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 throw();
  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()
 112       : _M_use_count(1), _M_weak_count(1) { }
 113
 114       virtual
 115       ~_Sp_counted_base() // nothrow
 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() = 0; // nothrow
 122
 123       // Called when _M_weak_count drops to zero.
 124       virtual void
 125       _M_destroy() // nothrow
 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() // nothrow
 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() // nothrow
 170       { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
 171
 172       void
 173       _M_weak_release() // nothrow
 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 // nothrow
 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&);
 201       _Sp_counted_base& operator=(_Sp_counted_base const&);
 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 : 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() // nothrow
 293       { delete _M_ptr; }
 294
 295       virtual void
 296       _M_destroy() // nothrow
 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() { }
 313
 314   template<>
 315     inline void
 316     _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() { }
 317
 318   template<>
 319     inline void
 320     _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() { }
 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 : public _Sp_counted_base<_Lp>
 325     {
 326       typedef typename _Alloc::template
 327           rebind<_Sp_counted_deleter>::other _My_alloc_type;
 328
 329       // Helper class that stores the Deleter and also acts as an allocator.
 330       // Used to dispose of the owned pointer and the internal refcount
 331       // Requires that copies of _Alloc can free each other's memory.
 332       struct _My_Deleter
 333       : public _My_alloc_type    // copy constructor must not throw
 334       {
 335         _Deleter _M_del;         // copy constructor must not throw
 336         _My_Deleter(_Deleter __d, const _Alloc& __a)
 337         : _My_alloc_type(__a), _M_del(__d) { }
 338       };
 339
 340     public:
 341       // __d(__p) must not throw.
 342       _Sp_counted_deleter(_Ptr __p, _Deleter __d)
 343       : _M_ptr(__p), _M_del(__d, _Alloc()) { }
 344
 345       // __d(__p) must not throw.
 346       _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a)
 347       : _M_ptr(__p), _M_del(__d, __a) { }
 348
 349       virtual void
 350       _M_dispose() // nothrow
 351       { _M_del._M_del(_M_ptr); }
 352
 353       virtual void
 354       _M_destroy() // nothrow
 355       {
 356         _My_alloc_type __a(_M_del);
 357         this->~_Sp_counted_deleter();
 358         __a.deallocate(this, 1);
 359       }
 360
 361       virtual void*
 362       _M_get_deleter(const std::type_info& __ti)
 363       {
 364 #ifdef __GXX_RTTI
 365         return __ti == typeid(_Deleter) ? &_M_del._M_del : 0;
 366 #else
 367         return 0;
 368 #endif
 369       }
 370
 371     protected:
 372       _Ptr             _M_ptr;  // copy constructor must not throw
 373       _My_Deleter      _M_del;  // copy constructor must not throw
 374     };
 375
 376   // helpers for make_shared / allocate_shared
 377
 378   template<typename _Tp>
 379     struct _Sp_destroy_inplace
 380     {
 381       void operator()(_Tp* __p) const { if (__p) __p->~_Tp(); }
 382     };
 383
 384   struct _Sp_make_shared_tag { };
 385
 386   template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
 387     class _Sp_counted_ptr_inplace
 388     : public _Sp_counted_deleter<_Tp*, _Sp_destroy_inplace<_Tp>, _Alloc, _Lp>
 389     {
 390       typedef _Sp_counted_deleter<_Tp*, _Sp_destroy_inplace<_Tp>, _Alloc, _Lp>
 391         _Base_type;
 392
 393     public:
 394       explicit
 395       _Sp_counted_ptr_inplace(_Alloc __a)
 396       : _Base_type(static_cast<_Tp*>(0), _Sp_destroy_inplace<_Tp>(), __a)
 397       , _M_storage()
 398       {
 399         void* __p = &_M_storage;
 400         ::new (__p) _Tp();  // might throw
 401         _Base_type::_M_ptr = static_cast<_Tp*>(__p);
 402       }
 403
 404       template<typename... _Args>
 405         _Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)
 406         : _Base_type(static_cast<_Tp*>(0), _Sp_destroy_inplace<_Tp>(), __a)
 407         , _M_storage()
 408         {
 409           void* __p = &_M_storage;
 410           ::new (__p) _Tp(std::forward<_Args>(__args)...);  // might throw
 411           _Base_type::_M_ptr = static_cast<_Tp*>(__p);
 412         }
 413
 414       // Override because the allocator needs to know the dynamic type
 415       virtual void
 416       _M_destroy() // nothrow
 417       {
 418         typedef typename _Alloc::template
 419             rebind<_Sp_counted_ptr_inplace>::other _My_alloc_type;
 420         _My_alloc_type __a(_Base_type::_M_del);
 421         this->~_Sp_counted_ptr_inplace();
 422         __a.deallocate(this, 1);
 423       }
 424
 425       // Sneaky trick so __shared_ptr can get the managed pointer
 426       virtual void*
 427       _M_get_deleter(const std::type_info& __ti)
 428       {
 429 #ifdef __GXX_RTTI
 430         return __ti == typeid(_Sp_make_shared_tag)
 431                ? static_cast<void*>(&_M_storage)
 432                : _Base_type::_M_get_deleter(__ti);
 433 #else
 434         return 0;
 435 #endif
 436       }
 437
 438     private:
 439       typename aligned_storage<sizeof(_Tp), alignment_of<_Tp>::value>::type
 440         _M_storage;
 441     };
 442
 443   template<_Lock_policy _Lp>
 444     class __shared_count
 445     {
 446     public:
 447       constexpr __shared_count() : _M_pi(0) // nothrow
 448       { }
 449
 450       template<typename _Ptr>
 451         explicit
 452         __shared_count(_Ptr __p) : _M_pi(0)
 453         {
 454           __try
 455             {
 456               _M_pi = new _Sp_counted_ptr<_Ptr, _Lp>(__p);
 457             }
 458           __catch(...)
 459             {
 460               delete __p;
 461               __throw_exception_again;
 462             }
 463         }
 464
 465       template<typename _Ptr, typename _Deleter>
 466         __shared_count(_Ptr __p, _Deleter __d) : _M_pi(0)
 467         {
 468           // The allocator's value_type doesn't matter, will rebind it anyway.
 469           typedef std::allocator<int> _Alloc;
 470           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 471           typedef std::allocator<_Sp_cd_type> _Alloc2;
 472           _Alloc2 __a2;
 473           __try
 474             {
 475               _M_pi = __a2.allocate(1);
 476               ::new(static_cast<void*>(_M_pi)) _Sp_cd_type(__p, __d);
 477             }
 478           __catch(...)
 479             {
 480               __d(__p); // Call _Deleter on __p.
 481               if (_M_pi)
 482                 __a2.deallocate(static_cast<_Sp_cd_type*>(_M_pi), 1);
 483               __throw_exception_again;
 484             }
 485         }
 486
 487       template<typename _Ptr, typename _Deleter, typename _Alloc>
 488         __shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
 489         {
 490           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 491           typedef typename _Alloc::template rebind<_Sp_cd_type>::other _Alloc2;
 492           _Alloc2 __a2(__a);
 493           __try
 494             {
 495               _M_pi = __a2.allocate(1);
 496               ::new(static_cast<void*>(_M_pi)) _Sp_cd_type(__p, __d, __a);
 497             }
 498           __catch(...)
 499             {
 500               __d(__p); // Call _Deleter on __p.
 501               if (_M_pi)
 502                 __a2.deallocate(static_cast<_Sp_cd_type*>(_M_pi), 1);
 503               __throw_exception_again;
 504             }
 505         }
 506
 507       template<typename _Tp, typename _Alloc, typename... _Args>
 508         __shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,
 509                        _Args&&... __args)
 510         : _M_pi(0)
 511         {
 512           typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
 513           typedef typename _Alloc::template rebind<_Sp_cp_type>::other _Alloc2;
 514           _Alloc2 __a2(__a);
 515           __try
 516             {
 517               _M_pi = __a2.allocate(1);
 518               ::new(static_cast<void*>(_M_pi)) _Sp_cp_type(__a,
 519                     std::forward<_Args>(__args)...);
 520             }
 521           __catch(...)
 522             {
 523               if (_M_pi)
 524                 __a2.deallocate(static_cast<_Sp_cp_type*>(_M_pi), 1);
 525               __throw_exception_again;
 526             }
 527         }
 528
 529 #if _GLIBCXX_USE_DEPRECATED
 530       // Special case for auto_ptr<_Tp> to provide the strong guarantee.
