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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 | } | ||