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| 1 | +/* | |
| 2 | + * Copyright (c) 2000, 2008, 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.util.concurrent.atomic.AtomicReferenceFieldUpdater; | |
| 29 | +import java.io.IOException; | |
| 30 | + | |
| 31 | + | |
| 32 | +/** | |
| 33 | + * A token representing the registration of a {@link SelectableChannel} with a | |
| 34 | + * {@link Selector}. | |
| 35 | + * | |
| 36 | + * <p> A selection key is created each time a channel is registered with a | |
| 37 | + * selector. A key remains valid until it is <i>cancelled</i> by invoking its | |
| 38 | + * {@link #cancel cancel} method, by closing its channel, or by closing its | |
| 39 | + * selector. Cancelling a key does not immediately remove it from its | |
| 40 | + * selector; it is instead added to the selector's <a | |
| 41 | + * href="Selector.html#ks"><i>cancelled-key set</i></a> for removal during the | |
| 42 | + * next selection operation. The validity of a key may be tested by invoking | |
| 43 | + * its {@link #isValid isValid} method. | |
| 44 | + * | |
| 45 | + * <a name="opsets"> | |
| 46 | + * | |
| 47 | + * <p> A selection key contains two <i>operation sets</i> represented as | |
| 48 | + * integer values. Each bit of an operation set denotes a category of | |
| 49 | + * selectable operations that are supported by the key's channel. | |
| 50 | + * | |
| 51 | + * <ul> | |
| 52 | + * | |
| 53 | + * <li><p> The <i>interest set</i> determines which operation categories will | |
| 54 | + * be tested for readiness the next time one of the selector's selection | |
| 55 | + * methods is invoked. The interest set is initialized with the value given | |
| 56 | + * when the key is created; it may later be changed via the {@link | |
| 57 | + * #interestOps(int)} method. </p></li> | |
| 58 | + * | |
| 59 | + * <li><p> The <i>ready set</i> identifies the operation categories for which | |
| 60 | + * the key's channel has been detected to be ready by the key's selector. | |
| 61 | + * The ready set is initialized to zero when the key is created; it may later | |
| 62 | + * be updated by the selector during a selection operation, but it cannot be | |
| 63 | + * updated directly. </p></li> | |
| 64 | + * | |
| 65 | + * </ul> | |
| 66 | + * | |
| 67 | + * <p> That a selection key's ready set indicates that its channel is ready for | |
| 68 | + * some operation category is a hint, but not a guarantee, that an operation in | |
| 69 | + * such a category may be performed by a thread without causing the thread to | |
| 70 | + * block. A ready set is most likely to be accurate immediately after the | |
| 71 | + * completion of a selection operation. It is likely to be made inaccurate by | |
| 72 | + * external events and by I/O operations that are invoked upon the | |
| 73 | + * corresponding channel. | |
| 74 | + * | |
| 75 | + * <p> This class defines all known operation-set bits, but precisely which | |
| 76 | + * bits are supported by a given channel depends upon the type of the channel. | |
| 77 | + * Each subclass of {@link SelectableChannel} defines an {@link | |
| 78 | + * SelectableChannel#validOps() validOps()} method which returns a set | |
| 79 | + * identifying just those operations that are supported by the channel. An | |
| 80 | + * attempt to set or test an operation-set bit that is not supported by a key's | |
| 81 | + * channel will result in an appropriate run-time exception. | |
| 82 | + * | |
| 83 | + * <p> It is often necessary to associate some application-specific data with a | |
