libstdc++
shared_ptr_base.h
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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  */
65  {
66  public:
67  virtual char const*
68  what() const noexcept;
69 
70  virtual ~bad_weak_ptr() noexcept;
71  };
72 
73  // Substitute for bad_weak_ptr object in the case of -fno-exceptions.
74  inline void
75  __throw_bad_weak_ptr()
76  { _GLIBCXX_THROW_OR_ABORT(bad_weak_ptr()); }
77 
78  using __gnu_cxx::_Lock_policy;
79  using __gnu_cxx::__default_lock_policy;
80  using __gnu_cxx::_S_single;
81  using __gnu_cxx::_S_mutex;
82  using __gnu_cxx::_S_atomic;
83 
84  // Empty helper class except when the template argument is _S_mutex.
85  template<_Lock_policy _Lp>
86  class _Mutex_base
87  {
88  protected:
89  // The atomic policy uses fully-fenced builtins, single doesn't care.
90  enum { _S_need_barriers = 0 };
91  };
92 
93  template<>
94  class _Mutex_base<_S_mutex>
95  : public __gnu_cxx::__mutex
96  {
97  protected:
98  // This policy is used when atomic builtins are not available.
99  // The replacement atomic operations might not have the necessary
100  // memory barriers.
101  enum { _S_need_barriers = 1 };
102  };
103 
104  template<_Lock_policy _Lp = __default_lock_policy>
105  class _Sp_counted_base
106  : public _Mutex_base<_Lp>
107  {
108  public:
109  _Sp_counted_base() noexcept
110  : _M_use_count(1), _M_weak_count(1) { }
111 
112  virtual
113  ~_Sp_counted_base() noexcept
114  { }
115 
116  // Called when _M_use_count drops to zero, to release the resources
117  // managed by *this.
118  virtual void
119  _M_dispose() noexcept = 0;
120 
121  // Called when _M_weak_count drops to zero.
122  virtual void
123  _M_destroy() noexcept
124  { delete this; }
125 
126  virtual void*
127  _M_get_deleter(const std::type_info&) = 0;
128 
129  void
130  _M_add_ref_copy()
131  { __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
132 
133  void
134  _M_add_ref_lock();
135 
136  void
137  _M_release() noexcept
138  {
139  // Be race-detector-friendly. For more info see bits/c++config.
140  _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_use_count);
141  if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
142  {
143  _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_use_count);
144  _M_dispose();
145  // There must be a memory barrier between dispose() and destroy()
146  // to ensure that the effects of dispose() are observed in the
147  // thread that runs destroy().
148  // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
149  if (_Mutex_base<_Lp>::_S_need_barriers)
150  {
151  _GLIBCXX_READ_MEM_BARRIER;
152  _GLIBCXX_WRITE_MEM_BARRIER;
153  }
154 
155  // Be race-detector-friendly. For more info see bits/c++config.
156  _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
157  if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
158  -1) == 1)
159  {
160  _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
161  _M_destroy();
162  }
163  }
164  }
165 
166  void
167  _M_weak_add_ref() noexcept
168  { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
169 
170  void
171  _M_weak_release() noexcept
172  {
173  // Be race-detector-friendly. For more info see bits/c++config.
174  _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
175  if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
176  {
177  _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
178  if (_Mutex_base<_Lp>::_S_need_barriers)
179  {
180  // See _M_release(),
181  // destroy() must observe results of dispose()
182  _GLIBCXX_READ_MEM_BARRIER;
183  _GLIBCXX_WRITE_MEM_BARRIER;
184  }
185  _M_destroy();
186  }
187  }
188 
189  long
190  _M_get_use_count() const noexcept
191  {
192  // No memory barrier is used here so there is no synchronization
193  // with other threads.
194  return __atomic_load_n(&_M_use_count, __ATOMIC_RELAXED);
195  }
196 
197  private:
198  _Sp_counted_base(_Sp_counted_base const&) = delete;
199  _Sp_counted_base& operator=(_Sp_counted_base const&) = delete;
200 
201  _Atomic_word _M_use_count; // #shared
202  _Atomic_word _M_weak_count; // #weak + (#shared != 0)
203  };
204 
205  template<>
206  inline void
207  _Sp_counted_base<_S_single>::
208  _M_add_ref_lock()
209  {
210  if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
211  {
212  _M_use_count = 0;
213  __throw_bad_weak_ptr();
214  }
215  }
216 
217  template<>
218  inline void
219  _Sp_counted_base<_S_mutex>::
220  _M_add_ref_lock()
221  {
222  __gnu_cxx::__scoped_lock sentry(*this);
223  if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
224  {
225  _M_use_count = 0;
226  __throw_bad_weak_ptr();
227  }
228  }
229 
230  template<>
231  inline void
232  _Sp_counted_base<_S_atomic>::
233  _M_add_ref_lock()
234  {
235  // Perform lock-free add-if-not-zero operation.
236  _Atomic_word __count = _M_use_count;
237  do
238  {
239  if (__count == 0)
240  __throw_bad_weak_ptr();
241  // Replace the current counter value with the old value + 1, as
242  // long as it's not changed meanwhile.
243  }
244  while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
245  true, __ATOMIC_ACQ_REL,
246  __ATOMIC_RELAXED));
247  }
248 
249 
250  // Forward declarations.
