include/salhelper/simplereferenceobject.hxx

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  17  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  18  */
  19
  20 #ifndef _SALHELPER_SIMPLEREFERENCEOBJECT_HXX_
  21 #define _SALHELPER_SIMPLEREFERENCEOBJECT_HXX_
  22
  23 #include "osl/interlck.h"
  24 #include "sal/types.h"
  25 #include "salhelperdllapi.h"
  26
  27 #include <cstddef>
  28 #include <new>
  29
  30 namespace salhelper {
  31
  32 /** A simple base implementation for reference-counted objects.
  33
  34     Classes that want to implement a reference-counting mechanism based on the
  35     acquire()/release() interface should derive from this class.
  36
  37     The reason to have class local operators new and delete here is technical.
  38     Imagine a class D derived from SimpleReferenceObject, but implemented in
  39     another shared library that happens to use different global operators new
  40     and delete from those used in this shared library (which, sadly, seems to
  41     be possible with shared libraries).  Now, without the class local
  42     operators new and delete here, a code sequence like "new D" would use the
  43     global operator new as found in the other shared library, while the code
  44     sequence "delete this" in release() would use the global operator delete
  45     as found in this shared library---and these two operators would not be
  46     guaranteed to match.
  47
  48     There are no overloaded operators new and delete for placement new here,
  49     because it is felt that the concept of placement new does not work well
  50     with the concept of reference-counted objects; so it seems best to simply
  51     leave those operators out.
  52
  53     The same problem as with operators new and delete would also be there with
  54     operators new[] and delete[].  But since arrays of reference-counted
  55     objects are of no use, anyway, it seems best to simply declare and not
  56     define (private) operators new[] and delete[].
  57  */
  58 class SALHELPER_DLLPUBLIC SimpleReferenceObject
  59 {
  60 public:
  61     inline SimpleReferenceObject() SAL_THROW(()): m_nCount(0) {}
  62
  63     /** @attention
  64         The results are undefined if, for any individual instance of
  65         SimpleReferenceObject, the total number of calls to acquire() exceeds
  66         the total number of calls to release() by a platform dependent amount
  67         (which, hopefully, is quite large).
  68      */
  69     inline void acquire() SAL_THROW(())
  70     { osl_atomic_increment(&m_nCount); }
  71
  72     inline void release() SAL_THROW(())
  73     { if (osl_atomic_decrement(&m_nCount) == 0) delete this; }
  74
  75     /** see general class documentation
  76      */
  77     static void * operator new(std::size_t nSize) SAL_THROW((std::bad_alloc));
  78
  79     /** see general class documentation
  80      */
  81     static void * operator new(std::size_t nSize,
  82                                std::nothrow_t const & rNothrow)
  83         SAL_THROW(());
  84
  85     /** see general class documentation
  86      */
  87     static void operator delete(void * pPtr) SAL_THROW(());
  88
  89     /** see general class documentation
  90      */
  91     static void operator delete(void * pPtr, std::nothrow_t const & rNothrow)
  92         SAL_THROW(());
  93
  94 protected:
  95     virtual ~SimpleReferenceObject() SAL_THROW(());
  96
  97 private:
  98     oslInterlockedCount m_nCount;
  99
 100     /** not implemented
 101      */
 102     SALHELPER_DLLPRIVATE SimpleReferenceObject(SimpleReferenceObject &);
 103
 104     /** not implemented
 105      */
 106     SALHELPER_DLLPRIVATE void operator =(SimpleReferenceObject);
 107
 108     /// @cond INTERNAL
 109
 110 #ifdef _MSC_VER
 111 /* We can't now have these private with MSVC2008 at least, it leads to
 112    compilation errors in xmloff and other places.
 113 */
 114 protected:
 115 #endif
 116     /** not implemented (see general class documentation)
 117      */
 118     static void * operator new[](std::size_t);
 119
 120     /** not implemented (see general class documentation)
 121      */
 122     static void operator delete[](void * pPtr);
 123
 124     /// @endcond
 125 };
 126
 127 }
 128
 129 #endif // _SALHELPER_SIMPLEREFERENCEOBJECT_HXX_
 130
 131 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */