gcc-4_8-branch/libstdc++-v3/include/bits/shared_ptr_base.h

   1 // shared_ptr and weak_ptr implementation details -*- C++ -*-
   2
   3 // Copyright (C) 2007-2013 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 // GCC Note: Based on files from version 1.32.0 of the Boost library.
  26
  27 //  shared_count.hpp
  28 //  Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
  29
  30 //  shared_ptr.hpp
  31 //  Copyright (C) 1998, 1999 Greg Colvin and Beman Dawes.
  32 //  Copyright (C) 2001, 2002, 2003 Peter Dimov
  33
  34 //  weak_ptr.hpp
  35 //  Copyright (C) 2001, 2002, 2003 Peter Dimov
  36
  37 //  enable_shared_from_this.hpp
  38 //  Copyright (C) 2002 Peter Dimov
  39
  40 // Distributed under the Boost Software License, Version 1.0. (See
  41 // accompanying file LICENSE_1_0.txt or copy at
  42 // http://www.boost.org/LICENSE_1_0.txt)
  43
  44 /** @file bits/shared_ptr_base.h
  45  *  This is an internal header file, included by other library headers.
  46  *  Do not attempt to use it directly. @headername{memory}
  47  */
  48
  49 #ifndef _SHARED_PTR_BASE_H
  50 #define _SHARED_PTR_BASE_H 1
  51
  52 namespace std _GLIBCXX_VISIBILITY(default)
  53 {
  54 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  55
  56 #if _GLIBCXX_USE_DEPRECATED
  57   template<typename> class auto_ptr;
  58 #endif
  59
  60  /**
  61    *  @brief  Exception possibly thrown by @c shared_ptr.
  62    *  @ingroup exceptions
  63    */
  64   class bad_weak_ptr : public std::exception
  65   {
  66   public:
  67     virtual char const*
  68     what() const noexcept;
  69
  70     virtual ~bad_weak_ptr() noexcept;
  71   };
  72
  73   // Substitute for bad_weak_ptr object in the case of -fno-exceptions.
  74   inline void
  75   __throw_bad_weak_ptr()
  76   { _GLIBCXX_THROW_OR_ABORT(bad_weak_ptr()); }
  77
  78   using __gnu_cxx::_Lock_policy;
  79   using __gnu_cxx::__default_lock_policy;
  80   using __gnu_cxx::_S_single;
  81   using __gnu_cxx::_S_mutex;
  82   using __gnu_cxx::_S_atomic;
  83
  84   // Empty helper class except when the template argument is _S_mutex.
  85   template<_Lock_policy _Lp>
  86     class _Mutex_base
  87     {
  88     protected:
  89       // The atomic policy uses fully-fenced builtins, single doesn't care.
  90       enum { _S_need_barriers = 0 };
  91     };
  92
  93   template<>
  94     class _Mutex_base<_S_mutex>
  95     : public __gnu_cxx::__mutex
  96     {
  97     protected:
  98       // This policy is used when atomic builtins are not available.
  99       // The replacement atomic operations might not have the necessary
 100       // memory barriers.
 101       enum { _S_need_barriers = 1 };
 102     };
 103
 104   template<_Lock_policy _Lp = __default_lock_policy>
 105     class _Sp_counted_base
 106     : public _Mutex_base<_Lp>
 107     {
 108     public:
 109       _Sp_counted_base() noexcept
 110       : _M_use_count(1), _M_weak_count(1) { }
 111
 112       virtual
 113       ~_Sp_counted_base() noexcept
 114       { }
 115
 116       // Called when _M_use_count drops to zero, to release the resources
 117       // managed by *this.
 118       virtual void
 119       _M_dispose() noexcept = 0;
 120
 121       // Called when _M_weak_count drops to zero.
 122       virtual void
 123       _M_destroy() noexcept
 124       { delete this; }
 125
 126       virtual void*
 127       _M_get_deleter(const std::type_info&) = 0;
 128
 129       void
 130       _M_add_ref_copy()
 131       { __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
 132
 133       void
 134       _M_add_ref_lock();
 135
 136       void
 137       _M_release() noexcept
 138       {
 139         // Be race-detector-friendly.  For more info see bits/c++config.
 140         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_use_count);
 141         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
 142           {
 143             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_use_count);
 144             _M_dispose();
 145             // There must be a memory barrier between dispose() and destroy()
 146             // to ensure that the effects of dispose() are observed in the
 147             // thread that runs destroy().
 148             // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
 149             if (_Mutex_base<_Lp>::_S_need_barriers)
 150               {
 151                 _GLIBCXX_READ_MEM_BARRIER;
 152                 _GLIBCXX_WRITE_MEM_BARRIER;
 153               }
 154
 155             // Be race-detector-friendly.  For more info see bits/c++config.
 156             _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 157             if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
 158                                                        -1) == 1)
 159               {
 160                 _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 161                 _M_destroy();
 162               }
 163           }
 164       }
 165
 166       void
 167       _M_weak_add_ref() noexcept
 168       { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
 169
 170       void
 171       _M_weak_release() noexcept
 172       {
 173         // Be race-detector-friendly. For more info see bits/c++config.
 174         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
 175         if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
 176           {
 177             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
 178             if (_Mutex_base<_Lp>::_S_need_barriers)
 179               {
 180                 // See _M_release(),
 181                 // destroy() must observe results of dispose()
 182                 _GLIBCXX_READ_MEM_BARRIER;
 183                 _GLIBCXX_WRITE_MEM_BARRIER;
 184               }
 185             _M_destroy();
 186           }
 187       }
 188
 189       long
 190       _M_get_use_count() const noexcept
 191       {
 192         // No memory barrier is used here so there is no synchronization
 193         // with other threads.
