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

   1 // shared_ptr and weak_ptr implementation details -*- C++ -*-
   2
   3 // Copyright (C) 2007-2013 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 <ext/aligned_buffer.h>
  53
  54 namespace std _GLIBCXX_VISIBILITY(default)
  55 {
  56 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  57
  58 #if _GLIBCXX_USE_DEPRECATED
  59   template<typename> class auto_ptr;
  60 #endif
  61
  62  /**
  63    *  @brief  Exception possibly thrown by @c shared_ptr.
  64    *  @ingroup exceptions
  65    */
  66   class bad_weak_ptr : public std::exception
  67   {
  68   public:
  69     virtual char const*
  70     what() const noexcept;
  71
  72     virtual ~bad_weak_ptr() noexcept;
  73   };
  74
  75   // Substitute for bad_weak_ptr object in the case of -fno-exceptions.
  76   inline void
  77   __throw_bad_weak_ptr()
  78   { _GLIBCXX_THROW_OR_ABORT(bad_weak_ptr()); }
  79
  80   using __gnu_cxx::_Lock_policy;
  81   using __gnu_cxx::__default_lock_policy;
  82   using __gnu_cxx::_S_single;
  83   using __gnu_cxx::_S_mutex;
  84   using __gnu_cxx::_S_atomic;
  85
  86   // Empty helper class except when the template argument is _S_mutex.
  87   template<_Lock_policy _Lp>
  88     class _Mutex_base
  89     {
  90     protected:
  91       // The atomic policy uses fully-fenced builtins, single doesn't care.
  92       enum { _S_need_barriers = 0 };
  93     };
  94
  95   template<>
  96     class _Mutex_base<_S_mutex>
  97     : public __gnu_cxx::__mutex
  98     {
  99     protected:
 100       // This policy is used when atomic builtins are not available.
 101       // The replacement atomic operations might not have the necessary
 102       // memory barriers.
 103       enum { _S_need_barriers = 1 };
 104     };
 105
 106   template<_Lock_policy _Lp = __default_lock_policy>
 107     class _Sp_counted_base
 108     : public _Mutex_base<_Lp>
 109     {
 110     public:
 111       _Sp_counted_base() noexcept
 112       : _M_use_count(1), _M_weak_count(1) { }
 113
 114       virtual
 115       ~_Sp_counted_base() noexcept
 116       { }
 117
 118       // Called when _M_use_count drops to zero, to release the resources
 119       // managed by *this.
 120       virtual void
 121       _M_dispose() noexcept = 0;
 122
 123       // Called when _M_weak_count drops to zero.
 124       virtual void
 125       _M_destroy() noexcept
 126       { delete this; }
 127
 128       virtual void*
 129       _M_get_deleter(const std::type_info&) noexcept = 0;
 130
 131       void
 132       _M_add_ref_copy()
 133       { __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
 134
 135       void
 136       _M_add_ref_lock();
 137
 138       void
 139       _M_release() noexcept
 140       {
 141         // Be race-detector-friendly.  For more info see bits/c++config.
 142         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_use_count);
 143         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
 144           {
 145             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_use_count);
 146             _M_dispose();
 147             // There must be a memory barrier between dispose() and destroy()
 148             // to ensure that the effects of dispose() are observed in the
 149             // thread that runs destroy().
 150             // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
 151             if (_Mutex_base<_Lp>::_S_need_barriers)
 152               {
 153                 _GLIBCXX_READ_MEM_BARRIER;
 154                 _GLIBCXX_WRITE_MEM_BARRIER;
 155               }
 156
 157             // Be race-detector-friendly.  For more info see bits/c++config.
 158             _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 159             if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
 160                                                        -1) == 1)
 161               {
 162                 _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 163                 _M_destroy();
 164               }
 165           }
 166       }
 167
 168       void
 169       _M_weak_add_ref() noexcept
 170       { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
 171
 172       void
 173       _M_weak_release() noexcept
 174       {
 175         // Be race-detector-friendly. For more info see bits/c++config.
 176         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 177         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
 178           {
 179             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 180             if (_Mutex_base<_Lp>::_S_need_barriers)
 181               {
 182                 // See _M_release(),
 183                 // destroy() must observe results of dispose()
 184                 _GLIBCXX_READ_MEM_BARRIER;
 185                 _GLIBCXX_WRITE_MEM_BARRIER;
 186               }
 187             _M_destroy();
 188           }
 189       }
 190
 191       long
 192       _M_get_use_count() const noexcept
 193       {
 194         // No memory barrier is used here so there is no synchronization
 195         // with other threads.
 196         return __atomic_load_n(&_M_use_count, __ATOMIC_RELAXED);
 197       }
 198
 199     private:
 200       _Sp_counted_base(_Sp_counted_base const&) = delete;
 201       _Sp_counted_base& operator=(_Sp_counted_base const&) = delete;
 202
 203       _Atomic_word  _M_use_count;     // #shared
 204       _Atomic_word  _M_weak_count;    // #weak + (#shared != 0)
 205     };
 206
 207   template<>
 208     inline void
 209     _Sp_counted_base<_S_single>::
 210     _M_add_ref_lock()
 211     {
 212       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 213         {
 214           _M_use_count = 0;
 215           __throw_bad_weak_ptr();
 216         }
 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_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
 252   // Forward declarations.
