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    }