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

   1 // shared_ptr and weak_ptr implementation details -*- C++ -*-
   2
   3 // Copyright (C) 2007-2012 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 #if _GLIBCXX_USE_DEPRECATED
  57   template<typename> class auto_ptr;
  58 #endif
  59
  60  /**
  61    *  @brief  Exception possibly thrown by @c shared_ptr.
  62    *  @ingroup exceptions
  63    */
  64   class bad_weak_ptr : public std::exception
  65   {
  66   public:
  67     virtual char const*
  68     what() const noexcept;
  69
  70     virtual ~bad_weak_ptr() noexcept;
  71   };
  72
  73   // Substitute for bad_weak_ptr object in the case of -fno-exceptions.
  74   inline void
  75   __throw_bad_weak_ptr()
  76   { _GLIBCXX_THROW_OR_ABORT(bad_weak_ptr()); }
  77
  78   using __gnu_cxx::_Lock_policy;
  79   using __gnu_cxx::__default_lock_policy;
  80   using __gnu_cxx::_S_single;
  81   using __gnu_cxx::_S_mutex;
  82   using __gnu_cxx::_S_atomic;
  83
  84   // Empty helper class except when the template argument is _S_mutex.
  85   template<_Lock_policy _Lp>
  86     class _Mutex_base
  87     {
  88     protected:
  89       // The atomic policy uses fully-fenced builtins, single doesn't care.
  90       enum { _S_need_barriers = 0 };
  91     };
  92
  93   template<>
  94     class _Mutex_base<_S_mutex>
  95     : public __gnu_cxx::__mutex
  96     {
  97     protected:
  98       // This policy is used when atomic builtins are not available.
  99       // The replacement atomic operations might not have the necessary
 100       // memory barriers.
 101       enum { _S_need_barriers = 1 };
 102     };
 103
 104   template<_Lock_policy _Lp = __default_lock_policy>
 105     class _Sp_counted_base
 106     : public _Mutex_base<_Lp>
 107     {
 108     public:
 109       _Sp_counted_base() noexcept
 110       : _M_use_count(1), _M_weak_count(1) { }
 111
 112       virtual
 113       ~_Sp_counted_base() noexcept
 114       { }
 115
 116       // Called when _M_use_count drops to zero, to release the resources
 117       // managed by *this.
 118       virtual void
 119       _M_dispose() noexcept = 0;
 120
 121       // Called when _M_weak_count drops to zero.
 122       virtual void
 123       _M_destroy() noexcept
 124       { delete this; }
 125
 126       virtual void*
 127       _M_get_deleter(const std::type_info&) = 0;
 128
 129       void
 130       _M_add_ref_copy()
 131       { __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
 132
 133       void
 134       _M_add_ref_lock();
 135
 136       void
 137       _M_release() noexcept
 138       {
 139         // Be race-detector-friendly.  For more info see bits/c++config.
 140         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_use_count);
 141         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
 142           {
 143             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_use_count);
 144             _M_dispose();
 145             // There must be a memory barrier between dispose() and destroy()
 146             // to ensure that the effects of dispose() are observed in the
 147             // thread that runs destroy().
 148             // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
 149             if (_Mutex_base<_Lp>::_S_need_barriers)
 150               {
 151                 _GLIBCXX_READ_MEM_BARRIER;
 152                 _GLIBCXX_WRITE_MEM_BARRIER;
 153               }
 154
 155             // Be race-detector-friendly.  For more info see bits/c++config.
 156             _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 157             if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
 158                                                        -1) == 1)
 159               {
 160                 _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 161                 _M_destroy();
 162               }
 163           }
 164       }
 165
 166       void
 167       _M_weak_add_ref() noexcept
 168       { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
 169
 170       void
 171       _M_weak_release() noexcept
 172       {
 173         // Be race-detector-friendly. For more info see bits/c++config.
 174         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 175         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
 176           {
 177             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 178             if (_Mutex_base<_Lp>::_S_need_barriers)
 179               {
 180                 // See _M_release(),
 181                 // destroy() must observe results of dispose()
 182                 _GLIBCXX_READ_MEM_BARRIER;
 183                 _GLIBCXX_WRITE_MEM_BARRIER;
 184               }
 185             _M_destroy();
 186           }
 187       }
 188
 189       long
 190       _M_get_use_count() const noexcept
 191       {
 192         // No memory barrier is used here so there is no synchronization
 193         // with other threads.
 194         return __atomic_load_n(&_M_use_count, __ATOMIC_RELAXED);
 195       }
 196
 197     private:
 198       _Sp_counted_base(_Sp_counted_base const&) = delete;
 199       _Sp_counted_base& operator=(_Sp_counted_base const&) = delete;
 200
 201       _Atomic_word  _M_use_count;     // #shared
 202       _Atomic_word  _M_weak_count;    // #weak + (#shared != 0)
 203     };
 204
 205   template<>
 206     inline void
 207     _Sp_counted_base<_S_single>::
 208     _M_add_ref_lock()
 209     {
 210       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 211         {
 212           _M_use_count = 0;
 213           __throw_bad_weak_ptr();
 214         }
 215     }
 216
 217   template<>
 218     inline void
 219     _Sp_counted_base<_S_mutex>::
 220     _M_add_ref_lock()
 221     {
 222       __gnu_cxx::__scoped_lock sentry(*this);
 223       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 224         {
 225           _M_use_count = 0;
 226           __throw_bad_weak_ptr();
 227         }
 228     }
 229
 230   template<>
 231     inline void
 232     _Sp_counted_base<_S_atomic>::
 233     _M_add_ref_lock()
 234     {
 235       // Perform lock-free add-if-not-zero operation.