251  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
252  class __shared_ptr;
253 
254  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
255  class __weak_ptr;
256 
257  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
258  class __enable_shared_from_this;
259 
260  template<typename _Tp>
261  class shared_ptr;
262 
263  template<typename _Tp>
264  class weak_ptr;
265 
266  template<typename _Tp>
267  struct owner_less;
268 
269  template<typename _Tp>
270  class enable_shared_from_this;
271 
272  template<_Lock_policy _Lp = __default_lock_policy>
273  class __weak_count;
274 
275  template<_Lock_policy _Lp = __default_lock_policy>
276  class __shared_count;
277 
278 
279  // Counted ptr with no deleter or allocator support
280  template<typename _Ptr, _Lock_policy _Lp>
281  class _Sp_counted_ptr final : public _Sp_counted_base<_Lp>
282  {
283  public:
284  explicit
285  _Sp_counted_ptr(_Ptr __p)
286  : _M_ptr(__p) { }
287 
288  virtual void
289  _M_dispose() noexcept
290  { delete _M_ptr; }
291 
292  virtual void
293  _M_destroy() noexcept
294  { delete this; }
295 
296  virtual void*
297  _M_get_deleter(const std::type_info&)
298  { return 0; }
299 
300  _Sp_counted_ptr(const _Sp_counted_ptr&) = delete;
301  _Sp_counted_ptr& operator=(const _Sp_counted_ptr&) = delete;
302 
303  protected:
304  _Ptr _M_ptr; // copy constructor must not throw
305  };
306 
307  template<>
308  inline void
309  _Sp_counted_ptr<nullptr_t, _S_single>::_M_dispose() noexcept { }
310 
311  template<>
312  inline void
313  _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() noexcept { }
314 
315  template<>
316  inline void
317  _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }
318 
319  // Support for custom deleter and/or allocator
320  template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>
321  class _Sp_counted_deleter final : public _Sp_counted_base<_Lp>
322  {
323  // Helper class that stores the Deleter and also acts as an allocator.
324  // Used to dispose of the owned pointer and the internal refcount
325  // Requires that copies of _Alloc can free each other's memory.
326  struct _My_Deleter
327  : public _Alloc // copy constructor must not throw
328  {
329  _Deleter _M_del; // copy constructor must not throw
330  _My_Deleter(_Deleter __d, const _Alloc& __a)
331  : _Alloc(__a), _M_del(__d) { }
332  };
333 
334  public:
335  // __d(__p) must not throw.
336  _Sp_counted_deleter(_Ptr __p, _Deleter __d)
337  : _M_ptr(__p), _M_del(__d, _Alloc()) { }
338 
339  // __d(__p) must not throw.
340  _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a)
341  : _M_ptr(__p), _M_del(__d, __a) { }
342 
343  ~_Sp_counted_deleter() noexcept { }
344 
345  virtual void
346  _M_dispose() noexcept
347  { _M_del._M_del(_M_ptr); }
348 
349  virtual void
350  _M_destroy() noexcept
351  {
352  typedef typename allocator_traits<_Alloc>::template
353  rebind_traits<_Sp_counted_deleter> _Alloc_traits;
354  typename _Alloc_traits::allocator_type __a(_M_del);
355  _Alloc_traits::destroy(__a, this);
356  _Alloc_traits::deallocate(__a, this, 1);
357  }
358 
359  virtual void*
360  _M_get_deleter(const std::type_info& __ti)
361  {
362 #ifdef __GXX_RTTI
363  return __ti == typeid(_Deleter) ? &_M_del._M_del : 0;
364 #else
365  return 0;
366 #endif
367  }
368 
369  protected:
370  _Ptr _M_ptr; // copy constructor must not throw
371  _My_Deleter _M_del; // copy constructor must not throw
372  };
373 
374  // helpers for make_shared / allocate_shared
375 
376  struct _Sp_make_shared_tag { };
377 
378  template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
379  class _Sp_counted_ptr_inplace final : public _Sp_counted_base<_Lp>
380  {
381  // Helper class that stores the pointer and also acts as an allocator.
382  // Used to dispose of the owned pointer and the internal refcount
383  // Requires that copies of _Alloc can free each other's memory.
384  struct _Impl
385  : public _Alloc // copy constructor must not throw
386  {
387  _Impl(_Alloc __a) : _Alloc(__a), _M_ptr() { }
388  _Tp* _M_ptr;
389  };
390 
391  public:
392  template<typename... _Args>
393  _Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)
394  : _M_impl(__a), _M_storage()
395  {
396  _M_impl._M_ptr = static_cast<_Tp*>(static_cast<void*>(&_M_storage));
397  // _GLIBCXX_RESOLVE_LIB_DEFECTS
398  // 2070. allocate_shared should use allocator_traits<A>::construct
399  allocator_traits<_Alloc>::construct(__a, _M_impl._M_ptr,
400  std::forward<_Args>(__args)...); // might throw
401  }
402 
403  ~_Sp_counted_ptr_inplace() noexcept { }
404 
405  virtual void
406  _M_dispose() noexcept
407  { allocator_traits<_Alloc>::destroy(_M_impl, _M_impl._M_ptr); }
408 
409  // Override because the allocator needs to know the dynamic type
410  virtual void
411  _M_destroy() noexcept
412  {
413  typedef typename allocator_traits<_Alloc>::template
414  rebind_traits<_Sp_counted_ptr_inplace> _Alloc_traits;
415  typename _Alloc_traits::allocator_type __a(_M_impl);
416  _Alloc_traits::destroy(__a, this);
417  _Alloc_traits::deallocate(__a, this, 1);
418  }
419 
420  // Sneaky trick so __shared_ptr can get the managed pointer
421  virtual void*
422  _M_get_deleter(const std::type_info& __ti) noexcept
423  {
424 #ifdef __GXX_RTTI
425  return __ti == typeid(_Sp_make_shared_tag)
426  ? static_cast<void*>(&_M_storage)
427  : 0;
428 #else
429  return 0;
430 #endif
431  }
432 
433  private:
434  _Impl _M_impl;
435  typename aligned_storage<sizeof(_Tp), alignment_of<_Tp>::value>::type
436  _M_storage;
437  };
438 
439  template<_Lock_policy _Lp>
440  class __shared_count
441  {
442  public:
443  constexpr __shared_count() noexcept : _M_pi(0)
444  { }
445 
446  template<typename _Ptr>
447  explicit
448  __shared_count(_Ptr __p) : _M_pi(0)
449  {
450  __try
451  {
452  _M_pi = new _Sp_counted_ptr<_Ptr, _Lp>(__p);
453  }
454  __catch(...)
