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)
 499         : __shared_count(__p, std::move(__d), allocator<void>())
 500         { }
 501
 502       template<typename _Ptr, typename _Deleter, typename _Alloc>
 503         __shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
 504         {
 505           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 506           typedef typename allocator_traits<_Alloc>::template
 507             rebind_traits<_Sp_cd_type> _Alloc_traits;
 508           typename _Alloc_traits::allocator_type __a2(__a);
 509           _Sp_cd_type* __mem = 0;
 510           __try
 511             {
 512               __mem = _Alloc_traits::allocate(__a2, 1);
 513               _Alloc_traits::construct(__a2, __mem,
 514                   __p, std::move(__d), std::move(__a));
 515               _M_pi = __mem;
 516             }
 517           __catch(...)
 518             {
 519               __d(__p); // Call _Deleter on __p.
 520               if (__mem)
 521                 _Alloc_traits::deallocate(__a2, __mem, 1);
 522               __throw_exception_again;
 523             }
 524         }
 525
 526       template<typename _Tp, typename _Alloc, typename... _Args>
 527         __shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,
 528                        _Args&&... __args)
 529         : _M_pi(0)
 530         {
 531           typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
 532           typedef typename allocator_traits<_Alloc>::template
 533             rebind_traits<_Sp_cp_type> _Alloc_traits;
 534           typename _Alloc_traits::allocator_type __a2(__a);
 535           _Sp_cp_type* __mem = _Alloc_traits::allocate(__a2, 1);
 536           __try
 537             {
 538               _Alloc_traits::construct(__a2, __mem, std::move(__a),
 539                     std::forward<_Args>(__args)...);
 540               _M_pi = __mem;
 541             }
 542           __catch(...)
 543             {
 544               _Alloc_traits::deallocate(__a2, __mem, 1);
 545               __throw_exception_again;
 546             }
 547         }
 548
 549 #if _GLIBCXX_USE_DEPRECATED
 550       // Special case for auto_ptr<_Tp> to provide the strong guarantee.
 551       template<typename _Tp>
 552         explicit
 553         __shared_count(std::auto_ptr<_Tp>&& __r);
 554 #endif
 555
 556       // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
 557       template<typename _Tp, typename _Del>
 558         explicit
 559         __shared_count(std::unique_ptr<_Tp, _Del>&& __r) : _M_pi(0)
 560         {
 561           using _Ptr = typename unique_ptr<_Tp, _Del>::pointer;
 562           using _Del2 = typename conditional<is_reference<_Del>::value,
 563               reference_wrapper<typename remove_reference<_Del>::type>,
 564               _Del>::type;
 565           using _Sp_cd_type
 566             = _Sp_counted_deleter<_Ptr, _Del2, allocator<void>, _Lp>;
 567           using _Alloc = allocator<_Sp_cd_type>;
 568           using _Alloc_traits = allocator_traits<_Alloc>;
 569           _Alloc __a;
 570           _Sp_cd_type* __mem = _Alloc_traits::allocate(__a, 1);
 571           _Alloc_traits::construct(__a, __mem, __r.release(),
 572                                    __r.get_deleter());  // non-throwing
 573           _M_pi = __mem;
 574         }
 575
 576       // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
 577       explicit __shared_count(const __weak_count<_Lp>& __r);
 578
 579       ~__shared_count() noexcept
 580       {
 581         if (_M_pi != nullptr)
 582           _M_pi->_M_release();
 583       }
 584
 585       __shared_count(const __shared_count& __r) noexcept
 586       : _M_pi(__r._M_pi)
 587       {
 588         if (_M_pi != 0)
 589           _M_pi->_M_add_ref_copy();
 590       }
 591
 592       __shared_count&
 593       operator=(const __shared_count& __r) noexcept
 594       {
 595         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 596         if (__tmp != _M_pi)
 597           {
 598             if (__tmp != 0)
 599               __tmp->_M_add_ref_copy();
 600             if (_M_pi != 0)
 601               _M_pi->_M_release();
 602             _M_pi = __tmp;
 603           }