 236       _Atomic_word __count = _M_use_count;
 237       do
 238         {
 239           if (__count == 0)
 240             __throw_bad_weak_ptr();
 241           // Replace the current counter value with the old value + 1, as
 242           // long as it's not changed meanwhile.
 243         }
 244       while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
 245                                           true, __ATOMIC_ACQ_REL,
 246                                           __ATOMIC_RELAXED));
 247     }
 248
 249
 250   // Forward declarations.
 251   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 252     class __shared_ptr;
 253
 254   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 255     class __weak_ptr;
 256
 257   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 258     class __enable_shared_from_this;
 259
 260   template<typename _Tp>
 261     class shared_ptr;
 262
 263   template<typename _Tp>
 264     class weak_ptr;
 265
 266   template<typename _Tp>
 267     struct owner_less;
 268
 269   template<typename _Tp>
 270     class enable_shared_from_this;
 271
 272   template<_Lock_policy _Lp = __default_lock_policy>
 273     class __weak_count;
 274
 275   template<_Lock_policy _Lp = __default_lock_policy>
 276     class __shared_count;
 277
 278
 279   // Counted ptr with no deleter or allocator support
 280   template<typename _Ptr, _Lock_policy _Lp>
 281     class _Sp_counted_ptr final : public _Sp_counted_base<_Lp>
 282     {
 283     public:
 284       explicit
 285       _Sp_counted_ptr(_Ptr __p)
 286       : _M_ptr(__p) { }
 287
 288       virtual void
 289       _M_dispose() noexcept
 290       { delete _M_ptr; }
 291
 292       virtual void
 293       _M_destroy() noexcept
 294       { delete this; }
 295
 296       virtual void*
 297       _M_get_deleter(const std::type_info&)
 298       { return 0; }
 299
 300       _Sp_counted_ptr(const _Sp_counted_ptr&) = delete;
 301       _Sp_counted_ptr& operator=(const _Sp_counted_ptr&) = delete;
 302
 303     protected:
 304       _Ptr             _M_ptr;  // copy constructor must not throw
 305     };
 306
 307   template<>
 308     inline void
 309     _Sp_counted_ptr<nullptr_t, _S_single>::_M_dispose() noexcept { }
 310
 311   template<>
 312     inline void
 313     _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() noexcept { }
 314
 315   template<>
 316     inline void
 317     _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }
 318
 319   // Support for custom deleter and/or allocator
 320   template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>
 321     class _Sp_counted_deleter final : public _Sp_counted_base<_Lp>
 322     {
 323       // Helper class that stores the Deleter and also acts as an allocator.
 324       // Used to dispose of the owned pointer and the internal refcount
 325       // Requires that copies of _Alloc can free each other's memory.
 326       struct _My_Deleter
 327       : public _Alloc           // copy constructor must not throw
 328       {
 329         _Deleter _M_del;        // copy constructor must not throw
 330         _My_Deleter(_Deleter __d, const _Alloc& __a)
 331         : _Alloc(__a), _M_del(__d) { }
 332       };
 333
 334     public:
 335       // __d(__p) must not throw.
 336       _Sp_counted_deleter(_Ptr __p, _Deleter __d)
 337       : _M_ptr(__p), _M_del(__d, _Alloc()) { }
 338
 339       // __d(__p) must not throw.
 340       _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a)
 341       : _M_ptr(__p), _M_del(__d, __a) { }
 342
 343       ~_Sp_counted_deleter() noexcept { }
 344
 345       virtual void
 346       _M_dispose() noexcept
 347       { _M_del._M_del(_M_ptr); }
 348
 349       virtual void
 350       _M_destroy() noexcept
 351       {
 352         typedef typename allocator_traits<_Alloc>::template
 353           rebind_traits<_Sp_counted_deleter> _Alloc_traits;
 354         typename _Alloc_traits::allocator_type __a(_M_del);
 355         _Alloc_traits::destroy(__a, this);
 356         _Alloc_traits::deallocate(__a, this, 1);
 357       }
 358
 359       virtual void*
 360       _M_get_deleter(const std::type_info& __ti)
 361       {
 362 #ifdef __GXX_RTTI
 363         return __ti == typeid(_Deleter) ? &_M_del._M_del : 0;
 364 #else
 365         return 0;
 366 #endif
 367       }
 368
 369     protected:
 370       _Ptr             _M_ptr;  // copy constructor must not throw
 371       _My_Deleter      _M_del;  // copy constructor must not throw
 372     };
 373
 374   // helpers for make_shared / allocate_shared
 375
 376   struct _Sp_make_shared_tag { };
 377
 378   template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
 379     class _Sp_counted_ptr_inplace final : public _Sp_counted_base<_Lp>
 380     {
 381       // Helper class that stores the pointer and also acts as an allocator.
