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

   1 // shared_ptr and weak_ptr implementation details -*- C++ -*-
   2
   3 // Copyright (C) 2007-2014 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 <bits/allocated_ptr.h>
  53 #include <ext/aligned_buffer.h>
  54
  55 namespace std _GLIBCXX_VISIBILITY(default)
  56 {
  57 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  58
  59 #if _GLIBCXX_USE_DEPRECATED
  60   template<typename> class auto_ptr;
  61 #endif
  62
  63  /**
  64    *  @brief  Exception possibly thrown by @c shared_ptr.
  65    *  @ingroup exceptions
  66    */
  67   class bad_weak_ptr : public std::exception
  68   {
  69   public:
  70     virtual char const*
  71     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                 _GLIBCXX_READ_MEM_BARRIER;
 158                 _GLIBCXX_WRITE_MEM_BARRIER;
 159               }
 160
 161             // Be race-detector-friendly.  For more info see bits/c++config.
 162             _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 163             if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
 164                                                        -1) == 1)
 165               {
 166                 _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 167                 _M_destroy();
 168               }
 169           }
 170       }
 171
 172       void
 173       _M_weak_add_ref() noexcept
 174       { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
 175
 176       void
 177       _M_weak_release() noexcept
 178       {
 179         // Be race-detector-friendly. For more info see bits/c++config.
 180         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 181         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
 182           {
 183             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 184             if (_Mutex_base<_Lp>::_S_need_barriers)
 185               {
 186                 // See _M_release(),
 187                 // destroy() must observe results of dispose()
 188                 _GLIBCXX_READ_MEM_BARRIER;
 189                 _GLIBCXX_WRITE_MEM_BARRIER;
 190               }
 191             _M_destroy();
 192           }
 193       }
 194
 195       long
 196       _M_get_use_count() const noexcept
 197       {
 198         // No memory barrier is used here so there is no synchronization
 199         // with other threads.
 200         return __atomic_load_n(&_M_use_count, __ATOMIC_RELAXED);
 201       }
 202
 203     private:
 204       _Sp_counted_base(_Sp_counted_base const&) = delete;
 205       _Sp_counted_base& operator=(_Sp_counted_base const&) = delete;
 206
 207       _Atomic_word  _M_use_count;     // #shared
 208       _Atomic_word  _M_weak_count;    // #weak + (#shared != 0)
 209     };
 210
 211   template<>
 212     inline void
 213     _Sp_counted_base<_S_single>::
 214     _M_add_ref_lock()
 215     {
 216       if (_M_use_count == 0)
 217         __throw_bad_weak_ptr();
 218       ++_M_use_count;
 219     }
 220
 221   template<>
 222     inline void
 223     _Sp_counted_base<_S_mutex>::
 224     _M_add_ref_lock()
 225     {
 226       __gnu_cxx::__scoped_lock sentry(*this);
 227       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 228         {
 229           _M_use_count = 0;
 230           __throw_bad_weak_ptr();
 231         }
 232     }
 233
 234   template<>
 235     inline void
 236     _Sp_counted_base<_S_atomic>::
 237     _M_add_ref_lock()
 238     {
 239       // Perform lock-free add-if-not-zero operation.
 240       _Atomic_word __count = _M_get_use_count();
 241       do
 242         {
 243           if (__count == 0)
 244             __throw_bad_weak_ptr();
 245           // Replace the current counter value with the old value + 1, as
 246           // long as it's not changed meanwhile.
 247         }
 248       while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
 249                                           true, __ATOMIC_ACQ_REL,
 250                                           __ATOMIC_RELAXED));
 251     }
 252
 253   template<>
 254     inline bool
 255     _Sp_counted_base<_S_single>::
 256     _M_add_ref_lock_nothrow()
 257     {
 258       if (_M_use_count == 0)
 259         return false;
 260       ++_M_use_count;
 261       return true;
 262     }
 263
 264   template<>
 265     inline bool
 266     _Sp_counted_base<_S_mutex>::
 267     _M_add_ref_lock_nothrow()
 268     {
 269       __gnu_cxx::__scoped_lock sentry(*this);
 270       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 271         {
 272           _M_use_count = 0;
 273           return false;
 274         }
 275       return true;
 276     }
 277
 278   template<>
 279     inline bool
 280     _Sp_counted_base<_S_atomic>::
 281     _M_add_ref_lock_nothrow()
 282     {
 283       // Perform lock-free add-if-not-zero operation.
 284       _Atomic_word __count = _M_get_use_count();
 285       do
 286         {
 287           if (__count == 0)
 288             return false;
 289           // Replace the current counter value with the old value + 1, as
 290           // long as it's not changed meanwhile.
 291         }
 292       while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
 293                                           true, __ATOMIC_ACQ_REL,
 294                                           __ATOMIC_RELAXED));
 295       return true;
 296     }
 297
 298   template<>
 299     inline void
 300     _Sp_counted_base<_S_single>::_M_add_ref_copy()
 301     { ++_M_use_count; }
 302
 303   template<>
 304     inline void
 305     _Sp_counted_base<_S_single>::_M_release() noexcept
 306     {
 307       if (--_M_use_count == 0)
 308         {
 309           _M_dispose();
 310           if (--_M_weak_count == 0)
 311             _M_destroy();
 312         }
 313     }
 314
 315   template<>
 316     inline void
 317     _Sp_counted_base<_S_single>::_M_weak_add_ref() noexcept
 318     { ++_M_weak_count; }
 319
 320   template<>
 321     inline void
 322     _Sp_counted_base<_S_single>::_M_weak_release() noexcept
 323     {
 324       if (--_M_weak_count == 0)
 325         _M_destroy();
 326     }
 327
 328   template<>
 329     inline long
 330     _Sp_counted_base<_S_single>::_M_get_use_count() const noexcept
 331     { return _M_use_count; }
 332
 333
 334   // Forward declarations.
