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 namespace std _GLIBCXX_VISIBILITY(default)
  53 {
  54 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  55
  56  /**
  57    *  @brief  Exception possibly thrown by @c shared_ptr.
  58    *  @ingroup exceptions
  59    */
  60   class bad_weak_ptr : public std::exception
  61   {
  62   public:
  63     virtual char const*
  64     what() const throw()
  65     { return "std::bad_weak_ptr"; }
  66   };
  67
  68   // Substitute for bad_weak_ptr object in the case of -fno-exceptions.
  69   inline void
  70   __throw_bad_weak_ptr()
  71   {
  72 #if __EXCEPTIONS
  73     throw bad_weak_ptr();
  74 #else
  75     __builtin_abort();
  76 #endif
  77   }
  78
  79   using __gnu_cxx::_Lock_policy;
  80   using __gnu_cxx::__default_lock_policy;
  81   using __gnu_cxx::_S_single;
  82   using __gnu_cxx::_S_mutex;
  83   using __gnu_cxx::_S_atomic;
  84
  85   // Empty helper class except when the template argument is _S_mutex.
  86   template<_Lock_policy _Lp>
  87     class _Mutex_base
  88     {
  89     protected:
  90       // The atomic policy uses fully-fenced builtins, single doesn't care.
  91       enum { _S_need_barriers = 0 };
  92     };
  93
  94   template<>
  95     class _Mutex_base<_S_mutex>
  96     : public __gnu_cxx::__mutex
  97     {
  98     protected:
  99       // This policy is used when atomic builtins are not available.
 100       // The replacement atomic operations might not have the necessary
 101       // memory barriers.
 102       enum { _S_need_barriers = 1 };
 103     };
 104
 105   template<_Lock_policy _Lp = __default_lock_policy>
 106     class _Sp_counted_base
 107     : public _Mutex_base<_Lp>
 108     {
 109     public:
 110       _Sp_counted_base()
 111       : _M_use_count(1), _M_weak_count(1) { }
 112
 113       virtual
 114       ~_Sp_counted_base() // nothrow
 115       { }
 116
 117       // Called when _M_use_count drops to zero, to release the resources
 118       // managed by *this.
 119       virtual void
 120       _M_dispose() = 0; // nothrow
 121
 122       // Called when _M_weak_count drops to zero.
 123       virtual void
 124       _M_destroy() // nothrow
 125       { delete this; }
 126
 127       virtual void*
 128       _M_get_deleter(const std::type_info&) = 0;
 129
 130       void
 131       _M_add_ref_copy()
 132       { __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
 133
 134       void
 135       _M_add_ref_lock();
 136
 137       void
 138       _M_release() // nothrow
 139       {
 140         // Be race-detector-friendly.  For more info see bits/c++config.
 141         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_use_count);
 142         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
 143           {
 144             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_use_count);
 145             _M_dispose();
 146             // There must be a memory barrier between dispose() and destroy()
 147             // to ensure that the effects of dispose() are observed in the
 148             // thread that runs destroy().
 149             // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
 150             if (_Mutex_base<_Lp>::_S_need_barriers)
 151               {
 152                 _GLIBCXX_READ_MEM_BARRIER;
 153                 _GLIBCXX_WRITE_MEM_BARRIER;
 154               }
 155
 156             // Be race-detector-friendly.  For more info see bits/c++config.
 157             _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 158             if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
 159                                                        -1) == 1)
 160               {
 161                 _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 162                 _M_destroy();
 163               }
 164           }
 165       }
 166
 167       void
 168       _M_weak_add_ref() // nothrow
 169       { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
 170
 171       void
 172       _M_weak_release() // nothrow
 173       {
 174         // Be race-detector-friendly. For more info see bits/c++config.
 175         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 176         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
 177           {
 178             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 179             if (_Mutex_base<_Lp>::_S_need_barriers)
 180               {
 181                 // See _M_release(),
 182                 // destroy() must observe results of dispose()
 183                 _GLIBCXX_READ_MEM_BARRIER;
 184                 _GLIBCXX_WRITE_MEM_BARRIER;
 185               }
 186             _M_destroy();
 187           }
 188       }
 189
 190       long
 191       _M_get_use_count() const // nothrow
 192       {
 193         // No memory barrier is used here so there is no synchronization
 194         // with other threads.
