001/* FileLock.java --
002   Copyright (C) 2002, 2005 Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038package java.nio.channels;
039
040import gnu.java.lang.CPStringBuilder;
041
042import java.io.IOException;
043
044/**
045 * @since 1.4
046 */
047public abstract class FileLock
048  implements AutoCloseable
049{
050  private final FileChannel channel;
051  private final long position;
052  private final long size;
053  private final boolean shared;
054
055  /**
056   * Initializes the file lock.
057   *
058   * @exception IllegalArgumentException If the preconditions on the parameters do not hold
059   */
060  protected FileLock(FileChannel channel, long position, long size,
061                     boolean shared)
062  {
063    if (position < 0 || size < 0)
064      throw new IllegalArgumentException();
065
066    this.channel = channel;
067    this.position = position;
068    this.size = size;
069    this.shared = shared;
070  }
071
072  /**
073   * Tells whether or not this lock is valid.
074   */
075  public abstract boolean isValid();
076
077  /**
078   * Releases this lock.
079   *
080   * @exception IOException If an error occurs
081   * @exception ClosedChannelException If the locked channel is no longer open.
082   */
083  public abstract void release() throws IOException;
084
085  /**
086   * Returns the file channel upon whose file this lock is held.
087   */
088  public final FileChannel channel()
089  {
090    return channel;
091  }
092
093  /**
094   * Tells whether this lock is shared.
095   */
096  public final boolean isShared()
097  {
098    return shared;
099  }
100
101  /**
102   * Tells whether or not this lock overlaps the given lock range.
103   */
104  public final boolean overlaps(long position, long size)
105  {
106    if (position > this.position + this.size)
107      return false;
108
109    if (position + size < this.position)
110      return false;
111
112    return true;
113  }
114
115  /**
116   * Returns the position within the file of the first byte of the
117   * locked region.
118   */
119  public final long position()
120  {
121    return position;
122  }
123
124  /**
125   * Returns the size of the locked region in bytes.
126   */
127  public final long size()
128  {
129    return size;
130  }
131
132  /**
133   * Returns a string describing the range, type, and validity of this lock.
134   */
135  public final String toString()
136  {
137    CPStringBuilder buf = new CPStringBuilder(getClass().getName());
138    buf.append("[");
139    buf.append(position);
140    buf.append(":");
141    buf.append(size);
142    if (shared)
143      buf.append(" shared");
144    else
145      buf.append(" exclusive");
146    if (isValid())
147      buf.append(" valid]");
148    else
149      buf.append(" invalid]");
150    return buf.toString();
151  }
152}