 194         return __atomic_load_n(&_M_use_count, __ATOMIC_RELAXED);
 195       }
 196
 197     private:
 198       _Sp_counted_base(_Sp_counted_base const&) = delete;
 199       _Sp_counted_base& operator=(_Sp_counted_base const&) = delete;
 200
 201       _Atomic_word  _M_use_count;     // #shared
 202       _Atomic_word  _M_weak_count;    // #weak + (#shared != 0)
 203     };
 204
 205   template<>
 206     inline void
 207     _Sp_counted_base<_S_single>::
 208     _M_add_ref_lock()
 209     {
 210       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 211         {
 212           _M_use_count = 0;
 213           __throw_bad_weak_ptr();
 214         }
 215     }
 216
 217   template<>
 218     inline void
 219     _Sp_counted_base<_S_mutex>::
 220     _M_add_ref_lock()
 221     {
 222       __gnu_cxx::__scoped_lock sentry(*this);
 223       if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
 224         {
 225           _M_use_count = 0;
 226           __throw_bad_weak_ptr();
 227         }
 228     }
 229
 230   template<>
 231     inline void
 232     _Sp_counted_base<_S_atomic>::
 233     _M_add_ref_lock()
 234     {
 235       // Perform lock-free add-if-not-zero operation.
 236       _Atomic_word __count = _M_get_use_count();
 237       do
 238         {
 239           if (__count == 0)
 240             __throw_bad_weak_ptr();
 241           // Replace the current counter value with the old value + 1, as
 242           // long as it's not changed meanwhile.
 243         }
 244       while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
 245                                           true, __ATOMIC_ACQ_REL,
 246                                           __ATOMIC_RELAXED));
 247     }
 248
 249
 250   // Forward declarations.
 251   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 252     class __shared_ptr;
 253
 254   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 255     class __weak_ptr;
 256
 257   template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
 258     class __enable_shared_from_this;
 259
 260   template<typename _Tp>
 261     class shared_ptr;
 262
 263   template<typename _Tp>
 264     class weak_ptr;
 265
 266   template<typename _Tp>
 267     struct owner_less;
 268
 269   template<typename _Tp>
 270     class enable_shared_from_this;
 271
 272   template<_Lock_policy _Lp = __default_lock_policy>
 273     class __weak_count;
 274
 275   template<_Lock_policy _Lp = __default_lock_policy>
 276     class __shared_count;
 277
 278
 279   // Counted ptr with no deleter or allocator support
 280   template<typename _Ptr, _Lock_policy _Lp>
 281     class _Sp_counted_ptr final : public _Sp_counted_base<_Lp>
 282     {
 283     public:
 284       explicit
 285       _Sp_counted_ptr(_Ptr __p)
 286       : _M_ptr(__p) { }
 287
 288       virtual void
 289       _M_dispose() noexcept
 290       { delete _M_ptr; }
 291
 292       virtual void
 293       _M_destroy() noexcept
 294       { delete this; }
 295
 296       virtual void*
 297       _M_get_deleter(const std::type_info&)
 298       { return 0; }
 299
 300       _Sp_counted_ptr(const _Sp_counted_ptr&) = delete;
 301       _Sp_counted_ptr& operator=(const _Sp_counted_ptr&) = delete;
 302
 303     protected:
 304       _Ptr             _M_ptr;  // copy constructor must not throw
 305     };
 306
 307   template<>
 308     inline void
 309     _Sp_counted_ptr<nullptr_t, _S_single>::_M_dispose() noexcept { }
 310
 311   template<>
 312     inline void
 313     _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() noexcept { }
 314
 315   template<>
 316     inline void
 317     _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }
 318
 319   // Support for custom deleter and/or allocator
 320   template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>
 321     class _Sp_counted_deleter final : public _Sp_counted_base<_Lp>
 322     {
 323       // Helper class that stores the Deleter and also acts as an allocator.
 324       // Used to dispose of the owned pointer and the internal refcount
 325       // Requires that copies of _Alloc can free each other's memory.
 326       struct _My_Deleter
 327       : public _Alloc           // copy constructor must not throw
 328       {
 329         _Deleter _M_del;        // copy constructor must not throw
 330         _My_Deleter(_Deleter __d, const _Alloc& __a)
 331         : _Alloc(__a), _M_del(__d) { }
 332       };
 333
 334     public:
 335       // __d(__p) must not throw.
 336       _Sp_counted_deleter(_Ptr __p, _Deleter __d)
 337       : _M_ptr(__p), _M_del(__d, _Alloc()) { }
 338
 339       // __d(__p) must not throw.
 340       _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a)
 341       : _M_ptr(__p), _M_del(__d, __a) { }
 342
 343       ~_Sp_counted_deleter() noexcept { }
 344
 345       virtual void
 346       _M_dispose() noexcept
 347       { _M_del._M_del(_M_ptr); }
 348
 349       virtual void
 350       _M_destroy() noexcept
 351       {
 352         typedef typename allocator_traits<_Alloc>::template
 353           rebind_traits<_Sp_counted_deleter> _Alloc_traits;
 354         typename _Alloc_traits::allocator_type __a(_M_del);
 355         _Alloc_traits::destroy(__a, this);
 356         _Alloc_traits::deallocate(__a, this, 1);
 357       }
 358
 359       virtual void*
 360       _M_get_deleter(const std::type_info& __ti)
 361       {
 362 #ifdef __GXX_RTTI
 363         return __ti == typeid(_Deleter) ? &_M_del._M_del : 0;
 364 #else
 365         return 0;
 366 #endif
 367       }
 368
 369     protected:
 370       _Ptr             _M_ptr;  // copy constructor must not throw
 371       _My_Deleter      _M_del;  // copy constructor must not throw
 372     };
 373
 374   // helpers for make_shared / allocate_shared
 375
 376   struct _Sp_make_shared_tag { };
 377
 378   template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
 379     class _Sp_counted_ptr_inplace final : public _Sp_counted_base<_Lp>
 380     {
 381       // Helper class that stores the pointer and also acts as an allocator.
