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/*
Calimero 2 - A library for KNX network access
Copyright (c) 2006, 2011 B. Malinowsky
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
Linking this library statically or dynamically with other modules is
making a combined work based on this library. Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.
As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under terms
of your choice, provided that you also meet, for each linked independent
module, the terms and conditions of the license of that module. An
independent module is a module which is not derived from or based on
this library. If you modify this library, you may extend this exception
to your version of the library, but you are not obligated to do so. If
you do not wish to do so, delete this exception statement from your
version.
*/
package tuwien.auto.calimero.buffer.cache;
import tuwien.auto.calimero.exception.KNXIllegalArgumentException;
/**
* Holds a key and a value entry and is used by a {@link Cache}.
*
* The key object is not allowed to change after creation of a cache object.
* An access count is maintained to tell the number of requests for this
* CacheObject by a cache.
* The usage value might be used by a caching policy to store a different way of
* access counting.
* A timestamp is stored of the most recent assignment of a value object hold by
* this CacheObject. This timestamp is created with
* {@link System#currentTimeMillis()}.
*
* @author B. Malinowsky
* @see Cache
* @see System#currentTimeMillis()
*/
public class CacheObject
{
/**
* The value object hold by this cache object.
*/
protected Object value;
private final Object key;
// hit count (increment count) of this object
private int count;
// timestamp of last value assignment
private volatile long timestamp;
// client usage indicator of this object (cache specific)
private volatile int usage;
/**
* Creates a CacheObject associated with key holding a
* value entry.
*
*
* @param key key of this {@link CacheObject}
* @param value value of this {@link CacheObject}
*/
public CacheObject(final Object key, final Object value)
{
if (key == null || value == null)
throw new KNXIllegalArgumentException(
"key and value must not be null");
this.key = key;
this.value = value;
resetTimestamp();
}
/**
* Returns the key associated with this cache object.
*
*
* @return the key object
*/
public Object getKey()
{
return key;
}
/**
* Gets the value entry hold by this cache object.
*
* Note that the value is guaranteed to be always a non null
* reference.
*
* @return the value object
*/
public synchronized Object getValue()
{
return value;
}
/**
* Returns the most up to date timestamp of the moment the current value
* object was assigned to this cache object, or the moment this object was
* {@link Cache#put(CacheObject)} into a cache.
*
*
* @return the timestamp in milliseconds of type long
* @see System#currentTimeMillis()
*/
public final long getTimestamp()
{
return timestamp;
}
/**
* Sets the timestamp to time = now.
*
* The timestamp is obtained by {@link System#currentTimeMillis()}.
*/
public final void resetTimestamp()
{
timestamp = System.currentTimeMillis();
}
/**
* Returns the access count this cache object was queried from the cache.
*
*
* @return the access count
*/
public final synchronized int getCount()
{
return count;
}
/**
* Increments the access count by 1.
*
* It is invoked by a {@link Cache} implementation to record a client access to
* this object.
*/
public final synchronized void incCount()
{
++count;
}
/**
* Sets the access count to 0.
*
*/
protected final synchronized void resetCount()
{
count = 0;
}
/**
* Returns the usage value of this cache object as defined by a particular cache.
*
*
* @return the usage value
*/
public final int getUsage()
{
return usage;
}
/**
* Sets a new usage value.
*
* The usage value might be used by a caching policy to store a different
* way of access counting.
*
* @param newUsage new usage value
*/
protected final void setUsage(final int newUsage)
{
usage = newUsage;
}
}