 335   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 336     class __shared_ptr;
 337
 338   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 339     class __weak_ptr;
 340
 341   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 342     class __enable_shared_from_this;
 343
 344   template<typename _Tp>
 345     class shared_ptr;
 346
 347   template<typename _Tp>
 348     class weak_ptr;
 349
 350   template<typename _Tp>
 351     struct owner_less;
 352
 353   template<typename _Tp>
 354     class enable_shared_from_this;
 355
 356   template<_Lock_policy _Lp = __default_lock_policy>
 357     class __weak_count;
 358
 359   template<_Lock_policy _Lp = __default_lock_policy>
 360     class __shared_count;
 361
 362
 363   // Counted ptr with no deleter or allocator support
 364   template<typename _Ptr, _Lock_policy _Lp>
 365     class _Sp_counted_ptr final : public _Sp_counted_base<_Lp>
 366     {
 367     public:
 368       explicit
 369       _Sp_counted_ptr(_Ptr __p) noexcept
 370       : _M_ptr(__p) { }
 371
 372       virtual void
 373       _M_dispose() noexcept
 374       { delete _M_ptr; }
 375
 376       virtual void
 377       _M_destroy() noexcept
 378       { delete this; }
 379
 380       virtual void*
 381       _M_get_deleter(const std::type_info&) noexcept
 382       { return nullptr; }
 383
 384       _Sp_counted_ptr(const _Sp_counted_ptr&) = delete;
 385       _Sp_counted_ptr& operator=(const _Sp_counted_ptr&) = delete;
 386
 387     private:
 388       _Ptr             _M_ptr;
 389     };
 390
 391   template<>
 392     inline void
 393     _Sp_counted_ptr<nullptr_t, _S_single>::_M_dispose() noexcept { }
 394
 395   template<>
 396     inline void
 397     _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() noexcept { }
 398
 399   template<>
 400     inline void
 401     _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }
 402
 403   template<int _Nm, typename _Tp,
 404            bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>
 405     struct _Sp_ebo_helper;
 406
 407   /// Specialization using EBO.
 408   template<int _Nm, typename _Tp>
 409     struct _Sp_ebo_helper<_Nm, _Tp, true> : private _Tp
 410     {
 411       explicit _Sp_ebo_helper(const _Tp& __tp) : _Tp(__tp) { }
 412
 413       static _Tp&
 414       _S_get(_Sp_ebo_helper& __eboh) { return static_cast<_Tp&>(__eboh); }
 415     };
 416
 417   /// Specialization not using EBO.
 418   template<int _Nm, typename _Tp>
 419     struct _Sp_ebo_helper<_Nm, _Tp, false>
 420     {
 421       explicit _Sp_ebo_helper(const _Tp& __tp) : _M_tp(__tp) { }
 422
 423       static _Tp&
 424       _S_get(_Sp_ebo_helper& __eboh)
 425       { return __eboh._M_tp; }
 426
 427     private:
 428       _Tp _M_tp;
 429     };
 430
 431   // Support for custom deleter and/or allocator
 432   template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>
 433     class _Sp_counted_deleter final : public _Sp_counted_base<_Lp>
 434     {
 435       class _Impl : _Sp_ebo_helper<0, _Deleter>, _Sp_ebo_helper<1, _Alloc>
 436       {
 437         typedef _Sp_ebo_helper<0, _Deleter>     _Del_base;
 438         typedef _Sp_ebo_helper<1, _Alloc>       _Alloc_base;
 439
 440       public:
 441         _Impl(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept
 442         : _M_ptr(__p), _Del_base(__d), _Alloc_base(__a)
 443         { }
 444
 445         _Deleter& _M_del() noexcept { return _Del_base::_S_get(*this); }
 446         _Alloc& _M_alloc() noexcept { return _Alloc_base::_S_get(*this); }
 447
 448         _Ptr _M_ptr;
 449       };
 450
 451     public:
 452       using __allocator_type = __alloc_rebind<_Alloc, _Sp_counted_deleter>;
 453
 454       // __d(__p) must not throw.
 455       _Sp_counted_deleter(_Ptr __p, _Deleter __d) noexcept
 456       : _M_impl(__p, __d, _Alloc()) { }
 457
 458       // __d(__p) must not throw.
 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         __shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
 590         {
 591           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 592           __try
 593             {
 594               typename _Sp_cd_type::__allocator_type __a2(__a);
 595               auto __guard = std::__allocate_guarded(__a2);
 596               _Sp_cd_type* __mem = __guard.get();
 597               ::new (__mem) _Sp_cd_type(__p, std::move(__d), std::move(__a));
 598               _M_pi = __mem;
 599               __guard = nullptr;
 600             }
 601           __catch(...)
 602             {
 603               __d(__p); // Call _Deleter on __p.
