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 gnu.java.lang.CPStringBuilder;
041    
042    import java.io.IOException;
043    
044    /**
045     * @since 1.4
046     */
047    public 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    }