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

   1 // shared_ptr and weak_ptr implementation details -*- C++ -*-
   2
   3 // Copyright (C) 2007, 2008, 2009, 2010, 2011 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 namespace std _GLIBCXX_VISIBILITY(default)
  53 {
  54 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  55
  56  /**
  57    *  @brief  Exception possibly thrown by @c shared_ptr.
  58    *  @ingroup exceptions
  59    */
  60   class bad_weak_ptr : public std::exception
  61   {
  62   public:
  63     virtual char const*
  64     what() const noexcept;
  65
  66     virtual ~bad_weak_ptr() throw();
  67   };
  68
  69   // Substitute for bad_weak_ptr object in the case of -fno-exceptions.
  70   inline void
  71   __throw_bad_weak_ptr()
  72   {
  73 #if __EXCEPTIONS
  74     throw bad_weak_ptr();
  75 #else
  76     __builtin_abort();
  77 #endif
  78   }
  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&) = 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 const_cast<const volatile _Atomic_word&>(_M_use_count);
 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;
 239       do
 240         {
 241           __count = _M_use_count;
 242           if (__count == 0)
 243             __throw_bad_weak_ptr();
 244
 245           // Replace the current counter value with the old value + 1, as
 246           // long as it's not changed meanwhile.
 247         }
 248       while (!__sync_bool_compare_and_swap(&_M_use_count, __count,
 249                                            __count + 1));
 250     }
 251
 252
 253   // Forward declarations.
 254   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 255     class __shared_ptr;
 256
 257   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 258     class __weak_ptr;
 259
 260   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 261     class __enable_shared_from_this;
 262
 263   template<typename _Tp>
 264     class shared_ptr;
 265
 266   template<typename _Tp>
 267     class weak_ptr;
 268
 269   template<typename _Tp>
 270     struct owner_less;
 271
 272   template<typename _Tp>
 273     class enable_shared_from_this;
 274
 275   template<_Lock_policy _Lp = __default_lock_policy>
 276     class __weak_count;
 277
 278   template<_Lock_policy _Lp = __default_lock_policy>
 279     class __shared_count;
 280
 281
 282   // Counted ptr with no deleter or allocator support
 283   template<typename _Ptr, _Lock_policy _Lp>
 284     class _Sp_counted_ptr final : public _Sp_counted_base<_Lp>
 285     {
 286     public:
 287       explicit
 288       _Sp_counted_ptr(_Ptr __p)
 289       : _M_ptr(__p) { }
 290
 291       virtual void
 292       _M_dispose() noexcept
 293       { delete _M_ptr; }
 294
 295       virtual void
 296       _M_destroy() noexcept
 297       { delete this; }
 298
 299       virtual void*
 300       _M_get_deleter(const std::type_info&)
 301       { return 0; }
 302
 303       _Sp_counted_ptr(const _Sp_counted_ptr&) = delete;
 304       _Sp_counted_ptr& operator=(const _Sp_counted_ptr&) = delete;
 305
 306     protected:
 307       _Ptr             _M_ptr;  // copy constructor must not throw
 308     };
 309
 310   template<>
 311     inline void
 312     _Sp_counted_ptr<nullptr_t, _S_single>::_M_dispose() noexcept { }
 313
 314   template<>
 315     inline void
 316     _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() noexcept { }
 317
 318   template<>
 319     inline void
 320     _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }
 321
 322   // Support for custom deleter and/or allocator
 323   template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>
 324     class _Sp_counted_deleter final : public _Sp_counted_base<_Lp>
 325     {
 326       // Helper class that stores the Deleter and also acts as an allocator.
 327       // Used to dispose of the owned pointer and the internal refcount
 328       // Requires that copies of _Alloc can free each other's memory.
 329       struct _My_Deleter
 330       : public _Alloc           // copy constructor must not throw
 331       {
 332         _Deleter _M_del;        // copy constructor must not throw
 333         _My_Deleter(_Deleter __d, const _Alloc& __a)
 334         : _Alloc(__a), _M_del(__d) { }
 335       };
 336
 337     public:
 338       // __d(__p) must not throw.
 339       _Sp_counted_deleter(_Ptr __p, _Deleter __d)
 340       : _M_ptr(__p), _M_del(__d, _Alloc()) { }
 341
 342       // __d(__p) must not throw.