 195         return const_cast<const volatile _Atomic_word&>(_M_use_count);
 196       }
 197
 198     private:
 199       _Sp_counted_base(_Sp_counted_base const&);
 200       _Sp_counted_base& operator=(_Sp_counted_base const&);
 201
 202       _Atomic_word  _M_use_count;     // #shared
 203       _Atomic_word  _M_weak_count;    // #weak + (#shared != 0)
 204     };
 205
 206   template<>
 207     inline void
 208     _Sp_counted_base<_S_single>::
 209     _M_add_ref_lock()
 210     {
 211       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 212         {
 213           _M_use_count = 0;
 214           __throw_bad_weak_ptr();
 215         }
 216     }
 217
 218   template<>
 219     inline void
 220     _Sp_counted_base<_S_mutex>::
 221     _M_add_ref_lock()
 222     {
 223       __gnu_cxx::__scoped_lock sentry(*this);
 224       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 225         {
 226           _M_use_count = 0;
 227           __throw_bad_weak_ptr();
 228         }
 229     }
 230
 231   template<>
 232     inline void
 233     _Sp_counted_base<_S_atomic>::
 234     _M_add_ref_lock()
 235     {
 236       // Perform lock-free add-if-not-zero operation.
 237       _Atomic_word __count;
 238       do
 239         {
 240           __count = _M_use_count;
 241           if (__count == 0)
 242             __throw_bad_weak_ptr();
 243
 244           // Replace the current counter value with the old value + 1, as
 245           // long as it's not changed meanwhile.
 246         }
 247       while (!__sync_bool_compare_and_swap(&_M_use_count, __count,
 248                                            __count + 1));
 249     }
 250
 251
 252   // Forward declarations.
 253   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 254     class __shared_ptr;
 255
 256   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 257     class __weak_ptr;
 258
 259   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 260     class __enable_shared_from_this;
 261
 262   template<typename _Tp>
 263     class shared_ptr;
 264
 265   template<typename _Tp>
 266     class weak_ptr;
 267
 268   template<typename _Tp>
 269     struct owner_less;
 270
 271   template<typename _Tp>
 272     class enable_shared_from_this;
 273
 274   template<_Lock_policy _Lp = __default_lock_policy>
 275     class __weak_count;
 276
 277   template<_Lock_policy _Lp = __default_lock_policy>
 278     class __shared_count;
 279
 280
 281   // Counted ptr with no deleter or allocator support
 282   template<typename _Ptr, _Lock_policy _Lp>
 283     class _Sp_counted_ptr : public _Sp_counted_base<_Lp>
 284     {
 285     public:
 286       explicit
 287       _Sp_counted_ptr(_Ptr __p)
 288       : _M_ptr(__p) { }
 289
 290       virtual void
 291       _M_dispose() // nothrow
 292       { delete _M_ptr; }
 293
 294       virtual void
 295       _M_destroy() // nothrow
 296       { delete this; }
 297
 298       virtual void*
 299       _M_get_deleter(const std::type_info&)
 300       { return 0; }
 301
 302       _Sp_counted_ptr(const _Sp_counted_ptr&) = delete;
 303       _Sp_counted_ptr& operator=(const _Sp_counted_ptr&) = delete;
 304
 305     protected:
 306       _Ptr             _M_ptr;  // copy constructor must not throw
 307     };
 308
 309   template<>
 310     inline void
 311     _Sp_counted_ptr<nullptr_t, _S_single>::_M_dispose() { }
 312
 313   template<>
 314     inline void
 315     _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() { }
 316
 317   template<>
 318     inline void
 319     _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() { }
 320
 321   // Support for custom deleter and/or allocator
 322   template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>
 323     class _Sp_counted_deleter : public _Sp_counted_base<_Lp>
 324     {
 325       typedef typename _Alloc::template
 326           rebind<_Sp_counted_deleter>::other _My_alloc_type;
 327
 328       // Helper class that stores the Deleter and also acts as an allocator.
 329       // Used to dispose of the owned pointer and the internal refcount
 330       // Requires that copies of _Alloc can free each other's memory.
 331       struct _My_Deleter
 332       : public _My_alloc_type    // copy constructor must not throw
 333       {
 334         _Deleter _M_del;         // copy constructor must not throw
 335         _My_Deleter(_Deleter __d, const _Alloc& __a)
 336         : _My_alloc_type(__a), _M_del(__d) { }
 337       };
 338
 339     public:
 340       // __d(__p) must not throw.
 341       _Sp_counted_deleter(_Ptr __p, _Deleter __d)
 342       : _M_ptr(__p), _M_del(__d, _Alloc()) { }
 343
 344       // __d(__p) must not throw.