 604               __throw_exception_again;
 605             }
 606         }
 607
 608       template<typename _Tp, typename _Alloc, typename... _Args>
 609         __shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,
 610                        _Args&&... __args)
 611         : _M_pi(0)
 612         {
 613           typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
 614           typename _Sp_cp_type::__allocator_type __a2(__a);
 615           auto __guard = std::__allocate_guarded(__a2);
 616           _Sp_cp_type* __mem = __guard.get();
 617           ::new (__mem) _Sp_cp_type(std::move(__a),
 618                                     std::forward<_Args>(__args)...);
 619           _M_pi = __mem;
 620           __guard = nullptr;
 621         }
 622
 623 #if _GLIBCXX_USE_DEPRECATED
 624       // Special case for auto_ptr<_Tp> to provide the strong guarantee.
 625       template<typename _Tp>
 626         explicit
 627         __shared_count(std::auto_ptr<_Tp>&& __r);
 628 #endif
 629
 630       // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
 631       template<typename _Tp, typename _Del>
 632         explicit
 633         __shared_count(std::unique_ptr<_Tp, _Del>&& __r) : _M_pi(0)
 634         {
 635           using _Ptr = typename unique_ptr<_Tp, _Del>::pointer;
 636           using _Del2 = typename conditional<is_reference<_Del>::value,
 637               reference_wrapper<typename remove_reference<_Del>::type>,
 638               _Del>::type;
 639           using _Sp_cd_type
 640             = _Sp_counted_deleter<_Ptr, _Del2, allocator<void>, _Lp>;
 641           using _Alloc = allocator<_Sp_cd_type>;
 642           using _Alloc_traits = allocator_traits<_Alloc>;
 643           _Alloc __a;
 644           _Sp_cd_type* __mem = _Alloc_traits::allocate(__a, 1);
 645           _Alloc_traits::construct(__a, __mem, __r.release(),
 646                                    __r.get_deleter());  // non-throwing
 647           _M_pi = __mem;
 648         }
 649
 650       // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
 651       explicit __shared_count(const __weak_count<_Lp>& __r);
 652
 653       // Does not throw if __r._M_get_use_count() == 0, caller must check.
 654       explicit __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t);
 655
 656       ~__shared_count() noexcept
 657       {
 658         if (_M_pi != nullptr)
 659           _M_pi->_M_release();
 660       }
 661
 662       __shared_count(const __shared_count& __r) noexcept
 663       : _M_pi(__r._M_pi)
 664       {
 665         if (_M_pi != 0)
 666           _M_pi->_M_add_ref_copy();
 667       }
 668
 669       __shared_count&
 670       operator=(const __shared_count& __r) noexcept
 671       {
 672         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 673         if (__tmp != _M_pi)
 674           {
 675             if (__tmp != 0)
 676               __tmp->_M_add_ref_copy();
 677             if (_M_pi != 0)
 678               _M_pi->_M_release();
 679             _M_pi = __tmp;
 680           }
 681         return *this;
 682       }
 683
 684       void
 685       _M_swap(__shared_count& __r) noexcept
 686       {
 687         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 688         __r._M_pi = _M_pi;
 689         _M_pi = __tmp;
 690       }
 691
 692       long
 693       _M_get_use_count() const noexcept
 694       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 695
 696       bool
 697       _M_unique() const noexcept
 698       { return this->_M_get_use_count() == 1; }
 699
 700       void*
 701       _M_get_deleter(const std::type_info& __ti) const noexcept
 702       { return _M_pi ? _M_pi->_M_get_deleter(__ti) : nullptr; }
 703
 704       bool
 705       _M_less(const __shared_count& __rhs) const noexcept
 706       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 707
 708       bool
 709       _M_less(const __weak_count<_Lp>& __rhs) const noexcept
 710       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 711
 712       // Friend function injected into enclosing namespace and found by ADL
 713       friend inline bool
 714       operator==(const __shared_count& __a, const __shared_count& __b) noexcept
 715       { return __a._M_pi == __b._M_pi; }
 716
 717     private:
 718       friend class __weak_count<_Lp>;
 719
 720       _Sp_counted_base<_Lp>*  _M_pi;
 721     };
 722
 723
 724   template<_Lock_policy _Lp>
 725     class __weak_count
 726     {
 727     public:
 728       constexpr __weak_count() noexcept : _M_pi(nullptr)
 729       { }
 730
 731       __weak_count(const __shared_count<_Lp>& __r) noexcept
 732       : _M_pi(__r._M_pi)
 733       {
 734         if (_M_pi != nullptr)
 735           _M_pi->_M_weak_add_ref();
 736       }
 737
 738       __weak_count(const __weak_count& __r) noexcept
 739       : _M_pi(__r._M_pi)
 740       {
 741         if (_M_pi != nullptr)
 742           _M_pi->_M_weak_add_ref();
 743       }
 744
 745       __weak_count(__weak_count&& __r) noexcept
 746       : _M_pi(__r._M_pi)
 747       { __r._M_pi = nullptr; }
 748
 749       ~__weak_count() noexcept
 750       {
 751         if (_M_pi != nullptr)
 752           _M_pi->_M_weak_release();
 753       }
 754
 755       __weak_count&
 756       operator=(const __shared_count<_Lp>& __r) noexcept
 757       {
 758         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 759         if (__tmp != nullptr)
 760           __tmp->_M_weak_add_ref();
 761         if (_M_pi != nullptr)
 762           _M_pi->_M_weak_release();
 763         _M_pi = __tmp;
 764         return *this;
 765       }
 766
 767       __weak_count&
 768       operator=(const __weak_count& __r) noexcept
 769       {
 770         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 771         if (__tmp != nullptr)
 772           __tmp->_M_weak_add_ref();
 773         if (_M_pi != nullptr)
 774           _M_pi->_M_weak_release();
 775         _M_pi = __tmp;
 776         return *this;
 777       }
 778
 779       __weak_count&
 780       operator=(__weak_count&& __r) noexcept
 781       {
 782         if (_M_pi != nullptr)
 783           _M_pi->_M_weak_release();
