001 /*
002 * Copyright 2000-2001 Sun Microsystems, Inc. All Rights Reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation. Sun designates this
008 * particular file as subject to the "Classpath" exception as provided
009 * by Sun in the LICENSE file that accompanied this code.
010 *
011 * This code is distributed in the hope that it will be useful, but WITHOUT
012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014 * version 2 for more details (a copy is included in the LICENSE file that
015 * accompanied this code).
016 *
017 * You should have received a copy of the GNU General Public License version
018 * 2 along with this work; if not, write to the Free Software Foundation,
019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020 *
021 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022 * CA 95054 USA or visit www.sun.com if you need additional information or
023 * have any questions.
024 */
025
026 package java.nio.channels;
027
028 import java.io.IOException;
029 import java.nio.channels.spi.AbstractInterruptibleChannel;
030 import java.nio.channels.spi.SelectorProvider;
031
032 /**
033 * A channel that can be multiplexed via a {@link Selector}.
034 *
035 * <p> In order to be used with a selector, an instance of this class must
036 * first be <i>registered</i> via the {@link #register(Selector,int,Object)
037 * register} method. This method returns a new {@link SelectionKey} object
038 * that represents the channel's registration with the selector.
039 *
040 * <p> Once registered with a selector, a channel remains registered until it
041 * is <i>deregistered</i>. This involves deallocating whatever resources were
042 * allocated to the channel by the selector.
043 *
044 * <p> A channel cannot be deregistered directly; instead, the key representing
045 * its registration must be <i>cancelled</i>. Cancelling a key requests that
046 * the channel be deregistered during the selector's next selection operation.
047 * A key may be cancelled explicitly by invoking its {@link
048 * SelectionKey#cancel() cancel} method. All of a channel's keys are cancelled
049 * implicitly when the channel is closed, whether by invoking its {@link
050 * Channel#close close} method or by interrupting a thread blocked in an I/O
051 * operation upon the channel.
052 *
053 * <p> If the selector itself is closed then the channel will be deregistered,
054 * and the key representing its registration will be invalidated, without
055 * further delay.
056 *
057 * <p> A channel may be registered at most once with any particular selector.
058 *
059 * <p> Whether or not a channel is registered with one or more selectors may be
060 * determined by invoking the {@link #isRegistered isRegistered} method.
061 *
062 * <p> Selectable channels are safe for use by multiple concurrent
063 * threads. </p>
064 *
065 *
066 * <a name="bm">
067 * <h4>Blocking mode</h4>
068 *
069 * A selectable channel is either in <i>blocking</i> mode or in
070 * <i>non-blocking</i> mode. In blocking mode, every I/O operation invoked
071 * upon the channel will block until it completes. In non-blocking mode an I/O
072 * operation will never block and may transfer fewer bytes than were requested
073 * or possibly no bytes at all. The blocking mode of a selectable channel may
074 * be determined by invoking its {@link #isBlocking isBlocking} method.
075 *
076 * <p> Newly-created selectable channels are always in blocking mode.
077 * Non-blocking mode is most useful in conjunction with selector-based
078 * multiplexing. A channel must be placed into non-blocking mode before being
079 * registered with a selector, and may not be returned to blocking mode until
080 * it has been deregistered.
081 *
082 *
083 * @author Mark Reinhold
084 * @author JSR-51 Expert Group
085 * @version 1.41, 07/05/05
086 * @since 1.4
087 *
088 * @see SelectionKey
089 * @see Selector
090 */
091
092 public abstract class SelectableChannel extends
093 AbstractInterruptibleChannel implements Channel {
094
095 /**
096 * Initializes a new instance of this class.
097 */
098 protected SelectableChannel() {
099 }
100
101 /**
102 * Returns the provider that created this channel.
