include/AD/memory/ref.h

   1 //////////////////////////////////////////////////////////////////////////////
   2 // NOTICE:
   3 //
   4 // ADLib, Prop and their related set of tools and documentation are in the
   5 // public domain.   The author(s) of this software reserve no copyrights on
   6 // the source code and any code generated using the tools.  You are encouraged
   7 // to use ADLib and Prop to develop software, in both academic and commercial
   8 // settings, and are free to incorporate any part of ADLib and Prop into
   9 // your programs.
  10 //
  11 // Although you are under no obligation to do so, we strongly recommend that
  12 // you give away all software developed using our tools.
  13 //
  14 // We also ask that credit be given to us when ADLib and/or Prop are used in
  15 // your programs, and that this notice be preserved intact in all the source
  16 // code.
  17 //
  18 // This software is still under development and we welcome any suggestions
  19 // and help from the users.
  20 //
  21 // Allen Leung
  22 // 1994
  23 //////////////////////////////////////////////////////////////////////////////
  24
  25 #ifndef reference_counted_objects_h
  26 #define reference_counted_objects_h
  27
  28 //////////////////////////////////////////////////////////////////////////////
  29 //  Reference counted objects base class.
  30 //////////////////////////////////////////////////////////////////////////////
  31 class RefObj {
  32    int _ref_count; // reference count
  33 public:
  34    //////////////////////////////////////////////////////////////////////////
  35    //  Constructor and destructor
  36    //////////////////////////////////////////////////////////////////////////
  37            inline  RefObj() : _ref_count(1) {}
  38    virtual inline ~RefObj() {}
  39
  40    //////////////////////////////////////////////////////////////////////////
  41    //  Check if the pointer is actually valid.
  42    //////////////////////////////////////////////////////////////////////////
  43    inline static int _boxed(void * obj) { return (unsigned long)obj >= 4096; }
  44
  45    //////////////////////////////////////////////////////////////////////////
  46    //  Reference counting primitives.
  47    //////////////////////////////////////////////////////////////////////////
  48    inline static void _inc(RefObj * obj)
  49       { if (RefObj::_boxed(obj)) ++obj->_ref_count; }
  50    inline static void _dec(RefObj * obj)
  51       { if (RefObj::_boxed(obj) && --obj->_ref_count == 0) delete obj; }
  52 };
  53
  54 //////////////////////////////////////////////////////////////////////////////
  55 // Ref<T> handles the reference counting of a pointer to class |T|.
  56 // It is a smart pointer.
  57 //////////////////////////////////////////////////////////////////////////////
  58
  59 template <class T>
  60    class Ref {
  61       const T&  operator * () const;  // for safety, no deferencing is allowed.
  62
  63       T * obj;  // actual pointer to object (must be derived from RefObj)
  64
  65    public:
  66       ///////////////////////////////////////////////////////////////////////
  67       //  Constructors and destructor.
  68       ///////////////////////////////////////////////////////////////////////
  69       inline  Ref(T * x = 0) : obj(x)     {}
  70       inline  Ref(Ref& r)    : obj(r.obj) { RefObj::_inc(obj); }
  71       inline ~Ref()                       { RefObj::_dec(obj); }
  72
  73       ///////////////////////////////////////////////////////////////////////
  74       //  Conversions and pinning.
  75       //  Pinning increments the reference on an object and returns
  76       //  its raw pointer.   This raw pointer is assumed to be single
  77       //  threaded and placed into some other Ref<T> type.
  78       ///////////////////////////////////////////////////////////////////////
  79       inline operator int () const { return (int)obj; }
  80       inline T * _pin ()           { RefObj::_inc(obj); return obj; }
  81       inline T * _raw ()           { return obj; }
  82
  83       ///////////////////////////////////////////////////////////////////////
  84       //  Assignments.
  85       ///////////////////////////////////////////////////////////////////////
  86       inline Ref& operator = (Ref& r)
  87          {  if (obj != r.obj) {
  88                RefObj::_inc(r.obj);
  89                RefObj::_dec(obj);
  90                obj = r.obj;
  91             }
  92             return *this;
  93          }
  94
  95       inline Ref& operator = (T * x)
  96          {  if (obj != x) { RefObj::_dec(obj); obj = x; }
  97             return *this;
  98          }
  99
 100       ///////////////////////////////////////////////////////////////////////
 101       //  Dereferencing operators.
 102       ///////////////////////////////////////////////////////////////////////
 103       inline const T * operator -> () const { return obj; }
 104       inline       T * operator -> ()       { return obj; }
 105    };
 106
 107 #endif