001 /* FileLock.java --
002 Copyright (C) 2002, 2005 Free Software Foundation, Inc.
003
004 This file is part of GNU Classpath.
005
006 GNU Classpath is free software; you can redistribute it and/or modify
007 it under the terms of the GNU General Public License as published by
008 the Free Software Foundation; either version 2, or (at your option)
009 any later version.
010
011 GNU Classpath is distributed in the hope that it will be useful, but
012 WITHOUT ANY WARRANTY; without even the implied warranty of
013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014 General Public License for more details.
015
016 You should have received a copy of the GNU General Public License
017 along with GNU Classpath; see the file COPYING. If not, write to the
018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019 02110-1301 USA.
020
021 Linking this library statically or dynamically with other modules is
022 making a combined work based on this library. Thus, the terms and
023 conditions of the GNU General Public License cover the whole
024 combination.
025
026 As a special exception, the copyright holders of this library give you
027 permission to link this library with independent modules to produce an
028 executable, regardless of the license terms of these independent
029 modules, and to copy and distribute the resulting executable under
030 terms of your choice, provided that you also meet, for each linked
031 independent module, the terms and conditions of the license of that
032 module. An independent module is a module which is not derived from
033 or based on this library. If you modify this library, you may extend
034 this exception to your version of the library, but you are not
035 obligated to do so. If you do not wish to do so, delete this
036 exception statement from your version. */
037
038 package java.nio.channels;
039
040 import java.io.IOException;
041
042
043 /**
044 * @since 1.4
045 */
046 public abstract class FileLock
047 {
048 private final FileChannel channel;
049 private final long position;
050 private final long size;
051 private final boolean shared;
052
053 /**
054 * Initializes the file lock.
055 *
056 * @exception IllegalArgumentException If the preconditions on the parameters do not hold
057 */
058 protected FileLock(FileChannel channel, long position, long size,
059 boolean shared)
060 {
061 if (position < 0 || size < 0)
062 throw new IllegalArgumentException();
063
064 this.channel = channel;
065 this.position = position;
066 this.size = size;
067 this.shared = shared;
068 }
069
070 /**
071 * Tells whether or not this lock is valid.
072 */
073 public abstract boolean isValid();
074
075 /**
076 * Releases this lock.
077 *
078 * @exception IOException If an error occurs
079 * @exception ClosedChannelException If the locked channel is no longer open.
080 */
081 public abstract void release() throws IOException;
082
083 /**
084 * Returns the file channel upon whose file this lock is held.
085 */
086 public final FileChannel channel()
087 {
088 return channel;
089 }
090
091 /**
092 * Tells whether this lock is shared.
093 */
094 public final boolean isShared()
095 {
096 return shared;
097 }
098
099 /**
100 * Tells whether or not this lock overlaps the given lock range.
101 */
102 public final boolean overlaps(long position, long size)
103 {
104 if (position > this.position + this.size)
105 return false;
106
107 if (position + size < this.position)
108 return false;
109
110 return true;
111 }
112
113 /**
114 * Returns the position within the file of the first byte of the
115 * locked region.
116 */
117 public final long position()
118 {
119 return position;
120 }
121
122 /**
123 * Returns the size of the locked region in bytes.
124 */
125 public final long size()
126 {
127 return size;
128 }
129
130 /**
131 * Returns a string describing the range, type, and validity of this lock.
132 */
133 public final String toString()
134 {
135 StringBuffer buf = new StringBuffer(getClass().getName());
136 buf.append("[");
137 buf.append(position);
138 buf.append(":");
139 buf.append(size);
140 if (shared)
141 buf.append(" shared");
142 else
143 buf.append(" exclusive");
144 if (isValid())
145 buf.append(" valid]");
146 else
147 buf.append(" invalid]");
148 return buf.toString();
149 }
150 }