 659       { return __p; }
 660
 661       template<typename>
 662         friend class shared_ptr;
 663
 664       mutable weak_ptr<_Tp> _M_weak_this;
 665     };
 666 } // namespace fundamentals_v2
 667 } // namespace experimental
 668
 669   /// std::hash specialization for shared_ptr.
 670   template<typename _Tp>
 671     struct hash<experimental::shared_ptr<_Tp>>
 672     : public __hash_base<size_t, experimental::shared_ptr<_Tp>>
 673     {
 674       size_t
 675       operator()(const experimental::shared_ptr<_Tp>& __s) const noexcept
 676       { return std::hash<_Tp*>()(__s.get()); }
 677     };
 678
 679 _GLIBCXX_END_NAMESPACE_VERSION
 680 } // namespace std
 681
 682 #endif // __cplusplus <= 201103L
 683
 684 #endif // _GLIBCXX_EXPERIMENTAL_SHARED_PTR_H