COWReferenceBase.hpp

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#ifndef BLOCXX_CBLOCXX_REFERENCE_BASE_HPP_INCLUDE_GUARD_
#define BLOCXX_CBLOCXX_REFERENCE_BASE_HPP_INCLUDE_GUARD_
#include "blocxx/BLOCXX_config.h"
#include "blocxx/RefCount.hpp"

// The classes and functions defined in this file are not meant for general
// use, they are internal implementation details.  They may change at any time.

namespace BLOCXX_NAMESPACE
{

template<class T>
inline void COWRefSwap(T& x, T&y)
{
   T t = x;
   x = y;
   y = t;
}

// This class contains the non-templated code for COWReference, to help 
// minimize code bloat.
class BLOCXX_COMMON_API COWReferenceBase
{
protected:
   COWReferenceBase()
      : m_pRefCount(new RefCount) {}
   COWReferenceBase(const COWReferenceBase& arg)
      : m_pRefCount(arg.m_pRefCount)
   {
      m_pRefCount->inc();
   }
   void incRef()
   {
      m_pRefCount->inc();
   }
   
   bool decRef()
   {
      if (m_pRefCount->decAndTest())
      {
         delete m_pRefCount;
         return true;
      }
      return false;
   }

   bool refCountGreaterThanOne() const
   {
      return m_pRefCount->get() > 1;
   }
   
   // returns true if we're the only copy.
   bool getWriteLock()
   {
      if (m_pRefCount->decAndTest())
      {
         // only copy--don't need to clone, also not a race condition
         incRef();
         return true;
      }
      else
      {
         // need to become unique
         m_pRefCount = new RefCount;
         return false;
      }
   }
   
   void swap(COWReferenceBase& arg)
   {
      COWRefSwap(m_pRefCount, arg.m_pRefCount);
   }

   void useRefCountOf(const COWReferenceBase& arg)
   {
      decRef();
      m_pRefCount = arg.m_pRefCount;
      incRef();
   }

protected:
   RefCount* volatile m_pRefCount;
};

} // end namespace BLOCXX_NAMESPACE

#endif