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UniqueAccessExpireCache.h
//
// UniqueAccessExpireCache.h
//
// $Id: //poco/1.3/Foundation/include/Poco/UniqueAccessExpireCache.h#1 $
//
// Library: Foundation
// Package: Cache
// Module:  UniqueAccessExpireCache
//
// Definition of the UniqueAccessExpireCache 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
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// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef  Foundation_UniqueAccessExpireCache_INCLUDED
#define  Foundation_UniqueAccessExpireCache_INCLUDED


#include "Poco/AbstractCache.h"
#include "Poco/UniqueAccessExpireStrategy.h"


namespace Poco {


template <class TKey, class TValue> 
00051 class UniqueAccessExpireCache: public AbstractCache<TKey, TValue, UniqueAccessExpireStrategy<TKey, TValue> >
      /// An UniqueAccessExpireCache caches entries for a given time span. In contrast
      /// to ExpireCache which only allows to set a per cache expiration value, it allows to define 
      /// expiration per CacheEntry.
      /// Each TValue object must thus offer the following method:
      ///    
      ///    const Poco::Timespan& getTimeout() const;
      ///    
      /// which returns the relative timespan for how long the entry should be valid without being accessed!
      /// The absolute expire timepoint is calculated as now() + getTimeout().
      /// Accessing an object will update this absolute expire timepoint.
      /// You can use the Poco::AccessExpirationDecorator to add the getExpiration
      /// method to values that do not have a getExpiration function.
      ///
      /// Be careful when using an UniqueAccessExpireCache. A cache is often used
      /// like cache.has(x) followed by cache.get x). Note that it could happen
      /// that the "has" call works, then the current execution thread gets descheduled, time passes,
      /// the entry gets invalid, thus leading to an empty SharedPtr being returned 
      /// when "get" is invoked.
{
public:
      UniqueAccessExpireCache():
            AbstractCache<TKey, TValue, UniqueAccessExpireStrategy<TKey, TValue> >(UniqueAccessExpireStrategy<TKey, TValue>())
      {
      }

      ~UniqueAccessExpireCache()
      {
      }

private:
      UniqueAccessExpireCache(const UniqueAccessExpireCache& aCache);
      UniqueAccessExpireCache& operator = (const UniqueAccessExpireCache& aCache);
};


} // namespace Poco


#endif // Foundation_UniqueAccessExpireCache_INCLUDED

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