455  {
456  delete __p;
457  __throw_exception_again;
458  }
459  }
460 
461  template<typename _Ptr, typename _Deleter>
462  __shared_count(_Ptr __p, _Deleter __d) : _M_pi(0)
463  {
464  // The allocator's value_type doesn't matter, will rebind it anyway.
465  typedef std::allocator<int> _Alloc;
466  typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
467  typedef typename allocator_traits<_Alloc>::template
468  rebind_traits<_Sp_cd_type> _Alloc_traits;
469  typename _Alloc_traits::allocator_type __a;
470  _Sp_cd_type* __mem = 0;
471  __try
472  {
473  __mem = _Alloc_traits::allocate(__a, 1);
474  _Alloc_traits::construct(__a, __mem, __p, std::move(__d));
475  _M_pi = __mem;
476  }
477  __catch(...)
478  {
479  __d(__p); // Call _Deleter on __p.
480  if (__mem)
481  _Alloc_traits::deallocate(__a, __mem, 1);
482  __throw_exception_again;
483  }
484  }
485 
486  template<typename _Ptr, typename _Deleter, typename _Alloc>
487  __shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
488  {
489  typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
490  typedef typename allocator_traits<_Alloc>::template
491  rebind_traits<_Sp_cd_type> _Alloc_traits;
492  typename _Alloc_traits::allocator_type __a2(__a);
493  _Sp_cd_type* __mem = 0;
494  __try
495  {
496  __mem = _Alloc_traits::allocate(__a2, 1);
497  _Alloc_traits::construct(__a2, __mem,
498  __p, std::move(__d), std::move(__a));
499  _M_pi = __mem;
500  }
501  __catch(...)
502  {
503  __d(__p); // Call _Deleter on __p.
504  if (__mem)
505  _Alloc_traits::deallocate(__a2, __mem, 1);
506  __throw_exception_again;
507  }
508  }
509 
510  template<typename _Tp, typename _Alloc, typename... _Args>
511  __shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,
512  _Args&&... __args)
513  : _M_pi(0)
514  {
515  typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
516  typedef typename allocator_traits<_Alloc>::template
517  rebind_traits<_Sp_cp_type> _Alloc_traits;
518  typename _Alloc_traits::allocator_type __a2(__a);
519  _Sp_cp_type* __mem = _Alloc_traits::allocate(__a2, 1);
520  __try
521  {
522  _Alloc_traits::construct(__a2, __mem, std::move(__a),
523  std::forward<_Args>(__args)...);
524  _M_pi = __mem;
525  }
526  __catch(...)
527  {
528  _Alloc_traits::deallocate(__a2, __mem, 1);
529  __throw_exception_again;
530  }
531  }
532 
533 #if _GLIBCXX_USE_DEPRECATED
534  // Special case for auto_ptr<_Tp> to provide the strong guarantee.
535  template<typename _Tp>
536  explicit
537  __shared_count(std::auto_ptr<_Tp>&& __r);
538 #endif
539 
540  // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
541  template<typename _Tp, typename _Del>
542  explicit
543  __shared_count(std::unique_ptr<_Tp, _Del>&& __r)
544  : _M_pi(_S_create_from_up(std::move(__r)))
545  { __r.release(); }
546 
547  // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
548  explicit __shared_count(const __weak_count<_Lp>& __r);
549 
550  ~__shared_count() noexcept
551  {
552  if (_M_pi != 0)
553  _M_pi->_M_release();
554  }
555 
556  __shared_count(const __shared_count& __r) noexcept
557  : _M_pi(__r._M_pi)
558  {
559  if (_M_pi != 0)
560  _M_pi->_M_add_ref_copy();
561  }
562 
563  __shared_count&
564  operator=(const __shared_count& __r) noexcept
565  {
566  _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
567  if (__tmp != _M_pi)
568  {
569  if (__tmp != 0)
570  __tmp->_M_add_ref_copy();
571  if (_M_pi != 0)
572  _M_pi->_M_release();
573  _M_pi = __tmp;
574  }
575  return *this;
576  }
577 
578  void
579  _M_swap(__shared_count& __r) noexcept
580  {
581  _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
582  __r._M_pi = _M_pi;
583  _M_pi = __tmp;
584  }
585 
586  long
587  _M_get_use_count() const noexcept
588  { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
589 
590  bool
591  _M_unique() const noexcept
592  { return this->_M_get_use_count() == 1; }
593 
594  void*
595  _M_get_deleter(const std::type_info& __ti) const noexcept
596  { return _M_pi ? _M_pi->_M_get_deleter(__ti) : 0; }
597 
598  bool
599  _M_less(const __shared_count& __rhs) const noexcept
600  { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