 343       _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a)
 344       : _M_ptr(__p), _M_del(__d, __a) { }
 345
 346       virtual void
 347       _M_dispose() noexcept
 348       { _M_del._M_del(_M_ptr); }
 349
 350       virtual void
 351       _M_destroy() noexcept
 352       {
 353         typedef typename allocator_traits<_Alloc>::template
 354           rebind_traits<_Sp_counted_deleter> _Alloc_traits;
 355         typename _Alloc_traits::allocator_type __a(_M_del);
 356         _Alloc_traits::destroy(__a, this);
 357         _Alloc_traits::deallocate(__a, this, 1);
 358       }
 359
 360       virtual void*
 361       _M_get_deleter(const std::type_info& __ti)
 362       {
 363 #ifdef __GXX_RTTI
 364         return __ti == typeid(_Deleter) ? &_M_del._M_del : 0;
 365 #else
 366         return 0;
 367 #endif
 368       }
 369
 370     protected:
 371       _Ptr             _M_ptr;  // copy constructor must not throw
 372       _My_Deleter      _M_del;  // copy constructor must not throw
 373     };
 374
 375   // helpers for make_shared / allocate_shared
 376
 377   struct _Sp_make_shared_tag { };
 378
 379   template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
 380     class _Sp_counted_ptr_inplace final : public _Sp_counted_base<_Lp>
 381     {
 382       // Helper class that stores the pointer and also acts as an allocator.
 383       // Used to dispose of the owned pointer and the internal refcount
 384       // Requires that copies of _Alloc can free each other's memory.
 385       struct _Impl
 386       : public _Alloc           // copy constructor must not throw
 387       {
 388         _Impl(_Alloc __a) : _Alloc(__a), _M_ptr() { }
 389         _Tp* _M_ptr;
 390       };
 391
 392     public:
 393       template<typename... _Args>
 394         _Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)
 395         : _M_impl(__a), _M_storage()
 396         {
 397           _M_impl._M_ptr = static_cast<_Tp*>(static_cast<void*>(&_M_storage));
 398           // _GLIBCXX_RESOLVE_LIB_DEFECTS
 399           // 2070.  allocate_shared should use allocator_traits<A>::construct
 400           allocator_traits<_Alloc>::construct(__a, _M_impl._M_ptr,
 401               std::forward<_Args>(__args)...); // might throw
 402         }
 403
 404       virtual void
 405       _M_dispose() noexcept
 406       { allocator_traits<_Alloc>::destroy(_M_impl, _M_impl._M_ptr); }
 407
 408       // Override because the allocator needs to know the dynamic type
 409       virtual void
 410       _M_destroy() noexcept
 411       {
 412         typedef typename allocator_traits<_Alloc>::template
 413           rebind_traits<_Sp_counted_ptr_inplace> _Alloc_traits;
 414         typename _Alloc_traits::allocator_type __a(_M_impl);
 415         _Alloc_traits::destroy(__a, this);
 416         _Alloc_traits::deallocate(__a, this, 1);
 417       }
 418
 419       // Sneaky trick so __shared_ptr can get the managed pointer
 420       virtual void*
 421       _M_get_deleter(const std::type_info& __ti) noexcept
 422       {
 423 #ifdef __GXX_RTTI
 424         return __ti == typeid(_Sp_make_shared_tag)
 425                ? static_cast<void*>(&_M_storage)
 426                : 0;
 427 #else
 428         return 0;
 429 #endif
 430       }
 431
 432     private:
 433       _Impl _M_impl;
 434       typename aligned_storage<sizeof(_Tp), alignment_of<_Tp>::value>::type
 435         _M_storage;
 436     };
 437
 438   template<_Lock_policy _Lp>
 439     class __shared_count
 440     {
 441     public:
 442       constexpr __shared_count() noexcept : _M_pi(0)
 443       { }
 444
 445       template<typename _Ptr>
 446         explicit
 447         __shared_count(_Ptr __p) : _M_pi(0)
 448         {
 449           __try
 450             {
 451               _M_pi = new _Sp_counted_ptr<_Ptr, _Lp>(__p);
 452             }
 453           __catch(...)
 454             {
 455               delete __p;
 456               __throw_exception_again;
 457             }
 458         }
 459
 460       template<typename _Ptr, typename _Deleter>
 461         __shared_count(_Ptr __p, _Deleter __d) : _M_pi(0)
 462         {
 463           // The allocator's value_type doesn't matter, will rebind it anyway.