 531       template<typename _Tp>
 532         explicit
 533         __shared_count(std::auto_ptr<_Tp>&& __r)
 534         : _M_pi(new _Sp_counted_ptr<_Tp*, _Lp>(__r.get()))
 535         { __r.release(); }
 536 #endif
 537
 538       // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
 539       template<typename _Tp, typename _Del>
 540         explicit
 541         __shared_count(std::unique_ptr<_Tp, _Del>&& __r)
 542         : _M_pi(_S_create_from_up(std::move(__r)))
 543         { __r.release(); }
 544
 545       // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
 546       explicit __shared_count(const __weak_count<_Lp>& __r);
 547
 548       ~__shared_count() // nothrow
 549       {
 550         if (_M_pi != 0)
 551           _M_pi->_M_release();
 552       }
 553
 554       __shared_count(const __shared_count& __r)
 555       : _M_pi(__r._M_pi) // nothrow
 556       {
 557         if (_M_pi != 0)
 558           _M_pi->_M_add_ref_copy();
 559       }
 560
 561       __shared_count&
 562       operator=(const __shared_count& __r) // nothrow
 563       {
 564         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 565         if (__tmp != _M_pi)
 566           {
 567             if (__tmp != 0)
 568               __tmp->_M_add_ref_copy();
 569             if (_M_pi != 0)
 570               _M_pi->_M_release();
 571             _M_pi = __tmp;
 572           }
 573         return *this;
 574       }
 575
 576       void
 577       _M_swap(__shared_count& __r) // nothrow
 578       {
 579         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 580         __r._M_pi = _M_pi;
 581         _M_pi = __tmp;
 582       }
 583
 584       long
 585       _M_get_use_count() const // nothrow
 586       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 587
 588       bool
 589       _M_unique() const // nothrow
 590       { return this->_M_get_use_count() == 1; }
 591
 592       void*
 593       _M_get_deleter(const std::type_info& __ti) const
 594       { return _M_pi ? _M_pi->_M_get_deleter(__ti) : 0; }
 595
 596       bool
 597       _M_less(const __shared_count& __rhs) const
 598       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 599
 600       bool
 601       _M_less(const __weak_count<_Lp>& __rhs) const
 602       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 603
 604       // Friend function injected into enclosing namespace and found by ADL
 605       friend inline bool
 606       operator==(const __shared_count& __a, const __shared_count& __b)
 607       { return __a._M_pi == __b._M_pi; }
 608
 609     private:
 610       friend class __weak_count<_Lp>;
 611
 612       template<typename _Tp, typename _Del>
 613         static _Sp_counted_base<_Lp>*
 614         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 615           typename std::enable_if<!std::is_reference<_Del>::value>::type* = 0)
 616         {
 617           return new _Sp_counted_deleter<_Tp*, _Del, std::allocator<_Tp>,
 618             _Lp>(__r.get(), __r.get_deleter());
 619         }
 620
 621       template<typename _Tp, typename _Del>
 622         static _Sp_counted_base<_Lp>*
 623         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 624           typename std::enable_if<std::is_reference<_Del>::value>::type* = 0)
 625         {
 626           typedef typename std::remove_reference<_Del>::type _Del1;
 627           typedef std::reference_wrapper<_Del1> _Del2;
 628           return new _Sp_counted_deleter<_Tp*, _Del2, std::allocator<_Tp>,
 629             _Lp>(__r.get(), std::ref(__r.get_deleter()));
 630         }
 631
 632       _Sp_counted_base<_Lp>*  _M_pi;
 633     };
 634
 635
 636   template<_Lock_policy _Lp>
 637     class __weak_count
 638     {
 639     public:
 640       constexpr __weak_count() : _M_pi(0) // nothrow
 641       { }
 642
 643       __weak_count(const __shared_count<_Lp>& __r) : _M_pi(__r._M_pi) // nothrow
 644       {
 645         if (_M_pi != 0)
 646           _M_pi->_M_weak_add_ref();
 647       }
 648
 649       __weak_count(const __weak_count<_Lp>& __r) : _M_pi(__r._M_pi) // nothrow
 650       {
 651         if (_M_pi != 0)
 652           _M_pi->_M_weak_add_ref();
 653       }
 654
 655       ~__weak_count() // nothrow
 656       {
 657         if (_M_pi != 0)
 658           _M_pi->_M_weak_release();
 659       }
 660
 661       __weak_count<_Lp>&
 662       operator=(const __shared_count<_Lp>& __r) // nothrow
 663       {
 664         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 665         if (__tmp != 0)
 666           __tmp->_M_weak_add_ref();
 667         if (_M_pi != 0)
 668           _M_pi->_M_weak_release();
 669         _M_pi = __tmp;
 670         return *this;
 671       }
 672
 673       __weak_count<_Lp>&
 674       operator=(const __weak_count<_Lp>& __r) // nothrow
 675       {
 676         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 677         if (__tmp != 0)
 678           __tmp->_M_weak_add_ref();
 679         if (_M_pi != 0)
 680           _M_pi->_M_weak_release();
 681         _M_pi = __tmp;
 682         return *this;
 683       }
 684
 685       void
 686       _M_swap(__weak_count<_Lp>& __r) // nothrow
 687       {
 688         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 689         __r._M_pi = _M_pi;
 690         _M_pi = __tmp;
 691       }
 692
 693       long
