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1   /**
2    *
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  You may obtain a copy of the License at
10   *
11   *     http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing, software
14   * distributed under the License is distributed on an "AS IS" BASIS,
15   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16   * See the License for the specific language governing permissions and
17   * limitations under the License.
18   */
19  package org.apache.hadoop.hbase.master;
20  
21  import org.apache.commons.logging.Log;
22  import org.apache.commons.logging.LogFactory;
23  import org.apache.hadoop.hbase.classification.InterfaceAudience;
24  import org.apache.hadoop.hbase.ServerName;
25  import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
26  import org.apache.hadoop.hbase.util.Pair;
27  
28  import java.util.ArrayList;
29  import java.util.Collections;
30  import java.util.Comparator;
31  import java.util.Date;
32  import java.util.HashMap;
33  import java.util.HashSet;
34  import java.util.Iterator;
35  import java.util.List;
36  import java.util.Map;
37  import java.util.Set;
38  
39  /**
40   * Class to hold dead servers list and utility querying dead server list.
41   * On znode expiration, servers are added here.
42   */
43  @InterfaceAudience.Private
44  public class DeadServer {
45    private static final Log LOG = LogFactory.getLog(DeadServer.class);
46  
47    /**
48     * Set of known dead servers.  On znode expiration, servers are added here.
49     * This is needed in case of a network partitioning where the server's lease
50     * expires, but the server is still running. After the network is healed,
51     * and it's server logs are recovered, it will be told to call server startup
52     * because by then, its regions have probably been reassigned.
53     */
54    private final Map<ServerName, Long> deadServers = new HashMap<ServerName, Long>();
55  
56    /**
57     * Number of dead servers currently being processed
58     */
59    private int numProcessing = 0;
60  
61    /**
62     * Whether a dead server is being processed currently.
63     */
64    private boolean processing = false;
65  
66    /**
67     * A dead server that comes back alive has a different start code. The new start code should be
68     *  greater than the old one, but we don't take this into account in this method.
69     *
70     * @param newServerName Servername as either <code>host:port</code> or
71     *                      <code>host,port,startcode</code>.
72     * @return true if this server was dead before and coming back alive again
73     */
74    public synchronized boolean cleanPreviousInstance(final ServerName newServerName) {
75      Iterator<ServerName> it = deadServers.keySet().iterator();
76      while (it.hasNext()) {
77        ServerName sn = it.next();
78        if (ServerName.isSameHostnameAndPort(sn, newServerName)) {
79          it.remove();
80          return true;
81        }
82      }
83  
84      return false;
85    }
86  
87    /**
88     * @param serverName server name.
89     * @return true if this server is on the dead servers list false otherwise
90     */
91    public synchronized boolean isDeadServer(final ServerName serverName) {
92      return deadServers.containsKey(serverName);
93    }
94  
95    /**
96     * Checks if there are currently any dead servers being processed by the
97     * master.  Returns true if at least one region server is currently being
98     * processed as dead.
99     *
100    * @return true if any RS are being processed as dead
101    */
102   public synchronized boolean areDeadServersInProgress() { return processing; }
103 
104   public synchronized Set<ServerName> copyServerNames() {
105     Set<ServerName> clone = new HashSet<ServerName>(deadServers.size());
106     clone.addAll(deadServers.keySet());
107     return clone;
108   }
109 
110   /**
111    * Adds the server to the dead server list if it's not there already.
112    * @param sn the server name
113    */
114   public synchronized void add(ServerName sn) {
115     processing = true;
116     if (!deadServers.containsKey(sn)){
117       deadServers.put(sn, EnvironmentEdgeManager.currentTime());
118     }
119   }
120 
121   /**
122    * Notify that we started processing this dead server.
123    * @param sn ServerName for the dead server.
124    */
125   public synchronized void notifyServer(ServerName sn) {
126     if (LOG.isDebugEnabled()) { LOG.debug("Started processing " + sn); }
127     processing = true;
128     numProcessing++;
129   }
130 
131   public synchronized void finish(ServerName sn) {
132     numProcessing--;
133     if (LOG.isDebugEnabled()) LOG.debug("Finished " + sn + "; numProcessing=" + numProcessing);
134 
135     assert numProcessing >= 0: "Number of dead servers in processing should always be non-negative";
136 
137     if (numProcessing < 0) {
138       LOG.error("Number of dead servers in processing = " + numProcessing
139           + ". Something went wrong, this should always be non-negative.");
140       numProcessing = 0;
141     }
142     if (numProcessing == 0) { processing = false; }
143   }
144 
145   public synchronized int size() {
146     return deadServers.size();
147   }
148 
149   public synchronized boolean isEmpty() {
150     return deadServers.isEmpty();
151   }
152 
153   public synchronized void cleanAllPreviousInstances(final ServerName newServerName) {
154     Iterator<ServerName> it = deadServers.keySet().iterator();
155     while (it.hasNext()) {
156       ServerName sn = it.next();
157       if (ServerName.isSameHostnameAndPort(sn, newServerName)) {
158         it.remove();
159       }
160     }
161   }
162 
163   public synchronized String toString() {
164     StringBuilder sb = new StringBuilder();
165     for (ServerName sn : deadServers.keySet()) {
166       if (sb.length() > 0) {
167         sb.append(", ");
168       }
169       sb.append(sn.toString());
170     }
171     return sb.toString();
172   }
173 
174   /**
175    * Extract all the servers dead since a given time, and sort them.
176    * @param ts the time, 0 for all
177    * @return a sorted array list, by death time, lowest values first.
178    */
179   public synchronized List<Pair<ServerName, Long>> copyDeadServersSince(long ts){
180     List<Pair<ServerName, Long>> res =  new ArrayList<Pair<ServerName, Long>>(size());
181 
182     for (Map.Entry<ServerName, Long> entry:deadServers.entrySet()){
183       if (entry.getValue() >= ts){
184         res.add(new Pair<ServerName, Long>(entry.getKey(), entry.getValue()));
185       }
186     }
187 
188     Collections.sort(res, ServerNameDeathDateComparator);
189     return res;
190   }
191   
192   /**
193    * Get the time when a server died
194    * @param deadServerName the dead server name
195    * @return the date when the server died 
196    */
197   public synchronized Date getTimeOfDeath(final ServerName deadServerName){
198     Long time = deadServers.get(deadServerName);
199     return time == null ? null : new Date(time);
200   }
201 
202   private static Comparator<Pair<ServerName, Long>> ServerNameDeathDateComparator =
203       new Comparator<Pair<ServerName, Long>>(){
204 
205     @Override
206     public int compare(Pair<ServerName, Long> o1, Pair<ServerName, Long> o2) {
207       return o1.getSecond().compareTo(o2.getSecond());
208     }
209   };
210 }