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


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 org.apache.ojb.otm.core.Transaction;
19 import org.apache.ojb.otm.lock.LockingException;
20 import org.apache.ojb.otm.lock.ObjectLock;
21
22 /**
23  *
24  * READ_COMMITTED IsolationStrategy.
25  *
26  * @author <a HREF="mailto:rraghuram@hotmail.com">Raghu Rajah</a>
27  * @author Thomas Mahler & David Dixon-Peugh
28  *
29  */
30 public class ReadCommittedIsolation extends AbstractIsolation
31 {
32
33     /**
34      * @see org.apache.ojb.otm.lock.TransactionIsolation#readLock(Transaction, ObjectLocks)
35      */
36     public void readLock(Transaction tx, ObjectLock lock)
37         throws LockingException
38     {
39         Transaction writer = lock.getWriter();
40         if (writer == null)
41         {
42             lock.readLock(tx);
43             if (lock.getWriter() != null)
44             {
45                 lock.releaseLock(tx);
46                 readLock(tx, lock);
47             }
48         }
49         else if (tx != writer)
50         {
51             lock.waitForTx(writer);
52             readLock(tx, lock);
53         }
54         // else if tx is the writer, it can also read.
55 }
56
57     /**
58      * @see org.apache.ojb.otm.lock.TransactionIsolation#writeLock(Transaction, ObjectLocks)
59      */
60     public void writeLock(Transaction tx, ObjectLock lock)
61         throws LockingException
62     {
63         lock.writeLock(tx);
64     }
65
66 }
67
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