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 38 import java.io.Serializable; 39 import java.lang.invoke.MethodHandles; 40 import java.lang.invoke.VarHandle; 41 import java.lang.reflect.Constructor; 42 import java.util.Collection; 43 import java.util.List; 44 import java.util.RandomAccess; 45 import java.util.concurrent.locks.LockSupport; 46 47 /** 48 * Abstract base class for tasks that run within a {@link ForkJoinPool}. 49 * A {@code ForkJoinTask} is a thread-like entity that is much 50 * lighter weight than a normal thread. Huge numbers of tasks and 51 * subtasks may be hosted by a small number of actual threads in a 52 * ForkJoinPool, at the price of some usage limitations. 53 * 54 * <p>A "main" {@code ForkJoinTask} begins execution when it is 55 * explicitly submitted to a {@link ForkJoinPool}, or, if not already 56 * engaged in a ForkJoin computation, commenced in the {@link 57 * ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or 58 * related methods. Once started, it will usually in turn start other 59 * subtasks. As indicated by the name of this class, many programs 60 * using {@code ForkJoinTask} employ only methods {@link #fork} and 61 * {@link #join}, or derivatives such as {@link 62 * #invokeAll(ForkJoinTask...) invokeAll}. However, this class also 63 * provides a number of other methods that can come into play in 64 * advanced usages, as well as extension mechanics that allow support 65 * of new forms of fork/join processing. 66 * 67 * <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}. 68 * The efficiency of {@code ForkJoinTask}s stems from a set of 69 * restrictions (that are only partially statically enforceable) 70 * reflecting their main use as computational tasks calculating pure 71 * functions or operating on purely isolated objects. The primary 72 * coordination mechanisms are {@link #fork}, that arranges 73 * asynchronous execution, and {@link #join}, that doesn't proceed 74 * until the task's result has been computed. Computations should 75 * ideally avoid {@code synchronized} methods or blocks, and should 76 * minimize other blocking synchronization apart from joining other 77 * tasks or using synchronizers such as Phasers that are advertised to 78 * cooperate with fork/join scheduling. Subdividable tasks should also 79 * not perform blocking I/O, and should ideally access variables that 80 * are completely independent of those accessed by other running 81 * tasks. These guidelines are loosely enforced by not permitting 82 * checked exceptions such as {@code IOExceptions} to be 83 * thrown. However, computations may still encounter unchecked 84 * exceptions, that are rethrown to callers attempting to join 85 * them. These exceptions may additionally include {@link 86 * RejectedExecutionException} stemming from internal resource 87 * exhaustion, such as failure to allocate internal task 88 * queues. Rethrown exceptions behave in the same way as regular 89 * exceptions, but, when possible, contain stack traces (as displayed 90 * for example using {@code ex.printStackTrace()}) of both the thread 91 * that initiated the computation as well as the thread actually 92 * encountering the exception; minimally only the latter. 93 * 94 * <p>It is possible to define and use ForkJoinTasks that may block, 95 * but doing so requires three further considerations: (1) Completion 96 * of few if any <em>other</em> tasks should be dependent on a task 97 * that blocks on external synchronization or I/O. Event-style async 98 * tasks that are never joined (for example, those subclassing {@link 99 * CountedCompleter}) often fall into this category. (2) To minimize 100 * resource impact, tasks should be small; ideally performing only the 101 * (possibly) blocking action. (3) Unless the {@link 102 * ForkJoinPool.ManagedBlocker} API is used, or the number of possibly 103 * blocked tasks is known to be less than the pool's {@link 104 * ForkJoinPool#getParallelism} level, the pool cannot guarantee that 105 * enough threads will be available to ensure progress or good 106 * performance. 107 * 108 * <p>The primary method for awaiting completion and extracting 109 * results of a task is {@link #join}, but there are several variants: 110 * The {@link Future#get} methods support interruptible and/or timed 111 * waits for completion and report results using {@code Future} 112 * conventions. Method {@link #invoke} is semantically 113 * equivalent to {@code fork(); join()} but always attempts to begin 114 * execution in the current thread. The "<em>quiet</em>" forms of 115 * these methods do not extract results or report exceptions. These 116 * may be useful when a set of tasks are being executed, and you need 117 * to delay processing of results or exceptions until all complete. 118 * Method {@code invokeAll} (available in multiple versions) 119 * performs the most common form of parallel invocation: forking a set 120 * of tasks and joining them all. 121 * 122 * <p>In the most typical usages, a fork-join pair act like a call 123 * (fork) and return (join) from a parallel recursive function. As is 124 * the case with other forms of recursive calls, returns (joins) 125 * should be performed innermost-first. For example, {@code a.fork(); 126 * b.fork(); b.join(); a.join();} is likely to be substantially more 127 * efficient than joining {@code a} before {@code b}. 