103 *
104 * @return The provider that created this channel
105 */
106 public abstract SelectorProvider provider();
107
108 /**
109 * Returns an <a href="SelectionKey.html#opsets">operation set</a>
110 * identifying this channel's supported operations. The bits that are set
111 * in this integer value denote exactly the operations that are valid for
112 * this channel. This method always returns the same value for a given
113 * concrete channel class. </p>
114 *
115 * @return The valid-operation set
116 */
117 public abstract int validOps();
118
119 // Internal state:
120 // keySet, may be empty but is never null, typ. a tiny array
121 // boolean isRegistered, protected by key set
122 // regLock, lock object to prevent duplicate registrations
123 // boolean isBlocking, protected by regLock
124
125 /**
126 * Tells whether or not this channel is currently registered with any
127 * selectors. A newly-created channel is not registered.
128 *
129 * <p> Due to the inherent delay between key cancellation and channel
130 * deregistration, a channel may remain registered for some time after all
131 * of its keys have been cancelled. A channel may also remain registered
132 * for some time after it is closed. </p>
133 *
134 * @return <tt>true</tt> if, and only if, this channel is registered
135 */
136 public abstract boolean isRegistered();
137
138 //
139 // sync(keySet) { return isRegistered; }
140
141 /**
142 * Retrieves the key representing the channel's registration with the given
143 * selector. </p>
144 *
145 * @return The key returned when this channel was last registered with the
146 * given selector, or <tt>null</tt> if this channel is not
147 * currently registered with that selector
148 */
149 public abstract SelectionKey keyFor(Selector sel);
150
151 //
152 // sync(keySet) { return findKey(sel); }
153
154 /**
155 * Registers this channel with the given selector, returning a selection
156 * key.
157 *
158 * <p> If this channel is currently registered with the given selector then
159 * the selection key representing that registration is returned. The key's
160 * interest set will have been changed to <tt>ops</tt>, as if by invoking
161 * the {@link SelectionKey#interestOps(int) interestOps(int)} method. If
162 * the <tt>att</tt> argument is not <tt>null</tt> then the key's attachment
163 * will have been set to that value. A {@link CancelledKeyException} will
164 * be thrown if the key has already been cancelled.
165 *
166 * <p> Otherwise this channel has not yet been registered with the given
167 * selector, so it is registered and the resulting new key is returned.
168 * The key's initial interest set will be <tt>ops</tt> and its attachment
169 * will be <tt>att</tt>.
170 *
171 * <p> This method may be invoked at any time. If this method is invoked
172 * while another invocation of this method or of the {@link
173 * #configureBlocking(boolean) configureBlocking} method is in progress
174 * then it will first block until the other operation is complete. This
175 * method will then synchronize on the selector's key set and therefore may
176 * block if invoked concurrently with another registration or selection
177 * operation involving the same selector. </p>
178 *
179 * <p> If this channel is closed while this operation is in progress then
180 * the key returned by this method will have been cancelled and will
181 * therefore be invalid. </p>
182 *
183 * @param sel
184 * The selector with which this channel is to be registered
185 *
186 * @param ops
187 * The interest set for the resulting key
188 *
189 * @param att
190 * The attachment for the resulting key; may be <tt>null</tt>
191 *
192 * @throws ClosedChannelException
193 * If this channel is closed
194 *
195 * @throws IllegalBlockingModeException
196 * If this channel is in blocking mode
197 *
198 * @throws IllegalSelectorException
199 * If this channel was not created by the same provider
200 * as the given selector
201 *
202 * @throws CancelledKeyException
203 * If this channel is currently registered with the given selector
204 * but the corresponding key has already been cancelled
205 *
206 * @throws IllegalArgumentException
207 * If a bit in the <tt>ops</tt> set does not correspond to an
208 * operation that is supported by this channel, that is, if
209 * <tt>set & ~validOps() != 0</tt>
210 *
211 * @return A key representing the registration of this channel with
212 * the given selector
213 */
214 public abstract SelectionKey register(Selector sel, int ops,
215 Object att) throws ClosedChannelException;
216
217 //
218 // sync(regLock) {
219 // sync(keySet) { look for selector }
220 // if (channel found) { set interest ops -- may block in selector;
221 // return key; }
222 // create new key -- may block somewhere in selector;
223 // sync(keySet) { add key; }
224 // attach(attachment);
225 // return key;
226 // }
227
228 /**
229 * Registers this channel with the given selector, returning a selection
230 * key.