 464           typedef std::allocator<int> _Alloc;
 465           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 466           typedef typename allocator_traits<_Alloc>::template
 467             rebind_traits<_Sp_cd_type> _Alloc_traits;
 468           typename _Alloc_traits::allocator_type __a;
 469           _Sp_cd_type* __mem = 0;
 470           __try
 471             {
 472               __mem = _Alloc_traits::allocate(__a, 1);
 473               _Alloc_traits::construct(__a, __mem, __p, std::move(__d));
 474               _M_pi = __mem;
 475             }
 476           __catch(...)
 477             {
 478               __d(__p); // Call _Deleter on __p.
 479               if (__mem)
 480                 _Alloc_traits::deallocate(__a, __mem, 1);
 481               __throw_exception_again;
 482             }
 483         }
 484
 485       template<typename _Ptr, typename _Deleter, typename _Alloc>
 486         __shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
 487         {
 488           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 489           typedef typename allocator_traits<_Alloc>::template
 490             rebind_traits<_Sp_cd_type> _Alloc_traits;
 491           typename _Alloc_traits::allocator_type __a2(__a);
 492           _Sp_cd_type* __mem = 0;
 493           __try
 494             {
 495               __mem = _Alloc_traits::allocate(__a2, 1);
 496               _Alloc_traits::construct(__a2, __mem,
 497                   __p, std::move(__d), std::move(__a));
 498               _M_pi = __mem;
 499             }
 500           __catch(...)
 501             {
 502               __d(__p); // Call _Deleter on __p.
 503               if (__mem)
 504                 _Alloc_traits::deallocate(__a2, __mem, 1);
 505               __throw_exception_again;
 506             }
 507         }
 508
 509       template<typename _Tp, typename _Alloc, typename... _Args>
 510         __shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,
 511                        _Args&&... __args)
 512         : _M_pi(0)
 513         {
 514           typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
 515           typedef typename allocator_traits<_Alloc>::template
 516             rebind_traits<_Sp_cp_type> _Alloc_traits;
 517           typename _Alloc_traits::allocator_type __a2(__a);
 518           _Sp_cp_type* __mem = _Alloc_traits::allocate(__a2, 1);
 519           __try
 520             {
 521               _Alloc_traits::construct(__a2, __mem, std::move(__a),
 522                     std::forward<_Args>(__args)...);
 523               _M_pi = __mem;
 524             }
 525           __catch(...)
 526             {
 527               _Alloc_traits::deallocate(__a2, __mem, 1);
 528               __throw_exception_again;
 529             }
 530         }
 531
 532 #if _GLIBCXX_USE_DEPRECATED
 533       // Special case for auto_ptr<_Tp> to provide the strong guarantee.
 534       template<typename _Tp>
 535         explicit
 536         __shared_count(std::auto_ptr<_Tp>&& __r)
 537         : _M_pi(new _Sp_counted_ptr<_Tp*, _Lp>(__r.get()))
 538         { __r.release(); }
 539 #endif
 540
 541       // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
 542       template<typename _Tp, typename _Del>
 543         explicit
 544         __shared_count(std::unique_ptr<_Tp, _Del>&& __r)
 545         : _M_pi(_S_create_from_up(std::move(__r)))
 546         { __r.release(); }
 547
 548       // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
 549       explicit __shared_count(const __weak_count<_Lp>& __r);
 550
 551       ~__shared_count() noexcept
 552       {
 553         if (_M_pi != 0)
 554           _M_pi->_M_release();
 555       }
 556
 557       __shared_count(const __shared_count& __r) noexcept
 558       : _M_pi(__r._M_pi)
 559       {
 560         if (_M_pi != 0)
 561           _M_pi->_M_add_ref_copy();
 562       }
 563
 564       __shared_count&
 565       operator=(const __shared_count& __r) noexcept
 566       {
 567         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 568         if (__tmp != _M_pi)
 569           {
 570             if (__tmp != 0)
 571               __tmp->_M_add_ref_copy();
 572             if (_M_pi != 0)
 573               _M_pi->_M_release();
 574             _M_pi = __tmp;
 575           }
 576         return *this;
 577       }
 578
 579       void
 580       _M_swap(__shared_count& __r) noexcept
 581       {
 582         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 583         __r._M_pi = _M_pi;
 584         _M_pi = __tmp;
 585       }
 586
 587       long
 588       _M_get_use_count() const noexcept
 589       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 590
 591       bool