 694       _M_get_use_count() const // nothrow
 695       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 696
 697       bool
 698       _M_less(const __weak_count& __rhs) const
 699       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 700
 701       bool
 702       _M_less(const __shared_count<_Lp>& __rhs) const
 703       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 704
 705       // Friend function injected into enclosing namespace and found by ADL
 706       friend inline bool
 707       operator==(const __weak_count& __a, const __weak_count& __b)
 708       { return __a._M_pi == __b._M_pi; }
 709
 710     private:
 711       friend class __shared_count<_Lp>;
 712
 713       _Sp_counted_base<_Lp>*  _M_pi;
 714     };
 715
 716   // Now that __weak_count is defined we can define this constructor:
 717   template<_Lock_policy _Lp>
 718     inline __shared_count<_Lp>:: __shared_count(const __weak_count<_Lp>& __r)
 719     : _M_pi(__r._M_pi)
 720     {
 721       if (_M_pi != 0)
 722         _M_pi->_M_add_ref_lock();
 723       else
 724         __throw_bad_weak_ptr();
 725     }
 726
 727
 728   // Support for enable_shared_from_this.
 729
 730   // Friend of __enable_shared_from_this.
 731   template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
 732     void
 733     __enable_shared_from_this_helper(const __shared_count<_Lp>&,
 734                                      const __enable_shared_from_this<_Tp1,
 735                                      _Lp>*, const _Tp2*);
 736
 737   // Friend of enable_shared_from_this.
 738   template<typename _Tp1, typename _Tp2>
 739     void
 740     __enable_shared_from_this_helper(const __shared_count<>&,
 741                                      const enable_shared_from_this<_Tp1>*,
 742                                      const _Tp2*);
 743
 744   template<_Lock_policy _Lp>
 745     inline void
 746     __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...)
 747     { }
 748
 749
 750   template<typename _Tp, _Lock_policy _Lp>
 751     class __shared_ptr
 752     {
 753     public:
 754       typedef _Tp   element_type;
 755
 756       constexpr __shared_ptr()
 757       : _M_ptr(0), _M_refcount() // never throws
 758       { }
 759
 760       template<typename _Tp1>
 761         explicit __shared_ptr(_Tp1* __p)
 762         : _M_ptr(__p), _M_refcount(__p)
 763         {
 764           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 765           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 766           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 767         }
 768
 769       template<typename _Tp1, typename _Deleter>
 770         __shared_ptr(_Tp1* __p, _Deleter __d)
 771         : _M_ptr(__p), _M_refcount(__p, __d)
 772         {
 773           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 774           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 775           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 776         }
 777
 778       template<typename _Tp1, typename _Deleter, typename _Alloc>
 779         __shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
 780         : _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
 781         {
 782           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 783           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 784           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 785         }
 786
 787       template<typename _Deleter>
 788         __shared_ptr(nullptr_t __p, _Deleter __d)
 789         : _M_ptr(0), _M_refcount(__p, __d)
 790         { }
 791
 792       template<typename _Deleter, typename _Alloc>
 793         __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
 794         : _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
 795         { }
 796
 797       template<typename _Tp1>
 798         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p)
 799         : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
 800         { }
 801
 802       //  generated copy constructor, assignment, destructor are fine.
 803
 804       template<typename _Tp1, typename = typename
 805                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 806         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r)
 807         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
 808         { }
 809
 810       __shared_ptr(__shared_ptr&& __r)
 811       : _M_ptr(__r._M_ptr), _M_refcount() // never throws
 812       {
 813         _M_refcount._M_swap(__r._M_refcount);
 814         __r._M_ptr = 0;
 815       }
 816
 817       template<typename _Tp1, typename = typename
 818                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 819         __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r)
 820         : _M_ptr(__r._M_ptr), _M_refcount() // never throws
 821         {
 822           _M_refcount._M_swap(__r._M_refcount);
 823           __r._M_ptr = 0;
 824         }
 825
 826       template<typename _Tp1>
 827         explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
 828         : _M_refcount(__r._M_refcount) // may throw
 829         {
 830           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 831
 832           // It is now safe to copy __r._M_ptr, as
 833           // _M_refcount(__r._M_refcount) did not throw.