 382       // Used to dispose of the owned pointer and the internal refcount
 383       // Requires that copies of _Alloc can free each other's memory.
 384       struct _Impl
 385       : public _Alloc           // copy constructor must not throw
 386       {
 387         _Impl(_Alloc __a) : _Alloc(__a), _M_ptr() { }
 388         _Tp* _M_ptr;
 389       };
 390
 391     public:
 392       template<typename... _Args>
 393         _Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)
 394         : _M_impl(__a)
 395         {
 396           _M_impl._M_ptr = static_cast<_Tp*>(static_cast<void*>(&_M_storage));
 397           // _GLIBCXX_RESOLVE_LIB_DEFECTS
 398           // 2070.  allocate_shared should use allocator_traits<A>::construct
 399           allocator_traits<_Alloc>::construct(__a, _M_impl._M_ptr,
 400               std::forward<_Args>(__args)...); // might throw
 401         }
 402
 403       ~_Sp_counted_ptr_inplace() noexcept { }
 404
 405       virtual void
 406       _M_dispose() noexcept
 407       { allocator_traits<_Alloc>::destroy(_M_impl, _M_impl._M_ptr); }
 408
 409       // Override because the allocator needs to know the dynamic type
 410       virtual void
 411       _M_destroy() noexcept
 412       {
 413         typedef typename allocator_traits<_Alloc>::template
 414           rebind_traits<_Sp_counted_ptr_inplace> _Alloc_traits;
 415         typename _Alloc_traits::allocator_type __a(_M_impl);
 416         _Alloc_traits::destroy(__a, this);
 417         _Alloc_traits::deallocate(__a, this, 1);
 418       }
 419
 420       // Sneaky trick so __shared_ptr can get the managed pointer
 421       virtual void*
 422       _M_get_deleter(const std::type_info& __ti) noexcept
 423       {
 424 #ifdef __GXX_RTTI
 425         return __ti == typeid(_Sp_make_shared_tag)
 426                ? static_cast<void*>(&_M_storage)
 427                : 0;
 428 #else
 429         return 0;
 430 #endif
 431       }
 432
 433     private:
 434       _Impl _M_impl;
 435       typename aligned_storage<sizeof(_Tp), alignment_of<_Tp>::value>::type
 436         _M_storage;
 437     };
 438
 439   template<_Lock_policy _Lp>
 440     class __shared_count
 441     {
 442     public:
 443       constexpr __shared_count() noexcept : _M_pi(0)
 444       { }
 445
 446       template<typename _Ptr>
 447         explicit
 448         __shared_count(_Ptr __p) : _M_pi(0)
 449         {
 450           __try
 451             {
 452               _M_pi = new _Sp_counted_ptr<_Ptr, _Lp>(__p);
 453             }
 454           __catch(...)
 455             {
 456               delete __p;
 457               __throw_exception_again;
 458             }
 459         }
 460
 461       template<typename _Ptr, typename _Deleter>
 462         __shared_count(_Ptr __p, _Deleter __d)
 463         : __shared_count(__p, std::move(__d), allocator<int>())
 464         { }
 465
 466       template<typename _Ptr, typename _Deleter, typename _Alloc>
 467         __shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
 468         {
 469           typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
 470           typedef typename allocator_traits<_Alloc>::template
 471             rebind_traits<_Sp_cd_type> _Alloc_traits;
 472           typename _Alloc_traits::allocator_type __a2(__a);
 473           _Sp_cd_type* __mem = 0;
 474           __try
 475             {
 476               __mem = _Alloc_traits::allocate(__a2, 1);
 477               _Alloc_traits::construct(__a2, __mem,
 478                   __p, std::move(__d), std::move(__a));
 479               _M_pi = __mem;
 480             }
 481           __catch(...)
 482             {
 483               __d(__p); // Call _Deleter on __p.
 484               if (__mem)
 485                 _Alloc_traits::deallocate(__a2, __mem, 1);
 486               __throw_exception_again;
 487             }
 488         }
 489
 490       template<typename _Tp, typename _Alloc, typename... _Args>
 491         __shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,
 492                        _Args&&... __args)
 493         : _M_pi(0)
 494         {
 495           typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
 496           typedef typename allocator_traits<_Alloc>::template
 497             rebind_traits<_Sp_cp_type> _Alloc_traits;
 498           typename _Alloc_traits::allocator_type __a2(__a);
 499           _Sp_cp_type* __mem = _Alloc_traits::allocate(__a2, 1);
 500           __try
 501             {
 502               _Alloc_traits::construct(__a2, __mem, std::move(__a),
 503                     std::forward<_Args>(__args)...);
 504               _M_pi = __mem;
 505             }
 506           __catch(...)
 507             {
 508               _Alloc_traits::deallocate(__a2, __mem, 1);
 509               __throw_exception_again;
 510             }
 511         }
 512
 513 #if _GLIBCXX_USE_DEPRECATED
 514       // Special case for auto_ptr<_Tp> to provide the strong guarantee.