601 
602  bool
603  _M_less(const __weak_count<_Lp>& __rhs) const noexcept
604  { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
605 
606  // Friend function injected into enclosing namespace and found by ADL
607  friend inline bool
608  operator==(const __shared_count& __a, const __shared_count& __b) noexcept
609  { return __a._M_pi == __b._M_pi; }
610 
611  private:
612  friend class __weak_count<_Lp>;
613 
614  template<typename _Tp, typename _Del>
615  static _Sp_counted_base<_Lp>*
616  _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
617  typename std::enable_if<!std::is_reference<_Del>::value>::type* = 0)
618  {
619  typedef typename unique_ptr<_Tp, _Del>::pointer _Ptr;
620  return new _Sp_counted_deleter<_Ptr, _Del, std::allocator<void>,
621  _Lp>(__r.get(), __r.get_deleter());
622  }
623 
624  template<typename _Tp, typename _Del>
625  static _Sp_counted_base<_Lp>*
626  _S_create_from_up(std::unique_ptr<_Tp, _Del>&& __r,
627  typename std::enable_if<std::is_reference<_Del>::value>::type* = 0)
628  {
629  typedef typename unique_ptr<_Tp, _Del>::pointer _Ptr;
630  typedef typename std::remove_reference<_Del>::type _Del1;
631  typedef std::reference_wrapper<_Del1> _Del2;
632  return new _Sp_counted_deleter<_Ptr, _Del2, std::allocator<void>,
633  _Lp>(__r.get(), std::ref(__r.get_deleter()));
634  }
635 
636  _Sp_counted_base<_Lp>* _M_pi;
637  };
638 
639 
640  template<_Lock_policy _Lp>
641  class __weak_count
642  {
643  public:
644  constexpr __weak_count() noexcept : _M_pi(0)
645  { }
646 
647  __weak_count(const __shared_count<_Lp>& __r) noexcept
648  : _M_pi(__r._M_pi)
649  {
650  if (_M_pi != 0)
651  _M_pi->_M_weak_add_ref();
652  }
653 
654  __weak_count(const __weak_count<_Lp>& __r) noexcept
655  : _M_pi(__r._M_pi)
656  {
657  if (_M_pi != 0)
658  _M_pi->_M_weak_add_ref();
659  }
660 
661  ~__weak_count() noexcept
662  {
663  if (_M_pi != 0)
664  _M_pi->_M_weak_release();
665  }
666 
667  __weak_count<_Lp>&
668  operator=(const __shared_count<_Lp>& __r) noexcept
669  {
670  _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
671  if (__tmp != 0)
672  __tmp->_M_weak_add_ref();
673  if (_M_pi != 0)
674  _M_pi->_M_weak_release();
675  _M_pi = __tmp;
676  return *this;
677  }
678 
679  __weak_count<_Lp>&
680  operator=(const __weak_count<_Lp>& __r) noexcept
681  {
682  _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
683  if (__tmp != 0)
684  __tmp->_M_weak_add_ref();
685  if (_M_pi != 0)
686  _M_pi->_M_weak_release();
687  _M_pi = __tmp;
688  return *this;
689  }
690 
691  void
692  _M_swap(__weak_count<_Lp>& __r) noexcept
693  {
694  _Sp_counted_base<_Lp>* __tmp = __r._M_pi;
695  __r._M_pi = _M_pi;
696  _M_pi = __tmp;
697  }
698 
699  long
700  _M_get_use_count() const noexcept
701  { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
702 
703  bool
704  _M_less(const __weak_count& __rhs) const noexcept
705  { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
706 
707  bool
708  _M_less(const __shared_count<_Lp>& __rhs) const noexcept
709  { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
710 
711  // Friend function injected into enclosing namespace and found by ADL
712  friend inline bool
713  operator==(const __weak_count& __a, const __weak_count& __b) noexcept
714  { return __a._M_pi == __b._M_pi; }
715 
716  private:
717  friend class __shared_count<_Lp>;
718 
719  _Sp_counted_base<_Lp>* _M_pi;
720  };
721 
722  // Now that __weak_count is defined we can define this constructor:
723  template<_Lock_policy _Lp>
724  inline __shared_count<_Lp>:: __shared_count(const __weak_count<_Lp>& __r)
725  : _M_pi(__r._M_pi)
726  {
727  if (_M_pi != 0)
728  _M_pi->_M_add_ref_lock();
729  else
730  __throw_bad_weak_ptr();
731  }
732 
733 
734  // Support for enable_shared_from_this.
735 
736  // Friend of __enable_shared_from_this.
737  template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
738  void
739  __enable_shared_from_this_helper(const __shared_count<_Lp>&,
740  const __enable_shared_from_this<_Tp1,
741  _Lp>*, const _Tp2*) noexcept;
742 
743  // Friend of enable_shared_from_this.