128 * 129 * <p>The execution status of tasks may be queried at several levels 130 * of detail: {@link #isDone} is true if a task completed in any way 131 * (including the case where a task was cancelled without executing); 132 * {@link #isCompletedNormally} is true if a task completed without 133 * cancellation or encountering an exception; {@link #isCancelled} is 134 * true if the task was cancelled (in which case {@link #getException} 135 * returns a {@link CancellationException}); and 136 * {@link #isCompletedAbnormally} is true if a task was either 137 * cancelled or encountered an exception, in which case {@link 138 * #getException} will return either the encountered exception or 139 * {@link CancellationException}. 140 * 141 * <p>The ForkJoinTask class is not usually directly subclassed. 142 * Instead, you subclass one of the abstract classes that support a 143 * particular style of fork/join processing, typically {@link 144 * RecursiveAction} for most computations that do not return results, 145 * {@link RecursiveTask} for those that do, and {@link 146 * CountedCompleter} for those in which completed actions trigger 147 * other actions. Normally, a concrete ForkJoinTask subclass declares 148 * fields comprising its parameters, established in a constructor, and 149 * then defines a {@code compute} method that somehow uses the control 150 * methods supplied by this base class. 151 * 152 * <p>Method {@link #join} and its variants are appropriate for use 153 * only when completion dependencies are acyclic; that is, the 154 * parallel computation can be described as a directed acyclic graph 155 * (DAG). Otherwise, executions may encounter a form of deadlock as 156 * tasks cyclically wait for each other. However, this framework 157 * supports other methods and techniques (for example the use of 158 * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that 159 * may be of use in constructing custom subclasses for problems that 160 * are not statically structured as DAGs. To support such usages, a 161 * ForkJoinTask may be atomically <em>tagged</em> with a {@code short} 162 * value using {@link #setForkJoinTaskTag} or {@link 163 * #compareAndSetForkJoinTaskTag} and checked using {@link 164 * #getForkJoinTaskTag}. The ForkJoinTask implementation does not use 165 * these {@code protected} methods or tags for any purpose, but they 166 * may be of use in the construction of specialized subclasses. For 167 * example, parallel graph traversals can use the supplied methods to 168 * avoid revisiting nodes/tasks that have already been processed. 169 * (Method names for tagging are bulky in part to encourage definition 170 * of methods that reflect their usage patterns.) 171 * 172 * <p>Most base support methods are {@code final}, to prevent 173 * overriding of implementations that are intrinsically tied to the 174 * underlying lightweight task scheduling framework. Developers 175 * creating new basic styles of fork/join processing should minimally 176 * implement {@code protected} methods {@link #exec}, {@link 177 * #setRawResult}, and {@link #getRawResult}, while also introducing 178 * an abstract computational method that can be implemented in its 179 * subclasses, possibly relying on other {@code protected} methods 180 * provided by this class. 181 * 182 * <p>ForkJoinTasks should perform relatively small amounts of 183 * computation. Large tasks should be split into smaller subtasks, 184 * usually via recursive decomposition. As a very rough rule of thumb, 185 * a task should perform more than 100 and less than 10000 basic 186 * computational steps, and should avoid indefinite looping. If tasks 187 * are too big, then parallelism cannot improve throughput. If too 188 * small, then memory and internal task maintenance overhead may 189 * overwhelm processing. 190 * 191 * <p>This class provides {@code adapt} methods for {@link Runnable} 192 * and {@link Callable}, that may be of use when mixing execution of 193 * {@code ForkJoinTasks} with other kinds of tasks. When all tasks are 194 * of this form, consider using a pool constructed in <em>asyncMode</em>. 195 * 196 * <p>ForkJoinTasks are {@code Serializable}, which enables them to be 197 * used in extensions such as remote execution frameworks. It is 198 * sensible to serialize tasks only before or after, but not during, 199 * execution. Serialization is not relied on during execution itself. 200 * 201 * @since 1.7 202 * @author Doug Lea 203 */ 204 public abstract class ForkJoinTask<V> implements Future<V>, Serializable { 205 206 /* 207 * See the internal documentation of class ForkJoinPool for a 208 * general implementation overview. ForkJoinTasks are mainly 209 * responsible for maintaining their "status" field amidst relays 210 * to methods in ForkJoinWorkerThread and ForkJoinPool. 211 * 212 * The methods of this class are more-or-less layered into 213 * (1) basic status maintenance 214 * (2) execution and awaiting completion 215 * (3) user-level methods that additionally report results. 216 * This is sometimes hard to see because this file orders exported 217 * methods in a way that flows well in javadocs. 218 * 219 * Revision notes: The use of "Aux" field replaces previous 220 * reliance on a table to hold exceptions and synchronized blocks 221 * and monitors to wait for completion. 222 */ 223 224 /** 225 * Nodes for threads waiting for completion, or holding a thrown 226 * exception (never both). Waiting threads prepend nodes 227 * Treiber-stack-style. Signallers detach and unpark 228 * waiters. Cancelled waiters try to unsplice. 