 515       template<typename _Tp>
 516         explicit
 517         __shared_count(std::auto_ptr<_Tp>&& __r);
 518 #endif
 519
 520       // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
 521       template<typename _Tp, typename _Del>
 522         explicit
 523         __shared_count(std::unique_ptr<_Tp, _Del>&& __r) : _M_pi(0)
 524         {
 525           using _Ptr = typename unique_ptr<_Tp, _Del>::pointer;
 526           using _Del2 = typename conditional<is_reference<_Del>::value,
 527               reference_wrapper<typename remove_reference<_Del>::type>,
 528               _Del>::type;
 529           using _Sp_cd_type
 530             = _Sp_counted_deleter<_Ptr, _Del2, allocator<void>, _Lp>;
 531           using _Alloc = allocator<_Sp_cd_type>;
 532           using _Alloc_traits = allocator_traits<_Alloc>;
 533           _Alloc __a;
 534           _Sp_cd_type* __mem = _Alloc_traits::allocate(__a, 1);
 535           _Alloc_traits::construct(__a, __mem, __r.release(),
 536                                    __r.get_deleter());  // non-throwing
 537           _M_pi = __mem;
 538         }
 539
 540       // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
 541       explicit __shared_count(const __weak_count<_Lp>& __r);
 542
 543       ~__shared_count() noexcept
 544       {
 545         if (_M_pi != nullptr)
 546           _M_pi->_M_release();
 547       }
 548
 549       __shared_count(const __shared_count& __r) noexcept
 550       : _M_pi(__r._M_pi)
 551       {
 552         if (_M_pi != 0)
 553           _M_pi->_M_add_ref_copy();
 554       }
 555
 556       __shared_count&
 557       operator=(const __shared_count& __r) noexcept
 558       {
 559         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 560         if (__tmp != _M_pi)
 561           {
 562             if (__tmp != 0)
 563               __tmp->_M_add_ref_copy();
 564             if (_M_pi != 0)
 565               _M_pi->_M_release();
 566             _M_pi = __tmp;
 567           }
 568         return *this;
 569       }
 570
 571       void
 572       _M_swap(__shared_count& __r) noexcept
 573       {
 574         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 575         __r._M_pi = _M_pi;
 576         _M_pi = __tmp;
 577       }
 578
 579       long
 580       _M_get_use_count() const noexcept
 581       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 582
 583       bool
 584       _M_unique() const noexcept
 585       { return this->_M_get_use_count() == 1; }
 586
 587       void*
 588       _M_get_deleter(const std::type_info& __ti) const noexcept
 589       { return _M_pi ? _M_pi->_M_get_deleter(__ti) : 0; }
 590
 591       bool
 592       _M_less(const __shared_count& __rhs) const noexcept
 593       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 594
 595       bool
 596       _M_less(const __weak_count<_Lp>& __rhs) const noexcept
 597       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 598
 599       // Friend function injected into enclosing namespace and found by ADL
 600       friend inline bool
 601       operator==(const __shared_count& __a, const __shared_count& __b) noexcept
 602       { return __a._M_pi == __b._M_pi; }
 603
 604     private:
 605       friend class __weak_count<_Lp>;
 606
 607       _Sp_counted_base<_Lp>*  _M_pi;
 608     };
 609
 610
 611   template<_Lock_policy _Lp>
 612     class __weak_count
 613     {
 614     public:
 615       constexpr __weak_count() noexcept : _M_pi(0)
 616       { }
 617
 618       __weak_count(const __shared_count<_Lp>& __r) noexcept
 619       : _M_pi(__r._M_pi)
 620       {
 621         if (_M_pi != 0)
 622           _M_pi->_M_weak_add_ref();
 623       }
 624
 625       __weak_count(const __weak_count<_Lp>& __r) noexcept
 626       : _M_pi(__r._M_pi)
 627       {
 628         if (_M_pi != 0)
 629           _M_pi->_M_weak_add_ref();
 630       }
 631
 632       ~__weak_count() noexcept
 633       {
 634         if (_M_pi != 0)
 635           _M_pi->_M_weak_release();
 636       }
 637
 638       __weak_count<_Lp>&
 639       operator=(const __shared_count<_Lp>& __r) noexcept
 640       {
 641         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 642         if (__tmp != 0)
 643           __tmp->_M_weak_add_ref();
 644         if (_M_pi != 0)
 645           _M_pi->_M_weak_release();
 646         _M_pi = __tmp;
 647         return *this;
 648       }
 649
 650       __weak_count<_Lp>&
 651       operator=(const __weak_count<_Lp>& __r) noexcept
 652       {
 653         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 654         if (__tmp != 0)
 655           __tmp->_M_weak_add_ref();
 656         if (_M_pi != 0)
 657           _M_pi->_M_weak_release();
 658         _M_pi = __tmp;
 659         return *this;
 660       }
 661
 662       void
 663       _M_swap(__weak_count<_Lp>& __r) noexcept
 664       {
 665         _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
 666         __r._M_pi = _M_pi;
 667         _M_pi = __tmp;
 668       }
 669
 670       long
 671       _M_get_use_count() const noexcept
 672       { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
 673
 674       bool
 675       _M_less(const __weak_count& __rhs) const noexcept
 676       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 677
 678       bool
 679       _M_less(const __shared_count<_Lp>& __rhs) const noexcept
 680       { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
 681
 682       // Friend function injected into enclosing namespace and found by ADL
 683       friend inline bool
 684       operator==(const __weak_count& __a, const __weak_count& __b) noexcept
 685       { return __a._M_pi == __b._M_pi; }
 686
 687     private:
 688       friend class __shared_count<_Lp>;
 689
 690       _Sp_counted_base<_Lp>*  _M_pi;
 691     };
 692
 693   // Now that __weak_count is defined we can define this constructor:
 694   template<_Lock_policy _Lp>
 695     inline __shared_count<_Lp>:: __shared_count(const __weak_count<_Lp>& __r)
 696     : _M_pi(__r._M_pi)
 697     {
 698       if (_M_pi != 0)
 699         _M_pi->_M_add_ref_lock();
 700       else
 701         __throw_bad_weak_ptr();
 702     }
 703
 704
 705   // Support for enable_shared_from_this.
