1 #ifndef BOOST_WEAK_PTR_HPP_INCLUDED

     2 #define BOOST_WEAK_PTR_HPP_INCLUDED

     3 

     4 //

     5 //  weak_ptr.hpp

     6 //

     7 //  Copyright (c) 2001, 2002, 2003 Peter Dimov

     8 //

     9 // Distributed under the Boost Software License, Version 1.0. (See

    10 // accompanying file LICENSE_1_0.txt or copy at

    11 // http://www.boost.org/LICENSE_1_0.txt)

    12 //

    13 //  See http://www.boost.org/libs/smart_ptr/weak_ptr.htm for documentation.

    14 //

    15 

    16 #include <memory> // boost.TR1 include order fix

    17 #include <boost/detail/shared_count.hpp>

    18 #include <boost/shared_ptr.hpp>

    19 

    20 #ifdef BOOST_MSVC  // moved here to work around VC++ compiler crash

    21 # pragma warning(push)

    22 # pragma warning(disable:4284) // odd return type for operator->

    23 #endif

    24 

    25 namespace boost

    26 {

    27 

    28 template<class T> class weak_ptr

    29 {

    30 private:

    31 

    32     // Borland 5.5.1 specific workarounds

    33     typedef weak_ptr<T> this_type;

    34 

    35 public:

    36 

    37     typedef T element_type;

    38 

    39     weak_ptr(): px(0), pn() // never throws in 1.30+

    40     {

    41     }

    42 

    43 //  generated copy constructor, assignment, destructor are fine

    44 

    45 

    46 //

    47 //  The "obvious" converting constructor implementation:

    48 //

    49 //  template<class Y>

    50 //  weak_ptr(weak_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws

    51 //  {

    52 //  }

    53 //

    54 //  has a serious problem.

    55 //

    56 //  r.px may already have been invalidated. The px(r.px)

    57 //  conversion may require access to *r.px (virtual inheritance).

    58 //

    59 //  It is not possible to avoid spurious access violations since

    60 //  in multithreaded programs r.px may be invalidated at any point.

    61 //

    62 

    63     template<class Y>

    64     weak_ptr(weak_ptr<Y> const & r): pn(r.pn) // never throws

    65     {

    66         px = r.lock().get();

    67     }

    68 

    69     template<class Y>

    70     weak_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws

    71     {

    72     }

    73 

    74 #if !defined(BOOST_MSVC) || (BOOST_MSVC >= 1300)

    75 

    76     template<class Y>

    77     weak_ptr & operator=(weak_ptr<Y> const & r) // never throws

    78     {

    79         px = r.lock().get();

    80         pn = r.pn;

    81         return *this;

    82     }

    83 

    84     template<class Y>

    85     weak_ptr & operator=(shared_ptr<Y> const & r) // never throws

    86     {

    87         px = r.px;

    88         pn = r.pn;

    89         return *this;

    90     }

    91 

    92 #endif

    93 

    94     shared_ptr<T> lock() const // never throws

    95     {

    96 #if defined(BOOST_HAS_THREADS)

    97 

    98         // optimization: avoid throw overhead

    99         if(expired())

   100         {

   101             return shared_ptr<element_type>();

   102         }

   103 

   104         try

   105         {

   106             return shared_ptr<element_type>(*this);

   107         }

   108         catch(bad_weak_ptr const &)

   109         {

   110             // Q: how can we get here?

   111             // A: another thread may have invalidated r after the use_count test above.

   112             return shared_ptr<element_type>();

   113         }

   114 

   115 #else

   116 

   117         // optimization: avoid try/catch overhead when single threaded

   118         return expired()? shared_ptr<element_type>(): shared_ptr<element_type>(*this);

   119 

   120 #endif

   121     }

   122 

   123     long use_count() const // never throws

   124     {

   125         return pn.use_count();

   126     }

   127 

   128     bool expired() const // never throws

   129     {

   130         return pn.use_count() == 0;

   131     }

   132 

   133     void reset() // never throws in 1.30+

   134     {

   135         this_type().swap(*this);

   136     }

   137 

   138     void swap(this_type & other) // never throws

   139     {

   140         std::swap(px, other.px);

   141         pn.swap(other.pn);

   142     }

   143 

   144     void _internal_assign(T * px2, boost::detail::shared_count const & pn2)

   145     {

   146         px = px2;

   147         pn = pn2;

   148     }

   149 

   150     template<class Y> bool _internal_less(weak_ptr<Y> const & rhs) const

   151     {

   152         return pn < rhs.pn;

   153     }

   154 

   155 // Tasteless as this may seem, making all members public allows member templates

   156 // to work in the absence of member template friends. (Matthew Langston)

   157 

   158 #ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS

   159 

   160 private:

   161 

   162     template<class Y> friend class weak_ptr;

   163     template<class Y> friend class shared_ptr;

   164 

   165 #endif

   166 

   167     T * px;                       // contained pointer

   168     boost::detail::weak_count pn; // reference counter

   169 

   170 };  // weak_ptr

   171 

   172 template<class T, class U> inline bool operator<(weak_ptr<T> const & a, weak_ptr<U> const & b)

   173 {

   174     return a._internal_less(b);

   175 }

   176 

   177 template<class T> void swap(weak_ptr<T> & a, weak_ptr<T> & b)

   178 {

   179     a.swap(b);

   180 }

   181 

   182 // deprecated, provided for backward compatibility

   183 template<class T> shared_ptr<T> make_shared(weak_ptr<T> const & r)

   184 {

   185     return r.lock();

   186 }

   187 

   188 } // namespace boost

   189 

   190 #ifdef BOOST_MSVC

   191 # pragma warning(pop)

   192 #endif    

   193 

   194 #endif  // #ifndef BOOST_WEAK_PTR_HPP_INCLUDED