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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 | } | ||