 706
 707   // Friend of __enable_shared_from_this.
 708   template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
 709     void
 710     __enable_shared_from_this_helper(const __shared_count<_Lp>&,
 711                                      const __enable_shared_from_this<_Tp1,
 712                                      _Lp>*, const _Tp2*) noexcept;
 713
 714   // Friend of enable_shared_from_this.
 715   template<typename _Tp1, typename _Tp2>
 716     void
 717     __enable_shared_from_this_helper(const __shared_count<>&,
 718                                      const enable_shared_from_this<_Tp1>*,
 719                                      const _Tp2*) noexcept;
 720
 721   template<_Lock_policy _Lp>
 722     inline void
 723     __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept
 724     { }
 725
 726
 727   template<typename _Tp, _Lock_policy _Lp>
 728     class __shared_ptr
 729     {
 730     public:
 731       typedef _Tp   element_type;
 732
 733       constexpr __shared_ptr() noexcept
 734       : _M_ptr(0), _M_refcount()
 735       { }
 736
 737       template<typename _Tp1>
 738         explicit __shared_ptr(_Tp1* __p)
 739         : _M_ptr(__p), _M_refcount(__p)
 740         {
 741           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 742           static_assert( sizeof(_Tp1) > 0, "incomplete type" );
 743           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 744         }
 745
 746       template<typename _Tp1, typename _Deleter>
 747         __shared_ptr(_Tp1* __p, _Deleter __d)
 748         : _M_ptr(__p), _M_refcount(__p, __d)
 749         {
 750           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 751           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 752           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 753         }
 754
 755       template<typename _Tp1, typename _Deleter, typename _Alloc>
 756         __shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
 757         : _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
 758         {
 759           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 760           // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
 761           __enable_shared_from_this_helper(_M_refcount, __p, __p);
 762         }
 763
 764       template<typename _Deleter>
 765         __shared_ptr(nullptr_t __p, _Deleter __d)
 766         : _M_ptr(0), _M_refcount(__p, __d)
 767         { }
 768
 769       template<typename _Deleter, typename _Alloc>
 770         __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
 771         : _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
 772         { }
 773
 774       template<typename _Tp1>
 775         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p) noexcept
 776         : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
 777         { }
 778
 779       __shared_ptr(const __shared_ptr&) noexcept = default;
 780       __shared_ptr& operator=(const __shared_ptr&) noexcept = default;
 781       ~__shared_ptr() = default;
 782
 783       template<typename _Tp1, typename = typename
 784                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 785         __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 786         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
 787         { }
 788
 789       __shared_ptr(__shared_ptr&& __r) noexcept
 790       : _M_ptr(__r._M_ptr), _M_refcount()
 791       {
 792         _M_refcount._M_swap(__r._M_refcount);
 793         __r._M_ptr = 0;
 794       }
 795
 796       template<typename _Tp1, typename = typename
 797                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
 798         __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
 799         : _M_ptr(__r._M_ptr), _M_refcount()
 800         {
 801           _M_refcount._M_swap(__r._M_refcount);
 802           __r._M_ptr = 0;
 803         }
 804
 805       template<typename _Tp1>
 806         explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
 807         : _M_refcount(__r._M_refcount) // may throw
 808         {
 809           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 810
 811           // It is now safe to copy __r._M_ptr, as
 812           // _M_refcount(__r._M_refcount) did not throw.
 813           _M_ptr = __r._M_ptr;
 814         }
 815
 816       // If an exception is thrown this constructor has no effect.
 817       template<typename _Tp1, typename _Del>
 818         __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
 819         : _M_ptr(__r.get()), _M_refcount()
 820         {
 821           __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 822           auto __tmp = __r.get();
 823           _M_refcount = __shared_count<_Lp>(std::move(__r));
 824           __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
 825         }
 826
 827 #if _GLIBCXX_USE_DEPRECATED
 828       // Postcondition: use_count() == 1 and __r.get() == 0
 829       template<typename _Tp1>
 830         __shared_ptr(std::auto_ptr<_Tp1>&& __r);
 831 #endif
 832
 833       /* TODO: use delegating constructor */
 834       constexpr __shared_ptr(nullptr_t) noexcept
 835       : _M_ptr(0), _M_refcount()
 836       { }
 837
 838       template<typename _Tp1>
 839         __shared_ptr&
 840         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
 841         {
 842           _M_ptr = __r._M_ptr;
 843           _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
 844           return *this;
 845         }
 846
 847 #if _GLIBCXX_USE_DEPRECATED
 848       template<typename _Tp1>
 849         __shared_ptr&
 850         operator=(std::auto_ptr<_Tp1>&& __r)
 851         {
 852           __shared_ptr(std::move(__r)).swap(*this);
 853           return *this;
 854         }
 855 #endif
 856
 857       __shared_ptr&
 858       operator=(__shared_ptr&& __r) noexcept
 859       {
 860         __shared_ptr(std::move(__r)).swap(*this);
 861         return *this;
 862       }
 863
 864       template<class _Tp1>
 865         __shared_ptr&
 866         operator=(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
 867         {
 868           __shared_ptr(std::move(__r)).swap(*this);
 869           return *this;
 870         }
 871
 872       template<typename _Tp1, typename _Del>
 873         __shared_ptr&
 874         operator=(std::unique_ptr<_Tp1, _Del>&& __r)
 875         {
 876           __shared_ptr(std::move(__r)).swap(*this);
 877           return *this;
 878         }
 879
 880       void
 881       reset() noexcept
 882       { __shared_ptr().swap(*this); }
 883
 884       template<typename _Tp1>
 885         void
 886         reset(_Tp1* __p) // _Tp1 must be complete.