 784         _M_pi = __r._M_pi;
 785         __r._M_pi = nullptr;
 786         return *this;
 787       }
 788
 789       void
 790       _M_swap(__weak_count& __r) noexcept
 791       {
 792         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 793         __r._M_pi = _M_pi;
 794         _M_pi = __tmp;
 795       }
 796
 797       long
 798       _M_get_use_count() const noexcept
 799       { return _M_pi != nullptr ? _M_pi->_M_get_use_count() : 0; }
 800
 801       bool
 802       _M_less(const __weak_count& __rhs) const noexcept
 803       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 804
 805       bool
 806       _M_less(const __shared_count<_Lp>& __rhs) const noexcept
 807       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 808
 809       // Friend function injected into enclosing namespace and found by ADL
 810       friend inline bool
 811       operator==(const __weak_count& __a, const __weak_count& __b) noexcept
 812       { return __a._M_pi == __b._M_pi; }
 813
 814     private:
 815       friend class __shared_count<_Lp>;
 816
 817       _Sp_counted_base<_Lp>*  _M_pi;
 818     };
 819
 820   // Now that __weak_count is defined we can define this constructor:
 821   template<_Lock_policy _Lp>
 822     inline
 823     __shared_count<_Lp>::__shared_count(const __weak_count<_Lp>& __r)
 824     : _M_pi(__r._M_pi)
 825     {
 826       if (_M_pi != nullptr)
 827         _M_pi->_M_add_ref_lock();
 828       else
 829         __throw_bad_weak_ptr();
 830     }
 831
 832   // Now that __weak_count is defined we can define this constructor:
 833   template<_Lock_policy _Lp>
 834     inline
 835     __shared_count<_Lp>::
 836     __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t)
 837     : _M_pi(__r._M_pi)
 838     {
 839       if (_M_pi != nullptr)
 840         if (!_M_pi->_M_add_ref_lock_nothrow())
 841           _M_pi = nullptr;
 842     }
 843
 844   // Support for enable_shared_from_this.
 845
 846   // Friend of __enable_shared_from_this.
 847   template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
 848     void
 849     __enable_shared_from_this_helper(const __shared_count<_Lp>&,
 850                                      const __enable_shared_from_this<_Tp1,
 851                                      _Lp>*, const _Tp2*) noexcept;
 852
 853   // Friend of enable_shared_from_this.
 854   template<typename _Tp1, typename _Tp2>
 855     void
 856     __enable_shared_from_this_helper(const __shared_count<>&,
 857                                      const enable_shared_from_this<_Tp1>*,
 858                                      const _Tp2*) noexcept;
 859
 860   template<_Lock_policy _Lp>
 861     inline void
 862     __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept
 863     { }
 864
 865
 866   template<typename _Tp, _Lock_policy _Lp>
 867     class __shared_ptr
 868     {
 869       template<typename _Ptr>
 870         using _Convertible
 871           = typename enable_if<is_convertible<_Ptr, _Tp*>::value>::type;
 872
 873     public:
 874       typedef _Tp   element_type;
 875
 876       constexpr __shared_ptr() noexcept
 877       : _M_ptr(0), _M_refcount()
 878       { }
 879
 880       template<typename _Tp1>
 881         explicit __shared_ptr(_Tp1* __p)
 882         : _M_ptr(__p), _M_refcount(__p)
 883         {
 884           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 885           static_assert( !is_void<_Tp1>::value, "incomplete type" );
 886           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 887           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 888         }
 889
 890       template<typename _Tp1, typename _Deleter>
 891         __shared_ptr(_Tp1* __p, _Deleter __d)
 892         : _M_ptr(__p), _M_refcount(__p, __d)
 893         {
 894           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 895           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 896           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 897         }
 898
 899       template<typename _Tp1, typename _Deleter, typename _Alloc>
 900         __shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
 901         : _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
 902         {
 903           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 904           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 905           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 906         }
 907
 908       template<typename _Deleter>
 909         __shared_ptr(nullptr_t __p, _Deleter __d)
 910         : _M_ptr(0), _M_refcount(__p, __d)
 911         { }
 912
 913       template<typename _Deleter, typename _Alloc>
 914         __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
 915         : _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
 916         { }
 917
 918       template<typename _Tp1>
 919         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p) noexcept
 920         : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
 921         { }
 922
 923       __shared_ptr(const __shared_ptr&) noexcept = default;
 924       __shared_ptr& operator=(const __shared_ptr&) noexcept = default;
 925       ~__shared_ptr() = default;
 926
 927       template<typename _Tp1, typename = _Convertible<_Tp1*>>
 928         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 929         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
 930         { }
 931
 932       __shared_ptr(__shared_ptr&& __r) noexcept
 933       : _M_ptr(__r._M_ptr), _M_refcount()
 934       {
 935         _M_refcount._M_swap(__r._M_refcount);
 936         __r._M_ptr = 0;
 937       }
 938
 939       template<typename _Tp1, typename = _Convertible<_Tp1*>>
 940         __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __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>
 948         explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
 949         : _M_refcount(__r._M_refcount) // may throw
 950         {
 951           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 952
 953           // It is now safe to copy __r._M_ptr, as
 954           // _M_refcount(__r._M_refcount) did not throw.