 382       // Used to dispose of the owned pointer and the internal refcount
 383       // Requires that copies of _Alloc can free each other's memory.
 384       struct _Impl
 385       : public _Alloc           // copy constructor must not throw
 386       {
 387         _Impl(_Alloc __a) : _Alloc(__a), _M_ptr() { }
 388         _Tp* _M_ptr;
 389       };
 390
 391     public:
 392       template<typename... _Args>
 393         _Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)
 394         : _M_impl(__a), _M_storage()
 395         {
 396           _M_impl._M_ptr = static_cast<_Tp*>(static_cast<void*>(&_M_storage));
 397           // _GLIBCXX_RESOLVE_LIB_DEFECTS
 398           // 2070.  allocate_shared should use allocator_traits<A>::construct
 399           allocator_traits<_Alloc>::construct(__a, _M_impl._M_ptr,
 400               std::forward<_Args>(__args)...); // might throw
 401         }
 402
 403       ~_Sp_counted_ptr_inplace() noexcept { }
 404
 405       virtual void
 406       _M_dispose() noexcept
 407       { allocator_traits<_Alloc>::destroy(_M_impl, _M_impl._M_ptr); }
 408
 409       // Override because the allocator needs to know the dynamic type
 410       virtual void
 411       _M_destroy() noexcept
 412       {
 413         typedef typename allocator_traits<_Alloc>::template
 414           rebind_traits<_Sp_counted_ptr_inplace> _Alloc_traits;
 415         typename _Alloc_traits::allocator_type __a(_M_impl);
 416         _Alloc_traits::destroy(__a, this);
 417         _Alloc_traits::deallocate(__a, this, 1);
 418       }
 419
 420       // Sneaky trick so __shared_ptr can get the managed pointer
 421       virtual void*
 422       _M_get_deleter(const std::type_info& __ti) noexcept
 423       {
 424 #ifdef __GXX_RTTI
 425         return __ti == typeid(_Sp_make_shared_tag)
 426                ? static_cast<void*>(&_M_storage)
 427                : 0;
 428 #else
 429         return 0;
 430 #endif
 431       }
 432
 433     private:
 434       _Impl _M_impl;
 435       typename aligned_storage<sizeof(_Tp), alignment_of<_Tp>::value>::type
 436         _M_storage;
 437     };
 438
 439   template<_Lock_policy _Lp>
 440     class __shared_count
 441     {
 442     public:
 443       constexpr __shared_count() noexcept : _M_pi(0)
 444       { }
 445
 446       template<typename _Ptr>
 447         explicit
 448         __shared_count(_Ptr __p) : _M_pi(0)
 449         {
 450           __try
 451             {
 452               _M_pi = new _Sp_counted_ptr<_Ptr, _Lp>(__p);
 453             }
 454           __catch(...)
 455             {
 456               delete __p;
 457               __throw_exception_again;
 458             }
 459         }
 460
 461       template<typename _Ptr, typename _Deleter>
 462         __shared_count(_Ptr __p, _Deleter __d) : _M_pi(0)
 463         {
 464           // The allocator's value_type doesn't matter, will rebind it anyway.
 465           typedef std::allocator<int> _Alloc;
 466           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 467           typedef typename allocator_traits<_Alloc>::template
 468             rebind_traits<_Sp_cd_type> _Alloc_traits;
 469           typename _Alloc_traits::allocator_type __a;
 470           _Sp_cd_type* __mem = 0;
 471           __try
 472             {
 473               __mem = _Alloc_traits::allocate(__a, 1);
 474               _Alloc_traits::construct(__a, __mem, __p, std::move(__d));
 475               _M_pi = __mem;
 476             }
 477           __catch(...)
 478             {
 479               __d(__p); // Call _Deleter on __p.
 480               if (__mem)
 481                 _Alloc_traits::deallocate(__a, __mem, 1);
 482               __throw_exception_again;
 483             }
 484         }
 485
 486       template<typename _Ptr, typename _Deleter, typename _Alloc>
 487         __shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
 488         {
 489           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 490           typedef typename allocator_traits<_Alloc>::template
 491             rebind_traits<_Sp_cd_type> _Alloc_traits;
 492           typename _Alloc_traits::allocator_type __a2(__a);
 493           _Sp_cd_type* __mem = 0;
 494           __try
 495             {
 496               __mem = _Alloc_traits::allocate(__a2, 1);
 497               _Alloc_traits::construct(__a2, __mem,
 498                   __p, std::move(__d), std::move(__a));
 499               _M_pi = __mem;
 500             }
 501           __catch(...)
 502             {
 503               __d(__p); // Call _Deleter on __p.
 504               if (__mem)
 505                 _Alloc_traits::deallocate(__a2, __mem, 1);
 506               __throw_exception_again;
 507             }
 508         }
 509
 510       template<typename _Tp, typename _Alloc, typename... _Args>
 511         __shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,
 512                        _Args&&... __args)
 513         : _M_pi(0)
 514         {
 515           typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
 516           typedef typename allocator_traits<_Alloc>::template
 517             rebind_traits<_Sp_cp_type> _Alloc_traits;
 518           typename _Alloc_traits::allocator_type __a2(__a);
 519           _Sp_cp_type* __mem = _Alloc_traits::allocate(__a2, 1);
 520           __try
 521             {
 522               _Alloc_traits::construct(__a2, __mem, std::move(__a),
 523                     std::forward<_Args>(__args)...);
 524               _M_pi = __mem;
 525             }
 526           __catch(...)