 834           _M_ptr = __r._M_ptr;
 835         }
 836
 837       // If an exception is thrown this constructor has no effect.
 838       template<typename _Tp1, typename _Del>
 839         __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
 840         : _M_ptr(__r.get()), _M_refcount()
 841         {
 842           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 843           _Tp1* __tmp = __r.get();
 844           _M_refcount = __shared_count<_Lp>(std::move(__r));
 845           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 846         }
 847
 848 #if _GLIBCXX_USE_DEPRECATED
 849       // Postcondition: use_count() == 1 and __r.get() == 0
 850       template<typename _Tp1>
 851         __shared_ptr(std::auto_ptr<_Tp1>&& __r)
 852         : _M_ptr(__r.get()), _M_refcount()
 853         {
 854           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 855           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 856           _Tp1* __tmp = __r.get();
 857           _M_refcount = __shared_count<_Lp>(std::move(__r));
 858           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 859         }
 860 #endif
 861
 862       /* TODO: use delegating constructor */
 863       constexpr __shared_ptr(nullptr_t)
 864       : _M_ptr(0), _M_refcount() // never throws
 865       { }
 866
 867       template<typename _Tp1>
 868         __shared_ptr&
 869         operator=(const __shared_ptr<_Tp1, _Lp>& __r) // never throws
 870         {
 871           _M_ptr = __r._M_ptr;
 872           _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
 873           return *this;
 874         }
 875
 876 #if _GLIBCXX_USE_DEPRECATED
 877       template<typename _Tp1>
 878         __shared_ptr&
 879         operator=(std::auto_ptr<_Tp1>&& __r)
 880         {
 881           __shared_ptr(std::move(__r)).swap(*this);
 882           return *this;
 883         }
 884 #endif
 885
 886       __shared_ptr&
 887       operator=(__shared_ptr&& __r)
 888       {
 889         __shared_ptr(std::move(__r)).swap(*this);
 890         return *this;
 891       }
 892
 893       template<class _Tp1>
 894         __shared_ptr&
 895         operator=(__shared_ptr<_Tp1, _Lp>&& __r)
 896         {
 897           __shared_ptr(std::move(__r)).swap(*this);
 898           return *this;
 899         }
 900
 901       template<typename _Tp1, typename _Del>
 902         __shared_ptr&
 903         operator=(std::unique_ptr<_Tp1, _Del>&& __r)
 904         {
 905           __shared_ptr(std::move(__r)).swap(*this);
 906           return *this;
 907         }
 908
 909       void
 910       reset() // never throws
 911       { __shared_ptr().swap(*this); }
 912
 913       template<typename _Tp1>
 914         void
 915         reset(_Tp1* __p) // _Tp1 must be complete.
 916         {
 917           // Catch self-reset errors.
 918           _GLIBCXX_DEBUG_ASSERT(__p == 0 || __p != _M_ptr);
 919           __shared_ptr(__p).swap(*this);
 920         }
 921
 922       template<typename _Tp1, typename _Deleter>
 923         void
 924         reset(_Tp1* __p, _Deleter __d)
 925         { __shared_ptr(__p, __d).swap(*this); }
 926
 927       template<typename _Tp1, typename _Deleter, typename _Alloc>
 928         void
 929         reset(_Tp1* __p, _Deleter __d, _Alloc __a)
 930         { __shared_ptr(__p, __d, std::move(__a)).swap(*this); }
 931
 932       // Allow class instantiation when _Tp is [cv-qual] void.
 933       typename std::add_lvalue_reference<_Tp>::type
 934       operator*() const // never throws
 935       {
 936         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 937         return *_M_ptr;
 938       }
 939
 940       _Tp*
 941       operator->() const // never throws
 942       {
 943         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 944         return _M_ptr;
 945       }
 946
 947       _Tp*
 948       get() const // never throws
 949       { return _M_ptr; }
 950
 951       explicit operator bool() const // never throws
 952       { return _M_ptr == 0 ? false : true; }
 953
 954       bool
 955       unique() const // never throws
 956       { return _M_refcount._M_unique(); }
 957
 958       long
 959       use_count() const // never throws
 960       { return _M_refcount._M_get_use_count(); }
 961
 962       void
 963       swap(__shared_ptr<_Tp, _Lp>& __other) // never throws
 964       {
 965         std::swap(_M_ptr, __other._M_ptr);
 966         _M_refcount._M_swap(__other._M_refcount);
 967       }
 968
 969       template<typename _Tp1>
 970         bool
 971         owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const
 972         { return _M_refcount._M_less(__rhs._M_refcount); }
 973
 974       template<typename _Tp1>
 975         bool
 976         owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const
 977         { return _M_refcount._M_less(__rhs._M_refcount); }
 978
 979 #ifdef __GXX_RTTI
 980     protected:
 981       // This constructor is non-standard, it is used by allocate_shared.
 982       template<typename _Alloc, typename... _Args>
 983         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
 984                      _Args&&... __args)
 985         : _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,
 986                                 std::forward<_Args>(__args)...)
 987         {
 988           // _M_ptr needs to point to the newly constructed object.
 989           // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
 990           void* __p = _M_refcount._M_get_deleter(typeid(__tag));
 991           _M_ptr = static_cast<_Tp*>(__p);
 992           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
 993         }
 994 #else
 995       template<typename _Alloc>
 996         struct _Deleter
 997         {
 998           void operator()(_Tp* __ptr)
 999           {
1000             _M_alloc.destroy(__ptr);
1001             _M_alloc.deallocate(__ptr, 1);
1002           }
1003           _Alloc _M_alloc;
1004         };
1005
1006       template<typename _Alloc, typename... _Args>
1007         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1008                      _Args&&... __args)
1009         : _M_ptr(), _M_refcount()
1010         {
1011           typedef typename _Alloc::template rebind<_Tp>::other _Alloc2;
1012           _Deleter<_Alloc2> __del = { _Alloc2(__a) };
1013           _M_ptr = __del._M_alloc.allocate(1);
1014           __try
1015             {
1016               __del._M_alloc.construct(_M_ptr, std::forward<_Args>(__args)...);
1017             }
1018           __catch(...)
1019             {
1020               __del._M_alloc.deallocate(_M_ptr, 1);
1021               __throw_exception_again;
1022             }
1023           __shared_count<_Lp> __count(_M_ptr, __del, __del._M_alloc);
1024           _M_refcount._M_swap(__count);
1025           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1026         }
1027 #endif
1028
1029       template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
1030                typename... _Args>
1031         friend __shared_ptr<_Tp1, _Lp1>
1032         __allocate_shared(const _Alloc& __a, _Args&&... __args);
1033
1034     private:
1035       void*
1036       _M_get_deleter(const std::type_info& __ti) const
1037       { return _M_refcount._M_get_deleter(__ti); }
1038
1039       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1040       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1041
1042       template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1043         friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&);
1044
1045       _Tp*                 _M_ptr;         // Contained pointer.
1046       __shared_count<_Lp>  _M_refcount;    // Reference counter.
1047     };
1048
1049
1050   // 20.8.13.2.7 shared_ptr comparisons
1051   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1052     inline bool
1053     operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1054                const __shared_ptr<_Tp2, _Lp>& __b)
1055     { return __a.get() == __b.get(); }
1056
1057   template<typename _Tp, _Lock_policy _Lp>
1058     inline bool
1059     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t)
1060     { return __a.get() == nullptr; }
1061
1062   template<typename _Tp, _Lock_policy _Lp>
1063     inline bool
1064     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __b)
1065     { return nullptr == __b.get(); }
1066
1067   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1068     inline bool
1069     operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1070                const __shared_ptr<_Tp2, _Lp>& __b)
1071     { return __a.get() != __b.get(); }
1072
1073   template<typename _Tp, _Lock_policy _Lp>
1074     inline bool
1075     operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t)
1076     { return __a.get() != nullptr; }
1077
1078   template<typename _Tp, _Lock_policy _Lp>
1079     inline bool
1080     operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __b)
1081     { return nullptr != __b.get(); }
1082
1083   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1084     inline bool
1085     operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1086               const __shared_ptr<_Tp2, _Lp>& __b)
1087     { return __a.get() < __b.get(); }
1088
1089   template<typename _Sp>
1090     struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1091     {
1092       bool
1093       operator()(const _Sp& __lhs, const _Sp& __rhs) const
1094       {
1095         typedef typename _Sp::element_type element_type;
1096         return std::less<element_type*>()(__lhs.get(), __rhs.get());
1097       }
1098     };
1099
1100   template<typename _Tp, _Lock_policy _Lp>
1101     struct less<__shared_ptr<_Tp, _Lp>>
1102     : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1103     { };
1104
1105   // 2.2.3.8 shared_ptr specialized algorithms.
