libstdc++-v3/include/bits/shared_ptr_base.h

   1 // shared_ptr and weak_ptr implementation details -*- C++ -*-
   2
   3 // Copyright (C) 2007-2016 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 bits/shared_ptr_base.h
  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_BASE_H
  50 #define _SHARED_PTR_BASE_H 1
  51
  52 #include <typeinfo>
  53 #include <bits/allocated_ptr.h>
  54 #include <ext/aligned_buffer.h>
  55
  56 namespace std _GLIBCXX_VISIBILITY(default)
  57 {
  58 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  59
  60 #if _GLIBCXX_USE_DEPRECATED
  61   template<typename> class auto_ptr;
  62 #endif
  63
  64  /**
  65    *  @brief  Exception possibly thrown by @c shared_ptr.
  66    *  @ingroup exceptions
  67    */
  68   class bad_weak_ptr : public std::exception
  69   {
  70   public:
  71     virtual char const* what() const noexcept;
  72
  73     virtual ~bad_weak_ptr() noexcept;
  74   };
  75
  76   // Substitute for bad_weak_ptr object in the case of -fno-exceptions.
  77   inline void
  78   __throw_bad_weak_ptr()
  79   { _GLIBCXX_THROW_OR_ABORT(bad_weak_ptr()); }
  80
  81   using __gnu_cxx::_Lock_policy;
  82   using __gnu_cxx::__default_lock_policy;
  83   using __gnu_cxx::_S_single;
  84   using __gnu_cxx::_S_mutex;
  85   using __gnu_cxx::_S_atomic;
  86
  87   // Empty helper class except when the template argument is _S_mutex.
  88   template<_Lock_policy _Lp>
  89     class _Mutex_base
  90     {
  91     protected:
  92       // The atomic policy uses fully-fenced builtins, single doesn't care.
  93       enum { _S_need_barriers = 0 };
  94     };
  95
  96   template<>
  97     class _Mutex_base<_S_mutex>
  98     : public __gnu_cxx::__mutex
  99     {
 100     protected:
 101       // This policy is used when atomic builtins are not available.
 102       // The replacement atomic operations might not have the necessary
 103       // memory barriers.
 104       enum { _S_need_barriers = 1 };
 105     };
 106
 107   template<_Lock_policy _Lp = __default_lock_policy>
 108     class _Sp_counted_base
 109     : public _Mutex_base<_Lp>
 110     {
 111     public:
 112       _Sp_counted_base() noexcept
 113       : _M_use_count(1), _M_weak_count(1) { }
 114
 115       virtual
 116       ~_Sp_counted_base() noexcept
 117       { }
 118
 119       // Called when _M_use_count drops to zero, to release the resources
 120       // managed by *this.
 121       virtual void
 122       _M_dispose() noexcept = 0;
 123
 124       // Called when _M_weak_count drops to zero.
 125       virtual void
 126       _M_destroy() noexcept
 127       { delete this; }
 128
 129       virtual void*
 130       _M_get_deleter(const std::type_info&) noexcept = 0;
 131
 132       void
 133       _M_add_ref_copy()
 134       { __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
 135
 136       void
 137       _M_add_ref_lock();
 138
 139       bool
 140       _M_add_ref_lock_nothrow();
 141
 142       void
 143       _M_release() noexcept
 144       {
 145         // Be race-detector-friendly.  For more info see bits/c++config.
 146         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_use_count);
 147         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
 148           {
 149             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_use_count);
 150             _M_dispose();
 151             // There must be a memory barrier between dispose() and destroy()
 152             // to ensure that the effects of dispose() are observed in the
 153             // thread that runs destroy().
 154             // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
 155             if (_Mutex_base<_Lp>::_S_need_barriers)
 156               {
 157                 __atomic_thread_fence (__ATOMIC_ACQ_REL);
 158               }
 159
 160             // Be race-detector-friendly.  For more info see bits/c++config.
 161             _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 162             if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
 163                                                        -1) == 1)
 164               {
 165                 _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 166                 _M_destroy();
 167               }
 168           }
 169       }
 170
 171       void
 172       _M_weak_add_ref() noexcept
 173       { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
 174
 175       void
 176       _M_weak_release() noexcept
 177       {
 178         // Be race-detector-friendly. For more info see bits/c++config.
 179         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 180         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
 181           {
 182             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 183             if (_Mutex_base<_Lp>::_S_need_barriers)
 184               {
 185                 // See _M_release(),
 186                 // destroy() must observe results of dispose()
 187                 __atomic_thread_fence (__ATOMIC_ACQ_REL);
 188               }
 189             _M_destroy();
 190           }
 191       }
 192
 193       long
 194       _M_get_use_count() const noexcept
 195       {
 196         // No memory barrier is used here so there is no synchronization
 197         // with other threads.
 198         return __atomic_load_n(&_M_use_count, __ATOMIC_RELAXED);
 199       }
 200
 201     private:
 202       _Sp_counted_base(_Sp_counted_base const&) = delete;
 203       _Sp_counted_base& operator=(_Sp_counted_base const&) = delete;
 204
 205       _Atomic_word  _M_use_count;     // #shared
 206       _Atomic_word  _M_weak_count;    // #weak + (#shared != 0)
 207     };
 208
 209   template<>
 210     inline void
 211     _Sp_counted_base<_S_single>::
 212     _M_add_ref_lock()
 213     {
 214       if (_M_use_count == 0)
 215         __throw_bad_weak_ptr();
 216       ++_M_use_count;
 217     }
 218
 219   template<>
 220     inline void
 221     _Sp_counted_base<_S_mutex>::
 222     _M_add_ref_lock()
 223     {
 224       __gnu_cxx::__scoped_lock sentry(*this);
 225       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 226         {
 227           _M_use_count = 0;
 228           __throw_bad_weak_ptr();
 229         }
 230     }
 231
 232   template<>
 233     inline void
 234     _Sp_counted_base<_S_atomic>::
 235     _M_add_ref_lock()
 236     {
 237       // Perform lock-free add-if-not-zero operation.
 238       _Atomic_word __count = _M_get_use_count();
 239       do
 240         {
 241           if (__count == 0)
 242             __throw_bad_weak_ptr();
 243           // Replace the current counter value with the old value + 1, as
 244           // long as it's not changed meanwhile.