229 */ 230 static final class Aux { 231 final Thread thread; 232 final Throwable ex; // null if a waiter 233 Aux next; // accessed only via memory-acquire chains 234 Aux(Thread thread, Throwable ex) { 235 this.thread = thread; 236 this.ex = ex; 237 } 238 final boolean casNext(Aux c, Aux v) { // used only in cancellation 239 return NEXT.compareAndSet(this, c, v); 240 } 241 private static final VarHandle NEXT; 242 static { 243 try { 244 NEXT = MethodHandles.lookup() 245 .findVarHandle(Aux.class, "next", Aux.class); 246 } catch (ReflectiveOperationException e) { 247 throw new ExceptionInInitializerError(e); 248 } 249 } 250 } 251 252 /* 253 * The status field holds bits packed into a single int to ensure 254 * atomicity. Status is initially zero, and takes on nonnegative 255 * values until completed, upon which it holds (sign bit) DONE, 256 * possibly with ABNORMAL (cancelled or exceptional) and THROWN 257 * (in which case an exception has been stored). A value of 258 * ABNORMAL without DONE signifies an interrupted wait. These 259 * control bits occupy only (some of) the upper half (16 bits) of 260 * status field. The lower bits are used for user-defined tags. 261 */ 262 private static final int DONE = 1 << 31; // must be negative 263 private static final int ABNORMAL = 1 << 16; 264 private static final int THROWN = 1 << 17; 265 private static final int SMASK = 0xffff; // short bits for tags 266 private static final int UNCOMPENSATE = 1 << 16; // helpJoin return sentinel 267 268 // Fields 269 volatile int status; // accessed directly by pool and workers 270 private transient volatile Aux aux; // either waiters or thrown Exception 271 272 // Support for atomic operations 273 private static final VarHandle STATUS; 274 private static final VarHandle AUX; 275 private int getAndBitwiseOrStatus(int v) { 276 return (int)STATUS.getAndBitwiseOr(this, v); 277 } 278 private boolean casStatus(int c, int v) { 279 return STATUS.weakCompareAndSet(this, c, v); 280 } 281 private boolean casAux(Aux c, Aux v) { 282 return AUX.compareAndSet(this, c, v); 283 } 284 285 /** Removes and unparks waiters */ 286 private void signalWaiters() { 287 for (Aux a; (a = aux) != null && a.ex == null; ) { 288 if (casAux(a, null)) { // detach entire list 289 for (Thread t; a != null; a = a.next) { 290 if ((t = a.thread) != Thread.currentThread() && t != null) 291 LockSupport.unpark(t); // don't self-signal 292 } 293 break; 294 } 295 } 296 } 297 298 /** 299 * Possibly blocks until task is done or interrupted or timed out. 300 * 301 * @param interruptible true if wait can be cancelled by interrupt 302 * @param deadline if non-zero use timed waits and possibly timeout 303 * @param pool if nonnull pool to uncompensate after unblocking 304 * @return status on exit, or ABNORMAL if interrupted while waiting 305 */ 306 private int awaitDone(boolean interruptible, long deadline, 307 ForkJoinPool pool) { 308 int s; 309 boolean interrupted = false, queued = false, parked = false; 310 Aux node = null; 311 while ((s = status) >= 0) { 312 Aux a; long ns; 313 if (parked && Thread.interrupted()) { 314 if (interruptible) { 315 s = ABNORMAL; 316 break; 317 } 318 interrupted = true; 319 } 320 else if (queued) { 321 if (deadline != 0L) { 322 if ((ns = deadline - System.nanoTime()) <= 0L) 323 break; 324 LockSupport.parkNanos(ns); 325 } 326 else 327 LockSupport.park(); 328 parked = true; 329 } 330 else if (node != null) { 331 if ((a = aux) != null && a.ex != null) 332 Thread.onSpinWait(); // exception in progress 333 else if (queued = casAux(node.next = a, node)) 334 LockSupport.setCurrentBlocker(this); 335 } 336 else { 337 try { 338 node = new Aux(Thread.currentThread(), null); 339 } catch (Throwable ex) { // try to cancel if cannot create 340 casStatus(s, s | (DONE | ABNORMAL)); 341 } 342 } 343 } 344 if (pool != null) 345 pool.uncompensate(); 346 347 if (queued) { 348 LockSupport.setCurrentBlocker(null); 349 if (s >= 0) { // cancellation similar to AbstractQueuedSynchronizer 350 outer: for (Aux a; (a = aux) != null && a.ex == null; ) { 351 for (Aux trail = null;;) { 352 Aux next = a.next; 353 if (a == node) { 354 if (trail != null) 355 trail.casNext(trail, next); 356 else if (casAux(a, next)) 357 break outer; // cannot be re-encountered 358 break; // restart 359 } else { 360 trail = a; 361 if ((a = next) == null) 362 break outer; 363 } 364 } 365 } 366 } 367 else { 368 signalWaiters(); // help clean or signal 369 if (interrupted) 370 Thread.currentThread().interrupt(); 371 } 372 } 373 return s; 374 } 375 376 /** 377 * Sets DONE status and wakes up threads waiting to join this task. 378 * @return status on exit 379 */ 380 private int setDone() { 381 int s = getAndBitwiseOrStatus(DONE) | DONE; 382 signalWaiters(); 383 return s; 384 } 385 386 /** 387 * Sets ABNORMAL DONE status unless already done, and wakes up threads 388 * waiting to join this task. 389 * @return status on exit 390 */ 391 private int trySetCancelled() { 392 int s; 393 do {} while ((s = status) >= 0 && !casStatus(s, s |= (DONE | ABNORMAL))); 394 signalWaiters(); 395 return s; 396 } 397 398 /** 399 * Records exception and sets ABNORMAL THROWN DONE status unless 400 * already done, and wakes up threads waiting to join this task. 401 * If losing a race with setDone or trySetCancelled, the exception 402 * may be recorded but not reported. 403 * 404 * @return status on exit 405 */ 406 final int trySetThrown(Throwable ex) { 407 Aux h = new Aux(Thread.currentThread(), ex), p = null; 408 boolean installed = false; 409 int s; 410 while ((s = status) >= 0) { 411 Aux a; 412 if (!installed && ((a = aux) == null || a.ex == null) && 413 (installed = casAux(a, h))) 414 p = a; // list of waiters replaced by h 415 if (installed && casStatus(s, s |= (DONE | ABNORMAL | THROWN))) 416 break; 417 } 418 for (; p != null; p = p.next) 419 LockSupport.unpark(p.thread); 420 return s; 421 } 422 423 /** 424 * Records exception unless already done. Overridable in subclasses. 