1106   template<typename _Tp, _Lock_policy _Lp>
1107     inline void
1108     swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b)
1109     { __a.swap(__b); }
1110
1111   // 2.2.3.9 shared_ptr casts
1112
1113   // The seemingly equivalent code:
1114   // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1115   // will eventually result in undefined behaviour, attempting to
1116   // delete the same object twice.
1117   /// static_pointer_cast
1118   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1119     inline __shared_ptr<_Tp, _Lp>
1120     static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
1121     { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1122
1123   // The seemingly equivalent code:
1124   // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1125   // will eventually result in undefined behaviour, attempting to
1126   // delete the same object twice.
1127   /// const_pointer_cast
1128   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1129     inline __shared_ptr<_Tp, _Lp>
1130     const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
1131     { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1132
1133   // The seemingly equivalent code:
1134   // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1135   // will eventually result in undefined behaviour, attempting to
1136   // delete the same object twice.
1137   /// dynamic_pointer_cast
1138   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1139     inline __shared_ptr<_Tp, _Lp>
1140     dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
1141     {
1142       if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1143         return __shared_ptr<_Tp, _Lp>(__r, __p);
1144       return __shared_ptr<_Tp, _Lp>();
1145     }
1146
1147
1148   template<typename _Tp, _Lock_policy _Lp>
1149     class __weak_ptr
1150     {
1151     public:
1152       typedef _Tp element_type;
1153
1154       constexpr __weak_ptr()
1155       : _M_ptr(0), _M_refcount() // never throws
1156       { }
1157
1158       // Generated copy constructor, assignment, destructor are fine.
1159
1160       // The "obvious" converting constructor implementation:
1161       //
1162       //  template<typename _Tp1>
1163       //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1164       //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1165       //    { }
1166       //
1167       // has a serious problem.
1168       //
1169       //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1170       //  conversion may require access to *__r._M_ptr (virtual inheritance).
1171       //
1172       // It is not possible to avoid spurious access violations since
1173       // in multithreaded programs __r._M_ptr may be invalidated at any point.
1174       template<typename _Tp1, typename = typename
1175                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1176         __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1177         : _M_refcount(__r._M_refcount) // never throws
1178         { _M_ptr = __r.lock().get(); }
1179
1180       template<typename _Tp1, typename = typename
1181                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1182         __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r)
1183         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1184         { }
1185
1186       template<typename _Tp1>
1187         __weak_ptr&
1188         operator=(const __weak_ptr<_Tp1, _Lp>& __r) // never throws
1189         {
1190           _M_ptr = __r.lock().get();
1191           _M_refcount = __r._M_refcount;
1192           return *this;
1193         }
1194
1195       template<typename _Tp1>
1196         __weak_ptr&
1197         operator=(const __shared_ptr<_Tp1, _Lp>& __r) // never throws
1198         {
1199           _M_ptr = __r._M_ptr;
1200           _M_refcount = __r._M_refcount;
1201           return *this;
1202         }
1203
1204       __shared_ptr<_Tp, _Lp>
1205       lock() const // never throws
1206       {
1207 #ifdef __GTHREADS
1208         // Optimization: avoid throw overhead.
1209         if (expired())
1210           return __shared_ptr<element_type, _Lp>();
1211
1212         __try
1213           {
1214             return __shared_ptr<element_type, _Lp>(*this);
1215           }
1216         __catch(const bad_weak_ptr&)
1217           {
1218             // Q: How can we get here?
1219             // A: Another thread may have invalidated r after the
1220             //    use_count test above.
1221             return __shared_ptr<element_type, _Lp>();
1222           }
1223
1224 #else
1225         // Optimization: avoid try/catch overhead when single threaded.