 955           _M_ptr = __r._M_ptr;
 956         }
 957
 958       // If an exception is thrown this constructor has no effect.
 959       template<typename _Tp1, typename _Del, typename
 960                = _Convertible<typename unique_ptr<_Tp1, _Del>::pointer>>
 961         __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
 962         : _M_ptr(__r.get()), _M_refcount()
 963         {
 964           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 965           auto __raw = _S_raw_ptr(__r.get());
 966           _M_refcount = __shared_count<_Lp>(std::move(__r));
 967           __enable_shared_from_this_helper(_M_refcount, __raw, __raw);
 968         }
 969
 970 #if _GLIBCXX_USE_DEPRECATED
 971       // Postcondition: use_count() == 1 and __r.get() == 0
 972       template<typename _Tp1>
 973         __shared_ptr(std::auto_ptr<_Tp1>&& __r);
 974 #endif
 975
 976       constexpr __shared_ptr(nullptr_t) noexcept : __shared_ptr() { }
 977
 978       template<typename _Tp1>
 979         __shared_ptr&
 980         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 981         {
 982           _M_ptr = __r._M_ptr;
 983           _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
 984           return *this;
 985         }
 986
 987 #if _GLIBCXX_USE_DEPRECATED
 988       template<typename _Tp1>
 989         __shared_ptr&
 990         operator=(std::auto_ptr<_Tp1>&& __r)
 991         {
 992           __shared_ptr(std::move(__r)).swap(*this);
 993           return *this;
 994         }
 995 #endif
 996
 997       __shared_ptr&
 998       operator=(__shared_ptr&& __r) noexcept
 999       {
1000         __shared_ptr(std::move(__r)).swap(*this);
1001         return *this;
1002       }
1003
1004       template<class _Tp1>
1005         __shared_ptr&
1006         operator=(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
1007         {
1008           __shared_ptr(std::move(__r)).swap(*this);
1009           return *this;
1010         }
1011
1012       template<typename _Tp1, typename _Del>
1013         __shared_ptr&
1014         operator=(std::unique_ptr<_Tp1, _Del>&& __r)
1015         {
1016           __shared_ptr(std::move(__r)).swap(*this);
1017           return *this;
1018         }
1019
1020       void
1021       reset() noexcept
1022       { __shared_ptr().swap(*this); }
1023
1024       template<typename _Tp1>
1025         void
1026         reset(_Tp1* __p) // _Tp1 must be complete.
1027         {
1028           // Catch self-reset errors.
1029           _GLIBCXX_DEBUG_ASSERT(__p == 0 || __p != _M_ptr);
1030           __shared_ptr(__p).swap(*this);
1031         }
1032
1033       template<typename _Tp1, typename _Deleter>
1034         void
1035         reset(_Tp1* __p, _Deleter __d)
1036         { __shared_ptr(__p, __d).swap(*this); }
1037
1038       template<typename _Tp1, typename _Deleter, typename _Alloc>
1039         void
1040         reset(_Tp1* __p, _Deleter __d, _Alloc __a)
1041         { __shared_ptr(__p, __d, std::move(__a)).swap(*this); }
1042
1043       // Allow class instantiation when _Tp is [cv-qual] void.
1044       typename std::add_lvalue_reference<_Tp>::type
1045       operator*() const noexcept
1046       {
1047         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
1048         return *_M_ptr;
1049       }
1050
1051       _Tp*
1052       operator->() const noexcept
1053       {
1054         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
1055         return _M_ptr;
1056       }
1057
1058       _Tp*
1059       get() const noexcept
1060       { return _M_ptr; }
1061
1062       explicit operator bool() const // never throws
1063       { return _M_ptr == 0 ? false : true; }
1064
1065       bool
1066       unique() const noexcept
1067       { return _M_refcount._M_unique(); }
1068
1069       long
1070       use_count() const noexcept
1071       { return _M_refcount._M_get_use_count(); }
1072
1073       void
1074       swap(__shared_ptr<_Tp, _Lp>& __other) noexcept
1075       {
1076         std::swap(_M_ptr, __other._M_ptr);
1077         _M_refcount._M_swap(__other._M_refcount);
1078       }
1079
1080       template<typename _Tp1>
1081         bool
1082         owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const
1083         { return _M_refcount._M_less(__rhs._M_refcount); }
1084
1085       template<typename _Tp1>
1086         bool
1087         owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const
1088         { return _M_refcount._M_less(__rhs._M_refcount); }
1089
1090 #if __cpp_rtti
1091     protected:
1092       // This constructor is non-standard, it is used by allocate_shared.
1093       template<typename _Alloc, typename... _Args>
1094         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1095                      _Args&&... __args)
1096         : _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,
1097                                 std::forward<_Args>(__args)...)
