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1   /**
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  package org.apache.hadoop.hbase.zookeeper;
19  
20  import org.apache.hadoop.classification.InterfaceAudience;
21  import org.apache.hadoop.hbase.Abortable;
22  import org.apache.hadoop.hbase.ServerName;
23  import org.apache.hadoop.hbase.exceptions.DeserializationException;
24  import org.apache.hadoop.hbase.protobuf.ProtobufUtil;
25  import org.apache.hadoop.hbase.protobuf.generated.HBaseProtos;
26  import org.apache.hadoop.hbase.protobuf.generated.ZooKeeperProtos;
27  import org.apache.zookeeper.KeeperException;
28  import org.apache.zookeeper.data.Stat;
29  
30  import java.io.IOException;
31  
32  /**
33   * Manages the location of the current active Master for the RegionServer.
34   * <p>
35   * Listens for ZooKeeper events related to the master address. The node
36   * <code>/master</code> will contain the address of the current master.
37   * This listener is interested in
38   * <code>NodeDeleted</code> and <code>NodeCreated</code> events on
39   * <code>/master</code>.
40   * <p>
41   * Utilizes {@link ZooKeeperNodeTracker} for zk interactions.
42   * <p>
43   * You can get the current master via {@link #getMasterAddress()} or via
44   * {@link #getMasterAddress(ZooKeeperWatcher)} if you do not have a running
45   * instance of this Tracker in your context.
46   * <p>
47   * This class also includes utility for interacting with the master znode, for
48   * writing and reading the znode content.
49   */
50  @InterfaceAudience.Private
51  public class MasterAddressTracker extends ZooKeeperNodeTracker {
52    /**
53     * Construct a master address listener with the specified
54     * <code>zookeeper</code> reference.
55     * <p>
56     * This constructor does not trigger any actions, you must call methods
57     * explicitly.  Normally you will just want to execute {@link #start()} to
58     * begin tracking of the master address.
59     *
60     * @param watcher zk reference and watcher
61     * @param abortable abortable in case of fatal error
62     */
63    public MasterAddressTracker(ZooKeeperWatcher watcher, Abortable abortable) {
64      super(watcher, watcher.getMasterAddressZNode(), abortable);
65    }
66  
67    /**
68     * Get the address of the current master if one is available.  Returns null
69     * if no current master.
70     * @return Server name or null if timed out.
71     */
72    public ServerName getMasterAddress() {
73      return getMasterAddress(false);
74    }
75  
76    /**
77     * Get the address of the current master if one is available.  Returns null
78     * if no current master. If refresh is set, try to load the data from ZK again,
79     * otherwise, cached data will be used.
80     *
81     * @param refresh whether to refresh the data by calling ZK directly.
82     * @return Server name or null if timed out.
83     */
84    public ServerName getMasterAddress(final boolean refresh) {
85      try {
86        return ServerName.parseFrom(super.getData(refresh));
87      } catch (DeserializationException e) {
88        LOG.warn("Failed parse", e);
89        return null;
90      }
91    }
92  
93    /**
94     * Get master address.
95     * Use this instead of {@link #getMasterAddress()} if you do not have an
96     * instance of this tracker in your context.
97     * @param zkw ZooKeeperWatcher to use
98     * @return ServerName stored in the the master address znode or null if no
99     * znode present.
100    * @throws KeeperException 
101    * @throws IOException 
102    */
103   public static ServerName getMasterAddress(final ZooKeeperWatcher zkw)
104   throws KeeperException, IOException {
105     byte [] data = ZKUtil.getData(zkw, zkw.getMasterAddressZNode());
106     if (data == null){
107       throw new IOException("Can't get master address from ZooKeeper; znode data == null");
108     }
109     try {
110       return ServerName.parseFrom(data);
111     } catch (DeserializationException e) {
112       KeeperException ke = new KeeperException.DataInconsistencyException();
113       ke.initCause(e);
114       throw ke;
115     }
116   }
117 
118   /**
119    * Set master address into the <code>master</code> znode or into the backup
120    * subdirectory of backup masters; switch off the passed in <code>znode</code>
121    * path.
122    * @param zkw The ZooKeeperWatcher to use.
123    * @param znode Where to create the znode; could be at the top level or it
124    * could be under backup masters
125    * @param master ServerName of the current master
126    * @return true if node created, false if not; a watch is set in both cases
127    * @throws KeeperException
128    */
129   public static boolean setMasterAddress(final ZooKeeperWatcher zkw,
130       final String znode, final ServerName master)
131   throws KeeperException {
132     return ZKUtil.createEphemeralNodeAndWatch(zkw, znode, toByteArray(master));
133   }
134 
135   /**
136    * Check if there is a master available.
137    * @return true if there is a master set, false if not.
138    */
139   public boolean hasMaster() {
140     return super.getData(false) != null;
141   }
142 
143   /**
144    * @param sn
145    * @return Content of the master znode as a serialized pb with the pb
146    * magic as prefix.
147    */
148    static byte [] toByteArray(final ServerName sn) {
149      ZooKeeperProtos.Master.Builder mbuilder = ZooKeeperProtos.Master.newBuilder();
150      HBaseProtos.ServerName.Builder snbuilder = HBaseProtos.ServerName.newBuilder();
151      snbuilder.setHostName(sn.getHostname());
152      snbuilder.setPort(sn.getPort());
153      snbuilder.setStartCode(sn.getStartcode());
154      mbuilder.setMaster(snbuilder.build());
155      return ProtobufUtil.prependPBMagic(mbuilder.build().toByteArray());
156    }
157 
158   /**
159    * delete the master znode if its content is same as the parameter
160    */
161   public static boolean deleteIfEquals(ZooKeeperWatcher zkw, final String content) {
162     if (content == null){
163       throw new IllegalArgumentException("Content must not be null");
164     }
165 
166     try {
167       Stat stat = new Stat();
168       byte[] data = ZKUtil.getDataNoWatch(zkw, zkw.getMasterAddressZNode(), stat);
169       ServerName sn = ServerName.parseFrom(data);
170       if (sn != null && content.equals(sn.toString())) {
171         return (ZKUtil.deleteNode(zkw, zkw.getMasterAddressZNode(), stat.getVersion()));
172       }
173     } catch (KeeperException e) {
174       LOG.warn("Can't get or delete the master znode", e);
175     } catch (DeserializationException e) {
176       LOG.warn("Can't get or delete the master znode", e);
177     }
178 
179     return false;
180   }
181 }