FileLock


1   /*
2    * The contents of this file are subject to the terms of the Common Development
3    * and Distribution License (the License). You may not use this file except in
4    * compliance with the License.
5    *
6    * You can obtain a copy of the License at http://www.netbeans.org/cddl.html
7    * or http://www.netbeans.org/cddl.txt.
8    *
9    * When distributing Covered Code, include this CDDL Header Notice in each file
10   * and include the License file at http://www.netbeans.org/cddl.txt.
11   * If applicable, add the following below the CDDL Header, with the fields
12   * enclosed by brackets [] replaced by your own identifying information:
13   * "Portions Copyrighted [year] [name of copyright owner]"
14   *
15   * The Original Software is NetBeans. The Initial Developer of the Original
16   * Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
17   * Microsystems, Inc. All Rights Reserved.
18   */
19  package org.openide.filesystems;
20  
21  import java.io.ByteArrayOutputStream  ;
22  import java.util.logging.Level  ;
23  import java.util.logging.Logger  ;
24  
25  
26  /** Represents an acquired lock on a <code>FileObject</code>.
27  * Typical usage includes locking the file in the editor on first
28  * modification, and then using this object to ensure exclusive access when
29  * overwriting the file (saving) by using {@link FileObject#getOutputStream}.
30  * Also used for renames, deletes, &amp;c.
31  * <p>Note that such locks are only used to protect against concurrent write accesses,
32  * and are not used for read operations (i.e. they are <em>not</em> write-one-read-many locks).
33  * Normally this is sufficient protection. If you really need an atomic read, you may
34  * simply lock the file, perform the read, and unlock it when done. The file will still
35  * be protected against writes, although the read operation did not request a lock.
36  *
37  * @see FileObject
38  *
39  * @author Petr Hamernik, Jaroslav Tulach, Ian Formanek
40  * @version 0.16, Jun 5, 1997
41  *
42  */
43  public class FileLock extends Object   {
44      // ========================= NONE file lock =====================================
45  
46      /** Constant that can be used in filesystems that do not support locking.
47       * Represents a lock which is never valid.
48      */
49      public static final FileLock NONE = new FileLock() {
50              /** @return false always. */
51              public boolean isValid() {
52                  return false;
53              }
54          };
55  
56      /** Determines if lock is locked or if it was released. */
57      private boolean locked = true;
58      private Throwable   lockedBy;
59  
60      public FileLock() {
61          assert (lockedBy = new Throwable  ()) != null;
62      }
63  
64      // ===============================================================================
65      //  This part of code could be used for monitoring of closing file streams.
66  
67      /*  public static java.util.HashMap locks = new java.util.HashMap();
68        public FileLock() {
69          locks.put(this, new Exception()); int size = locks.size();
70          System.out.println ("locks:"+(size-1)+" => "+size);
71        }
72        public void releaseLock() {
73          locked = false; locks.remove(this); int size = locks.size();
74          System.out.println ("locks:"+(size+1)+" => "+size);
75        } */
76  
77      //  End of the debug part
78      // ============================================================================
79      //  Begin of the original part
80  
81      /** Release this lock.
82      * In typical usage this method will be called in a <code>finally</code> clause.
83      */
84      public void releaseLock() {
85          locked = false;
86      }
87  
88      //  End of the original part
89      // ============================================================================
90  
91      /** Test whether this lock is still active, or released.
92      * @return <code>true</code> if lock is still active
93      */
94      public boolean isValid() {
95          return locked;
96      }
97  
98      /** Finalize this object. Calls {@link #releaseLock} to release the lock if the program
99      * for some reason failed to.
100     */
101     public void finalize() {
102         assert (!isValid()) : assertMessageForInvalidLocks();
103         releaseLock();
104     }
105 
106     private String   assertMessageForInvalidLocks() {
107         ByteArrayOutputStream   bos = new ByteArrayOutputStream  ();
108 
109         if (lockedBy != null) {
110             Logger.getLogger(FileLock.class.getName()).log(Level.WARNING, null,
111                               new Exception  ("Not released lock for file: " +
112                                             toString() +
113                                             " (traped in finalizer)").initCause(lockedBy));//NOI18N
114         }
115 
116         releaseLock();
117         return bos.toString();
118     }
119 }
120
A to Z: JavaDoc & Examples Daily Java News & Articles Open Source Projects Open Source Codes Free Computer Books Remove Frame
Free Books Free Magazines
Popular Tags