 245         }
 246       while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
 247                                           true, __ATOMIC_ACQ_REL,
 248                                           __ATOMIC_RELAXED));
 249     }
 250
 251   template<>
 252     inline bool
 253     _Sp_counted_base<_S_single>::
 254     _M_add_ref_lock_nothrow()
 255     {
 256       if (_M_use_count == 0)
 257         return false;
 258       ++_M_use_count;
 259       return true;
 260     }
 261
 262   template<>
 263     inline bool
 264     _Sp_counted_base<_S_mutex>::
 265     _M_add_ref_lock_nothrow()
 266     {
 267       __gnu_cxx::__scoped_lock sentry(*this);
 268       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 269         {
 270           _M_use_count = 0;
 271           return false;
 272         }
 273       return true;
 274     }
 275
 276   template<>
 277     inline bool
 278     _Sp_counted_base<_S_atomic>::
 279     _M_add_ref_lock_nothrow()
 280     {
 281       // Perform lock-free add-if-not-zero operation.
 282       _Atomic_word __count = _M_get_use_count();
 283       do
 284         {
 285           if (__count == 0)
 286             return false;
 287           // Replace the current counter value with the old value + 1, as
 288           // long as it's not changed meanwhile.
 289         }
 290       while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
 291                                           true, __ATOMIC_ACQ_REL,
 292                                           __ATOMIC_RELAXED));
 293       return true;
 294     }
 295
 296   template<>
 297     inline void
 298     _Sp_counted_base<_S_single>::_M_add_ref_copy()
 299     { ++_M_use_count; }
 300
 301   template<>
 302     inline void
 303     _Sp_counted_base<_S_single>::_M_release() noexcept
 304     {
 305       if (--_M_use_count == 0)
 306         {
 307           _M_dispose();
 308           if (--_M_weak_count == 0)
 309             _M_destroy();
 310         }
 311     }
 312
 313   template<>
 314     inline void
 315     _Sp_counted_base<_S_single>::_M_weak_add_ref() noexcept
 316     { ++_M_weak_count; }
 317
 318   template<>
 319     inline void
 320     _Sp_counted_base<_S_single>::_M_weak_release() noexcept
 321     {
 322       if (--_M_weak_count == 0)
 323         _M_destroy();
 324     }
 325
 326   template<>
 327     inline long
 328     _Sp_counted_base<_S_single>::_M_get_use_count() const noexcept
 329     { return _M_use_count; }
 330
 331
 332   // Forward declarations.
 333   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 334     class __shared_ptr;
 335
 336   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 337     class __weak_ptr;
 338
 339   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 340     class __enable_shared_from_this;
 341
 342   template<typename _Tp>
 343     class shared_ptr;
 344
 345   template<typename _Tp>
 346     class weak_ptr;
 347
 348   template<typename _Tp>
 349     struct owner_less;
 350
 351   template<typename _Tp>
 352     class enable_shared_from_this;
 353
 354   template<_Lock_policy _Lp = __default_lock_policy>
 355     class __weak_count;
 356
 357   template<_Lock_policy _Lp = __default_lock_policy>
 358     class __shared_count;
 359
 360
 361   // Counted ptr with no deleter or allocator support
 362   template<typename _Ptr, _Lock_policy _Lp>
 363     class _Sp_counted_ptr final : public _Sp_counted_base<_Lp>
 364     {
 365     public:
 366       explicit
 367       _Sp_counted_ptr(_Ptr __p) noexcept
 368       : _M_ptr(__p) { }
 369
 370       virtual void
 371       _M_dispose() noexcept
 372       { delete _M_ptr; }
 373
 374       virtual void
 375       _M_destroy() noexcept
 376       { delete this; }
 377
 378       virtual void*
 379       _M_get_deleter(const std::type_info&) noexcept
 380       { return nullptr; }
 381
 382       _Sp_counted_ptr(const _Sp_counted_ptr&) = delete;
 383       _Sp_counted_ptr& operator=(const _Sp_counted_ptr&) = delete;
 384
 385     private:
 386       _Ptr             _M_ptr;
 387     };
 388
 389   template<>
 390     inline void
 391     _Sp_counted_ptr<nullptr_t, _S_single>::_M_dispose() noexcept { }
 392
 393   template<>
 394     inline void
 395     _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() noexcept { }
 396
 397   template<>
 398     inline void
 399     _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }
 400
 401   template<int _Nm, typename _Tp,
 402            bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>
 403     struct _Sp_ebo_helper;
 404
 405   /// Specialization using EBO.
 406   template<int _Nm, typename _Tp>
 407     struct _Sp_ebo_helper<_Nm, _Tp, true> : private _Tp
 408     {
 409       explicit _Sp_ebo_helper(const _Tp& __tp) : _Tp(__tp) { }
 410
 411       static _Tp&
 412       _S_get(_Sp_ebo_helper& __eboh) { return static_cast<_Tp&>(__eboh); }
 413     };
 414
 415   /// Specialization not using EBO.
 416   template<int _Nm, typename _Tp>
 417     struct _Sp_ebo_helper<_Nm, _Tp, false>
 418     {
 419       explicit _Sp_ebo_helper(const _Tp& __tp) : _M_tp(__tp) { }
 420
 421       static _Tp&
 422       _S_get(_Sp_ebo_helper& __eboh)
 423       { return __eboh._M_tp; }
 424
 425     private:
 426       _Tp _M_tp;
 427     };
 428
 429   // Support for custom deleter and/or allocator
 430   template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>
 431     class _Sp_counted_deleter final : public _Sp_counted_base<_Lp>
 432     {
 433       class _Impl : _Sp_ebo_helper<0, _Deleter>, _Sp_ebo_helper<1, _Alloc>
 434       {
 435         typedef _Sp_ebo_helper<0, _Deleter>     _Del_base;
 436         typedef _Sp_ebo_helper<1, _Alloc>       _Alloc_base;
 437
 438       public:
 439         _GLIBCXX_ABI_TAG_EMPTY
 440         _Impl(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept
 441         : _M_ptr(__p), _Del_base(__d), _Alloc_base(__a)
 442         { }
 443
 444         _Deleter& _M_del() noexcept { return _Del_base::_S_get(*this); }
 445         _Alloc& _M_alloc() noexcept { return _Alloc_base::_S_get(*this); }
 446
 447         _Ptr _M_ptr;
 448       };
 449
 450     public:
 451       using __allocator_type = __alloc_rebind<_Alloc, _Sp_counted_deleter>;
 452
 453       // __d(__p) must not throw.
