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| 1 | +/* | |
| 2 | + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
| 3 | + * | |
| 4 | + * This code is free software; you can redistribute it and/or modify it | |
| 5 | + * under the terms of the GNU General Public License version 2 only, as | |
| 6 | + * published by the Free Software Foundation. Oracle designates this | |
| 7 | + * particular file as subject to the "Classpath" exception as provided | |
| 8 | + * by Oracle in the LICENSE file that accompanied this code. | |
| 9 | + * | |
| 10 | + * This code is distributed in the hope that it will be useful, but WITHOUT | |
| 11 | + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 12 | + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 13 | + * version 2 for more details (a copy is included in the LICENSE file that | |
| 14 | + * accompanied this code). | |
| 15 | + * | |
| 16 | + * You should have received a copy of the GNU General Public License version | |
| 17 | + * 2 along with this work; if not, write to the Free Software Foundation, | |
| 18 | + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
| 19 | + * | |
| 20 | + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 21 | + * or visit www.oracle.com if you need additional information or have any | |
| 22 | + * questions. | |
| 23 | + */ | |
| 24 | + | |
| 25 | +/* | |
| 26 | + * This file is available under and governed by the GNU General Public | |
| 27 | + * License version 2 only, as published by the Free Software Foundation. | |
| 28 | + * However, the following notice accompanied the original version of this | |
| 29 | + * file: | |
| 30 | + * | |
| 31 | + * Written by Doug Lea with assistance from members of JCP JSR-166 | |
| 32 | + * Expert Group and released to the public domain, as explained at | |
| 33 | + * http://creativecommons.org/publicdomain/zero/1.0/ | |
| 34 | + */ | |
| 35 | + | |
| 36 | +package java.util.concurrent; | |
| 37 | +import java.util.concurrent.locks.*; | |
| 38 | + | |
| 39 | +/** | |
| 40 | + * A cancellable asynchronous computation. This class provides a base | |
| 41 | + * implementation of {@link Future}, with methods to start and cancel | |
| 42 | + * a computation, query to see if the computation is complete, and | |
| 43 | + * retrieve the result of the computation. The result can only be | |
| 44 | + * retrieved when the computation has completed; the <tt>get</tt> | |
| 45 | + * method will block if the computation has not yet completed. Once | |
| 46 | + * the computation has completed, the computation cannot be restarted | |
| 47 | + * or cancelled. | |
| 48 | + * | |
| 49 | + * <p>A <tt>FutureTask</tt> can be used to wrap a {@link Callable} or | |
| 50 | + * {@link java.lang.Runnable} object. Because <tt>FutureTask</tt> | |
| 51 | + * implements <tt>Runnable</tt>, a <tt>FutureTask</tt> can be | |
| 52 | + * submitted to an {@link Executor} for execution. | |
| 53 | + * | |
| 54 | + * <p>In addition to serving as a standalone class, this class provides | |
| 55 | + * <tt>protected</tt> functionality that may be useful when creating | |
| 56 | + * customized task classes. | |
| 57 | + * | |
| 58 | + * @since 1.5 | |
| 59 | + * @author Doug Lea | |
| 60 | + * @param <V> The result type returned by this FutureTask's <tt>get</tt> method | |
| 61 | + */ | |
| 62 | +public class FutureTask<V> implements RunnableFuture<V> { | |
| 63 | + /** Synchronization control for FutureTask */ | |
| 64 | + private final Sync sync; | |
| 65 | + | |
| 66 | + /** | |
| 67 | + * Creates a <tt>FutureTask</tt> that will, upon running, execute the | |
| 68 | + * given <tt>Callable</tt>. | |
| 69 | + * | |
| 70 | + * @param callable the callable task | |