 345       _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a)
 346       : _M_ptr(__p), _M_del(__d, __a) { }
 347
 348       virtual void
 349       _M_dispose() // nothrow
 350       { _M_del._M_del(_M_ptr); }
 351
 352       virtual void
 353       _M_destroy() // nothrow
 354       {
 355         _My_alloc_type __a(_M_del);
 356         this->~_Sp_counted_deleter();
 357         __a.deallocate(this, 1);
 358       }
 359
 360       virtual void*
 361       _M_get_deleter(const std::type_info& __ti)
 362       {
 363 #ifdef __GXX_RTTI
 364         return __ti == typeid(_Deleter) ? &_M_del._M_del : 0;
 365 #else
 366         return 0;
 367 #endif
 368       }
 369
 370     protected:
 371       _Ptr             _M_ptr;  // copy constructor must not throw
 372       _My_Deleter      _M_del;  // copy constructor must not throw
 373     };
 374
 375   // helpers for make_shared / allocate_shared
 376
 377   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::_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::_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*, const _Alloc& __a,
 508                        _Args&&... __args)
 509         : _M_pi(0)
 510         {
 511           typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
 512           typedef typename _Alloc::template rebind<_Sp_cp_type>::other _Alloc2;
 513           _Alloc2 __a2(__a);
 514           __try
 515             {
 516               _M_pi = __a2.allocate(1);
 517               ::new(static_cast<void*>(_M_pi)) _Sp_cp_type(__a,
 518                     std::forward<_Args>(__args)...);
 519             }
 520           __catch(...)
 521             {
 522               if (_M_pi)
 523                 __a2.deallocate(static_cast<_Sp_cp_type*>(_M_pi), 1);
 524               __throw_exception_again;
 525             }
 526         }
 527
 528 #if _GLIBCXX_DEPRECATED
 529       // Special case for auto_ptr<_Tp> to provide the strong guarantee.
 530       template<typename _Tp>
 531         explicit
 532         __shared_count(std::auto_ptr<_Tp>&& __r)
 533         : _M_pi(new _Sp_counted_ptr<_Tp*, _Lp>(__r.get()))
 534         { __r.release(); }
 535 #endif
 536
 537       // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
 538       template<typename _Tp, typename _Del>
 539         explicit
 540         __shared_count(std::unique_ptr<_Tp, _Del>&& __r)
 541         : _M_pi(_S_create_from_up(std::move(__r)))
 542         { __r.release(); }
 543
 544       // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
 545       explicit __shared_count(const __weak_count<_Lp>& __r);
 546
 547       ~__shared_count() // nothrow
 548       {
 549         if (_M_pi != 0)
 550           _M_pi->_M_release();
 551       }
 552
 553       __shared_count(const __shared_count& __r)
 554       : _M_pi(__r._M_pi) // nothrow
 555       {
 556         if (_M_pi != 0)
 557           _M_pi->_M_add_ref_copy();
 558       }
 559
 560       __shared_count&
 561       operator=(const __shared_count& __r) // nothrow
 562       {
 563         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 564         if (__tmp != _M_pi)
 565           {
 566             if (__tmp != 0)
 567               __tmp->_M_add_ref_copy();
 568             if (_M_pi != 0)
 569               _M_pi->_M_release();
 570             _M_pi = __tmp;
 571           }
 572         return *this;
 573       }
 574
 575       void
 576       _M_swap(__shared_count& __r) // nothrow
 577       {
 578         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 579         __r._M_pi = _M_pi;
 580         _M_pi = __tmp;
 581       }
 582
 583       long
 584       _M_get_use_count() const // nothrow
 585       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 586
 587       bool
 588       _M_unique() const // nothrow
 589       { return this->_M_get_use_count() == 1; }
 590
 591       void*
 592       _M_get_deleter(const std::type_info& __ti) const
 593       { return _M_pi ? _M_pi->_M_get_deleter(__ti) : 0; }
 594
 595       bool
 596       _M_less(const __shared_count& __rhs) const
 597       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 598
 599       bool
 600       _M_less(const __weak_count<_Lp>& __rhs) const
 601       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 602
 603       // Friend function injected into enclosing namespace and found by ADL
 604       friend inline bool
 605       operator==(const __shared_count& __a, const __shared_count& __b)
 606       { return __a._M_pi == __b._M_pi; }
 607
 608     private:
 609       friend class __weak_count<_Lp>;
 610
 611       template<typename _Tp, typename _Del>
 612         static _Sp_counted_base<_Lp>*
 613         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 614           typename std::enable_if<!std::is_reference<_Del>::value>::type* = 0)
 615         {
 616           return new _Sp_counted_deleter<_Tp*, _Del, std::allocator<_Tp>,
 617             _Lp>(__r.get(), __r.get_deleter());
 618         }
 619
 620       template<typename _Tp, typename _Del>
 621         static _Sp_counted_base<_Lp>*
 622         _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
 623           typename std::enable_if<std::is_reference<_Del>::value>::type* = 0)
 624         {
 625           typedef typename std::remove_reference<_Del>::type _Del1;
 626           typedef std::reference_wrapper<_Del1> _Del2;
 627           return new _Sp_counted_deleter<_Tp*, _Del2, std::allocator<_Tp>,
 628             _Lp>(__r.get(), std::ref(__r.get_deleter()));
 629         }
 630
 631       _Sp_counted_base<_Lp>*  _M_pi;
 632     };
 633
 634
 635   template<_Lock_policy _Lp>
 636     class __weak_count
 637     {
 638     public:
