/**
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hbase.util;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.NavigableMap;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* A SortedMap implementation that uses Soft Reference values
* internally to make it play well with the GC when in a low-memory
* situation. Use as a cache where you also need SortedMap functionality.
*
* @param <K> key class
* @param <V> value class
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class SoftValueSortedMap<K,V> implements SortedMap<K,V> {
private final SortedMap<K, SoftValue<K,V>> internalMap;
private final ReferenceQueue<V> rq = new ReferenceQueue<V>();
private Object sync;
/** Constructor */
public SoftValueSortedMap() {
this(new TreeMap<K, SoftValue<K,V>>());
}
/**
* Constructor
* @param c comparator
*/
public SoftValueSortedMap(final Comparator<K> c) {
this(new TreeMap<K, SoftValue<K,V>>(c));
}
/** Internal constructor
* @param original object to wrap and synchronize on
*/
private SoftValueSortedMap(SortedMap<K,SoftValue<K,V>> original) {
this(original, original);
}
/** Internal constructor
* For headMap, tailMap, and subMap support
* @param original object to wrap
* @param sync object to synchronize on
*/
private SoftValueSortedMap(SortedMap<K,SoftValue<K,V>> original, Object sync) {
this.internalMap = original;
this.sync = sync;
}
/**
* Checks soft references and cleans any that have been placed on
* ReferenceQueue. Call if get/put etc. are not called regularly.
* Internally these call checkReferences on each access.
* @return How many references cleared.
*/
@SuppressWarnings("unchecked")
private int checkReferences() {
int i = 0;
for (Reference<? extends V> ref; (ref = this.rq.poll()) != null;) {
i++;
this.internalMap.remove(((SoftValue<K,V>)ref).key);
}
return i;
}
public V put(K key, V value) {
synchronized(sync) {
checkReferences();
SoftValue<K,V> oldValue = this.internalMap.put(key,
new SoftValue<K,V>(key, value, this.rq));
return oldValue == null ? null : oldValue.get();
}
}
@Override
public void putAll(Map<? extends K, ? extends V> m) {
throw new RuntimeException("Not implemented");
}
public V get(Object key) {
synchronized(sync) {
checkReferences();
SoftValue<K,V> value = this.internalMap.get(key);
if (value == null) {
return null;
}
if (value.get() == null) {
this.internalMap.remove(key);
return null;
}
return value.get();
}
}
public V remove(Object key) {
synchronized(sync) {
checkReferences();
SoftValue<K,V> value = this.internalMap.remove(key);
return value == null ? null : value.get();
}
}
public boolean containsKey(Object key) {
synchronized(sync) {
checkReferences();
return this.internalMap.containsKey(key);
}
}
public boolean containsValue(Object value) {
throw new UnsupportedOperationException("Don't support containsValue!");
}
public K firstKey() {
synchronized(sync) {
checkReferences();
return internalMap.firstKey();
}
}
public K lastKey() {
synchronized(sync) {
checkReferences();
return internalMap.lastKey();
}
}
public SoftValueSortedMap<K,V> headMap(K key) {
synchronized(sync) {
checkReferences();
return new SoftValueSortedMap<K,V>(this.internalMap.headMap(key), sync);
}
}
public SoftValueSortedMap<K,V> tailMap(K key) {
synchronized(sync) {
checkReferences();
return new SoftValueSortedMap<K,V>(this.internalMap.tailMap(key), sync);
}
}
public SoftValueSortedMap<K,V> subMap(K fromKey, K toKey) {
synchronized(sync) {
checkReferences();
return new SoftValueSortedMap<K,V>(this.internalMap.subMap(fromKey,
toKey), sync);
}
}
/*
* retrieves the value associated with the greatest key strictly less than
* the given key, or null if there is no such key
* @param key the key we're interested in
*/
public synchronized V lowerValueByKey(K key) {
synchronized(sync) {
checkReferences();
Map.Entry<K,SoftValue<K,V>> entry =
((NavigableMap<K, SoftValue<K,V>>) this.internalMap).lowerEntry(key);
if (entry==null) {
return null;
}
SoftValue<K,V> value=entry.getValue();
if (value==null) {
return null;
}
if (value.get() == null) {
this.internalMap.remove(key);
return null;
}
return value.get();
}
}
public boolean isEmpty() {
synchronized(sync) {
checkReferences();
return this.internalMap.isEmpty();
}
}
public int size() {
synchronized(sync) {
checkReferences();
return this.internalMap.size();
}
}
public void clear() {
synchronized(sync) {
checkReferences();
this.internalMap.clear();
}
}
public Set<K> keySet() {
synchronized(sync) {
checkReferences();
// this is not correct as per SortedMap contract (keySet should be
// modifiable)
// needed here so that another thread cannot modify the keyset
// without locking
return Collections.unmodifiableSet(this.internalMap.keySet());
}
}
public Comparator<? super K> comparator() {
return this.internalMap.comparator();
}
public Set<Map.Entry<K,V>> entrySet() {
synchronized(sync) {
checkReferences();
// this is not correct as per SortedMap contract (entrySet should be
// backed by map)
Set<Map.Entry<K, V>> realEntries = new LinkedHashSet<Map.Entry<K, V>>();
for (Map.Entry<K, SoftValue<K, V>> entry : this.internalMap.entrySet()) {
realEntries.add(entry.getValue());
}
return realEntries;
}
}
public Collection<V> values() {
synchronized(sync) {
checkReferences();
ArrayList<V> hardValues = new ArrayList<V>();
for (SoftValue<K,V> softValue : this.internalMap.values()) {
hardValues.add(softValue.get());
}
return hardValues;
}
}
private static class SoftValue<K,V> extends SoftReference<V> implements Map.Entry<K, V> {
final K key;
SoftValue(K key, V value, ReferenceQueue<V> q) {
super(value, q);
this.key = key;
}
public K getKey() {
return this.key;
}
public V getValue() {
return get();
}
public V setValue(V value) {
throw new RuntimeException("Not implemented");
}
}
}