 253   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 254     class __shared_ptr;
 255
 256   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 257     class __weak_ptr;
 258
 259   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 260     class __enable_shared_from_this;
 261
 262   template<typename _Tp>
 263     class shared_ptr;
 264
 265   template<typename _Tp>
 266     class weak_ptr;
 267
 268   template<typename _Tp>
 269     struct owner_less;
 270
 271   template<typename _Tp>
 272     class enable_shared_from_this;
 273
 274   template<_Lock_policy _Lp = __default_lock_policy>
 275     class __weak_count;
 276
 277   template<_Lock_policy _Lp = __default_lock_policy>
 278     class __shared_count;
 279
 280
 281   // Counted ptr with no deleter or allocator support
 282   template<typename _Ptr, _Lock_policy _Lp>
 283     class _Sp_counted_ptr final : public _Sp_counted_base<_Lp>
 284     {
 285     public:
 286       explicit
 287       _Sp_counted_ptr(_Ptr __p) noexcept
 288       : _M_ptr(__p) { }
 289
 290       virtual void
 291       _M_dispose() noexcept
 292       { delete _M_ptr; }
 293
 294       virtual void
 295       _M_destroy() noexcept
 296       { delete this; }
 297
 298       virtual void*
 299       _M_get_deleter(const std::type_info&) noexcept
 300       { return nullptr; }
 301
 302       _Sp_counted_ptr(const _Sp_counted_ptr&) = delete;
 303       _Sp_counted_ptr& operator=(const _Sp_counted_ptr&) = delete;
 304
 305     private:
 306       _Ptr             _M_ptr;
 307     };
 308
 309   template<>
 310     inline void
 311     _Sp_counted_ptr<nullptr_t, _S_single>::_M_dispose() noexcept { }
 312
 313   template<>
 314     inline void
 315     _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() noexcept { }
 316
 317   template<>
 318     inline void
 319     _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }
 320
 321   template<int _Nm, typename _Tp,
 322            bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>
 323     struct _Sp_ebo_helper;
 324
 325   /// Specialization using EBO.
 326   template<int _Nm, typename _Tp>
 327     struct _Sp_ebo_helper<_Nm, _Tp, true> : private _Tp
 328     {
 329       explicit _Sp_ebo_helper(const _Tp& __tp) : _Tp(__tp) { }
 330
 331       static _Tp&
 332       _S_get(_Sp_ebo_helper& __eboh) { return static_cast<_Tp&>(__eboh); }
 333     };
 334
 335   /// Specialization not using EBO.
 336   template<int _Nm, typename _Tp>
 337     struct _Sp_ebo_helper<_Nm, _Tp, false>
 338     {
 339       explicit _Sp_ebo_helper(const _Tp& __tp) : _M_tp(__tp) { }
 340
 341       static _Tp&
 342       _S_get(_Sp_ebo_helper& __eboh)
 343       { return __eboh._M_tp; }
 344
 345     private:
 346       _Tp _M_tp;
 347     };
 348
 349   // Support for custom deleter and/or allocator
 350   template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>
 351     class _Sp_counted_deleter final : public _Sp_counted_base<_Lp>
 352     {
 353       class _Impl : _Sp_ebo_helper<0, _Deleter>, _Sp_ebo_helper<1, _Alloc>
 354       {
 355         typedef _Sp_ebo_helper<0, _Deleter>     _Del_base;
 356         typedef _Sp_ebo_helper<1, _Alloc>       _Alloc_base;
 357
 358       public:
 359         _Impl(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept
 360         : _M_ptr(__p), _Del_base(__d), _Alloc_base(__a)
 361         { }
 362
 363         _Deleter& _M_del() noexcept { return _Del_base::_S_get(*this); }
 364         _Alloc& _M_alloc() noexcept { return _Alloc_base::_S_get(*this); }
 365
 366         _Ptr _M_ptr;
 367       };
 368
 369     public:
 370       // __d(__p) must not throw.
 371       _Sp_counted_deleter(_Ptr __p, _Deleter __d) noexcept
 372       : _M_impl(__p, __d, _Alloc()) { }
 373
 374       // __d(__p) must not throw.
 375       _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept
 376       : _M_impl(__p, __d, __a) { }
 377
 378       ~_Sp_counted_deleter() noexcept { }
 379
 380       virtual void
 381       _M_dispose() noexcept
 382       { _M_impl._M_del()(_M_impl._M_ptr); }
 383
 384       virtual void
 385       _M_destroy() noexcept
 386       {
 387         typedef typename allocator_traits<_Alloc>::template
 388           rebind_traits<_Sp_counted_deleter> _Alloc_traits;
 389         typename _Alloc_traits::allocator_type __a(_M_impl._M_alloc());
 390         _Alloc_traits::destroy(__a, this);
 391         _Alloc_traits::deallocate(__a, this, 1);
 392       }
 393
 394       virtual void*
 395       _M_get_deleter(const std::type_info& __ti) noexcept
 396       {
 397 #ifdef __GXX_RTTI
 398         return __ti == typeid(_Deleter) ? &_M_impl._M_del() : nullptr;
 399 #else
 400         return nullptr;
 401 #endif
 402       }
 403
 404     private:
 405       _Impl _M_impl;
 406     };
 407
 408   // helpers for make_shared / allocate_shared
 409
 410   struct _Sp_make_shared_tag { };
 411
 412   template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
 413     class _Sp_counted_ptr_inplace final : public _Sp_counted_base<_Lp>
 414     {
 415       class _Impl : _Sp_ebo_helper<0, _Alloc>
 416       {
 417         typedef _Sp_ebo_helper<0, _Alloc>       _A_base;
 418
 419       public:
 420         explicit _Impl(_Alloc __a) noexcept : _A_base(__a) { }
 421
 422         _Alloc& _M_alloc() noexcept { return _A_base::_S_get(*this); }
 423
 424         __gnu_cxx::__aligned_buffer<_Tp> _M_storage;
