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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.hive.shims;

import java.util.HashMap;
import java.util.Map;

import org.apache.hadoop.util.VersionInfo;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * ShimLoader.
 *
 */
public abstract class ShimLoader {
  private static final Logger LOG = LoggerFactory.getLogger(ShimLoader.class);
  public static final String HADOOP23VERSIONNAME = "0.23";

  private static volatile HadoopShims hadoopShims;

  /**
   * The names of the classes for shimming Hadoop for each major version.
   */
  private static final HashMap HADOOP_SHIM_CLASSES =
      new HashMap();

  static {
    HADOOP_SHIM_CLASSES.put(HADOOP23VERSIONNAME, "org.apache.hadoop.hive.shims.Hadoop23Shims");
  }

  /**
   * The names of the classes for shimming Hadoop's event counter
   */
  private static final HashMap EVENT_COUNTER_SHIM_CLASSES =
      new HashMap();

  static {
    EVENT_COUNTER_SHIM_CLASSES.put(HADOOP23VERSIONNAME, "org.apache.hadoop.log.metrics" +
        ".EventCounter");
  }

  /**
   * The names of the classes for shimming HadoopThriftAuthBridge
   */
  private static final HashMap HADOOP_THRIFT_AUTH_BRIDGE_CLASSES =
      new HashMap();

  static {
    HADOOP_THRIFT_AUTH_BRIDGE_CLASSES.put(HADOOP23VERSIONNAME,
        "org.apache.hadoop.hive.metastore.security.HadoopThriftAuthBridge23");
  }


  private static final String SCHEDULER_SHIM_CLASSE =
    "org.apache.hadoop.hive.schshim.FairSchedulerShim";

  /**
   * Factory method to get an instance of HadoopShims based on the
   * version of Hadoop on the classpath.
   */
  public static HadoopShims getHadoopShims() {
    if (hadoopShims == null) {
      synchronized (ShimLoader.class) {
        if (hadoopShims == null) {
          try {
            hadoopShims = loadShims(HADOOP_SHIM_CLASSES, HadoopShims.class);
          } catch (Throwable t) {
            LOG.error("Error loading shims", t);
            throw new RuntimeException(t);
          }
        }
      }
    }
    return hadoopShims;
  }


  private static  T loadShims(Map classMap, Class xface) {
    String vers = getMajorVersion();
    String className = classMap.get(vers);
    return createShim(className, xface);
  }

  private static  T createShim(String className, Class xface) {
    try {
      Class clazz = Class.forName(className);
      return xface.cast(clazz.newInstance());
    } catch (Exception e) {
      throw new RuntimeException("Could not load shims in class " + className, e);
    }
  }

  /**
   * Return the "major" version of Hadoop currently on the classpath.
   * Releases in the 1.x and 2.x series are mapped to the appropriate
   * 0.x release series, e.g. 1.x is mapped to "0.20S" and 2.x
   * is mapped to "0.23".
   */
  public static String getMajorVersion() {
    String vers = VersionInfo.getVersion();

    String[] parts = vers.split("\\.");
    if (parts.length < 2) {
      throw new RuntimeException("Illegal Hadoop Version: " + vers +
          " (expected A.B.* format)");
    }

    switch (Integer.parseInt(parts[0])) {
    case 2:
    case 3:
      return HADOOP23VERSIONNAME;
    default:
      throw new IllegalArgumentException("Unrecognized Hadoop major version number: " + vers);
    }
  }

  private ShimLoader() {
    // prevent instantiation
  }
}