org.apache.zookeeper.server.ResponseCache Maven / Gradle / Ivy
/*
* 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.zookeeper.server;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;
import org.apache.zookeeper.data.Stat;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
@SuppressWarnings("serial")
public class ResponseCache {
private static final Logger LOG = LoggerFactory.getLogger(ResponseCache.class);
// Magic number chosen to be "big enough but not too big"
public static final int DEFAULT_RESPONSE_CACHE_SIZE = 400;
private final int cacheSize;
private static class Entry {
public Stat stat;
public byte[] data;
}
private final Map cache;
public ResponseCache(int cacheSize) {
this.cacheSize = cacheSize;
cache = Collections.synchronizedMap(new LRUCache<>(cacheSize));
LOG.info("Response cache size is initialized with value {}.", cacheSize);
}
public int getCacheSize() {
return cacheSize;
}
public void put(String path, byte[] data, Stat stat) {
Entry entry = new Entry();
entry.data = data;
entry.stat = stat;
cache.put(path, entry);
}
public byte[] get(String key, Stat stat) {
Entry entry = cache.get(key);
if (entry == null) {
return null;
}
if (!stat.equals(entry.stat)) {
// The node has been modified, invalidate cache.
cache.remove(key);
return null;
} else {
return entry.data;
}
}
public boolean isEnabled() {
return cacheSize > 0;
}
private static class LRUCache extends LinkedHashMap {
private int cacheSize;
LRUCache(int cacheSize) {
super(cacheSize / 4);
this.cacheSize = cacheSize;
}
protected boolean removeEldestEntry(Map.Entry eldest) {
return size() >= cacheSize;
}
}
}