org.apache.hadoop.hbase.zookeeper.lock.DeletionWatcher.java Source code

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Here is the source code for org.apache.hadoop.hbase.zookeeper.lock.DeletionWatcher.java

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/**
 * 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 org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.zookeeper.ZooKeeperWrapper;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.EventType;

import java.util.concurrent.CountDownLatch;

/**
 * A ZooKeeper watcher meant to detect deletions of ZNodes.
 */
public class DeletionWatcher implements Watcher {

    private static final Log LOG = LogFactory.getLog(DeletionWatcher.class);

    private final ZooKeeperWrapper zooKeeperWrapper;
    private final String pathToWatch;
    private final CountDownLatch deletedLatch;

    private volatile Throwable exception;

    /**
     * Create a new instance of the deletion watcher.
     * @param zkWrapper
     * @param pathToWatch (Fully qualified) ZNode path that we are waiting to
     *                    be deleted.
     * @param deletedLatch Count down on this latch when deletion has occured.
     */
    public DeletionWatcher(ZooKeeperWrapper zkWrapper, String pathToWatch, CountDownLatch deletedLatch) {
        this.zooKeeperWrapper = zkWrapper;
        this.pathToWatch = pathToWatch;
        this.deletedLatch = deletedLatch;
        exception = null;
    }

    /**
     * Check if an exception has occurred when re-setting the watch.
     * @return True if we were unable to re-set a watch on a ZNode due to
     *         an exception.
     */
    public boolean hasException() {
        return exception != null;
    }

    /**
     * Get the last exception which has occurred when re-setting the watch.
     * Use hasException() to check whether or not an exception has occurred.
     * @return The last exception observed when re-setting the watch.
     */
    public Throwable getException() {
        return exception;
    }

    @Override
    public void process(WatchedEvent watchedEvent) {
        if (watchedEvent.getPath().equals(pathToWatch)) {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Processing event " + watchedEvent + " on " + pathToWatch);
            }
            try {
                if (watchedEvent.getType() == EventType.NodeDeleted
                        || !(zooKeeperWrapper.setWatchIfNodeExists(pathToWatch))) {
                    deletedLatch.countDown();
                }
            } catch (Throwable t) {
                exception = t;
                deletedLatch.countDown();
                LOG.error("Error when re-setting the watch on " + pathToWatch, t);
            }
        }
    }
}