1098         {
1099           // _M_ptr needs to point to the newly constructed object.
1100           // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
1101           void* __p = _M_refcount._M_get_deleter(typeid(__tag));
1102           _M_ptr = static_cast<_Tp*>(__p);
1103           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1104         }
1105 #else
1106       template<typename _Alloc>
1107         struct _Deleter
1108         {
1109           void operator()(_Tp* __ptr)
1110           {
1111             __allocated_ptr<_Alloc> __guard{ _M_alloc, __ptr };
1112             allocator_traits<_Alloc>::destroy(_M_alloc, __guard.get());
1113           }
1114           _Alloc _M_alloc;
1115         };
1116
1117       template<typename _Alloc, typename... _Args>
1118         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1119                      _Args&&... __args)
1120         : _M_ptr(), _M_refcount()
1121         {
1122           typedef typename allocator_traits<_Alloc>::template
1123             rebind_traits<_Tp> __traits;
1124           _Deleter<typename __traits::allocator_type> __del = { __a };
1125           auto __guard = std::__allocate_guarded(__del._M_alloc);
1126           _M_ptr = __guard.get();
1127           // _GLIBCXX_RESOLVE_LIB_DEFECTS
1128           // 2070. allocate_shared should use allocator_traits<A>::construct
1129           __traits::construct(__del._M_alloc, _M_ptr,
1130                               std::forward<_Args>(__args)...);
1131           __guard = nullptr;
1132           __shared_count<_Lp> __count(_M_ptr, __del, __del._M_alloc);
1133           _M_refcount._M_swap(__count);
1134           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1135         }
1136 #endif
1137
1138       template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
1139                typename... _Args>
1140         friend __shared_ptr<_Tp1, _Lp1>
1141         __allocate_shared(const _Alloc& __a, _Args&&... __args);
1142
1143       // This constructor is used by __weak_ptr::lock() and
1144       // shared_ptr::shared_ptr(const weak_ptr&, std::nothrow_t).
1145       __shared_ptr(const __weak_ptr<_Tp, _Lp>& __r, std::nothrow_t)
1146       : _M_refcount(__r._M_refcount, std::nothrow)
1147       {
1148         _M_ptr = _M_refcount._M_get_use_count() ? __r._M_ptr : nullptr;
1149       }
1150
1151       friend class __weak_ptr<_Tp, _Lp>;
1152
1153     private:
1154       void*
1155       _M_get_deleter(const std::type_info& __ti) const noexcept
1156       { return _M_refcount._M_get_deleter(__ti); }
1157
1158       template<typename _Tp1>
1159         static _Tp1*
1160         _S_raw_ptr(_Tp1* __ptr)
1161         { return __ptr; }
1162
1163       template<typename _Tp1>
1164         static auto
1165         _S_raw_ptr(_Tp1 __ptr) -> decltype(std::__addressof(*__ptr))
1166         { return std::__addressof(*__ptr); }
1167
1168       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1169       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1170
1171       template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1172         friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&) noexcept;
1173
1174       _Tp*                 _M_ptr;         // Contained pointer.
1175       __shared_count<_Lp>  _M_refcount;    // Reference counter.
1176     };
1177
1178
1179   // 20.7.2.2.7 shared_ptr comparisons
1180   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1181     inline bool
1182     operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1183                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1184     { return __a.get() == __b.get(); }
1185
1186   template<typename _Tp, _Lock_policy _Lp>
1187     inline bool
1188     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1189     { return !__a; }
1190
1191   template<typename _Tp, _Lock_policy _Lp>
1192     inline bool
1193     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1194     { return !__a; }
1195
1196   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1197     inline bool
1198     operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1199                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1200     { return __a.get() != __b.get(); }
1201
1202   template<typename _Tp, _Lock_policy _Lp>
1203     inline bool
1204     operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1205     { return (bool)__a; }
1206
1207   template<typename _Tp, _Lock_policy _Lp>
1208     inline bool
1209     operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1210     { return (bool)__a; }
1211
1212   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1213     inline bool
1214     operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1215               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1216     {
1217       typedef typename std::common_type<_Tp1*, _Tp2*>::type _CT;
1218       return std::less<_CT>()(__a.get(), __b.get());
1219     }
1220
1221   template<typename _Tp, _Lock_policy _Lp>
1222     inline bool
1223     operator<(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1224     { return std::less<_Tp*>()(__a.get(), nullptr); }
1225
1226   template<typename _Tp, _Lock_policy _Lp>
1227     inline bool
1228     operator<(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1229     { return std::less<_Tp*>()(nullptr, __a.get()); }
1230
1231   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1232     inline bool
1233     operator<=(const __shared_ptr<_Tp1, _Lp>& __a,
1234                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1235     { return !(__b < __a); }
1236
1237   template<typename _Tp, _Lock_policy _Lp>
1238     inline bool
1239     operator<=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1240     { return !(nullptr < __a); }
1241
1242   template<typename _Tp, _Lock_policy _Lp>
1243     inline bool
1244     operator<=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1245     { return !(__a < nullptr); }
1246
1247   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1248     inline bool
1249     operator>(const __shared_ptr<_Tp1, _Lp>& __a,
1250               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1251     { return (__b < __a); }
1252
1253   template<typename _Tp, _Lock_policy _Lp>
1254     inline bool
1255     operator>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1256     { return std::less<_Tp*>()(nullptr, __a.get()); }
1257
1258   template<typename _Tp, _Lock_policy _Lp>
1259     inline bool
1260     operator>(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1261     { return std::less<_Tp*>()(__a.get(), nullptr); }
1262
1263   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1264     inline bool
1265     operator>=(const __shared_ptr<_Tp1, _Lp>& __a,
1266                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1267     { return !(__a < __b); }
1268
1269   template<typename _Tp, _Lock_policy _Lp>
1270     inline bool
1271     operator>=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1272     { return !(__a < nullptr); }
1273
1274   template<typename _Tp, _Lock_policy _Lp>
1275     inline bool
1276     operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1277     { return !(nullptr < __a); }
1278
1279   template<typename _Sp>
1280     struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1281     {
1282       bool
1283       operator()(const _Sp& __lhs, const _Sp& __rhs) const noexcept
1284       {
1285         typedef typename _Sp::element_type element_type;
1286         return std::less<element_type*>()(__lhs.get(), __rhs.get());
1287       }
1288     };
1289
1290   template<typename _Tp, _Lock_policy _Lp>
1291     struct less<__shared_ptr<_Tp, _Lp>>
1292     : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1293     { };
1294
1295   // 20.7.2.2.8 shared_ptr specialized algorithms.
