RandomVictimPolicy.h

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/*
// $Id: //open/dev/fennel/cache/RandomVictimPolicy.h#10 $
// Fennel is a library of data storage and processing components.
// Copyright (C) 2005-2009 The Eigenbase Project
// Copyright (C) 2005-2009 SQLstream, Inc.
// Copyright (C) 2005-2009 LucidEra, Inc.
// Portions Copyright (C) 1999-2009 John V. Sichi
//
// This program is free software; you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation; either version 2 of the License, or (at your option)
// any later version approved by The Eigenbase Project.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

#ifndef Fennel_RandomVictimPolicy_Included
#define Fennel_RandomVictimPolicy_Included

#include <functional>
#include "fennel/synch/NullMutex.h"

FENNEL_BEGIN_NAMESPACE

template <class PageT>
class RandomVictimPolicy
{
    NullMutex nullMutex;

    std::vector<PageT *> pages;

    std::subtractive_rng randomNumberGenerator;

    friend class PageIterator;

public:
    // for use by CacheImpl when iterating over candidate victims
    typedef NullMutexGuard SharedGuard;
    typedef NullMutexGuard ExclusiveGuard;
    // TODO:  write an STL modulo_iterator
    class PageIterator
    {
        RandomVictimPolicy policy;
        uint iPage;

        PageT *getCurrent() const
        {
            return policy.pages[iPage];
        }

    public:
        PageIterator(RandomVictimPolicy &policyInit,uint iPageInit)
            : policy(policyInit)
        {
            iPage = iPageInit;
        }

        void operator ++ ()
        {
            iPage++;
            if (iPage >= policy.pages.size()) {
                iPage = 0;
            }
        }

        PageT *operator -> () const
        {
            return getCurrent();
        }

        operator PageT * () const
        {
            return getCurrent();
        }

        PageT &operator * () const
        {
            return *getCurrent();
        }

        bool operator == (PageIterator const &other) const
        {
            // NOTE:  assume policy object is same
            return iPage == other.iPage;
        }
    };

    typedef PageIterator DirtyPageIterator;

    RandomVictimPolicy()
    {
    }

    RandomVictimPolicy(const CacheParams &params)
    {
    }

    void setAllocatedPageCount(uint nCachePages)
    {
    }

    void registerPage(PageT &page)
    {
        pages.push_back(&page);
    }

    void unregisterPage(PageT &)
    {
        // TODO: zfong 1/8/08 - Should remove the page from the pages vector.
        // Otherwise, unallocated pages will be returned by getVictimRange().
    }

    void notifyPageAccess(PageT &, bool)
    {
    }

    void notifyPageNice(PageT &)
    {
    }

    void notifyPageMap(PageT &, bool)
    {
    }

    void notifyPageUnmap(PageT &, bool)
    {
    }

    void notifyPageUnpin(PageT &page)
    {
    }

    void notifyPageDirty(PageT &page)
    {
    }

    void notifyPageClean(PageT &page)
    {
    }

    void notifyPageDiscard(BlockId blockId)
    {
    }

    NullMutex &getMutex()
    {
        return nullMutex;
    }

    std::pair<PageIterator,PageIterator> getVictimRange()
    {
        uint iPage = randomNumberGenerator(pages.size());
        uint iPageEnd = iPage ? iPage-1 : pages.size();
        return std::pair<PageIterator,PageIterator>(
            PageIterator(*this,iPage),
            PageIterator(*this,iPageEnd));
    }

    std::pair<DirtyPageIterator,DirtyPageIterator> getDirtyVictimRange()
    {
        return
            static_cast<std::pair<DirtyPageIterator,DirtyPageIterator> >(
                getVictimRange());
    }
};

FENNEL_END_NAMESPACE

#endif

// End RandomVictimPolicy.h

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