org.apache.hadoop.hbase.master.ZKMasterAddressWatcher.java Source code

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Here is the source code for org.apache.hadoop.hbase.master.ZKMasterAddressWatcher.java

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/**
 * Copyright 2010 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.master;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.HServerAddress;
import org.apache.hadoop.hbase.Stoppable;
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.atomic.AtomicBoolean;

/**
 * ZooKeeper watcher for the master address.  Also watches the cluster state
 * flag so will shutdown this master if cluster has been shutdown.
 * <p>Used by the Master.  Waits on the master address ZNode delete event.  When
 * multiple masters are brought up, they race to become master by writing their
 * address to ZooKeeper. Whoever wins becomes the master, and the rest wait for
 * that ephemeral node in ZooKeeper to evaporate (meaning the master went down),
 * at which point they try to write their own address to become the new master.
 */
class ZKMasterAddressWatcher implements Watcher {
    private static final Log LOG = LogFactory.getLog(ZKMasterAddressWatcher.class);

    private ZooKeeperWrapper zookeeper;
    private final StoppableMaster stoppable;

    /**
     * Create this watcher using passed ZooKeeperWrapper instance.
     * @param zk ZooKeeper
     * @param flag Flag to set to request shutdown.
     */
    ZKMasterAddressWatcher(final ZooKeeperWrapper zk, final StoppableMaster stoppable) {
        this.stoppable = stoppable;
        this.zookeeper = zk;
    }

    /**
     * @see org.apache.zookeeper.Watcher#process(org.apache.zookeeper.WatchedEvent)
     */
    @Override
    public synchronized void process(WatchedEvent event) {
        EventType type = event.getType();
        if (type.equals(EventType.NodeDeleted)) {
            if (event.getPath().equals(this.zookeeper.clusterStateZNode)) {
                LOG.info("Cluster shutdown while waiting, shutting down" + " this master.");
                this.stoppable.requestClusterShutdown();
            } else if (event.getPath().equals(this.zookeeper.masterElectionZNode)) {
                LOG.info("Master address ZNode deleted, notifying waiting masters");
                notifyAll();
            }
        } else if (type.equals(EventType.NodeCreated)) {
            if (event.getPath().equals(this.zookeeper.clusterStateZNode)) {
                LOG.info("Resetting watch on cluster state node.");
                this.zookeeper.setClusterStateWatch();
            } else if (event.getPath().equals(this.zookeeper.masterElectionZNode)) {
                LOG.info("Master address ZNode created, check exists and reset watch");
                if (!zookeeper.exists(zookeeper.masterElectionZNode, true)) {
                    LOG.debug("Got NodeCreated for master node but it does not exist now" + ", notifying");
                    notifyAll();
                }
            }
        }
    }

    /**
     * Wait for master address to be available. This sets a watch in ZooKeeper and
     * blocks until the master address ZNode gets deleted.
     */
    private synchronized void waitForMasterAddressAvailability() {
        while (!stoppable.isStopped() && zookeeper.readMasterAddress(zookeeper) != null) {
            try {
                LOG.debug("Waiting for master address ZNode to be deleted " + "(Also watching cluster state node)");
                this.zookeeper.setClusterStateWatch();
                wait();
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
    }

    /**
     * Write address to zookeeper.  Parks here until we successfully write our
     * address (or until cluster shutdown).
     * @param address Address whose format is HServerAddress.toString
     */
    boolean writeAddressToZooKeeper(final HServerAddress address, boolean retry) {
        do {
            waitForMasterAddressAvailability();
            // Check if we need to shutdown instead of taking control
            if (stoppable.isStopped()) {
                LOG.debug("Won't start Master because of requested shutdown");
                return false;
            }
            if (this.zookeeper.writeMasterAddress(address)) {
                this.zookeeper.setClusterState(true);
                this.zookeeper.setClusterStateWatch();
                // Watch our own node
                this.zookeeper.readMasterAddress(zookeeper);
                return true;
            }
        } while (retry);
        return false;
    }

    /**
     * Reset the ZK in case a new connection is required
     * @param zookeeper new instance
     */
    public void setZookeeper(ZooKeeperWrapper zookeeper) {
        this.zookeeper = zookeeper;
    }

    synchronized void cancelMasterZNodeWait() {
        notifyAll();
    }

}