 604         return *this;
 605       }
 606
 607       void
 608       _M_swap(__shared_count& __r) noexcept
 609       {
 610         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 611         __r._M_pi = _M_pi;
 612         _M_pi = __tmp;
 613       }
 614
 615       long
 616       _M_get_use_count() const noexcept
 617       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 618
 619       bool
 620       _M_unique() const noexcept
 621       { return this->_M_get_use_count() == 1; }
 622
 623       void*
 624       _M_get_deleter(const std::type_info& __ti) const noexcept
 625       { return _M_pi ? _M_pi->_M_get_deleter(__ti) : nullptr; }
 626
 627       bool
 628       _M_less(const __shared_count& __rhs) const noexcept
 629       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 630
 631       bool
 632       _M_less(const __weak_count<_Lp>& __rhs) const noexcept
 633       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 634
 635       // Friend function injected into enclosing namespace and found by ADL
 636       friend inline bool
 637       operator==(const __shared_count& __a, const __shared_count& __b) noexcept
 638       { return __a._M_pi == __b._M_pi; }
 639
 640     private:
 641       friend class __weak_count<_Lp>;
 642
 643       _Sp_counted_base<_Lp>*  _M_pi;
 644     };
 645
 646
 647   template<_Lock_policy _Lp>
 648     class __weak_count
 649     {
 650     public:
 651       constexpr __weak_count() noexcept : _M_pi(0)
 652       { }
 653
 654       __weak_count(const __shared_count<_Lp>& __r) noexcept
 655       : _M_pi(__r._M_pi)
 656       {
 657         if (_M_pi != 0)
 658           _M_pi->_M_weak_add_ref();
 659       }
 660
 661       __weak_count(const __weak_count<_Lp>& __r) noexcept
 662       : _M_pi(__r._M_pi)
 663       {
 664         if (_M_pi != 0)
 665           _M_pi->_M_weak_add_ref();
 666       }
 667
 668       ~__weak_count() noexcept
 669       {
 670         if (_M_pi != 0)
 671           _M_pi->_M_weak_release();
 672       }
 673
 674       __weak_count<_Lp>&
 675       operator=(const __shared_count<_Lp>& __r) noexcept
 676       {
 677         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 678         if (__tmp != 0)
 679           __tmp->_M_weak_add_ref();
 680         if (_M_pi != 0)
 681           _M_pi->_M_weak_release();
 682         _M_pi = __tmp;
 683         return *this;
 684       }
 685
 686       __weak_count<_Lp>&
 687       operator=(const __weak_count<_Lp>& __r) noexcept
 688       {
 689         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 690         if (__tmp != 0)
 691           __tmp->_M_weak_add_ref();
 692         if (_M_pi != 0)
 693           _M_pi->_M_weak_release();
 694         _M_pi = __tmp;
 695         return *this;
 696       }
 697
 698       void
 699       _M_swap(__weak_count<_Lp>& __r) noexcept
 700       {
 701         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 702         __r._M_pi = _M_pi;
 703         _M_pi = __tmp;
 704       }
 705
 706       long
 707       _M_get_use_count() const noexcept
 708       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 709
 710       bool
 711       _M_less(const __weak_count& __rhs) const noexcept
 712       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 713
 714       bool
 715       _M_less(const __shared_count<_Lp>& __rhs) const noexcept
 716       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 717
 718       // Friend function injected into enclosing namespace and found by ADL
 719       friend inline bool
 720       operator==(const __weak_count& __a, const __weak_count& __b) noexcept
 721       { return __a._M_pi == __b._M_pi; }
 722
 723     private:
 724       friend class __shared_count<_Lp>;
 725
 726       _Sp_counted_base<_Lp>*  _M_pi;
 727     };
 728
 729   // Now that __weak_count is defined we can define this constructor:
 730   template<_Lock_policy _Lp>
 731     inline __shared_count<_Lp>:: __shared_count(const __weak_count<_Lp>& __r)
 732     : _M_pi(__r._M_pi)
 733     {
 734       if (_M_pi != 0)
 735         _M_pi->_M_add_ref_lock();
 736       else
 737         __throw_bad_weak_ptr();
 738     }
 739
 740
 741   // Support for enable_shared_from_this.