1296   template<typename _Tp, _Lock_policy _Lp>
1297     inline void
1298     swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b) noexcept
1299     { __a.swap(__b); }
1300
1301   // 20.7.2.2.9 shared_ptr casts
1302
1303   // The seemingly equivalent code:
1304   // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1305   // will eventually result in undefined behaviour, attempting to
1306   // delete the same object twice.
1307   /// static_pointer_cast
1308   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1309     inline __shared_ptr<_Tp, _Lp>
1310     static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1311     { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1312
1313   // The seemingly equivalent code:
1314   // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1315   // will eventually result in undefined behaviour, attempting to
1316   // delete the same object twice.
1317   /// const_pointer_cast
1318   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1319     inline __shared_ptr<_Tp, _Lp>
1320     const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1321     { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1322
1323   // The seemingly equivalent code:
1324   // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1325   // will eventually result in undefined behaviour, attempting to
1326   // delete the same object twice.
1327   /// dynamic_pointer_cast
1328   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1329     inline __shared_ptr<_Tp, _Lp>
1330     dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1331     {
1332       if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1333         return __shared_ptr<_Tp, _Lp>(__r, __p);
1334       return __shared_ptr<_Tp, _Lp>();
1335     }
1336
1337
1338   template<typename _Tp, _Lock_policy _Lp>
1339     class __weak_ptr
1340     {
1341       template<typename _Ptr>
1342         using _Convertible
1343           = typename enable_if<is_convertible<_Ptr, _Tp*>::value>::type;
1344
1345     public:
1346       typedef _Tp element_type;
1347
1348       constexpr __weak_ptr() noexcept
1349       : _M_ptr(nullptr), _M_refcount()
1350       { }
1351
1352       __weak_ptr(const __weak_ptr&) noexcept = default;
1353
1354       ~__weak_ptr() = default;
1355
1356       // The "obvious" converting constructor implementation:
1357       //
1358       //  template<typename _Tp1>
1359       //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1360       //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1361       //    { }
1362       //
1363       // has a serious problem.
1364       //
1365       //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1366       //  conversion may require access to *__r._M_ptr (virtual inheritance).
1367       //
1368       // It is not possible to avoid spurious access violations since
1369       // in multithreaded programs __r._M_ptr may be invalidated at any point.
1370       template<typename _Tp1, typename = _Convertible<_Tp1*>>
1371         __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1372         : _M_refcount(__r._M_refcount)
1373         { _M_ptr = __r.lock().get(); }
1374
1375       template<typename _Tp1, typename = _Convertible<_Tp1*>>
1376         __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1377         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
1378         { }
1379
1380       __weak_ptr(__weak_ptr&& __r) noexcept
1381       : _M_ptr(__r._M_ptr), _M_refcount(std::move(__r._M_refcount))
1382       { __r._M_ptr = nullptr; }
1383
1384       template<typename _Tp1, typename = _Convertible<_Tp1*>>
1385         __weak_ptr(__weak_ptr<_Tp1, _Lp>&& __r) noexcept
1386         : _M_ptr(__r.lock().get()), _M_refcount(std::move(__r._M_refcount))
1387         { __r._M_ptr = nullptr; }
1388
1389       __weak_ptr&
1390       operator=(const __weak_ptr& __r) noexcept = default;
1391
1392       template<typename _Tp1>
1393         __weak_ptr&
1394         operator=(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1395         {
1396           _M_ptr = __r.lock().get();
1397           _M_refcount = __r._M_refcount;
1398           return *this;
1399         }
1400
1401       template<typename _Tp1>
1402         __weak_ptr&
1403         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1404         {
1405           _M_ptr = __r._M_ptr;
1406           _M_refcount = __r._M_refcount;
1407           return *this;
1408         }
1409
1410       __weak_ptr&
1411       operator=(__weak_ptr&& __r) noexcept
1412       {
1413         _M_ptr = __r._M_ptr;
1414         _M_refcount = std::move(__r._M_refcount);
1415         __r._M_ptr = nullptr;
1416         return *this;
1417       }
1418
1419       template<typename _Tp1>
1420         __weak_ptr&
1421         operator=(__weak_ptr<_Tp1, _Lp>&& __r) noexcept
1422         {
1423           _M_ptr = __r.lock().get();
1424           _M_refcount = std::move(__r._M_refcount);
1425           __r._M_ptr = nullptr;
1426           return *this;
1427         }
1428
1429       __shared_ptr<_Tp, _Lp>
1430       lock() const noexcept
1431       { return __shared_ptr<element_type, _Lp>(*this, std::nothrow); }
1432
1433       long
1434       use_count() const noexcept
1435       { return _M_refcount._M_get_use_count(); }
1436
1437       bool
1438       expired() const noexcept
1439       { return _M_refcount._M_get_use_count() == 0; }
1440
1441       template<typename _Tp1>
1442         bool
1443         owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1444         { return _M_refcount._M_less(__rhs._M_refcount); }
1445
1446       template<typename _Tp1>
1447         bool
1448         owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1449         { return _M_refcount._M_less(__rhs._M_refcount); }
1450
1451       void
1452       reset() noexcept
1453       { __weak_ptr().swap(*this); }
1454
1455       void
1456       swap(__weak_ptr& __s) noexcept
1457       {
1458         std::swap(_M_ptr, __s._M_ptr);
1459         _M_refcount._M_swap(__s._M_refcount);
1460       }
1461
1462     private:
1463       // Used by __enable_shared_from_this.
