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 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  *  You should not attempt to use it directly.
  47  */
  48
  49 #ifndef _SHARED_PTR_BASE_H
  50 #define _SHARED_PTR_BASE_H 1
  51
  52 _GLIBCXX_BEGIN_NAMESPACE(std)
  53
  54  /**
  55    *  @brief  Exception possibly thrown by @c shared_ptr.
  56    *  @ingroup exceptions
  57    */
  58   class bad_weak_ptr : public std::exception
  59   {
  60   public:
  61     virtual char const*
  62     what() const throw()
  63     { return "std::bad_weak_ptr"; }
  64   };
  65
  66   // Substitute for bad_weak_ptr object in the case of -fno-exceptions.
  67   inline void
  68   __throw_bad_weak_ptr()
  69   {
  70 #if __EXCEPTIONS
  71     throw bad_weak_ptr();
  72 #else
  73     __builtin_abort();
  74 #endif
  75   }
  76
  77   using __gnu_cxx::_Lock_policy;
  78   using __gnu_cxx::__default_lock_policy;
  79   using __gnu_cxx::_S_single;
  80   using __gnu_cxx::_S_mutex;
  81   using __gnu_cxx::_S_atomic;
  82
  83   // Empty helper class except when the template argument is _S_mutex.
  84   template<_Lock_policy _Lp>
  85     class _Mutex_base
  86     {
  87     protected:
  88       // The atomic policy uses fully-fenced builtins, single doesn't care.
  89       enum { _S_need_barriers = 0 };
  90     };
  91
  92   template<>
  93     class _Mutex_base<_S_mutex>
  94     : public __gnu_cxx::__mutex
  95     {
  96     protected:
  97       // This policy is used when atomic builtins are not available.
  98       // The replacement atomic operations might not have the necessary
  99       // memory barriers.
 100       enum { _S_need_barriers = 1 };
 101     };
 102
 103   template<_Lock_policy _Lp = __default_lock_policy>
 104     class _Sp_counted_base
 105     : public _Mutex_base<_Lp>
 106     {
 107     public:
 108       _Sp_counted_base()
 109       : _M_use_count(1), _M_weak_count(1) { }
 110
 111       virtual
 112       ~_Sp_counted_base() // nothrow
 113       { }
 114
 115       // Called when _M_use_count drops to zero, to release the resources
 116       // managed by *this.
 117       virtual void
 118       _M_dispose() = 0; // nothrow
 119
 120       // Called when _M_weak_count drops to zero.
 121       virtual void
 122       _M_destroy() // nothrow
 123       { delete this; }
 124
 125       virtual void*
 126       _M_get_deleter(const std::type_info&) = 0;
 127
 128       void
 129       _M_add_ref_copy()
 130       { __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
 131
 132       void
 133       _M_add_ref_lock();
 134
 135       void
 136       _M_release() // nothrow
 137       {
 138         // Be race-detector-friendly.  For more info see bits/c++config.
 139         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_use_count);
 140         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
 141           {
 142             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_use_count);
 143             _M_dispose();
 144             // There must be a memory barrier between dispose() and destroy()
 145             // to ensure that the effects of dispose() are observed in the
 146             // thread that runs destroy().
 147             // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
 148             if (_Mutex_base<_Lp>::_S_need_barriers)
 149               {
 150                 _GLIBCXX_READ_MEM_BARRIER;
 151                 _GLIBCXX_WRITE_MEM_BARRIER;
 152               }
 153
 154             // Be race-detector-friendly.  For more info see bits/c++config.
 155             _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 156             if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
 157                                                        -1) == 1)
 158               {
 159                 _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 160                 _M_destroy();
 161               }
 162           }
 163       }
 164
 165       void
 166       _M_weak_add_ref() // nothrow
 167       { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
 168
 169       void
 170       _M_weak_release() // nothrow
 171       {
 172         // Be race-detector-friendly. For more info see bits/c++config.
 173         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 174         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
 175           {
 176             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 177             if (_Mutex_base<_Lp>::_S_need_barriers)
 178               {
 179                 // See _M_release(),
 180                 // destroy() must observe results of dispose()
 181                 _GLIBCXX_READ_MEM_BARRIER;
 182                 _GLIBCXX_WRITE_MEM_BARRIER;
 183               }
 184             _M_destroy();
 185           }
 186       }
 187
 188       long
 189       _M_get_use_count() const // nothrow
 190       {
 191         // No memory barrier is used here so there is no synchronization
 192         // with other threads.
 193         return const_cast<const volatile _Atomic_word&>(_M_use_count);
 194       }
 195
 196     private:
 197       _Sp_counted_base(_Sp_counted_base const&);
 198       _Sp_counted_base& operator=(_Sp_counted_base const&);
 199
 200       _Atomic_word  _M_use_count;     // #shared
 201       _Atomic_word  _M_weak_count;    // #weak + (#shared != 0)
 202     };
 203
 204   template<>
 205     inline void
 206     _Sp_counted_base<_S_single>::
 207     _M_add_ref_lock()
 208     {
 209       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 210         {
 211           _M_use_count = 0;
 212           __throw_bad_weak_ptr();
 213         }
 214     }
 215
 216   template<>
 217     inline void
 218     _Sp_counted_base<_S_mutex>::
 219     _M_add_ref_lock()
 220     {
 221       __gnu_cxx::__scoped_lock sentry(*this);
 222       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 223         {
 224           _M_use_count = 0;
 225           __throw_bad_weak_ptr();
 226         }
 227     }
 228
 229   template<>
 230     inline void
 231     _Sp_counted_base<_S_atomic>::
 232     _M_add_ref_lock()
 233     {
 234       // Perform lock-free add-if-not-zero operation.