 639       constexpr __weak_count() : _M_pi(0) // nothrow
 640       { }
 641
 642       __weak_count(const __shared_count<_Lp>& __r) : _M_pi(__r._M_pi) // nothrow
 643       {
 644         if (_M_pi != 0)
 645           _M_pi->_M_weak_add_ref();
 646       }
 647
 648       __weak_count(const __weak_count<_Lp>& __r) : _M_pi(__r._M_pi) // nothrow
 649       {
 650         if (_M_pi != 0)
 651           _M_pi->_M_weak_add_ref();
 652       }
 653
 654       ~__weak_count() // nothrow
 655       {
 656         if (_M_pi != 0)
 657           _M_pi->_M_weak_release();
 658       }
 659
 660       __weak_count<_Lp>&
 661       operator=(const __shared_count<_Lp>& __r) // nothrow
 662       {
 663         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 664         if (__tmp != 0)
 665           __tmp->_M_weak_add_ref();
 666         if (_M_pi != 0)
 667           _M_pi->_M_weak_release();
 668         _M_pi = __tmp;
 669         return *this;
 670       }
 671
 672       __weak_count<_Lp>&
 673       operator=(const __weak_count<_Lp>& __r) // nothrow
 674       {
 675         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 676         if (__tmp != 0)
 677           __tmp->_M_weak_add_ref();
 678         if (_M_pi != 0)
 679           _M_pi->_M_weak_release();
 680         _M_pi = __tmp;
 681         return *this;
 682       }
 683
 684       void
 685       _M_swap(__weak_count<_Lp>& __r) // nothrow
 686       {
 687         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 688         __r._M_pi = _M_pi;
 689         _M_pi = __tmp;
 690       }
 691
 692       long
 693       _M_get_use_count() const // nothrow
 694       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 695
 696       bool
 697       _M_less(const __weak_count& __rhs) const
 698       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 699
 700       bool
 701       _M_less(const __shared_count<_Lp>& __rhs) const
 702       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 703
 704       // Friend function injected into enclosing namespace and found by ADL
 705       friend inline bool
 706       operator==(const __weak_count& __a, const __weak_count& __b)
 707       { return __a._M_pi == __b._M_pi; }
 708
 709     private:
 710       friend class __shared_count<_Lp>;
 711
 712       _Sp_counted_base<_Lp>*  _M_pi;
 713     };
 714
 715   // Now that __weak_count is defined we can define this constructor:
 716   template<_Lock_policy _Lp>
 717     inline __shared_count<_Lp>:: __shared_count(const __weak_count<_Lp>& __r)
 718     : _M_pi(__r._M_pi)
 719     {
 720       if (_M_pi != 0)
 721         _M_pi->_M_add_ref_lock();
 722       else
 723         __throw_bad_weak_ptr();
 724     }
 725
 726
 727   // Support for enable_shared_from_this.
 728
 729   // Friend of __enable_shared_from_this.
 730   template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
 731     void
 732     __enable_shared_from_this_helper(const __shared_count<_Lp>&,
 733                                      const __enable_shared_from_this<_Tp1,
 734                                      _Lp>*, const _Tp2*);
 735
 736   // Friend of enable_shared_from_this.
 737   template<typename _Tp1, typename _Tp2>
 738     void
 739     __enable_shared_from_this_helper(const __shared_count<>&,
 740                                      const enable_shared_from_this<_Tp1>*,
 741                                      const _Tp2*);
 742
 743   template<_Lock_policy _Lp>
 744     inline void
 745     __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...)
 746     { }
 747
 748
 749   template<typename _Tp, _Lock_policy _Lp>
 750     class __shared_ptr
 751     {
 752     public:
 753       typedef _Tp   element_type;
 754
 755       constexpr __shared_ptr()
 756       : _M_ptr(0), _M_refcount() // never throws
 757       { }
 758
 759       template<typename _Tp1>
 760         explicit __shared_ptr(_Tp1* __p)
 761         : _M_ptr(__p), _M_refcount(__p)
 762         {
 763           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 764           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 765           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 766         }
 767
 768       template<typename _Tp1, typename _Deleter>
 769         __shared_ptr(_Tp1* __p, _Deleter __d)
 770         : _M_ptr(__p), _M_refcount(__p, __d)
 771         {
 772           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 773           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 774           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 775         }
 776
 777       template<typename _Tp1, typename _Deleter, typename _Alloc>
 778         __shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
 779         : _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
 780         {
 781           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 782           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 783           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 784         }
 785
 786       template<typename _Deleter>
 787         __shared_ptr(nullptr_t __p, _Deleter __d)
 788         : _M_ptr(0), _M_refcount(__p, __d)
 789         { }
 790
 791       template<typename _Deleter, typename _Alloc>
 792         __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
 793         : _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
 794         { }
 795
 796       template<typename _Tp1>
 797         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p)
 798         : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
 799         { }
 800
 801       //  generated copy constructor, assignment, destructor are fine.
 802
 803       template<typename _Tp1, typename = typename
 804                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 805         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r)
 806         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
 807         { }
 808
 809       __shared_ptr(__shared_ptr&& __r)
 810       : _M_ptr(__r._M_ptr), _M_refcount() // never throws
 811       {
 812         _M_refcount._M_swap(__r._M_refcount);
 813         __r._M_ptr = 0;
 814       }
 815
 816       template<typename _Tp1, typename = typename
 817                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 818         __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r)
 819         : _M_ptr(__r._M_ptr), _M_refcount() // never throws
 820         {
 821           _M_refcount._M_swap(__r._M_refcount);
 822           __r._M_ptr = 0;
 823         }
 824
 825       template<typename _Tp1>
 826         explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
 827         : _M_refcount(__r._M_refcount) // may throw
 828         {
 829           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 830
 831           // It is now safe to copy __r._M_ptr, as
 832           // _M_refcount(__r._M_refcount) did not throw.
 833           _M_ptr = __r._M_ptr;
 834         }
 835
 836       // If an exception is thrown this constructor has no effect.
 837       template<typename _Tp1, typename _Del>
 838         __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
 839         : _M_ptr(__r.get()), _M_refcount()
 840         {
 841           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 842           _Tp1* __tmp = __r.get();
 843           _M_refcount = __shared_count<_Lp>(std::move(__r));
 844           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 845         }
 846
 847 #if _GLIBCXX_DEPRECATED
 848       // Postcondition: use_count() == 1 and __r.get() == 0
 849       template<typename _Tp1>
 850         __shared_ptr(std::auto_ptr<_Tp1>&& __r)
 851         : _M_ptr(__r.get()), _M_refcount()
 852         {
 853           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 854           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 855           _Tp1* __tmp = __r.get();
 856           _M_refcount = __shared_count<_Lp>(std::move(__r));
 857           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 858         }
 859 #endif
 860
 861       /* TODO: use delegating constructor */
 862       constexpr __shared_ptr(nullptr_t)
 863       : _M_ptr(0), _M_refcount() // never throws
 864       { }
 865
 866       template<typename _Tp1>
 867         __shared_ptr&
 868         operator=(const __shared_ptr<_Tp1, _Lp>& __r) // never throws
 869         {
 870           _M_ptr = __r._M_ptr;
 871           _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
 872           return *this;
 873         }
 874
 875 #if _GLIBCXX_DEPRECATED
 876       template<typename _Tp1>
 877         __shared_ptr&
 878         operator=(std::auto_ptr<_Tp1>&& __r)
 879         {
 880           __shared_ptr(std::move(__r)).swap(*this);
 881           return *this;
 882         }
 883 #endif
 884
 885       __shared_ptr&
 886       operator=(__shared_ptr&& __r)
 887       {
 888         __shared_ptr(std::move(__r)).swap(*this);
 889         return *this;
 890       }
 891
 892       template<class _Tp1>
 893         __shared_ptr&
 894         operator=(__shared_ptr<_Tp1, _Lp>&& __r)
 895         {
 896           __shared_ptr(std::move(__r)).swap(*this);
 897           return *this;
 898         }
 899
 900       template<typename _Tp1, typename _Del>
 901         __shared_ptr&
 902         operator=(std::unique_ptr<_Tp1, _Del>&& __r)
 903         {
 904           __shared_ptr(std::move(__r)).swap(*this);
 905           return *this;
 906         }
 907
 908       void
 909       reset() // never throws
 910       { __shared_ptr().swap(*this); }
 911
 912       template<typename _Tp1>
 913         void
 914         reset(_Tp1* __p) // _Tp1 must be complete.
 915         {
 916           // Catch self-reset errors.
 917           _GLIBCXX_DEBUG_ASSERT(__p == 0 || __p != _M_ptr);
 918           __shared_ptr(__p).swap(*this);
 919         }
 920
 921       template<typename _Tp1, typename _Deleter>
 922         void
 923         reset(_Tp1* __p, _Deleter __d)
 924         { __shared_ptr(__p, __d).swap(*this); }
 925
 926       template<typename _Tp1, typename _Deleter, typename _Alloc>
 927         void
 928         reset(_Tp1* __p, _Deleter __d, _Alloc __a)
 929         { __shared_ptr(__p, __d, std::move(__a)).swap(*this); }
 930
 931       // Allow class instantiation when _Tp is [cv-qual] void.
