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

import com.google.common.base.Strings;
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 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 list of hostname resolved to a list of node
   *  in the network topology. This method initializes the class with the
   * right resolver implementation.
   * @param conf
   * @param hostNames
   * @return nodes {@link Node} after resolving the hostnames
   */
  public static List resolve(
      Configuration conf, List hostNames) {
    init(conf);
    return coreResolve(hostNames);
  }

  /**
   * 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);
  }

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

  private static Node coreResolve(String hostName) {
    List  tmpList = Collections.singletonList(hostName);
    return coreResolve(tmpList).get(0);
  }

  private static List coreResolve(List hostNames) {
    List nodes = new ArrayList(hostNames.size());
    List rNameList = dnsToSwitchMapping.resolve(hostNames);
    if (rNameList == null || rNameList.isEmpty()) {
      for (String hostName : hostNames) {
        nodes.add(new NodeBase(hostName, NetworkTopology.DEFAULT_RACK));
      }
      LOG.info("Got an error when resolve hostNames. Falling back to "
          + NetworkTopology.DEFAULT_RACK + " for all.");
    } else {
      for (int i = 0; i < hostNames.size(); i++) {
        if (Strings.isNullOrEmpty(rNameList.get(i))) {
          // fallback to use default rack
          nodes.add(new NodeBase(hostNames.get(i),
              NetworkTopology.DEFAULT_RACK));
          LOG.debug("Could not resolve {}. Falling back to {}",
              hostNames.get(i), NetworkTopology.DEFAULT_RACK);
        } else {
          nodes.add(new NodeBase(hostNames.get(i), rNameList.get(i)));
          LOG.debug("Resolved {} to {}", hostNames.get(i), rNameList.get(i));
        }
      }
    }
    return nodes;
  }

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

  /**
   * Only used by tests.
   */
  @Private
  @VisibleForTesting
  static void reset() {
    initCalled = false;
    dnsToSwitchMapping = null;
  }
}