 527             {
 528               _Alloc_traits::deallocate(__a2, __mem, 1);
 529               __throw_exception_again;
 530             }
 531         }
 532
 533 #if _GLIBCXX_USE_DEPRECATED
 534       // Special case for auto_ptr<_Tp> to provide the strong guarantee.
 535       template<typename _Tp>
 536         explicit
 537         __shared_count(std::auto_ptr<_Tp>&& __r);
 538 #endif
 539
 540       // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
 541       template<typename _Tp, typename _Del>
 542         explicit
 543         __shared_count(std::unique_ptr<_Tp, _Del>&& __r)
 544         : _M_pi(_S_create_from_up(std::move(__r)))
 545         { __r.release(); }
 546
 547       // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
 548       explicit __shared_count(const __weak_count<_Lp>& __r);
 549
 550       ~__shared_count() noexcept
 551       {
 552         if (_M_pi != 0)
 553           _M_pi->_M_release();
 554       }
 555
 556       __shared_count(const __shared_count& __r) noexcept
 557       : _M_pi(__r._M_pi)
 558       {
 559         if (_M_pi != 0)
 560           _M_pi->_M_add_ref_copy();
 561       }
 562
 563       __shared_count&
 564       operator=(const __shared_count& __r) noexcept
 565       {
 566         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 567         if (__tmp != _M_pi)
 568           {
 569             if (__tmp != 0)
 570               __tmp->_M_add_ref_copy();
 571             if (_M_pi != 0)
 572               _M_pi->_M_release();
 573             _M_pi = __tmp;
 574           }
 575         return *this;
 576       }
 577
 578       void
 579       _M_swap(__shared_count& __r) noexcept
 580       {
 581         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 582         __r._M_pi = _M_pi;
 583         _M_pi = __tmp;
 584       }
 585
 586       long
 587       _M_get_use_count() const noexcept
 588       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 589
 590       bool
 591       _M_unique() const noexcept
 592       { return this->_M_get_use_count() == 1; }
 593
 594       void*
 595       _M_get_deleter(const std::type_info& __ti) const noexcept
 596       { return _M_pi ? _M_pi->_M_get_deleter(__ti) : 0; }
 597
 598       bool
 599       _M_less(const __shared_count& __rhs) const noexcept
 600       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 601
 602       bool
 603       _M_less(const __weak_count<_Lp>& __rhs) const noexcept
 604       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 605
 606       // Friend function injected into enclosing namespace and found by ADL
 607       friend inline bool
 608       operator==(const __shared_count& __a, const __shared_count& __b) noexcept
 609       { return __a._M_pi == __b._M_pi; }
 610
 611     private:
 612       friend class __weak_count<_Lp>;
 613
 614       template<typename _Tp, typename _Del>
 615         static _Sp_counted_base<_Lp>*
 616         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 617           typename std::enable_if<!std::is_reference<_Del>::value>::type* = 0)
 618         {
 619           typedef typename unique_ptr<_Tp, _Del>::pointer _Ptr;
 620           return new _Sp_counted_deleter<_Ptr, _Del, std::allocator<void>,
 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 unique_ptr<_Tp, _Del>::pointer _Ptr;
 630           typedef typename std::remove_reference<_Del>::type _Del1;
 631           typedef std::reference_wrapper<_Del1> _Del2;
 632           return new _Sp_counted_deleter<_Ptr, _Del2, std::allocator<void>,
 633             _Lp>(__r.get(), std::ref(__r.get_deleter()));
 634         }
 635
 636       _Sp_counted_base<_Lp>*  _M_pi;
 637     };
 638
 639
 640   template<_Lock_policy _Lp>
 641     class __weak_count
 642     {
 643     public:
 644       constexpr __weak_count() noexcept : _M_pi(0)
 645       { }
 646
 647       __weak_count(const __shared_count<_Lp>& __r) noexcept
 648       : _M_pi(__r._M_pi)
 649       {
 650         if (_M_pi != 0)
 651           _M_pi->_M_weak_add_ref();
 652       }
 653
 654       __weak_count(const __weak_count<_Lp>& __r) noexcept
 655       : _M_pi(__r._M_pi)
 656       {
 657         if (_M_pi != 0)
 658           _M_pi->_M_weak_add_ref();
 659       }
 660
 661       ~__weak_count() noexcept
 662       {
 663         if (_M_pi != 0)
 664           _M_pi->_M_weak_release();
 665       }
 666
 667       __weak_count<_Lp>&
 668       operator=(const __shared_count<_Lp>& __r) noexcept
 669       {
 670         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 671         if (__tmp != 0)
 672           __tmp->_M_weak_add_ref();
 673         if (_M_pi != 0)
 674           _M_pi->_M_weak_release();
 675         _M_pi = __tmp;
 676         return *this;
 677       }
 678
 679       __weak_count<_Lp>&
 680       operator=(const __weak_count<_Lp>& __r) noexcept
 681       {
 682         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 683         if (__tmp != 0)
 684           __tmp->_M_weak_add_ref();
 685         if (_M_pi != 0)
 686           _M_pi->_M_weak_release();
 687         _M_pi = __tmp;
 688         return *this;
 689       }
 690
 691       void
 692       _M_swap(__weak_count<_Lp>& __r) noexcept
 693       {
 694         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 695         __r._M_pi = _M_pi;
 696         _M_pi = __tmp;
 697       }
 698
 699       long
 700       _M_get_use_count() const noexcept
 701       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 702