 235       _Atomic_word __count;
 236       do
 237         {
 238           __count = _M_use_count;
 239           if (__count == 0)
 240             __throw_bad_weak_ptr();
 241
 242           // Replace the current counter value with the old value + 1, as
 243           // long as it's not changed meanwhile.
 244         }
 245       while (!__sync_bool_compare_and_swap(&_M_use_count, __count,
 246                                            __count + 1));
 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 : 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() // nothrow
 290       { delete _M_ptr; }
 291
 292       virtual void
 293       _M_destroy() // nothrow
 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() { }
 310
 311   template<>
 312     inline void
 313     _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() { }
 314
 315   template<>
 316     inline void
 317     _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() { }
 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 : public _Sp_counted_ptr<_Ptr, _Lp>
 322     {
 323       typedef typename _Alloc::template
 324           rebind<_Sp_counted_deleter>::other _My_alloc_type;
 325
 326       // Helper class that stores the Deleter and also acts as an allocator.
 327       // Used to dispose of the owned pointer and the internal refcount
 328       // Requires that copies of _Alloc can free each other's memory.
 329       struct _My_Deleter
 330       : public _My_alloc_type    // copy constructor must not throw
 331       {
 332         _Deleter _M_del;         // copy constructor must not throw
 333         _My_Deleter(_Deleter __d, const _Alloc& __a)
 334           : _My_alloc_type(__a), _M_del(__d) { }
 335       };
 336
 337     protected:
 338       typedef _Sp_counted_ptr<_Ptr, _Lp> _Base_type;
 339
 340     public:
 341       // __d(__p) must not throw.
 342       _Sp_counted_deleter(_Ptr __p, _Deleter __d)
 343       : _Base_type(__p), _M_del(__d, _Alloc()) { }
 344
 345       // __d(__p) must not throw.
 346       _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a)
 347       : _Base_type(__p), _M_del(__d, __a) { }
 348
 349       virtual void
 350       _M_dispose() // nothrow
 351       { _M_del._M_del(_Base_type::_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       _My_Deleter      _M_del;  // copy constructor must not throw
 373     };
 374
 375   // helpers for make_shared / allocate_shared
 376
 377   template<typename _Tp>
 378     struct _Sp_destroy_inplace
 379     {
 380       void operator()(_Tp* __p) const { if (__p) __p->~_Tp(); }
 381     };
 382
 383   struct _Sp_make_shared_tag { };
 384
 385   template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
 386     class _Sp_counted_ptr_inplace
 387     : public _Sp_counted_deleter<_Tp*, _Sp_destroy_inplace<_Tp>, _Alloc, _Lp>
 388     {
 389       typedef _Sp_counted_deleter<_Tp*, _Sp_destroy_inplace<_Tp>, _Alloc, _Lp>
 390         _Base_type;
 391
 392     public:
 393       explicit
 394       _Sp_counted_ptr_inplace(_Alloc __a)
 395       : _Base_type(static_cast<_Tp*>(0), _Sp_destroy_inplace<_Tp>(), __a)
 396       , _M_storage()
 397       {
 398         void* __p = &_M_storage;
 399         ::new (__p) _Tp();  // might throw
 400         _Base_type::_Base_type::_M_ptr = static_cast<_Tp*>(__p);
 401       }
 402
 403       template<typename... _Args>
 404         _Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)
 405         : _Base_type(static_cast<_Tp*>(0), _Sp_destroy_inplace<_Tp>(), __a)
 406         , _M_storage()
 407         {
 408           void* __p = &_M_storage;
 409           ::new (__p) _Tp(std::forward<_Args>(__args)...);  // might throw
 410           _Base_type::_Base_type::_M_ptr = static_cast<_Tp*>(__p);
 411         }
 412
 413       // Override because the allocator needs to know the dynamic type
 414       virtual void
 415       _M_destroy() // nothrow
 416       {
 417         typedef typename _Alloc::template
 418             rebind<_Sp_counted_ptr_inplace>::other _My_alloc_type;
 419         _My_alloc_type __a(_Base_type::_M_del);
 420         this->~_Sp_counted_ptr_inplace();
 421         __a.deallocate(this, 1);
 422       }
 423
 424       // Sneaky trick so __shared_ptr can get the managed pointer
 425       virtual void*
 426       _M_get_deleter(const std::type_info& __ti)
 427       {
 428 #ifdef __GXX_RTTI
 429         return __ti == typeid(_Sp_make_shared_tag)
 430                ? static_cast<void*>(&_M_storage)
 431                : _Base_type::_M_get_deleter(__ti);
 432 #else
 433         return 0;
 434 #endif
 435       }
 436
 437     private:
 438       typename aligned_storage<sizeof(_Tp), alignment_of<_Tp>::value>::type
 439         _M_storage;
 440     };
 441
 442   template<_Lock_policy _Lp>
 443     class __shared_count
 444     {
 445     public:
 446       constexpr __shared_count() : _M_pi(0) // nothrow
 447       { }
 448
 449       template<typename _Ptr>
 450         explicit
 451         __shared_count(_Ptr __p) : _M_pi(0)
 452         {
 453           __try
 454             {
 455               _M_pi = new _Sp_counted_ptr<_Ptr, _Lp>(__p);
 456             }
 457           __catch(...)