 742
 743   // Friend of __enable_shared_from_this.
 744   template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
 745     void
 746     __enable_shared_from_this_helper(const __shared_count<_Lp>&,
 747                                      const __enable_shared_from_this<_Tp1,
 748                                      _Lp>*, const _Tp2*) noexcept;
 749
 750   // Friend of enable_shared_from_this.
 751   template<typename _Tp1, typename _Tp2>
 752     void
 753     __enable_shared_from_this_helper(const __shared_count<>&,
 754                                      const enable_shared_from_this<_Tp1>*,
 755                                      const _Tp2*) noexcept;
 756
 757   template<_Lock_policy _Lp>
 758     inline void
 759     __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept
 760     { }
 761
 762
 763   template<typename _Tp, _Lock_policy _Lp>
 764     class __shared_ptr
 765     {
 766     public:
 767       typedef _Tp   element_type;
 768
 769       constexpr __shared_ptr() noexcept
 770       : _M_ptr(0), _M_refcount()
 771       { }
 772
 773       template<typename _Tp1>
 774         explicit __shared_ptr(_Tp1* __p)
 775         : _M_ptr(__p), _M_refcount(__p)
 776         {
 777           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 778           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 779           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 780         }
 781
 782       template<typename _Tp1, typename _Deleter>
 783         __shared_ptr(_Tp1* __p, _Deleter __d)
 784         : _M_ptr(__p), _M_refcount(__p, __d)
 785         {
 786           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 787           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 788           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 789         }
 790
 791       template<typename _Tp1, typename _Deleter, typename _Alloc>
 792         __shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
 793         : _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
 794         {
 795           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 796           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 797           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 798         }
 799
 800       template<typename _Deleter>
 801         __shared_ptr(nullptr_t __p, _Deleter __d)
 802         : _M_ptr(0), _M_refcount(__p, __d)
 803         { }
 804
 805       template<typename _Deleter, typename _Alloc>
 806         __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
 807         : _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
 808         { }
 809
 810       template<typename _Tp1>
 811         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p) noexcept
 812         : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
 813         { }
 814
 815       __shared_ptr(const __shared_ptr&) noexcept = default;
 816       __shared_ptr& operator=(const __shared_ptr&) noexcept = default;
 817       ~__shared_ptr() = default;
 818
 819       template<typename _Tp1, typename = typename
 820                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 821         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 822         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
 823         { }
 824
 825       __shared_ptr(__shared_ptr&& __r) noexcept
 826       : _M_ptr(__r._M_ptr), _M_refcount()
 827       {
 828         _M_refcount._M_swap(__r._M_refcount);
 829         __r._M_ptr = 0;
 830       }
 831
 832       template<typename _Tp1, typename = typename
 833                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 834         __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
 835         : _M_ptr(__r._M_ptr), _M_refcount()
 836         {
 837           _M_refcount._M_swap(__r._M_refcount);
 838           __r._M_ptr = 0;
 839         }
 840
 841       template<typename _Tp1>
 842         explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
 843         : _M_refcount(__r._M_refcount) // may throw
 844         {
 845           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 846
 847           // It is now safe to copy __r._M_ptr, as
 848           // _M_refcount(__r._M_refcount) did not throw.
 849           _M_ptr = __r._M_ptr;
 850         }
 851
 852       // If an exception is thrown this constructor has no effect.