| 71 | + * @throws NullPointerException if callable is null | |
| 72 | + */ | |
| 73 | + public FutureTask(Callable<V> callable) { | |
| 74 | + if (callable == null) | |
| 75 | + throw new NullPointerException(); | |
| 76 | + sync = new Sync(callable); | |
| 77 | + } | |
| 78 | + | |
| 79 | + /** | |
| 80 | + * Creates a <tt>FutureTask</tt> that will, upon running, execute the | |
| 81 | + * given <tt>Runnable</tt>, and arrange that <tt>get</tt> will return the | |
| 82 | + * given result on successful completion. | |
| 83 | + * | |
| 84 | + * @param runnable the runnable task | |
| 85 | + * @param result the result to return on successful completion. If | |
| 86 | + * you don't need a particular result, consider using | |
| 87 | + * constructions of the form: | |
| 88 | + * {@code Future<?> f = new FutureTask<Void>(runnable, null)} | |
| 89 | + * @throws NullPointerException if runnable is null | |
| 90 | + */ | |
| 91 | + public FutureTask(Runnable runnable, V result) { | |
| 92 | + sync = new Sync(Executors.callable(runnable, result)); | |
| 93 | + } | |
| 94 | + | |
| 95 | + public boolean isCancelled() { | |
| 96 | + return sync.innerIsCancelled(); | |
| 97 | + } | |
| 98 | + | |
| 99 | + public boolean isDone() { | |
| 100 | + return sync.innerIsDone(); | |
| 101 | + } | |
| 102 | + | |
| 103 | + public boolean cancel(boolean mayInterruptIfRunning) { | |
| 104 | + return sync.innerCancel(mayInterruptIfRunning); | |
| 105 | + } | |
| 106 | + | |
| 107 | + /** | |
| 108 | + * @throws CancellationException {@inheritDoc} | |
| 109 | + */ | |
| 110 | + public V get() throws InterruptedException, ExecutionException { | |
| 111 | + return sync.innerGet(); | |
| 112 | + } | |
| 113 | + | |
| 114 | + /** | |
| 115 | + * @throws CancellationException {@inheritDoc} | |
| 116 | + */ | |
| 117 | + public V get(long timeout, TimeUnit unit) | |
| 118 | + throws InterruptedException, ExecutionException, TimeoutException { | |
| 119 | + return sync.innerGet(unit.toNanos(timeout)); | |
| 120 | + } | |
| 121 | + | |
| 122 | + /** | |
| 123 | + * Protected method invoked when this task transitions to state | |
| 124 | + * <tt>isDone</tt> (whether normally or via cancellation). The | |
| 125 | + * default implementation does nothing. Subclasses may override | |
| 126 | + * this method to invoke completion callbacks or perform | |
| 127 | + * bookkeeping. Note that you can query status inside the | |
| 128 | + * implementation of this method to determine whether this task | |
| 129 | + * has been cancelled. | |
| 130 | + */ | |
| 131 | + protected void done() { } | |
| 132 | + | |
| 133 | + /** | |
| 134 | + * Sets the result of this Future to the given value unless | |
| 135 | + * this future has already been set or has been cancelled. | |
| 136 | + * This method is invoked internally by the <tt>run</tt> method | |
| 137 | + * upon successful completion of the computation. | |
| 138 | + * @param v the value | |
| 139 | + */ | |
| 140 | + protected void set(V v) { | |
| 141 | + sync.innerSet(v); | |
| 142 | + } | |
| 143 | + | |
| 144 | + /** | |
| 145 | + * Causes this future to report an <tt>ExecutionException</tt> | |
| 146 | + * with the given throwable as its cause, unless this Future has | |
| 147 | + * already been set or has been cancelled. | |
| 148 | + * This method is invoked internally by the <tt>run</tt> method | |
| 149 | + * upon failure of the computation. | |
| 150 | + * @param t the cause of failure | |
| 151 | + */ | |
| 152 | + protected void setException(Throwable t) { | |
| 153 | + sync.innerSetException(t); | |
| 154 | + } | |
| 155 | + | |
| 156 | + // The following (duplicated) doc comment can be removed once | |
| 157 | + // | |
