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