HASingletonSupport


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22  package org.jboss.ha.singleton;
23  
24  import java.util.List  ;
25  
26  import javax.management.Notification  ;
27  
28  import org.jboss.ha.jmx.HAServiceMBeanSupport;
29  
30  /** 
31   * Base class for HA-Singleton services.
32   *
33   * @author <a HREF="mailto:ivelin@apache.org">Ivelin Ivanov</a>
34   * @author <a HREF="mailto:scott.stark@jboss.org">Scott Stark</a>
35   * @author <a HREF="mailto:dimitris@jboss.org">Dimitris Andreadis</a>
36   * @version $Revision: 46010 $
37   */
38  public class HASingletonSupport extends HAServiceMBeanSupport
39     implements HASingletonMBean, HASingleton
40  {
41     // Private Data --------------------------------------------------
42     
43     private boolean isMasterNode = false;
44     private HASingletonElectionPolicyMBean mElectionPolicyMB = null;
45  
46     // Constructors --------------------------------------------------
47     
48     /**
49      * Default CTOR
50      */
51     public HASingletonSupport()
52     {
53        // empty
54     }
55  
56     // Attributes ----------------------------------------------------
57     
58     /**
59      * @jmx:managed-attribute
60      * 
61      * @return true if this cluster node has the active mbean singleton, false otherwise
62      */
63     public boolean isMasterNode()
64     {
65        return isMasterNode;
66     }
67  
68     /**
69      * @see HASingletonSupportMBean#setHASingletonElectionPolicyMBean(HASingletonElectionPolicyMBean)
70      */
71     public void setHASingletonElectionPolicyMBean(HASingletonElectionPolicyMBean mb)
72     {
73        this.mElectionPolicyMB = mb;
74     }
75     
76     /**
77      * @see HASingletonSupportMBean#getHASingletonElectionPolicyMBean()
78      */
79     public HASingletonElectionPolicyMBean getHASingletonElectionPolicyMBean()
80     {
81        return this.mElectionPolicyMB;
82     }
83  
84     // Public --------------------------------------------------------
85  
86     /**
87      * Extending classes should override this method and implement the custom
88      * singleton logic. Only one node in the cluster is the active master.
89      * If the current node is elected for master, this method is invoked.
90      * When another node is elected for master for some reason, the
91      * stopSingleton() method is invokded.
92      * <p>
93      * When the extending class is a stateful singleton, it will
94      * usually use putDistributedState() and getDistributedState() to save in
95      * the cluster environment information that will be needed by the next node
96      * elected for master should the current master node fail.  
97      *
98      * @see HASingleton
99      */
100    public void startSingleton()
101    {
102       if (log.isDebugEnabled())
103          log.debug("startSingleton() : elected for master singleton node");
104 
105       // Extending classes will implement the singleton logic here
106    }
107 
108    /**
109     * Extending classes should override this method and implement the custom
110     * singleton logic. Only one node in the cluster is the active master.
111     * If the current node is master and another node is elected for master, this
112     * method is invoked.
113     * 
114     * @see HASingleton
115     */
116    public void stopSingleton()
117    {
118       if (log.isDebugEnabled())
119          log.debug("stopSingleton() : another node in the partition (if any) is elected for master");
120       
121       // Extending classes will implement the singleton logic here
122    }
123 
124 
125    /**
126     * When topology changes, a new master is elected based on the result
127     * of the isDRMMasterReplica() call.
128     * 
129     * @see HAServiceMBeanSupport#partitionTopologyChanged(List, int)
130     * @see  DistributedReplicantManager#isMasterReplica(String);
131     */
132    public void partitionTopologyChanged(List   newReplicants, int newViewID)
133    {
134       boolean isElectedNewMaster;
135       if (this.mElectionPolicyMB != null)
136          isElectedNewMaster = this.mElectionPolicyMB.isElectedMaster(this.getPartition());
137       else
138          isElectedNewMaster = isDRMMasterReplica();
139       
140       if (log.isDebugEnabled())
141       {
142          log.debug("partitionTopologyChanged, isElectedNewMaster=" + isElectedNewMaster
143             + ", isMasterNode=" + isMasterNode + ", viewID=" + newViewID);
144       }
145 
146       // if this node is already the master, don't bother electing it again
147       if (isElectedNewMaster && isMasterNode)
148       {
149          return;
150       }
151       // just becoming master
152       else if (isElectedNewMaster && !isMasterNode)
153       {
154          makeThisNodeMaster();
155       }
156       // transition from master to slave
157       else if (isMasterNode == true)
158       {
159          _stopOldMaster();
160       }
161    }
162 
163    /**
164     * This method will be invoked twice by the local node 
165     * when it stops as well as by the remote
166     */
167    public void _stopOldMaster()
168    {
169       log.debug("_stopOldMaster, isMasterNode=" + isMasterNode);
170       
171       try 
172       {
173          // since this is a cluster call, all nodes will hear it
174          // so if the node is not the master, then ignore 
175          if (isMasterNode == true)
176          {
177             isMasterNode = false;
178             
179             // notify stopping
180             sendLocalNotification(HASINGLETON_STOPPING_NOTIFICATION);
181             
182             // stop the singleton
183             stopSingleton();
184             
185             // notify stopped
186             sendLocalNotification(HASINGLETON_STOPPED_NOTIFICATION);
187          }
188       }
189       catch (Exception   ex)
190       {
191          log.error(
192             "_stopOldMaster failed. Will still try to start new master. " +
193             "You need to examine the reason why the old master wouldn't stop and resolve it. " +
194             "It is bad that the old singleton may still be running while we are starting a new one, " +
195             "so you need to resolve this ASAP.", ex);
196       }
197    }
198 
199    // Protected -----------------------------------------------------
200    
201    protected void makeThisNodeMaster()
202    {
203       try
204       {
205          // stop the old master (if there is one) before starting the new one
206 
207          // ovidiu 09/02/04 - temporary solution for Case 1843, use an asynchronous
208          // distributed call.
209          //callMethodOnPartition("_stopOldMaster", new Object[0], new Class[0]);
210          callAsyncMethodOnPartition("_stopOldMaster", new Object  [0], new Class  [0]);
211 
212          isMasterNode = true;
213          
214          // notify starting
215          sendLocalNotification(HASINGLETON_STARTING_NOTIFICATION);
216 
217          // start new master
218          startSingleton();
219          
220          // notify started
221          sendLocalNotification(HASINGLETON_STARTED_NOTIFICATION);         
222       }
223       catch (Exception   ex)
224       {
225          log.error("_stopOldMaster failed. New master singleton will not start.", ex);
226       }
227    }
228    
229    // Private -------------------------------------------------------
230    
231    private void sendLocalNotification(String   type)
232    {
233       Notification   n = new Notification  (type, this, getNextNotificationSequenceNumber());
234       super.sendNotificationToLocalListeners(n);
235    }
236 }
237
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