 425       };
 426
 427     public:
 428       template<typename... _Args>
 429         _Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)
 430         : _M_impl(__a)
 431         {
 432           // _GLIBCXX_RESOLVE_LIB_DEFECTS
 433           // 2070.  allocate_shared should use allocator_traits<A>::construct
 434           allocator_traits<_Alloc>::construct(__a, _M_ptr(),
 435               std::forward<_Args>(__args)...); // might throw
 436         }
 437
 438       ~_Sp_counted_ptr_inplace() noexcept { }
 439
 440       virtual void
 441       _M_dispose() noexcept
 442       {
 443         allocator_traits<_Alloc>::destroy(_M_impl._M_alloc(), _M_ptr());
 444       }
 445
 446       // Override because the allocator needs to know the dynamic type
 447       virtual void
 448       _M_destroy() noexcept
 449       {
 450         typedef typename allocator_traits<_Alloc>::template
 451           rebind_traits<_Sp_counted_ptr_inplace> _Alloc_traits;
 452         typename _Alloc_traits::allocator_type __a(_M_impl._M_alloc());
 453         _Alloc_traits::destroy(__a, this);
 454         _Alloc_traits::deallocate(__a, this, 1);
 455       }
 456
 457       // Sneaky trick so __shared_ptr can get the managed pointer
 458       virtual void*
 459       _M_get_deleter(const std::type_info& __ti) noexcept
 460       {
 461 #ifdef __GXX_RTTI
 462         if (__ti == typeid(_Sp_make_shared_tag))
 463           return const_cast<typename remove_cv<_Tp>::type*>(_M_ptr());
 464 #endif
 465         return nullptr;
 466       }
 467
 468     private:
 469       _Tp* _M_ptr() noexcept { return _M_impl._M_storage._M_ptr(); }
 470
 471       _Impl _M_impl;
 472     };
 473
 474
 475   template<_Lock_policy _Lp>
 476     class __shared_count
 477     {
 478     public:
 479       constexpr __shared_count() noexcept : _M_pi(0)
 480       { }
 481
 482       template<typename _Ptr>
 483         explicit
 484         __shared_count(_Ptr __p) : _M_pi(0)
 485         {
 486           __try
 487             {
 488               _M_pi = new _Sp_counted_ptr<_Ptr, _Lp>(__p);
 489             }
 490           __catch(...)
 491             {
 492               delete __p;
 493               __throw_exception_again;
 494             }
 495         }
 496
 497       template<typename _Ptr, typename _Deleter>
 498         __shared_count(_Ptr __p, _Deleter __d) : _M_pi(0)
 499         {
 500           // The allocator's value_type doesn't matter, will rebind it anyway.
 501           typedef std::allocator<int> _Alloc;
 502           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 503           typedef typename allocator_traits<_Alloc>::template
 504             rebind_traits<_Sp_cd_type> _Alloc_traits;
 505           typename _Alloc_traits::allocator_type __a;
 506           _Sp_cd_type* __mem = 0;
 507           __try
 508             {
 509               __mem = _Alloc_traits::allocate(__a, 1);
 510               _Alloc_traits::construct(__a, __mem, __p, std::move(__d));
 511               _M_pi = __mem;
 512             }
 513           __catch(...)
 514             {
 515               __d(__p); // Call _Deleter on __p.
 516               if (__mem)
 517                 _Alloc_traits::deallocate(__a, __mem, 1);
 518               __throw_exception_again;
 519             }
 520         }
 521
 522       template<typename _Ptr, typename _Deleter, typename _Alloc>
 523         __shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
 524         {
 525           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 526           typedef typename allocator_traits<_Alloc>::template
 527             rebind_traits<_Sp_cd_type> _Alloc_traits;
 528           typename _Alloc_traits::allocator_type __a2(__a);
 529           _Sp_cd_type* __mem = 0;
 530           __try
 531             {
 532               __mem = _Alloc_traits::allocate(__a2, 1);
 533               _Alloc_traits::construct(__a2, __mem,
 534                   __p, std::move(__d), std::move(__a));
 535               _M_pi = __mem;
 536             }
 537           __catch(...)
 538             {
 539               __d(__p); // Call _Deleter on __p.
 540               if (__mem)
 541                 _Alloc_traits::deallocate(__a2, __mem, 1);
 542               __throw_exception_again;
 543             }
 544         }
 545
 546       template<typename _Tp, typename _Alloc, typename... _Args>
 547         __shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,
 548                        _Args&&... __args)
 549         : _M_pi(0)
 550         {
 551           typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
 552           typedef typename allocator_traits<_Alloc>::template
 553             rebind_traits<_Sp_cp_type> _Alloc_traits;
 554           typename _Alloc_traits::allocator_type __a2(__a);
 555           _Sp_cp_type* __mem = _Alloc_traits::allocate(__a2, 1);
 556           __try
 557             {
 558               _Alloc_traits::construct(__a2, __mem, std::move(__a),
 559                     std::forward<_Args>(__args)...);
 560               _M_pi = __mem;
 561             }
 562           __catch(...)
 563             {
 564               _Alloc_traits::deallocate(__a2, __mem, 1);
 565               __throw_exception_again;
 566             }
 567         }
 568
 569 #if _GLIBCXX_USE_DEPRECATED
 570       // Special case for auto_ptr<_Tp> to provide the strong guarantee.