744  template<typename _Tp1, typename _Tp2>
745  void
746  __enable_shared_from_this_helper(const __shared_count<>&,
747  const enable_shared_from_this<_Tp1>*,
748  const _Tp2*) noexcept;
749 
750  template<_Lock_policy _Lp>
751  inline void
752  __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept
753  { }
754 
755 
756  template<typename _Tp, _Lock_policy _Lp>
757  class __shared_ptr
758  {
759  public:
760  typedef _Tp element_type;
761 
762  constexpr __shared_ptr() noexcept
763  : _M_ptr(0), _M_refcount()
764  { }
765 
766  template<typename _Tp1>
767  explicit __shared_ptr(_Tp1* __p)
768  : _M_ptr(__p), _M_refcount(__p)
769  {
770  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
771  static_assert( sizeof(_Tp1) > 0, "incomplete type" );
772  __enable_shared_from_this_helper(_M_refcount, __p, __p);
773  }
774 
775  template<typename _Tp1, typename _Deleter>
776  __shared_ptr(_Tp1* __p, _Deleter __d)
777  : _M_ptr(__p), _M_refcount(__p, __d)
778  {
779  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
780  // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
781  __enable_shared_from_this_helper(_M_refcount, __p, __p);
782  }
783 
784  template<typename _Tp1, typename _Deleter, typename _Alloc>
785  __shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
786  : _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
787  {
788  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
789  // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
790  __enable_shared_from_this_helper(_M_refcount, __p, __p);
791  }
792 
793  template<typename _Deleter>
794  __shared_ptr(nullptr_t __p, _Deleter __d)
795  : _M_ptr(0), _M_refcount(__p, __d)
796  { }
797 
798  template<typename _Deleter, typename _Alloc>
799  __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
800  : _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
801  { }
802 
803  template<typename _Tp1>
804  __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p) noexcept
805  : _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
806  { }
807 
808  __shared_ptr(const __shared_ptr&) noexcept = default;
809  __shared_ptr& operator=(const __shared_ptr&) noexcept = default;
810  ~__shared_ptr() = default;
811 
812  template<typename _Tp1, typename = typename
813  std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
814  __shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
815  : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
816  { }
817 
818  __shared_ptr(__shared_ptr&& __r) noexcept
819  : _M_ptr(__r._M_ptr), _M_refcount()
820  {
821  _M_refcount._M_swap(__r._M_refcount);
822  __r._M_ptr = 0;
823  }
824 
825  template<typename _Tp1, typename = typename
827  __shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
828  : _M_ptr(__r._M_ptr), _M_refcount()
829  {
830  _M_refcount._M_swap(__r._M_refcount);
831  __r._M_ptr = 0;
832  }
833 
834  template<typename _Tp1>
835  explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
836  : _M_refcount(__r._M_refcount) // may throw
837  {
838  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
839 
840  // It is now safe to copy __r._M_ptr, as
841  // _M_refcount(__r._M_refcount) did not throw.
842  _M_ptr = __r._M_ptr;
843  }
844 
845  // If an exception is thrown this constructor has no effect.
846  template<typename _Tp1, typename _Del>
847  __shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
848  : _M_ptr(__r.get()), _M_refcount()
849  {
850  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
851  auto __tmp = std::__addressof(*__r.get());
852  _M_refcount = __shared_count<_Lp>(std::move(__r));
853  __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
854  }
855 
856 #if _GLIBCXX_USE_DEPRECATED
857  // Postcondition: use_count() == 1 and __r.get() == 0
858  template<typename _Tp1>
859  __shared_ptr(std::auto_ptr<_Tp1>&& __r);
860 #endif
861 
862  /* TODO: use delegating constructor */
863  constexpr __shared_ptr(nullptr_t) noexcept
864  : _M_ptr(0), _M_refcount()
865  { }
866 
867  template<typename _Tp1>
868  __shared_ptr&
869  operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
870  {
871  _M_ptr = __r._M_ptr;
872  _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
873  return *this;
874  }
875 
876 #if _GLIBCXX_USE_DEPRECATED
877  template<typename _Tp1>
878  __shared_ptr&
879  operator=(std::auto_ptr<_Tp1>&& __r)
880  {
881  __shared_ptr(std::move(__r)).swap(*this);
882  return *this;
883  }
884 #endif
885 
886  __shared_ptr&
887  operator=(__shared_ptr&& __r) noexcept
888  {
889  __shared_ptr(std::move(__r)).swap(*this);
890  return *this;
891  }
892 
893  template<class _Tp1>
894  __shared_ptr&
895  operator=(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
896  {
897  __shared_ptr(std::move(__r)).swap(*this);
898  return *this;
899  }
900 
901  template<typename _Tp1, typename _Del>
902  __shared_ptr&
903  operator=(std::unique_ptr<_Tp1, _Del>&& __r)
904  {
905  __shared_ptr(std::move(__r)).swap(*this);
906  return *this;
907  }
908 
909  void
910  reset() noexcept
911  { __shared_ptr().swap(*this); }
912 
913  template<typename _Tp1>
914  void
915  reset(_Tp1* __p) // _Tp1 must be complete.
916  {
917  // Catch self-reset errors.
918  _GLIBCXX_DEBUG_ASSERT(__p == 0 || __p != _M_ptr);
919  __shared_ptr(__p).swap(*this);
920  }
921 
922  template<typename _Tp1, typename _Deleter>
923  void
924  reset(_Tp1* __p, _Deleter __d)
925  { __shared_ptr(__p, __d).swap(*this); }
926 
927  template<typename _Tp1, typename _Deleter, typename _Alloc>
928  void
929  reset(_Tp1* __p, _Deleter __d, _Alloc __a)
930  { __shared_ptr(__p, __d, std::move(__a)).swap(*this); }
931 
932  // Allow class instantiation when _Tp is [cv-qual] void.
