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ExpireStrategy.h
//
// ExpireStrategy.h
//
// $Id: //poco/1.4/Foundation/include/Poco/ExpireStrategy.h#1 $
//
// Library: Foundation
// Package: Cache
// Module:  ExpireStrategy
//
// Definition of the ExpireStrategy class.
//
// Copyright (c) 2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Foundation_ExpireStrategy_INCLUDED
#define Foundation_ExpireStrategy_INCLUDED


#include "Poco/KeyValueArgs.h"
#include "Poco/ValidArgs.h"
#include "Poco/AbstractStrategy.h"
#include "Poco/Bugcheck.h"
#include "Poco/Timestamp.h"
#include "Poco/EventArgs.h"
#include <set>
#include <map>


namespace Poco {


template < 
      class TKey,
      class TValue
>
00060 class ExpireStrategy: public AbstractStrategy<TKey, TValue>
      /// An ExpireStrategy implements time based expiration of cache entries
{
public:
      typedef std::multimap<Timestamp, TKey>     TimeIndex;
      typedef typename TimeIndex::iterator       IndexIterator;
      typedef typename TimeIndex::const_iterator ConstIndexIterator;
      typedef std::map<TKey, IndexIterator>      Keys;
      typedef typename Keys::iterator            Iterator;

public:
00071       ExpireStrategy(Timestamp::TimeDiff expireTimeInMilliSec): _expireTime(expireTimeInMilliSec * 1000)
            /// Create an expire strategy. Note that the smallest allowed caching time is 25ms.
            /// Anything lower than that is not useful with current operating systems.
      {
            if (_expireTime < 25000) throw InvalidArgumentException("expireTime must be at least 25 ms");  
      }

      ~ExpireStrategy()
      {
      }

      void onAdd(const void*, const KeyValueArgs <TKey, TValue>& args)
      {
            Timestamp now;
            IndexIterator it = _keyIndex.insert(typename TimeIndex::value_type(now, args.key()));
            std::pair<Iterator, bool> stat = _keys.insert(typename Keys::value_type(args.key(), it));
            if (!stat.second)
            {
                  _keyIndex.erase(stat.first->second);
                  stat.first->second = it;
            }
      }

00094       void onRemove(const void*, const TKey& key)
      {
            Iterator it = _keys.find(key);
            if (it != _keys.end())
            {
                  _keyIndex.erase(it->second);
                  _keys.erase(it);
            }
      }

00104       void onGet(const void*, const TKey& key)
      {
            // get triggers no changes in an expire
      }

00109       void onClear(const void*, const EventArgs& args)
      {
            _keys.clear();
            _keyIndex.clear();
      }

00115       void onIsValid(const void*, ValidArgs<TKey>& args)
      {
            Iterator it = _keys.find(args.key());
            if (it != _keys.end())
            {
                  if (it->second->first.isElapsed(_expireTime))
                  {
                        args.invalidate();
                  }
            }
            else //not found: probably removed by onReplace
                  args.invalidate();
      }

00129       void onReplace(const void*, std::set<TKey>& elemsToRemove)
      {
            // Note: replace only informs the cache which elements
            // it would like to remove!
            // it does not remove them on its own!
            IndexIterator it = _keyIndex.begin();
            while (it != _keyIndex.end() && it->first.isElapsed(_expireTime))
            {
                  elemsToRemove.insert(it->second);
                  ++it;
            }
      }

protected:
      Timestamp::TimeDiff _expireTime;
      Keys      _keys;     /// For faster replacement of keys, the iterator points to the _keyIndex map
00145       TimeIndex _keyIndex; /// Maps time to key value
};


} // namespace Poco


#endif // Foundation_ExpireStrategy_INCLUDED

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