| 158 | + // 6270645: Javadoc comments should be inherited from most derived | |
| 159 | + // superinterface or superclass | |
| 160 | + // is fixed. | |
| 161 | + /** | |
| 162 | + * Sets this Future to the result of its computation | |
| 163 | + * unless it has been cancelled. | |
| 164 | + */ | |
| 165 | + public void run() { | |
| 166 | + sync.innerRun(); | |
| 167 | + } | |
| 168 | + | |
| 169 | + /** | |
| 170 | + * Executes the computation without setting its result, and then | |
| 171 | + * resets this Future to initial state, failing to do so if the | |
| 172 | + * computation encounters an exception or is cancelled. This is | |
| 173 | + * designed for use with tasks that intrinsically execute more | |
| 174 | + * than once. | |
| 175 | + * @return true if successfully run and reset | |
| 176 | + */ | |
| 177 | + protected boolean runAndReset() { | |
| 178 | + return sync.innerRunAndReset(); | |
| 179 | + } | |
| 180 | + | |
| 181 | + /** | |
| 182 | + * Synchronization control for FutureTask. Note that this must be | |
| 183 | + * a non-static inner class in order to invoke the protected | |
| 184 | + * <tt>done</tt> method. For clarity, all inner class support | |
| 185 | + * methods are same as outer, prefixed with "inner". | |
| 186 | + * | |
| 187 | + * Uses AQS sync state to represent run status | |
| 188 | + */ | |
| 189 | + private final class Sync extends AbstractQueuedSynchronizer { | |
| 190 | + private static final long serialVersionUID = -7828117401763700385L; | |
| 191 | + | |
| 192 | + /** State value representing that task is ready to run */ | |
| 193 | + private static final int READY = 0; | |
| 194 | + /** State value representing that task is running */ | |
| 195 | + private static final int RUNNING = 1; | |
| 196 | + /** State value representing that task ran */ | |
| 197 | + private static final int RAN = 2; | |
| 198 | + /** State value representing that task was cancelled */ | |
| 199 | + private static final int CANCELLED = 4; | |
| 200 | + | |
| 201 | + /** The underlying callable */ | |
| 202 | + private final Callable<V> callable; | |
| 203 | + /** The result to return from get() */ | |
| 204 | + private V result; | |
| 205 | + /** The exception to throw from get() */ | |
| 206 | + private Throwable exception; | |
| 207 | + | |
| 208 | + /** | |
| 209 | + * The thread running task. When nulled after set/cancel, this | |
| 210 | + * indicates that the results are accessible. Must be | |
| 211 | + * volatile, to ensure visibility upon completion. | |
| 212 | + */ | |
| 213 | + private volatile Thread runner; | |
| 214 | + | |
| 215 | + Sync(Callable<V> callable) { | |
| 216 | + this.callable = callable; | |
| 217 | + } | |
| 218 | + | |
| 219 | + private boolean ranOrCancelled(int state) { | |
| 220 | + return (state & (RAN | CANCELLED)) != 0; | |
| 221 | + } | |
| 222 | + | |
| 223 | + /** | |
| 224 | + * Implements AQS base acquire to succeed if ran or cancelled | |
| 225 | + */ | |
| 226 | + protected int tryAcquireShared(int ignore) { | |
| 227 | + return innerIsDone() ? 1 : -1; | |
| 228 | + } | |
| 229 | + | |
| 230 | + /** | |
| 231 | + * Implements AQS base release to always signal after setting | |
| 232 | + * final done status by nulling runner thread. | |
| 233 | + */ | |
| 234 | + protected boolean tryReleaseShared(int ignore) { | |
| 235 | + runner = null; | |
| 236 | + return true; | |
| 237 | + } | |
| 238 | + | |
| 239 | + boolean innerIsCancelled() { | |
| 240 | + return getState() == CANCELLED; | |
| 241 | + } | |
| 242 | + | |
| 243 | + boolean innerIsDone() { | |
| 244 | + return ranOrCancelled(getState()) && runner == null; | |
| 245 | + } | |
| 246 | + | |
| 247 | + V innerGet() throws InterruptedException, ExecutionException { | |