933  typename std::add_lvalue_reference<_Tp>::type
934  operator*() const noexcept
935  {
936  _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
937  return *_M_ptr;
938  }
939 
940  _Tp*
941  operator->() const noexcept
942  {
943  _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
944  return _M_ptr;
945  }
946 
947  _Tp*
948  get() const noexcept
949  { return _M_ptr; }
950 
951  explicit operator bool() const // never throws
952  { return _M_ptr == 0 ? false : true; }
953 
954  bool
955  unique() const noexcept
956  { return _M_refcount._M_unique(); }
957 
958  long
959  use_count() const noexcept
960  { return _M_refcount._M_get_use_count(); }
961 
962  void
963  swap(__shared_ptr<_Tp, _Lp>& __other) noexcept
964  {
965  std::swap(_M_ptr, __other._M_ptr);
966  _M_refcount._M_swap(__other._M_refcount);
967  }
968 
969  template<typename _Tp1>
970  bool
971  owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const
972  { return _M_refcount._M_less(__rhs._M_refcount); }
973 
974  template<typename _Tp1>
975  bool
976  owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const
977  { return _M_refcount._M_less(__rhs._M_refcount); }
978 
979 #ifdef __GXX_RTTI
980  protected:
981  // This constructor is non-standard, it is used by allocate_shared.
982  template<typename _Alloc, typename... _Args>
983  __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
984  _Args&&... __args)
985  : _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,
986  std::forward<_Args>(__args)...)
987  {
988  // _M_ptr needs to point to the newly constructed object.
989  // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
990  void* __p = _M_refcount._M_get_deleter(typeid(__tag));
991  _M_ptr = static_cast<_Tp*>(__p);
992  __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
993  }
994 #else
995  template<typename _Alloc>
996  struct _Deleter
997  {
998  void operator()(_Tp* __ptr)
999  {
1000  typedef allocator_traits<_Alloc> _Alloc_traits;
1001  _Alloc_traits::destroy(_M_alloc, __ptr);
1002  _Alloc_traits::deallocate(_M_alloc, __ptr, 1);
1003  }
1004  _Alloc _M_alloc;
1005  };
1006 
1007  template<typename _Alloc, typename... _Args>
1008  __shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
1009  _Args&&... __args)
1010  : _M_ptr(), _M_refcount()
1011  {
1012  typedef typename _Alloc::template rebind<_Tp>::other _Alloc2;
1013  _Deleter<_Alloc2> __del = { _Alloc2(__a) };
1014  typedef allocator_traits<_Alloc2> __traits;
1015  _M_ptr = __traits::allocate(__del._M_alloc, 1);
1016  __try
1017  {
1018  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1019  // 2070. allocate_shared should use allocator_traits<A>::construct
1020  __traits::construct(__del._M_alloc, _M_ptr,
1021  std::forward<_Args>(__args)...);
1022  }
1023  __catch(...)
1024  {
1025  __traits::deallocate(__del._M_alloc, _M_ptr, 1);
1026  __throw_exception_again;
1027  }
1028  __shared_count<_Lp> __count(_M_ptr, __del, __del._M_alloc);
1029  _M_refcount._M_swap(__count);
1030  __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
1031  }
1032 #endif
1033 
1034  template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
1035  typename... _Args>
1036  friend __shared_ptr<_Tp1, _Lp1>
1037  __allocate_shared(const _Alloc& __a, _Args&&... __args);
1038 
1039  private:
1040  void*
1041  _M_get_deleter(const std::type_info& __ti) const noexcept
1042  { return _M_refcount._M_get_deleter(__ti); }
1043 
1044  template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1045  template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1046 
1047  template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
1048  friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&) noexcept;
1049 
1050  _Tp* _M_ptr; // Contained pointer.
1051  __shared_count<_Lp> _M_refcount; // Reference counter.
1052  };
1053 
1054 
1055  // 20.7.2.2.7 shared_ptr comparisons
1056  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1057  inline bool
1058  operator==(const __shared_ptr<_Tp1, _Lp>& __a,
1059  const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1060  { return __a.get() == __b.get(); }
1061 
1062  template<typename _Tp, _Lock_policy _Lp>
1063  inline bool
1064  operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1065  { return !__a; }
1066 
1067  template<typename _Tp, _Lock_policy _Lp>
1068  inline bool
1069  operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1070  { return !__a; }
1071 
1072  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1073  inline bool
1074  operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
1075  const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1076  { return __a.get() != __b.get(); }
1077 
1078  template<typename _Tp, _Lock_policy _Lp>
1079  inline bool
1080  operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1081  { return (bool)__a; }
1082 
1083  template<typename _Tp, _Lock_policy _Lp>
1084  inline bool
1085  operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1086  { return (bool)__a; }
1087 
1088  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1089  inline bool
1090  operator<(const __shared_ptr<_Tp1, _Lp>& __a,
1091  const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1092  {
1093  typedef typename std::common_type<_Tp1*, _Tp2*>::type _CT;
1094  return std::less<_CT>()(__a.get(), __b.get());
1095  }
1096 
1097  template<typename _Tp, _Lock_policy _Lp>
1098  inline bool
1099  operator<(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1100  { return std::less<_Tp*>()(__a.get(), nullptr); }
1101 
1102  template<typename _Tp, _Lock_policy _Lp>
1103  inline bool
1104  operator<(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1105  { return std::less<_Tp*>()(nullptr, __a.get()); }
1106 
1107  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1108  inline bool
1109  operator<=(const __shared_ptr<_Tp1, _Lp>& __a,
1110  const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1111  { return !(__b < __a); }
1112 
