xapian-core/include/xapian/intrusive_ptr.h

   1 #ifndef XAPIAN_INCLUDED_INTRUSIVE_PTR_H
   2 #define XAPIAN_INCLUDED_INTRUSIVE_PTR_H
   3
   4 //
   5 //  Based on Boost's intrusive_ptr.hpp
   6 //
   7 //  Copyright (c) 2001, 2002 Peter Dimov
   8 //  Copyright (c) 2011,2013,2014,2015,2016 Olly Betts
   9 //
  10 // Distributed under the Boost Software License, Version 1.0.
  11 //
  12 // Boost Software License - Version 1.0 - August 17th, 2003
  13 //
  14 // Permission is hereby granted, free of charge, to any person or organization
  15 // obtaining a copy of the software and accompanying documentation covered by
  16 // this license (the "Software") to use, reproduce, display, distribute,
  17 // execute, and transmit the Software, and to prepare derivative works of the
  18 // Software, and to permit third-parties to whom the Software is furnished to
  19 // do so, all subject to the following:
  20 //
  21 // The copyright notices in the Software and this entire statement, including
  22 // the above license grant, this restriction and the following disclaimer,
  23 // must be included in all copies of the Software, in whole or in part, and
  24 // all derivative works of the Software, unless such copies or derivative
  25 // works are solely in the form of machine-executable object code generated by
  26 // a source language processor.
  27 //
  28 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  29 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  30 // FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
  31 // SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
  32 // FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
  33 // ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  34 // DEALINGS IN THE SOFTWARE.
  35 //
  36 //  See http://www.boost.org/libs/smart_ptr/intrusive_ptr.html for documentation.
  37 //
  38
  39 #if !defined XAPIAN_IN_XAPIAN_H && !defined XAPIAN_LIB_BUILD
  40 # error "Never use <xapian/intrusive_ptr.h> directly; include <xapian.h> instead."
  41 #endif
  42
  43 namespace Xapian {
  44 namespace Internal {
  45
  46 /// Base class for objects managed by intrusive_ptr.
  47 class intrusive_base {
  48     /// Prevent copying.
  49     intrusive_base(const intrusive_base&);
  50
  51     /// Prevent assignment.
  52     void operator=(const intrusive_base&);
  53
  54   public:
  55     /** Construct with no references.
  56      *
  57      *  The references get added if/when this object is put into an
  58      *  intrusive_ptr.
  59      */
  60     intrusive_base() : _refs(0) { }
  61
  62     /* There's no need for a virtual destructor here as we never delete a
  63      * subclass of intrusive_base by calling delete on intrusive_base*.
  64      */
  65
  66     /** Reference count.
  67      *
  68      *  This needs to be mutable so we can add/remove references through const
  69      *  pointers.
  70      */
  71     mutable unsigned _refs;
  72 };
  73
  74 //
  75 //  intrusive_ptr
  76 //
  77
  78 /// A smart pointer that uses intrusive reference counting.
  79 template<class T> class intrusive_ptr
  80 {
  81 private:
  82
  83     typedef intrusive_ptr this_type;
  84
  85 public:
  86
  87     intrusive_ptr(): px( 0 )
  88     {
  89     }
  90
  91     intrusive_ptr( T * p): px( p )
  92     {
  93         if( px != 0 ) ++px->_refs;
  94     }
  95
  96     template<class U>
  97     intrusive_ptr( intrusive_ptr<U> const & rhs )
  98     : px( rhs.get() )
  99     {
 100         if( px != 0 ) ++px->_refs;
 101     }
 102
 103     intrusive_ptr(intrusive_ptr const & rhs): px( this == &rhs ? 0 : rhs.px )
 104     {
 105         if( px != 0 ) ++px->_refs;
 106     }
 107
 108     ~intrusive_ptr()
 109     {
 110         if( px != 0 && --px->_refs == 0 ) delete px;
 111     }
 112
 113     intrusive_ptr & operator=(intrusive_ptr const & rhs)
 114     {
 115         this_type(rhs).swap(*this);
 116         return *this;
 117     }
 118
 119     intrusive_ptr & operator=(T * rhs)
 120     {
 121         this_type(rhs).swap(*this);
 122         return *this;
 123     }
 124
 125     T * get() const
 126     {
 127         return px;
 128     }
 129
 130     T & operator*() const
 131     {
 132         return *px;
 133     }
 134
 135     T * operator->() const
 136     {
 137         return px;
 138     }
 139
 140     void swap(intrusive_ptr & rhs)
 141     {
 142         T * tmp = px;
 143         px = rhs.px;
 144         rhs.px = tmp;
 145     }
 146
 147 private:
 148
 149     T * px;
 150 };
 151
 152 template<class T, class U> inline bool operator==(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b)
 153 {
 154     return a.get() == b.get();
 155 }
 156
 157 template<class T, class U> inline bool operator!=(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b)
 158 {
 159     return a.get() != b.get();
 160 }
 161
 162 template<class T, class U> inline bool operator==(intrusive_ptr<T> const & a, U * b)
 163 {
 164     return a.get() == b;
 165 }
 166
 167 template<class T, class U> inline bool operator!=(intrusive_ptr<T> const & a, U * b)
 168 {
 169     return a.get() != b;
 170 }
 171
 172 template<class T, class U> inline bool operator==(T * a, intrusive_ptr<U> const & b)
 173 {
 174     return a == b.get();
 175 }
 176
 177 template<class T, class U> inline bool operator!=(T * a, intrusive_ptr<U> const & b)
 178 {
 179     return a != b.get();
 180 }
 181
 182 /// Base class for objects managed by opt_intrusive_ptr.
