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
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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 * {@code try} ... {@code finally} block:
47 *
48 * <blockquote><pre id="be">
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 final 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 {@code try} ... {@code finally} 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 {@code try} ... {@code finally} 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 }