 458             {
 459               delete __p;
 460               __throw_exception_again;
 461             }
 462         }
 463
 464       template<typename _Ptr, typename _Deleter>
 465         __shared_count(_Ptr __p, _Deleter __d) : _M_pi(0)
 466         {
 467           // The allocator's value_type doesn't matter, will rebind it anyway.
 468           typedef std::allocator<int> _Alloc;
 469           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 470           typedef std::allocator<_Sp_cd_type> _Alloc2;
 471           _Alloc2 __a2;
 472           __try
 473             {
 474               _M_pi = __a2.allocate(1);
 475               ::new(static_cast<void*>(_M_pi)) _Sp_cd_type(__p, __d);
 476             }
 477           __catch(...)
 478             {
 479               __d(__p); // Call _Deleter on __p.
 480               if (_M_pi)
 481                 __a2.deallocate(static_cast<_Sp_cd_type*>(_M_pi), 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 _Alloc::template rebind<_Sp_cd_type>::other _Alloc2;
 491           _Alloc2 __a2(__a);
 492           __try
 493             {
 494               _M_pi = __a2.allocate(1);
 495               ::new(static_cast<void*>(_M_pi)) _Sp_cd_type(__p, __d, __a);
 496             }
 497           __catch(...)
 498             {
 499               __d(__p); // Call _Deleter on __p.
 500               if (_M_pi)
 501                 __a2.deallocate(static_cast<_Sp_cd_type*>(_M_pi), 1);
 502               __throw_exception_again;
 503             }
 504         }
 505
 506       template<typename _Tp, typename _Alloc, typename... _Args>
 507         __shared_count(_Sp_make_shared_tag, _Tp*, _Alloc __a, _Args&&... __args)
 508         : _M_pi(0)
 509         {
 510           typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
 511           typedef typename _Alloc::template rebind<_Sp_cp_type>::other _Alloc2;
 512           _Alloc2 __a2(__a);
 513           __try
 514             {
 515               _M_pi = __a2.allocate(1);
 516               ::new(static_cast<void*>(_M_pi)) _Sp_cp_type(__a,
 517                     std::forward<_Args>(__args)...);
 518             }
 519           __catch(...)
 520             {
 521               if (_M_pi)
 522                 __a2.deallocate(static_cast<_Sp_cp_type*>(_M_pi), 1);
 523               __throw_exception_again;
 524             }
 525         }
 526
 527 #if _GLIBCXX_DEPRECATED
 528       // Special case for auto_ptr<_Tp> to provide the strong guarantee.
 529       template<typename _Tp>
 530         explicit
 531         __shared_count(std::auto_ptr<_Tp>&& __r)
 532         : _M_pi(new _Sp_counted_ptr<_Tp*, _Lp>(__r.get()))
 533         { __r.release(); }
 534 #endif
 535
 536       // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
 537       template<typename _Tp, typename _Del>
 538         explicit
 539         __shared_count(std::unique_ptr<_Tp, _Del>&& __r)
 540         : _M_pi(_S_create_from_up(std::move(__r)))
 541         { __r.release(); }
 542
 543       // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
 544       explicit __shared_count(const __weak_count<_Lp>& __r);
 545
 546       ~__shared_count() // nothrow
 547       {
 548         if (_M_pi != 0)
 549           _M_pi->_M_release();
 550       }
 551
 552       __shared_count(const __shared_count& __r)
 553       : _M_pi(__r._M_pi) // nothrow
 554       {
 555         if (_M_pi != 0)
 556           _M_pi->_M_add_ref_copy();
 557       }
 558
 559       __shared_count&
 560       operator=(const __shared_count& __r) // nothrow
 561       {
 562         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 563         if (__tmp != _M_pi)
 564           {
 565             if (__tmp != 0)
 566               __tmp->_M_add_ref_copy();
 567             if (_M_pi != 0)
 568               _M_pi->_M_release();
 569             _M_pi = __tmp;
 570           }
 571         return *this;
 572       }
 573
 574       void
 575       _M_swap(__shared_count& __r) // nothrow
 576       {
 577         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 578         __r._M_pi = _M_pi;
 579         _M_pi = __tmp;
 580       }
 581
 582       long
 583       _M_get_use_count() const // nothrow
 584       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 585
 586       bool
 587       _M_unique() const // nothrow
 588       { return this->_M_get_use_count() == 1; }
 589
 590       void*
 591       _M_get_deleter(const std::type_info& __ti) const
 592       { return _M_pi ? _M_pi->_M_get_deleter(__ti) : 0; }
 593
 594       bool
 595       _M_less(const __shared_count& __rhs) const
 596       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 597
 598       bool
