J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 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. Sun designates this |
| 7 | * particular file as subject to the "Classpath" exception as provided |
| 8 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 21 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 22 | * have any 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/licenses/publicdomain |
| 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 | * <tt>Future<?> f = new FutureTask<Object>(runnable, null)</tt> |
| 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 | } |