StrongPullConsistencyWrapper


1   /*
2     Copyright (C) 2001-2002 Renaud Pawlak <renaud@aopsys.com>
3   
4     This program is free software; you can redistribute it and/or modify
5     it under the terms of the GNU Lesser General Public License as
6     published by the Free Software Foundation; either version 2 of the
7     License, or (at your option) any later version.
8   
9     This program is distributed in the hope that it will be useful,
10    but WITHOUT ANY WARRANTY; without even the implied warranty of
11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12    GNU Lesser General Public License for more details.
13  
14    You should have received a copy of the GNU Lesser General Public License
15    along with this program; if not, write to the Free Software
16    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
17  
18  package org.objectweb.jac.aspects.distribution.consistency;
19  
20  import java.util.*;
21  import org.apache.log4j.Logger;
22  import org.objectweb.jac.core.*;
23  import org.objectweb.jac.core.dist.*;
24  import org.objectweb.jac.core.rtti.ClassRepository;
25  import org.objectweb.jac.util.*;
26  
27  /**
28   * This wrapper class implements the core protocol for a strong
29   * consistency that is based on a pull strategy.
30   *
31   * <p>On contrary to the <code>StrongPushConsistencyWrapper</code>,
32   * this protocol pulls the data from the other replicas. Indeed, each
33   * time a data is read and is not locally available, it is fetched
34   * from the known replicas.<p>
35   *
36   * @see StrongPushConsistencyWrapper
37   * 
38   * @author <a HREF="http://cedric.cnam.fr/~pawlak/index-english.html">Renaud Pawlak</a>
39   */
40  
41  public class StrongPullConsistencyWrapper extends ConsistencyWrapper {
42      static Logger logger = Logger.getLogger("consistency");
43  
44      String   hosts = null;
45  
46      /**
47      * A friendly constructor for a pull consistency wrapper.
48      *
49      * @param hosts a regular expression that defines the host where
50      * the consistency protocol is installed */
51  
52      public StrongPullConsistencyWrapper(AspectComponent ac, String   hosts) {
53          super(ac);
54          this.hosts = hosts;
55          knownReplicas = null;
56      } 
57  
58      /** An empty constructor for the Consistency class. */
59      public StrongPullConsistencyWrapper(AspectComponent ac) {
60          super(ac);
61      } 
62  
63      /**
64      * This wrapping method first try to use the wrappee to get the
65      * result of the read method.<p>
66      * 
67      * If this result is null or if an exception occurs, it considers
68      * that the read information was not locally present and tries to
69      * fetch it from the replicas it knows (recursivelly all the
70      * replicas are finally asked). If none of the replica returns a
71      * value, it returns null or throws an exception.
72      *
73      * @return the value returned by the wrapped read method */
74  
75      public Object   whenRead(Interaction interaction) {
76  
77          Object   ret = null;
78        
79          ret = proceed(interaction);
80  
81          logger.debug("Pull knownReplicas = "+knownReplicas);
82  
83          if (ret == null) {
84  
85              if (knownReplicas != null) {
86                  Collaboration c = Collaboration.get();
87                  Vector asked_replicas = (Vector)c.getAttribute(visitedReplicas);
88                  if (asked_replicas == null) {
89                      asked_replicas = (Vector)c.addAttribute( 
90                          visitedReplicas, new Vector());
91                  }
92  
93                  //System.out.println ( "########### " + notified_replicas );
94                  try {
95                      Vector new_ar = new Vector();
96                      RemoteRef cur_replica = RemoteRef.create( 
97                          NameRepository.get().getName(interaction.wrappee), 
98                          interaction.wrappee);
99                 
100                     for (int i = 0; i < knownReplicas.size(); i++) {
101                         if ( (! asked_replicas.contains( knownReplicas.get(i) ) ) &&
102                              (! ((RemoteRef)knownReplicas.get(i)).getRemCont().isLocal()) ) {
103                      
104                             Vector kr = new Vector(knownReplicas);
105                             kr.remove(knownReplicas.get(i));
106                             new_ar.clear();
107                             new_ar.addAll(asked_replicas);
108                             new_ar.addAll(kr);
109                             new_ar.add(cur_replica);
110                             c.addAttribute(visitedReplicas, new_ar);
111                      
112                             logger.debug("(strong pull) read event on " + 
113                                       interaction.wrappee + ":" + 
114                                       interaction.method + ":" + 
115                                       ((RemoteRef)knownReplicas.get(i)).getRemCont().getName());
116                             ret = ((RemoteRef)knownReplicas.get(i)).invokeRoleMethod(
117                                 "acceptRemoteRead",
118                                 new Object  [] { null,
119                                                new Object  [] { interaction.method,
120                                                               interaction.args } } );
121                             if (ret != null) {
122                                 break;
123                             }
124                         }
125                     }
126                 } finally {
127                     c.addAttribute(visitedReplicas, null);
128                 }
129             }
130         }   
131         return ret;
132     }
133       
134     /**
135     * Try to read the method asked by <code>whenRead</code>.<p>
136     *
137     * The data is :<p>
138     * <ul><pre>
139     * data[0] = the read method name string
140     * data[1] = an array that contains the arguments of the read method 
141     * </pre></ul>
142     *
143     * @param remoteReplica the replica that received the read event
144     * @param data the read event data
145     * @return the return value of the <code>data[0]</code> method*/
146 
147     public Object   acceptRemoteRead(Wrappee wrappee, RemoteRef remoteReplica,
148                                    Object  [] data) {
149         logger.debug("(strong pull) remote read event on " + 
150                      wrappee + ":" + (String  )data[0]);
151         return ClassRepository.get().getClass(wrappee).getMethod((String  )data[0]).invoke(
152             wrappee , (Object  [])data[1] );
153     }
154    
155       
156 }
157
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