old-autovect-branch/libjava/classpath/java/nio/channels/FileLock.java

   1 /* FileLock.java --
   2    Copyright (C) 2002, 2005 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package java.nio.channels;
  39
  40 import java.io.IOException;
  41
  42
  43 /**
  44  * @since 1.4
  45  */
  46 public abstract class FileLock
  47 {
  48   private final FileChannel channel;
  49   private final long position;
  50   private final long size;
  51   private final boolean shared;
  52
  53   /**
  54    * Initializes the file lock.
  55    *
  56    * @exception IllegalArgumentException If the preconditions on the parameters do not hold
  57    */
  58   protected FileLock(FileChannel channel, long position, long size,
  59                      boolean shared)
  60   {
  61     if (position < 0 || size < 0)
  62       throw new IllegalArgumentException();
  63
  64     this.channel = channel;
  65     this.position = position;
  66     this.size = size;
  67     this.shared = shared;
  68   }
  69
  70   /**
  71    * Tells whether or not this lock is valid.
  72    */
  73   public abstract boolean isValid();
  74
  75   /**
  76    * Releases this lock.
  77    *
  78    * @exception IOException If an error occurs
  79    * @exception ClosedChannelException If the locked channel is no longer open.
  80    */
  81   public abstract void release() throws IOException;
  82
  83   /**
  84    * Returns the file channel upon whose file this lock is held.
  85    */
  86   public final FileChannel channel()
  87   {
  88     return channel;
  89   }
  90
  91   /**
  92    * Tells whether this lock is shared.
  93    */
  94   public final boolean isShared()
  95   {
  96     return shared;
  97   }
  98
  99   /**
 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 }