 887         {
 888           // Catch self-reset errors.
 889           _GLIBCXX_DEBUG_ASSERT(__p == 0 || __p != _M_ptr);
 890           __shared_ptr(__p).swap(*this);
 891         }
 892
 893       template<typename _Tp1, typename _Deleter>
 894         void
 895         reset(_Tp1* __p, _Deleter __d)
 896         { __shared_ptr(__p, __d).swap(*this); }
 897
 898       template<typename _Tp1, typename _Deleter, typename _Alloc>
 899         void
 900         reset(_Tp1* __p, _Deleter __d, _Alloc __a)
 901         { __shared_ptr(__p, __d, std::move(__a)).swap(*this); }
 902
 903       // Allow class instantiation when _Tp is [cv-qual] void.
 904       typename std::add_lvalue_reference<_Tp>::type
 905       operator*() const noexcept
 906       {
 907         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 908         return *_M_ptr;
 909       }
 910
 911       _Tp*
 912       operator->() const noexcept
 913       {
 914         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 915         return _M_ptr;
 916       }
 917
 918       _Tp*
 919       get() const noexcept
 920       { return _M_ptr; }
 921
 922       explicit operator bool() const // never throws
 923       { return _M_ptr == 0 ? false : true; }
 924
 925       bool
 926       unique() const noexcept
 927       { return _M_refcount._M_unique(); }
 928
 929       long
 930       use_count() const noexcept
 931       { return _M_refcount._M_get_use_count(); }
 932
 933       void
 934       swap(__shared_ptr<_Tp, _Lp>& __other) noexcept
 935       {
 936         std::swap(_M_ptr, __other._M_ptr);
 937         _M_refcount._M_swap(__other._M_refcount);
 938       }
 939
 940       template<typename _Tp1>
 941         bool
 942         owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const
 943         { return _M_refcount._M_less(__rhs._M_refcount); }
 944
 945       template<typename _Tp1>
 946         bool
 947         owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const
 948         { return _M_refcount._M_less(__rhs._M_refcount); }
 949
 950 #ifdef __GXX_RTTI
 951     protected:
 952       // This constructor is non-standard, it is used by allocate_shared.
 953       template<typename _Alloc, typename... _Args>
 954         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
 955                      _Args&&... __args)
 956         : _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,
 957                                 std::forward<_Args>(__args)...)
 958         {
 959           // _M_ptr needs to point to the newly constructed object.
 960           // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
 961           void* __p = _M_refcount._M_get_deleter(typeid(__tag));
 962           _M_ptr = static_cast<_Tp*>(__p);
 963           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
 964         }
 965 #else
 966       template<typename _Alloc>
 967         struct _Deleter
 968         {
 969           void operator()(_Tp* __ptr)
 970           {
 971             typedef allocator_traits<_Alloc> _Alloc_traits;
 972             _Alloc_traits::destroy(_M_alloc, __ptr);
 973             _Alloc_traits::deallocate(_M_alloc, __ptr, 1);
 974           }
 975           _Alloc _M_alloc;
 976         };
 977
 978       template<typename _Alloc, typename... _Args>
 979         __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
 980                      _Args&&... __args)
 981         : _M_ptr(), _M_refcount()
 982         {
 983           typedef typename _Alloc::template rebind<_Tp>::other _Alloc2;
 984           _Deleter<_Alloc2> __del = { _Alloc2(__a) };
 985           typedef allocator_traits<_Alloc2> __traits;
 986           _M_ptr = __traits::allocate(__del._M_alloc, 1);
 987           __try
 988             {
 989               // _GLIBCXX_RESOLVE_LIB_DEFECTS
 990               // 2070. allocate_shared should use allocator_traits<A>::construct
 991               __traits::construct(__del._M_alloc, _M_ptr,
 992                                   std::forward<_Args>(__args)...);
 993             }
 994           __catch(...)
 995             {
 996               __traits::deallocate(__del._M_alloc, _M_ptr, 1);
 997               __throw_exception_again;
 998             }
 999           __shared_count<_Lp> __count(_M_ptr, __del, __del._M_alloc);
1000           _M_refcount._M_swap(__count);
1001           __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1002         }
1003 #endif
1004
1005       template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
1006                typename... _Args>
1007         friend __shared_ptr<_Tp1, _Lp1>
1008         __allocate_shared(const _Alloc& __a, _Args&&... __args);
1009
1010     private:
1011       void*
1012       _M_get_deleter(const std::type_info& __ti) const noexcept
1013       { return _M_refcount._M_get_deleter(__ti); }
1014
1015       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1016       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1017
1018       template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1019         friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&) noexcept;
1020
1021       _Tp*                 _M_ptr;         // Contained pointer.
1022       __shared_count<_Lp>  _M_refcount;    // Reference counter.
