hadoop CacheableIPList 源码
haddop CacheableIPList 代码
文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/CacheableIPList.java
/**
* 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.util;
/**
* CacheableIPList loads a list of subnets from a file.
* The list is cached and the cache can be refreshed by specifying cache timeout.
* A negative value of cache timeout disables any caching.
*
* Thread safe.
*/
public class CacheableIPList implements IPList {
private final long cacheTimeout;
private volatile long cacheExpiryTimeStamp;
private volatile FileBasedIPList ipList;
public CacheableIPList(FileBasedIPList ipList, long cacheTimeout) {
this.cacheTimeout = cacheTimeout;
this.ipList = ipList;
updateCacheExpiryTime();
}
/**
* Reloads the ip list
*/
private void reset() {
ipList = ipList.reload();
updateCacheExpiryTime();
}
private void updateCacheExpiryTime() {
if (cacheTimeout < 0) {
cacheExpiryTimeStamp = -1; // no automatic cache expiry.
}else {
cacheExpiryTimeStamp = System.currentTimeMillis() + cacheTimeout;
}
}
/**
* Refreshes the ip list
*/
public void refresh () {
cacheExpiryTimeStamp = 0;
}
@Override
public boolean isIn(String ipAddress) {
//is cache expired
//Uses Double Checked Locking using volatile
if (cacheExpiryTimeStamp >= 0 && cacheExpiryTimeStamp < System.currentTimeMillis()) {
synchronized(this) {
//check if cache expired again
if (cacheExpiryTimeStamp < System.currentTimeMillis()) {
reset();
}
}
}
return ipList.isIn(ipAddress);
}
}
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