View Javadoc
1   /*
2    * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
6    * under the terms of the GNU General Public License version 2 only, as
7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
18   * 2 along with this work; if not, write to the Free Software Foundation,
19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
21   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22   * or visit www.oracle.com if you need additional information or have any
23   * questions.
24   */
25  
26  package java.nio.channels.spi;
27  
28  import java.io.IOException;
29  import java.nio.channels.SelectionKey;
30  import java.nio.channels.Selector;
31  import java.util.HashSet;
32  import java.util.Set;
33  import sun.nio.ch.Interruptible;
34  import java.util.concurrent.atomic.AtomicBoolean;
35  
36  
37  /**
38   * Base implementation class for selectors.
39   *
40   * <p> This class encapsulates the low-level machinery required to implement
41   * the interruption of selection operations.  A concrete selector class must
42   * invoke the {@link #begin begin} and {@link #end end} methods before and
43   * after, respectively, invoking an I/O operation that might block
44   * indefinitely.  In order to ensure that the {@link #end end} method is always
45   * invoked, these methods should be used within a
46   * <tt>try</tt>&nbsp;...&nbsp;<tt>finally</tt> block:
47   *
48   * <blockquote><pre>
49   * try {
50   *     begin();
51   *     // Perform blocking I/O operation here
52   *     ...
53   * } finally {
54   *     end();
55   * }</pre></blockquote>
56   *
57   * <p> This class also defines methods for maintaining a selector's
58   * cancelled-key set and for removing a key from its channel's key set, and
59   * declares the abstract {@link #register register} method that is invoked by a
60   * selectable channel's {@link AbstractSelectableChannel#register register}
61   * method in order to perform the actual work of registering a channel.  </p>
62   *
63   *
64   * @author Mark Reinhold
65   * @author JSR-51 Expert Group
66   * @since 1.4
67   */
68  
69  public abstract class AbstractSelector
70      extends Selector
71  {
72  
73      private AtomicBoolean selectorOpen = new AtomicBoolean(true);
74  
75      // The provider that created this selector
76      private final SelectorProvider provider;
77  
78      /**
79       * Initializes a new instance of this class.
80       *
81       * @param  provider
82       *         The provider that created this selector
83       */
84      protected AbstractSelector(SelectorProvider provider) {
85          this.provider = provider;
86      }
87  
88      private final Set<SelectionKey> cancelledKeys = new HashSet<SelectionKey>();
89  
90      void cancel(SelectionKey k) {                       // package-private
91          synchronized (cancelledKeys) {
92              cancelledKeys.add(k);
93          }
94      }
95  
96      /**
97       * Closes this selector.
98       *
99       * <p> If the selector has already been closed then this method returns
100      * immediately.  Otherwise it marks the selector as closed and then invokes
101      * the {@link #implCloseSelector implCloseSelector} method in order to
102      * complete the close operation.  </p>
103      *
104      * @throws  IOException
105      *          If an I/O error occurs
106      */
107     public final void close() throws IOException {
108         boolean open = selectorOpen.getAndSet(false);
109         if (!open)
110             return;
111         implCloseSelector();
112     }
113 
114     /**
115      * Closes this selector.
116      *
117      * <p> This method is invoked by the {@link #close close} method in order
118      * to perform the actual work of closing the selector.  This method is only
119      * invoked if the selector has not yet been closed, and it is never invoked
120      * more than once.
121      *
122      * <p> An implementation of this method must arrange for any other thread
123      * that is blocked in a selection operation upon this selector to return
124      * immediately as if by invoking the {@link
125      * java.nio.channels.Selector#wakeup wakeup} method. </p>
126      *
127      * @throws  IOException
128      *          If an I/O error occurs while closing the selector
129      */
130     protected abstract void implCloseSelector() throws IOException;
131 
132     public final boolean isOpen() {
133         return selectorOpen.get();
134     }
135 
136     /**
137      * Returns the provider that created this channel.
138      *
139      * @return  The provider that created this channel
140      */
141     public final SelectorProvider provider() {
142         return provider;
143     }
144 
145     /**
146      * Retrieves this selector's cancelled-key set.
147      *
148      * <p> This set should only be used while synchronized upon it.  </p>
149      *
150      * @return  The cancelled-key set
151      */
152     protected final Set<SelectionKey> cancelledKeys() {
153         return cancelledKeys;
154     }
155 
156     /**
157      * Registers the given channel with this selector.
158      *
159      * <p> This method is invoked by a channel's {@link
160      * AbstractSelectableChannel#register register} method in order to perform
161      * the actual work of registering the channel with this selector.  </p>
162      *
163      * @param  ch
164      *         The channel to be registered
165      *
166      * @param  ops
167      *         The initial interest set, which must be valid
168      *
169      * @param  att
170      *         The initial attachment for the resulting key
171      *
172      * @return  A new key representing the registration of the given channel
173      *          with this selector
174      */
175     protected abstract SelectionKey register(AbstractSelectableChannel ch,
176                                              int ops, Object att);
177 
178     /**
179      * Removes the given key from its channel's key set.
180      *
181      * <p> This method must be invoked by the selector for each channel that it
182      * deregisters.  </p>
183      *
184      * @param  key
185      *         The selection key to be removed
186      */
187     protected final void deregister(AbstractSelectionKey key) {
188         ((AbstractSelectableChannel)key.channel()).removeKey(key);
189     }
190 
191 
192     // -- Interruption machinery --
193 
194     private Interruptible interruptor = null;
195 
196     /**
197      * Marks the beginning of an I/O operation that might block indefinitely.
198      *
199      * <p> This method should be invoked in tandem with the {@link #end end}
200      * method, using a <tt>try</tt>&nbsp;...&nbsp;<tt>finally</tt> block as
201      * shown <a href="#be">above</a>, in order to implement interruption for
202      * this selector.
203      *
204      * <p> Invoking this method arranges for the selector's {@link
205      * Selector#wakeup wakeup} method to be invoked if a thread's {@link
206      * Thread#interrupt interrupt} method is invoked while the thread is
207      * blocked in an I/O operation upon the selector.  </p>
208      */
209     protected final void begin() {
210         if (interruptor == null) {
211             interruptor = new Interruptible() {
212                     public void interrupt(Thread ignore) {
213                         AbstractSelector.this.wakeup();
214                     }};
215         }
216         AbstractInterruptibleChannel.blockedOn(interruptor);
217         Thread me = Thread.currentThread();
218         if (me.isInterrupted())
219             interruptor.interrupt(me);
220     }
221 
222     /**
223      * Marks the end of an I/O operation that might block indefinitely.
224      *
225      * <p> This method should be invoked in tandem with the {@link #begin begin}
226      * method, using a <tt>try</tt>&nbsp;...&nbsp;<tt>finally</tt> block as
227      * shown <a href="#be">above</a>, in order to implement interruption for
228      * this selector.  </p>
229      */
230     protected final void end() {
231         AbstractInterruptibleChannel.blockedOn(null);
232     }
233 
234 }