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{
049  private final FileChannel channel;
050  private final long position;
051  private final long size;
052  private final boolean shared;
053
054  /**
055   * Initializes the file lock.
056   *
057   * @exception IllegalArgumentException If the preconditions on the parameters do not hold
058   */
059  protected FileLock(FileChannel channel, long position, long size,
060                     boolean shared)
061  {
062    if (position < 0 || size < 0)
063      throw new IllegalArgumentException();
064
065    this.channel = channel;
066    this.position = position;
067    this.size = size;
068    this.shared = shared;
069  }
070
071  /**
072   * Tells whether or not this lock is valid.
073   */
074  public abstract boolean isValid();
075
076  /**
077   * Releases this lock.
078   *
079   * @exception IOException If an error occurs
080   * @exception ClosedChannelException If the locked channel is no longer open.
081   */
082  public abstract void release() throws IOException;
083
084  /**
085   * Returns the file channel upon whose file this lock is held.
086   */
087  public final FileChannel channel()
088  {
089    return channel;
090  }
091
092  /**
093   * Tells whether this lock is shared.
094   */
095  public final boolean isShared()
096  {
097    return shared;
098  }
099
100  /**
101   * Tells whether or not this lock overlaps the given lock range.
102   */
103  public final boolean overlaps(long position, long size)
104  {
105    if (position > this.position + this.size)
106      return false;
107
108    if (position + size < this.position)
109      return false;
110
111    return true;
112  }
113
114  /**
115   * Returns the position within the file of the first byte of the
116   * locked region.
117   */
118  public final long position()
119  {
120    return position;
121  }
122
123  /**
124   * Returns the size of the locked region in bytes.
125   */
126  public final long size()
127  {
128    return size;
129  }
130
131  /**
132   * Returns a string describing the range, type, and validity of this lock.
133   */
134  public final String toString()
135  {
136    CPStringBuilder buf = new CPStringBuilder(getClass().getName());
137    buf.append("[");
138    buf.append(position);
139    buf.append(":");
140    buf.append(size);
141    if (shared)
142      buf.append(" shared");
143    else
144      buf.append(" exclusive");
145    if (isValid())
146      buf.append(" valid]");
147    else
148      buf.append(" invalid]");
149    return buf.toString();
150  }
151}