libjava/java/nio/channels/spi/AbstractSelectableChannel.java

   1 /* AbstractSelectableChannel.java
   2    Copyright (C) 2002, 2003, 2004 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., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 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.spi;
  39
  40 import java.io.IOException;
  41 import java.nio.channels.ClosedChannelException;
  42 import java.nio.channels.SelectableChannel;
  43 import java.nio.channels.SelectionKey;
  44 import java.nio.channels.Selector;
  45 import java.util.LinkedList;
  46 import java.util.List;
  47 import java.util.ListIterator;
  48
  49 public abstract class AbstractSelectableChannel extends SelectableChannel
  50 {
  51   private boolean blocking = true;
  52   private Object LOCK = new Object();
  53   private SelectorProvider provider;
  54   private LinkedList keys = new LinkedList();
  55
  56   /**
  57    * Initializes the channel
  58    */
  59   protected AbstractSelectableChannel (SelectorProvider provider)
  60   {
  61     this.provider = provider;
  62   }
  63
  64   /**
  65    * Retrieves the object upon which the configureBlocking and register
  66    * methods synchronize.
  67    */
  68   public final Object blockingLock ()
  69   {
  70     return LOCK;
  71   }
  72
  73   /**
  74    * Adjusts this channel's blocking mode.
  75    */
  76   public final SelectableChannel configureBlocking (boolean blocking)
  77     throws IOException
  78   {
  79     synchronized (blockingLock())
  80       {
  81         if (this.blocking != blocking)
  82           {
  83             implConfigureBlocking(blocking);
  84             this.blocking = blocking;
  85           }
  86       }
  87
  88     return this;
  89   }
  90
  91   /**
  92    * Closes this channel.
  93    *
  94    * @exception IOException If an error occurs
  95    */
  96   protected final void implCloseChannel () throws IOException
  97   {
  98     implCloseSelectableChannel ();
  99   }
 100
 101   /**
 102    * Closes this selectable channel.
 103    */
 104   protected abstract void implCloseSelectableChannel () throws IOException;
 105
 106   /**
 107    * Adjusts this channel's blocking mode.
 108    */
 109   protected abstract void implConfigureBlocking (boolean block)
 110     throws IOException;
 111
 112   /**
 113    * Tells whether or not every I/O operation on this channel will block
 114    * until it completes.
 115    */
 116   public final boolean isBlocking()
 117   {
 118     return blocking;
 119   }
 120
 121   /**
 122    * Tells whether or not this channel is currently registered with
 123    * any selectors.
 124    */
 125   public final boolean isRegistered()
 126   {
 127     return !keys.isEmpty();
 128   }
 129
 130   /**
 131    * Retrieves the key representing the channel's registration with the
 132    * given selector.
 133    */
 134   public final SelectionKey keyFor(Selector selector)
 135   {
 136     if (! isOpen())
 137       return null;
 138
 139     try
 140       {
 141         synchronized(blockingLock())
 142           {
 143             return locate (selector);
 144           }
 145       }
 146     catch (Exception e)
 147       {
 148         return null;
 149       }
 150   }
 151
 152   /**
 153    * Returns the provider that created this channel.
 154    */
 155   public final SelectorProvider provider ()
 156   {
 157     return provider;
 158   }
 159
 160   private SelectionKey locate (Selector selector)
 161   {
 162     ListIterator it = keys.listIterator ();
 163
 164     while (it.hasNext ())
 165       {
 166         SelectionKey key = (SelectionKey) it.next();
 167
 168         if (key.selector() == selector)
 169           return key;
 170       }
 171
 172     return null;
 173   }
 174
 175   /**
 176    * Registers this channel with the given selector, returning a selection key.
 177    *
 178    * @exception ClosedChannelException If the channel is already closed.
 179    */
 180   public final SelectionKey register (Selector selin, int ops, Object att)
 181     throws ClosedChannelException
 182   {
 183     if (!isOpen ())
 184       throw new ClosedChannelException();
 185
 186     SelectionKey key = null;
 187     AbstractSelector selector = (AbstractSelector) selin;
 188
 189     synchronized (blockingLock())
 190       {
 191         key = locate (selector);
 192
 193         if (key != null)
 194           {
 195             if (att != null)
 196               key.attach (att);
 197           }
 198         else
 199           {
 200             key = selector.register (this, ops, att);
 201
 202             if (key != null)
 203               addSelectionKey (key);
 204           }
 205       }
 206
 207     return key;
 208   }
 209
 210   void addSelectionKey(SelectionKey key)
 211   {
 212     keys.add(key);
 213   }
 214
 215   // This method gets called by AbstractSelector.deregister().
 216   void removeSelectionKey(SelectionKey key)
 217   {
 218     keys.remove(key);
 219   }
 220 }