1023     };
1024
1025
1026   // 20.7.2.2.7 shared_ptr comparisons
1027   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1028     inline bool
1029     operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1030                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1031     { return __a.get() == __b.get(); }
1032
1033   template<typename _Tp, _Lock_policy _Lp>
1034     inline bool
1035     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1036     { return !__a; }
1037
1038   template<typename _Tp, _Lock_policy _Lp>
1039     inline bool
1040     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1041     { return !__a; }
1042
1043   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1044     inline bool
1045     operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1046                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1047     { return __a.get() != __b.get(); }
1048
1049   template<typename _Tp, _Lock_policy _Lp>
1050     inline bool
1051     operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1052     { return (bool)__a; }
1053
1054   template<typename _Tp, _Lock_policy _Lp>
1055     inline bool
1056     operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1057     { return (bool)__a; }
1058
1059   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1060     inline bool
1061     operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1062               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1063     {
1064       typedef typename std::common_type<_Tp1*, _Tp2*>::type _CT;
1065       return std::less<_CT>()(__a.get(), __b.get());
1066     }
1067
1068   template<typename _Tp, _Lock_policy _Lp>
1069     inline bool
1070     operator<(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1071     { return std::less<_Tp*>()(__a.get(), nullptr); }
1072
1073   template<typename _Tp, _Lock_policy _Lp>
1074     inline bool
1075     operator<(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1076     { return std::less<_Tp*>()(nullptr, __a.get()); }
1077
1078   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1079     inline bool
1080     operator<=(const __shared_ptr<_Tp1, _Lp>& __a,
1081                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1082     { return !(__b < __a); }
1083
1084   template<typename _Tp, _Lock_policy _Lp>
1085     inline bool
1086     operator<=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1087     { return !(nullptr < __a); }
1088
1089   template<typename _Tp, _Lock_policy _Lp>
1090     inline bool
1091     operator<=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1092     { return !(__a < nullptr); }
1093
1094   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1095     inline bool
1096     operator>(const __shared_ptr<_Tp1, _Lp>& __a,
1097               const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1098     { return (__b < __a); }
1099
1100   template<typename _Tp, _Lock_policy _Lp>
1101     inline bool
1102     operator>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1103     { return std::less<_Tp*>()(nullptr, __a.get()); }
1104
1105   template<typename _Tp, _Lock_policy _Lp>
1106     inline bool
1107     operator>(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1108     { return std::less<_Tp*>()(__a.get(), nullptr); }
1109
1110   template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1111     inline bool
1112     operator>=(const __shared_ptr<_Tp1, _Lp>& __a,
1113                const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1114     { return !(__a < __b); }
1115
1116   template<typename _Tp, _Lock_policy _Lp>
1117     inline bool
1118     operator>=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1119     { return !(__a < nullptr); }
1120
1121   template<typename _Tp, _Lock_policy _Lp>
1122     inline bool
1123     operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1124     { return !(nullptr < __a); }
1125
1126   template<typename _Sp>
1127     struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1128     {
1129       bool
1130       operator()(const _Sp& __lhs, const _Sp& __rhs) const noexcept
1131       {
1132         typedef typename _Sp::element_type element_type;
1133         return std::less<element_type*>()(__lhs.get(), __rhs.get());
1134       }
1135     };
1136
1137   template<typename _Tp, _Lock_policy _Lp>
1138     struct less<__shared_ptr<_Tp, _Lp>>
1139     : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1140     { };
1141
1142   // 2.2.3.8 shared_ptr specialized algorithms.
1143   template<typename _Tp, _Lock_policy _Lp>
1144     inline void
1145     swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b) noexcept
1146     { __a.swap(__b); }
1147
1148   // 2.2.3.9 shared_ptr casts
1149
1150   // The seemingly equivalent code:
1151   // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1152   // will eventually result in undefined behaviour, attempting to
1153   // delete the same object twice.
1154   /// static_pointer_cast
1155   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1156     inline __shared_ptr<_Tp, _Lp>
1157     static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1158     { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1159
1160   // The seemingly equivalent code:
1161   // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1162   // will eventually result in undefined behaviour, attempting to
1163   // delete the same object twice.
1164   /// const_pointer_cast
1165   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1166     inline __shared_ptr<_Tp, _Lp>
1167     const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1168     { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1169
1170   // The seemingly equivalent code:
1171   // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1172   // will eventually result in undefined behaviour, attempting to
1173   // delete the same object twice.
1174   /// dynamic_pointer_cast
1175   template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1176     inline __shared_ptr<_Tp, _Lp>
1177     dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1178     {
1179       if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1180         return __shared_ptr<_Tp, _Lp>(__r, __p);
1181       return __shared_ptr<_Tp, _Lp>();
1182     }
1183
1184
1185   template<typename _Tp, _Lock_policy _Lp>
1186     class __weak_ptr
1187     {
1188     public:
1189       typedef _Tp element_type;
1190
1191       constexpr __weak_ptr() noexcept
1192       : _M_ptr(0), _M_refcount()
1193       { }
1194
1195       __weak_ptr(const __weak_ptr&) noexcept = default;
1196       __weak_ptr& operator=(const __weak_ptr&) noexcept = default;
1197       ~__weak_ptr() = default;
1198
1199       // The "obvious" converting constructor implementation:
1200       //
1201       //  template<typename _Tp1>
1202       //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1203       //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1204       //    { }
1205       //
1206       // has a serious problem.
1207       //
1208       //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1209       //  conversion may require access to *__r._M_ptr (virtual inheritance).
1210       //
1211       // It is not possible to avoid spurious access violations since
1212       // in multithreaded programs __r._M_ptr may be invalidated at any point.
1213       template<typename _Tp1, typename = typename
1214                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1215         __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1216         : _M_refcount(__r._M_refcount)
1217         { _M_ptr = __r.lock().get(); }
1218
1219       template<typename _Tp1, typename = typename
1220                std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1221         __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1222         : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
1223         { }
1224
1225       template<typename _Tp1>
1226         __weak_ptr&
1227         operator=(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1228         {
1229           _M_ptr = __r.lock().get();
1230           _M_refcount = __r._M_refcount;
1231           return *this;
1232         }
1233
1234       template<typename _Tp1>
1235         __weak_ptr&
1236         operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1237         {
1238           _M_ptr = __r._M_ptr;
1239           _M_refcount = __r._M_refcount;
1240           return *this;
1241         }
1242
1243       __shared_ptr<_Tp, _Lp>
1244       lock() const noexcept
1245       {
1246 #ifdef __GTHREADS
1247         // Optimization: avoid throw overhead.
