ClientGmsImpl


1   // $Id: ClientGmsImpl.java,v 1.9 2005/04/20 20:25:46 belaban Exp $
2   
3   package org.jgroups.protocols;
4   
5   
6   import org.jgroups.Address;
7   import org.jgroups.Event;
8   import org.jgroups.View;
9   import org.jgroups.ViewId;
10  import org.jgroups.blocks.GroupRequest;
11  import org.jgroups.blocks.MethodCall;
12  import org.jgroups.util.Util;
13  
14  import java.util.Enumeration  ;
15  import java.util.Hashtable  ;
16  import java.util.Vector  ;
17  
18  
19  /**
20   * Client part of GMS. Whenever a new member wants to join a group, it starts in the CLIENT role.
21   * No multicasts to the group will be received and processed until the member has been joined and
22   * turned into a SERVER (either coordinator or participant, mostly just participant). This class
23   * only implements <code>Join</code> (called by clients who want to join a certain group, and
24   * <code>ViewChange</code> which is called by the coordinator that was contacted by this client, to
25   * tell the client what its initial membership is.
26   * 
27   * @author Bela Ban
28   * @version $Revision: 1.9 $
29   */
30  public class ClientGmsImpl extends GmsImpl {
31      final Vector   initial_mbrs=new Vector  (7);
32      final Object   view_installation_mutex=new Object  ();
33      boolean joined=false;
34  
35  
36      public ClientGmsImpl(GMS g) {
37          gms=g;
38      }
39  
40  
41      public void init() {
42          initial_mbrs.removeAllElements();
43          joined=false;
44      }
45  
46  
47      /**
48       * Will generate a CONNECT_OK event. Determines the coordinator and sends a unicast
49       * join() message to it. If successful, we wait for a ViewChange (can time out).
50       * If view change is received, impl is changed to an instance of ParticipantGmsImpl.
51       * Otherwise, we continue trying to send join() messages to the coordinator,
52       * until we succeed (or there is no member in the group. In this case, we create
53       * our own singleton group).
54       * <p>When GMS.disable_initial_coord is set to true, then we won't become coordinator on receiving an initial
55       * membership of 0, but instead will retry (forever) until we get an initial membership of > 0.
56       * 
57       * @param mbr Our own address (assigned through SET_LOCAL_ADDRESS)
58       */
59      public void join(Address mbr) {
60          Address coord=null;
61          Event view_evt;
62  
63          while(!joined) {
64              findInitialMembers();
65              if(joined) {
66                   if(log.isInfoEnabled()) log.info("joined successfully");
67                  return;
68              }
69              if(initial_mbrs.size() == 0) {
70                  if(gms.disable_initial_coord) {
71  
72                          if(log.isInfoEnabled()) log.info("received an initial membership of 0, but " +
73                                  "cannot become coordinator (disable_initial_coord=" + gms.disable_initial_coord +
74                                  "), will retry fetching the initial membership");
75                      continue;
76                  }
77                  joined=true;
78                  gms.view_id=new ViewId(mbr);       // create singleton view with mbr as only member
79                  gms.members.add(mbr);
80                  view_evt=new Event(Event.VIEW_CHANGE,
81                          gms.makeView(gms.members.getMembers(), gms.view_id));
82                  gms.passDown(view_evt);
83                  gms.passUp(view_evt);
84                  gms.becomeCoordinator();
85  
86                  gms.passUp(new Event(Event.BECOME_SERVER));
87                  gms.passDown(new Event(Event.BECOME_SERVER));
88                   if(log.isInfoEnabled()) log.info("created group (first member)");
89                  break;
90              }
91  
92              coord=determineCoord(initial_mbrs);
93              if(coord == null) {
94                  if(log.isWarnEnabled()) log.warn("could not determine coordinator " +
95                                                   "from responses " + initial_mbrs);
96                  continue;
97              }
98  
99              synchronized(view_installation_mutex) {
100                 try {
101                     if(log.isInfoEnabled()) log.info("sending handleJoin() to " + coord);
102                     MethodCall call=new MethodCall("handleJoin", new Object  []{mbr}, new Class  []{Address.class});
103                     gms.callRemoteMethod(coord, call, GroupRequest.GET_NONE, 0);
104                     view_installation_mutex.wait(gms.join_timeout);  // wait for view -> handleView()
105                 }
106                 catch(Exception   e) {
107                     if(log.isErrorEnabled()) log.error("exception is " + e);
108                     continue;
109                 }
110             } // end synchronized
111 
112             if(joined) {
113                 if(log.isInfoEnabled()) log.info("joined successfully");
114                 return;  // --> SUCCESS
115             }
116             else {
117                 if(log.isInfoEnabled()) log.info("failed, retrying");
118                 Util.sleep(gms.join_retry_timeout);
119             }
120 
121         }  // end while
122     }
123 
124 
125     public void leave(Address mbr) {
126         wrongMethod("leave");
127     }
128 
129 
130     public void suspect(Address mbr) {
131         // wrongMethod("suspect");
132     }
133 
134 
135     public void merge(Vector   other_coords) {
136         wrongMethod("merge");
137     }
138 
139 
140     public boolean handleJoin(Address mbr) {
141         wrongMethod("handleJoin");
142         return false;
143     }
144 
145 
146     /**
147      * Returns false. Clients don't handle leave() requests
148      */
149     public void handleLeave(Address mbr, boolean suspected) {
150         wrongMethod("handleLeave");
151     }
152 
153 
154     /**
155      * Install the first view in which we are a member. This is essentially a confirmation
156      * of our JOIN request (see join() above).