425 * 426 * @return status on exit 427 */ 428 int trySetException(Throwable ex) { 429 return trySetThrown(ex); 430 } 431 432 /** 433 * Constructor for subclasses to call. 434 */ 435 public ForkJoinTask() {} 436 437 static boolean isExceptionalStatus(int s) { // needed by subclasses 438 return (s & THROWN) != 0; 439 } 440 441 /** 442 * Unless done, calls exec and records status if completed, but 443 * doesn't wait for completion otherwise. 444 * 445 * @return status on exit from this method 446 */ 447 final int doExec() { 448 int s; boolean completed; 449 if ((s = status) >= 0) { 450 try { 451 completed = exec(); 452 } catch (Throwable rex) { 453 s = trySetException(rex); 454 completed = false; 455 } 456 if (completed) 457 s = setDone(); 458 } 459 return s; 460 } 461 462 /** 463 * Helps and/or waits for completion from join, get, or invoke; 464 * called from either internal or external threads. 465 * 466 * @param ran true if task known to have been exec'd 467 * @param interruptible true if park interruptibly when external 468 * @param timed true if use timed wait 469 * @param nanos if timed, timeout value 470 * @return ABNORMAL if interrupted, else status on exit 471 */ 472 private int awaitJoin(boolean ran, boolean interruptible, boolean timed, 473 long nanos) { 474 boolean internal; ForkJoinPool p; ForkJoinPool.WorkQueue q; int s; 475 Thread t; ForkJoinWorkerThread wt; 476 if (internal = ((t = Thread.currentThread()) 477 instanceof ForkJoinWorkerThread)) { 478 p = (wt = (ForkJoinWorkerThread)t).pool; 479 q = wt.workQueue; 480 } 481 else { 482 p = ForkJoinPool.common; 483 q = ForkJoinPool.commonQueue(); 484 if (interruptible && Thread.interrupted()) 485 return ABNORMAL; 486 } 487 if ((s = status) < 0) 488 return s; 489 long deadline = 0L; 490 if (timed) { 491 if (nanos <= 0L) 492 return 0; 493 else if ((deadline = nanos + System.nanoTime()) == 0L) 494 deadline = 1L; 495 } 496 ForkJoinPool uncompensate = null; 497 if (q != null && p != null) { // try helping 498 if ((!timed || p.isSaturated()) && 499 ((this instanceof CountedCompleter) ? 500 (s = p.helpComplete(this, q, internal)) < 0 : 501 (q.tryRemove(this, internal) && (s = doExec()) < 0))) 502 return s; 503 if (internal) { 504 if ((s = p.helpJoin(this, q)) < 0) 505 return s; 506 if (s == UNCOMPENSATE) 507 uncompensate = p; 508 interruptible = false; 509 } 510 } 511 return awaitDone(interruptible, deadline, uncompensate); 512 } 513 514 /** 515 * Cancels, ignoring any exceptions thrown by cancel. Cancel is 516 * spec'ed not to throw any exceptions, but if it does anyway, we 517 * have no recourse, so guard against this case. 518 */ 519 static final void cancelIgnoringExceptions(Future<?> t) { 520 if (t != null) { 521 try { 522 t.cancel(true); 523 } catch (Throwable ignore) { 524 } 525 } 526 } 527 528 /** 529 * Returns a rethrowable exception for this task, if available. 530 * To provide accurate stack traces, if the exception was not 531 * thrown by the current thread, we try to create a new exception 532 * of the same type as the one thrown, but with the recorded 533 * exception as its cause. If there is no such constructor, we 534 * instead try to use a no-arg constructor, followed by initCause, 535 * to the same effect. If none of these apply, or any fail due to 536 * other exceptions, we return the recorded exception, which is 537 * still correct, although it may contain a misleading stack 538 * trace. 539 * 540 * @return the exception, or null if none 541 */ 542 private Throwable getThrowableException() { 543 Throwable ex; Aux a; 544 if ((a = aux) == null) 545 ex = null; 546 else if ((ex = a.ex) != null && a.thread != Thread.currentThread()) { 547 try { 548 Constructor<?> noArgCtor = null, oneArgCtor = null; 549 for (Constructor<?> c : ex.getClass().getConstructors()) { 550 Class<?>[] ps = c.getParameterTypes(); 551 if (ps.length == 0) 552 noArgCtor = c; 553 else if (ps.length == 1 && ps[0] == Throwable.class) { 554 oneArgCtor = c; 555 break; 556 } 557 } 558 if (oneArgCtor != null) 559 ex = (Throwable)oneArgCtor.newInstance(ex); 560 else if (noArgCtor != null) { 561 Throwable rx = (Throwable)noArgCtor.newInstance(); 562 rx.initCause(ex); 563 ex = rx; 564 } 565 } catch (Exception ignore) { 566 } 567 } 568 return ex; 569 } 570 571 /** 572 * Returns exception associated with the given status, or null if none. 573 */ 574 private Throwable getException(int s) { 575 Throwable ex = null; 576 if ((s & ABNORMAL) != 0 && 577 ((s & THROWN) == 0 || (ex = getThrowableException()) == null)) 578 ex = new CancellationException(); 579 return ex; 580 } 581 582 /** 583 * Throws exception associated with the given status, or 584 * CancellationException if none recorded. 585 */ 586 private void reportException(int s) { 587 ForkJoinTask.<RuntimeException>uncheckedThrow( 588 (s & THROWN) != 0 ? getThrowableException() : null); 589 } 590 591 /** 592 * Throws exception for (timed or untimed) get, wrapping if 593 * necessary in an ExecutionException. 594 */ 595 private void reportExecutionException(int s) { 596 Throwable ex = null; 597 if (s == ABNORMAL) 598 ex = new InterruptedException(); 599 else if (s >= 0) 600 ex = new TimeoutException(); 601 else if ((s & THROWN) != 0 && (ex = getThrowableException()) != null) 602 ex = new ExecutionException(ex); 603 ForkJoinTask.