 599       _M_less(const __weak_count<_Lp>& __rhs) const
 600       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 601
 602       // Friend function injected into enclosing namespace and found by ADL
 603       friend inline bool
 604       operator==(const __shared_count& __a, const __shared_count& __b)
 605       { return __a._M_pi == __b._M_pi; }
 606
 607     private:
 608       friend class __weak_count<_Lp>;
 609
 610       template<typename _Tp, typename _Del>
 611         static _Sp_counted_base<_Lp>*
 612         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 613           typename std::enable_if<!std::is_reference<_Del>::value>::type* = 0)
 614         {
 615           return new _Sp_counted_deleter<_Tp*, _Del, std::allocator<_Tp>,
 616             _Lp>(__r.get(), __r.get_deleter());
 617         }
 618
 619       template<typename _Tp, typename _Del>
 620         static _Sp_counted_base<_Lp>*
 621         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 622           typename std::enable_if<std::is_reference<_Del>::value>::type* = 0)
 623         {
 624           typedef typename std::remove_reference<_Del>::type _Del1;
 625           typedef std::reference_wrapper<_Del1> _Del2;
 626           return new _Sp_counted_deleter<_Tp*, _Del2, std::allocator<_Tp>,
 627             _Lp>(__r.get(), std::ref(__r.get_deleter()));
 628         }
 629
 630       _Sp_counted_base<_Lp>*  _M_pi;
 631     };
 632
 633
 634   template<_Lock_policy _Lp>
 635     class __weak_count
 636     {
 637     public:
 638       constexpr __weak_count() : _M_pi(0) // nothrow
 639       { }
 640
 641       __weak_count(const __shared_count<_Lp>& __r) : _M_pi(__r._M_pi) // nothrow
 642       {
 643         if (_M_pi != 0)
 644           _M_pi->_M_weak_add_ref();
 645       }
 646
 647       __weak_count(const __weak_count<_Lp>& __r) : _M_pi(__r._M_pi) // nothrow
 648       {
 649         if (_M_pi != 0)
 650           _M_pi->_M_weak_add_ref();
 651       }
 652
 653       ~__weak_count() // nothrow
 654       {
 655         if (_M_pi != 0)
 656           _M_pi->_M_weak_release();
 657       }
 658
 659       __weak_count<_Lp>&
 660       operator=(const __shared_count<_Lp>& __r) // nothrow
 661       {
 662         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 663         if (__tmp != 0)
 664           __tmp->_M_weak_add_ref();
 665         if (_M_pi != 0)
 666           _M_pi->_M_weak_release();
 667         _M_pi = __tmp;
 668         return *this;
 669       }
 670
 671       __weak_count<_Lp>&
 672       operator=(const __weak_count<_Lp>& __r) // nothrow
 673       {
 674         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 675         if (__tmp != 0)
 676           __tmp->_M_weak_add_ref();
 677         if (_M_pi != 0)
 678           _M_pi->_M_weak_release();
 679         _M_pi = __tmp;
 680         return *this;
 681       }
 682
 683       void
 684       _M_swap(__weak_count<_Lp>& __r) // nothrow
 685       {
 686         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 687         __r._M_pi = _M_pi;
 688         _M_pi = __tmp;
 689       }
 690
 691       long
 692       _M_get_use_count() const // nothrow
 693       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 694
 695       bool
 696       _M_less(const __weak_count& __rhs) const
 697       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 698
 699       bool
 700       _M_less(const __shared_count<_Lp>& __rhs) const
 701       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 702
 703       // Friend function injected into enclosing namespace and found by ADL
 704       friend inline bool
 705       operator==(const __weak_count& __a, const __weak_count& __b)
 706       { return __a._M_pi == __b._M_pi; }
 707
 708     private:
 709       friend class __shared_count<_Lp>;
 710
 711       _Sp_counted_base<_Lp>*  _M_pi;
 712     };
 713
 714   // Now that __weak_count is defined we can define this constructor:
 715   template<_Lock_policy _Lp>
 716     inline __shared_count<_Lp>:: __shared_count(const __weak_count<_Lp>& __r)
 717     : _M_pi(__r._M_pi)
 718     {
 719       if (_M_pi != 0)
 720         _M_pi->_M_add_ref_lock();
 721       else
 722         __throw_bad_weak_ptr();
 723     }
 724
 725
 726   // Support for enable_shared_from_this.
 727
 728   // Friend of __enable_shared_from_this.
 729   template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
 730     void
 731     __enable_shared_from_this_helper(const __shared_count<_Lp>&,
 732                                      const __enable_shared_from_this<_Tp1,
 733                                      _Lp>*, const _Tp2*);
 734
 735   // Friend of enable_shared_from_this.