 183 class opt_intrusive_base {
 184   public:
 185     opt_intrusive_base(const opt_intrusive_base&) : _refs(0) { }
 186
 187     opt_intrusive_base& operator=(const opt_intrusive_base&) {
 188         // Don't touch _refs.
 189         return *this;
 190     }
 191
 192     /** Construct object which is initially not reference counted.
 193      *
 194      *  The reference counting starts if release() is called.
 195      */
 196     opt_intrusive_base() : _refs(0) { }
 197
 198     /* Subclasses of opt_intrusive_base may be deleted by calling delete on a
 199      * pointer to opt_intrusive_base.
 200      */
 201     virtual ~opt_intrusive_base() { }
 202
 203     void ref() const {
 204         if (_refs == 0)
 205             _refs = 2;
 206         else
 207             ++_refs;
 208     }
 209
 210     void unref() const {
 211         if (--_refs == 1)
 212             delete this;
 213     }
 214
 215     /** Reference count.
 216      *
 217      *  This needs to be mutable so we can add/remove references through const
 218      *  pointers.
 219      */
 220     mutable unsigned _refs;
 221
 222   protected:
 223     /** Start reference counting.
 224      *
 225      *  The object is constructed with _refs set to 0, meaning it isn't being
 226      *  reference counted.
 227      *
 228      *  Calling release() sets _refs to 1 if it is 0, and from then
 229      *  opt_intrusive_ptr will increment and decrement _refs.  If it is
 230      *  decremented to 1, the object is deleted.
 231      */
 232     void release() const {
 233         if (_refs == 0)
 234             _refs = 1;
 235     }
 236 };
 237
 238 //
 239 //  opt_intrusive_ptr
 240 //
 241
 242 /// A smart pointer that optionally uses intrusive reference counting.
 243 template<class T> class opt_intrusive_ptr
 244 {
 245 private:
 246
 247     typedef opt_intrusive_ptr this_type;
 248
 249 public:
 250
 251     opt_intrusive_ptr(): px( 0 ), counting( false )
 252     {
 253     }
 254
 255     opt_intrusive_ptr( T * p): px( p ), counting( px != 0 && px->_refs )
 256     {
 257         if( counting ) ++px->_refs;
 258     }
 259
 260     template<class U>
 261     opt_intrusive_ptr( opt_intrusive_ptr<U> const & rhs )
 262     : px( rhs.get() ), counting( rhs.counting )
 263     {
 264         if( counting ) ++px->_refs;
 265     }
 266
 267     opt_intrusive_ptr(opt_intrusive_ptr const & rhs)
 268     : px( this == &rhs ? 0 : rhs.px ),
 269       counting( this == &rhs ? false : rhs.counting )
 270     {
 271         if( counting ) ++px->_refs;
 272     }
 273
 274     ~opt_intrusive_ptr()
 275     {
 276         if( counting && --px->_refs == 1 ) delete px;
 277     }
 278
 279     opt_intrusive_ptr & operator=(opt_intrusive_ptr const & rhs)
 280     {
 281         this_type(rhs).swap(*this);
 282         return *this;
 283     }
 284
 285     opt_intrusive_ptr & operator=(T * rhs)
 286     {
 287         this_type(rhs).swap(*this);
 288         return *this;
 289     }
 290
 291     T * get() const
 292     {
 293         return px;
 294     }
 295
 296     T & operator*() const
 297     {
 298         return *px;
 299     }
 300
 301     T * operator->() const
 302     {
 303         return px;
 304     }
 305
 306     void swap(opt_intrusive_ptr & rhs)
 307     {
 308         T * tmp = px;
 309         px = rhs.px;
 310         rhs.px = tmp;
 311         bool tmp2 = counting;
 312         counting = rhs.counting;
 313         rhs.counting = tmp2;
 314     }
 315
 316 private:
 317
 318     T * px;
 319
 320     bool counting;
 321 };
 322
 323 template<class T, class U> inline bool operator==(opt_intrusive_ptr<T> const & a, opt_intrusive_ptr<U> const & b)
 324 {
 325     return a.get() == b.get();
 326 }
 327
 328 template<class T, class U> inline bool operator!=(opt_intrusive_ptr<T> const & a, opt_intrusive_ptr<U> const & b)
 329 {
 330     return a.get() != b.get();
 331 }
 332
 333 template<class T, class U> inline bool operator==(opt_intrusive_ptr<T> const & a, U * b)
 334 {
 335     return a.get() == b;
 336 }
 337
 338 template<class T, class U> inline bool operator!=(opt_intrusive_ptr<T> const & a, U * b)
 339 {
 340     return a.get() != b;
 341 }
 342
 343 template<class T, class U> inline bool operator==(T * a, opt_intrusive_ptr<U> const & b)
 344 {
 345     return a == b.get();
 346 }
 347
 348 template<class T, class U> inline bool operator!=(T * a, opt_intrusive_ptr<U> const & b)
 349 {
 350     return a != b.get();
 351 }
 352
 353 }
 354 }
 355
 356 #endif // XAPIAN_INCLUDED_INTRUSIVE_PTR_H