<RuntimeException>uncheckedThrow(ex); 604 } 605 606 /** 607 * A version of "sneaky throw" to relay exceptions in other 608 * contexts. 609 */ 610 static void rethrow(Throwable ex) { 611 ForkJoinTask.<RuntimeException>uncheckedThrow(ex); 612 } 613 614 /** 615 * The sneaky part of sneaky throw, relying on generics 616 * limitations to evade compiler complaints about rethrowing 617 * unchecked exceptions. If argument null, throws 618 * CancellationException. 619 */ 620 @SuppressWarnings("unchecked") static <T extends Throwable> 621 void uncheckedThrow(Throwable t) throws T { 622 if (t == null) 623 t = new CancellationException(); 624 throw (T)t; // rely on vacuous cast 625 } 626 627 // public methods 628 629 /** 630 * Arranges to asynchronously execute this task in the pool the 631 * current task is running in, if applicable, or using the {@link 632 * ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. While 633 * it is not necessarily enforced, it is a usage error to fork a 634 * task more than once unless it has completed and been 635 * reinitialized. Subsequent modifications to the state of this 636 * task or any data it operates on are not necessarily 637 * consistently observable by any thread other than the one 638 * executing it unless preceded by a call to {@link #join} or 639 * related methods, or a call to {@link #isDone} returning {@code 640 * true}. 641 * 642 * @return {@code this}, to simplify usage 643 */ 644 public final ForkJoinTask<V> fork() { 645 Thread t; ForkJoinWorkerThread w; 646 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) 647 (w = (ForkJoinWorkerThread)t).workQueue.push(this, w.pool); 648 else 649 ForkJoinPool.common.externalPush(this); 650 return this; 651 } 652 653 /** 654 * Returns the result of the computation when it 655 * {@linkplain #isDone is done}. 656 * This method differs from {@link #get()} in that abnormal 657 * completion results in {@code RuntimeException} or {@code Error}, 658 * not {@code ExecutionException}, and that interrupts of the 659 * calling thread do <em>not</em> cause the method to abruptly 660 * return by throwing {@code InterruptedException}. 661 * 662 * @return the computed result 663 */ 664 public final V join() { 665 int s; 666 if ((s = status) >= 0) 667 s = awaitJoin(false, false, false, 0L); 668 if ((s & ABNORMAL) != 0) 669 reportException(s); 670 return getRawResult(); 671 } 672 673 /** 674 * Commences performing this task, awaits its completion if 675 * necessary, and returns its result, or throws an (unchecked) 676 * {@code RuntimeException} or {@code Error} if the underlying 677 * computation did so. 678 * 679 * @return the computed result 680 */ 681 public final V invoke() { 682 int s; 683 if ((s = doExec()) >= 0) 684 s = awaitJoin(true, false, false, 0L); 685 if ((s & ABNORMAL) != 0) 686 reportException(s); 687 return getRawResult(); 688 } 689 690 /** 691 * Forks the given tasks, returning when {@code isDone} holds for 692 * each task or an (unchecked) exception is encountered, in which 693 * case the exception is rethrown. If more than one task 694 * encounters an exception, then this method throws any one of 695 * these exceptions. If any task encounters an exception, the 696 * other may be cancelled. However, the execution status of 697 * individual tasks is not guaranteed upon exceptional return. The 698 * status of each task may be obtained using {@link 699 * #getException()} and related methods to check if they have been 700 * cancelled, completed normally or exceptionally, or left 701 * unprocessed. 702 * 703 * @param t1 the first task 704 * @param t2 the second task 705 * @throws NullPointerException if any task is null 706 */ 707 public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) { 708 int s1, s2; 709 if (t1 == null || t2 == null) 710 throw new NullPointerException(); 711 t2.fork(); 712 if ((s1 = t1.doExec()) >= 0) 713 s1 = t1.awaitJoin(true, false, false, 0L); 714 if ((s1 & ABNORMAL) != 0) { 715 cancelIgnoringExceptions(t2); 716 t1.reportException(s1); 717 } 718 else if (((s2 = t2.awaitJoin(false, false, false, 0L)) & ABNORMAL) != 0) 719 t2.reportException(s2); 720 } 721 722 /** 723 * Forks the given tasks, returning when {@code isDone} holds for 724 * each task or an (unchecked) exception is encountered, in which 725 * case the exception is rethrown. If more than one task 726 * encounters an exception, then this method throws any one of 727 * these exceptions. If any task encounters an exception, others 728 * may be cancelled. However, the execution status of individual 729 * tasks is not guaranteed upon exceptional return. The status of 730 * each task may be obtained using {@link #getException()} and 731 * related methods to check if they have been cancelled, completed 732 * normally or exceptionally, or left unprocessed. 733 * 734 * @param tasks the tasks 735 * @throws NullPointerException if any task is null 736 */ 737 public static void invokeAll(ForkJoinTask<?>... tasks) { 738 Throwable ex = null; 739 int last = tasks.length - 1; 740 for (int i = last; i >= 0; --i) { 741 ForkJoinTask<?> t; 742 if ((t = tasks[i]) == null) { 743 ex = new NullPointerException(); 744 break; 745 } 746 if (i == 0) { 747 int s; 748 if ((s = t.doExec()) >= 0) 749 s = t.awaitJoin(true, false, false, 0L); 750 if ((s & ABNORMAL) != 0) 751 ex = t.getException(s); 752 break; 753 } 754 t.fork(); 755 } 756 if (ex == null) { 757 for (int i = 1; i <= last; ++i) { 758 ForkJoinTask<?