tuwien.auto.calimero.buffer.cache.LFUCache Maven / Gradle / Ivy
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/*
Calimero 2 - A library for KNX network access
Copyright (c) 2006, 2014 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 java.util.Comparator;
import java.util.SortedMap;
import java.util.TreeMap;
/**
* A {@link Cache} using a LFU replacement policy.
*
* The usage value of {@link CacheObject#getUsage()} equals the access count,
* {@link CacheObject#getCount()}.
*
* @author B. Malinowsky
*/
public class LFUCache extends ExpiringCache
{
private final SortedMap tree;
private int maxSize;
private long hits;
private long misses;
/**
* Creates a new LFU cache.
*
* Optionally, a maximum cache size and an expiring time can be specified.
*
* @param cacheSize maximum number of {@link CacheObject}s in the cache, or
* 0 for no maximum
* @param timeToExpire time in seconds for cache objects to stay valid,
* or 0 for no expiring
*/
public LFUCache(final int cacheSize, final int timeToExpire)
{
super(timeToExpire);
if (cacheSize > 0)
maxSize = cacheSize;
tree = new TreeMap<>(new LFUObjectCompare());
}
/**
* {@inheritDoc}
* If expiring of cache objects is set, and the timestamp of a
* {@link CacheObject} is renewed after it has been put into the cache, a
* new {@link #put(CacheObject)} is required for that object to apply the
* timestamp and keep the cache in a consistent state.
*/
@Override
public synchronized void put(final CacheObject obj)
{
// ensure sweeping is on if we have expiring objects
startSweeper();
final Object old = map.remove(obj.getKey());
if (old != null)
tree.remove(old);
else
ensureSizeLimits();
obj.resetTimestamp();
map.put(obj.getKey(), obj);
tree.put(obj, obj);
}
/* (non-Javadoc)
* @see tuwien.auto.calimero.buffer.cache.Cache#get(java.lang.Object)
*/
@Override
public synchronized CacheObject get(final Object key)
{
final CacheObject o = map.get(key);
if (o != null) {
tree.remove(o);
updateAccess(o);
tree.put(o, o);
++hits;
}
else
++misses;
return o;
}
/* (non-Javadoc)
* @see tuwien.auto.calimero.buffer.cache.Cache#remove(java.lang.Object)
*/
@Override
public synchronized void remove(final Object key)
{
final Object o = map.remove(key);
if (o != null)
tree.remove(o);
}
/* (non-Javadoc)
* @see tuwien.auto.calimero.buffer.cache.Cache#clear()
*/
@Override
public synchronized void clear()
{
stopSweeper();
map.clear();
tree.clear();
}
/* (non-Javadoc)
* @see tuwien.auto.calimero.buffer.cache.Cache#statistic()
*/
@Override
public synchronized Statistic statistic()
{
return new StatisticImpl(hits, misses);
}
/* (non-Javadoc)
* @see tuwien.auto.calimero.buffer.cache.ExpiringCache#notifyRemoved(
* tuwien.auto.calimero.buffer.cache.CacheObject)
*/
@Override
protected final void notifyRemoved(final CacheObject obj)
{
tree.remove(obj);
}
private void ensureSizeLimits()
{
if (maxSize > 0)
while (map.size() >= maxSize)
remove(tree.firstKey().getKey());
}
private static class LFUObjectCompare implements Comparator
{
LFUObjectCompare() {}
@Override
public int compare(final CacheObject o1, final CacheObject o2)
{
if (o1.getUsage() > o2.getUsage())
return 1;
if (o1.getUsage() < o2.getUsage())
return -1;
if (o1.getCount() > o2.getCount())
return 1;
if (o1.getCount() < o2.getCount())
return -1;
return 0;
}
}
}