01: /*
02: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
03: *
04: * Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
05: *
06: * The contents of this file are subject to the terms of either the GNU
07: * General Public License Version 2 only ("GPL") or the Common Development
08: * and Distribution License("CDDL") (collectively, the "License"). You
09: * may not use this file except in compliance with the License. You can obtain
10: * a copy of the License at https://glassfish.dev.java.net/public/CDDL+GPL.html
11: * or glassfish/bootstrap/legal/LICENSE.txt. See the License for the specific
12: * language governing permissions and limitations under the License.
13: *
14: * When distributing the software, include this License Header Notice in each
15: * file and include the License file at glassfish/bootstrap/legal/LICENSE.txt.
16: * Sun designates this particular file as subject to the "Classpath" exception
17: * as provided by Sun in the GPL Version 2 section of the License file that
18: * accompanied this code. If applicable, add the following below the License
19: * Header, with the fields enclosed by brackets [] replaced by your own
20: * identifying information: "Portions Copyrighted [year]
21: * [name of copyright owner]"
22: *
23: * Contributor(s):
24: *
25: * If you wish your version of this file to be governed by only the CDDL or
26: * only the GPL Version 2, indicate your decision by adding "[Contributor]
27: * elects to include this software in this distribution under the [CDDL or GPL
28: * Version 2] license." If you don't indicate a single choice of license, a
29: * recipient has the option to distribute your version of this file under
30: * either the CDDL, the GPL Version 2 or to extend the choice of license to
31: * its licensees as provided above. However, if you add GPL Version 2 code
32: * and therefore, elected the GPL Version 2 license, then the option applies
33: * only if the new code is made subject to such option by the copyright
34: * holder.
35: */
36: package javax.persistence;
37:
38: /**
39: * Lock modes that can be specified by means of the
40: * {@link EntityManager#lock EntityManager.lock()} method.
41: *
42: * <p> The semantics of requesting locks of type
43: * {@link LockModeType#READ LockModeType.READ} and {@link
44: * LockModeType#WRITE LockModeType.WRITE} are the following.
45: *
46: * <p> If transaction T1 calls lock(entity, {@link
47: * LockModeType#READ LockModeType.READ}) on a versioned object,
48: * the entity manager must ensure that neither of the following
49: * phenomena can occur:
50: * <ul>
51: * <li> P1 (Dirty read): Transaction T1 modifies a row.
52: * Another transaction T2 then reads that row and obtains
53: * the modified value, before T1 has committed or rolled back.
54: * Transaction T2 eventually commits successfully; it does not
55: * matter whether T1 commits or rolls back and whether it does
56: * so before or after T2 commits.
57: * <li>
58: * </li> P2 (Non-repeatable read): Transaction T1 reads a row.
59: * Another transaction T2 then modifies or deletes that row,
60: * before T1 has committed. Both transactions eventually commit
61: * successfully.
62: * </li>
63: * </ul>
64: *
65: * <p> Lock modes must always prevent the phenomena P1 and P2.
66: *
67: * <p> In addition, calling lock(entity, LockModeType.WRITE) on
68: * a versioned object, will also force an update (increment) to
69: * the entity's version column.
70: *
71: * <p> The persistence implementation is not required to support
72: * calling {@link EntityManager#lock EntityManager.lock()} on a
73: * non-versioned object. When it cannot support a such lock call,
74: * it must throw the {@link PersistenceException}.
75: *
76: *
77: * @since Java Persistence 1.0
78: */
79: public enum LockModeType {
80:
81: /** Read lock */
82: READ,
83:
84: /** Write lock */
85: WRITE
86: }
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