> t; 759 if ((t = tasks[i]) != null) { 760 int s; 761 if ((s = t.status) >= 0) 762 s = t.awaitJoin(false, false, false, 0L); 763 if ((s & ABNORMAL) != 0 && (ex = t.getException(s)) != null) 764 break; 765 } 766 } 767 } 768 if (ex != null) { 769 for (int i = 1; i <= last; ++i) 770 cancelIgnoringExceptions(tasks[i]); 771 rethrow(ex); 772 } 773 } 774 775 /** 776 * Forks all tasks in the specified collection, returning when 777 * {@code isDone} holds for each task or an (unchecked) exception 778 * is encountered, in which case the exception is rethrown. If 779 * more than one task encounters an exception, then this method 780 * throws any one of these exceptions. If any task encounters an 781 * exception, others may be cancelled. However, the execution 782 * status of individual tasks is not guaranteed upon exceptional 783 * return. The status of each task may be obtained using {@link 784 * #getException()} and related methods to check if they have been 785 * cancelled, completed normally or exceptionally, or left 786 * unprocessed. 787 * 788 * @param tasks the collection of tasks 789 * @param <T> the type of the values returned from the tasks 790 * @return the tasks argument, to simplify usage 791 * @throws NullPointerException if tasks or any element are null 792 */ 793 public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) { 794 if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) { 795 invokeAll(tasks.toArray(new ForkJoinTask<?>[0])); 796 return tasks; 797 } 798 @SuppressWarnings("unchecked") 799 List<? extends ForkJoinTask<?>> ts = 800 (List<? extends ForkJoinTask<?>>) tasks; 801 Throwable ex = null; 802 int last = ts.size() - 1; // nearly same as array version 803 for (int i = last; i >= 0; --i) { 804 ForkJoinTask<?> t; 805 if ((t = ts.get(i)) == null) { 806 ex = new NullPointerException(); 807 break; 808 } 809 if (i == 0) { 810 int s; 811 if ((s = t.doExec()) >= 0) 812 s = t.awaitJoin(true, false, false, 0L); 813 if ((s & ABNORMAL) != 0) 814 ex = t.getException(s); 815 break; 816 } 817 t.fork(); 818 } 819 if (ex == null) { 820 for (int i = 1; i <= last; ++i) { 821 ForkJoinTask<?> t; 822 if ((t = ts.get(i)) != null) { 823 int s; 824 if ((s = t.status) >= 0) 825 s = t.awaitJoin(false, false, false, 0L); 826 if ((s & ABNORMAL) != 0 && (ex = t.getException(s)) != null) 827 break; 828 } 829 } 830 } 831 if (ex != null) { 832 for (int i = 1; i <= last; ++i) 833 cancelIgnoringExceptions(ts.get(i)); 834 rethrow(ex); 835 } 836 return tasks; 837 } 838 839 /** 840 * Attempts to cancel execution of this task. This attempt will 841 * fail if the task has already completed or could not be 842 * cancelled for some other reason. If successful, and this task 843 * has not started when {@code cancel} is called, execution of 844 * this task is suppressed. After this method returns 845 * successfully, unless there is an intervening call to {@link 846 * #reinitialize}, subsequent calls to {@link #isCancelled}, 847 * {@link #isDone}, and {@code cancel} will return {@code true} 848 * and calls to {@link #join} and related methods will result in 849 * {@code CancellationException}. 850 * 851 * <p>This method may be overridden in subclasses, but if so, must 852 * still ensure that these properties hold. In particular, the 853 * {@code cancel} method itself must not throw exceptions. 854 * 855 * <p>This method is designed to be invoked by <em>other</em> 856 * tasks. To terminate the current task, you can just return or 857 * throw an unchecked exception from its computation method, or 858 * invoke {@link #completeExceptionally(Throwable)}. 859 * 860 * @param mayInterruptIfRunning this value has no effect in the 861 * default implementation because interrupts are not used to 862 * control cancellation. 863 * 864 * @return {@code true} if this task is now cancelled 865 */ 866 public boolean cancel(boolean mayInterruptIfRunning) { 867 return (trySetCancelled() & (ABNORMAL | THROWN)) == ABNORMAL; 868 } 869 870 public final boolean isDone() { 871 return status < 0; 872 } 873 874 public final boolean isCancelled() { 875 return (status & (ABNORMAL | THROWN)) == ABNORMAL; 876 } 877 878 /** 879 * Returns {@code true} if this task threw an exception or was cancelled. 880 * 881 * @return {@code true} if this task threw an exception or was cancelled 882 */ 883 public final boolean isCompletedAbnormally() { 884 return (status & ABNORMAL) != 0; 885 } 886 887 /** 888 * Returns {@code true} if this task completed without throwing an 889 * exception and was not cancelled. 890 * 891 * @return {@code true} if this task completed without throwing an 892 * exception and was not cancelled 893 */ 894 public final boolean isCompletedNormally() { 895 return (status & (DONE | ABNORMAL)) == DONE; 896 } 897 898 /** 899 * Returns the exception thrown by the base computation, or a 900 * {@code CancellationException} if cancelled, or {@code null} if 901 * none or if the method has not yet completed. 902 * 903 * @return the exception, or {@code null} if none 904 */ 905 public final Throwable getException() { 906 return getException(status); 907 } 908 909 /** 910 * Completes this task abnormally, and if not already aborted or 911 * cancelled, causes it to throw the given exception upon 912 * {@code join} and related operations. This method may be used 913 * to induce exceptions in asynchronous tasks, or to force 914 * completion of tasks that would not otherwise complete. Its use 915 * in other situations is discouraged. This method is 916 * overridable, but overridden versions must invoke {@code super} 917 * implementation to maintain guarantees. 