 454       _Sp_counted_deleter(_Ptr __p, _Deleter __d) noexcept
 455       : _M_impl(__p, __d, _Alloc()) { }
 456
 457       // __d(__p) must not throw.
 458       _GLIBCXX_ABI_TAG_EMPTY
 459       _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept
 460       : _M_impl(__p, __d, __a) { }
 461
 462       ~_Sp_counted_deleter() noexcept { }
 463
 464       virtual void
 465       _M_dispose() noexcept
 466       { _M_impl._M_del()(_M_impl._M_ptr); }
 467
 468       virtual void
 469       _M_destroy() noexcept
 470       {
 471         __allocator_type __a(_M_impl._M_alloc());
 472         __allocated_ptr<__allocator_type> __guard_ptr{ __a, this };
 473         this->~_Sp_counted_deleter();
 474       }
 475
 476       virtual void*
 477       _M_get_deleter(const std::type_info& __ti) noexcept
 478       {
 479 #if __cpp_rtti
 480         // _GLIBCXX_RESOLVE_LIB_DEFECTS
 481         // 2400. shared_ptr's get_deleter() should use addressof()
 482         return __ti == typeid(_Deleter)
 483           ? std::__addressof(_M_impl._M_del())
 484           : nullptr;
 485 #else
 486         return nullptr;
 487 #endif
 488       }
 489
 490     private:
 491       _Impl _M_impl;
 492     };
 493
 494   // helpers for make_shared / allocate_shared
 495
 496   struct _Sp_make_shared_tag { };
 497
 498   template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
 499     class _Sp_counted_ptr_inplace final : public _Sp_counted_base<_Lp>
 500     {
 501       class _Impl : _Sp_ebo_helper<0, _Alloc>
 502       {
 503         typedef _Sp_ebo_helper<0, _Alloc>       _A_base;
 504
 505       public:
 506         explicit _Impl(_Alloc __a) noexcept : _A_base(__a) { }
 507
 508         _Alloc& _M_alloc() noexcept { return _A_base::_S_get(*this); }
 509
 510         __gnu_cxx::__aligned_buffer<_Tp> _M_storage;
 511       };
 512
 513     public:
 514       using __allocator_type = __alloc_rebind<_Alloc, _Sp_counted_ptr_inplace>;
 515
 516       template<typename... _Args>
 517         _Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)
 518         : _M_impl(__a)
 519         {
 520           // _GLIBCXX_RESOLVE_LIB_DEFECTS
 521           // 2070.  allocate_shared should use allocator_traits<A>::construct
 522           allocator_traits<_Alloc>::construct(__a, _M_ptr(),
 523               std::forward<_Args>(__args)...); // might throw
 524         }
 525
 526       ~_Sp_counted_ptr_inplace() noexcept { }
 527
 528       virtual void
 529       _M_dispose() noexcept
 530       {
 531         allocator_traits<_Alloc>::destroy(_M_impl._M_alloc(), _M_ptr());
 532       }
 533
 534       // Override because the allocator needs to know the dynamic type
 535       virtual void
 536       _M_destroy() noexcept
 537       {
 538         __allocator_type __a(_M_impl._M_alloc());
 539         __allocated_ptr<__allocator_type> __guard_ptr{ __a, this };
 540         this->~_Sp_counted_ptr_inplace();
 541       }
 542
 543       // Sneaky trick so __shared_ptr can get the managed pointer
 544       virtual void*
 545       _M_get_deleter(const std::type_info& __ti) noexcept
 546       {
 547 #if __cpp_rtti
 548         if (__ti == typeid(_Sp_make_shared_tag))
 549           return const_cast<typename remove_cv<_Tp>::type*>(_M_ptr());
 550 #endif
 551         return nullptr;
 552       }
 553
 554     private:
 555       _Tp* _M_ptr() noexcept { return _M_impl._M_storage._M_ptr(); }
 556
 557       _Impl _M_impl;
 558     };
 559
 560
 561   template<_Lock_policy _Lp>
 562     class __shared_count
 563     {
 564     public:
 565       constexpr __shared_count() noexcept : _M_pi(0)
 566       { }
 567
 568       template<typename _Ptr>
 569         explicit
 570         __shared_count(_Ptr __p) : _M_pi(0)
 571         {
 572           __try
 573             {
 574               _M_pi = new _Sp_counted_ptr<_Ptr, _Lp>(__p);
 575             }
 576           __catch(...)
 577             {
 578               delete __p;
 579               __throw_exception_again;
 580             }
 581         }
 582
 583       template<typename _Ptr, typename _Deleter>
 584         __shared_count(_Ptr __p, _Deleter __d)
 585         : __shared_count(__p, std::move(__d), allocator<void>())
 586         { }
 587
 588       template<typename _Ptr, typename _Deleter, typename _Alloc>
 589         _GLIBCXX_ABI_TAG_EMPTY
 590         __shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
 591         {
 592           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 593           __try
 594             {
 595               typename _Sp_cd_type::__allocator_type __a2(__a);
 596               auto __guard = std::__allocate_guarded(__a2);
 597               _Sp_cd_type* __mem = __guard.get();
 598               ::new (__mem) _Sp_cd_type(__p, std::move(__d), std::move(__a));
 599               _M_pi = __mem;
 600               __guard = nullptr;
 601             }
 602           __catch(...)
 603             {
 604               __d(__p); // Call _Deleter on __p.
 605               __throw_exception_again;
 606             }
 607         }
 608
 609       template<typename _Tp, typename _Alloc, typename... _Args>
 610         __shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,
 611                        _Args&&... __args)
 612         : _M_pi(0)
 613         {
 614           typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
 615           typename _Sp_cp_type::__allocator_type __a2(__a);
 616           auto __guard = std::__allocate_guarded(__a2);
 617           _Sp_cp_type* __mem = __guard.get();
 618           ::new (__mem) _Sp_cp_type(std::move(__a),
 619                                     std::forward<_Args>(__args)...);
 620           _M_pi = __mem;
 621           __guard = nullptr;
 622         }
 623
 624 #if _GLIBCXX_USE_DEPRECATED
 625       // Special case for auto_ptr<_Tp> to provide the strong guarantee.