| 248 | + acquireSharedInterruptibly(0); | |
| 249 | + if (getState() == CANCELLED) | |
| 250 | + throw new CancellationException(); | |
| 251 | + if (exception != null) | |
| 252 | + throw new ExecutionException(exception); | |
| 253 | + return result; | |
| 254 | + } | |
| 255 | + | |
| 256 | + V innerGet(long nanosTimeout) throws InterruptedException, ExecutionException, TimeoutException { | |
| 257 | + if (!tryAcquireSharedNanos(0, nanosTimeout)) | |
| 258 | + throw new TimeoutException(); | |
| 259 | + if (getState() == CANCELLED) | |
| 260 | + throw new CancellationException(); | |
| 261 | + if (exception != null) | |
| 262 | + throw new ExecutionException(exception); | |
| 263 | + return result; | |
| 264 | + } | |
| 265 | + | |
| 266 | + void innerSet(V v) { | |
| 267 | + for (;;) { | |
| 268 | + int s = getState(); | |
| 269 | + if (s == RAN) | |
| 270 | + return; | |
| 271 | + if (s == CANCELLED) { | |
| 272 | + // aggressively release to set runner to null, | |
| 273 | + // in case we are racing with a cancel request | |
| 274 | + // that will try to interrupt runner | |
| 275 | + releaseShared(0); | |
| 276 | + return; | |
| 277 | + } | |
| 278 | + if (compareAndSetState(s, RAN)) { | |
| 279 | + result = v; | |
| 280 | + releaseShared(0); | |
| 281 | + done(); | |
| 282 | + return; | |
| 283 | + } | |
| 284 | + } | |
| 285 | + } | |
| 286 | + | |
| 287 | + void innerSetException(Throwable t) { | |
| 288 | + for (;;) { | |
| 289 | + int s = getState(); | |
| 290 | + if (s == RAN) | |
| 291 | + return; | |
| 292 | + if (s == CANCELLED) { | |
| 293 | + // aggressively release to set runner to null, | |
| 294 | + // in case we are racing with a cancel request | |
| 295 | + // that will try to interrupt runner | |
| 296 | + releaseShared(0); | |
| 297 | + return; | |
| 298 | + } | |
| 299 | + if (compareAndSetState(s, RAN)) { | |
| 300 | + exception = t; | |
| 301 | + releaseShared(0); | |
| 302 | + done(); | |
| 303 | + return; | |
| 304 | + } | |
| 305 | + } | |
| 306 | + } | |
| 307 | + | |
| 308 | + boolean innerCancel(boolean mayInterruptIfRunning) { | |
| 309 | + for (;;) { | |
| 310 | + int s = getState(); | |
| 311 | + if (ranOrCancelled(s)) | |
| 312 | + return false; | |
| 313 | + if (compareAndSetState(s, CANCELLED)) | |
| 314 | + break; | |
| 315 | + } | |
| 316 | + if (mayInterruptIfRunning) { | |
| 317 | + Thread r = runner; | |
| 318 | + if (r != null) | |
| 319 | + r.interrupt(); | |
| 320 | + } | |
| 321 | + releaseShared(0); | |
| 322 | + done(); | |
| 323 | + return true; | |
| 324 | + } | |
| 325 | + | |
| 326 | + void innerRun() { | |
| 327 | + if (!compareAndSetState(READY, RUNNING)) | |
| 328 | + return; | |
| 329 | + | |
| 330 | + runner = Thread.currentThread(); | |
| 331 | + if (getState() == RUNNING) { // recheck after setting thread | |
| 332 | + V result; | |
| 333 | + try { | |
| 334 | + result = callable.call(); | |
| 335 | + } catch (Throwable ex) { | |
| 336 | + setException(ex); | |
| 337 | + return; | |
| 338 | + } | |
| 339 | + set(result); | |
| 340 | + } else { | |
| 341 | + releaseShared(0); // cancel | |
| 342 | + } | |
| 343 | + } | |
| 344 | + | |
| 345 | + boolean innerRunAndReset() { | |
| 346 | + if (!compareAndSetState(READY, RUNNING)) | |
| 347 | + return false; | |
| 348 | + try { | |
| 349 | + runner = Thread.currentThread(); | |
| 350 | + if (getState() == RUNNING) | |
| 351 | + callable.call(); // don't set result | |
| 352 | + runner = null; | |
| 353 | + return compareAndSetState(RUNNING, READY); | |
| 354 | + } catch (Throwable ex) { | |
| 355 | + setException(ex); | |
| 356 | + return false; | |
| 357 | + } | |
| 358 | + } | |
| 359 | + } | |
| 360 | +} | |