1464       void
1465       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
1466       {
1467         _M_ptr = __ptr;
1468         _M_refcount = __refcount;
1469       }
1470
1471       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1472       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1473       friend class __enable_shared_from_this<_Tp, _Lp>;
1474       friend class enable_shared_from_this<_Tp>;
1475
1476       _Tp*               _M_ptr;         // Contained pointer.
1477       __weak_count<_Lp>  _M_refcount;    // Reference counter.
1478     };
1479
1480   // 20.7.2.3.6 weak_ptr specialized algorithms.
1481   template<typename _Tp, _Lock_policy _Lp>
1482     inline void
1483     swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b) noexcept
1484     { __a.swap(__b); }
1485
1486   template<typename _Tp, typename _Tp1>
1487     struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1488     {
1489       bool
1490       operator()(const _Tp& __lhs, const _Tp& __rhs) const
1491       { return __lhs.owner_before(__rhs); }
1492
1493       bool
1494       operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1495       { return __lhs.owner_before(__rhs); }
1496
1497       bool
1498       operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1499       { return __lhs.owner_before(__rhs); }
1500     };
1501
1502   template<typename _Tp, _Lock_policy _Lp>
1503     struct owner_less<__shared_ptr<_Tp, _Lp>>
1504     : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1505     { };
1506
1507   template<typename _Tp, _Lock_policy _Lp>
1508     struct owner_less<__weak_ptr<_Tp, _Lp>>
1509     : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1510     { };
1511
1512
1513   template<typename _Tp, _Lock_policy _Lp>
1514     class __enable_shared_from_this
1515     {
1516     protected:
1517       constexpr __enable_shared_from_this() noexcept { }
1518
1519       __enable_shared_from_this(const __enable_shared_from_this&) noexcept { }
1520
1521       __enable_shared_from_this&
1522       operator=(const __enable_shared_from_this&) noexcept
1523       { return *this; }
1524
1525       ~__enable_shared_from_this() { }
1526
1527     public:
1528       __shared_ptr<_Tp, _Lp>
1529       shared_from_this()
1530       { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1531
1532       __shared_ptr<const _Tp, _Lp>
1533       shared_from_this() const
1534       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1535
1536     private:
1537       template<typename _Tp1>
1538         void
1539         _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
1540         { _M_weak_this._M_assign(__p, __n); }
1541
1542       template<typename _Tp1>
1543         friend void
1544         __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
1545                                          const __enable_shared_from_this* __pe,
1546                                          const _Tp1* __px) noexcept
1547         {
1548           if (__pe != 0)
1549             __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
1550         }
1551
1552       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
1553     };
1554
1555
1556   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1557     inline __shared_ptr<_Tp, _Lp>
1558     __allocate_shared(const _Alloc& __a, _Args&&... __args)
1559     {
1560       return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
1561                                     std::forward<_Args>(__args)...);
1562     }
1563
1564   template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1565     inline __shared_ptr<_Tp, _Lp>
1566     __make_shared(_Args&&... __args)
1567     {
1568       typedef typename std::remove_const<_Tp>::type _Tp_nc;
1569       return std::__allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1570                                               std::forward<_Args>(__args)...);
1571     }
1572
1573   /// std::hash specialization for __shared_ptr.
1574   template<typename _Tp, _Lock_policy _Lp>
1575     struct hash<__shared_ptr<_Tp, _Lp>>
1576     : public __hash_base<size_t, __shared_ptr<_Tp, _Lp>>
1577     {
1578       size_t
1579       operator()(const __shared_ptr<_Tp, _Lp>& __s) const noexcept
1580       { return std::hash<_Tp*>()(__s.get()); }
1581     };
1582
1583 _GLIBCXX_END_NAMESPACE_VERSION
1584 } // namespace
1585
1586 #endif // _SHARED_PTR_BASE_H