 626       template<typename _Tp>
 627         explicit
 628         __shared_count(std::auto_ptr<_Tp>&& __r);
 629 #endif
 630
 631       // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
 632       template<typename _Tp, typename _Del>
 633         explicit
 634         __shared_count(std::unique_ptr<_Tp, _Del>&& __r) : _M_pi(0)
 635         {
 636           // _GLIBCXX_RESOLVE_LIB_DEFECTS
 637           // 2415. Inconsistency between unique_ptr and shared_ptr
 638           if (__r.get() == nullptr)
 639             return;
 640
 641           using _Ptr = typename unique_ptr<_Tp, _Del>::pointer;
 642           using _Del2 = typename conditional<is_reference<_Del>::value,
 643               reference_wrapper<typename remove_reference<_Del>::type>,
 644               _Del>::type;
 645           using _Sp_cd_type
 646             = _Sp_counted_deleter<_Ptr, _Del2, allocator<void>, _Lp>;
 647           using _Alloc = allocator<_Sp_cd_type>;
 648           using _Alloc_traits = allocator_traits<_Alloc>;
 649           _Alloc __a;
 650           _Sp_cd_type* __mem = _Alloc_traits::allocate(__a, 1);
 651           _Alloc_traits::construct(__a, __mem, __r.release(),
 652                                    __r.get_deleter());  // non-throwing
 653           _M_pi = __mem;
 654         }
 655
 656       // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
 657       explicit __shared_count(const __weak_count<_Lp>& __r);
 658
 659       // Does not throw if __r._M_get_use_count() == 0, caller must check.
 660       explicit __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t);
 661
 662       ~__shared_count() noexcept
 663       {
 664         if (_M_pi != nullptr)
 665           _M_pi->_M_release();
 666       }
 667
 668       __shared_count(const __shared_count& __r) noexcept
 669       : _M_pi(__r._M_pi)
 670       {
 671         if (_M_pi != 0)
 672           _M_pi->_M_add_ref_copy();
 673       }
 674
 675       __shared_count&
 676       operator=(const __shared_count& __r) noexcept
 677       {
 678         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 679         if (__tmp != _M_pi)
 680           {
 681             if (__tmp != 0)
 682               __tmp->_M_add_ref_copy();
 683             if (_M_pi != 0)
 684               _M_pi->_M_release();
 685             _M_pi = __tmp;
 686           }
 687         return *this;
 688       }
 689
 690       void
 691       _M_swap(__shared_count& __r) noexcept
 692       {
 693         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 694         __r._M_pi = _M_pi;
 695         _M_pi = __tmp;
 696       }
 697
 698       long
 699       _M_get_use_count() const noexcept
 700       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 701
 702       bool
 703       _M_unique() const noexcept
 704       { return this->_M_get_use_count() == 1; }
 705
 706       void*
 707       _M_get_deleter(const std::type_info& __ti) const noexcept
 708       { return _M_pi ? _M_pi->_M_get_deleter(__ti) : nullptr; }
 709
 710       bool
 711       _M_less(const __shared_count& __rhs) const noexcept
 712       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 713
 714       bool
 715       _M_less(const __weak_count<_Lp>& __rhs) const noexcept
 716       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 717
 718       // Friend function injected into enclosing namespace and found by ADL
 719       friend inline bool
 720       operator==(const __shared_count& __a, const __shared_count& __b) noexcept
 721       { return __a._M_pi == __b._M_pi; }
 722
 723     private:
 724       friend class __weak_count<_Lp>;
 725
 726       _Sp_counted_base<_Lp>*  _M_pi;
 727     };
 728
 729
 730   template<_Lock_policy _Lp>
 731     class __weak_count
 732     {
 733     public:
 734       constexpr __weak_count() noexcept : _M_pi(nullptr)
 735       { }
 736
 737       __weak_count(const __shared_count<_Lp>& __r) noexcept
 738       : _M_pi(__r._M_pi)
 739       {
 740         if (_M_pi != nullptr)
 741           _M_pi->_M_weak_add_ref();
 742       }
 743
 744       __weak_count(const __weak_count& __r) noexcept
 745       : _M_pi(__r._M_pi)
 746       {
 747         if (_M_pi != nullptr)
 748           _M_pi->_M_weak_add_ref();
 749       }
 750
 751       __weak_count(__weak_count&& __r) noexcept
 752       : _M_pi(__r._M_pi)
 753       { __r._M_pi = nullptr; }
 754
 755       ~__weak_count() noexcept
 756       {
 757         if (_M_pi != nullptr)
 758           _M_pi->_M_weak_release();
 759       }
 760
 761       __weak_count&
 762       operator=(const __shared_count<_Lp>& __r) noexcept
 763       {
 764         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 765         if (__tmp != nullptr)
 766           __tmp->_M_weak_add_ref();
 767         if (_M_pi != nullptr)
 768           _M_pi->_M_weak_release();
 769         _M_pi = __tmp;
 770         return *this;
 771       }
 772
 773       __weak_count&
 774       operator=(const __weak_count& __r) noexcept
 775       {
 776         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 777         if (__tmp != nullptr)
 778           __tmp->_M_weak_add_ref();
 779         if (_M_pi != nullptr)
 780           _M_pi->_M_weak_release();
 781         _M_pi = __tmp;
 782         return *this;
 783       }
 784
 785       __weak_count&
 786       operator=(__weak_count&& __r) noexcept
 787       {
 788         if (_M_pi != nullptr)
 789           _M_pi->_M_weak_release();
 790         _M_pi = __r._M_pi;
 791         __r._M_pi = nullptr;
 792         return *this;
 793       }
 794
 795       void
 796       _M_swap(__weak_count& __r) noexcept
 797       {
 798         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 799         __r._M_pi = _M_pi;
 800         _M_pi = __tmp;
 801       }
 802
 803       long
 804       _M_get_use_count() const noexcept
 805       { return _M_pi != nullptr ? _M_pi->_M_get_use_count() : 0; }
 806
 807       bool
 808       _M_less(const __weak_count& __rhs) const noexcept
 809       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 810
 811       bool
 812       _M_less(const __shared_count<_Lp>& __rhs) const noexcept
 813       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 814
 815       // Friend function injected into enclosing namespace and found by ADL
 816       friend inline bool
 817       operator==(const __weak_count& __a, const __weak_count& __b) noexcept
 818       { return __a._M_pi == __b._M_pi; }
 819
 820     private:
 821       friend class __shared_count<_Lp>;
 822
 823       _Sp_counted_base<_Lp>*  _M_pi;
 824     };
 825
 826   // Now that __weak_count is defined we can define this constructor:
 827   template<_Lock_policy _Lp>
 828     inline
 829     __shared_count<_Lp>::__shared_count(const __weak_count<_Lp>& __r)
 830     : _M_pi(__r._M_pi)
 831     {
 832       if (_M_pi != nullptr)
 833         _M_pi->_M_add_ref_lock();
 834       else
 835         __throw_bad_weak_ptr();
 836     }
 837
 838   // Now that __weak_count is defined we can define this constructor:
 839   template<_Lock_policy _Lp>
 840     inline
 841     __shared_count<_Lp>::
 842     __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t)
 843     : _M_pi(__r._M_pi)
 844     {
 845       if (_M_pi != nullptr)
 846         if (!_M_pi->_M_add_ref_lock_nothrow())
 847           _M_pi = nullptr;
 848     }
 849
 850   // Support for enable_shared_from_this.