 853       template<typename _Tp1, typename _Del>
 854         __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
 855         : _M_ptr(__r.get()), _M_refcount()
 856         {
 857           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 858           auto __raw = _S_raw_ptr(__r.get());
 859           _M_refcount = __shared_count<_Lp>(std::move(__r));
 860           __enable_shared_from_this_helper(_M_refcount, __raw, __raw);
 861         }
 862
 863 #if _GLIBCXX_USE_DEPRECATED
 864       // Postcondition: use_count() == 1 and __r.get() == 0
 865       template<typename _Tp1>
 866         __shared_ptr(std::auto_ptr<_Tp1>&& __r);
 867 #endif
 868
 869       /* TODO: use delegating constructor */
 870       constexpr __shared_ptr(nullptr_t) noexcept
 871       : _M_ptr(0), _M_refcount()
 872       { }
 873
 874       template<typename _Tp1>
 875         __shared_ptr&
 876         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 877         {
 878           _M_ptr = __r._M_ptr;
 879           _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
 880           return *this;
 881         }
 882
 883 #if _GLIBCXX_USE_DEPRECATED
 884       template<typename _Tp1>
 885         __shared_ptr&
 886         operator=(std::auto_ptr<_Tp1>&& __r)
 887         {
 888           __shared_ptr(std::move(__r)).swap(*this);
 889           return *this;
 890         }
 891 #endif
 892
 893       __shared_ptr&
 894       operator=(__shared_ptr&& __r) noexcept
 895       {
 896         __shared_ptr(std::move(__r)).swap(*this);
 897         return *this;
 898       }
 899
 900       template<class _Tp1>
 901         __shared_ptr&
 902         operator=(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
 903         {
 904           __shared_ptr(std::move(__r)).swap(*this);
 905           return *this;
 906         }
 907
 908       template<typename _Tp1, typename _Del>
 909         __shared_ptr&
 910         operator=(std::unique_ptr<_Tp1, _Del>&& __r)
 911         {
 912           __shared_ptr(std::move(__r)).swap(*this);
 913           return *this;
 914         }
 915
 916       void
 917       reset() noexcept
 918       { __shared_ptr().swap(*this); }
 919
 920       template<typename _Tp1>
 921         void
 922         reset(_Tp1* __p) // _Tp1 must be complete.
 923         {
 924           // Catch self-reset errors.
 925           _GLIBCXX_DEBUG_ASSERT(__p == 0 || __p != _M_ptr);
 926           __shared_ptr(__p).swap(*this);
 927         }
 928
 929       template<typename _Tp1, typename _Deleter>
 930         void
 931         reset(_Tp1* __p, _Deleter __d)
 932         { __shared_ptr(__p, __d).swap(*this); }
 933
 934       template<typename _Tp1, typename _Deleter, typename _Alloc>
 935         void
 936         reset(_Tp1* __p, _Deleter __d, _Alloc __a)
 937         { __shared_ptr(__p, __d, std::move(__a)).swap(*this); }
 938
 939       // Allow class instantiation when _Tp is [cv-qual] void.
 940       typename std::add_lvalue_reference<_Tp>::type
 941       operator*() const noexcept
 942       {
 943         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 944         return *_M_ptr;
 945       }
 946
 947       _Tp*
 948       operator->() const noexcept
 949       {
 950         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 951         return _M_ptr;
 952       }
 953
 954       _Tp*
 955       get() const noexcept
 956       { return _M_ptr; }
 957
 958       explicit operator bool() const // never throws
 959       { return _M_ptr == 0 ? false : true; }
 960
 961       bool
 962       unique() const noexcept
 963       { return _M_refcount._M_unique(); }
 964
 965       long
 966       use_count() const noexcept
 967       { return _M_refcount._M_get_use_count(); }
 968
 969       void
 970       swap(__shared_ptr<_Tp, _Lp>& __other) noexcept
 971       {
 972         std::swap(_M_ptr, __other._M_ptr);
 973         _M_refcount._M_swap(__other._M_refcount);
 974       }
 975
 976       template<typename _Tp1>
 977         bool
 978         owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const
 979         { return _M_refcount._M_less(__rhs._M_refcount); }
 980
 981       template<typename _Tp1>
 982         bool
 983         owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const
 984         { return _M_refcount._M_less(__rhs._M_refcount); }
 985
 986 #ifdef __GXX_RTTI
 987     protected:
 988       // This constructor is non-standard, it is used by allocate_shared.