 736   template<typename _Tp1, typename _Tp2>
 737     void
 738     __enable_shared_from_this_helper(const __shared_count<>&,
 739                                      const enable_shared_from_this<_Tp1>*,
 740                                      const _Tp2*);
 741
 742   template<_Lock_policy _Lp>
 743     inline void
 744     __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...)
 745     { }
 746
 747
 748   template<typename _Tp, _Lock_policy _Lp>
 749     class __shared_ptr
 750     {
 751     public:
 752       typedef _Tp   element_type;
 753
 754       constexpr __shared_ptr()
 755       : _M_ptr(0), _M_refcount() // never throws
 756       { }
 757
 758       template<typename _Tp1>
 759         explicit __shared_ptr(_Tp1* __p)
 760         : _M_ptr(__p), _M_refcount(__p)
 761         {
 762           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 763           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 764           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 765         }
 766
 767       template<typename _Tp1, typename _Deleter>
 768         __shared_ptr(_Tp1* __p, _Deleter __d)
 769         : _M_ptr(__p), _M_refcount(__p, __d)
 770         {
 771           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 772           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 773           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 774         }
 775
 776       template<typename _Tp1, typename _Deleter, typename _Alloc>
 777         __shared_ptr(_Tp1* __p, _Deleter __d, const _Alloc& __a)
 778         : _M_ptr(__p), _M_refcount(__p, __d, __a)
 779         {
 780           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 781           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 782           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 783         }
 784
 785       template<typename _Deleter>
 786         __shared_ptr(nullptr_t __p, _Deleter __d)
 787         : _M_ptr(0), _M_refcount(__p, __d)
 788         { }
 789
 790       template<typename _Deleter, typename _Alloc>
 791         __shared_ptr(nullptr_t __p, _Deleter __d, const _Alloc& __a)
 792         : _M_ptr(0), _M_refcount(__p, __d, __a)
 793         { }
 794
 795       template<typename _Tp1>
 796         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p)
 797         : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
 798         { }
 799
 800       //  generated copy constructor, assignment, destructor are fine.
 801
 802       template<typename _Tp1, typename = typename
 803                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 804         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r)
 805         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
 806         { }
 807
 808       __shared_ptr(__shared_ptr&& __r)
 809       : _M_ptr(__r._M_ptr), _M_refcount() // never throws
 810       {
 811         _M_refcount._M_swap(__r._M_refcount);
 812         __r._M_ptr = 0;
 813       }
 814
 815       template<typename _Tp1, typename = typename
 816                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 817         __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r)
 818         : _M_ptr(__r._M_ptr), _M_refcount() // never throws
 819         {
 820           _M_refcount._M_swap(__r._M_refcount);
 821           __r._M_ptr = 0;
 822         }
 823
 824       template<typename _Tp1>
 825         explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
 826         : _M_refcount(__r._M_refcount) // may throw
 827         {
 828           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 829
 830           // It is now safe to copy __r._M_ptr, as
 831           // _M_refcount(__r._M_refcount) did not throw.
 832           _M_ptr = __r._M_ptr;
 833         }
 834
 835       // If an exception is thrown this constructor has no effect.
 836       template<typename _Tp1, typename _Del>
 837         __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
 838         : _M_ptr(__r.get()), _M_refcount()
 839         {
 840           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 841           _Tp1* __tmp = __r.get();
 842           _M_refcount = __shared_count<_Lp>(std::move(__r));
 843           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 844         }
 845
 846 #if _GLIBCXX_DEPRECATED
 847       // Postcondition: use_count() == 1 and __r.get() == 0
 848       template<typename _Tp1>
 849         __shared_ptr(std::auto_ptr<_Tp1>&& __r)
 850         : _M_ptr(__r.get()), _M_refcount()
 851         {
 852           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 853           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 854           _Tp1* __tmp = __r.get();
 855           _M_refcount = __shared_count<_Lp>(std::move(__r));
 856           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 857         }
 858 #endif
 859
 860       /* TODO: use delegating constructor */
 861       constexpr __shared_ptr(nullptr_t)
 862       : _M_ptr(0), _M_refcount() // never throws
 863       { }
 864
 865       template<typename _Tp1>
 866         __shared_ptr&
 867         operator=(const __shared_ptr<_Tp1, _Lp>& __r) // never throws
 868         {
 869           _M_ptr = __r._M_ptr;
 870           _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
 871           return *this;
 872         }
 873
 874 #if _GLIBCXX_DEPRECATED
 875       template<typename _Tp1>
 876         __shared_ptr&
 877         operator=(std::auto_ptr<_Tp1>&& __r)
 878         {
 879           __shared_ptr(std::move(__r)).swap(*this);
 880           return *this;
 881         }
 882 #endif
 883
 884       __shared_ptr&
 885       operator=(__shared_ptr&& __r)
 886       {
 887         __shared_ptr(std::move(__r)).swap(*this);
 888         return *this;
 889       }
 890
 891       template<class _Tp1>
 892         __shared_ptr&
 893         operator=(__shared_ptr<_Tp1, _Lp>&& __r)
 894         {
 895           __shared_ptr(std::move(__r)).swap(*this);
 896           return *this;
 897         }
 898
 899       template<typename _Tp1, typename _Del>
 900         __shared_ptr&
 901         operator=(std::unique_ptr<_Tp1, _Del>&& __r)
 902         {
 903           __shared_ptr(std::move(__r)).swap(*this);
 904           return *this;
 905         }
 906
 907       void
 908       reset() // never throws
 909       { __shared_ptr().swap(*this); }
 910
 911       template<typename _Tp1>
 912         void
 913         reset(_Tp1* __p) // _Tp1 must be complete.