1113  template<typename _Tp, _Lock_policy _Lp>
1114  inline bool
1115  operator<=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1116  { return !(nullptr < __a); }
1117 
1118  template<typename _Tp, _Lock_policy _Lp>
1119  inline bool
1120  operator<=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1121  { return !(__a < nullptr); }
1122 
1123  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1124  inline bool
1125  operator>(const __shared_ptr<_Tp1, _Lp>& __a,
1126  const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1127  { return (__b < __a); }
1128 
1129  template<typename _Tp, _Lock_policy _Lp>
1130  inline bool
1131  operator>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1132  { return std::less<_Tp*>()(nullptr, __a.get()); }
1133 
1134  template<typename _Tp, _Lock_policy _Lp>
1135  inline bool
1136  operator>(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1137  { return std::less<_Tp*>()(__a.get(), nullptr); }
1138 
1139  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
1140  inline bool
1141  operator>=(const __shared_ptr<_Tp1, _Lp>& __a,
1142  const __shared_ptr<_Tp2, _Lp>& __b) noexcept
1143  { return !(__a < __b); }
1144 
1145  template<typename _Tp, _Lock_policy _Lp>
1146  inline bool
1147  operator>=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
1148  { return !(__a < nullptr); }
1149 
1150  template<typename _Tp, _Lock_policy _Lp>
1151  inline bool
1152  operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
1153  { return !(nullptr < __a); }
1154 
1155  template<typename _Sp>
1156  struct _Sp_less : public binary_function<_Sp, _Sp, bool>
1157  {
1158  bool
1159  operator()(const _Sp& __lhs, const _Sp& __rhs) const noexcept
1160  {
1161  typedef typename _Sp::element_type element_type;
1162  return std::less<element_type*>()(__lhs.get(), __rhs.get());
1163  }
1164  };
1165 
1166  template<typename _Tp, _Lock_policy _Lp>
1167  struct less<__shared_ptr<_Tp, _Lp>>
1168  : public _Sp_less<__shared_ptr<_Tp, _Lp>>
1169  { };
1170 
1171  // 2.2.3.8 shared_ptr specialized algorithms.
1172  template<typename _Tp, _Lock_policy _Lp>
1173  inline void
1174  swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b) noexcept
1175  { __a.swap(__b); }
1176 
1177  // 2.2.3.9 shared_ptr casts
1178 
1179  // The seemingly equivalent code:
1180  // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
1181  // will eventually result in undefined behaviour, attempting to
1182  // delete the same object twice.
1183  /// static_pointer_cast
1184  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1185  inline __shared_ptr<_Tp, _Lp>
1186  static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1187  { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
1188 
1189  // The seemingly equivalent code:
1190  // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
1191  // will eventually result in undefined behaviour, attempting to
1192  // delete the same object twice.
1193  /// const_pointer_cast
1194  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1195  inline __shared_ptr<_Tp, _Lp>
1196  const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1197  { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
1198 
1199  // The seemingly equivalent code:
1200  // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
1201  // will eventually result in undefined behaviour, attempting to
1202  // delete the same object twice.
1203  /// dynamic_pointer_cast
1204  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
1205  inline __shared_ptr<_Tp, _Lp>
1206  dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1207  {
1208  if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
1209  return __shared_ptr<_Tp, _Lp>(__r, __p);
1210  return __shared_ptr<_Tp, _Lp>();
1211  }
1212 
1213 
1214  template<typename _Tp, _Lock_policy _Lp>
1215  class __weak_ptr
1216  {
1217  public:
1218  typedef _Tp element_type;
1219 
1220  constexpr __weak_ptr() noexcept
1221  : _M_ptr(0), _M_refcount()
1222  { }
1223 
1224  __weak_ptr(const __weak_ptr&) noexcept = default;
1225  __weak_ptr& operator=(const __weak_ptr&) noexcept = default;
1226  ~__weak_ptr() = default;
1227 
1228  // The "obvious" converting constructor implementation:
1229  //
1230  // template<typename _Tp1>
1231  // __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
1232  // : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
1233  // { }
1234  //
1235  // has a serious problem.
1236  //
1237  // __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
1238  // conversion may require access to *__r._M_ptr (virtual inheritance).
1239  //
1240  // It is not possible to avoid spurious access violations since
1241  // in multithreaded programs __r._M_ptr may be invalidated at any point.
1242  template<typename _Tp1, typename = typename
1243  std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
1244  __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1245  : _M_refcount(__r._M_refcount)
1246  { _M_ptr = __r.lock().get(); }
1247 
1248  template<typename _Tp1, typename = typename
1250  __weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1251  : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
1252  { }
1253 
1254  template<typename _Tp1>
1255  __weak_ptr&
1256  operator=(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
1257  {
1258  _M_ptr = __r.lock().get();
1259  _M_refcount = __r._M_refcount;
1260  return *this;
1261  }
1262 
1263  template<typename _Tp1>
1264  __weak_ptr&
1265  operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
1266  {
1267  _M_ptr = __r._M_ptr;
1268  _M_refcount = __r._M_refcount;
1269  return *this;
1270  }
1271 
1272  __shared_ptr<_Tp, _Lp>
1273  lock() const noexcept
1274  {
1275 #ifdef __GTHREADS
1276  // Optimization: avoid throw overhead.
1277  if (expired())
1278  return __shared_ptr<element_type, _Lp>();
1279 
1280  __try
1281  {
1282  return __shared_ptr<element_type, _Lp>(*this);
1283  }
1284  __catch(const bad_weak_ptr&)
1285  {
1286  // Q: How can we get here?