| 84 | + * selection key, for example an object that represents the state of a | |
| 85 | + * higher-level protocol and handles readiness notifications in order to | |
| 86 | + * implement that protocol. Selection keys therefore support the | |
| 87 | + * <i>attachment</i> of a single arbitrary object to a key. An object can be | |
| 88 | + * attached via the {@link #attach attach} method and then later retrieved via | |
| 89 | + * the {@link #attachment() attachment} method. | |
| 90 | + * | |
| 91 | + * <p> Selection keys are safe for use by multiple concurrent threads. The | |
| 92 | + * operations of reading and writing the interest set will, in general, be | |
| 93 | + * synchronized with certain operations of the selector. Exactly how this | |
| 94 | + * synchronization is performed is implementation-dependent: In a naive | |
| 95 | + * implementation, reading or writing the interest set may block indefinitely | |
| 96 | + * if a selection operation is already in progress; in a high-performance | |
| 97 | + * implementation, reading or writing the interest set may block briefly, if at | |
| 98 | + * all. In any case, a selection operation will always use the interest-set | |
| 99 | + * value that was current at the moment that the operation began. </p> | |
| 100 | + * | |
| 101 | + * | |
| 102 | + * @author Mark Reinhold | |
| 103 | + * @author JSR-51 Expert Group | |
| 104 | + * @since 1.4 | |
| 105 | + * | |
| 106 | + * @see SelectableChannel | |
| 107 | + * @see Selector | |
| 108 | + */ | |
| 109 | + | |
| 110 | +public abstract class SelectionKey { | |
| 111 | + | |
| 112 | + /** | |
| 113 | + * Constructs an instance of this class. | |
| 114 | + */ | |
| 115 | + protected SelectionKey() { } | |
| 116 | + | |
| 117 | + | |
| 118 | + // -- Channel and selector operations -- | |
| 119 | + | |
| 120 | + /** | |
| 121 | + * Returns the channel for which this key was created. This method will | |
| 122 | + * continue to return the channel even after the key is cancelled. </p> | |
| 123 | + * | |
| 124 | + * @return This key's channel | |
| 125 | + */ | |
| 126 | + public abstract SelectableChannel channel(); | |
| 127 | + | |
| 128 | + /** | |
| 129 | + * Returns the selector for which this key was created. This method will | |
| 130 | + * continue to return the selector even after the key is cancelled. </p> | |
| 131 | + * | |
| 132 | + * @return This key's selector | |
| 133 | + */ | |
| 134 | + public abstract Selector selector(); | |
| 135 | + | |
| 136 | + /** | |
| 137 | + * Tells whether or not this key is valid. | |
| 138 | + * | |
| 139 | + * <p> A key is valid upon creation and remains so until it is cancelled, | |
| 140 | + * its channel is closed, or its selector is closed. </p> | |
| 141 | + * | |
| 142 | + * @return <tt>true</tt> if, and only if, this key is valid | |
| 143 | + */ | |
| 144 | + public abstract boolean isValid(); | |
| 145 | + | |
| 146 | + /** | |
| 147 | + * Requests that the registration of this key's channel with its selector | |
| 148 | + * be cancelled. Upon return the key will be invalid and will have been | |
| 149 | + * added to its selector's cancelled-key set. The key will be removed from | |
| 150 | + * all of the selector's key sets during the next selection operation. | |
| 151 | + * | |
| 152 | + * <p> If this key has already been cancelled then invoking this method has | |
| 153 | + * no effect. Once cancelled, a key remains forever invalid. </p> | |
| 154 | + * | |
| 155 | + * <p> This method may be invoked at any time. It synchronizes on the | |