 703       bool
 704       _M_less(const __weak_count& __rhs) const noexcept
 705       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 706
 707       bool
 708       _M_less(const __shared_count<_Lp>& __rhs) const noexcept
 709       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 710
 711       // Friend function injected into enclosing namespace and found by ADL
 712       friend inline bool
 713       operator==(const __weak_count& __a, const __weak_count& __b) noexcept
 714       { return __a._M_pi == __b._M_pi; }
 715
 716     private:
 717       friend class __shared_count<_Lp>;
 718
 719       _Sp_counted_base<_Lp>*  _M_pi;
 720     };
 721
 722   // Now that __weak_count is defined we can define this constructor:
 723   template<_Lock_policy _Lp>
 724     inline __shared_count<_Lp>:: __shared_count(const __weak_count<_Lp>& __r)
 725     : _M_pi(__r._M_pi)
 726     {
 727       if (_M_pi != 0)
 728         _M_pi->_M_add_ref_lock();
 729       else
 730         __throw_bad_weak_ptr();
 731     }
 732
 733
 734   // Support for enable_shared_from_this.
 735
 736   // Friend of __enable_shared_from_this.
 737   template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
 738     void
 739     __enable_shared_from_this_helper(const __shared_count<_Lp>&,
 740                                      const __enable_shared_from_this<_Tp1,
 741                                      _Lp>*, const _Tp2*) noexcept;
 742
 743   // Friend of enable_shared_from_this.
 744   template<typename _Tp1, typename _Tp2>
 745     void
 746     __enable_shared_from_this_helper(const __shared_count<>&,
 747                                      const enable_shared_from_this<_Tp1>*,
 748                                      const _Tp2*) noexcept;
 749
 750   template<_Lock_policy _Lp>
 751     inline void
 752     __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept
 753     { }
 754
 755
 756   template<typename _Tp, _Lock_policy _Lp>
 757     class __shared_ptr
 758     {
 759     public:
 760       typedef _Tp   element_type;
 761
 762       constexpr __shared_ptr() noexcept
 763       : _M_ptr(0), _M_refcount()
 764       { }
 765
 766       template<typename _Tp1>
 767         explicit __shared_ptr(_Tp1* __p)
 768         : _M_ptr(__p), _M_refcount(__p)
 769         {
 770           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 771           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 772           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 773         }
 774
 775       template<typename _Tp1, typename _Deleter>
 776         __shared_ptr(_Tp1* __p, _Deleter __d)
 777         : _M_ptr(__p), _M_refcount(__p, __d)
 778         {
 779           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 780           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 781           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 782         }
 783
 784       template<typename _Tp1, typename _Deleter, typename _Alloc>
 785         __shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
 786         : _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
 787         {
 788           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 789           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 790           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 791         }
 792
 793       template<typename _Deleter>
 794         __shared_ptr(nullptr_t __p, _Deleter __d)
 795         : _M_ptr(0), _M_refcount(__p, __d)
 796         { }
 797
 798       template<typename _Deleter, typename _Alloc>
 799         __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
 800         : _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
 801         { }
 802
 803       template<typename _Tp1>
 804         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p) noexcept
 805         : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
 806         { }
 807
 808       __shared_ptr(const __shared_ptr&) noexcept = default;
 809       __shared_ptr& operator=(const __shared_ptr&) noexcept = default;
 810       ~__shared_ptr() = default;
 811
 812       template<typename _Tp1, typename = typename
 813                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 814         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 815         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
 816         { }
 817
 818       __shared_ptr(__shared_ptr&& __r) noexcept
 819       : _M_ptr(__r._M_ptr), _M_refcount()
 820       {
 821         _M_refcount._M_swap(__r._M_refcount);
 822         __r._M_ptr = 0;
 823       }
 824
 825       template<typename _Tp1, typename = typename
 826                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 827         __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
 828         : _M_ptr(__r._M_ptr), _M_refcount()
 829         {
 830           _M_refcount._M_swap(__r._M_refcount);
 831           __r._M_ptr = 0;
 832         }
 833
 834       template<typename _Tp1>
 835         explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
 836         : _M_refcount(__r._M_refcount) // may throw
 837         {
 838           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 839
 840           // It is now safe to copy __r._M_ptr, as
 841           // _M_refcount(__r._M_refcount) did not throw.
 842           _M_ptr = __r._M_ptr;
 843         }
 844
 845       // If an exception is thrown this constructor has no effect.