 851
 852   // Friend of __enable_shared_from_this.
 853   template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
 854     void
 855     __enable_shared_from_this_helper(const __shared_count<_Lp>&,
 856                                      const __enable_shared_from_this<_Tp1,
 857                                      _Lp>*, const _Tp2*) noexcept;
 858
 859   // Friend of enable_shared_from_this.
 860   template<typename _Tp1, typename _Tp2>
 861     void
 862     __enable_shared_from_this_helper(const __shared_count<>&,
 863                                      const enable_shared_from_this<_Tp1>*,
 864                                      const _Tp2*) noexcept;
 865
 866   template<_Lock_policy _Lp>
 867     inline void
 868     __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept
 869     { }
 870
 871
 872   template<typename _Tp, _Lock_policy _Lp>
 873     class __shared_ptr
 874     {
 875       template<typename _Ptr>
 876         using _Convertible
 877           = typename enable_if<is_convertible<_Ptr, _Tp*>::value>::type;
 878
 879     public:
 880       typedef _Tp   element_type;
 881
 882       constexpr __shared_ptr() noexcept
 883       : _M_ptr(0), _M_refcount()
 884       { }
 885
 886       template<typename _Tp1>
 887         explicit __shared_ptr(_Tp1* __p)
 888         : _M_ptr(__p), _M_refcount(__p)
 889         {
 890           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 891           static_assert( !is_void<_Tp1>::value, "incomplete type" );
 892           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 893           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 894         }
 895
 896       template<typename _Tp1, typename _Deleter>
 897         __shared_ptr(_Tp1* __p, _Deleter __d)
 898         : _M_ptr(__p), _M_refcount(__p, __d)
 899         {
 900           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 901           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 902           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 903         }
 904
 905       template<typename _Tp1, typename _Deleter, typename _Alloc>
 906         _GLIBCXX_ABI_TAG_EMPTY
 907         __shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
 908         : _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
 909         {
 910           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 911           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 912           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 913         }
 914
 915       template<typename _Deleter>
 916         __shared_ptr(nullptr_t __p, _Deleter __d)
 917         : _M_ptr(0), _M_refcount(__p, __d)
 918         { }
 919
 920       template<typename _Deleter, typename _Alloc>
 921         _GLIBCXX_ABI_TAG_EMPTY
 922         __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
 923         : _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
 924         { }
 925
 926       template<typename _Tp1>
 927         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p) noexcept
 928         : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
 929         { }
 930
 931       __shared_ptr(const __shared_ptr&) noexcept = default;
 932       __shared_ptr& operator=(const __shared_ptr&) noexcept = default;
 933       ~__shared_ptr() = default;
 934
 935       template<typename _Tp1, typename = _Convertible<_Tp1*>>
 936         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 937         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
 938         { }
 939
 940       __shared_ptr(__shared_ptr&& __r) noexcept
 941       : _M_ptr(__r._M_ptr), _M_refcount()
 942       {
 943         _M_refcount._M_swap(__r._M_refcount);
 944         __r._M_ptr = 0;
 945       }
 946
 947       template<typename _Tp1, typename = _Convertible<_Tp1*>>
 948         __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
 949         : _M_ptr(__r._M_ptr), _M_refcount()
 950         {
 951           _M_refcount._M_swap(__r._M_refcount);
 952           __r._M_ptr = 0;
 953         }
 954
 955       template<typename _Tp1>
 956         explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
 957         : _M_refcount(__r._M_refcount) // may throw
 958         {
 959           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 960
 961           // It is now safe to copy __r._M_ptr, as
 962           // _M_refcount(__r._M_refcount) did not throw.
 963           _M_ptr = __r._M_ptr;
 964         }
 965
 966       // If an exception is thrown this constructor has no effect.
 967       template<typename _Tp1, typename _Del, typename
 968                = _Convertible<typename unique_ptr<_Tp1, _Del>::pointer>>
 969         __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
 970         : _M_ptr(__r.get()), _M_refcount()
 971         {
 972           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 973           auto __raw = _S_raw_ptr(__r.get());
 974           _M_refcount = __shared_count<_Lp>(std::move(__r));
 975           __enable_shared_from_this_helper(_M_refcount, __raw, __raw);
 976         }
 977
 978 #if _GLIBCXX_USE_DEPRECATED
 979       // Postcondition: use_count() == 1 and __r.get() == 0
 980       template<typename _Tp1>
 981         __shared_ptr(std::auto_ptr<_Tp1>&& __r);
 982 #endif
 983
 984       constexpr __shared_ptr(nullptr_t) noexcept : __shared_ptr() { }
 985
 986       template<typename _Tp1>
 987         __shared_ptr&
 988         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 989         {
 990           _M_ptr = __r._M_ptr;
 991           _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
 992           return *this;
 993         }
 994
 995 #if _GLIBCXX_USE_DEPRECATED
 996       template<typename _Tp1>
 997         __shared_ptr&
 998         operator=(std::auto_ptr<_Tp1>&& __r)
 999         {
1000           __shared_ptr(std::move(__r)).swap(*this);
1001           return *this;
1002         }
1003 #endif
1004
1005       __shared_ptr&
1006       operator=(__shared_ptr&& __r) noexcept
1007       {
1008         __shared_ptr(std::move(__r)).swap(*this);
1009         return *this;
1010       }
1011
1012       template<class _Tp1>
1013         __shared_ptr&
1014         operator=(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
1015         {
1016           __shared_ptr(std::move(__r)).swap(*this);
1017           return *this;
1018         }
1019
1020       template<typename _Tp1, typename _Del>
1021         __shared_ptr&
1022         operator=(std::unique_ptr<_Tp1, _Del>&& __r)
1023         {
1024           __shared_ptr(std::move(__r)).swap(*this);
1025           return *this;
1026         }
1027
1028       void
1029       reset() noexcept
1030       { __shared_ptr().swap(*this); }
1031
1032       template<typename _Tp1>
1033         void
1034         reset(_Tp1* __p) // _Tp1 must be complete.