| 156 | + * selector's cancelled-key set, and therefore may block briefly if invoked | |
| 157 | + * concurrently with a cancellation or selection operation involving the | |
| 158 | + * same selector. </p> | |
| 159 | + */ | |
| 160 | + public abstract void cancel(); | |
| 161 | + | |
| 162 | + | |
| 163 | + // -- Operation-set accessors -- | |
| 164 | + | |
| 165 | + /** | |
| 166 | + * Retrieves this key's interest set. | |
| 167 | + * | |
| 168 | + * <p> It is guaranteed that the returned set will only contain operation | |
| 169 | + * bits that are valid for this key's channel. | |
| 170 | + * | |
| 171 | + * <p> This method may be invoked at any time. Whether or not it blocks, | |
| 172 | + * and for how long, is implementation-dependent. </p> | |
| 173 | + * | |
| 174 | + * @return This key's interest set | |
| 175 | + * | |
| 176 | + * @throws CancelledKeyException | |
| 177 | + * If this key has been cancelled | |
| 178 | + */ | |
| 179 | + public abstract int interestOps(); | |
| 180 | + | |
| 181 | + /** | |
| 182 | + * Sets this key's interest set to the given value. | |
| 183 | + * | |
| 184 | + * <p> This method may be invoked at any time. Whether or not it blocks, | |
| 185 | + * and for how long, is implementation-dependent. </p> | |
| 186 | + * | |
| 187 | + * @param ops The new interest set | |
| 188 | + * | |
| 189 | + * @return This selection key | |
| 190 | + * | |
| 191 | + * @throws IllegalArgumentException | |
| 192 | + * If a bit in the set does not correspond to an operation that | |
| 193 | + * is supported by this key's channel, that is, if | |
| 194 | + * <tt>(ops & ~channel().validOps()) != 0</tt> | |
| 195 | + * | |
| 196 | + * @throws CancelledKeyException | |
| 197 | + * If this key has been cancelled | |
| 198 | + */ | |
| 199 | + public abstract SelectionKey interestOps(int ops); | |
| 200 | + | |
| 201 | + /** | |
| 202 | + * Retrieves this key's ready-operation set. | |
| 203 | + * | |
| 204 | + * <p> It is guaranteed that the returned set will only contain operation | |
| 205 | + * bits that are valid for this key's channel. </p> | |
| 206 | + * | |
| 207 | + * @return This key's ready-operation set | |
| 208 | + * | |
| 209 | + * @throws CancelledKeyException | |
| 210 | + * If this key has been cancelled | |
| 211 | + */ | |
| 212 | + public abstract int readyOps(); | |
| 213 | + | |
| 214 | + | |
| 215 | + // -- Operation bits and bit-testing convenience methods -- | |
| 216 | + | |
| 217 | + /** | |
| 218 | + * Operation-set bit for read operations. | |
| 219 | + * | |
| 220 | + * <p> Suppose that a selection key's interest set contains | |
| 221 | + * <tt>OP_READ</tt> at the start of a <a | |
| 222 | + * href="Selector.html#selop">selection operation</a>. If the selector | |
| 223 | + * detects that the corresponding channel is ready for reading, has reached | |
| 224 | + * end-of-stream, has been remotely shut down for further reading, or has | |
| 225 | + * an error pending, then it will add <tt>OP_READ</tt> to the key's | |
| 226 | + * ready-operation set and add the key to its selected-key set. </p> | |
| 227 | + */ | |
| 228 | + public static final int OP_READ = 1 << 0; | |
| 229 | + | |
| 230 | + /** | |
| 231 | + * Operation-set bit for write operations. </p> | |
| 232 | + * | |
| 233 | + * <p> Suppose that a selection key's interest set contains | |
| 234 | + * <tt>OP_WRITE</tt> at the start of a <a | |
| 235 | + * href="Selector.html#selop">selection operation</a>. If the selector | |
| 236 | + * detects that the corresponding channel is ready for writing, has been | |
