// // UniqueAccessExpireCache.h // // $Id: //poco/1.4/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. // // SPDX-License-Identifier: BSL-1.0 // #ifndef Foundation_UniqueAccessExpireCache_INCLUDED #define Foundation_UniqueAccessExpireCache_INCLUDED #include "Poco/AbstractCache.h" #include "Poco/UniqueAccessExpireStrategy.h" namespace Poco { template < class TKey, class TValue, class TMutex = FastMutex, class TEventMutex = FastMutex > class UniqueAccessExpireCache: public AbstractCache<TKey, TValue, UniqueAccessExpireStrategy<TKey, TValue>, TMutex, TEventMutex> /// 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>, TMutex, TEventMutex>(UniqueAccessExpireStrategy<TKey, TValue>()) { } ~UniqueAccessExpireCache() { } private: UniqueAccessExpireCache(const UniqueAccessExpireCache& aCache); UniqueAccessExpireCache& operator = (const UniqueAccessExpireCache& aCache); }; } // namespace Poco #endif // Foundation_UniqueAccessExpireCache_INCLUDED