Source for java.nio.channels.FileLock

   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: }