 592       _M_unique() const noexcept
 593       { return this->_M_get_use_count() == 1; }
 594
 595       void*
 596       _M_get_deleter(const std::type_info& __ti) const noexcept
 597       { return _M_pi ? _M_pi->_M_get_deleter(__ti) : 0; }
 598
 599       bool
 600       _M_less(const __shared_count& __rhs) const noexcept
 601       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 602
 603       bool
 604       _M_less(const __weak_count<_Lp>& __rhs) const noexcept
 605       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 606
 607       // Friend function injected into enclosing namespace and found by ADL
 608       friend inline bool
 609       operator==(const __shared_count& __a, const __shared_count& __b) noexcept
 610       { return __a._M_pi == __b._M_pi; }
 611
 612     private:
 613       friend class __weak_count<_Lp>;
 614
 615       template<typename _Tp, typename _Del>
 616         static _Sp_counted_base<_Lp>*
 617         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 618           typename std::enable_if<!std::is_reference<_Del>::value>::type* = 0)
 619         {
 620           return new _Sp_counted_deleter<_Tp*, _Del, std::allocator<_Tp>,
 621             _Lp>(__r.get(), __r.get_deleter());
 622         }
 623
 624       template<typename _Tp, typename _Del>
 625         static _Sp_counted_base<_Lp>*
 626         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 627           typename std::enable_if<std::is_reference<_Del>::value>::type* = 0)
 628         {
 629           typedef typename std::remove_reference<_Del>::type _Del1;
 630           typedef std::reference_wrapper<_Del1> _Del2;
 631           return new _Sp_counted_deleter<_Tp*, _Del2, std::allocator<_Tp>,
 632             _Lp>(__r.get(), std::ref(__r.get_deleter()));
 633         }
 634
 635       _Sp_counted_base<_Lp>*  _M_pi;
 636     };
 637
 638
 639   template<_Lock_policy _Lp>
 640     class __weak_count
 641     {
 642     public:
 643       constexpr __weak_count() noexcept : _M_pi(0)
 644       { }
 645
 646       __weak_count(const __shared_count<_Lp>& __r) noexcept
 647       : _M_pi(__r._M_pi)
 648       {
 649         if (_M_pi != 0)
 650           _M_pi->_M_weak_add_ref();
 651       }
 652
 653       __weak_count(const __weak_count<_Lp>& __r) noexcept
 654       : _M_pi(__r._M_pi)
 655       {
 656         if (_M_pi != 0)
 657           _M_pi->_M_weak_add_ref();
 658       }
 659
 660       ~__weak_count() noexcept
 661       {
 662         if (_M_pi != 0)
 663           _M_pi->_M_weak_release();
 664       }
 665
 666       __weak_count<_Lp>&
 667       operator=(const __shared_count<_Lp>& __r) noexcept
 668       {
 669         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 670         if (__tmp != 0)
 671           __tmp->_M_weak_add_ref();
 672         if (_M_pi != 0)
 673           _M_pi->_M_weak_release();
 674         _M_pi = __tmp;
 675         return *this;
 676       }
 677
 678       __weak_count<_Lp>&
 679       operator=(const __weak_count<_Lp>& __r) noexcept
 680       {
 681         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 682         if (__tmp != 0)
 683           __tmp->_M_weak_add_ref();
 684         if (_M_pi != 0)
 685           _M_pi->_M_weak_release();
 686         _M_pi = __tmp;
 687         return *this;
 688       }
 689
 690       void
 691       _M_swap(__weak_count<_Lp>& __r) noexcept
 692       {
 693         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 694         __r._M_pi = _M_pi;
 695         _M_pi = __tmp;
 696       }
 697
 698       long
 699       _M_get_use_count() const noexcept
 700       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 701
 702       bool
 703       _M_less(const __weak_count& __rhs) const noexcept
 704       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 705
 706       bool
 707       _M_less(const __shared_count<_Lp>& __rhs) const noexcept
 708       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 709
 710       // Friend function injected into enclosing namespace and found by ADL
 711       friend inline bool
 712       operator==(const __weak_count& __a, const __weak_count& __b) noexcept
 713       { return __a._M_pi == __b._M_pi; }
 714
 715     private:
 716       friend class __shared_count<_Lp>;
 717
 718       _Sp_counted_base<_Lp>*  _M_pi;
 719     };
 720
 721   // Now that __weak_count is defined we can define this constructor:
 722   template<_Lock_policy _Lp>
 723     inline __shared_count<_Lp>:: __shared_count(const __weak_count<_Lp>& __r)
 724     : _M_pi(__r._M_pi)
 725     {
 726       if (_M_pi != 0)
 727         _M_pi->_M_add_ref_lock();
 728       else
 729         __throw_bad_weak_ptr();
 730     }
 731
 732
 733   // Support for enable_shared_from_this.
