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;
27
28 import java.io.IOException;
29 import java.nio.channels.spi.AbstractInterruptibleChannel;
30 import java.nio.channels.spi.SelectorProvider;
31
32
33 /**
34 * A channel that can be multiplexed via a {@link Selector}.
35 *
36 * <p> In order to be used with a selector, an instance of this class must
37 * first be <i>registered</i> via the {@link #register(Selector,int,Object)
38 * register} method. This method returns a new {@link SelectionKey} object
39 * that represents the channel's registration with the selector.
40 *
41 * <p> Once registered with a selector, a channel remains registered until it
42 * is <i>deregistered</i>. This involves deallocating whatever resources were
43 * allocated to the channel by the selector.
44 *
45 * <p> A channel cannot be deregistered directly; instead, the key representing
46 * its registration must be <i>cancelled</i>. Cancelling a key requests that
47 * the channel be deregistered during the selector's next selection operation.
48 * A key may be cancelled explicitly by invoking its {@link
49 * SelectionKey#cancel() cancel} method. All of a channel's keys are cancelled
50 * implicitly when the channel is closed, whether by invoking its {@link
51 * Channel#close close} method or by interrupting a thread blocked in an I/O
52 * operation upon the channel.
53 *
54 * <p> If the selector itself is closed then the channel will be deregistered,
55 * and the key representing its registration will be invalidated, without
56 * further delay.
57 *
58 * <p> A channel may be registered at most once with any particular selector.
59 *
60 * <p> Whether or not a channel is registered with one or more selectors may be
61 * determined by invoking the {@link #isRegistered isRegistered} method.
62 *
63 * <p> Selectable channels are safe for use by multiple concurrent
64 * threads. </p>
65 *
66 *
67 * <a id="bm"></a>
68 * <h2>Blocking mode</h2>
69 *
70 * A selectable channel is either in <i>blocking</i> mode or in
71 * <i>non-blocking</i> mode. In blocking mode, every I/O operation invoked
72 * upon the channel will block until it completes. In non-blocking mode an I/O
73 * operation will never block and may transfer fewer bytes than were requested
74 * or possibly no bytes at all. The blocking mode of a selectable channel may
75 * be determined by invoking its {@link #isBlocking isBlocking} method.
76 *
77 * <p> Newly-created selectable channels are always in blocking mode.
78 * Non-blocking mode is most useful in conjunction with selector-based
79 * multiplexing. A channel must be placed into non-blocking mode before being
80 * registered with a selector, and may not be returned to blocking mode until
81 * it has been deregistered.
82 *
83 *
84 * @author Mark Reinhold
85 * @author JSR-51 Expert Group
86 * @since 1.4
87 *
88 * @see SelectionKey
89 * @see Selector
90 */
91
92 public abstract class SelectableChannel
93 extends AbstractInterruptibleChannel
94 implements Channel
95 {
96
97 /**
98 * Initializes a new instance of this class.
99 */
100 protected SelectableChannel() { }
101
102 /**
103 * Returns the provider that created this channel.
104 *
105 * @return The provider that created this channel
106 */
107 public abstract SelectorProvider provider();
108
109 /**
110 * Returns an <a href="SelectionKey.html#opsets">operation set</a>
111 * identifying this channel's supported operations. The bits that are set
112 * in this integer value denote exactly the operations that are valid for
113 * this channel. This method always returns the same value for a given
114 * concrete channel class.
115 *
116 * @return The valid-operation set
117 */
118 public abstract int validOps();
119
120 // Internal state:
121 // keySet, may be empty but is never null, typ. a tiny array
122 // boolean isRegistered, protected by key set
123 // regLock, lock object to prevent duplicate registrations
124 // boolean isBlocking, protected by regLock
125
126 /**
127 * Tells whether or not this channel is currently registered with any
128 * selectors. A newly-created channel is not registered.
129 *
130 * <p> Due to the inherent delay between key cancellation and channel
131 * deregistration, a channel may remain registered for some time after all
132 * of its keys have been cancelled. A channel may also remain registered
133 * for some time after it is closed. </p>
134 *
135 * @return {@code true} if, and only if, this channel is registered
136 */
137 public abstract boolean isRegistered();
138 //
139 // sync(keySet) { return isRegistered; }
140
141 /**
142 * Retrieves the key representing the channel's registration with the given
143 * selector.
144 *
145 * @param sel
146 * The selector
147 *
148 * @return The key returned when this channel was last registered with the
149 * given selector, or {@code null} if this channel is not
150 * currently registered with that selector
151 */
152 public abstract SelectionKey keyFor(Selector sel);
153 //
154 // sync(keySet) { return findKey(sel); }
155
156 /**
157 * Registers this channel with the given selector, returning a selection
158 * key.
159 *
160 * <p> If this channel is currently registered with the given selector then
161 * the selection key representing that registration is returned. The key's
162 * interest set will have been changed to {@code ops}, as if by invoking
163 * the {@link SelectionKey#interestOps(int) interestOps(int)} method. If
164 * the {@code att} argument is not {@code null} then the key's attachment
165 * will have been set to that value. A {@link CancelledKeyException} will
166 * be thrown if the key has already been cancelled.
167 *
168 * <p> Otherwise this channel has not yet been registered with the given
169 * selector, so it is registered and the resulting new key is returned.
170 * The key's initial interest set will be {@code ops} and its attachment
171 * will be {@code att}.