1035         {
1036           // Catch self-reset errors.
1037           __glibcxx_assert(__p == 0 || __p != _M_ptr);
1038           __shared_ptr(__p).swap(*this);
1039         }
1040
1041       template<typename _Tp1, typename _Deleter>
1042         void
1043         reset(_Tp1* __p, _Deleter __d)
1044         { __shared_ptr(__p, __d).swap(*this); }
1045
1046       template<typename _Tp1, typename _Deleter, typename _Alloc>
1047         _GLIBCXX_ABI_TAG_EMPTY
1048         void
1049         reset(_Tp1* __p, _Deleter __d, _Alloc __a)
1050         { __shared_ptr(__p, __d, std::move(__a)).swap(*this); }
1051
1052       // Allow class instantiation when _Tp is [cv-qual] void.
1053       typename std::add_lvalue_reference<_Tp>::type
1054       operator*() const noexcept
1055       {
1056         __glibcxx_assert(_M_ptr != 0);
1057         return *_M_ptr;
1058       }
1059
1060       _Tp*
1061       operator->() const noexcept
1062       {
1063         _GLIBCXX_DEBUG_PEDASSERT(_M_ptr != 0);
1064         return _M_ptr;
1065       }
1066
1067       _Tp*
1068       get() const noexcept
1069       { return _M_ptr; }
1070
1071       explicit operator bool() const // never throws
1072       { return _M_ptr == 0 ? false : true; }
1073
1074       bool
1075       unique() const noexcept
1076       { return _M_refcount._M_unique(); }
1077
1078       long
1079       use_count() const noexcept
1080       { return _M_refcount._M_get_use_count(); }
1081
1082       void
1083       swap(__shared_ptr<_Tp, _Lp>& __other) noexcept
1084       {
1085         std::swap(_M_ptr, __other._M_ptr);
1086         _M_refcount._M_swap(__other._M_refcount);
1087       }
1088
1089       template<typename _Tp1>
1090         bool
1091         owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const
1092         { return _M_refcount._M_less(__rhs._M_refcount); }
1093
1094       template<typename _Tp1>
1095         bool
1096         owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const
1097         { return _M_refcount._M_less(__rhs._M_refcount); }
1098
1099 #if __cpp_rtti
1100     protected:
1101       // This constructor is non-standard, it is used by allocate_shared.
1102       template<typename _Alloc, typename... _Args>
1103         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1104                      _Args&&... __args)
1105         : _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,
1106                                 std::forward<_Args>(__args)...)
1107         {
1108           // _M_ptr needs to point to the newly constructed object.
1109           // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
1110           void* __p = _M_refcount._M_get_deleter(typeid(__tag));
1111           _M_ptr = static_cast<_Tp*>(__p);
1112           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1113         }
1114 #else
1115       template<typename _Alloc>
1116         struct _Deleter
1117         {
1118           void operator()(typename _Alloc::value_type* __ptr)
1119           {
1120             __allocated_ptr<_Alloc> __guard{ _M_alloc, __ptr };
1121             allocator_traits<_Alloc>::destroy(_M_alloc, __guard.get());
1122           }
1123           _Alloc _M_alloc;
1124         };
1125
1126       template<typename _Alloc, typename... _Args>
1127         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1128                      _Args&&... __args)
1129         : _M_ptr(), _M_refcount()
1130         {
1131           typedef typename allocator_traits<_Alloc>::template
1132             rebind_traits<typename std::remove_cv<_Tp>::type> __traits;
1133           _Deleter<typename __traits::allocator_type> __del = { __a };
1134           auto __guard = std::__allocate_guarded(__del._M_alloc);
1135           auto __ptr = __guard.get();
1136           // _GLIBCXX_RESOLVE_LIB_DEFECTS
1137           // 2070. allocate_shared should use allocator_traits<A>::construct
1138           __traits::construct(__del._M_alloc, __ptr,
1139                               std::forward<_Args>(__args)...);
1140           __guard = nullptr;
1141           __shared_count<_Lp> __count(__ptr, __del, __del._M_alloc);
1142           _M_refcount._M_swap(__count);
1143           _M_ptr = __ptr;
1144           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1145         }
1146 #endif
1147
1148       template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
1149                typename... _Args>
1150         friend __shared_ptr<_Tp1, _Lp1>
1151         __allocate_shared(const _Alloc& __a, _Args&&... __args);
1152
1153       // This constructor is used by __weak_ptr::lock() and
1154       // shared_ptr::shared_ptr(const weak_ptr&, std::nothrow_t).
1155       __shared_ptr(const __weak_ptr<_Tp, _Lp>& __r, std::nothrow_t)
1156       : _M_refcount(__r._M_refcount, std::nothrow)
1157       {
1158         _M_ptr = _M_refcount._M_get_use_count() ? __r._M_ptr : nullptr;
1159       }
1160
1161       friend class __weak_ptr<_Tp, _Lp>;
1162
1163     private:
1164       void*
1165       _M_get_deleter(const std::type_info& __ti) const noexcept
1166       { return _M_refcount._M_get_deleter(__ti); }
1167
1168       template<typename _Tp1>
1169         static _Tp1*
1170         _S_raw_ptr(_Tp1* __ptr)
1171         { return __ptr; }
1172
1173       template<typename _Tp1>
1174         static auto
1175         _S_raw_ptr(_Tp1 __ptr) -> decltype(std::__addressof(*__ptr))
1176         { return std::__addressof(*__ptr); }
1177
1178       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1179       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1180
1181       template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1182         friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&) noexcept;
1183
1184       _Tp*                 _M_ptr;         // Contained pointer.
1185       __shared_count<_Lp>  _M_refcount;    // Reference counter.