1226         return expired() ? __shared_ptr<element_type, _Lp>()
1227                          : __shared_ptr<element_type, _Lp>(*this);
1228
1229 #endif
1230       } // XXX MT
1231
1232       long
1233       use_count() const // never throws
1234       { return _M_refcount._M_get_use_count(); }
1235
1236       bool
1237       expired() const // never throws
1238       { return _M_refcount._M_get_use_count() == 0; }
1239
1240       template<typename _Tp1>
1241         bool
1242         owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1243         { return _M_refcount._M_less(__rhs._M_refcount); }
1244
1245       template<typename _Tp1>
1246         bool
1247         owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1248         { return _M_refcount._M_less(__rhs._M_refcount); }
1249
1250       void
1251       reset() // never throws
1252       { __weak_ptr().swap(*this); }
1253
1254       void
1255       swap(__weak_ptr& __s) // never throws
1256       {
1257         std::swap(_M_ptr, __s._M_ptr);
1258         _M_refcount._M_swap(__s._M_refcount);
1259       }
1260
1261     private:
1262       // Used by __enable_shared_from_this.
1263       void
1264       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount)
1265       {
1266         _M_ptr = __ptr;
1267         _M_refcount = __refcount;
1268       }
1269
1270       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1271       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1272       friend class __enable_shared_from_this<_Tp, _Lp>;
1273       friend class enable_shared_from_this<_Tp>;
1274
1275       _Tp*               _M_ptr;         // Contained pointer.
1276       __weak_count<_Lp>  _M_refcount;    // Reference counter.
1277     };
1278
1279   // 20.8.13.3.7 weak_ptr specialized algorithms.
1280   template<typename _Tp, _Lock_policy _Lp>
1281     inline void
1282     swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b)
1283     { __a.swap(__b); }
1284
1285   template<typename _Tp, typename _Tp1>
1286     struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1287     {
1288       bool
1289       operator()(const _Tp& __lhs, const _Tp& __rhs) const
1290       { return __lhs.owner_before(__rhs); }
1291
1292       bool
1293       operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1294       { return __lhs.owner_before(__rhs); }
1295
1296       bool
1297       operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1298       { return __lhs.owner_before(__rhs); }
1299     };
1300
1301   template<typename _Tp, _Lock_policy _Lp>
1302     struct owner_less<__shared_ptr<_Tp, _Lp>>
1303     : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1304     { };
1305
1306   template<typename _Tp, _Lock_policy _Lp>
1307     struct owner_less<__weak_ptr<_Tp, _Lp>>
1308     : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1309     { };
1310
1311
1312   template<typename _Tp, _Lock_policy _Lp>
1313     class __enable_shared_from_this
1314     {
1315     protected:
1316       constexpr __enable_shared_from_this() { }
1317
1318       __enable_shared_from_this(const __enable_shared_from_this&) { }
1319
1320       __enable_shared_from_this&
1321       operator=(const __enable_shared_from_this&)
1322       { return *this; }
1323
1324       ~__enable_shared_from_this() { }
1325
1326     public:
1327       __shared_ptr<_Tp, _Lp>
1328       shared_from_this()
1329       { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1330
1331       __shared_ptr<const _Tp, _Lp>
1332       shared_from_this() const
1333       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1334
1335     private:
1336       template<typename _Tp1>
1337         void
1338         _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const
1339         { _M_weak_this._M_assign(__p, __n); }
1340
1341       template<typename _Tp1>
1342         friend void
1343         __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
1344                                          const __enable_shared_from_this* __pe,
1345                                          const _Tp1* __px)
1346         {
1347           if (__pe != 0)
1348             __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
1349         }
1350
1351       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
1352     };
1353
1354
1355   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1356     inline __shared_ptr<_Tp, _Lp>
1357     __allocate_shared(const _Alloc& __a, _Args&&... __args)
1358     {
1359       return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
1360                                     std::forward<_Args>(__args)...);
1361     }
1362
1363   template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1364     inline __shared_ptr<_Tp, _Lp>
1365     __make_shared(_Args&&... __args)
1366     {
1367       typedef typename std::remove_const<_Tp>::type _Tp_nc;
1368       return __allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1369                                          std::forward<_Args>(__args)...);
1370     }
1371
1372   /// std::hash specialization for __shared_ptr.
1373   template<typename _Tp, _Lock_policy _Lp>
1374     struct hash<__shared_ptr<_Tp, _Lp>>
1375     : public std::unary_function<__shared_ptr<_Tp, _Lp>, size_t>
1376     {
1377       size_t
1378       operator()(const __shared_ptr<_Tp, _Lp>& __s) const
1379       { return std::hash<_Tp*>()(__s.get()); }
1380     };
1381
1382 _GLIBCXX_END_NAMESPACE_VERSION
1383 } // namespace
1384
1385 #endif // _SHARED_PTR_BASE_H