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/*
* 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.dubbo.common.utils;
import java.util.LinkedHashMap;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* LRU-2
*
* When the data accessed for the first time, add it to history list. If the size of history list reaches max capacity, eliminate the earliest data (first in first out).
* When the data already exists in the history list, and be accessed for the second time, then it will be put into cache.
*
* TODO, consider replacing with ConcurrentHashMap to improve performance under concurrency
*/
public class LRU2Cache extends LinkedHashMap {
private static final long serialVersionUID = -5167631809472116969L;
private static final float DEFAULT_LOAD_FACTOR = 0.75f;
private static final int DEFAULT_MAX_CAPACITY = 1000;
private final Lock lock = new ReentrantLock();
private volatile int maxCapacity;
// as history list
private PreCache preCache;
public LRU2Cache() {
this(DEFAULT_MAX_CAPACITY);
}
public LRU2Cache(int maxCapacity) {
super(16, DEFAULT_LOAD_FACTOR, true);
this.maxCapacity = maxCapacity;
this.preCache = new PreCache<>(maxCapacity);
}
@Override
protected boolean removeEldestEntry(java.util.Map.Entry eldest) {
return size() > maxCapacity;
}
@Override
public boolean containsKey(Object key) {
lock.lock();
try {
return super.containsKey(key);
} finally {
lock.unlock();
}
}
@Override
public V get(Object key) {
lock.lock();
try {
return super.get(key);
} finally {
lock.unlock();
}
}
@Override
public V put(K key, V value) {
lock.lock();
try {
if (preCache.containsKey(key)) {
// add it to cache
preCache.remove(key);
return super.put(key, value);
} else {
// add it to history list
preCache.put(key, true);
return value;
}
} finally {
lock.unlock();
}
}
@Override
public V remove(Object key) {
lock.lock();
try {
preCache.remove(key);
return super.remove(key);
} finally {
lock.unlock();
}
}
@Override
public int size() {
lock.lock();
try {
return super.size();
} finally {
lock.unlock();
}
}
@Override
public void clear() {
lock.lock();
try {
preCache.clear();
super.clear();
} finally {
lock.unlock();
}
}
public int getMaxCapacity() {
return maxCapacity;
}
public void setMaxCapacity(int maxCapacity) {
preCache.setMaxCapacity(maxCapacity);
this.maxCapacity = maxCapacity;
}
static class PreCache extends LinkedHashMap {
private volatile int maxCapacity;
public PreCache() {
this(DEFAULT_MAX_CAPACITY);
}
public PreCache(int maxCapacity) {
super(16, DEFAULT_LOAD_FACTOR, true);
this.maxCapacity = maxCapacity;
}
@Override
protected boolean removeEldestEntry(java.util.Map.Entry eldest) {
return size() > maxCapacity;
}
public void setMaxCapacity(int maxCapacity) {
this.maxCapacity = maxCapacity;
}
}
}