 914         {
 915           // Catch self-reset errors.
 916           _GLIBCXX_DEBUG_ASSERT(__p == 0 || __p != _M_ptr);
 917           __shared_ptr(__p).swap(*this);
 918         }
 919
 920       template<typename _Tp1, typename _Deleter>
 921         void
 922         reset(_Tp1* __p, _Deleter __d)
 923         { __shared_ptr(__p, __d).swap(*this); }
 924
 925       template<typename _Tp1, typename _Deleter, typename _Alloc>
 926         void
 927         reset(_Tp1* __p, _Deleter __d, const _Alloc& __a)
 928         { __shared_ptr(__p, __d, __a).swap(*this); }
 929
 930       // Allow class instantiation when _Tp is [cv-qual] void.
 931       typename std::add_lvalue_reference<_Tp>::type
 932       operator*() const // never throws
 933       {
 934         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 935         return *_M_ptr;
 936       }
 937
 938       _Tp*
 939       operator->() const // never throws
 940       {
 941         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 942         return _M_ptr;
 943       }
 944
 945       _Tp*
 946       get() const // never throws
 947       { return _M_ptr; }
 948
 949       explicit operator bool() const // never throws
 950       { return _M_ptr == 0 ? false : true; }
 951
 952       bool
 953       unique() const // never throws
 954       { return _M_refcount._M_unique(); }
 955
 956       long
 957       use_count() const // never throws
 958       { return _M_refcount._M_get_use_count(); }
 959
 960       void
 961       swap(__shared_ptr<_Tp, _Lp>& __other) // never throws
 962       {
 963         std::swap(_M_ptr, __other._M_ptr);
 964         _M_refcount._M_swap(__other._M_refcount);
 965       }
 966
 967       template<typename _Tp1>
 968         bool
 969         owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const
 970         { return _M_refcount._M_less(__rhs._M_refcount); }
 971
 972       template<typename _Tp1>
 973         bool
 974         owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const
 975         { return _M_refcount._M_less(__rhs._M_refcount); }
 976
 977 #ifdef __GXX_RTTI
 978     protected:
 979       // This constructor is non-standard, it is used by allocate_shared.
 980       template<typename _Alloc, typename... _Args>
 981         __shared_ptr(_Sp_make_shared_tag __tag, _Alloc __a, _Args&&... __args)
 982         : _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,
 983                                 std::forward<_Args>(__args)...)
 984         {
 985           // _M_ptr needs to point to the newly constructed object.
 986           // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
 987           void* __p = _M_refcount._M_get_deleter(typeid(__tag));
 988           _M_ptr = static_cast<_Tp*>(__p);
 989           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
 990         }
 991 #else
 992       template<typename _Alloc>
 993         struct _Deleter
 994         {
 995           void operator()(_Tp* __ptr)
 996           {
 997             _M_alloc.destroy(__ptr);
 998             _M_alloc.deallocate(__ptr, 1);
 999           }
1000           _Alloc _M_alloc;
1001         };
1002
1003       template<typename _Alloc, typename... _Args>
1004         __shared_ptr(_Sp_make_shared_tag __tag, _Alloc __a, _Args&&... __args)
1005         : _M_ptr(), _M_refcount()
1006         {
1007           typedef typename _Alloc::template rebind<_Tp>::other _Alloc2;
1008           _Deleter<_Alloc2> __del = { _Alloc2(__a) };
1009           _M_ptr = __del._M_alloc.allocate(1);
1010           __try
1011             {
1012               __del._M_alloc.construct(_M_ptr, std::forward<_Args>(__args)...);
1013             }
1014           __catch(...)
1015             {
1016               __del._M_alloc.deallocate(_M_ptr, 1);
1017               __throw_exception_again;
1018             }
1019           __shared_count<_Lp> __count(_M_ptr, __del, __del._M_alloc);
1020           _M_refcount._M_swap(__count);
1021           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1022         }
1023 #endif
1024
1025       template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
1026                typename... _Args>
1027         friend __shared_ptr<_Tp1, _Lp1>
1028         __allocate_shared(_Alloc __a, _Args&&... __args);
1029
1030     private:
1031       void*
1032       _M_get_deleter(const std::type_info& __ti) const
1033       { return _M_refcount._M_get_deleter(__ti); }
1034
1035       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1036       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1037
1038       template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1039         friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&);
1040
1041       _Tp*                 _M_ptr;         // Contained pointer.
1042       __shared_count<_Lp>  _M_refcount;    // Reference counter.
