001/* 002 * Copyright The Apache Software Foundation 003 * 004 * Licensed to the Apache Software Foundation (ASF) under one 005 * or more contributor license agreements. See the NOTICE file 006 * distributed with this work for additional information 007 * regarding copyright ownership. The ASF licenses this file 008 * to you under the Apache License, Version 2.0 (the 009 * "License"); you may not use this file except in compliance 010 * with the License. You may obtain a copy of the License at 011 * 012 * http://www.apache.org/licenses/LICENSE-2.0 013 * 014 * Unless required by applicable law or agreed to in writing, software 015 * distributed under the License is distributed on an "AS IS" BASIS, 016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 017 * See the License for the specific language governing permissions and 018 * limitations under the License. 019 */ 020package org.apache.hadoop.hbase.zookeeper; 021 022import java.util.concurrent.CountDownLatch; 023 024import org.apache.yetus.audience.InterfaceAudience; 025import org.apache.zookeeper.KeeperException; 026import org.slf4j.Logger; 027import org.slf4j.LoggerFactory; 028 029/** 030 * A ZooKeeper watcher meant to detect deletions of ZNodes. 031 */ 032@InterfaceAudience.Private 033public class DeletionListener extends ZKListener { 034 035 private static final Logger LOG = LoggerFactory.getLogger(DeletionListener.class); 036 037 private final String pathToWatch; 038 private final CountDownLatch deletedLatch; 039 040 private volatile Throwable exception; 041 042 /** 043 * Create a new instance of the deletion watcher. 044 * @param zkWatcher ZookeeperWatcher instance 045 * @param pathToWatch (Fully qualified) ZNode path that we are waiting to 046 * be deleted. 047 * @param deletedLatch Count down on this latch when deletion has occurred. 048 */ 049 public DeletionListener(ZKWatcher zkWatcher, String pathToWatch, 050 CountDownLatch deletedLatch) { 051 super(zkWatcher); 052 this.pathToWatch = pathToWatch; 053 this.deletedLatch = deletedLatch; 054 exception = null; 055 } 056 057 /** 058 * Check if an exception has occurred when re-setting the watch. 059 * @return True if we were unable to re-set a watch on a ZNode due to 060 * an exception. 061 */ 062 public boolean hasException() { 063 return exception != null; 064 } 065 066 /** 067 * Get the last exception which has occurred when re-setting the watch. 068 * Use hasException() to check whether or not an exception has occurred. 069 * @return The last exception observed when re-setting the watch. 070 */ 071 public Throwable getException() { 072 return exception; 073 } 074 075 @Override 076 public void nodeDataChanged(String path) { 077 if (!path.equals(pathToWatch)) { 078 return; 079 } 080 try { 081 if (!(ZKUtil.setWatchIfNodeExists(watcher, pathToWatch))) { 082 deletedLatch.countDown(); 083 } 084 } catch (KeeperException ex) { 085 exception = ex; 086 deletedLatch.countDown(); 087 LOG.error("Error when re-setting the watch on " + pathToWatch, ex); 088 } 089 } 090 091 @Override 092 public void nodeDeleted(String path) { 093 if (!path.equals(pathToWatch)) { 094 return; 095 } 096 if (LOG.isDebugEnabled()) { 097 LOG.debug("Processing delete on {}", pathToWatch); 098 } 099 deletedLatch.countDown(); 100 } 101}