 571       template<typename _Tp>
 572         explicit
 573         __shared_count(std::auto_ptr<_Tp>&& __r);
 574 #endif
 575
 576       // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
 577       template<typename _Tp, typename _Del>
 578         explicit
 579         __shared_count(std::unique_ptr<_Tp, _Del>&& __r)
 580         : _M_pi(_S_create_from_up(std::move(__r)))
 581         { __r.release(); }
 582
 583       // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
 584       explicit __shared_count(const __weak_count<_Lp>& __r);
 585
 586       ~__shared_count() noexcept
 587       {
 588         if (_M_pi != 0)
 589           _M_pi->_M_release();
 590       }
 591
 592       __shared_count(const __shared_count& __r) noexcept
 593       : _M_pi(__r._M_pi)
 594       {
 595         if (_M_pi != 0)
 596           _M_pi->_M_add_ref_copy();
 597       }
 598
 599       __shared_count&
 600       operator=(const __shared_count& __r) noexcept
 601       {
 602         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 603         if (__tmp != _M_pi)
 604           {
 605             if (__tmp != 0)
 606               __tmp->_M_add_ref_copy();
 607             if (_M_pi != 0)
 608               _M_pi->_M_release();
 609             _M_pi = __tmp;
 610           }
 611         return *this;
 612       }
 613
 614       void
 615       _M_swap(__shared_count& __r) noexcept
 616       {
 617         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 618         __r._M_pi = _M_pi;
 619         _M_pi = __tmp;
 620       }
 621
 622       long
 623       _M_get_use_count() const noexcept
 624       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 625
 626       bool
 627       _M_unique() const noexcept
 628       { return this->_M_get_use_count() == 1; }
 629
 630       void*
 631       _M_get_deleter(const std::type_info& __ti) const noexcept
 632       { return _M_pi ? _M_pi->_M_get_deleter(__ti) : nullptr; }
 633
 634       bool
 635       _M_less(const __shared_count& __rhs) const noexcept
 636       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 637
 638       bool
 639       _M_less(const __weak_count<_Lp>& __rhs) const noexcept
 640       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 641
 642       // Friend function injected into enclosing namespace and found by ADL
 643       friend inline bool
 644       operator==(const __shared_count& __a, const __shared_count& __b) noexcept
 645       { return __a._M_pi == __b._M_pi; }
 646
 647     private:
 648       friend class __weak_count<_Lp>;
 649
 650       template<typename _Tp, typename _Del>
 651         static _Sp_counted_base<_Lp>*
 652         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 653           typename std::enable_if<!std::is_reference<_Del>::value>::type* = 0)
 654         {
 655           typedef typename unique_ptr<_Tp, _Del>::pointer _Ptr;
 656           return new _Sp_counted_deleter<_Ptr, _Del, std::allocator<void>,
 657             _Lp>(__r.get(), __r.get_deleter());
 658         }
 659
 660       template<typename _Tp, typename _Del>
 661         static _Sp_counted_base<_Lp>*
 662         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 663           typename std::enable_if<std::is_reference<_Del>::value>::type* = 0)
 664         {
 665           typedef typename unique_ptr<_Tp, _Del>::pointer _Ptr;
 666           typedef typename std::remove_reference<_Del>::type _Del1;
 667           typedef std::reference_wrapper<_Del1> _Del2;
 668           return new _Sp_counted_deleter<_Ptr, _Del2, std::allocator<void>,
 669             _Lp>(__r.get(), std::ref(__r.get_deleter()));
 670         }
 671
 672       _Sp_counted_base<_Lp>*  _M_pi;
 673     };
 674
 675
 676   template<_Lock_policy _Lp>
 677     class __weak_count
 678     {
 679     public:
 680       constexpr __weak_count() noexcept : _M_pi(0)
 681       { }
 682
 683       __weak_count(const __shared_count<_Lp>& __r) noexcept
 684       : _M_pi(__r._M_pi)
 685       {
 686         if (_M_pi != 0)
 687           _M_pi->_M_weak_add_ref();
 688       }
 689
 690       __weak_count(const __weak_count<_Lp>& __r) noexcept
 691       : _M_pi(__r._M_pi)
 692       {
 693         if (_M_pi != 0)
 694           _M_pi->_M_weak_add_ref();
 695       }
 696
 697       ~__weak_count() noexcept
 698       {
 699         if (_M_pi != 0)
 700           _M_pi->_M_weak_release();
 701       }
 702
 703       __weak_count<_Lp>&
 704       operator=(const __shared_count<_Lp>& __r) noexcept
 705       {
 706         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 707         if (__tmp != 0)
 708           __tmp->_M_weak_add_ref();
 709         if (_M_pi != 0)
 710           _M_pi->_M_weak_release();
 711         _M_pi = __tmp;
 712         return *this;
 713       }
 714
 715       __weak_count<_Lp>&
 716       operator=(const __weak_count<_Lp>& __r) noexcept
 717       {
 718         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 719         if (__tmp != 0)
 720           __tmp->_M_weak_add_ref();
 721         if (_M_pi != 0)
 722           _M_pi->_M_weak_release();
 723         _M_pi = __tmp;
 724         return *this;
 725       }
 726
 727       void
 728       _M_swap(__weak_count<_Lp>& __r) noexcept
 729       {
 730         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 731         __r._M_pi = _M_pi;
 732         _M_pi = __tmp;
 733       }
 734
 735       long
 736       _M_get_use_count() const noexcept
 737       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 738
 739       bool
 740       _M_less(const __weak_count& __rhs) const noexcept
 741       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 742
 743       bool
 744       _M_less(const __shared_count<_Lp>& __rhs) const noexcept
 745       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 746
 747       // Friend function injected into enclosing namespace and found by ADL
 748       friend inline bool
 749       operator==(const __weak_count& __a, const __weak_count& __b) noexcept
 750       { return __a._M_pi == __b._M_pi; }
 751
 752     private:
 753       friend class __shared_count<_Lp>;
 754
 755       _Sp_counted_base<_Lp>*  _M_pi;
 756     };
 757
 758   // Now that __weak_count is defined we can define this constructor:
 759   template<_Lock_policy _Lp>
 760     inline __shared_count<_Lp>:: __shared_count(const __weak_count<_Lp>& __r)
 761     : _M_pi(__r._M_pi)
 762     {
 763       if (_M_pi != 0)
 764         _M_pi->_M_add_ref_lock();
 765       else
 766         __throw_bad_weak_ptr();
 767     }
 768
 769
 770   // Support for enable_shared_from_this.