1043     };
1044
1045
1046   // 20.8.13.2.7 shared_ptr comparisons
1047   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1048     inline bool
1049     operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1050                const __shared_ptr<_Tp2, _Lp>& __b)
1051     { return __a.get() == __b.get(); }
1052
1053   template<typename _Tp, _Lock_policy _Lp>
1054     inline bool
1055     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t)
1056     { return __a.get() == nullptr; }
1057
1058   template<typename _Tp, _Lock_policy _Lp>
1059     inline bool
1060     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __b)
1061     { return nullptr == __b.get(); }
1062
1063   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1064     inline bool
1065     operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1066                const __shared_ptr<_Tp2, _Lp>& __b)
1067     { return __a.get() != __b.get(); }
1068
1069   template<typename _Tp, _Lock_policy _Lp>
1070     inline bool
1071     operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t)
1072     { return __a.get() != nullptr; }
1073
1074   template<typename _Tp, _Lock_policy _Lp>
1075     inline bool
1076     operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __b)
1077     { return nullptr != __b.get(); }
1078
1079   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1080     inline bool
1081     operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1082               const __shared_ptr<_Tp2, _Lp>& __b)
1083     { return __a.get() < __b.get(); }
1084
1085   template<typename _Sp>
1086     struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1087     {
1088       bool
1089       operator()(const _Sp& __lhs, const _Sp& __rhs) const
1090       {
1091         typedef typename _Sp::element_type element_type;
1092         return std::less<element_type*>()(__lhs.get(), __rhs.get());
1093       }
1094     };
1095
1096   template<typename _Tp, _Lock_policy _Lp>
1097     struct less<__shared_ptr<_Tp, _Lp>>
1098     : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1099     { };
1100
1101   // 2.2.3.8 shared_ptr specialized algorithms.
1102   template<typename _Tp, _Lock_policy _Lp>
1103     inline void
1104     swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b)
1105     { __a.swap(__b); }
1106
1107   // 2.2.3.9 shared_ptr casts
1108
1109   // The seemingly equivalent code:
1110   // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1111   // will eventually result in undefined behaviour, attempting to
1112   // delete the same object twice.
1113   /// static_pointer_cast
1114   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1115     inline __shared_ptr<_Tp, _Lp>
1116     static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
1117     { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1118
1119   // The seemingly equivalent code:
1120   // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1121   // will eventually result in undefined behaviour, attempting to
1122   // delete the same object twice.
1123   /// const_pointer_cast
1124   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1125     inline __shared_ptr<_Tp, _Lp>
1126     const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
1127     { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1128
1129   // The seemingly equivalent code:
1130   // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1131   // will eventually result in undefined behaviour, attempting to
1132   // delete the same object twice.
1133   /// dynamic_pointer_cast
1134   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1135     inline __shared_ptr<_Tp, _Lp>
1136     dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
1137     {
1138       if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1139         return __shared_ptr<_Tp, _Lp>(__r, __p);
1140       return __shared_ptr<_Tp, _Lp>();
1141     }
1142
1143
1144   template<typename _Tp, _Lock_policy _Lp>
1145     class __weak_ptr
1146     {
1147     public:
1148       typedef _Tp element_type;
1149
1150       constexpr __weak_ptr()
1151       : _M_ptr(0), _M_refcount() // never throws
1152       { }
1153
1154       // Generated copy constructor, assignment, destructor are fine.
1155
1156       // The "obvious" converting constructor implementation:
1157       //
1158       //  template<typename _Tp1>
1159       //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1160       //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1161       //    { }
1162       //
1163       // has a serious problem.
1164       //
1165       //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1166       //  conversion may require access to *__r._M_ptr (virtual inheritance).
1167       //
1168       // It is not possible to avoid spurious access violations since
1169       // in multithreaded programs __r._M_ptr may be invalidated at any point.
1170       template<typename _Tp1, typename = typename
1171                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1172         __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1173         : _M_refcount(__r._M_refcount) // never throws
1174         { _M_ptr = __r.lock().get(); }
1175
1176       template<typename _Tp1, typename = typename
1177                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1178         __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r)
1179         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1180         { }
1181
1182       template<typename _Tp1>
1183         __weak_ptr&
1184         operator=(const __weak_ptr<_Tp1, _Lp>& __r) // never throws
1185         {
1186           _M_ptr = __r.lock().get();
1187           _M_refcount = __r._M_refcount;
1188           return *this;
1189         }
1190
1191       template<typename _Tp1>
1192         __weak_ptr&
1193         operator=(const __shared_ptr<_Tp1, _Lp>& __r) // never throws
1194         {
1195           _M_ptr = __r._M_ptr;
1196           _M_refcount = __r._M_refcount;
1197           return *this;
1198         }
1199
1200       __shared_ptr<_Tp, _Lp>
1201       lock() const // never throws
1202       {
1203 #ifdef __GTHREADS
1204         // Optimization: avoid throw overhead.
1205         if (expired())
1206           return __shared_ptr<element_type, _Lp>();
1207
1208         __try
1209           {
1210             return __shared_ptr<element_type, _Lp>(*this);
1211           }
1212         __catch(const bad_weak_ptr&)
1213           {
1214             // Q: How can we get here?
