OWBI1_COWIntrusiveCountableBase.hpp

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00001 /*******************************************************************************
00002 * Copyright (C) 2004 Vintela, Inc. All rights reserved.
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00007 *  - Redistributions of source code must retain the above copyright notice,
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00010 *  - Redistributions in binary form must reproduce the above copyright notice,
00011 *    this list of conditions and the following disclaimer in the documentation
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00014 *  - Neither the name of Vintela, Inc. nor the names of its
00015 *    contributors may be used to endorse or promote products derived from this
00016 *    software without specific prior written permission.
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00018 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS''
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00030 
00035 //
00036 //  Copyright (c) 2001, 2002 Peter Dimov
00037 //
00038 //  Permission to copy, use, modify, sell and distribute this software
00039 //  is granted provided this copyright notice appears in all copies.
00040 //  This software is provided "as is" without express or implied
00041 //  warranty, and with no claim as to its suitability for any purpose.
00042 //
00043 
00044 #ifndef OWBI1_COWBI1_INTRUSIVE_COUNTABLE_BASE_HPP_INCLUDE_GUARD_
00045 #define OWBI1_COWBI1_INTRUSIVE_COUNTABLE_BASE_HPP_INCLUDE_GUARD_
00046 
00047 #include "OWBI1_config.h"
00048 #include "OWBI1_RefCount.hpp"
00049 
00050 namespace OWBI1
00051 {
00052 
00060 class OWBI1_OWBI1PROVIFC_API COWIntrusiveCountableBase
00061 {
00062 private:
00063    RefCount m_usecount;
00064 
00065 protected:
00066    COWIntrusiveCountableBase(COWIntrusiveCountableBase const &)
00067       : m_usecount(0)
00068    {}
00069 
00070    COWIntrusiveCountableBase & operator=(COWIntrusiveCountableBase const &x)
00071    {
00072       // don't assign or change the ref count, since it won't be different.
00073       return *this;
00074    }
00075 
00076    COWIntrusiveCountableBase(): m_usecount(0)
00077    {
00078    }
00079 
00080    virtual ~COWIntrusiveCountableBase();
00081 
00082    RefCount getRefCount() const
00083    {
00084       return m_usecount;
00085    }
00086 
00087 public:
00088    inline friend void COWIntrusiveReferenceAddRef(COWIntrusiveCountableBase * p)
00089    {
00090       p->m_usecount.inc();
00091    }
00092 
00093    inline friend void COWIntrusiveReferenceRelease(COWIntrusiveCountableBase * p)
00094    {
00095       if (p->m_usecount.decAndTest())
00096          delete p;
00097    }
00098    
00099    inline friend bool COWIntrusiveReferenceUnique(COWIntrusiveCountableBase* p)
00100    {
00101       return p->m_usecount.get() == 1;
00102    }
00103 
00104    template <typename T>
00105    inline friend T* COWIntrusiveReferenceClone(T* p)
00106    {
00107       // this needs to happen first to avoid a race condition between 
00108       // another thread deleting the object and this one making a copy.
00109       T* tmp = p->clone();
00110       if (p->m_usecount.decAndTest())
00111       {
00112          // only copy--don't need to clone, also not a race condition.
00113          // undo the decAndTest.
00114          p->m_usecount.inc();
00115          delete tmp; // we won't need this anymore.
00116          return p;
00117       }
00118       else
00119       {
00120          // need to become unique
00121          if (tmp) COWIntrusiveReferenceAddRef(tmp);
00122 
00123          return tmp;
00124       }
00125    }
00126 };
00127 
00128 } // end namespace OWBI1
00129 
00130 #endif
00131 
00132 

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