231 *
232 * <p> An invocation of this convenience method of the form
233 *
234 * <blockquote><tt>sc.register(sel, ops)</tt></blockquote>
235 *
236 * behaves in exactly the same way as the invocation
237 *
238 * <blockquote><tt>sc.{@link
239 * #register(java.nio.channels.Selector,int,java.lang.Object)
240 * register}(sel, ops, null)</tt></blockquote>
241 *
242 * @param sel
243 * The selector with which this channel is to be registered
244 *
245 * @param ops
246 * The interest set for the resulting key
247 *
248 * @throws ClosedChannelException
249 * If this channel is closed
250 *
251 * @throws IllegalBlockingModeException
252 * If this channel is in blocking mode
253 *
254 * @throws IllegalSelectorException
255 * If this channel was not created by the same provider
256 * as the given selector
257 *
258 * @throws CancelledKeyException
259 * If this channel is currently registered with the given selector
260 * but the corresponding key has already been cancelled
261 *
262 * @throws IllegalArgumentException
263 * If a bit in <tt>ops</tt> does not correspond to an operation
264 * that is supported by this channel, that is, if <tt>set &
265 * ~validOps() != 0</tt>
266 *
267 * @return A key representing the registration of this channel with
268 * the given selector
269 */
270 public final SelectionKey register(Selector sel, int ops)
271 throws ClosedChannelException {
272 return register(sel, ops, null);
273 }
274
275 /**
276 * Adjusts this channel's blocking mode.
277 *
278 * <p> If this channel is registered with one or more selectors then an
279 * attempt to place it into blocking mode will cause an {@link
280 * IllegalBlockingModeException} to be thrown.
281 *
282 * <p> This method may be invoked at any time. The new blocking mode will
283 * only affect I/O operations that are initiated after this method returns.
284 * For some implementations this may require blocking until all pending I/O
285 * operations are complete.
286 *
287 * <p> If this method is invoked while another invocation of this method or
288 * of the {@link #register(Selector, int) register} method is in progress
289 * then it will first block until the other operation is complete. </p>
290 *
291 * @param block If <tt>true</tt> then this channel will be placed in
292 * blocking mode; if <tt>false</tt> then it will be placed
293 * non-blocking mode
294 *
295 * @return This selectable channel
296 *
297 * @throws ClosedChannelException
298 * If this channel is closed
299 *
300 * @throws IllegalBlockingModeException
301 * If <tt>block</tt> is <tt>true</tt> and this channel is
302 * registered with one or more selectors
303 *
304 * @throws IOException
305 * If an I/O error occurs
306 */
307 public abstract SelectableChannel configureBlocking(boolean block)
308 throws IOException;
309
310 //
311 // sync(regLock) {
312 // sync(keySet) { throw IBME if block && isRegistered; }
313 // change mode;
314 // }
315
316 /**
317 * Tells whether or not every I/O operation on this channel will block
318 * until it completes. A newly-created channel is always in blocking mode.
319 *
320 * <p> If this channel is closed then the value returned by this method is
321 * not specified. </p>
322 *
323 * @return <tt>true</tt> if, and only if, this channel is in blocking mode
324 */
325 public abstract boolean isBlocking();
326
327 /**
328 * Retrieves the object upon which the {@link #configureBlocking
329 * configureBlocking} and {@link #register register} methods synchronize.
330 * This is often useful in the implementation of adaptors that require a
331 * specific blocking mode to be maintained for a short period of time.
332 * </p>
333 *
334 * @return The blocking-mode lock object
335 */
336 public abstract Object blockingLock();
337
338 }
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