1287  // A: Another thread may have invalidated r after the
1288  // use_count test above.
1289  return __shared_ptr<element_type, _Lp>();
1290  }
1291 
1292 #else
1293  // Optimization: avoid try/catch overhead when single threaded.
1294  return expired() ? __shared_ptr<element_type, _Lp>()
1295  : __shared_ptr<element_type, _Lp>(*this);
1296 
1297 #endif
1298  } // XXX MT
1299 
1300  long
1301  use_count() const noexcept
1302  { return _M_refcount._M_get_use_count(); }
1303 
1304  bool
1305  expired() const noexcept
1306  { return _M_refcount._M_get_use_count() == 0; }
1307 
1308  template<typename _Tp1>
1309  bool
1310  owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
1311  { return _M_refcount._M_less(__rhs._M_refcount); }
1312 
1313  template<typename _Tp1>
1314  bool
1315  owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
1316  { return _M_refcount._M_less(__rhs._M_refcount); }
1317 
1318  void
1319  reset() noexcept
1320  { __weak_ptr().swap(*this); }
1321 
1322  void
1323  swap(__weak_ptr& __s) noexcept
1324  {
1325  std::swap(_M_ptr, __s._M_ptr);
1326  _M_refcount._M_swap(__s._M_refcount);
1327  }
1328 
1329  private:
1330  // Used by __enable_shared_from_this.
1331  void
1332  _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
1333  {
1334  _M_ptr = __ptr;
1335  _M_refcount = __refcount;
1336  }
1337 
1338  template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
1339  template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
1340  friend class __enable_shared_from_this<_Tp, _Lp>;
1341  friend class enable_shared_from_this<_Tp>;
1342 
1343  _Tp* _M_ptr; // Contained pointer.
1344  __weak_count<_Lp> _M_refcount; // Reference counter.
1345  };
1346 
1347  // 20.7.2.3.6 weak_ptr specialized algorithms.
1348  template<typename _Tp, _Lock_policy _Lp>
1349  inline void
1350  swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b) noexcept
1351  { __a.swap(__b); }
1352 
1353  template<typename _Tp, typename _Tp1>
1354  struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
1355  {
1356  bool
1357  operator()(const _Tp& __lhs, const _Tp& __rhs) const
1358  { return __lhs.owner_before(__rhs); }
1359 
1360  bool
1361  operator()(const _Tp& __lhs, const _Tp1& __rhs) const
1362  { return __lhs.owner_before(__rhs); }
1363 
1364  bool
1365  operator()(const _Tp1& __lhs, const _Tp& __rhs) const
1366  { return __lhs.owner_before(__rhs); }
1367  };
1368 
1369  template<typename _Tp, _Lock_policy _Lp>
1370  struct owner_less<__shared_ptr<_Tp, _Lp>>
1371  : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
1372  { };
1373 
1374  template<typename _Tp, _Lock_policy _Lp>
1375  struct owner_less<__weak_ptr<_Tp, _Lp>>
1376  : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
1377  { };
1378 
1379 
1380  template<typename _Tp, _Lock_policy _Lp>
1381  class __enable_shared_from_this
1382  {
1383  protected:
1384  constexpr __enable_shared_from_this() noexcept { }
1385 
1386  __enable_shared_from_this(const __enable_shared_from_this&) noexcept { }
1387 
1388  __enable_shared_from_this&
1389  operator=(const __enable_shared_from_this&) noexcept
1390  { return *this; }
1391 
1392  ~__enable_shared_from_this() { }
1393 
1394  public:
1395  __shared_ptr<_Tp, _Lp>
1396  shared_from_this()
1397  { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
1398 
1399  __shared_ptr<const _Tp, _Lp>
1400  shared_from_this() const
1401  { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
1402 
1403  private:
1404  template<typename _Tp1>
1405  void
1406  _M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
1407  { _M_weak_this._M_assign(__p, __n); }
1408 
1409  template<typename _Tp1>
1410  friend void
1411  __enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
1412  const __enable_shared_from_this* __pe,
1413  const _Tp1* __px) noexcept
1414  {
1415  if (__pe != 0)
1416  __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
1417  }
1418 
1419  mutable __weak_ptr<_Tp, _Lp> _M_weak_this;
1420  };
1421 
1422 
1423  template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
1424  inline __shared_ptr<_Tp, _Lp>
1425  __allocate_shared(const _Alloc& __a, _Args&&... __args)
1426  {
1427  return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
1428  std::forward<_Args>(__args)...);
1429  }
1430 
1431  template<typename _Tp, _Lock_policy _Lp, typename... _Args>
1432  inline __shared_ptr<_Tp, _Lp>
1433  __make_shared(_Args&&... __args)
1434  {
1435  typedef typename std::remove_const<_Tp>::type _Tp_nc;
1436  return std::__allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
1437  std::forward<_Args>(__args)...);
1438  }
1439 
1440  /// std::hash specialization for __shared_ptr.
1441  template<typename _Tp, _Lock_policy _Lp>
1442  struct hash<__shared_ptr<_Tp, _Lp>>
1443  : public __hash_base<size_t, __shared_ptr<_Tp, _Lp>>
1444  {
1445  size_t
1446  operator()(const __shared_ptr<_Tp, _Lp>& __s) const noexcept
1447  { return std::hash<_Tp*>()(__s.get()); }
1448  };
1449 
1450 _GLIBCXX_END_NAMESPACE_VERSION
1451 } // namespace
1452 
1453 #endif // _SHARED_PTR_BASE_H