/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
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; version 2 of the License.
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
*/
/*
* Created on Jan 2, 2012
*/
package com.bigdata.rdf.lexicon;
import com.bigdata.cache.ConcurrentWeakValueCacheWithBatchedUpdates;
import com.bigdata.rdf.internal.IV;
import com.bigdata.rdf.model.BigdataValue;
/**
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public class TermCache<K extends IV<?, ?>, V extends BigdataValue> implements
ITermCache<K, V> {
private final ConcurrentWeakValueCacheWithBatchedUpdates<IV<?, ?>, V> delegate;
public TermCache(
final ConcurrentWeakValueCacheWithBatchedUpdates<IV<?, ?>, V> delegate) {
if (delegate == null)
throw new IllegalArgumentException();
this.delegate = delegate;
}
@Override
public int size() {
return delegate.size();
}
@Override
public V get(final K k) {
return delegate.get(k);
}
/**
* {@inheritDoc}
* <p>
*
* @see https://sourceforge.net/apps/trac/bigdata/ticket/437 (Thread-local
* cache combined with unbounded thread pools causes effective memory
* leak)
*/
@Override
public V putIfAbsent(final K k, final V v) {
V tmp = delegate.get(k);
if(tmp != null) {
// No need to write on the map.
return tmp;
}
/*
* Clone the IV in order to ensure that the hard reference from the IV
* to the BigdataValue cached on the IV has been cleared before we enter
* the IV into the map.
*
* Note: If the key has a hard reference to the value then the value can
* never become only weakly reachable. That turns the term cache into a
* a memory leak! This is why we break the IV.cache reference here.
*
* Note: We do not need to break the cache reference for the vocabulary
* IVs. They are already pinned by a hard reference and hence will never
* become only weakly reachable. There is also only a limited number of
* such vocabulary IVs so the size of the map never becomes a problem.
* Finally, the vocabulary IVs tend to be frequently used, so having
* them pinned is useful.
*/
return delegate.putIfAbsent(k.clone(true/*clearCache*/), v);
}
@Override
public void clear() {
delegate.clear();
}
}