 771
 772   // Friend of __enable_shared_from_this.
 773   template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
 774     void
 775     __enable_shared_from_this_helper(const __shared_count<_Lp>&,
 776                                      const __enable_shared_from_this<_Tp1,
 777                                      _Lp>*, const _Tp2*) noexcept;
 778
 779   // Friend of enable_shared_from_this.
 780   template<typename _Tp1, typename _Tp2>
 781     void
 782     __enable_shared_from_this_helper(const __shared_count<>&,
 783                                      const enable_shared_from_this<_Tp1>*,
 784                                      const _Tp2*) noexcept;
 785
 786   template<_Lock_policy _Lp>
 787     inline void
 788     __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept
 789     { }
 790
 791
 792   template<typename _Tp, _Lock_policy _Lp>
 793     class __shared_ptr
 794     {
 795     public:
 796       typedef _Tp   element_type;
 797
 798       constexpr __shared_ptr() noexcept
 799       : _M_ptr(0), _M_refcount()
 800       { }
 801
 802       template<typename _Tp1>
 803         explicit __shared_ptr(_Tp1* __p)
 804         : _M_ptr(__p), _M_refcount(__p)
 805         {
 806           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 807           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 808           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 809         }
 810
 811       template<typename _Tp1, typename _Deleter>
 812         __shared_ptr(_Tp1* __p, _Deleter __d)
 813         : _M_ptr(__p), _M_refcount(__p, __d)
 814         {
 815           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 816           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 817           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 818         }
 819
 820       template<typename _Tp1, typename _Deleter, typename _Alloc>
 821         __shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
 822         : _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
 823         {
 824           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 825           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 826           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 827         }
 828
 829       template<typename _Deleter>
 830         __shared_ptr(nullptr_t __p, _Deleter __d)
 831         : _M_ptr(0), _M_refcount(__p, __d)
 832         { }
 833
 834       template<typename _Deleter, typename _Alloc>
 835         __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
 836         : _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
 837         { }
 838
 839       template<typename _Tp1>
 840         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p) noexcept
 841         : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
 842         { }
 843
 844       __shared_ptr(const __shared_ptr&) noexcept = default;
 845       __shared_ptr& operator=(const __shared_ptr&) noexcept = default;
 846       ~__shared_ptr() = default;
 847
 848       template<typename _Tp1, typename = typename
 849                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 850         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 851         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
 852         { }
 853
 854       __shared_ptr(__shared_ptr&& __r) noexcept
 855       : _M_ptr(__r._M_ptr), _M_refcount()
 856       {
 857         _M_refcount._M_swap(__r._M_refcount);
 858         __r._M_ptr = 0;
 859       }
 860
 861       template<typename _Tp1, typename = typename
 862                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 863         __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
 864         : _M_ptr(__r._M_ptr), _M_refcount()
 865         {
 866           _M_refcount._M_swap(__r._M_refcount);
 867           __r._M_ptr = 0;
 868         }
 869
 870       template<typename _Tp1>
 871         explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
 872         : _M_refcount(__r._M_refcount) // may throw
 873         {
 874           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 875
 876           // It is now safe to copy __r._M_ptr, as
 877           // _M_refcount(__r._M_refcount) did not throw.
 878           _M_ptr = __r._M_ptr;
 879         }
 880
 881       // If an exception is thrown this constructor has no effect.
 882       template<typename _Tp1, typename _Del>
 883         __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
 884         : _M_ptr(__r.get()), _M_refcount()
 885         {
 886           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 887           auto __tmp = std::__addressof(*__r.get());
 888           _M_refcount = __shared_count<_Lp>(std::move(__r));
 889           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 890         }
 891
 892 #if _GLIBCXX_USE_DEPRECATED
 893       // Postcondition: use_count() == 1 and __r.get() == 0
 894       template<typename _Tp1>
 895         __shared_ptr(std::auto_ptr<_Tp1>&& __r);
 896 #endif
 897
 898       /* TODO: use delegating constructor */
 899       constexpr __shared_ptr(nullptr_t) noexcept
 900       : _M_ptr(0), _M_refcount()
 901       { }
 902
 903       template<typename _Tp1>
 904         __shared_ptr&
 905         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 906         {
 907           _M_ptr = __r._M_ptr;
 908           _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
 909           return *this;
 910         }
 911
 912 #if _GLIBCXX_USE_DEPRECATED
 913       template<typename _Tp1>
 914         __shared_ptr&
 915         operator=(std::auto_ptr<_Tp1>&& __r)
 916         {
 917           __shared_ptr(std::move(__r)).swap(*this);
 918           return *this;
 919         }
 920 #endif
 921
 922       __shared_ptr&
 923       operator=(__shared_ptr&& __r) noexcept
 924       {
 925         __shared_ptr(std::move(__r)).swap(*this);
 926         return *this;
 927       }
 928
 929       template<class _Tp1>
 930         __shared_ptr&
 931         operator=(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
 932         {
 933           __shared_ptr(std::move(__r)).swap(*this);
 934           return *this;
 935         }
 936
 937       template<typename _Tp1, typename _Del>
 938         __shared_ptr&
 939         operator=(std::unique_ptr<_Tp1, _Del>&& __r)
 940         {
 941           __shared_ptr(std::move(__r)).swap(*this);
 942           return *this;
 943         }
 944
 945       void
 946       reset() noexcept
 947       { __shared_ptr().swap(*this); }
 948
 949       template<typename _Tp1>
 950         void
 951         reset(_Tp1* __p) // _Tp1 must be complete.
