COWIntrusiveCountableBase.hpp

Go to the documentation of this file.

/*******************************************************************************
* Copyright (C) 2005, Vintela, Inc. All rights reserved.
* Copyright (C) 2006, 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., 
*       nor Novell, Inc., 
*       nor the names of its contributors or employees 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 THE COPYRIGHT OWNER OR 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 COWIntrusiveCountableBase; 
void COWIntrusiveReferenceAddRef(COWIntrusiveCountableBase * p); 
void COWIntrusiveReferenceRelease(COWIntrusiveCountableBase * p); 
bool COWIntrusiveReferenceUnique(COWIntrusiveCountableBase* p); 
template <typename T> T* COWIntrusiveReferenceClone(T* p); 

class BLOCXX_COMMON_API COWIntrusiveCountableBase
{
private:
   RefCount m_usecount;

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

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

   COWIntrusiveCountableBase(): m_usecount(0)
   {
   }

   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>
   friend T* COWIntrusiveReferenceClone(T* p); 
};

template <typename T>
inline 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