918 * 919 * @param ex the exception to throw. If this exception is not a 920 * {@code RuntimeException} or {@code Error}, the actual exception 921 * thrown will be a {@code RuntimeException} with cause {@code ex}. 922 */ 923 public void completeExceptionally(Throwable ex) { 924 trySetException((ex instanceof RuntimeException) || 925 (ex instanceof Error) ? ex : 926 new RuntimeException(ex)); 927 } 928 929 /** 930 * Completes this task, and if not already aborted or cancelled, 931 * returning the given value as the result of subsequent 932 * invocations of {@code join} and related operations. This method 933 * may be used to provide results for asynchronous tasks, or to 934 * provide alternative handling for tasks that would not otherwise 935 * complete normally. Its use in other situations is 936 * discouraged. This method is overridable, but overridden 937 * versions must invoke {@code super} implementation to maintain 938 * guarantees. 939 * 940 * @param value the result value for this task 941 */ 942 public void complete(V value) { 943 try { 944 setRawResult(value); 945 } catch (Throwable rex) { 946 trySetException(rex); 947 return; 948 } 949 setDone(); 950 } 951 952 /** 953 * Completes this task normally without setting a value. The most 954 * recent value established by {@link #setRawResult} (or {@code 955 * null} by default) will be returned as the result of subsequent 956 * invocations of {@code join} and related operations. 957 * 958 * @since 1.8 959 */ 960 public final void quietlyComplete() { 961 setDone(); 962 } 963 964 /** 965 * Waits if necessary for the computation to complete, and then 966 * retrieves its result. 967 * 968 * @return the computed result 969 * @throws CancellationException if the computation was cancelled 970 * @throws ExecutionException if the computation threw an 971 * exception 972 * @throws InterruptedException if the current thread is not a 973 * member of a ForkJoinPool and was interrupted while waiting 974 */ 975 public final V get() throws InterruptedException, ExecutionException { 976 int s; 977 if (((s = awaitJoin(false, true, false, 0L)) & ABNORMAL) != 0) 978 reportExecutionException(s); 979 return getRawResult(); 980 } 981 982 /** 983 * Waits if necessary for at most the given time for the computation 984 * to complete, and then retrieves its result, if available. 985 * 986 * @param timeout the maximum time to wait 987 * @param unit the time unit of the timeout argument 988 * @return the computed result 989 * @throws CancellationException if the computation was cancelled 990 * @throws ExecutionException if the computation threw an 991 * exception 992 * @throws InterruptedException if the current thread is not a 993 * member of a ForkJoinPool and was interrupted while waiting 994 * @throws TimeoutException if the wait timed out 995 */ 996 public final V get(long timeout, TimeUnit unit) 997 throws InterruptedException, ExecutionException, TimeoutException { 998 int s; 999 if ((s = awaitJoin(false, true, true, unit.toNanos(timeout))) >= 0 || 1000 (s & ABNORMAL) != 0) 1001 reportExecutionException(s); 1002 return getRawResult(); 1003 } 1004 1005 /** 1006 * Joins this task, without returning its result or throwing its 1007 * exception. This method may be useful when processing 1008 * collections of tasks when some have been cancelled or otherwise 1009 * known to have aborted. 1010 */ 1011 public final void quietlyJoin() { 1012 if (status >= 0) 1013 awaitJoin(false, false, false, 0L); 1014 } 1015 1016 /** 1017 * Commences performing this task and awaits its completion if 1018 * necessary, without returning its result or throwing its 1019 * exception. 1020 */ 1021 public final void quietlyInvoke() { 1022 if (doExec() >= 0) 1023 awaitJoin(true, false, false, 0L); 1024 } 1025 1026 /** 1027 * Possibly executes tasks until the pool hosting the current task 1028 * {@linkplain ForkJoinPool#isQuiescent is quiescent}. This 1029 * method may be of use in designs in which many tasks are forked, 1030 * but none are explicitly joined, instead executing them until 1031 * all are processed. 1032 */ 1033 public static void helpQuiesce() { 1034 Thread t; ForkJoinWorkerThread w; ForkJoinPool p; 1035 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread && 1036 (p = (w = (ForkJoinWorkerThread)t).pool) != null) 1037 p.helpQuiescePool(w.workQueue, Long.MAX_VALUE, false); 1038 else 1039 ForkJoinPool.common.externalHelpQuiescePool(Long.MAX_VALUE, false); 1040 } 1041 1042 /** 1043 * Resets the internal bookkeeping state of this task, allowing a 1044 * subsequent {@code fork}. This method allows repeated reuse of 1045 * this task, but only if reuse occurs when this task has either 1046 * never been forked, or has been forked, then completed and all 1047 * outstanding joins of this task have also completed. Effects 1048 * under any other usage conditions are not guaranteed. 1049 * This method may be useful when executing 1050 * pre-constructed trees of subtasks in loops. 1051 * 1052 * <p>Upon completion of this method, {@code isDone()} reports 1053 * {@code false}, and {@code getException()} reports {@code 1054 * null}. However, the value returned by {@code getRawResult} is 1055 * unaffected. To clear this value, you can invoke {@code 1056 * setRawResult(null)}. 1057 */ 1058 public void reinitialize() { 1059 aux = null; 1060 status = 0; 1061 } 1062 1063 /** 1064 * Returns the pool hosting the current thread, or {@code null} 1065 * if the current thread is executing outside of any ForkJoinPool. 1066 * 1067 * <p>This method returns {@code null} if and only if {@link 1068 * #inForkJoinPool} returns {@code false}. 