001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.zookeeper;
019
020import java.util.concurrent.CountDownLatch;
021import org.apache.yetus.audience.InterfaceAudience;
022import org.apache.zookeeper.KeeperException;
023import org.slf4j.Logger;
024import org.slf4j.LoggerFactory;
025
026/**
027 * A ZooKeeper watcher meant to detect deletions of ZNodes.
028 */
029@InterfaceAudience.Private
030public class DeletionListener extends ZKListener {
031
032  private static final Logger LOG = LoggerFactory.getLogger(DeletionListener.class);
033
034  private final String pathToWatch;
035  private final CountDownLatch deletedLatch;
036
037  private volatile Throwable exception;
038
039  /**
040   * Create a new instance of the deletion watcher.
041   * @param zkWatcher    ZookeeperWatcher instance
042   * @param pathToWatch  (Fully qualified) ZNode path that we are waiting to be deleted.
043   * @param deletedLatch Count down on this latch when deletion has occurred.
044   */
045  public DeletionListener(ZKWatcher zkWatcher, String pathToWatch, CountDownLatch deletedLatch) {
046    super(zkWatcher);
047    this.pathToWatch = pathToWatch;
048    this.deletedLatch = deletedLatch;
049    exception = null;
050  }
051
052  /**
053   * Check if an exception has occurred when re-setting the watch.
054   * @return True if we were unable to re-set a watch on a ZNode due to an exception.
055   */
056  public boolean hasException() {
057    return exception != null;
058  }
059
060  /**
061   * Get the last exception which has occurred when re-setting the watch. Use hasException() to
062   * check whether or not an exception has occurred.
063   * @return The last exception observed when re-setting the watch.
064   */
065  public Throwable getException() {
066    return exception;
067  }
068
069  @Override
070  public void nodeDataChanged(String path) {
071    if (!path.equals(pathToWatch)) {
072      return;
073    }
074    try {
075      if (!(ZKUtil.setWatchIfNodeExists(watcher, pathToWatch))) {
076        deletedLatch.countDown();
077      }
078    } catch (KeeperException ex) {
079      exception = ex;
080      deletedLatch.countDown();
081      LOG.error("Error when re-setting the watch on " + pathToWatch, ex);
082    }
083  }
084
085  @Override
086  public void nodeDeleted(String path) {
087    if (!path.equals(pathToWatch)) {
088      return;
089    }
090    if (LOG.isDebugEnabled()) {
091      LOG.debug("Processing delete on {}", pathToWatch);
092    }
093    deletedLatch.countDown();
094  }
095}