/**
    * Copyright The Apache Software Foundation
    *
    * 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.hbase.zookeeper.lock;
  
  import java.io.IOException;
  import java.util.List;
  import java.util.SortedSet;
  import java.util.TreeSet;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.zookeeper.ZKUtil;
  import org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher;
  
  /**
   * ZooKeeper based read lock: does not exclude other read locks, but excludes
   * and is excluded by write locks.
   */
  @InterfaceAudience.Private
  public class ZKInterProcessReadLock extends ZKInterProcessLockBase {
  
    private static final Log LOG = LogFactory.getLog(ZKInterProcessReadLock.class);
  
    public ZKInterProcessReadLock(ZooKeeperWatcher zooKeeperWatcher,
        String znode, byte[] metadata, MetadataHandler handler) {
      super(zooKeeperWatcher, znode, metadata, handler, READ_LOCK_CHILD_NODE_PREFIX);
    }
  
    /**
     * {@inheritDoc}
     */
    @Override
    protected String getLockPath(String createdZNode, List<String> children) throws IOException {
      TreeSet<String> writeChildren =
          new TreeSet<String>(ZNodeComparator.COMPARATOR);
      for (String child : children) {
        if (isChildWriteLock(child)) {
          writeChildren.add(child);
        }
      }
      if (writeChildren.isEmpty()) {
        return null;
      }
      SortedSet<String> lowerChildren = writeChildren.headSet(createdZNode);
      if (lowerChildren.isEmpty()) {
        return null;
      }
      String pathToWatch = lowerChildren.last();
      String nodeHoldingLock = lowerChildren.first();
      String znode = ZKUtil.joinZNode(parentLockNode, nodeHoldingLock);
      handleLockMetadata(znode);
  
      return pathToWatch;
    }
  }