1248         if (expired())
1249           return __shared_ptr<element_type, _Lp>();
1250
1251         __try
1252           {
1253             return __shared_ptr<element_type, _Lp>(*this);
1254           }
1255         __catch(const bad_weak_ptr&)
1256           {
1257             // Q: How can we get here?
1258             // A: Another thread may have invalidated r after the
1259             //    use_count test above.
1260             return __shared_ptr<element_type, _Lp>();
1261           }
1262
1263 #else
1264         // Optimization: avoid try/catch overhead when single threaded.
1265         return expired() ? __shared_ptr<element_type, _Lp>()
1266                          : __shared_ptr<element_type, _Lp>(*this);
1267
1268 #endif
1269       } // XXX MT
1270
1271       long
1272       use_count() const noexcept
1273       { return _M_refcount._M_get_use_count(); }
1274
1275       bool
1276       expired() const noexcept
1277       { return _M_refcount._M_get_use_count() == 0; }
1278
1279       template<typename _Tp1>
1280         bool
1281         owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1282         { return _M_refcount._M_less(__rhs._M_refcount); }
1283
1284       template<typename _Tp1>
1285         bool
1286         owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1287         { return _M_refcount._M_less(__rhs._M_refcount); }
1288
1289       void
1290       reset() noexcept
1291       { __weak_ptr().swap(*this); }
1292
1293       void
1294       swap(__weak_ptr& __s) noexcept
1295       {
1296         std::swap(_M_ptr, __s._M_ptr);
1297         _M_refcount._M_swap(__s._M_refcount);
1298       }
1299
1300     private:
1301       // Used by __enable_shared_from_this.
1302       void
1303       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
1304       {
1305         _M_ptr = __ptr;
1306         _M_refcount = __refcount;
1307       }
1308
1309       template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1310       template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1311       friend class __enable_shared_from_this<_Tp, _Lp>;
1312       friend class enable_shared_from_this<_Tp>;
1313
1314       _Tp*               _M_ptr;         // Contained pointer.
1315       __weak_count<_Lp>  _M_refcount;    // Reference counter.
1316     };
1317
1318   // 20.7.2.3.6 weak_ptr specialized algorithms.
1319   template<typename _Tp, _Lock_policy _Lp>
1320     inline void
1321     swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b) noexcept
1322     { __a.swap(__b); }
1323
1324   template<typename _Tp, typename _Tp1>
1325     struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1326     {
1327       bool
1328       operator()(const _Tp& __lhs, const _Tp& __rhs) const
1329       { return __lhs.owner_before(__rhs); }
1330
1331       bool
1332       operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1333       { return __lhs.owner_before(__rhs); }
1334
1335       bool
1336       operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1337       { return __lhs.owner_before(__rhs); }
1338     };
1339
1340   template<typename _Tp, _Lock_policy _Lp>
1341     struct owner_less<__shared_ptr<_Tp, _Lp>>
1342     : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1343     { };
1344
1345   template<typename _Tp, _Lock_policy _Lp>
1346     struct owner_less<__weak_ptr<_Tp, _Lp>>
1347     : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1348     { };
1349
1350
1351   template<typename _Tp, _Lock_policy _Lp>
1352     class __enable_shared_from_this
1353     {
1354     protected:
1355       constexpr __enable_shared_from_this() noexcept { }
1356
1357       __enable_shared_from_this(const __enable_shared_from_this&) noexcept { }
1358
1359       __enable_shared_from_this&
1360       operator=(const __enable_shared_from_this&) noexcept
1361       { return *this; }
1362
1363       ~__enable_shared_from_this() { }
1364
1365     public:
1366       __shared_ptr<_Tp, _Lp>
1367       shared_from_this()
1368       { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1369
1370       __shared_ptr<const _Tp, _Lp>
1371       shared_from_this() const
1372       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1373
1374     private:
1375       template<typename _Tp1>
1376         void
1377         _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
1378         { _M_weak_this._M_assign(__p, __n); }
1379
1380       template<typename _Tp1>
1381         friend void
1382         __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
1383                                          const __enable_shared_from_this* __pe,
1384                                          const _Tp1* __px) noexcept
1385         {
1386           if (__pe != 0)
1387             __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
1388         }
1389
1390       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
1391     };
1392
1393
1394   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1395     inline __shared_ptr<_Tp, _Lp>
1396     __allocate_shared(const _Alloc& __a, _Args&&... __args)
1397     {
1398       return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
1399                                     std::forward<_Args>(__args)...);
1400     }
1401
1402   template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1403     inline __shared_ptr<_Tp, _Lp>
1404     __make_shared(_Args&&... __args)
1405     {
1406       typedef typename std::remove_const<_Tp>::type _Tp_nc;
1407       return std::__allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1408                                               std::forward<_Args>(__args)...);
1409     }
1410
1411   /// std::hash specialization for __shared_ptr.
1412   template<typename _Tp, _Lock_policy _Lp>
1413     struct hash<__shared_ptr<_Tp, _Lp>>
1414     : public __hash_base<size_t, __shared_ptr<_Tp, _Lp>>
1415     {
1416       size_t
1417       operator()(const __shared_ptr<_Tp, _Lp>& __s) const noexcept
1418       { return std::hash<_Tp*>()(__s.get()); }
1419     };
1420
1421 _GLIBCXX_END_NAMESPACE_VERSION
1422 } // namespace
1423
1424 #endif // _SHARED_PTR_BASE_H