1215             // A: Another thread may have invalidated r after the
1216             //    use_count test above.
1217             return __shared_ptr<element_type, _Lp>();
1218           }
1219
1220 #else
1221         // Optimization: avoid try/catch overhead when single threaded.
1222         return expired() ? __shared_ptr<element_type, _Lp>()
1223                          : __shared_ptr<element_type, _Lp>(*this);
1224
1225 #endif
1226       } // XXX MT
1227
1228       long
1229       use_count() const // never throws
1230       { return _M_refcount._M_get_use_count(); }
1231
1232       bool
1233       expired() const // never throws
1234       { return _M_refcount._M_get_use_count() == 0; }
1235
1236       template<typename _Tp1>
1237         bool
1238         owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1239         { return _M_refcount._M_less(__rhs._M_refcount); }
1240
1241       template<typename _Tp1>
1242         bool
1243         owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1244         { return _M_refcount._M_less(__rhs._M_refcount); }
1245
1246       void
1247       reset() // never throws
1248       { __weak_ptr().swap(*this); }
1249
1250       void
1251       swap(__weak_ptr& __s) // never throws
1252       {
1253         std::swap(_M_ptr, __s._M_ptr);
1254         _M_refcount._M_swap(__s._M_refcount);
1255       }
1256
1257     private:
1258       // Used by __enable_shared_from_this.
1259       void
1260       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount)
1261       {
1262         _M_ptr = __ptr;
1263         _M_refcount = __refcount;
1264       }
1265
1266       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1267       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1268       friend class __enable_shared_from_this<_Tp, _Lp>;
1269       friend class enable_shared_from_this<_Tp>;
1270
1271       _Tp*               _M_ptr;         // Contained pointer.
1272       __weak_count<_Lp>  _M_refcount;    // Reference counter.
1273     };
1274
1275   // 20.8.13.3.7 weak_ptr specialized algorithms.
1276   template<typename _Tp, _Lock_policy _Lp>
1277     inline void
1278     swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b)
1279     { __a.swap(__b); }
1280
1281   template<typename _Tp, typename _Tp1>
1282     struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1283     {
1284       bool
1285       operator()(const _Tp& __lhs, const _Tp& __rhs) const
1286       { return __lhs.owner_before(__rhs); }
1287
1288       bool
1289       operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1290       { return __lhs.owner_before(__rhs); }
1291
1292       bool
1293       operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1294       { return __lhs.owner_before(__rhs); }
1295     };
1296
1297   template<typename _Tp, _Lock_policy _Lp>
1298     struct owner_less<__shared_ptr<_Tp, _Lp>>
1299     : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1300     { };
1301
1302   template<typename _Tp, _Lock_policy _Lp>
1303     struct owner_less<__weak_ptr<_Tp, _Lp>>
1304     : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1305     { };
1306
1307
1308   template<typename _Tp, _Lock_policy _Lp>
1309     class __enable_shared_from_this
1310     {
1311     protected:
1312       constexpr __enable_shared_from_this() { }
1313
1314       __enable_shared_from_this(const __enable_shared_from_this&) { }
1315
1316       __enable_shared_from_this&
1317       operator=(const __enable_shared_from_this&)
1318       { return *this; }
1319
1320       ~__enable_shared_from_this() { }
1321
1322     public:
1323       __shared_ptr<_Tp, _Lp>
1324       shared_from_this()
1325       { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1326
1327       __shared_ptr<const _Tp, _Lp>
1328       shared_from_this() const
1329       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1330
1331     private:
1332       template<typename _Tp1>
1333         void
1334         _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const
1335         { _M_weak_this._M_assign(__p, __n); }
1336
1337       template<typename _Tp1>
1338         friend void
1339         __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
1340                                          const __enable_shared_from_this* __pe,
1341                                          const _Tp1* __px)
1342         {
1343           if (__pe != 0)
1344             __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
1345         }
1346
1347       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
1348     };
1349
1350
1351   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1352     inline __shared_ptr<_Tp, _Lp>
1353     __allocate_shared(_Alloc __a, _Args&&... __args)
1354     {
1355       return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(),
1356           std::forward<_Alloc>(__a), std::forward<_Args>(__args)...);
1357     }
1358
1359   template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1360     inline __shared_ptr<_Tp, _Lp>
1361     __make_shared(_Args&&... __args)
1362     {
1363       typedef typename std::remove_const<_Tp>::type _Tp_nc;
1364       return __allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1365                                          std::forward<_Args>(__args)...);
1366     }
1367
1368   /// std::hash specialization for __shared_ptr.
1369   template<typename _Tp, _Lock_policy _Lp>
1370     struct hash<__shared_ptr<_Tp, _Lp>>
1371     : public std::unary_function<__shared_ptr<_Tp, _Lp>, size_t>
1372     {
1373       size_t
1374       operator()(const __shared_ptr<_Tp, _Lp>& __s) const
1375       { return std::hash<_Tp*>()(__s.get()); }
1376     };
1377
1378 _GLIBCXX_END_NAMESPACE
1379
1380 #endif // _SHARED_PTR_BASE_H