 952         {
 953           // Catch self-reset errors.
 954           _GLIBCXX_DEBUG_ASSERT(__p == 0 || __p != _M_ptr);
 955           __shared_ptr(__p).swap(*this);
 956         }
 957
 958       template<typename _Tp1, typename _Deleter>
 959         void
 960         reset(_Tp1* __p, _Deleter __d)
 961         { __shared_ptr(__p, __d).swap(*this); }
 962
 963       template<typename _Tp1, typename _Deleter, typename _Alloc>
 964         void
 965         reset(_Tp1* __p, _Deleter __d, _Alloc __a)
 966         { __shared_ptr(__p, __d, std::move(__a)).swap(*this); }
 967
 968       // Allow class instantiation when _Tp is [cv-qual] void.
 969       typename std::add_lvalue_reference<_Tp>::type
 970       operator*() const noexcept
 971       {
 972         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 973         return *_M_ptr;
 974       }
 975
 976       _Tp*
 977       operator->() const noexcept
 978       {
 979         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 980         return _M_ptr;
 981       }
 982
 983       _Tp*
 984       get() const noexcept
 985       { return _M_ptr; }
 986
 987       explicit operator bool() const // never throws
 988       { return _M_ptr == 0 ? false : true; }
 989
 990       bool
 991       unique() const noexcept
 992       { return _M_refcount._M_unique(); }
 993
 994       long
 995       use_count() const noexcept
 996       { return _M_refcount._M_get_use_count(); }
 997
 998       void
 999       swap(__shared_ptr<_Tp, _Lp>& __other) noexcept
1000       {
1001         std::swap(_M_ptr, __other._M_ptr);
1002         _M_refcount._M_swap(__other._M_refcount);
1003       }
1004
1005       template<typename _Tp1>
1006         bool
1007         owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const
1008         { return _M_refcount._M_less(__rhs._M_refcount); }
1009
1010       template<typename _Tp1>
1011         bool
1012         owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const
1013         { return _M_refcount._M_less(__rhs._M_refcount); }
1014
1015 #ifdef __GXX_RTTI
1016     protected:
1017       // This constructor is non-standard, it is used by allocate_shared.
1018       template<typename _Alloc, typename... _Args>
1019         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1020                      _Args&&... __args)
1021         : _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,
1022                                 std::forward<_Args>(__args)...)
1023         {
1024           // _M_ptr needs to point to the newly constructed object.
1025           // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
1026           void* __p = _M_refcount._M_get_deleter(typeid(__tag));
1027           _M_ptr = static_cast<_Tp*>(__p);
1028           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1029         }
1030 #else
1031       template<typename _Alloc>
1032         struct _Deleter
1033         {
1034           void operator()(_Tp* __ptr)
1035           {
1036             typedef allocator_traits<_Alloc> _Alloc_traits;
1037             _Alloc_traits::destroy(_M_alloc, __ptr);
1038             _Alloc_traits::deallocate(_M_alloc, __ptr, 1);
1039           }
1040           _Alloc _M_alloc;
1041         };
1042
1043       template<typename _Alloc, typename... _Args>
1044         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1045                      _Args&&... __args)
1046         : _M_ptr(), _M_refcount()
1047         {
1048           typedef typename _Alloc::template rebind<_Tp>::other _Alloc2;
1049           _Deleter<_Alloc2> __del = { _Alloc2(__a) };
1050           typedef allocator_traits<_Alloc2> __traits;
1051           _M_ptr = __traits::allocate(__del._M_alloc, 1);
1052           __try
1053             {
1054               // _GLIBCXX_RESOLVE_LIB_DEFECTS
1055               // 2070. allocate_shared should use allocator_traits<A>::construct
1056               __traits::construct(__del._M_alloc, _M_ptr,
1057                                   std::forward<_Args>(__args)...);
1058             }
1059           __catch(...)
1060             {
1061               __traits::deallocate(__del._M_alloc, _M_ptr, 1);
1062               __throw_exception_again;
1063             }
1064           __shared_count<_Lp> __count(_M_ptr, __del, __del._M_alloc);
1065           _M_refcount._M_swap(__count);
1066           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1067         }
1068 #endif
1069
1070       template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
1071                typename... _Args>
1072         friend __shared_ptr<_Tp1, _Lp1>
1073         __allocate_shared(const _Alloc& __a, _Args&&... __args);
1074
1075     private:
1076       void*
1077       _M_get_deleter(const std::type_info& __ti) const noexcept
1078       { return _M_refcount._M_get_deleter(__ti); }
1079
1080       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1081       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1082
1083       template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1084         friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&) noexcept;
1085
1086       _Tp*                 _M_ptr;         // Contained pointer.
1087       __shared_count<_Lp>  _M_refcount;    // Reference counter.