| 237 | + * remotely shut down for further writing, or has an error pending, then it | |
| 238 | + * will add <tt>OP_WRITE</tt> to the key's ready set and add the key to its | |
| 239 | + * selected-key set. </p> | |
| 240 | + */ | |
| 241 | + public static final int OP_WRITE = 1 << 2; | |
| 242 | + | |
| 243 | + /** | |
| 244 | + * Operation-set bit for socket-connect operations. </p> | |
| 245 | + * | |
| 246 | + * <p> Suppose that a selection key's interest set contains | |
| 247 | + * <tt>OP_CONNECT</tt> at the start of a <a | |
| 248 | + * href="Selector.html#selop">selection operation</a>. If the selector | |
| 249 | + * detects that the corresponding socket channel is ready to complete its | |
| 250 | + * connection sequence, or has an error pending, then it will add | |
| 251 | + * <tt>OP_CONNECT</tt> to the key's ready set and add the key to its | |
| 252 | + * selected-key set. </p> | |
| 253 | + */ | |
| 254 | + public static final int OP_CONNECT = 1 << 3; | |
| 255 | + | |
| 256 | + /** | |
| 257 | + * Operation-set bit for socket-accept operations. </p> | |
| 258 | + * | |
| 259 | + * <p> Suppose that a selection key's interest set contains | |
| 260 | + * <tt>OP_ACCEPT</tt> at the start of a <a | |
| 261 | + * href="Selector.html#selop">selection operation</a>. If the selector | |
| 262 | + * detects that the corresponding server-socket channel is ready to accept | |
| 263 | + * another connection, or has an error pending, then it will add | |
| 264 | + * <tt>OP_ACCEPT</tt> to the key's ready set and add the key to its | |
| 265 | + * selected-key set. </p> | |
| 266 | + */ | |
| 267 | + public static final int OP_ACCEPT = 1 << 4; | |
| 268 | + | |
| 269 | + /** | |
| 270 | + * Tests whether this key's channel is ready for reading. | |
| 271 | + * | |
| 272 | + * <p> An invocation of this method of the form <tt>k.isReadable()</tt> | |
| 273 | + * behaves in exactly the same way as the expression | |
| 274 | + * | |
| 275 | + * <blockquote><pre> | |
| 276 | + * k.readyOps() & OP_READ != 0</pre></blockquote> | |
| 277 | + * | |
| 278 | + * <p> If this key's channel does not support read operations then this | |
| 279 | + * method always returns <tt>false</tt>. </p> | |
| 280 | + * | |
| 281 | + * @return <tt>true</tt> if, and only if, | |
| 282 | + * <tt>readyOps()</tt> <tt>&</tt> <tt>OP_READ</tt> is | |
| 283 | + * nonzero | |
| 284 | + * | |
| 285 | + * @throws CancelledKeyException | |
| 286 | + * If this key has been cancelled | |
| 287 | + */ | |
| 288 | + public final boolean isReadable() { | |
| 289 | + return (readyOps() & OP_READ) != 0; | |
| 290 | + } | |
| 291 | + | |
| 292 | + /** | |
| 293 | + * Tests whether this key's channel is ready for writing. | |
| 294 | + * | |
| 295 | + * <p> An invocation of this method of the form <tt>k.isWritable()</tt> | |
| 296 | + * behaves in exactly the same way as the expression | |
| 297 | + * | |
| 298 | + * <blockquote><pre> | |
| 299 | + * k.readyOps() & OP_WRITE != 0</pre></blockquote> | |
| 300 | + * | |
| 301 | + * <p> If this key's channel does not support write operations then this | |
| 302 | + * method always returns <tt>false</tt>. </p> | |
| 303 | + * | |
| 304 | + * @return <tt>true</tt> if, and only if, | |
| 305 | + * <tt>readyOps()</tt> <tt>&</tt> <tt>OP_WRITE</tt> | |
| 306 | + * is nonzero | |
| 307 | + * | |
| 308 | + * @throws CancelledKeyException | |
| 309 | + * If this key has been cancelled | |
| 310 | + */ | |
| 311 | + public final boolean isWritable() { | |
| 312 | + return (readyOps() & OP_WRITE) != 0; | |
| 313 | + } | |
| 314 | + | |
| 315 | + /** | |
