    001package net.sf.cpsolver.ifs.util;
    002
    003import java.lang.ref.Reference;
    004import java.lang.ref.ReferenceQueue;
    005import java.lang.ref.SoftReference;
    006import java.lang.ref.WeakReference;
    007import java.util.ArrayList;
    008import java.util.Collection;
    009import java.util.HashSet;
    010import java.util.HashMap;
    011import java.util.Iterator;
    012import java.util.List;
    013import java.util.Map;
    014import java.util.Set;
    015
    016import org.apache.log4j.Logger;
    017
    018/**
    019 * Simple table cache (key, value) using java soft references.
    020 *
    021 * @version IFS 1.2 (Iterative Forward Search)<br>
    022 *          Copyright (C) 2006 - 2010 Tomáš Müller<br>
    023 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    024 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    025 * <br>
    026 *          This library is free software; you can redistribute it and/or modify
    027 *          it under the terms of the GNU Lesser General Public License as
    028 *          published by the Free Software Foundation; either version 3 of the
    029 *          License, or (at your option) any later version. <br>
    030 * <br>
    031 *          This library is distributed in the hope that it will be useful, but
    032 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    033 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    034 *          Lesser General Public License for more details. <br>
    035 * <br>
    036 *          You should have received a copy of the GNU Lesser General Public
    037 *          License along with this library; if not see
    038 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    039 */
    040
    041public class SoftCache<K, V> implements Map<K, V> {
    042    private static Logger sLogger = Logger.getLogger(SoftCache.class);
    043    private HashMap<K, Reference<V>> iCache = new HashMap<K, Reference<V>>();
    044    private ReferenceQueue<V> iQueue = new ReferenceQueue<V>();
    045
    046    public SoftCache() {
    047        new SoftCacheCleanupThread().start();
    048    }
    049
    050    @Override
    051    public synchronized boolean isEmpty() {
    052        return iCache.isEmpty();
    053    }
    054
    055    @Override
    056    public synchronized void clear() {
    057        iCache.clear();
    058    }
    059
    060    @Override
    061    public synchronized boolean containsKey(Object key) {
    062        return iCache.containsKey(key);
    063    }
    064
    065    @Override
    066    public synchronized boolean containsValue(Object value) {
    067        for (Iterator<Reference<V>> i = iCache.values().iterator(); i.hasNext();) {
    068            Reference<V> ref = i.next();
    069            if (value.equals(ref.get()))
    070                return true;
    071        }
    072        return false;
    073    }
    074
    075    @Override
    076    public synchronized V get(Object key) {
    077        Reference<V> ref = iCache.get(key);
    078        return (ref == null ? null : ref.get());
    079    }
    080
    081    @Override
    082    public synchronized V remove(Object key) {
    083        Reference<V> ref = iCache.remove(key);
    084        return (ref == null ? null : ref.get());
    085    }
    086
    087    @Override
    088    public V put(K key, V value) {
    089        return putReference(key, new SoftReference<V>(value, iQueue));
    090    }
    091
    092    public Object putSoft(K key, V value) {
    093        return putReference(key, new SoftReference<V>(value, iQueue));
    094    }
    095
    096    public Object putWeak(K key, V value) {
    097        return putReference(key, new WeakReference<V>(value, iQueue));
    098    }
    099
    100    private synchronized V putReference(K key, Reference<V> ref) {
    101        Reference<V> old = iCache.put(key, ref);
    102        return (old == null ? null : old.get());
    103    }
    104
    105    @Override
    106    public void putAll(Map<? extends K, ? extends V> map) {
    107        for (Map.Entry<? extends K, ? extends V> entry : map.entrySet()) {
    108            put(entry.getKey(), entry.getValue());
    109        }
    110    }
    111
    112    @Override
    113    public synchronized int size() {
    114        return iCache.size();
    115    }
    116
    117    @Override
    118    public synchronized Set<K> keySet() {
