/*
 * LensKit, an open source recommender systems toolkit.
 * Copyright 2010-2013 Regents of the University of Minnesota and contributors
 * Work on LensKit has been funded by the National Science Foundation under
 * grants IIS 05-34939, 08-08692, 08-12148, and 10-17697.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 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., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */
package org.grouplens.lenskit.data.snapshot;

import it.unimi.dsi.fastutil.longs.Long2ObjectMap;
import it.unimi.dsi.fastutil.longs.Long2ObjectMaps;
import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
import org.grouplens.lenskit.collections.FastCollection;
import org.grouplens.lenskit.data.pref.IndexedPreference;
import org.grouplens.lenskit.data.pref.Preferences;
import org.grouplens.lenskit.vectors.SparseVector;

import javax.annotation.OverridingMethodsMustInvokeSuper;

/**
 * Base class for implementing preference snapshots.
 */
public abstract class AbstractPreferenceSnapshot implements PreferenceSnapshot {
    /**
     * The user vector cache.
     */
    protected volatile Long2ObjectMap<SparseVector> cache;

    /**
     * Initialize the snapshot.
     */
    public AbstractPreferenceSnapshot() {
        cache = Long2ObjectMaps.synchronize(new Long2ObjectOpenHashMap<SparseVector>());
    }

    @Override
    public SparseVector userRatingVector(long userId) {
        SparseVector data = cache.get(userId);
        if (data != null) {
            return data;
        } else {
            FastCollection<IndexedPreference> prefs = this.getUserRatings(userId);
            data = Preferences.userPreferenceVector(prefs).freeze();
            cache.put(userId, data);
            return data;
        }
    }

    @Override
    @OverridingMethodsMustInvokeSuper
    public void close() {
        cache = null;
    }
}

@@ -1690,17 +1690,8 @@
 ted 
-volatile 
 Long
@@ -1722,16 +1722,16 @@
  cache;%0A
+
 %0A    /**
@@ -1975,24 +1975,101 @@
 g userId) %7B%0A
+        // FIXME Don't make this so locky%0A        synchronized (cache) %7B%0A    
         Spar
@@ -2111,16 +2111,20 @@
         
+    
 if (data
@@ -2139,32 +2139,36 @@
 ) %7B%0A            
+  
+  
 return data;%0A   
@@ -2172,16 +2172,20 @@
         
+    
 %7D else %7B
@@ -2197,16 +2197,20 @@
         
+ 
+   
 FastColl
@@ -2284,16 +2284,20 @@
         
+    
 data = P
@@ -2353,24 +2353,28 @@
             
+ 
+   
 cache.put(us
@@ -2386,16 +2386,20 @@
  data);%0A
+    
         
@@ -2407,32 +2407,46 @@
    return data;%0A
+            %7D%0A
         %7D%0A    %7D%0A

Fix locking bugs in preference snapshot caching