View


1   // $Id: View.java,v 1.7 2005/04/20 10:32:36 belaban Exp $
2   
3   package org.jgroups;
4   
5   
6   import org.jgroups.util.Streamable;
7   import org.jgroups.util.Util;
8   
9   import java.io.*;
10  import java.util.Vector  ;
11  import java.util.Iterator  ;
12  
13  
14  /**
15   * A view is a local representation of the current membership of a group
16   * Only one view is installed in a channel at a time
17   * Views contain the address of its creator, an ID and a list of member addresses
18   * These adresses are ordered, and the first address is always the coordinator of the view
19   * This way, each member of the group knows who the new coordinator will be if the current one
20   * crashes or leaves the group.
21   * The views are sent between members using the VIEW_CHANGE event.
22   */
23  public class View implements Externalizable, Cloneable  , Streamable {
24      /* A view is uniquely identified by its ViewID
25       * The view id contains the creator address and a Lamport time.
26       * The Lamport time is the highest timestamp seen or sent from a view.
27       * if a view change comes in with a lower Lamport time, the event is discarded.
28       */
29      protected ViewId vid=null;
30  
31      /**
32       * A list containing all the members of the view
33       * This list is always ordered, with the coordinator being the first member.
34       * the second member will be the new coordinator if the current one disappears
35       * or leaves the group.
36       */
37      protected Vector   members=null;
38  
39  
40      /**
41       * creates an empty view, should not be used
42       */
43      public View() {
44      }
45  
46  
47      /**
48       * Creates a new view
49       *
50       * @param vid     The view id of this view (can not be null)
51       * @param members Contains a list of all the members in the view, can be empty but not null.
52       */
53      public View(ViewId vid, Vector   members) {
54          this.vid=vid;
55          this.members=members;
56      }
57  
58  
59      /**
60       * Creates a new view
61       *
62       * @param creator The creator of this view (can not be null)
63       * @param id      The lamport timestamp of this view
64       * @param members Contains a list of all the members in the view, can be empty but not null.
65       */
66      public View(Address creator, long id, Vector   members) {
67          this(new ViewId(creator, id), members);
68      }
69  
70  
71      /**
72       * returns the view ID of this view
73       * if this view was created with the empty constructur, null will be returned
74       *
75       * @return the view ID of this view
76       */
77      public ViewId getVid() {
78          return vid;
79      }
80  
81      /**
82       * returns the creator of this view
83       * if this view was created with the empty constructur, null will be returned
84       *
85       * @return the creator of this view in form of an Address object
86       */
87      public Address getCreator() {
88          return vid != null ? vid.getCoordAddress() : null;
89      }
90  
91      /**
92       * Returns a reference to the List of members (ordered)
93       * Do NOT change this list, hence your will invalidate the view
94       * Make a copy if you have to modify it.
95       *
96       * @return a reference to the ordered list of members in this view
97       */
98      public Vector   getMembers() {
99          return members;
100     }
101 
102     /**
103      * returns true, if this view contains a certain member
104      *
105      * @param mbr - the address of the member,
106      * @return true if this view contains the member, false if it doesn't
107      *         if the argument mbr is null, this operation returns false
108      */
109     public boolean containsMember(Address mbr) {
110         if(mbr == null || members == null) {
111             return false;
112         }
113         return members.contains(mbr);
114     }
115 
116 
117     public boolean equals(Object   obj) {
118         if(obj == null)
119             return false;
120         if(vid != null) {
121             int rc=vid.compareTo(((View)obj).vid);
122             if(rc != 0)
123                 return false;
124             if(members != null && ((View)obj).members != null) {
125                 return members.equals(((View)obj).members);
126             }
127         }
128         return false;
129     }
130 
131     /**
132      * returns the number of members in this view
133      *
134      * @return the number of members in this view 0..n
135      */
136     public int size() {
137         return members == null ? 0 : members.size();
138     }
139 
140 
141     /**
142      * creates a copy of this view
143      *
144      * @return a copy of this view
145      */
146     public Object   clone() {
147         ViewId vid2=vid != null ? (ViewId)vid.clone() : null;
148         Vector   members2=members != null ? (Vector  )members.clone() : null;
149         return new View(vid2, members2);
150     }
151 
152 
153     /**
154      * debug only
155      */
156     public String   printDetails() {
157         StringBuffer   ret=new StringBuffer  ();
158         ret.append(vid).append("\n\t");
159         if(members != null) {
160             for(int i=0; i < members.size(); i++) {
161                 ret.append(members.elementAt(i)).append("\n\t");
162             }
163             ret.append('\n');
164         }
165         return ret.toString();
166     }
167 
168 
169     public String   toString() {
170         StringBuffer   ret=new StringBuffer  (64);
171         ret.append(vid + " " + members);
172         return ret.toString();
173     }
174 
175 
176     public void writeExternal(ObjectOutput out) throws IOException {
177         out.writeObject(vid);
178         out.writeObject(members);
179     }
180 
181 
182     public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException   {
183         vid=(ViewId)in.readObject();
184         members=(Vector  )in.readObject();
185     }
186 
187 
188     public void writeTo(DataOutputStream out) throws IOException {
189         // vid
190         if(vid != null) {
191             out.write(1);
192             vid.writeTo(out);
193         }
194         else
195             out.write(0);
196 
197         // members:
198         if(members != null) {
199             out.write(1);
200             out.writeInt(members.size());
201             for(Iterator   it=members.iterator(); it.hasNext();) {
202                 Address addr=(Address)it.next();
203                 Util.writeAddress(addr, out);
204             }
205         }
206         else
207             out.write(0);
208     }
209 
210 
211     public void readFrom(DataInputStream in) throws IOException, IllegalAccessException  , InstantiationException   {
212         int b;
213         // vid:
214         b=in.read();
215         if(b == 1) {
216             vid=new ViewId();
217             vid.readFrom(in);
218         }
219 
220         // members:
221         b=in.read();
222         if(b == 1) {
223             b=in.readInt();
224             members=new Vector  (b);
225             Address addr;
226             for(int i=0; i < b; i++) {
227                 addr=Util.readAddress(in);
228                 members.add(addr);
229             }
230         }
231     }
232 
233 
234 }
235
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