org.apache.hadoop.yarn.util.RackResolver.java Source code

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Here is the source code for org.apache.hadoop.yarn.util.RackResolver.java

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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.hadoop.yarn.util;

import java.util.Collections;
import java.util.List;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceAudience.Private;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
import org.apache.hadoop.net.CachedDNSToSwitchMapping;
import org.apache.hadoop.net.DNSToSwitchMapping;
import org.apache.hadoop.net.NetworkTopology;
import org.apache.hadoop.net.Node;
import org.apache.hadoop.net.NodeBase;
import org.apache.hadoop.net.ScriptBasedMapping;
import org.apache.hadoop.util.ReflectionUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.annotations.VisibleForTesting;

@InterfaceAudience.LimitedPrivate({ "YARN", "MAPREDUCE" })
public final class RackResolver {
    private static DNSToSwitchMapping dnsToSwitchMapping;
    private static boolean initCalled = false;
    private static final Logger LOG = LoggerFactory.getLogger(RackResolver.class);

    /**
     * Hide the default constructor for utility class.
     */
    private RackResolver() {
    }

    public synchronized static void init(Configuration conf) {
        if (initCalled) {
            return;
        }
        initCalled = true;
        Class<? extends DNSToSwitchMapping> dnsToSwitchMappingClass = conf.getClass(
                CommonConfigurationKeysPublic.NET_TOPOLOGY_NODE_SWITCH_MAPPING_IMPL_KEY, ScriptBasedMapping.class,
                DNSToSwitchMapping.class);
        try {
            DNSToSwitchMapping newInstance = ReflectionUtils.newInstance(dnsToSwitchMappingClass, conf);
            // Wrap around the configured class with the Cached implementation so as
            // to save on repetitive lookups.
            // Check if the impl is already caching, to avoid double caching.
            dnsToSwitchMapping = ((newInstance instanceof CachedDNSToSwitchMapping) ? newInstance
                    : new CachedDNSToSwitchMapping(newInstance));
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Utility method for getting a hostname resolved to a node in the
     * network topology. This method initializes the class with the
     * right resolver implementation.
     * @param conf
     * @param hostName
     * @return node {@link Node} after resolving the hostname
     */
    public static Node resolve(Configuration conf, String hostName) {
        init(conf);
        return coreResolve(hostName);
    }

    /**
     * Utility method for getting a hostname resolved to a node in the
     * network topology. This method doesn't initialize the class.
     * Call {@link #init(Configuration)} explicitly.
     * @param hostName
     * @return node {@link Node} after resolving the hostname
     */
    public static Node resolve(String hostName) {
        if (!initCalled) {
            throw new IllegalStateException("RackResolver class not yet initialized");
        }
        return coreResolve(hostName);
    }

    private static Node coreResolve(String hostName) {
        List<String> tmpList = Collections.singletonList(hostName);
        List<String> rNameList = dnsToSwitchMapping.resolve(tmpList);
        String rName = NetworkTopology.DEFAULT_RACK;
        if (rNameList == null || rNameList.get(0) == null) {
            LOG.debug("Could not resolve {}. Falling back to {}", hostName, NetworkTopology.DEFAULT_RACK);
        } else {
            rName = rNameList.get(0);
            LOG.debug("Resolved {} to {}", hostName, rName);
        }
        return new NodeBase(hostName, rName);
    }

    /**
     * Only used by tests.
     */
    @Private
    @VisibleForTesting
    static DNSToSwitchMapping getDnsToSwitchMapping() {
        return dnsToSwitchMapping;
    }
}