172 *
173 * <p> This method may be invoked at any time. If this method is invoked
174 * while another invocation of this method or of the {@link
175 * #configureBlocking(boolean) configureBlocking} method is in progress
176 * then it will first block until the other operation is complete. This
177 * method will then synchronize on the selector's key set and therefore may
178 * block if invoked concurrently with another registration or selection
179 * operation involving the same selector. </p>
180 *
181 * <p> If this channel is closed while this operation is in progress then
182 * the key returned by this method will have been cancelled and will
183 * therefore be invalid. </p>
184 *
185 * @param sel
186 * The selector with which this channel is to be registered
187 *
188 * @param ops
189 * The interest set for the resulting key
190 *
191 * @param att
192 * The attachment for the resulting key; may be {@code null}
193 *
194 * @throws ClosedChannelException
195 * If this channel is closed
196 *
197 * @throws ClosedSelectorException
198 * If the selector is closed
199 *
200 * @throws IllegalBlockingModeException
201 * If this channel is in blocking mode
202 *
203 * @throws IllegalSelectorException
204 * If this channel was not created by the same provider
205 * as the given selector
206 *
207 * @throws CancelledKeyException
208 * If this channel is currently registered with the given selector
209 * but the corresponding key has already been cancelled
210 *
211 * @throws IllegalArgumentException
212 * If a bit in the {@code ops} set does not correspond to an
213 * operation that is supported by this channel, that is, if
214 * {@code set & ~validOps() != 0}
215 *
216 * @return A key representing the registration of this channel with
217 * the given selector
218 */
219 public abstract SelectionKey register(Selector sel, int ops, Object att)
220 throws ClosedChannelException;
221 //
222 // sync(regLock) {
223 // sync(keySet) { look for selector }
224 // if (channel found) { set interest ops -- may block in selector;
225 // return key; }
226 // create new key -- may block somewhere in selector;
227 // sync(keySet) { add key; }
228 // attach(attachment);
229 // return key;
230 // }
231
232 /**
233 * Registers this channel with the given selector, returning a selection
234 * key.
235 *
236 * <p> An invocation of this convenience method of the form
237 *
238 * <blockquote>{@code sc.register(sel, ops)}</blockquote>
239 *
240 * behaves in exactly the same way as the invocation
241 *
242 * <blockquote>{@code sc.}{@link
243 * #register(java.nio.channels.Selector,int,java.lang.Object)
244 * register(sel, ops, null)}</blockquote>
245 *
246 * @param sel
247 * The selector with which this channel is to be registered
248 *
249 * @param ops
250 * The interest set for the resulting key
251 *
252 * @throws ClosedChannelException
253 * If this channel is closed
254 *
255 * @throws ClosedSelectorException
256 * If the selector is closed
257 *
258 * @throws IllegalBlockingModeException
259 * If this channel is in blocking mode
260 *
261 * @throws IllegalSelectorException
262 * If this channel was not created by the same provider
263 * as the given selector
264 *
265 * @throws CancelledKeyException
266 * If this channel is currently registered with the given selector
267 * but the corresponding key has already been cancelled
268 *
269 * @throws IllegalArgumentException
270 * If a bit in {@code ops} does not correspond to an operation
271 * that is supported by this channel, that is, if {@code set &
272 * ~validOps() != 0}
273 *
274 * @return A key representing the registration of this channel with
275 * the given selector
276 */
277 public final SelectionKey register(Selector sel, int ops)
278 throws ClosedChannelException
279 {
280 return register(sel, ops, null);
281 }
282
283 /**
284 * Adjusts this channel's blocking mode.
285 *
286 * <p> If this channel is registered with one or more selectors then an
287 * attempt to place it into blocking mode will cause an {@link
288 * IllegalBlockingModeException} to be thrown.
289 *
290 * <p> This method may be invoked at any time. The new blocking mode will
291 * only affect I/O operations that are initiated after this method returns.
292 * For some implementations this may require blocking until all pending I/O
293 * operations are complete.
294 *
295 * <p> If this method is invoked while another invocation of this method or
296 * of the {@link #register(Selector, int) register} method is in progress
297 * then it will first block until the other operation is complete. </p>
298 *
299 * @param block If {@code true} then this channel will be placed in
300 * blocking mode; if {@code false} then it will be placed
301 * non-blocking mode
302 *
303 * @return This selectable channel
304 *
305 * @throws ClosedChannelException
306 * If this channel is closed
307 *
308 * @throws IllegalBlockingModeException
309 * If {@code block} is {@code true} and this channel is
310 * registered with one or more selectors
311 *
312 * @throws IOException
313 * If an I/O error occurs
314 */
315 public abstract SelectableChannel configureBlocking(boolean block)
316 throws IOException;
317 //
318 // sync(regLock) {
319 // sync(keySet) { throw IBME if block && isRegistered; }
320 // change mode;
321 // }
322
323 /**
324 * Tells whether or not every I/O operation on this channel will block
325 * until it completes. A newly-created channel is always in blocking mode.
326 *
327 * <p> If this channel is closed then the value returned by this method is
328 * not specified. </p>
329 *
330 * @return {@code true} if, and only if, this channel is in blocking mode
331 */
332 public abstract boolean isBlocking();
333
334 /**
335 * Retrieves the object upon which the {@link #configureBlocking
336 * configureBlocking} and {@link #register register} methods synchronize.
337 * This is often useful in the implementation of adaptors that require a
338 * specific blocking mode to be maintained for a short period of time.
339 *
340 * @return The blocking-mode lock object
341 */
342 public abstract Object blockingLock();
343
344 }