001: /*
002: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
003: *
004: * Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
005: *
006: * The contents of this file are subject to the terms of either the GNU
007: * General Public License Version 2 only ("GPL") or the Common
008: * Development and Distribution License("CDDL") (collectively, the
009: * "License"). You may not use this file except in compliance with the
010: * License. You can obtain a copy of the License at
011: * http://www.netbeans.org/cddl-gplv2.html
012: * or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
013: * specific language governing permissions and limitations under the
014: * License. When distributing the software, include this License Header
015: * Notice in each file and include the License file at
016: * nbbuild/licenses/CDDL-GPL-2-CP. Sun designates this
017: * particular file as subject to the "Classpath" exception as provided
018: * by Sun in the GPL Version 2 section of the License file that
019: * accompanied this code. If applicable, add the following below the
020: * License Header, with the fields enclosed by brackets [] replaced by
021: * your own identifying information:
022: * "Portions Copyrighted [year] [name of copyright owner]"
023: *
024: * Contributor(s):
025: *
026: * The Original Software is NetBeans. The Initial Developer of the Original
027: * Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
028: * Microsystems, Inc. All Rights Reserved.
029: *
030: * If you wish your version of this file to be governed by only the CDDL
031: * or only the GPL Version 2, indicate your decision by adding
032: * "[Contributor] elects to include this software in this distribution
033: * under the [CDDL or GPL Version 2] license." If you do not indicate a
034: * single choice of license, a recipient has the option to distribute
035: * your version of this file under either the CDDL, the GPL Version 2 or
036: * to extend the choice of license to its licensees as provided above.
037: * However, if you add GPL Version 2 code and therefore, elected the GPL
038: * Version 2 license, then the option applies only if the new code is
039: * made subject to such option by the copyright holder.
040: */
041: package org.openide.filesystems;
042:
043: import java.io.ByteArrayOutputStream;
044: import java.util.logging.Level;
045: import java.util.logging.Logger;
046:
047: /** Represents an acquired lock on a <code>FileObject</code>.
048: * Typical usage includes locking the file in the editor on first
049: * modification, and then using this object to ensure exclusive access when
050: * overwriting the file (saving) by using {@link FileObject#getOutputStream}.
051: * Also used for renames, deletes, &c.
052: * <p>Note that such locks are only used to protect against concurrent write accesses,
053: * and are not used for read operations (i.e. they are <em>not</em> write-one-read-many locks).
054: * Normally this is sufficient protection. If you really need an atomic read, you may
055: * simply lock the file, perform the read, and unlock it when done. The file will still
056: * be protected against writes, although the read operation did not request a lock.
057: *
058: * @see FileObject
059: *
060: * @author Petr Hamernik, Jaroslav Tulach, Ian Formanek
061: * @version 0.16, Jun 5, 1997
062: *
063: */
064: public class FileLock extends Object {
065: // ========================= NONE file lock =====================================
066:
067: /** Constant that can be used in filesystems that do not support locking.
068: * Represents a lock which is never valid.
069: */
070: public static final FileLock NONE = new FileLock() {
071: /** @return false always. */
072: public boolean isValid() {
073: return false;
074: }
075: };
076:
077: /** Determines if lock is locked or if it was released. */
078: private boolean locked = true;
079: private Throwable lockedBy;
080:
081: public FileLock() {
082: assert (lockedBy = new Throwable()) != null;
083: }
084:
085: // ===============================================================================
086: // This part of code could be used for monitoring of closing file streams.
087:
088: /* public static java.util.HashMap locks = new java.util.HashMap();
089: public FileLock() {
090: locks.put(this, new Exception()); int size = locks.size();
091: System.out.println ("locks:"+(size-1)+" => "+size);
092: }
093: public void releaseLock() {
094: locked = false; locks.remove(this); int size = locks.size();
095: System.out.println ("locks:"+(size+1)+" => "+size);
096: } */
097:
098: // End of the debug part
099: // ============================================================================
100: // Begin of the original part
101: /** Release this lock.
102: * In typical usage this method will be called in a <code>finally</code> clause.
103: */
104: public void releaseLock() {
105: locked = false;
106: }
107:
108: // End of the original part
109: // ============================================================================
110:
111: /** Test whether this lock is still active, or released.
112: * @return <code>true</code> if lock is still active
113: */
114: public boolean isValid() {
115: return locked;
116: }
117:
118: /** Finalize this object. Calls {@link #releaseLock} to release the lock if the program
119: * for some reason failed to.
120: */
121: public void finalize() {
122: assert (!isValid()) : assertMessageForInvalidLocks();
123: releaseLock();
124: }
125:
126: private String assertMessageForInvalidLocks() {
127: ByteArrayOutputStream bos = new ByteArrayOutputStream();
128:
129: if (lockedBy != null) {
130: Logger.getLogger(FileLock.class.getName()).log(
131: Level.WARNING,
132: null,
133: new Exception("Not released lock for file: "
134: + toString() + " (traped in finalizer)")
135: .initCause(lockedBy));//NOI18N
136: }
137:
138: releaseLock();
139: return bos.toString();
140: }
141: }
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