blocxx

COWReferenceBase.hpp

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00001 /*******************************************************************************
00002 * Copyright (C) 2005, Vintela, Inc. All rights reserved.
00003 * Copyright (C) 2006, 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:
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00020 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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00032 
00033 
00038 #ifndef BLOCXX_CBLOCXX_REFERENCE_BASE_HPP_INCLUDE_GUARD_
00039 #define BLOCXX_CBLOCXX_REFERENCE_BASE_HPP_INCLUDE_GUARD_
00040 #include "blocxx/BLOCXX_config.h"
00041 #include "blocxx/RefCount.hpp"
00042 
00043 // The classes and functions defined in this file are not meant for general
00044 // use, they are internal implementation details.  They may change at any time.
00045 
00046 namespace BLOCXX_NAMESPACE
00047 {
00048 
00050 template<class T>
00051 inline void COWRefSwap(T& x, T&y)
00052 {
00053    T t = x;
00054    x = y;
00055    y = t;
00056 }
00057 
00059 // This class contains the non-templated code for COWReference, to help 
00060 // minimize code bloat.
00061 class BLOCXX_COMMON_API COWReferenceBase
00062 {
00063 protected:
00064    COWReferenceBase()
00065       : m_pRefCount(new RefCount) {}
00066    COWReferenceBase(const COWReferenceBase& arg)
00067       : m_pRefCount(arg.m_pRefCount)
00068    {
00069       m_pRefCount->inc();
00070    }
00071    void incRef()
00072    {
00073       m_pRefCount->inc();
00074    }
00075    
00076    bool decRef()
00077    {
00078       if (m_pRefCount->decAndTest())
00079       {
00080          delete m_pRefCount;
00081          return true;
00082       }
00083       return false;
00084    }
00085 
00086    bool refCountGreaterThanOne() const
00087    {
00088       return m_pRefCount->get() > 1;
00089    }
00090    
00091    // returns true if we're the only copy.
00092    bool getWriteLock()
00093    {
00094       if (m_pRefCount->decAndTest())
00095       {
00096          // only copy--don't need to clone, also not a race condition
00097          incRef();
00098          return true;
00099       }
00100       else
00101       {
00102          // need to become unique
00103          m_pRefCount = new RefCount;
00104          return false;
00105       }
00106    }
00107    
00108    void swap(COWReferenceBase& arg)
00109    {
00110       COWRefSwap(m_pRefCount, arg.m_pRefCount);
00111    }
00112 
00113    void useRefCountOf(const COWReferenceBase& arg)
00114    {
00115       decRef();
00116       m_pRefCount = arg.m_pRefCount;
00117       incRef();
00118    }
00119 
00120 protected:
00121    RefCount* volatile m_pRefCount;
00122 };
00123 
00124 } // end namespace BLOCXX_NAMESPACE
00125 
00126 #endif
00127 
00128