 734
 735   // Friend of __enable_shared_from_this.
 736   template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
 737     void
 738     __enable_shared_from_this_helper(const __shared_count<_Lp>&,
 739                                      const __enable_shared_from_this<_Tp1,
 740                                      _Lp>*, const _Tp2*) noexcept;
 741
 742   // Friend of enable_shared_from_this.
 743   template<typename _Tp1, typename _Tp2>
 744     void
 745     __enable_shared_from_this_helper(const __shared_count<>&,
 746                                      const enable_shared_from_this<_Tp1>*,
 747                                      const _Tp2*) noexcept;
 748
 749   template<_Lock_policy _Lp>
 750     inline void
 751     __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept
 752     { }
 753
 754
 755   template<typename _Tp, _Lock_policy _Lp>
 756     class __shared_ptr
 757     {
 758     public:
 759       typedef _Tp   element_type;
 760
 761       constexpr __shared_ptr() noexcept
 762       : _M_ptr(0), _M_refcount()
 763       { }
 764
 765       template<typename _Tp1>
 766         explicit __shared_ptr(_Tp1* __p)
 767         : _M_ptr(__p), _M_refcount(__p)
 768         {
 769           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 770           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 771           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 772         }
 773
 774       template<typename _Tp1, typename _Deleter>
 775         __shared_ptr(_Tp1* __p, _Deleter __d)
 776         : _M_ptr(__p), _M_refcount(__p, __d)
 777         {
 778           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 779           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 780           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 781         }
 782
 783       template<typename _Tp1, typename _Deleter, typename _Alloc>
 784         __shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
 785         : _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
 786         {
 787           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 788           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 789           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 790         }
 791
 792       template<typename _Deleter>
 793         __shared_ptr(nullptr_t __p, _Deleter __d)
 794         : _M_ptr(0), _M_refcount(__p, __d)
 795         { }
 796
 797       template<typename _Deleter, typename _Alloc>
 798         __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
 799         : _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
 800         { }
 801
 802       template<typename _Tp1>
 803         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p) noexcept
 804         : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
 805         { }
 806
 807       __shared_ptr(const __shared_ptr&) noexcept = default;
 808       __shared_ptr& operator=(const __shared_ptr&) noexcept = default;
 809       ~__shared_ptr() = default;
 810
 811       template<typename _Tp1, typename = typename
 812                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 813         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 814         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
 815         { }
 816
 817       __shared_ptr(__shared_ptr&& __r) noexcept
 818       : _M_ptr(__r._M_ptr), _M_refcount()
 819       {
 820         _M_refcount._M_swap(__r._M_refcount);
 821         __r._M_ptr = 0;
 822       }
 823
 824       template<typename _Tp1, typename = typename
 825                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 826         __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
 827         : _M_ptr(__r._M_ptr), _M_refcount()
 828         {
 829           _M_refcount._M_swap(__r._M_refcount);
 830           __r._M_ptr = 0;
 831         }
 832
 833       template<typename _Tp1>
 834         explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
 835         : _M_refcount(__r._M_refcount) // may throw
 836         {
 837           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 838
 839           // It is now safe to copy __r._M_ptr, as
 840           // _M_refcount(__r._M_refcount) did not throw.
 841           _M_ptr = __r._M_ptr;
 842         }
 843
 844       // If an exception is thrown this constructor has no effect.
 845       template<typename _Tp1, typename _Del>
 846         __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
 847         : _M_ptr(__r.get()), _M_refcount()
 848         {
 849           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 850           _Tp1* __tmp = __r.get();
 851           _M_refcount = __shared_count<_Lp>(std::move(__r));
 852           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 853         }
 854
 855 #if _GLIBCXX_USE_DEPRECATED
 856       // Postcondition: use_count() == 1 and __r.get() == 0
 857       template<typename _Tp1>
 858         __shared_ptr(std::auto_ptr<_Tp1>&& __r)
 859         : _M_ptr(__r.get()), _M_refcount()
 860         {
 861           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 862           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 863           _Tp1* __tmp = __r.get();
 864           _M_refcount = __shared_count<_Lp>(std::move(__r));
 865           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 866         }
 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, _Lock_policy _Lp1> friend class __shared_ptr;
1052       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1053
1054       template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1055         friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&) noexcept;
1056
1057       _Tp*                 _M_ptr;         // Contained pointer.
1058       __shared_count<_Lp>  _M_refcount;    // Reference counter.
1059     };
1060
1061
1062   // 20.8.13.2.7 shared_ptr comparisons
1063   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1064     inline bool
1065     operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1066                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1067     { return __a.get() == __b.get(); }
1068
1069   template<typename _Tp, _Lock_policy _Lp>
1070     inline bool
1071     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1072     { return !__a; }
1073
1074   template<typename _Tp, _Lock_policy _Lp>
1075     inline bool
1076     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1077     { return !__a; }
1078
1079   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1080     inline bool
1081     operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1082                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1083     { return __a.get() != __b.get(); }
1084
1085   template<typename _Tp, _Lock_policy _Lp>
1086     inline bool
1087     operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1088     { return (bool)__a; }
1089
1090   template<typename _Tp, _Lock_policy _Lp>
1091     inline bool
1092     operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1093     { return (bool)__a; }
1094
1095   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1096     inline bool
1097     operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1098               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1099     {
1100       typedef typename std::common_type<_Tp1*, _Tp2*>::type _CT;
1101       return std::less<_CT>()(__a.get(), __b.get());
1102     }
1103
1104   template<typename _Tp, _Lock_policy _Lp>
1105     inline bool
1106     operator<(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1107     { return std::less<_Tp*>()(__a.get(), nullptr); }
1108
1109   template<typename _Tp, _Lock_policy _Lp>
1110     inline bool
1111     operator<(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1112     { return std::less<_Tp*>()(nullptr, __a.get()); }
1113
1114   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1115     inline bool
1116     operator<=(const __shared_ptr<_Tp1, _Lp>& __a,
1117                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1118     { return !(__b < __a); }
1119
1120   template<typename _Tp, _Lock_policy _Lp>
1121     inline bool
1122     operator<=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1123     { return !(nullptr < __a); }
1124
1125   template<typename _Tp, _Lock_policy _Lp>
1126     inline bool
1127     operator<=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1128     { return !(__a < nullptr); }
1129
1130   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1131     inline bool
1132     operator>(const __shared_ptr<_Tp1, _Lp>& __a,
1133               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1134     { return (__b < __a); }
1135
1136   template<typename _Tp, _Lock_policy _Lp>
1137     inline bool
1138     operator>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1139     { return std::less<_Tp*>()(nullptr, __a.get()); }
1140
1141   template<typename _Tp, _Lock_policy _Lp>
1142     inline bool
1143     operator>(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1144     { return std::less<_Tp*>()(__a.get(), nullptr); }
1145
1146   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1147     inline bool
1148     operator>=(const __shared_ptr<_Tp1, _Lp>& __a,
1149                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1150     { return !(__a < __b); }
1151
1152   template<typename _Tp, _Lock_policy _Lp>
1153     inline bool
1154     operator>=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1155     { return !(__a < nullptr); }
1156
1157   template<typename _Tp, _Lock_policy _Lp>
1158     inline bool
1159     operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1160     { return !(nullptr < __a); }
1161
1162   template<typename _Sp>
1163     struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1164     {
1165       bool
1166       operator()(const _Sp& __lhs, const _Sp& __rhs) const noexcept
1167       {
1168         typedef typename _Sp::element_type element_type;
1169         return std::less<element_type*>()(__lhs.get(), __rhs.get());
1170       }
1171     };
1172
1173   template<typename _Tp, _Lock_policy _Lp>
1174     struct less<__shared_ptr<_Tp, _Lp>>
1175     : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1176     { };
1177
1178   // 2.2.3.8 shared_ptr specialized algorithms.