157      */
158     public void handleViewChange(ViewId new_view, Vector   mems) {
159         if(gms.local_addr != null && mems != null && mems.contains(gms.local_addr)) {
160             synchronized(view_installation_mutex) {  // wait until JOIN is sent (above)
161                 joined=true;
162                 view_installation_mutex.notifyAll();
163                 gms.installView(new_view, mems);
164                 gms.becomeParticipant();
165                 gms.passUp(new Event(Event.BECOME_SERVER));
166                 gms.passDown(new Event(Event.BECOME_SERVER));
167             }
168             synchronized(initial_mbrs) {    // in case findInitialMembers() is still running:
169                 initial_mbrs.notifyAll();   // this will unblock it
170             }
171         }
172         else
173             if(log.isWarnEnabled()) log.warn("am not member of " + mems + ", will not install view");
174     }
175 
176 
177     /**
178      * Returns immediately. Clients don't handle merge() requests
179      */
180     public View handleMerge(ViewId other_view, Vector   other_members) {
181         wrongMethod("handleMerge");
182         return null;
183     }
184 
185 
186     /**
187      * Returns immediately. Clients don't handle suspect() requests
188      */
189     public void handleSuspect(Address mbr) {
190         wrongMethod("handleSuspect");
191         return;
192     }
193 
194 
195     public boolean handleUpEvent(Event evt) {
196         Vector   tmp;
197 
198         switch(evt.getType()) {
199 
200             case Event.FIND_INITIAL_MBRS_OK:
201                 tmp=(Vector  )evt.getArg();
202                 synchronized(initial_mbrs) {
203                     if(tmp != null && tmp.size() > 0)
204                         for(int i=0; i < tmp.size(); i++)
205                             initial_mbrs.addElement(tmp.elementAt(i));
206                     initial_mbrs.notifyAll();
207                 }
208                 return false;  // don't pass up the stack
209         }
210 
211         return true;
212     }
213 
214 
215 
216 
217 
218     /* --------------------------- Private Methods ------------------------------------ */
219 
220 
221 
222 
223 
224 
225 
226     /**
227      * Pings initial members. Removes self before returning vector of initial members.
228      * Uses IP multicast or gossiping, depending on parameters.
229      */
230     void findInitialMembers() {
231         PingRsp ping_rsp;
232 
233         synchronized(initial_mbrs) {
234             initial_mbrs.removeAllElements();
235             gms.passDown(Event.FIND_INITIAL_MBRS_EVT);
236             if(initial_mbrs.size() == 0) {
237                 try {
238                     initial_mbrs.wait();
239                 }
240                 catch(Exception   e) {
241                 }
242             }
243 
244             for(int i=0; i < initial_mbrs.size(); i++) {
245                 ping_rsp=(PingRsp)initial_mbrs.elementAt(i);
246                 if(ping_rsp.own_addr != null && gms.local_addr != null &&
247                         ping_rsp.own_addr.equals(gms.local_addr)) {
248                     initial_mbrs.removeElementAt(i);
249                     break;
250                 }
251             }
252         }
253     }
254 
255 
256     /**
257      * The coordinator is determined by a majority vote. If there are an equal number of votes for
258      * more than 1 candidate, we determine the winner randomly.
259      */
260     Address determineCoord(Vector   mbrs) {
261         PingRsp mbr;
262         Hashtable   votes;
263         int count, most_votes;
264         Address winner=null, tmp;
265 
266         if(mbrs == null || mbrs.size() < 1)
267             return null;
268 
269         votes=new Hashtable  (5);
270 
271         // count *all* the votes (unlike the 2000 election)
272         for(int i=0; i < mbrs.size(); i++) {
273             mbr=(PingRsp)mbrs.elementAt(i);
274             if(mbr.coord_addr != null) {
275                 if(!votes.containsKey(mbr.coord_addr))
276                     votes.put(mbr.coord_addr, new Integer  (1));
277                 else {
278                     count=((Integer  )votes.get(mbr.coord_addr)).intValue();
279                     votes.put(mbr.coord_addr, new Integer  (count + 1));
280                 }
281             }
282         }
283 
284          {
285             if(votes.size() > 1)
286                 if(log.isWarnEnabled()) log.warn("there was more than 1 candidate for coordinator: " + votes);
287             else
288                 if(log.isInfoEnabled()) log.info("election results: " + votes);
289         }
290     
291 
292         // determine who got the most votes
293         most_votes=0;
294         for(Enumeration   e=votes.keys(); e.hasMoreElements();) {
295             tmp=(Address)e.nextElement();
296             count=((Integer  )votes.get(tmp)).intValue();
297             if(count > most_votes) {
298                 winner=tmp;
299 // fixed July 15 2003 (patch submitted by Darren Hobbs, patch-id=771418)
300                 most_votes=count;
301             }
302         }
303         votes.clear();
304         return winner;
305     }
306 
307 
308 }
309
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