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Java > Open Source Codes > org > apache > ojb > otm > lock > isolation > RepeatableReadIsolation


1 package org.apache.ojb.otm.lock.isolation;
2
3 /* Copyright 2003-2005 The Apache Software Foundation
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * You may obtain a copy of the License at
8  *
9  * http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  */
17
18 import java.util.Collection JavaDoc;
19 import java.util.Iterator JavaDoc;
20
21 import org.apache.ojb.otm.core.Transaction;
22 import org.apache.ojb.otm.lock.LockingException;
23 import org.apache.ojb.otm.lock.ObjectLock;
24
25 public class RepeatableReadIsolation extends AbstractIsolation
26 {
27
28     /**
29      * @see org.apache.ojb.otm.lock.isolation.TransactionIsolation#readLock(Transaction, ObjectLock)
30      */
31     public void readLock(Transaction tx, ObjectLock lock)
32         throws LockingException
33     {
34         Transaction writer = lock.getWriter();
35         if (writer == null)
36         {
37             lock.readLock(tx);
38             if (lock.getWriter() != null)
39             {
40                 lock.releaseLock(tx);
41                 readLock(tx, lock);
42             }
43         }
44         else if (tx != writer)
45         {
46             lock.waitForTx(writer);
47             readLock(tx, lock);
48         }
49         // else if tx is the writer, it can also read.
50 }
51
52     /**
53      * @see org.apache.ojb.otm.lock.isolation.TransactionIsolation#writeLock(Transaction, ObjectLock)
54      */
55     public void writeLock(Transaction tx, ObjectLock lock)
56         throws LockingException
57     {
58         Collection JavaDoc readers = lock.getReaders();
59         
60         if (!readers.isEmpty())
61         {
62             for (Iterator JavaDoc it = readers.iterator(); it.hasNext(); )
63             {
64                 Transaction reader = (Transaction) it.next();
65
66                 if (reader != tx)
67                 {
68                     lock.waitForTx(reader);
69                     writeLock(tx, lock);
70                     return;
71                 }
72             }
73         }
74         
75         lock.writeLock(tx);
76         readers = lock.getReaders();
77         if (readers.size() > 1)
78         {
79             lock.releaseLock(tx);
80             writeLock(tx, lock);
81         }
82     }
83 }
84
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