 846       template<typename _Tp1, typename _Del>
 847         __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
 848         : _M_ptr(__r.get()), _M_refcount()
 849         {
 850           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 851           auto __tmp = std::__addressof(*__r.get());
 852           _M_refcount = __shared_count<_Lp>(std::move(__r));
 853           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 854         }
 855
 856 #if _GLIBCXX_USE_DEPRECATED
 857       // Postcondition: use_count() == 1 and __r.get() == 0
 858       template<typename _Tp1>
 859         __shared_ptr(std::auto_ptr<_Tp1>&& __r);
 860 #endif
 861
 862       /* TODO: use delegating constructor */
 863       constexpr __shared_ptr(nullptr_t) noexcept
 864       : _M_ptr(0), _M_refcount()
 865       { }
 866
 867       template<typename _Tp1>
 868         __shared_ptr&
 869         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 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) noexcept
 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) noexcept
 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() noexcept
 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 noexcept
 935       {
 936         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 937         return *_M_ptr;
 938       }
 939
 940       _Tp*
 941       operator->() const noexcept
 942       {
 943         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 944         return _M_ptr;
 945       }
 946
 947       _Tp*
 948       get() const noexcept
 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 noexcept
 956       { return _M_refcount._M_unique(); }
 957
 958       long
 959       use_count() const noexcept
 960       { return _M_refcount._M_get_use_count(); }
 961
 962       void
 963       swap(__shared_ptr<_Tp, _Lp>& __other) noexcept
 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             typedef allocator_traits<_Alloc> _Alloc_traits;
1001             _Alloc_traits::destroy(_M_alloc, __ptr);
1002             _Alloc_traits::deallocate(_M_alloc, __ptr, 1);
1003           }
1004           _Alloc _M_alloc;
1005         };
1006
1007       template<typename _Alloc, typename... _Args>
1008         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1009                      _Args&&... __args)
1010         : _M_ptr(), _M_refcount()
1011         {
1012           typedef typename _Alloc::template rebind<_Tp>::other _Alloc2;
1013           _Deleter<_Alloc2> __del = { _Alloc2(__a) };
1014           typedef allocator_traits<_Alloc2> __traits;
1015           _M_ptr = __traits::allocate(__del._M_alloc, 1);
1016           __try
1017             {
1018               // _GLIBCXX_RESOLVE_LIB_DEFECTS
1019               // 2070. allocate_shared should use allocator_traits<A>::construct
1020               __traits::construct(__del._M_alloc, _M_ptr,
1021                                   std::forward<_Args>(__args)...);
1022             }
1023           __catch(...)
1024             {
1025               __traits::deallocate(__del._M_alloc, _M_ptr, 1);
1026               __throw_exception_again;
1027             }
1028           __shared_count<_Lp> __count(_M_ptr, __del, __del._M_alloc);
1029           _M_refcount._M_swap(__count);
1030           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1031         }
1032 #endif
1033
1034       template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
1035                typename... _Args>
1036         friend __shared_ptr<_Tp1, _Lp1>
1037         __allocate_shared(const _Alloc& __a, _Args&&... __args);
1038
1039     private:
1040       void*
1041       _M_get_deleter(const std::type_info& __ti) const noexcept
1042       { return _M_refcount._M_get_deleter(__ti); }
1043
1044       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1045       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1046
1047       template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1048         friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&) noexcept;
1049
1050       _Tp*                 _M_ptr;         // Contained pointer.
1051       __shared_count<_Lp>  _M_refcount;    // Reference counter.
1052     };
1053
1054
1055   // 20.7.2.2.7 shared_ptr comparisons
1056   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1057     inline bool
1058     operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1059                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1060     { return __a.get() == __b.get(); }
1061
1062   template<typename _Tp, _Lock_policy _Lp>
1063     inline bool
1064     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1065     { return !__a; }
1066
1067   template<typename _Tp, _Lock_policy _Lp>
1068     inline bool
1069     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1070     { return !__a; }
1071
1072   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1073     inline bool
1074     operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1075                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1076     { return __a.get() != __b.get(); }
1077
1078   template<typename _Tp, _Lock_policy _Lp>
1079     inline bool
1080     operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1081     { return (bool)__a; }
1082
1083   template<typename _Tp, _Lock_policy _Lp>
1084     inline bool
1085     operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1086     { return (bool)__a; }
1087
1088   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1089     inline bool
1090     operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1091               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1092     {
1093       typedef typename std::common_type<_Tp1*, _Tp2*>::type _CT;
1094       return std::less<_CT>()(__a.get(), __b.get());
1095     }
1096
1097   template<typename _Tp, _Lock_policy _Lp>
1098     inline bool
1099     operator<(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1100     { return std::less<_Tp*>()(__a.get(), nullptr); }
1101
1102   template<typename _Tp, _Lock_policy _Lp>
1103     inline bool
1104     operator<(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1105     { return std::less<_Tp*>()(nullptr, __a.get()); }
1106
1107   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1108     inline bool
1109     operator<=(const __shared_ptr<_Tp1, _Lp>& __a,
1110                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1111     { return !(__b < __a); }
1112
1113   template<typename _Tp, _Lock_policy _Lp>
1114     inline bool
