hadoop RandomResolver 源码
haddop RandomResolver 代码
文件路径：/hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/order/RandomResolver.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.hdfs.server.federation.resolver.order;
import java.util.Set;
import java.util.concurrent.ThreadLocalRandom;
import org.apache.commons.collections.CollectionUtils;
import org.apache.hadoop.hdfs.server.federation.resolver.PathLocation;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.hadoop.thirdparty.com.google.common.collect.Iterables;
/**
* Order the destinations randomly.
*/
public class RandomResolver implements OrderedResolver {
private static final Logger LOG =
LoggerFactory.getLogger(RandomResolver.class);
/**
* Get a random name space from the path.
*
* @param path Path ignored by this policy.
* @param loc Federated location with multiple destinations.
* @return Random name space.
*/
public String getFirstNamespace(final String path, final PathLocation loc) {
final Set<String> namespaces = (loc == null) ? null : loc.getNamespaces();
if (CollectionUtils.isEmpty(namespaces)) {
LOG.error("Cannot get namespaces for {}", loc);
return null;
}
final int index = ThreadLocalRandom.current().nextInt(namespaces.size());
return Iterables.get(namespaces, index);
}
}
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