 932       typename std::add_lvalue_reference<_Tp>::type
 933       operator*() const // never throws
 934       {
 935         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 936         return *_M_ptr;
 937       }
 938
 939       _Tp*
 940       operator->() const // never throws
 941       {
 942         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 943         return _M_ptr;
 944       }
 945
 946       _Tp*
 947       get() const // never throws
 948       { return _M_ptr; }
 949
 950       explicit operator bool() const // never throws
 951       { return _M_ptr == 0 ? false : true; }
 952
 953       bool
 954       unique() const // never throws
 955       { return _M_refcount._M_unique(); }
 956
 957       long
 958       use_count() const // never throws
 959       { return _M_refcount._M_get_use_count(); }
 960
 961       void
 962       swap(__shared_ptr<_Tp, _Lp>& __other) // never throws
 963       {
 964         std::swap(_M_ptr, __other._M_ptr);
 965         _M_refcount._M_swap(__other._M_refcount);
 966       }
 967
 968       template<typename _Tp1>
 969         bool
 970         owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const
 971         { return _M_refcount._M_less(__rhs._M_refcount); }
 972
 973       template<typename _Tp1>
 974         bool
 975         owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const
 976         { return _M_refcount._M_less(__rhs._M_refcount); }
 977
 978 #ifdef __GXX_RTTI
 979     protected:
 980       // This constructor is non-standard, it is used by allocate_shared.
 981       template<typename _Alloc, typename... _Args>
 982         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
 983                      _Args&&... __args)
 984         : _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,
 985                                 std::forward<_Args>(__args)...)
 986         {
 987           // _M_ptr needs to point to the newly constructed object.
 988           // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
 989           void* __p = _M_refcount._M_get_deleter(typeid(__tag));
 990           _M_ptr = static_cast<_Tp*>(__p);
 991           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
 992         }
 993 #else
 994       template<typename _Alloc>
 995         struct _Deleter
 996         {
 997           void operator()(_Tp* __ptr)
 998           {
 999             _M_alloc.destroy(__ptr);
1000             _M_alloc.deallocate(__ptr, 1);
1001           }
1002           _Alloc _M_alloc;
1003         };
1004
1005       template<typename _Alloc, typename... _Args>
1006         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1007                      _Args&&... __args)
1008         : _M_ptr(), _M_refcount()
1009         {
1010           typedef typename _Alloc::template rebind<_Tp>::other _Alloc2;
1011           _Deleter<_Alloc2> __del = { _Alloc2(__a) };
1012           _M_ptr = __del._M_alloc.allocate(1);
1013           __try
1014             {
1015               __del._M_alloc.construct(_M_ptr, std::forward<_Args>(__args)...);
1016             }
1017           __catch(...)
1018             {
1019               __del._M_alloc.deallocate(_M_ptr, 1);
1020               __throw_exception_again;
1021             }
1022           __shared_count<_Lp> __count(_M_ptr, __del, __del._M_alloc);
1023           _M_refcount._M_swap(__count);
1024           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1025         }
1026 #endif
1027
1028       template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
1029                typename... _Args>
1030         friend __shared_ptr<_Tp1, _Lp1>
1031         __allocate_shared(const _Alloc& __a, _Args&&... __args);
1032
1033     private:
1034       void*
1035       _M_get_deleter(const std::type_info& __ti) const
1036       { return _M_refcount._M_get_deleter(__ti); }
1037
1038       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1039       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1040
1041       template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1042         friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&);
1043
1044       _Tp*                 _M_ptr;         // Contained pointer.
1045       __shared_count<_Lp>  _M_refcount;    // Reference counter.
