KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > com > daffodilwoods > daffodildb > server > datasystem > persistentsystem > UserLock


1 package com.daffodilwoods.daffodildb.server.datasystem.persistentsystem;
2
3 import java.util.*;
4
5 import com.daffodilwoods.daffodildb.utils.comparator.*;
6 import com.daffodilwoods.database.general.*;
7 import com.daffodilwoods.database.resource.*;
8
9 /**
10  * It provides lock for writing on databaseFile
11  */
12 public class UserLock{
13
14 /**
15  * Maintains currently which user has taken lock on dataBaseFile
16  */
17    private Object JavaDoc lock = null;
18    private long time ;
19    private Map lockMap;
20    Vector waiters = new Vector();
21
22    UserLock() {
23        lockMap = Collections.synchronizedMap(new TreeMap(new CRvbmjgjfeDpnqbsbups()));
24    }
25
26    /**
27     * provides lock on databaseFile if no user has lock on databaseFile
28     * @param user which requires lock on database file
29     * @return true if lock is given to current user
30     * @throws DException If lock is used by another user and can not be given to current user
31     */
32
33    synchronized final boolean getLock(DatabaseUser user) throws DException {
34      while(true){
35            if((lock == null || user.equals(lock)) && (lockMap.size() == 0)){
36               lock = user;
37               time = System.currentTimeMillis();
38
39                 return true;
40             }
41             try {
42                 wait(20);
43             }
44             catch (InterruptedException JavaDoc ex) {
45             }
46             if((System.currentTimeMillis() - time) > 3000){
47             }
48         }
49     }
50
51    final boolean getLock(DatabaseUser user,ArrayList userTableNames) throws DException {
52        while(true){
53            synchronized (this){
54                if( lock == null && checkLock(userTableNames) == null ){
55                    for (int i = 0; i < userTableNames.size(); i++){
56                        QualifiedIdentifier tableName = (QualifiedIdentifier)userTableNames.get(i);
57                        user.addTable(tableName);
58                        Object JavaDoc obj = lockMap.put(tableName,user);
59                         time = System.currentTimeMillis();
60
61                    }
62                    return true;
63                }
64            }
65
66                wait(user,userTableNames);
67        }
68    }
69
70     /**
71      * UnLocks the File if lock was taken by specified user
72      * @param user to unlock database file
73      */
74
75    final synchronized void unLock(DatabaseUser user) throws DException{
76      ArrayList tableNames = user.getTableNames();
77      if(user.equals(lock)){
78        lock = null;
79      }
80      for (int i = 0; i < tableNames.size(); i++) {
81        lockMap.remove(tableNames.get(i));
82
83      }
84      {
85             notify(tableNames);
86         }
87     }
88
89     private QualifiedIdentifier checkLock(ArrayList tableNames){
90         for (int i = 0,len = tableNames.size() ; i < len; i++) {
91             if((DatabaseUser)lockMap.get(tableNames.get(i)) != null){
92                 return (QualifiedIdentifier)tableNames.get(i);
93             }
94         }
95         return null;
96     }
97
98     private void wait(DatabaseUser user,ArrayList userTableNames) {
99         Wait w = new Wait();
100         w.user = user;
101         w.list = userTableNames;
102         waiters.add(w);
103         time = System.currentTimeMillis();
104         do{
105         w.doWait();
106         if(System.currentTimeMillis() - time > 3000){
107         }
108         }while(checkLock(w.list) != null);
109         waiters.remove(w);
110     }
111
112     private void notify(ArrayList userTableNames) {
113         for(int i = 0; i < waiters.size() ; i++) {
114             try {
115                 Wait w = (Wait)waiters.get(i);
116                 if(checkLock(w.list) == null){
117                     w.signal();
118                     return;
119                 }
120             }
121             catch (ArrayIndexOutOfBoundsException JavaDoc ex) {
122             }
123         }
124     }
125
126     private class Wait{
127         DatabaseUser user;
128         ArrayList list;
129
130         public synchronized void doWait() {
131             try {
132                 this.wait(3000);
133             }
134             catch (InterruptedException JavaDoc ex) {
135             }
136         }
137
138         public synchronized void signal() {
139             this.notify();
140         }
141     }
142 }
143
Popular Tags