1088     };
1089
1090
1091   // 20.7.2.2.7 shared_ptr comparisons
1092   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1093     inline bool
1094     operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1095                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1096     { return __a.get() == __b.get(); }
1097
1098   template<typename _Tp, _Lock_policy _Lp>
1099     inline bool
1100     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1101     { return !__a; }
1102
1103   template<typename _Tp, _Lock_policy _Lp>
1104     inline bool
1105     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1106     { return !__a; }
1107
1108   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1109     inline bool
1110     operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1111                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1112     { return __a.get() != __b.get(); }
1113
1114   template<typename _Tp, _Lock_policy _Lp>
1115     inline bool
1116     operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1117     { return (bool)__a; }
1118
1119   template<typename _Tp, _Lock_policy _Lp>
1120     inline bool
1121     operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1122     { return (bool)__a; }
1123
1124   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1125     inline bool
1126     operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1127               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1128     {
1129       typedef typename std::common_type<_Tp1*, _Tp2*>::type _CT;
1130       return std::less<_CT>()(__a.get(), __b.get());
1131     }
1132
1133   template<typename _Tp, _Lock_policy _Lp>
1134     inline bool
1135     operator<(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1136     { return std::less<_Tp*>()(__a.get(), nullptr); }
1137
1138   template<typename _Tp, _Lock_policy _Lp>
1139     inline bool
1140     operator<(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1141     { return std::less<_Tp*>()(nullptr, __a.get()); }
1142
1143   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1144     inline bool
1145     operator<=(const __shared_ptr<_Tp1, _Lp>& __a,
1146                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1147     { return !(__b < __a); }
1148
1149   template<typename _Tp, _Lock_policy _Lp>
1150     inline bool
1151     operator<=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1152     { return !(nullptr < __a); }
1153
1154   template<typename _Tp, _Lock_policy _Lp>
1155     inline bool
1156     operator<=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1157     { return !(__a < nullptr); }
1158
1159   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1160     inline bool
1161     operator>(const __shared_ptr<_Tp1, _Lp>& __a,
1162               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1163     { return (__b < __a); }
1164
1165   template<typename _Tp, _Lock_policy _Lp>
1166     inline bool
1167     operator>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1168     { return std::less<_Tp*>()(nullptr, __a.get()); }
1169
1170   template<typename _Tp, _Lock_policy _Lp>
1171     inline bool
1172     operator>(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1173     { return std::less<_Tp*>()(__a.get(), nullptr); }
1174
1175   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1176     inline bool
1177     operator>=(const __shared_ptr<_Tp1, _Lp>& __a,
1178                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1179     { return !(__a < __b); }
1180
1181   template<typename _Tp, _Lock_policy _Lp>
1182     inline bool
1183     operator>=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1184     { return !(__a < nullptr); }
1185
1186   template<typename _Tp, _Lock_policy _Lp>
1187     inline bool
1188     operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1189     { return !(nullptr < __a); }
1190
1191   template<typename _Sp>
1192     struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1193     {
1194       bool
1195       operator()(const _Sp& __lhs, const _Sp& __rhs) const noexcept
1196       {
1197         typedef typename _Sp::element_type element_type;
1198         return std::less<element_type*>()(__lhs.get(), __rhs.get());
1199       }
1200     };
1201
1202   template<typename _Tp, _Lock_policy _Lp>
1203     struct less<__shared_ptr<_Tp, _Lp>>
1204     : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1205     { };
1206
1207   // 20.7.2.2.8 shared_ptr specialized algorithms.
1208   template<typename _Tp, _Lock_policy _Lp>
1209     inline void
1210     swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b) noexcept
1211     { __a.swap(__b); }
1212
1213   // 20.7.2.2.9 shared_ptr casts
1214
1215   // The seemingly equivalent code:
1216   // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1217   // will eventually result in undefined behaviour, attempting to
1218   // delete the same object twice.
1219   /// static_pointer_cast
1220   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1221     inline __shared_ptr<_Tp, _Lp>
1222     static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1223     { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1224
1225   // The seemingly equivalent code:
1226   // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1227   // will eventually result in undefined behaviour, attempting to
1228   // delete the same object twice.
1229   /// const_pointer_cast
1230   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1231     inline __shared_ptr<_Tp, _Lp>
1232     const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1233     { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1234
1235   // The seemingly equivalent code:
1236   // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1237   // will eventually result in undefined behaviour, attempting to
1238   // delete the same object twice.
1239   /// dynamic_pointer_cast
1240   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1241     inline __shared_ptr<_Tp, _Lp>
1242     dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1243     {
1244       if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1245         return __shared_ptr<_Tp, _Lp>(__r, __p);
1246       return __shared_ptr<_Tp, _Lp>();
1247     }
1248
1249
1250   template<typename _Tp, _Lock_policy _Lp>
1251     class __weak_ptr
1252     {
1253     public:
1254       typedef _Tp element_type;
1255
1256       constexpr __weak_ptr() noexcept
1257       : _M_ptr(0), _M_refcount()
1258       { }
1259
1260       __weak_ptr(const __weak_ptr&) noexcept = default;
1261       __weak_ptr& operator=(const __weak_ptr&) noexcept = default;
1262       ~__weak_ptr() = default;
1263
1264       // The "obvious" converting constructor implementation:
1265       //
1266       //  template<typename _Tp1>
1267       //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1268       //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1269       //    { }
1270       //
1271       // has a serious problem.
1272       //
1273       //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1274       //  conversion may require access to *__r._M_ptr (virtual inheritance).
1275       //
1276       // It is not possible to avoid spurious access violations since
1277       // in multithreaded programs __r._M_ptr may be invalidated at any point.
1278       template<typename _Tp1, typename = typename
1279                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1280         __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1281         : _M_refcount(__r._M_refcount)
1282         { _M_ptr = __r.lock().get(); }
1283
1284       template<typename _Tp1, typename = typename
1285                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1286         __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1287         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
1288         { }
1289
1290       template<typename _Tp1>
1291         __weak_ptr&
1292         operator=(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1293         {
1294           _M_ptr = __r.lock().get();
1295           _M_refcount = __r._M_refcount;
1296           return *this;
1297         }
1298
1299       template<typename _Tp1>
1300         __weak_ptr&
1301         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1302         {
1303           _M_ptr = __r._M_ptr;
1304           _M_refcount = __r._M_refcount;
1305           return *this;
1306         }
1307
1308       __shared_ptr<_Tp, _Lp>
1309       lock() const noexcept
1310       {
1311 #ifdef __GTHREADS
1312         // Optimization: avoid throw overhead.
