COWIntrusiveCountableBase.hpp

Go to the documentation of this file.

/*******************************************************************************
* Copyright (C) 2004 Vintela, Inc. All rights reserved.
* Copyright (C) 2005 Novell, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
*  - Redistributions of source code must retain the above copyright notice,
*    this list of conditions and the following disclaimer.
*
*  - Redistributions in binary form must reproduce the above copyright notice,
*    this list of conditions and the following disclaimer in the documentation
*    and/or other materials provided with the distribution.
*
*  - Neither the name of Vintela, Inc., Novell, Inc., nor the names of its
*    contributors may be used to endorse or promote products derived from this
*    software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS''
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL Vintela, Inc., Novell, Inc., OR THE 
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 
* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*******************************************************************************/


//
//  Copyright (c) 2001, 2002 Peter Dimov
//
//  Permission to copy, use, modify, sell and distribute this software
//  is granted provided this copyright notice appears in all copies.
//  This software is provided "as is" without express or implied
//  warranty, and with no claim as to its suitability for any purpose.
//

#ifndef BLOCXX_COW_INTRUSIVE_COUNTABLE_BASE_HPP_INCLUDE_GUARD_
#define BLOCXX_COW_INTRUSIVE_COUNTABLE_BASE_HPP_INCLUDE_GUARD_

#include "blocxx/BLOCXX_config.h"
#include "blocxx/RefCount.hpp"

namespace BLOCXX_NAMESPACE
{

class BLOCXX_COMMON_API COWIntrusiveCountableBase
{
private:
   RefCount m_usecount;

protected:
   COWIntrusiveCountableBase(COWIntrusiveCountableBase const &)
      : m_usecount(0)
   {
   }

   COWIntrusiveCountableBase(): m_usecount(0)
   {
   }

   COWIntrusiveCountableBase& operator=(COWIntrusiveCountableBase const &x)
   {
      // don't assign or change the ref count, since it won't be different.
      return *this;
   }

   virtual ~COWIntrusiveCountableBase();

   RefCount getRefCount() const
   {
      return m_usecount;
   }

public:

   inline friend void COWIntrusiveReferenceAddRef(COWIntrusiveCountableBase * p)
   {
      p->m_usecount.inc();
   }

   inline friend void COWIntrusiveReferenceRelease(COWIntrusiveCountableBase * p)
   {
      if (p->m_usecount.decAndTest())
         delete p;
   }
   
   inline friend bool COWIntrusiveReferenceUnique(COWIntrusiveCountableBase* p)
   {
      return p->m_usecount.get() == 1;
   }

   template <typename T>
   inline friend T* COWIntrusiveReferenceClone(T* p)
   {
      // this needs to happen first to avoid a race condition between 
      // another thread deleting the object and this one making a copy.
      T* tmp = p->clone();
      if (p->m_usecount.decAndTest())
      {
         // only copy--don't need to clone, also not a race condition.
         // undo the decAndTest.
         p->m_usecount.inc();
         delete tmp; // we won't need this anymore.
         return p;
      }
      else
      {
         // need to become unique
         if (tmp)
            COWIntrusiveReferenceAddRef(tmp);
         return tmp;
      }
   }
};

} // end namespace BLOCXX_NAMESPACE

#endif

---