 989       template<typename _Alloc, typename... _Args>
 990         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
 991                      _Args&&... __args)
 992         : _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,
 993                                 std::forward<_Args>(__args)...)
 994         {
 995           // _M_ptr needs to point to the newly constructed object.
 996           // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
 997           void* __p = _M_refcount._M_get_deleter(typeid(__tag));
 998           _M_ptr = static_cast<_Tp*>(__p);
 999           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1000         }
1001 #else
1002       template<typename _Alloc>
1003         struct _Deleter
1004         {
1005           void operator()(_Tp* __ptr)
1006           {
1007             typedef allocator_traits<_Alloc> _Alloc_traits;
1008             _Alloc_traits::destroy(_M_alloc, __ptr);
1009             _Alloc_traits::deallocate(_M_alloc, __ptr, 1);
1010           }
1011           _Alloc _M_alloc;
1012         };
1013
1014       template<typename _Alloc, typename... _Args>
1015         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1016                      _Args&&... __args)
1017         : _M_ptr(), _M_refcount()
1018         {
1019           typedef typename _Alloc::template rebind<_Tp>::other _Alloc2;
1020           _Deleter<_Alloc2> __del = { _Alloc2(__a) };
1021           typedef allocator_traits<_Alloc2> __traits;
1022           _M_ptr = __traits::allocate(__del._M_alloc, 1);
1023           __try
1024             {
1025               // _GLIBCXX_RESOLVE_LIB_DEFECTS
1026               // 2070. allocate_shared should use allocator_traits<A>::construct
1027               __traits::construct(__del._M_alloc, _M_ptr,
1028                                   std::forward<_Args>(__args)...);
1029             }
1030           __catch(...)
1031             {
1032               __traits::deallocate(__del._M_alloc, _M_ptr, 1);
1033               __throw_exception_again;
1034             }
1035           __shared_count<_Lp> __count(_M_ptr, __del, __del._M_alloc);
1036           _M_refcount._M_swap(__count);
1037           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1038         }
1039 #endif
1040
1041       template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
1042                typename... _Args>
1043         friend __shared_ptr<_Tp1, _Lp1>
1044         __allocate_shared(const _Alloc& __a, _Args&&... __args);
1045
1046     private:
1047       void*
1048       _M_get_deleter(const std::type_info& __ti) const noexcept
1049       { return _M_refcount._M_get_deleter(__ti); }
1050
1051       template<typename _Tp1>
1052         static _Tp1*
1053         _S_raw_ptr(_Tp1* __ptr)
1054         { return __ptr; }
1055
1056       template<typename _Tp1>
1057         static auto
1058         _S_raw_ptr(_Tp1 __ptr) -> decltype(std::__addressof(*__ptr))
1059         { return std::__addressof(*__ptr); }
1060
1061       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1062       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1063
1064       template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1065         friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&) noexcept;
1066
1067       _Tp*                 _M_ptr;         // Contained pointer.
1068       __shared_count<_Lp>  _M_refcount;    // Reference counter.
1069     };
1070
1071
1072   // 20.7.2.2.7 shared_ptr comparisons
1073   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1074     inline bool
1075     operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1076                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1077     { return __a.get() == __b.get(); }
1078
1079   template<typename _Tp, _Lock_policy _Lp>
1080     inline bool
1081     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1082     { return !__a; }
1083
1084   template<typename _Tp, _Lock_policy _Lp>
1085     inline bool
1086     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1087     { return !__a; }
1088
1089   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1090     inline bool
1091     operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1092                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1093     { return __a.get() != __b.get(); }
1094
1095   template<typename _Tp, _Lock_policy _Lp>
1096     inline bool
1097     operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1098     { return (bool)__a; }
1099
1100   template<typename _Tp, _Lock_policy _Lp>
1101     inline bool
1102     operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1103     { return (bool)__a; }
1104
1105   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1106     inline bool
1107     operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1108               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1109     {
1110       typedef typename std::common_type<_Tp1*, _Tp2*>::type _CT;
1111       return std::less<_CT>()(__a.get(), __b.get());
1112     }
1113
1114   template<typename _Tp, _Lock_policy _Lp>
1115     inline bool
1116     operator<(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1117     { return std::less<_Tp*>()(__a.get(), nullptr); }
1118
1119   template<typename _Tp, _Lock_policy _Lp>
1120     inline bool
1121     operator<(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1122     { return std::less<_Tp*>()(nullptr, __a.get()); }
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     { return !(__b < __a); }
1129
1130   template<typename _Tp, _Lock_policy _Lp>
1131     inline bool
1132     operator<=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1133     { return !(nullptr < __a); }
1134
1135   template<typename _Tp, _Lock_policy _Lp>
1136     inline bool
1137     operator<=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1138     { return !(__a < nullptr); }
1139
1140   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1141     inline bool
1142     operator>(const __shared_ptr<_Tp1, _Lp>& __a,
1143               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1144     { return (__b < __a); }
1145
1146   template<typename _Tp, _Lock_policy _Lp>
1147     inline bool
1148     operator>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1149     { return std::less<_Tp*>()(nullptr, __a.get()); }
1150
1151   template<typename _Tp, _Lock_policy _Lp>
1152     inline bool
1153     operator>(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1154     { return std::less<_Tp*>()(__a.get(), nullptr); }
1155
1156   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1157     inline bool
1158     operator>=(const __shared_ptr<_Tp1, _Lp>& __a,
1159                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1160     { return !(__a < __b); }
1161
1162   template<typename _Tp, _Lock_policy _Lp>
1163     inline bool
1164     operator>=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1165     { return !(__a < nullptr); }
1166
1167   template<typename _Tp, _Lock_policy _Lp>
1168     inline bool
1169     operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1170     { return !(nullptr < __a); }
1171
1172   template<typename _Sp>
1173     struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1174     {
1175       bool
1176       operator()(const _Sp& __lhs, const _Sp& __rhs) const noexcept
1177       {
1178         typedef typename _Sp::element_type element_type;
1179         return std::less<element_type*>()(__lhs.get(), __rhs.get());
1180       }
1181     };
1182
1183   template<typename _Tp, _Lock_policy _Lp>
1184     struct less<__shared_ptr<_Tp, _Lp>>
1185     : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1186     { };
1187
1188   // 20.7.2.2.8 shared_ptr specialized algorithms.
1189   template<typename _Tp, _Lock_policy _Lp>
1190     inline void
1191     swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b) noexcept
1192     { __a.swap(__b); }
1193
1194   // 20.7.2.2.9 shared_ptr casts
1195
1196   // The seemingly equivalent code:
1197   // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1198   // will eventually result in undefined behaviour, attempting to
1199   // delete the same object twice.
1200   /// static_pointer_cast
1201   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1202     inline __shared_ptr<_Tp, _Lp>
1203     static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1204     { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1205
1206   // The seemingly equivalent code:
1207   // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1208   // will eventually result in undefined behaviour, attempting to
1209   // delete the same object twice.
1210   /// const_pointer_cast
1211   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1212     inline __shared_ptr<_Tp, _Lp>
1213     const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1214     { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1215
1216   // The seemingly equivalent code:
1217   // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1218   // will eventually result in undefined behaviour, attempting to
1219   // delete the same object twice.
1220   /// dynamic_pointer_cast
1221   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1222     inline __shared_ptr<_Tp, _Lp>
1223     dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1224     {
1225       if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1226         return __shared_ptr<_Tp, _Lp>(__r, __p);
1227       return __shared_ptr<_Tp, _Lp>();
1228     }
1229
1230
1231   template<typename _Tp, _Lock_policy _Lp>
1232     class __weak_ptr
1233     {
1234     public:
1235       typedef _Tp element_type;
1236
1237       constexpr __weak_ptr() noexcept
1238       : _M_ptr(0), _M_refcount()
1239       { }
1240
1241       __weak_ptr(const __weak_ptr&) noexcept = default;
1242       __weak_ptr& operator=(const __weak_ptr&) noexcept = default;
1243       ~__weak_ptr() = default;
1244
1245       // The "obvious" converting constructor implementation:
1246       //
1247       //  template<typename _Tp1>
1248       //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1249       //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1250       //    { }
1251       //
1252       // has a serious problem.
1253       //
1254       //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1255       //  conversion may require access to *__r._M_ptr (virtual inheritance).
1256       //
1257       // It is not possible to avoid spurious access violations since
1258       // in multithreaded programs __r._M_ptr may be invalidated at any point.
1259       template<typename _Tp1, typename = typename
1260                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1261         __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1262         : _M_refcount(__r._M_refcount)
1263         { _M_ptr = __r.lock().get(); }
1264
1265       template<typename _Tp1, typename = typename
1266                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1267         __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1268         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
1269         { }
1270
1271       template<typename _Tp1>
1272         __weak_ptr&
1273         operator=(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1274         {
1275           _M_ptr = __r.lock().get();
1276           _M_refcount = __r._M_refcount;
1277           return *this;
1278         }
1279
1280       template<typename _Tp1>
1281         __weak_ptr&
1282         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1283         {
1284           _M_ptr = __r._M_ptr;
1285           _M_refcount = __r._M_refcount;
1286           return *this;
1287         }
1288
1289       __shared_ptr<_Tp, _Lp>
1290       lock() const noexcept
1291       {
1292 #ifdef __GTHREADS
1293         // Optimization: avoid throw overhead.
1294         if (expired())
1295           return __shared_ptr<element_type, _Lp>();
1296
1297         __try
1298           {
1299             return __shared_ptr<element_type, _Lp>(*this);
1300           }
1301         __catch(const bad_weak_ptr&)
1302           {
1303             // Q: How can we get here?
1304             // A: Another thread may have invalidated r after the
1305             //    use_count test above.
1306             return __shared_ptr<element_type, _Lp>();
1307           }
1308
1309 #else
1310         // Optimization: avoid try/catch overhead when single threaded.
1311         return expired() ? __shared_ptr<element_type, _Lp>()
1312                          : __shared_ptr<element_type, _Lp>(*this);
1313
1314 #endif
1315       } // XXX MT
1316
1317       long
1318       use_count() const noexcept
1319       { return _M_refcount._M_get_use_count(); }
1320
1321       bool
1322       expired() const noexcept
1323       { return _M_refcount._M_get_use_count() == 0; }
1324
1325       template<typename _Tp1>
1326         bool
1327         owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1328         { return _M_refcount._M_less(__rhs._M_refcount); }
1329
1330       template<typename _Tp1>
1331         bool
1332         owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1333         { return _M_refcount._M_less(__rhs._M_refcount); }
1334
1335       void
1336       reset() noexcept
1337       { __weak_ptr().swap(*this); }
1338
1339       void
1340       swap(__weak_ptr& __s) noexcept
1341       {
1342         std::swap(_M_ptr, __s._M_ptr);
1343         _M_refcount._M_swap(__s._M_refcount);
1344       }
1345
1346     private:
1347       // Used by __enable_shared_from_this.
