COWReferenceBase.hpp

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00001 /*******************************************************************************
00002 * Copyright (C) 2004 Vintela, Inc. All rights reserved.
00003 * Copyright (C) 2005 Novell, Inc. All rights reserved.
00004 *
00005 * Redistribution and use in source and binary forms, with or without
00006 * modification, are permitted provided that the following conditions are met:
00007 *
00008 *  - Redistributions of source code must retain the above copyright notice,
00009 *    this list of conditions and the following disclaimer.
00010 *
00011 *  - Redistributions in binary form must reproduce the above copyright notice,
00012 *    this list of conditions and the following disclaimer in the documentation
00013 *    and/or other materials provided with the distribution.
00014 *
00015 *  - Neither the name of Vintela, Inc., Novell, Inc., nor the names of its
00016 *    contributors may be used to endorse or promote products derived from this
00017 *    software without specific prior written permission.
00018 *
00019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS''
00020 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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00022 * ARE DISCLAIMED. IN NO EVENT SHALL Vintela, Inc., Novell, Inc., OR THE 
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00031 
00032 
00037 #ifndef BLOCXX_COW_REFERENCE_BASE_HPP_INCLUDE_GUARD_
00038 #define BLOCXX_COW_REFERENCE_BASE_HPP_INCLUDE_GUARD_
00039 #include "blocxx/BLOCXX_config.h"
00040 #include "blocxx/RefCount.hpp"
00041 
00042 // The classes and functions defined in this file are not meant for general
00043 // use, they are internal implementation details.  They may change at any time.
00044 
00045 namespace BLOCXX_NAMESPACE
00046 {
00047 
00049 template<class T>
00050 inline void COWRefSwap(T& x, T&y)
00051 {
00052    T t = x;
00053    x = y;
00054    y = t;
00055 }
00056 
00058 // This class contains the non-templated code for COWReference, to help 
00059 // minimize code bloat.
00060 class BLOCXX_COMMON_API COWReferenceBase
00061 {
00062 protected:
00063    COWReferenceBase()
00064       : m_pRefCount(new RefCount) {}
00065    COWReferenceBase(const COWReferenceBase& arg)
00066       : m_pRefCount(arg.m_pRefCount)
00067    {
00068       m_pRefCount->inc();
00069    }
00070    void incRef()
00071    {
00072       m_pRefCount->inc();
00073    }
00074    
00075    bool decRef()
00076    {
00077       if (m_pRefCount->decAndTest())
00078       {
00079          delete m_pRefCount;
00080          return true;
00081       }
00082       return false;
00083    }
00084 
00085    bool refCountGreaterThanOne() const
00086    {
00087       return m_pRefCount->get() > 1;
00088    }
00089    
00090    // returns true if we're the only copy.
00091    bool getWriteLock()
00092    {
00093       if (m_pRefCount->decAndTest())
00094       {
00095          // only copy--don't need to clone, also not a race condition
00096          incRef();
00097          return true;
00098       }
00099       else
00100       {
00101          // need to become unique
00102          m_pRefCount = new RefCount;
00103          return false;
00104       }
00105    }
00106    
00107    void swap(COWReferenceBase& arg)
00108    {
00109       COWRefSwap(m_pRefCount, arg.m_pRefCount);
00110    }
00111 
00112 #ifdef BLOCXX_CHECK_NULL_REFERENCES
00113    static void throwNULLException();
00114    static void checkNull(const void* p)
00115    {
00116       if (p == 0)
00117       {
00118          throwNULLException();
00119       }
00120    }
00121 #endif
00122 
00123    void useRefCountOf(const COWReferenceBase& arg)
00124    {
00125       decRef(); 
00126       m_pRefCount = arg.m_pRefCount;
00127       incRef(); 
00128    }
00129 
00130 protected:
00131    RefCount* volatile m_pRefCount;
00132 };
00133 
00134 } // end namespace BLOCXX_NAMESPACE
00135 
00136 #endif
00137 
00138 

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