Added UniqueAccess caches

Foundation/include/Poco/UniqueAccessExpireCache.h

@@ -39,31 +39,51 @@
 #ifndef  Foundation_UniqueAccessExpireCache_INCLUDED
 #define  Foundation_UniqueAccessExpireCache_INCLUDED
 
+
 #include "Poco/AbstractCache.h"
-#include "Poco/UniqueExpireCache.h"
 #include "Poco/UniqueAccessExpireStrategy.h"
 
-namespace Poco
-{ 
-	template <class TKey, class TValue>
-	class UniqueAccessExpireCache: public Poco::AbstractCache<TKey, TValue, Poco::UniqueAccessExpireStrategy<TKey, TValue> >
+
+namespace Poco {
+
+
+template <class TKey, class TValue> 
+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& getExpiration() 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() + getExpiration().
+	/// 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>())
 	{
-		friend class Poco::UniqueAccessExpireStrategy<TKey, TValue>;
-		
-		public:
-			UniqueAccessExpireCache ():
-				Poco::AbstractCache<TKey, TValue, Poco::UniqueAccessExpireStrategy<TKey, TValue> > (UniqueAccessExpireStrategy<TKey, TValue> (this))
-			{
-			}
+	}
+
+	~UniqueAccessExpireCache()
+	{
+	}
+
+private:
+	UniqueAccessExpireCache(const UniqueAccessExpireCache& aCache);
+	UniqueAccessExpireCache& operator = (const UniqueAccessExpireCache& aCache);
+};
 
-			~UniqueAccessExpireCache ()
-			{
-			}
 
-		private:
-			UniqueAccessExpireCache (const Poco::UniqueExpireCache<TKey, TValue>& aCache);
-			UniqueAccessExpireCache& operator = (const Poco::UniqueExpireCache<TKey, TValue>& aCache);
-	};
 } // namespace Poco
 
 #endif