1186     };
1187
1188
1189   // 20.7.2.2.7 shared_ptr comparisons
1190   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1191     inline bool
1192     operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1193                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1194     { return __a.get() == __b.get(); }
1195
1196   template<typename _Tp, _Lock_policy _Lp>
1197     inline bool
1198     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1199     { return !__a; }
1200
1201   template<typename _Tp, _Lock_policy _Lp>
1202     inline bool
1203     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1204     { return !__a; }
1205
1206   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1207     inline bool
1208     operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1209                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1210     { return __a.get() != __b.get(); }
1211
1212   template<typename _Tp, _Lock_policy _Lp>
1213     inline bool
1214     operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1215     { return (bool)__a; }
1216
1217   template<typename _Tp, _Lock_policy _Lp>
1218     inline bool
1219     operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1220     { return (bool)__a; }
1221
1222   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1223     inline bool
1224     operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1225               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1226     {
1227       typedef typename std::common_type<_Tp1*, _Tp2*>::type _CT;
1228       return std::less<_CT>()(__a.get(), __b.get());
1229     }
1230
1231   template<typename _Tp, _Lock_policy _Lp>
1232     inline bool
1233     operator<(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1234     { return std::less<_Tp*>()(__a.get(), nullptr); }
1235
1236   template<typename _Tp, _Lock_policy _Lp>
1237     inline bool
1238     operator<(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1239     { return std::less<_Tp*>()(nullptr, __a.get()); }
1240
1241   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1242     inline bool
1243     operator<=(const __shared_ptr<_Tp1, _Lp>& __a,
1244                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1245     { return !(__b < __a); }
1246
1247   template<typename _Tp, _Lock_policy _Lp>
1248     inline bool
1249     operator<=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1250     { return !(nullptr < __a); }
1251
1252   template<typename _Tp, _Lock_policy _Lp>
1253     inline bool
1254     operator<=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1255     { return !(__a < nullptr); }
1256
1257   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1258     inline bool
1259     operator>(const __shared_ptr<_Tp1, _Lp>& __a,
1260               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1261     { return (__b < __a); }
1262
1263   template<typename _Tp, _Lock_policy _Lp>
1264     inline bool
1265     operator>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1266     { return std::less<_Tp*>()(nullptr, __a.get()); }
1267
1268   template<typename _Tp, _Lock_policy _Lp>
1269     inline bool
1270     operator>(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1271     { return std::less<_Tp*>()(__a.get(), nullptr); }
1272
1273   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1274     inline bool
1275     operator>=(const __shared_ptr<_Tp1, _Lp>& __a,
1276                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1277     { return !(__a < __b); }
1278
1279   template<typename _Tp, _Lock_policy _Lp>
1280     inline bool
1281     operator>=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1282     { return !(__a < nullptr); }
1283
1284   template<typename _Tp, _Lock_policy _Lp>
1285     inline bool
1286     operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1287     { return !(nullptr < __a); }
1288
1289   template<typename _Sp>
1290     struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1291     {
1292       bool
1293       operator()(const _Sp& __lhs, const _Sp& __rhs) const noexcept
1294       {
1295         typedef typename _Sp::element_type element_type;
1296         return std::less<element_type*>()(__lhs.get(), __rhs.get());
1297       }
1298     };
1299
1300   template<typename _Tp, _Lock_policy _Lp>
1301     struct less<__shared_ptr<_Tp, _Lp>>
1302     : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1303     { };
1304
1305   // 20.7.2.2.8 shared_ptr specialized algorithms.
1306   template<typename _Tp, _Lock_policy _Lp>
1307     inline void
1308     swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b) noexcept
1309     { __a.swap(__b); }
1310
1311   // 20.7.2.2.9 shared_ptr casts
1312
1313   // The seemingly equivalent code:
1314   // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1315   // will eventually result in undefined behaviour, attempting to
1316   // delete the same object twice.
1317   /// static_pointer_cast
1318   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1319     inline __shared_ptr<_Tp, _Lp>
1320     static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1321     { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1322
1323   // The seemingly equivalent code:
1324   // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1325   // will eventually result in undefined behaviour, attempting to
1326   // delete the same object twice.
1327   /// const_pointer_cast
1328   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1329     inline __shared_ptr<_Tp, _Lp>
1330     const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1331     { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1332
1333   // The seemingly equivalent code:
1334   // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1335   // will eventually result in undefined behaviour, attempting to
1336   // delete the same object twice.
1337   /// dynamic_pointer_cast
1338   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1339     inline __shared_ptr<_Tp, _Lp>
1340     dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1341     {
1342       if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1343         return __shared_ptr<_Tp, _Lp>(__r, __p);
1344       return __shared_ptr<_Tp, _Lp>();
1345     }
1346
1347
1348   template<typename _Tp, _Lock_policy _Lp>
1349     class __weak_ptr
1350     {
1351       template<typename _Ptr>
1352         using _Convertible
1353           = typename enable_if<is_convertible<_Ptr, _Tp*>::value>::type;
1354
1355     public:
1356       typedef _Tp element_type;
1357
1358       constexpr __weak_ptr() noexcept
1359       : _M_ptr(nullptr), _M_refcount()
1360       { }
1361
1362       __weak_ptr(const __weak_ptr&) noexcept = default;
1363
1364       ~__weak_ptr() = default;
1365
1366       // The "obvious" converting constructor implementation:
1367       //
1368       //  template<typename _Tp1>
1369       //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1370       //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1371       //    { }
1372       //
1373       // has a serious problem.
1374       //
1375       //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1376       //  conversion may require access to *__r._M_ptr (virtual inheritance).
1377       //
1378       // It is not possible to avoid spurious access violations since
1379       // in multithreaded programs __r._M_ptr may be invalidated at any point.