1348       void
1349       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
1350       {
1351         _M_ptr = __ptr;
1352         _M_refcount = __refcount;
1353       }
1354
1355       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1356       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1357       friend class __enable_shared_from_this<_Tp, _Lp>;
1358       friend class enable_shared_from_this<_Tp>;
1359
1360       _Tp*               _M_ptr;         // Contained pointer.
1361       __weak_count<_Lp>  _M_refcount;    // Reference counter.
1362     };
1363
1364   // 20.7.2.3.6 weak_ptr specialized algorithms.
1365   template<typename _Tp, _Lock_policy _Lp>
1366     inline void
1367     swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b) noexcept
1368     { __a.swap(__b); }
1369
1370   template<typename _Tp, typename _Tp1>
1371     struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1372     {
1373       bool
1374       operator()(const _Tp& __lhs, const _Tp& __rhs) const
1375       { return __lhs.owner_before(__rhs); }
1376
1377       bool
1378       operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1379       { return __lhs.owner_before(__rhs); }
1380
1381       bool
1382       operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1383       { return __lhs.owner_before(__rhs); }
1384     };
1385
1386   template<typename _Tp, _Lock_policy _Lp>
1387     struct owner_less<__shared_ptr<_Tp, _Lp>>
1388     : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1389     { };
1390
1391   template<typename _Tp, _Lock_policy _Lp>
1392     struct owner_less<__weak_ptr<_Tp, _Lp>>
1393     : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1394     { };
1395
1396
1397   template<typename _Tp, _Lock_policy _Lp>
1398     class __enable_shared_from_this
1399     {
1400     protected:
1401       constexpr __enable_shared_from_this() noexcept { }
1402
1403       __enable_shared_from_this(const __enable_shared_from_this&) noexcept { }
1404
1405       __enable_shared_from_this&
1406       operator=(const __enable_shared_from_this&) noexcept
1407       { return *this; }
1408
1409       ~__enable_shared_from_this() { }
1410
1411     public:
1412       __shared_ptr<_Tp, _Lp>
1413       shared_from_this()
1414       { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1415
1416       __shared_ptr<const _Tp, _Lp>
1417       shared_from_this() const
1418       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1419
1420     private:
1421       template<typename _Tp1>
1422         void
1423         _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
1424         { _M_weak_this._M_assign(__p, __n); }
1425
1426       template<typename _Tp1>
1427         friend void
1428         __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
1429                                          const __enable_shared_from_this* __pe,
1430                                          const _Tp1* __px) noexcept
1431         {
1432           if (__pe != 0)
1433             __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
1434         }
1435
1436       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
1437     };
1438
1439
1440   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1441     inline __shared_ptr<_Tp, _Lp>
1442     __allocate_shared(const _Alloc& __a, _Args&&... __args)
1443     {
1444       return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
1445                                     std::forward<_Args>(__args)...);
1446     }
1447
1448   template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1449     inline __shared_ptr<_Tp, _Lp>
1450     __make_shared(_Args&&... __args)
1451     {
1452       typedef typename std::remove_const<_Tp>::type _Tp_nc;
1453       return std::__allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1454                                               std::forward<_Args>(__args)...);
1455     }
1456
1457   /// std::hash specialization for __shared_ptr.
1458   template<typename _Tp, _Lock_policy _Lp>
1459     struct hash<__shared_ptr<_Tp, _Lp>>
1460     : public __hash_base<size_t, __shared_ptr<_Tp, _Lp>>
1461     {
1462       size_t
1463       operator()(const __shared_ptr<_Tp, _Lp>& __s) const noexcept
1464       { return std::hash<_Tp*>()(__s.get()); }
1465     };
1466
1467 _GLIBCXX_END_NAMESPACE_VERSION
1468 } // namespace
1469
1470 #endif // _SHARED_PTR_BASE_H