include/salhelper/simplereferenceobject.hxx

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  19
  20 #ifndef INCLUDED_SALHELPER_SIMPLEREFERENCEOBJECT_HXX
  21 #define INCLUDED_SALHELPER_SIMPLEREFERENCEOBJECT_HXX
  22
  23 #include <osl/interlck.h>
  24 #include <salhelper/salhelperdllapi.h>
  25
  26 #include <cstddef>
  27 #include <new>
  28
  29 namespace salhelper {
  30
  31 /** A simple base implementation for reference-counted objects.
  32
  33     Classes that want to implement a reference-counting mechanism based on the
  34     acquire()/release() interface should derive from this class.
  35
  36     The reason to have class local operators new and delete here is technical.
  37     Imagine a class D derived from SimpleReferenceObject, but implemented in
  38     another shared library that happens to use different global operators new
  39     and delete from those used in this shared library (which, sadly, seems to
  40     be possible with shared libraries).  Now, without the class local
  41     operators new and delete here, a code sequence like "new D" would use the
  42     global operator new as found in the other shared library, while the code
  43     sequence "delete this" in release() would use the global operator delete
  44     as found in this shared library---and these two operators would not be
  45     guaranteed to match.
  46
  47     There are no overloaded operators new and delete for placement new here,
  48     because it is felt that the concept of placement new does not work well
  49     with the concept of reference-counted objects; so it seems best to simply
  50     leave those operators out.
  51
  52     The same problem as with operators new and delete would also be there with
  53     operators new[] and delete[].  But since arrays of reference-counted
  54     objects are of no use, anyway, it seems best to simply declare and not
  55     define (private) operators new[] and delete[].
  56  */
  57 class SALHELPER_DLLPUBLIC SimpleReferenceObject
  58 {
  59 public:
  60     SimpleReferenceObject(): m_nCount(0) {}
  61
  62     /** @attention
  63         The results are undefined if, for any individual instance of
  64         SimpleReferenceObject, the total number of calls to acquire() exceeds
  65         the total number of calls to release() by a platform dependent amount
  66         (which, hopefully, is quite large).
  67      */
  68     void acquire()
  69     { osl_atomic_increment(&m_nCount); }
  70
  71     void release()
  72     { if (osl_atomic_decrement(&m_nCount) == 0) delete this; }
  73
  74     /** see general class documentation
  75      */
  76     static void * operator new(std::size_t nSize);
  77
  78     /** see general class documentation
  79      */
  80     static void * operator new(std::size_t nSize,
  81                                std::nothrow_t const & rNothrow);
  82
  83     /** see general class documentation
  84      */
  85     static void operator delete(void * pPtr);
  86
  87     /** see general class documentation
  88      */
  89     static void operator delete(void * pPtr, std::nothrow_t const & rNothrow);
  90
  91 protected:
  92     virtual ~SimpleReferenceObject();
  93
  94 private:
  95     oslInterlockedCount m_nCount;
  96
  97     /** not implemented
  98      */
  99     SimpleReferenceObject(SimpleReferenceObject &) SAL_DELETED_FUNCTION;
 100
 101     /** not implemented
 102      */
 103     void operator =(SimpleReferenceObject) SAL_DELETED_FUNCTION;
 104
 105     /// @cond INTERNAL
 106
 107 #ifdef _MSC_VER
 108 /* We can't now have these private with MSVC2008 at least, it leads to
 109    compilation errors in xmloff and other places.
 110 */
 111 protected:
 112 #endif
 113     /** not implemented (see general class documentation)
 114      */
 115     static void * operator new[](std::size_t);
 116
 117     /** not implemented (see general class documentation)
 118      */
 119     static void operator delete[](void * pPtr);
 120
 121     /// @endcond
 122 };
 123
 124 }
 125
 126 #endif // INCLUDED_SALHELPER_SIMPLEREFERENCEOBJECT_HXX
 127
 128 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */