# Poco

# template < class TKey, class TValue >

# class UniqueExpireCache

Library: Foundation
Package: Cache
Header: Poco/UniqueExpireCache.h

## Description

An UniqueExpireCache caches entries for a given time amount. 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::Timestamp& getExpiration() const;

which returns the absolute timepoint when the entry will be invalidated. Accessing an object will NOT update this absolute expire timepoint. You can use the Poco::ExpirationDecorator to add the getExpiration method to values that do not have a getExpiration function.

Be careful when using an UniqueExpireCache. 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.

## Inheritance

Direct Base Classes: AbstractCache < TKey, TValue, UniqueExpireStrategy < TKey, TValue > >

All Base Classes: AbstractCache < TKey, TValue, UniqueExpireStrategy < TKey, TValue > >

## Constructors

### UniqueExpireCache

UniqueExpireCache();

## Destructor

### ~UniqueExpireCache

~UniqueExpireCache();