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Java > Open Source Codes > com > hp > hpl > jena > rdf > model > ModelLock


1 /*
2  * (c) Copyright 2003, 2004, 2005 Hewlett-Packard Development Company, LP
3  * [See end of file]
4  */
5
6 /**
7  * A model lock.
8  * Critical section support for multithreaed access to a model
9  * within a single JVM. See also transactions support.
10  *
11  * Examples if application code:
12  * <pre>
13  * try {
14  * model.enterCriticalSection(ModelLock.READ) ;
15  * ...
16  * } finally { model.leaveCriticalSection() ; }
17  * </pre>
18  *
19  * Nested locks are provided for:
20  * <pre>
21  * try {
22  * model.enterCriticalSection(ModelLock.WRITE) ;
23  * libraryCall() ;
24  * ...
25  * } finally { model.leaveCriticalSection() ; }
26  *
27  * void libraryCall()
28  * {
29  * try {
30  * model.enterCriticalSection(ModelLock.READ) ;
31  * ... do library stuff ...
32  * } finally { model.leaveCriticalSection() ; }
33  * }
34  * </pre>
35  * Iterators should be used inside a critical section and not passed outside
36  * the concurrency controlled block.
37  * <pre>
38  * try {
39  * model.enterCriticalSection(ModelLock.READ) ;
40  * StmtIterator sIter = ... ;
41  * for ( ; sIter.next; )
42  * {
43  * ...
44  * }
45  * sIter.close() ;
46  * } finally { model.leaveCriticalSection() ; }
47  * </pre>
48  *
49  * Note that if a library operation needs a write lock, the application must either have no
50  * locks or a write lock when calling. Lock promotion is not supported - it can lead to
51  * deadlock.
52  *
53  * The hard work of locking is done by the
54  * <a HREF="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html">util.concurrent</a>.
55  * This is a convenience wrapper that provides nested locks, a special case of reentrant locks,
56  * that does some checking.
57  *
58  * @author Andy Seaborne
59  * @version $Id: ModelLock.java,v 1.4 2005/02/21 12:14:09 andy_seaborne Exp $
60  */
61
62
63 package com.hp.hpl.jena.rdf.model ;
64
65 public interface ModelLock
66 {
67     /** Descriptive name for lock requests - read lock */
68     public static final boolean READ = true ;
69
70     /** Descriptive name for lock requests - write lock */
71     public static final boolean WRITE = false ;
72
73
74     /** Enter a critical section.
75      * The application must call leaveCriticialSection.
76      * @see #leaveCriticalSection
77      *
78      * @param readLockRequested true implies a read lock,false implies write lock.
79      */
80
81     public void enterCriticalSection(boolean readLockRequested) ;
82
83     /** Leave a critical section. Releases the lock form the matching enterCriticalSection
84      * @see #enterCriticalSection
85      */
86
87     public void leaveCriticalSection() ;
88 }
89
90
91 /*
92  * (c) Copyright 2003, 2004, 2005 Hewlett-Packard Development Company, LP
93  * All rights reserved.
94  *
95  * Redistribution and use in source and binary forms, with or without
96  * modification, are permitted provided that the following conditions
97  * are met:
98  * 1. Redistributions of source code must retain the above copyright
99  * notice, this list of conditions and the following disclaimer.
100  * 2. Redistributions in binary form must reproduce the above copyright
101  * notice, this list of conditions and the following disclaimer in the
102  * documentation and/or other materials provided with the distribution.
103  * 3. The name of the author may not be used to endorse or promote products
104  * derived from this software without specific prior written permission.
105  *
106  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
107  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
108  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
109  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
110  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
111  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
112  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
113  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
114  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
115  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
116  */
117
118
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