OW_COWIntrusiveCountableBase.hpp

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00002 * Copyright (C) 2004 Vintela, Inc. All rights reserved.
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00007 *  - Redistributions of source code must retain the above copyright notice,
00008 *    this list of conditions and the following disclaimer.
00009 *
00010 *  - Redistributions in binary form must reproduce the above copyright notice,
00011 *    this list of conditions and the following disclaimer in the documentation
00012 *    and/or other materials provided with the distribution.
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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
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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 OW_COW_INTRUSIVE_COUNTABLE_BASE_HPP_INCLUDE_GUARD_
00045 #define OW_COW_INTRUSIVE_COUNTABLE_BASE_HPP_INCLUDE_GUARD_
00046 
00047 #include "OW_config.h"
00048 #include "OW_RefCount.hpp"
00049 
00050 namespace OW_NAMESPACE
00051 {
00052 
00061 class COWIntrusiveCountableBase; 
00062 void COWIntrusiveReferenceAddRef(COWIntrusiveCountableBase * p); 
00063 void COWIntrusiveReferenceRelease(COWIntrusiveCountableBase * p); 
00064 bool COWIntrusiveReferenceUnique(COWIntrusiveCountableBase* p); 
00065 template <typename T> T* COWIntrusiveReferenceClone(T* p); 
00066 
00067 class OW_COMMON_API COWIntrusiveCountableBase
00068 {
00069 private:
00070    RefCount m_usecount;
00071 
00072 protected:
00073    COWIntrusiveCountableBase(COWIntrusiveCountableBase const &)
00074       : m_usecount(0)
00075    {}
00076 
00077    COWIntrusiveCountableBase & operator=(COWIntrusiveCountableBase const &x)
00078    {
00079       // don't assign or change the ref count, since it won't be different.
00080       return *this;
00081    }
00082 
00083    COWIntrusiveCountableBase(): m_usecount(0)
00084    {
00085    }
00086 
00087    virtual ~COWIntrusiveCountableBase();
00088 
00089    RefCount getRefCount() const
00090    {
00091       return m_usecount;
00092    }
00093 
00094 public:
00095    inline friend void COWIntrusiveReferenceAddRef(COWIntrusiveCountableBase * p)
00096    {
00097       p->m_usecount.inc();
00098    }
00099 
00100    inline friend void COWIntrusiveReferenceRelease(COWIntrusiveCountableBase * p)
00101    {
00102       if (p->m_usecount.decAndTest())
00103          delete p;
00104    }
00105    
00106    inline friend bool COWIntrusiveReferenceUnique(COWIntrusiveCountableBase* p)
00107    {
00108       return p->m_usecount.get() == 1;
00109    }
00110 
00111    template <typename T>
00112    friend T* COWIntrusiveReferenceClone(T* p); 
00113 };
00114 
00115 template <typename T>
00116 inline T* COWIntrusiveReferenceClone(T* p)
00117 {
00118    // this needs to happen first to avoid a race condition between 
00119    // another thread deleting the object and this one making a copy.
00120    T* tmp = p->clone();
00121    if (p->m_usecount.decAndTest())
00122    {
00123       // only copy--don't need to clone, also not a race condition.
00124       // undo the decAndTest.
00125       p->m_usecount.inc();
00126       delete tmp; // we won't need this anymore.
00127       return p;
00128    }
00129    else
00130    {
00131       // need to become unique
00132       if (tmp) COWIntrusiveReferenceAddRef(tmp);
00133 
00134       return tmp;
00135    }
00136 }
00137 
00138 } // end namespace OW_NAMESPACE
00139 
00140 #endif
00141 
00142 

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