1380       template<typename _Tp1, typename = _Convertible<_Tp1*>>
1381         __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1382         : _M_refcount(__r._M_refcount)
1383         { _M_ptr = __r.lock().get(); }
1384
1385       template<typename _Tp1, typename = _Convertible<_Tp1*>>
1386         __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1387         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
1388         { }
1389
1390       __weak_ptr(__weak_ptr&& __r) noexcept
1391       : _M_ptr(__r._M_ptr), _M_refcount(std::move(__r._M_refcount))
1392       { __r._M_ptr = nullptr; }
1393
1394       template<typename _Tp1, typename = _Convertible<_Tp1*>>
1395         __weak_ptr(__weak_ptr<_Tp1, _Lp>&& __r) noexcept
1396         : _M_ptr(__r.lock().get()), _M_refcount(std::move(__r._M_refcount))
1397         { __r._M_ptr = nullptr; }
1398
1399       __weak_ptr&
1400       operator=(const __weak_ptr& __r) noexcept = default;
1401
1402       template<typename _Tp1>
1403         __weak_ptr&
1404         operator=(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1405         {
1406           _M_ptr = __r.lock().get();
1407           _M_refcount = __r._M_refcount;
1408           return *this;
1409         }
1410
1411       template<typename _Tp1>
1412         __weak_ptr&
1413         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1414         {
1415           _M_ptr = __r._M_ptr;
1416           _M_refcount = __r._M_refcount;
1417           return *this;
1418         }
1419
1420       __weak_ptr&
1421       operator=(__weak_ptr&& __r) noexcept
1422       {
1423         _M_ptr = __r._M_ptr;
1424         _M_refcount = std::move(__r._M_refcount);
1425         __r._M_ptr = nullptr;
1426         return *this;
1427       }
1428
1429       template<typename _Tp1>
1430         __weak_ptr&
1431         operator=(__weak_ptr<_Tp1, _Lp>&& __r) noexcept
1432         {
1433           _M_ptr = __r.lock().get();
1434           _M_refcount = std::move(__r._M_refcount);
1435           __r._M_ptr = nullptr;
1436           return *this;
1437         }
1438
1439       __shared_ptr<_Tp, _Lp>
1440       lock() const noexcept
1441       { return __shared_ptr<element_type, _Lp>(*this, std::nothrow); }
1442
1443       long
1444       use_count() const noexcept
1445       { return _M_refcount._M_get_use_count(); }
1446
1447       bool
1448       expired() const noexcept
1449       { return _M_refcount._M_get_use_count() == 0; }
1450
1451       template<typename _Tp1>
1452         bool
1453         owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1454         { return _M_refcount._M_less(__rhs._M_refcount); }
1455
1456       template<typename _Tp1>
1457         bool
1458         owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1459         { return _M_refcount._M_less(__rhs._M_refcount); }
1460
1461       void
1462       reset() noexcept
1463       { __weak_ptr().swap(*this); }
1464
1465       void
1466       swap(__weak_ptr& __s) noexcept
1467       {
1468         std::swap(_M_ptr, __s._M_ptr);
1469         _M_refcount._M_swap(__s._M_refcount);
1470       }
1471
1472     private:
1473       // Used by __enable_shared_from_this.
1474       void
1475       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
1476       {
1477         if (use_count() == 0)
1478           {
1479             _M_ptr = __ptr;
1480             _M_refcount = __refcount;
1481           }
1482       }
1483
1484       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1485       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1486       friend class __enable_shared_from_this<_Tp, _Lp>;
1487       friend class enable_shared_from_this<_Tp>;
1488
1489       _Tp*               _M_ptr;         // Contained pointer.
1490       __weak_count<_Lp>  _M_refcount;    // Reference counter.
1491     };
1492
1493   // 20.7.2.3.6 weak_ptr specialized algorithms.
1494   template<typename _Tp, _Lock_policy _Lp>
1495     inline void
1496     swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b) noexcept
1497     { __a.swap(__b); }
1498
1499   template<typename _Tp, typename _Tp1>
1500     struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1501     {
1502       bool
1503       operator()(const _Tp& __lhs, const _Tp& __rhs) const
1504       { return __lhs.owner_before(__rhs); }
1505
1506       bool
1507       operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1508       { return __lhs.owner_before(__rhs); }
1509
1510       bool
1511       operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1512       { return __lhs.owner_before(__rhs); }
1513     };
1514
1515   template<typename _Tp, _Lock_policy _Lp>
1516     struct owner_less<__shared_ptr<_Tp, _Lp>>
1517     : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1518     { };
1519
1520   template<typename _Tp, _Lock_policy _Lp>
1521     struct owner_less<__weak_ptr<_Tp, _Lp>>
1522     : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1523     { };
1524
1525
1526   template<typename _Tp, _Lock_policy _Lp>
1527     class __enable_shared_from_this
1528     {
1529     protected:
1530       constexpr __enable_shared_from_this() noexcept { }
1531
1532       __enable_shared_from_this(const __enable_shared_from_this&) noexcept { }
1533
1534       __enable_shared_from_this&
1535       operator=(const __enable_shared_from_this&) noexcept
1536       { return *this; }
1537
1538       ~__enable_shared_from_this() { }
1539
1540     public:
1541       __shared_ptr<_Tp, _Lp>
1542       shared_from_this()
1543       { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1544
1545       __shared_ptr<const _Tp, _Lp>
1546       shared_from_this() const
1547       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1548
1549     private:
1550       template<typename _Tp1>
1551         void
1552         _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
1553         { _M_weak_this._M_assign(__p, __n); }
1554
1555       template<_Lock_policy _Lp1, typename _Tp1, typename _Tp2>
1556         friend void
1557         __enable_shared_from_this_helper(const __shared_count<_Lp1>&,
1558                                          const __enable_shared_from_this<_Tp1,
1559                                          _Lp1>*, const _Tp2*) noexcept;
1560
1561       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
1562     };
1563
1564   template<_Lock_policy _Lp1, typename _Tp1, typename _Tp2>
1565     inline void
1566     __enable_shared_from_this_helper(const __shared_count<_Lp1>& __pn,
1567                                      const __enable_shared_from_this<_Tp1,
1568                                      _Lp1>* __pe,
1569                                      const _Tp2* __px) noexcept
1570     {
1571       if (__pe != nullptr)
1572         __pe->_M_weak_assign(const_cast<_Tp2*>(__px), __pn);
1573     }
1574
1575   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1576     inline __shared_ptr<_Tp, _Lp>
1577     __allocate_shared(const _Alloc& __a, _Args&&... __args)
1578     {
1579       return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
1580                                     std::forward<_Args>(__args)...);
1581     }
1582
1583   template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1584     inline __shared_ptr<_Tp, _Lp>
1585     __make_shared(_Args&&... __args)
1586     {
1587       typedef typename std::remove_const<_Tp>::type _Tp_nc;
1588       return std::__allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1589                                               std::forward<_Args>(__args)...);
1590     }
1591
1592   /// std::hash specialization for __shared_ptr.
1593   template<typename _Tp, _Lock_policy _Lp>
1594     struct hash<__shared_ptr<_Tp, _Lp>>
1595     : public __hash_base<size_t, __shared_ptr<_Tp, _Lp>>
1596     {
1597       size_t
1598       operator()(const __shared_ptr<_Tp, _Lp>& __s) const noexcept
1599       { return std::hash<_Tp*>()(__s.get()); }
1600     };
1601
1602 _GLIBCXX_END_NAMESPACE_VERSION
1603 } // namespace
1604
1605 #endif // _SHARED_PTR_BASE_H