1313         if (expired())
1314           return __shared_ptr<element_type, _Lp>();
1315
1316         __try
1317           {
1318             return __shared_ptr<element_type, _Lp>(*this);
1319           }
1320         __catch(const bad_weak_ptr&)
1321           {
1322             // Q: How can we get here?
1323             // A: Another thread may have invalidated r after the
1324             //    use_count test above.
1325             return __shared_ptr<element_type, _Lp>();
1326           }
1327
1328 #else
1329         // Optimization: avoid try/catch overhead when single threaded.
1330         return expired() ? __shared_ptr<element_type, _Lp>()
1331                          : __shared_ptr<element_type, _Lp>(*this);
1332
1333 #endif
1334       } // XXX MT
1335
1336       long
1337       use_count() const noexcept
1338       { return _M_refcount._M_get_use_count(); }
1339
1340       bool
1341       expired() const noexcept
1342       { return _M_refcount._M_get_use_count() == 0; }
1343
1344       template<typename _Tp1>
1345         bool
1346         owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1347         { return _M_refcount._M_less(__rhs._M_refcount); }
1348
1349       template<typename _Tp1>
1350         bool
1351         owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1352         { return _M_refcount._M_less(__rhs._M_refcount); }
1353
1354       void
1355       reset() noexcept
1356       { __weak_ptr().swap(*this); }
1357
1358       void
1359       swap(__weak_ptr& __s) noexcept
1360       {
1361         std::swap(_M_ptr, __s._M_ptr);
1362         _M_refcount._M_swap(__s._M_refcount);
1363       }
1364
1365     private:
1366       // Used by __enable_shared_from_this.
1367       void
1368       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
1369       {
1370         _M_ptr = __ptr;
1371         _M_refcount = __refcount;
1372       }
1373
1374       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1375       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1376       friend class __enable_shared_from_this<_Tp, _Lp>;
1377       friend class enable_shared_from_this<_Tp>;
1378
1379       _Tp*               _M_ptr;         // Contained pointer.
1380       __weak_count<_Lp>  _M_refcount;    // Reference counter.
1381     };
1382
1383   // 20.7.2.3.6 weak_ptr specialized algorithms.
1384   template<typename _Tp, _Lock_policy _Lp>
1385     inline void
1386     swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b) noexcept
1387     { __a.swap(__b); }
1388
1389   template<typename _Tp, typename _Tp1>
1390     struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1391     {
1392       bool
1393       operator()(const _Tp& __lhs, const _Tp& __rhs) const
1394       { return __lhs.owner_before(__rhs); }
1395
1396       bool
1397       operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1398       { return __lhs.owner_before(__rhs); }
1399
1400       bool
1401       operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1402       { return __lhs.owner_before(__rhs); }
1403     };
1404
1405   template<typename _Tp, _Lock_policy _Lp>
1406     struct owner_less<__shared_ptr<_Tp, _Lp>>
1407     : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1408     { };
1409
1410   template<typename _Tp, _Lock_policy _Lp>
1411     struct owner_less<__weak_ptr<_Tp, _Lp>>
1412     : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1413     { };
1414
1415
1416   template<typename _Tp, _Lock_policy _Lp>
1417     class __enable_shared_from_this
1418     {
1419     protected:
1420       constexpr __enable_shared_from_this() noexcept { }
1421
1422       __enable_shared_from_this(const __enable_shared_from_this&) noexcept { }
1423
1424       __enable_shared_from_this&
1425       operator=(const __enable_shared_from_this&) noexcept
1426       { return *this; }
1427
1428       ~__enable_shared_from_this() { }
1429
1430     public:
1431       __shared_ptr<_Tp, _Lp>
1432       shared_from_this()
1433       { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1434
1435       __shared_ptr<const _Tp, _Lp>
1436       shared_from_this() const
1437       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1438
1439     private:
1440       template<typename _Tp1>
1441         void
1442         _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
1443         { _M_weak_this._M_assign(__p, __n); }
1444
1445       template<typename _Tp1>
1446         friend void
1447         __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
1448                                          const __enable_shared_from_this* __pe,
1449                                          const _Tp1* __px) noexcept
1450         {
1451           if (__pe != 0)
1452             __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
1453         }
1454
1455       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
1456     };
1457
1458
1459   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1460     inline __shared_ptr<_Tp, _Lp>
1461     __allocate_shared(const _Alloc& __a, _Args&&... __args)
1462     {
1463       return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
1464                                     std::forward<_Args>(__args)...);
1465     }
1466
1467   template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1468     inline __shared_ptr<_Tp, _Lp>
1469     __make_shared(_Args&&... __args)
1470     {
1471       typedef typename std::remove_const<_Tp>::type _Tp_nc;
1472       return std::__allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1473                                               std::forward<_Args>(__args)...);
1474     }
1475
1476   /// std::hash specialization for __shared_ptr.
1477   template<typename _Tp, _Lock_policy _Lp>
1478     struct hash<__shared_ptr<_Tp, _Lp>>
1479     : public __hash_base<size_t, __shared_ptr<_Tp, _Lp>>
1480     {
1481       size_t
1482       operator()(const __shared_ptr<_Tp, _Lp>& __s) const noexcept
1483       { return std::hash<_Tp*>()(__s.get()); }
1484     };
1485
1486 _GLIBCXX_END_NAMESPACE_VERSION
1487 } // namespace
1488
1489 #endif // _SHARED_PTR_BASE_H