1115     operator<=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1116     { return !(nullptr < __a); }
1117
1118   template<typename _Tp, _Lock_policy _Lp>
1119     inline bool
1120     operator<=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1121     { return !(__a < nullptr); }
1122
1123   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1124     inline bool
1125     operator>(const __shared_ptr<_Tp1, _Lp>& __a,
1126               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1127     { return (__b < __a); }
1128
1129   template<typename _Tp, _Lock_policy _Lp>
1130     inline bool
1131     operator>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1132     { return std::less<_Tp*>()(nullptr, __a.get()); }
1133
1134   template<typename _Tp, _Lock_policy _Lp>
1135     inline bool
1136     operator>(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1137     { return std::less<_Tp*>()(__a.get(), nullptr); }
1138
1139   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1140     inline bool
1141     operator>=(const __shared_ptr<_Tp1, _Lp>& __a,
1142                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1143     { return !(__a < __b); }
1144
1145   template<typename _Tp, _Lock_policy _Lp>
1146     inline bool
1147     operator>=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1148     { return !(__a < nullptr); }
1149
1150   template<typename _Tp, _Lock_policy _Lp>
1151     inline bool
1152     operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1153     { return !(nullptr < __a); }
1154
1155   template<typename _Sp>
1156     struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1157     {
1158       bool
1159       operator()(const _Sp& __lhs, const _Sp& __rhs) const noexcept
1160       {
1161         typedef typename _Sp::element_type element_type;
1162         return std::less<element_type*>()(__lhs.get(), __rhs.get());
1163       }
1164     };
1165
1166   template<typename _Tp, _Lock_policy _Lp>
1167     struct less<__shared_ptr<_Tp, _Lp>>
1168     : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1169     { };
1170
1171   // 2.2.3.8 shared_ptr specialized algorithms.
1172   template<typename _Tp, _Lock_policy _Lp>
1173     inline void
1174     swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b) noexcept
1175     { __a.swap(__b); }
1176
1177   // 2.2.3.9 shared_ptr casts
1178
1179   // The seemingly equivalent code:
1180   // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1181   // will eventually result in undefined behaviour, attempting to
1182   // delete the same object twice.
1183   /// static_pointer_cast
1184   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1185     inline __shared_ptr<_Tp, _Lp>
1186     static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1187     { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1188
1189   // The seemingly equivalent code:
1190   // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1191   // will eventually result in undefined behaviour, attempting to
1192   // delete the same object twice.
1193   /// const_pointer_cast
1194   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1195     inline __shared_ptr<_Tp, _Lp>
1196     const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1197     { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1198
1199   // The seemingly equivalent code:
1200   // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1201   // will eventually result in undefined behaviour, attempting to
1202   // delete the same object twice.
1203   /// dynamic_pointer_cast
1204   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1205     inline __shared_ptr<_Tp, _Lp>
1206     dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1207     {
1208       if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1209         return __shared_ptr<_Tp, _Lp>(__r, __p);
1210       return __shared_ptr<_Tp, _Lp>();
1211     }
1212
1213
1214   template<typename _Tp, _Lock_policy _Lp>
1215     class __weak_ptr
1216     {
1217     public:
1218       typedef _Tp element_type;
1219
1220       constexpr __weak_ptr() noexcept
1221       : _M_ptr(0), _M_refcount()
1222       { }
1223
1224       __weak_ptr(const __weak_ptr&) noexcept = default;
1225       __weak_ptr& operator=(const __weak_ptr&) noexcept = default;
1226       ~__weak_ptr() = default;
1227
1228       // The "obvious" converting constructor implementation:
1229       //
1230       //  template<typename _Tp1>
1231       //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1232       //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1233       //    { }
1234       //
1235       // has a serious problem.
1236       //
1237       //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1238       //  conversion may require access to *__r._M_ptr (virtual inheritance).
1239       //
1240       // It is not possible to avoid spurious access violations since
1241       // in multithreaded programs __r._M_ptr may be invalidated at any point.
1242       template<typename _Tp1, typename = typename
1243                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1244         __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1245         : _M_refcount(__r._M_refcount)
1246         { _M_ptr = __r.lock().get(); }
1247
1248       template<typename _Tp1, typename = typename
1249                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1250         __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1251         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
1252         { }
1253
1254       template<typename _Tp1>
1255         __weak_ptr&
1256         operator=(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1257         {
1258           _M_ptr = __r.lock().get();
1259           _M_refcount = __r._M_refcount;
1260           return *this;
1261         }
1262
1263       template<typename _Tp1>
1264         __weak_ptr&
1265         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1266         {
1267           _M_ptr = __r._M_ptr;
1268           _M_refcount = __r._M_refcount;
1269           return *this;
1270         }
1271
1272       __shared_ptr<_Tp, _Lp>
1273       lock() const noexcept
1274       {
1275 #ifdef __GTHREADS
1276         // Optimization: avoid throw overhead.
1277         if (expired())
1278           return __shared_ptr<element_type, _Lp>();
1279
1280         __try
1281           {
1282             return __shared_ptr<element_type, _Lp>(*this);
1283           }
1284         __catch(const bad_weak_ptr&)
1285           {
1286             // Q: How can we get here?
