boost/smart_ptr/weak_ptr.hpp

   1 #ifndef BOOST_SMART_PTR_WEAK_PTR_HPP_INCLUDED
   2 #define BOOST_SMART_PTR_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/smart_ptr/detail/shared_count.hpp>
  18 #include <boost/smart_ptr/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 #if !defined( BOOST_SP_NO_SP_CONVERTIBLE )
  65
  66     weak_ptr( weak_ptr<Y> const & r, typename detail::sp_enable_if_convertible<Y,T>::type = detail::sp_empty() )
  67
  68 #else
  69
  70     weak_ptr( weak_ptr<Y> const & r )
  71
  72 #endif
  73     : px(r.lock().get()), pn(r.pn) // never throws
  74     {
  75     }
  76
  77 #if defined( BOOST_HAS_RVALUE_REFS )
  78
  79     template<class Y>
  80 #if !defined( BOOST_SP_NO_SP_CONVERTIBLE )
  81
  82     weak_ptr( weak_ptr<Y> && r, typename detail::sp_enable_if_convertible<Y,T>::type = detail::sp_empty() )
  83
  84 #else
  85
  86     weak_ptr( weak_ptr<Y> && r )
  87
  88 #endif
  89     : px(r.lock().get()), pn(std::move(r.pn)) // never throws
  90     {
  91         r.px = 0;
  92     }
  93
  94     // for better efficiency in the T == Y case
  95     weak_ptr( weak_ptr && r ): px( r.px ), pn(std::move(r.pn)) // never throws
  96     {
  97         r.px = 0;
  98     }
  99
 100     // for better efficiency in the T == Y case
 101     weak_ptr & operator=( weak_ptr && r ) // never throws
 102     {
 103         this_type( std::move( r ) ).swap( *this );
 104         return *this;
 105     }
 106
 107
 108 #endif
 109
 110     template<class Y>
 111 #if !defined( BOOST_SP_NO_SP_CONVERTIBLE )
 112
 113     weak_ptr( shared_ptr<Y> const & r, typename detail::sp_enable_if_convertible<Y,T>::type = detail::sp_empty() )
 114
 115 #else
 116
 117     weak_ptr( shared_ptr<Y> const & r )
 118
 119 #endif
 120     : px( r.px ), pn( r.pn ) // never throws
 121     {
 122     }
 123
 124 #if !defined(BOOST_MSVC) || (BOOST_MSVC >= 1300)
 125
 126     template<class Y>
 127     weak_ptr & operator=(weak_ptr<Y> const & r) // never throws
 128     {
 129         px = r.lock().get();
 130         pn = r.pn;
 131         return *this;
 132     }
 133
 134 #if defined( BOOST_HAS_RVALUE_REFS )
 135
 136     template<class Y>
 137     weak_ptr & operator=(weak_ptr<Y> && r)
 138     {
 139         this_type( std::move( r ) ).swap( *this );
 140         return *this;
 141     }
 142
 143 #endif
 144
 145     template<class Y>
 146     weak_ptr & operator=(shared_ptr<Y> const & r) // never throws
 147     {
 148         px = r.px;
 149         pn = r.pn;
 150         return *this;
 151     }
 152
 153 #endif
 154
 155     shared_ptr<T> lock() const // never throws
 156     {
 157         return shared_ptr<element_type>( *this, boost::detail::sp_nothrow_tag() );
 158     }
 159
 160     long use_count() const // never throws
 161     {
 162         return pn.use_count();
 163     }
 164
 165     bool expired() const // never throws
 166     {
 167         return pn.use_count() == 0;
 168     }
 169
 170     bool _empty() const // extension, not in std::weak_ptr
 171     {
 172         return pn.empty();
 173     }
 174
 175     void reset() // never throws in 1.30+
 176     {
 177         this_type().swap(*this);
 178     }
 179
 180     void swap(this_type & other) // never throws
 181     {
 182         std::swap(px, other.px);
 183         pn.swap(other.pn);
 184     }
 185
 186     void _internal_assign(T * px2, boost::detail::shared_count const & pn2)
 187     {
 188         px = px2;
 189         pn = pn2;
 190     }
 191
 192     template<class Y> bool _internal_less(weak_ptr<Y> const & rhs) const
 193     {
 194         return pn < rhs.pn;
 195     }
 196
 197 // Tasteless as this may seem, making all members public allows member templates
 198 // to work in the absence of member template friends. (Matthew Langston)
 199
 200 #ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
 201
 202 private:
 203
 204     template<class Y> friend class weak_ptr;
 205     template<class Y> friend class shared_ptr;
 206
 207 #endif
 208
 209     T * px;                       // contained pointer
 210     boost::detail::weak_count pn; // reference counter
 211
 212 };  // weak_ptr
 213
 214 template<class T, class U> inline bool operator<(weak_ptr<T> const & a, weak_ptr<U> const & b)
 215 {
 216     return a._internal_less(b);
 217 }
 218
 219 template<class T> void swap(weak_ptr<T> & a, weak_ptr<T> & b)
 220 {
 221     a.swap(b);
 222 }
 223
 224 } // namespace boost
 225
 226 #ifdef BOOST_MSVC
 227 # pragma warning(pop)
 228 #endif
 229
 230 #endif  // #ifndef BOOST_SMART_PTR_WEAK_PTR_HPP_INCLUDED