| 316 | + * Tests whether this key's channel has either finished, or failed to | |
| 317 | + * finish, its socket-connection operation. | |
| 318 | + * | |
| 319 | + * <p> An invocation of this method of the form <tt>k.isConnectable()</tt> | |
| 320 | + * behaves in exactly the same way as the expression | |
| 321 | + * | |
| 322 | + * <blockquote><pre> | |
| 323 | + * k.readyOps() & OP_CONNECT != 0</pre></blockquote> | |
| 324 | + * | |
| 325 | + * <p> If this key's channel does not support socket-connect operations | |
| 326 | + * then this method always returns <tt>false</tt>. </p> | |
| 327 | + * | |
| 328 | + * @return <tt>true</tt> if, and only if, | |
| 329 | + * <tt>readyOps()</tt> <tt>&</tt> <tt>OP_CONNECT</tt> | |
| 330 | + * is nonzero | |
| 331 | + * | |
| 332 | + * @throws CancelledKeyException | |
| 333 | + * If this key has been cancelled | |
| 334 | + */ | |
| 335 | + public final boolean isConnectable() { | |
| 336 | + return (readyOps() & OP_CONNECT) != 0; | |
| 337 | + } | |
| 338 | + | |
| 339 | + /** | |
| 340 | + * Tests whether this key's channel is ready to accept a new socket | |
| 341 | + * connection. | |
| 342 | + * | |
| 343 | + * <p> An invocation of this method of the form <tt>k.isAcceptable()</tt> | |
| 344 | + * behaves in exactly the same way as the expression | |
| 345 | + * | |
| 346 | + * <blockquote><pre> | |
| 347 | + * k.readyOps() & OP_ACCEPT != 0</pre></blockquote> | |
| 348 | + * | |
| 349 | + * <p> If this key's channel does not support socket-accept operations then | |
| 350 | + * this method always returns <tt>false</tt>. </p> | |
| 351 | + * | |
| 352 | + * @return <tt>true</tt> if, and only if, | |
| 353 | + * <tt>readyOps()</tt> <tt>&</tt> <tt>OP_ACCEPT</tt> | |
| 354 | + * is nonzero | |
| 355 | + * | |
| 356 | + * @throws CancelledKeyException | |
| 357 | + * If this key has been cancelled | |
| 358 | + */ | |
| 359 | + public final boolean isAcceptable() { | |
| 360 | + return (readyOps() & OP_ACCEPT) != 0; | |
| 361 | + } | |
| 362 | + | |
| 363 | + | |
| 364 | + // -- Attachments -- | |
| 365 | + | |
| 366 | + private volatile Object attachment = null; | |
| 367 | + | |
| 368 | + private static final AtomicReferenceFieldUpdater<SelectionKey,Object> | |
| 369 | + attachmentUpdater = AtomicReferenceFieldUpdater.newUpdater( | |
| 370 | + SelectionKey.class, Object.class, "attachment" | |
| 371 | + ); | |
| 372 | + | |
| 373 | + /** | |
| 374 | + * Attaches the given object to this key. | |
| 375 | + * | |
| 376 | + * <p> An attached object may later be retrieved via the {@link #attachment() | |
| 377 | + * attachment} method. Only one object may be attached at a time; invoking | |
| 378 | + * this method causes any previous attachment to be discarded. The current | |
| 379 | + * attachment may be discarded by attaching <tt>null</tt>. </p> | |
| 380 | + * | |
| 381 | + * @param ob | |
| 382 | + * The object to be attached; may be <tt>null</tt> | |
| 383 | + * | |
| 384 | + * @return The previously-attached object, if any, | |
| 385 | + * otherwise <tt>null</tt> | |
| 386 | + */ | |
| 387 | + public final Object attach(Object ob) { | |
| 388 | + return attachmentUpdater.getAndSet(this, ob); | |
| 389 | + } | |
| 390 | + | |
| 391 | + /** | |
| 392 | + * Retrieves the current attachment. </p> | |
| 393 | + * | |
| 394 | + * @return The object currently attached to this key, | |
| 395 | + * or <tt>null</tt> if there is no attachment | |
| 396 | + */ | |
| 397 | + public final Object attachment() { | |
| 398 | + return attachment; | |
| 399 | + } | |
| 400 | + | |
| 401 | +} | |