1046     };
1047
1048
1049   // 20.8.13.2.7 shared_ptr comparisons
1050   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1051     inline bool
1052     operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1053                const __shared_ptr<_Tp2, _Lp>& __b)
1054     { return __a.get() == __b.get(); }
1055
1056   template<typename _Tp, _Lock_policy _Lp>
1057     inline bool
1058     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t)
1059     { return __a.get() == nullptr; }
1060
1061   template<typename _Tp, _Lock_policy _Lp>
1062     inline bool
1063     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __b)
1064     { return nullptr == __b.get(); }
1065
1066   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1067     inline bool
1068     operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1069                const __shared_ptr<_Tp2, _Lp>& __b)
1070     { return __a.get() != __b.get(); }
1071
1072   template<typename _Tp, _Lock_policy _Lp>
1073     inline bool
1074     operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t)
1075     { return __a.get() != nullptr; }
1076
1077   template<typename _Tp, _Lock_policy _Lp>
1078     inline bool
1079     operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __b)
1080     { return nullptr != __b.get(); }
1081
1082   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1083     inline bool
1084     operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1085               const __shared_ptr<_Tp2, _Lp>& __b)
1086     { return __a.get() < __b.get(); }
1087
1088   template<typename _Sp>
1089     struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1090     {
1091       bool
1092       operator()(const _Sp& __lhs, const _Sp& __rhs) const
1093       {
1094         typedef typename _Sp::element_type element_type;
1095         return std::less<element_type*>()(__lhs.get(), __rhs.get());
1096       }
1097     };
1098
1099   template<typename _Tp, _Lock_policy _Lp>
1100     struct less<__shared_ptr<_Tp, _Lp>>
1101     : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1102     { };
1103
1104   // 2.2.3.8 shared_ptr specialized algorithms.
1105   template<typename _Tp, _Lock_policy _Lp>
1106     inline void
1107     swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b)
1108     { __a.swap(__b); }
1109
1110   // 2.2.3.9 shared_ptr casts
1111
1112   // The seemingly equivalent code:
1113   // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1114   // will eventually result in undefined behaviour, attempting to
1115   // delete the same object twice.
1116   /// static_pointer_cast
1117   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1118     inline __shared_ptr<_Tp, _Lp>
1119     static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
1120     { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1121
1122   // The seemingly equivalent code:
1123   // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1124   // will eventually result in undefined behaviour, attempting to
1125   // delete the same object twice.
1126   /// const_pointer_cast
1127   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1128     inline __shared_ptr<_Tp, _Lp>
1129     const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
1130     { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1131
1132   // The seemingly equivalent code:
1133   // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1134   // will eventually result in undefined behaviour, attempting to
1135   // delete the same object twice.
1136   /// dynamic_pointer_cast
1137   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1138     inline __shared_ptr<_Tp, _Lp>
1139     dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r)
1140     {
1141       if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1142         return __shared_ptr<_Tp, _Lp>(__r, __p);
1143       return __shared_ptr<_Tp, _Lp>();
1144     }
1145
1146
1147   template<typename _Tp, _Lock_policy _Lp>
1148     class __weak_ptr
1149     {
1150     public:
1151       typedef _Tp element_type;
1152
1153       constexpr __weak_ptr()
1154       : _M_ptr(0), _M_refcount() // never throws
1155       { }
1156
1157       // Generated copy constructor, assignment, destructor are fine.
1158
1159       // The "obvious" converting constructor implementation:
1160       //
1161       //  template<typename _Tp1>
1162       //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1163       //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1164       //    { }
1165       //
1166       // has a serious problem.
1167       //
1168       //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1169       //  conversion may require access to *__r._M_ptr (virtual inheritance).
1170       //
1171       // It is not possible to avoid spurious access violations since
1172       // in multithreaded programs __r._M_ptr may be invalidated at any point.
1173       template<typename _Tp1, typename = typename
1174                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1175         __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1176         : _M_refcount(__r._M_refcount) // never throws
1177         { _M_ptr = __r.lock().get(); }
1178
1179       template<typename _Tp1, typename = typename
1180                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1181         __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r)
1182         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1183         { }
1184
1185       template<typename _Tp1>
1186         __weak_ptr&
1187         operator=(const __weak_ptr<_Tp1, _Lp>& __r) // never throws
1188         {
1189           _M_ptr = __r.lock().get();
1190           _M_refcount = __r._M_refcount;
1191           return *this;
1192         }
1193
1194       template<typename _Tp1>
1195         __weak_ptr&
1196         operator=(const __shared_ptr<_Tp1, _Lp>& __r) // never throws
1197         {
1198           _M_ptr = __r._M_ptr;
1199           _M_refcount = __r._M_refcount;
1200           return *this;
1201         }
1202
1203       __shared_ptr<_Tp, _Lp>
1204       lock() const // never throws
1205       {
1206 #ifdef __GTHREADS
1207         // Optimization: avoid throw overhead.
1208         if (expired())
1209           return __shared_ptr<element_type, _Lp>();
1210
1211         __try
1212           {
1213             return __shared_ptr<element_type, _Lp>(*this);
1214           }
1215         __catch(const bad_weak_ptr&)
1216           {
1217             // Q: How can we get here?
1218             // A: Another thread may have invalidated r after the
1219             //    use_count test above.
1220             return __shared_ptr<element_type, _Lp>();
1221           }
1222
1223 #else
1224         // Optimization: avoid try/catch overhead when single threaded.
