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/*
* The MIT License (MIT)
*
* Copyright (c) 2014-2016 Christian Schudt
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package rocks.xmpp.util.cache;
import java.util.Collection;
import java.util.Map;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedDeque;
import java.util.function.BiFunction;
import java.util.function.Function;
/**
* A simple concurrent implementation of a least-recently-used cache.
* <p>
* This cache is keeps a maximal number of items in memory and removes the least-recently-used item, when new items are added.
*
* @param <K> The key.
* @param <V> The value.
* @author Christian Schudt
* @see <a href="http://javadecodedquestions.blogspot.de/2013/02/java-cache-static-data-loading.html">http://javadecodedquestions.blogspot.de/2013/02/java-cache-static-data-loading.html</a>
* @see <a href="http://stackoverflow.com/a/22891780">http://stackoverflow.com/a/22891780</a>
*/
public final class LruCache<K, V> implements Map<K, V> {
private final int maxEntries;
private final Map<K, V> map;
final Queue<K> queue;
public LruCache(final int maxEntries) {
this.maxEntries = maxEntries;
this.map = new ConcurrentHashMap<>(maxEntries);
// Don't use a ConcurrentLinkedQueue here.
// There's a JDK bug, leading to OutOfMemoryError and high CPU usage:
// https://bugs.openjdk.java.net/browse/JDK-8054446
this.queue = new ConcurrentLinkedDeque<>();
}
@Override
public final int size() {
return map.size();
}
@Override
public final boolean isEmpty() {
return map.isEmpty();
}
@Override
public final boolean containsKey(final Object key) {
return map.containsKey(key);
}
@Override
public final boolean containsValue(final Object value) {
return map.containsValue(value);
}
@SuppressWarnings("unchecked")
@Override
public final V get(final Object key) {
final V v = map.get(key);
if (v != null) {
// Remove the key from the queue and re-add it to the tail. It is now the most recently used key.
keyUsed((K) key);
}
return v;
}
@Override
public final V put(final K key, final V value) {
V v = map.put(key, value);
keyUsed(key);
limit();
return v;
}
@Override
public final V remove(final Object key) {
queue.remove(key);
return map.remove(key);
}
@Override
public final void putAll(final Map<? extends K, ? extends V> m) {
for (Map.Entry<? extends K, ? extends V> entry : m.entrySet()) {
put(entry.getKey(), entry.getValue());
}
}
@Override
public final void clear() {
queue.clear();
map.clear();
}
@Override
public final Set<K> keySet() {
return map.keySet();
}
@Override
public final Collection<V> values() {
return map.values();
}
@Override
public final Set<Entry<K, V>> entrySet() {
return map.entrySet();
}
// Default methods
@Override
public final V putIfAbsent(final K key, final V value) {
final V v = map.putIfAbsent(key, value);
if (v == null) {
keyUsed(key);
}
limit();
return v;
}
@Override
public final boolean remove(final Object key, final Object value) {
final boolean removed = map.remove(key, value);
if (removed) {
queue.remove(key);
}
return removed;
}
@Override
public final boolean replace(final K key, final V oldValue, final V newValue) {
final boolean replaced = map.replace(key, oldValue, newValue);
if (replaced) {
keyUsed(key);
}
return replaced;
}
@Override
public final V replace(final K key, final V value) {
final V v = map.replace(key, value);
if (v != null) {
keyUsed(key);
}
return v;
}
@Override
public final V computeIfAbsent(final K key, final Function<? super K, ? extends V> mappingFunction) {
return map.computeIfAbsent(key, mappingFunction.<V>andThen(v -> {
keyUsed(key);
limit();
return v;
}));
}
@Override
public final V computeIfPresent(final K key, final BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
return map.computeIfPresent(key, remappingFunction.<V>andThen(v -> {
keyUsed(key);
limit();
return v;
}));
}
@Override
public final V compute(final K key, final BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
return map.compute(key, remappingFunction.<V>andThen(v -> {
keyUsed(key);
limit();
return v;
}));
}
@Override
public final V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
return map.merge(key, value, remappingFunction.<V>andThen(v -> {
keyUsed(key);
limit();
return v;
}));
}
private void limit() {
while (queue.size() > maxEntries) {
final K oldestKey = queue.poll();
if (oldestKey != null) {
map.remove(oldestKey);
}
}
}
private void keyUsed(final K key) {
// remove it from the queue and re-add it, to make it the most recently used key.
queue.remove(key);
queue.offer(key);
}
}
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