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 gnu.java.lang.CPStringBuilder;
  41: 
  42: import java.io.IOException;
  43: 
  44: /**
  45:  * @since 1.4
  46:  */
  47: public abstract class FileLock
  48: {
  49:   private final FileChannel channel;
  50:   private final long position;
  51:   private final long size;
  52:   private final boolean shared;
  53: 
  54:   /**
  55:    * Initializes the file lock.
  56:    *
  57:    * @exception IllegalArgumentException If the preconditions on the parameters do not hold
  58:    */
  59:   protected FileLock(FileChannel channel, long position, long size,
  60:                      boolean shared)
  61:   {
  62:     if (position < 0 || size < 0)
  63:       throw new IllegalArgumentException();
  64: 
  65:     this.channel = channel;
  66:     this.position = position;
  67:     this.size = size;
  68:     this.shared = shared;
  69:   }
  70: 
  71:   /**
  72:    * Tells whether or not this lock is valid.
  73:    */
  74:   public abstract boolean isValid();
  75: 
  76:   /**
  77:    * Releases this lock.
  78:    *
  79:    * @exception IOException If an error occurs
  80:    * @exception ClosedChannelException If the locked channel is no longer open.
  81:    */
  82:   public abstract void release() throws IOException;
  83: 
  84:   /**
  85:    * Returns the file channel upon whose file this lock is held.
  86:    */
  87:   public final FileChannel channel()
  88:   {
  89:     return channel;
  90:   }
  91: 
  92:   /**
  93:    * Tells whether this lock is shared.
  94:    */
  95:   public final boolean isShared()
  96:   {
  97:     return shared;
  98:   }
  99: 
 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: }