1287             // A: Another thread may have invalidated r after the
1288             //    use_count test above.
1289             return __shared_ptr<element_type, _Lp>();
1290           }
1291
1292 #else
1293         // Optimization: avoid try/catch overhead when single threaded.
1294         return expired() ? __shared_ptr<element_type, _Lp>()
1295                          : __shared_ptr<element_type, _Lp>(*this);
1296
1297 #endif
1298       } // XXX MT
1299
1300       long
1301       use_count() const noexcept
1302       { return _M_refcount._M_get_use_count(); }
1303
1304       bool
1305       expired() const noexcept
1306       { return _M_refcount._M_get_use_count() == 0; }
1307
1308       template<typename _Tp1>
1309         bool
1310         owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1311         { return _M_refcount._M_less(__rhs._M_refcount); }
1312
1313       template<typename _Tp1>
1314         bool
1315         owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1316         { return _M_refcount._M_less(__rhs._M_refcount); }
1317
1318       void
1319       reset() noexcept
1320       { __weak_ptr().swap(*this); }
1321
1322       void
1323       swap(__weak_ptr& __s) noexcept
1324       {
1325         std::swap(_M_ptr, __s._M_ptr);
1326         _M_refcount._M_swap(__s._M_refcount);
1327       }
1328
1329     private:
1330       // Used by __enable_shared_from_this.
1331       void
1332       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
1333       {
1334         _M_ptr = __ptr;
1335         _M_refcount = __refcount;
1336       }
1337
1338       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1339       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1340       friend class __enable_shared_from_this<_Tp, _Lp>;
1341       friend class enable_shared_from_this<_Tp>;
1342
1343       _Tp*               _M_ptr;         // Contained pointer.
1344       __weak_count<_Lp>  _M_refcount;    // Reference counter.
1345     };
1346
1347   // 20.7.2.3.6 weak_ptr specialized algorithms.
1348   template<typename _Tp, _Lock_policy _Lp>
1349     inline void
1350     swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b) noexcept
1351     { __a.swap(__b); }
1352
1353   template<typename _Tp, typename _Tp1>
1354     struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1355     {
1356       bool
1357       operator()(const _Tp& __lhs, const _Tp& __rhs) const
1358       { return __lhs.owner_before(__rhs); }
1359
1360       bool
1361       operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1362       { return __lhs.owner_before(__rhs); }
1363
1364       bool
1365       operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1366       { return __lhs.owner_before(__rhs); }
1367     };
1368
1369   template<typename _Tp, _Lock_policy _Lp>
1370     struct owner_less<__shared_ptr<_Tp, _Lp>>
1371     : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1372     { };
1373
1374   template<typename _Tp, _Lock_policy _Lp>
1375     struct owner_less<__weak_ptr<_Tp, _Lp>>
1376     : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1377     { };
1378
1379
1380   template<typename _Tp, _Lock_policy _Lp>
1381     class __enable_shared_from_this
1382     {
1383     protected:
1384       constexpr __enable_shared_from_this() noexcept { }
1385
1386       __enable_shared_from_this(const __enable_shared_from_this&) noexcept { }
1387
1388       __enable_shared_from_this&
1389       operator=(const __enable_shared_from_this&) noexcept
1390       { return *this; }
1391
1392       ~__enable_shared_from_this() { }
1393
1394     public:
1395       __shared_ptr<_Tp, _Lp>
1396       shared_from_this()
1397       { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1398
1399       __shared_ptr<const _Tp, _Lp>
1400       shared_from_this() const
1401       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1402
1403     private:
1404       template<typename _Tp1>
1405         void
1406         _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
1407         { _M_weak_this._M_assign(__p, __n); }
1408
1409       template<typename _Tp1>
1410         friend void
1411         __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
1412                                          const __enable_shared_from_this* __pe,
1413                                          const _Tp1* __px) noexcept
1414         {
1415           if (__pe != 0)
1416             __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
1417         }
1418
1419       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
1420     };
1421
1422
1423   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1424     inline __shared_ptr<_Tp, _Lp>
1425     __allocate_shared(const _Alloc& __a, _Args&&... __args)
1426     {
1427       return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
1428                                     std::forward<_Args>(__args)...);
1429     }
1430
1431   template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1432     inline __shared_ptr<_Tp, _Lp>
1433     __make_shared(_Args&&... __args)
1434     {
1435       typedef typename std::remove_const<_Tp>::type _Tp_nc;
1436       return std::__allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1437                                               std::forward<_Args>(__args)...);
1438     }
1439
1440   /// std::hash specialization for __shared_ptr.
1441   template<typename _Tp, _Lock_policy _Lp>
1442     struct hash<__shared_ptr<_Tp, _Lp>>
1443     : public __hash_base<size_t, __shared_ptr<_Tp, _Lp>>
1444     {
1445       size_t
1446       operator()(const __shared_ptr<_Tp, _Lp>& __s) const noexcept
1447       { return std::hash<_Tp*>()(__s.get()); }
1448     };
1449
1450 _GLIBCXX_END_NAMESPACE_VERSION
1451 } // namespace
1452
1453 #endif // _SHARED_PTR_BASE_H