1179   template<typename _Tp, _Lock_policy _Lp>
1180     inline void
1181     swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b) noexcept
1182     { __a.swap(__b); }
1183
1184   // 2.2.3.9 shared_ptr casts
1185
1186   // The seemingly equivalent code:
1187   // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1188   // will eventually result in undefined behaviour, attempting to
1189   // delete the same object twice.
1190   /// static_pointer_cast
1191   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1192     inline __shared_ptr<_Tp, _Lp>
1193     static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1194     { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1195
1196   // The seemingly equivalent code:
1197   // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1198   // will eventually result in undefined behaviour, attempting to
1199   // delete the same object twice.
1200   /// const_pointer_cast
1201   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1202     inline __shared_ptr<_Tp, _Lp>
1203     const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1204     { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1205
1206   // The seemingly equivalent code:
1207   // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1208   // will eventually result in undefined behaviour, attempting to
1209   // delete the same object twice.
1210   /// dynamic_pointer_cast
1211   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1212     inline __shared_ptr<_Tp, _Lp>
1213     dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1214     {
1215       if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1216         return __shared_ptr<_Tp, _Lp>(__r, __p);
1217       return __shared_ptr<_Tp, _Lp>();
1218     }
1219
1220
1221   template<typename _Tp, _Lock_policy _Lp>
1222     class __weak_ptr
1223     {
1224     public:
1225       typedef _Tp element_type;
1226
1227       constexpr __weak_ptr() noexcept
1228       : _M_ptr(0), _M_refcount()
1229       { }
1230
1231       __weak_ptr(const __weak_ptr&) noexcept = default;
1232       __weak_ptr& operator=(const __weak_ptr&) noexcept = default;
1233       ~__weak_ptr() = default;
1234
1235       // The "obvious" converting constructor implementation:
1236       //
1237       //  template<typename _Tp1>
1238       //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1239       //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1240       //    { }
1241       //
1242       // has a serious problem.
1243       //
1244       //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1245       //  conversion may require access to *__r._M_ptr (virtual inheritance).
1246       //
1247       // It is not possible to avoid spurious access violations since
1248       // in multithreaded programs __r._M_ptr may be invalidated at any point.
1249       template<typename _Tp1, typename = typename
1250                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1251         __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1252         : _M_refcount(__r._M_refcount)
1253         { _M_ptr = __r.lock().get(); }
1254
1255       template<typename _Tp1, typename = typename
1256                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1257         __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1258         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
1259         { }
1260
1261       template<typename _Tp1>
1262         __weak_ptr&
1263         operator=(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1264         {
1265           _M_ptr = __r.lock().get();
1266           _M_refcount = __r._M_refcount;
1267           return *this;
1268         }
1269
1270       template<typename _Tp1>
1271         __weak_ptr&
1272         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1273         {
1274           _M_ptr = __r._M_ptr;
1275           _M_refcount = __r._M_refcount;
1276           return *this;
1277         }
1278
1279       __shared_ptr<_Tp, _Lp>
1280       lock() const noexcept
1281       {
1282 #ifdef __GTHREADS
1283         // Optimization: avoid throw overhead.
1284         if (expired())
1285           return __shared_ptr<element_type, _Lp>();
1286
1287         __try
1288           {
1289             return __shared_ptr<element_type, _Lp>(*this);
1290           }
1291         __catch(const bad_weak_ptr&)
1292           {
1293             // Q: How can we get here?
1294             // A: Another thread may have invalidated r after the
1295             //    use_count test above.
1296             return __shared_ptr<element_type, _Lp>();
1297           }
1298
1299 #else
1300         // Optimization: avoid try/catch overhead when single threaded.
1301         return expired() ? __shared_ptr<element_type, _Lp>()
1302                          : __shared_ptr<element_type, _Lp>(*this);
1303
1304 #endif
1305       } // XXX MT
1306
1307       long
1308       use_count() const noexcept
1309       { return _M_refcount._M_get_use_count(); }
1310
1311       bool
1312       expired() const noexcept
1313       { return _M_refcount._M_get_use_count() == 0; }
1314
1315       template<typename _Tp1>
1316         bool
1317         owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1318         { return _M_refcount._M_less(__rhs._M_refcount); }
1319
1320       template<typename _Tp1>
1321         bool
1322         owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1323         { return _M_refcount._M_less(__rhs._M_refcount); }
1324
1325       void
1326       reset() noexcept
1327       { __weak_ptr().swap(*this); }
1328
1329       void
1330       swap(__weak_ptr& __s) noexcept
1331       {
1332         std::swap(_M_ptr, __s._M_ptr);
1333         _M_refcount._M_swap(__s._M_refcount);
1334       }
1335
1336     private:
1337       // Used by __enable_shared_from_this.