1225         return expired() ? __shared_ptr<element_type, _Lp>()
1226                          : __shared_ptr<element_type, _Lp>(*this);
1227
1228 #endif
1229       } // XXX MT
1230
1231       long
1232       use_count() const // never throws
1233       { return _M_refcount._M_get_use_count(); }
1234
1235       bool
1236       expired() const // never throws
1237       { return _M_refcount._M_get_use_count() == 0; }
1238
1239       template<typename _Tp1>
1240         bool
1241         owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1242         { return _M_refcount._M_less(__rhs._M_refcount); }
1243
1244       template<typename _Tp1>
1245         bool
1246         owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1247         { return _M_refcount._M_less(__rhs._M_refcount); }
1248
1249       void
1250       reset() // never throws
1251       { __weak_ptr().swap(*this); }
1252
1253       void
1254       swap(__weak_ptr& __s) // never throws
1255       {
1256         std::swap(_M_ptr, __s._M_ptr);
1257         _M_refcount._M_swap(__s._M_refcount);
1258       }
1259
1260     private:
1261       // Used by __enable_shared_from_this.
1262       void
1263       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount)
1264       {
1265         _M_ptr = __ptr;
1266         _M_refcount = __refcount;
1267       }
1268
1269       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1270       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1271       friend class __enable_shared_from_this<_Tp, _Lp>;
1272       friend class enable_shared_from_this<_Tp>;
1273
1274       _Tp*               _M_ptr;         // Contained pointer.
1275       __weak_count<_Lp>  _M_refcount;    // Reference counter.
1276     };
1277
1278   // 20.8.13.3.7 weak_ptr specialized algorithms.
1279   template<typename _Tp, _Lock_policy _Lp>
1280     inline void
1281     swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b)
1282     { __a.swap(__b); }
1283
1284   template<typename _Tp, typename _Tp1>
1285     struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1286     {
1287       bool
1288       operator()(const _Tp& __lhs, const _Tp& __rhs) const
1289       { return __lhs.owner_before(__rhs); }
1290
1291       bool
1292       operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1293       { return __lhs.owner_before(__rhs); }
1294
1295       bool
1296       operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1297       { return __lhs.owner_before(__rhs); }
1298     };
1299
1300   template<typename _Tp, _Lock_policy _Lp>
1301     struct owner_less<__shared_ptr<_Tp, _Lp>>
1302     : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1303     { };
1304
1305   template<typename _Tp, _Lock_policy _Lp>
1306     struct owner_less<__weak_ptr<_Tp, _Lp>>
1307     : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1308     { };
1309
1310
1311   template<typename _Tp, _Lock_policy _Lp>
1312     class __enable_shared_from_this
1313     {
1314     protected:
1315       constexpr __enable_shared_from_this() { }
1316
1317       __enable_shared_from_this(const __enable_shared_from_this&) { }
1318
1319       __enable_shared_from_this&
1320       operator=(const __enable_shared_from_this&)
1321       { return *this; }
1322
1323       ~__enable_shared_from_this() { }
1324
1325     public:
1326       __shared_ptr<_Tp, _Lp>
1327       shared_from_this()
1328       { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1329
1330       __shared_ptr<const _Tp, _Lp>
1331       shared_from_this() const
1332       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1333
1334     private:
1335       template<typename _Tp1>
1336         void
1337         _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const
1338         { _M_weak_this._M_assign(__p, __n); }
1339
1340       template<typename _Tp1>
1341         friend void
1342         __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
1343                                          const __enable_shared_from_this* __pe,
1344                                          const _Tp1* __px)
1345         {
1346           if (__pe != 0)
1347             __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
1348         }
1349
1350       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
1351     };
1352
1353
1354   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1355     inline __shared_ptr<_Tp, _Lp>
1356     __allocate_shared(const _Alloc& __a, _Args&&... __args)
1357     {
1358       return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
1359                                     std::forward<_Args>(__args)...);
1360     }
1361
1362   template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1363     inline __shared_ptr<_Tp, _Lp>
1364     __make_shared(_Args&&... __args)
1365     {
1366       typedef typename std::remove_const<_Tp>::type _Tp_nc;
1367       return __allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1368                                          std::forward<_Args>(__args)...);
1369     }
1370
1371   /// std::hash specialization for __shared_ptr.
1372   template<typename _Tp, _Lock_policy _Lp>
1373     struct hash<__shared_ptr<_Tp, _Lp>>
1374     : public std::unary_function<__shared_ptr<_Tp, _Lp>, size_t>
1375     {
1376       size_t
1377       operator()(const __shared_ptr<_Tp, _Lp>& __s) const
1378       { return std::hash<_Tp*>()(__s.get()); }
1379     };
1380
1381 _GLIBCXX_END_NAMESPACE_VERSION
1382 } // namespace
1383
1384 #endif // _SHARED_PTR_BASE_H