    119        return iCache.keySet();
    120    }
    121
    122    @Override
    123    public synchronized Collection<V> values() {
    124        List<V> ret = new ArrayList<V>(iCache.size());
    125        for (Reference<V> ref : iCache.values()) {
    126            V value = ref.get();
    127            if (value != null)
    128                ret.add(value);
    129        }
    130        return ret;
    131    }
    132
    133    @Override
    134    public synchronized Set<Map.Entry<K, V>> entrySet() {
    135        Set<Map.Entry<K, V>> ret = new HashSet<Map.Entry<K, V>>(iCache.size());
    136        for (Map.Entry<K, Reference<V>> entry : iCache.entrySet()) {
    137            if (entry.getValue().get() != null)
    138                ret.add(new Entry<K, V>(entry.getKey(), entry.getValue().get()));
    139
    140        }
    141        return ret;
    142    }
    143
    144    public synchronized void cleanDeallocated() {
    145        int nrCleaned = 0;
    146        for (Iterator<Map.Entry<K, Reference<V>>> i = iCache.entrySet().iterator(); i.hasNext();) {
    147            Map.Entry<K, Reference<V>> entry = i.next();
    148            if (entry.getValue().get() == null) {
    149                i.remove();
    150                nrCleaned++;
    151            }
    152        }
    153        sLogger.debug("cleaned " + nrCleaned + " of " + (iCache.size() + nrCleaned) + " items.");
    154    }
    155
    156    private ReferenceQueue<V> getQueue() {
    157        return iQueue;
    158    }
    159
    160    private class SoftCacheCleanupThread extends Thread {
    161        private SoftCacheCleanupThread() {
    162            setDaemon(true);
    163            setName("SoftCacheCleanup");
    164        }
    165
    166        @Override
    167        public void run() {
    168            try {
    169                while (true) {
    170                    ReferenceQueue<V> q = getQueue();
    171                    if (q == null)
    172                        break; // soft cache deallocated -- stop the thread
    173                    if (q.remove(10000) == null)
    174                        continue; // was there something deallocated?
    175                    while (q.poll() != null) {
    176                    } // pull all the deallocated references from the queue
    177                    cleanDeallocated(); // clean the cache
    178                }
    179                sLogger.debug("cache terminated");
    180            } catch (Exception e) {
    181                sLogger.error("cleanup thread failed, reason:" + e.getMessage(), e);
    182            }
    183        }
    184    }
    185
    186    private static class Entry<K, V> implements Map.Entry<K, V> {
    187        private K iKey = null;
    188        private V iValue = null;
    189
    190        private Entry(K key, V value) {
    191            iKey = key;
    192            iValue = value;
    193        }
    194
    195        @Override
    196        public boolean equals(Object o) {
    197            if (o == null || !(o instanceof Map.Entry<?, ?>))
    198                return false;
    199            Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
    200            return (getKey() == null ? e.getKey() == null : getKey().equals(e.getKey()))
    201                    && (getValue() == null ? e.getValue() == null : getValue().equals(e.getValue()));
    202        }
    203
    204        @Override
    205        public int hashCode() {
    206            return (getKey() == null ? 0 : getKey().hashCode()) ^ (getValue() == null ? 0 : getValue().hashCode());
    207        }
    208
    209        @Override
    210        public K getKey() {
    211            return iKey;
    212        }
    213
    214        @Override
    215        public V getValue() {
    216            return iValue;
    217        }
    218
    219        @Override
    220        public V setValue(V value) throws UnsupportedOperationException {
    221            throw new UnsupportedOperationException();
    222        }
    223    }
    224
    225    public static void test() {
    226        for (int t = 0; t < 10; t++) {
    227            SoftCache<Integer, byte[]> x = new SoftCache<Integer, byte[]>();
    228            for (int i = 0; i < 1000000; i++)
    229                x.put(new Integer(i), new byte[1024]);
    230        }
    231    }
    232}