1338       void
1339       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
1340       {
1341         _M_ptr = __ptr;
1342         _M_refcount = __refcount;
1343       }
1344
1345       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1346       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1347       friend class __enable_shared_from_this<_Tp, _Lp>;
1348       friend class enable_shared_from_this<_Tp>;
1349
1350       _Tp*               _M_ptr;         // Contained pointer.
1351       __weak_count<_Lp>  _M_refcount;    // Reference counter.
1352     };
1353
1354   // 20.8.13.3.7 weak_ptr specialized algorithms.
1355   template<typename _Tp, _Lock_policy _Lp>
1356     inline void
1357     swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b) noexcept
1358     { __a.swap(__b); }
1359
1360   template<typename _Tp, typename _Tp1>
1361     struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1362     {
1363       bool
1364       operator()(const _Tp& __lhs, const _Tp& __rhs) const
1365       { return __lhs.owner_before(__rhs); }
1366
1367       bool
1368       operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1369       { return __lhs.owner_before(__rhs); }
1370
1371       bool
1372       operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1373       { return __lhs.owner_before(__rhs); }
1374     };
1375
1376   template<typename _Tp, _Lock_policy _Lp>
1377     struct owner_less<__shared_ptr<_Tp, _Lp>>
1378     : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1379     { };
1380
1381   template<typename _Tp, _Lock_policy _Lp>
1382     struct owner_less<__weak_ptr<_Tp, _Lp>>
1383     : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1384     { };
1385
1386
1387   template<typename _Tp, _Lock_policy _Lp>
1388     class __enable_shared_from_this
1389     {
1390     protected:
1391       constexpr __enable_shared_from_this() noexcept { }
1392
1393       __enable_shared_from_this(const __enable_shared_from_this&) noexcept { }
1394
1395       __enable_shared_from_this&
1396       operator=(const __enable_shared_from_this&) noexcept
1397       { return *this; }
1398
1399       ~__enable_shared_from_this() { }
1400
1401     public:
1402       __shared_ptr<_Tp, _Lp>
1403       shared_from_this()
1404       { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1405
1406       __shared_ptr<const _Tp, _Lp>
1407       shared_from_this() const
1408       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1409
1410     private:
1411       template<typename _Tp1>
1412         void
1413         _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
1414         { _M_weak_this._M_assign(__p, __n); }
1415
1416       template<typename _Tp1>
1417         friend void
1418         __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
1419                                          const __enable_shared_from_this* __pe,
1420                                          const _Tp1* __px) noexcept
1421         {
1422           if (__pe != 0)
1423             __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
1424         }
1425
1426       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
1427     };
1428
1429
1430   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1431     inline __shared_ptr<_Tp, _Lp>
1432     __allocate_shared(const _Alloc& __a, _Args&&... __args)
1433     {
1434       return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
1435                                     std::forward<_Args>(__args)...);
1436     }
1437
1438   template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1439     inline __shared_ptr<_Tp, _Lp>
1440     __make_shared(_Args&&... __args)
1441     {
1442       typedef typename std::remove_const<_Tp>::type _Tp_nc;
1443       return std::__allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1444                                               std::forward<_Args>(__args)...);
1445     }
1446
1447   /// std::hash specialization for __shared_ptr.
1448   template<typename _Tp, _Lock_policy _Lp>
1449     struct hash<__shared_ptr<_Tp, _Lp>>
1450     : public __hash_base<size_t, __shared_ptr<_Tp, _Lp>>
1451     {
1452       size_t
1453       operator()(const __shared_ptr<_Tp, _Lp>& __s) const noexcept
1454       { return std::hash<_Tp*>()(__s.get()); }
1455     };
1456
1457 _GLIBCXX_END_NAMESPACE_VERSION
1458 } // namespace
1459
1460 #endif // _SHARED_PTR_BASE_H