1069 * 1070 * @return the pool, or {@code null} if none 1071 */ 1072 public static ForkJoinPool getPool() { 1073 Thread t; 1074 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? 1075 ((ForkJoinWorkerThread) t).pool : null); 1076 } 1077 1078 /** 1079 * Returns {@code true} if the current thread is a {@link 1080 * ForkJoinWorkerThread} executing as a ForkJoinPool computation. 1081 * 1082 * @return {@code true} if the current thread is a {@link 1083 * ForkJoinWorkerThread} executing as a ForkJoinPool computation, 1084 * or {@code false} otherwise 1085 */ 1086 public static boolean inForkJoinPool() { 1087 return Thread.currentThread() instanceof ForkJoinWorkerThread; 1088 } 1089 1090 /** 1091 * Tries to unschedule this task for execution. This method will 1092 * typically (but is not guaranteed to) succeed if this task is 1093 * the most recently forked task by the current thread, and has 1094 * not commenced executing in another thread. This method may be 1095 * useful when arranging alternative local processing of tasks 1096 * that could have been, but were not, stolen. 1097 * 1098 * @return {@code true} if unforked 1099 */ 1100 public boolean tryUnfork() { 1101 Thread t; ForkJoinPool.WorkQueue q; 1102 return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) 1103 ? (q = ((ForkJoinWorkerThread)t).workQueue) != null 1104 && q.tryUnpush(this) 1105 : (q = ForkJoinPool.commonQueue()) != null 1106 && q.externalTryUnpush(this); 1107 } 1108 1109 /** 1110 * Returns an estimate of the number of tasks that have been 1111 * forked by the current worker thread but not yet executed. This 1112 * value may be useful for heuristic decisions about whether to 1113 * fork other tasks. 1114 * 1115 * @return the number of tasks 1116 */ 1117 public static int getQueuedTaskCount() { 1118 Thread t; ForkJoinPool.WorkQueue q; 1119 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) 1120 q = ((ForkJoinWorkerThread)t).workQueue; 1121 else 1122 q = ForkJoinPool.commonQueue(); 1123 return (q == null) ? 0 : q.queueSize(); 1124 } 1125 1126 /** 1127 * Returns an estimate of how many more locally queued tasks are 1128 * held by the current worker thread than there are other worker 1129 * threads that might steal them, or zero if this thread is not 1130 * operating in a ForkJoinPool. This value may be useful for 1131 * heuristic decisions about whether to fork other tasks. In many 1132 * usages of ForkJoinTasks, at steady state, each worker should 1133 * aim to maintain a small constant surplus (for example, 3) of 1134 * tasks, and to process computations locally if this threshold is 1135 * exceeded. 1136 * 1137 * @return the surplus number of tasks, which may be negative 1138 */ 1139 public static int getSurplusQueuedTaskCount() { 1140 return ForkJoinPool.getSurplusQueuedTaskCount(); 1141 } 1142 1143 // Extension methods 1144 1145 /** 1146 * Returns the result that would be returned by {@link #join}, even 1147 * if this task completed abnormally, or {@code null} if this task 1148 * is not known to have been completed. This method is designed 1149 * to aid debugging, as well as to support extensions. Its use in 1150 * any other context is discouraged. 1151 * 1152 * @return the result, or {@code null} if not completed 1153 */ 1154 public abstract V getRawResult(); 1155 1156 /** 1157 * Forces the given value to be returned as a result. This method 1158 * is designed to support extensions, and should not in general be 1159 * called otherwise. 1160 * 1161 * @param value the value 1162 */ 1163 protected abstract void setRawResult(V value); 1164 1165 /** 1166 * Immediately performs the base action of this task and returns 1167 * true if, upon return from this method, this task is guaranteed 1168 * to have completed. This method may return false otherwise, to 1169 * indicate that this task is not necessarily complete (or is not 1170 * known to be complete), for example in asynchronous actions that 1171 * require explicit invocations of completion methods. This method 1172 * may also throw an (unchecked) exception to indicate abnormal 1173 * exit. This method is designed to support extensions, and should 1174 * not in general be called otherwise. 1175 * 1176 * @return {@code true} if this task is known to have completed normally 1177 */ 1178 protected abstract boolean exec(); 1179 1180 /** 1181 * Returns, but does not unschedule or execute, a task queued by 1182 * the current thread but not yet executed, if one is immediately 1183 * available. There is no guarantee that this task will actually 1184 * be polled or executed next. Conversely, this method may return 1185 * null even if a task exists but cannot be accessed without 1186 * contention with other threads. This method is designed 1187 * primarily to support extensions, and is unlikely to be useful 1188 * otherwise. 1189 * 1190 * @return the next task, or {@code null} if none are available 1191 */ 1192 protected static ForkJoinTask<?> peekNextLocalTask() { 1193 Thread t; ForkJoinPool.WorkQueue q; 1194 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) 1195 q = ((ForkJoinWorkerThread)t).workQueue; 1196 else 1197 q = ForkJoinPool.commonQueue(); 1198 return (q == null) ? null : q.peek(); 1199 } 1200 1201 /** 1202 * Unschedules and returns, without executing, the next task 1203 * queued by the current thread but not yet executed, if the 1204 * current thread is operating in a ForkJoinPool. This method is 1205 * designed primarily to support extensions, and is unlikely to be 1206 * useful otherwise. 1207 * 1208 * @return the next task, or {@code null} if none are available 1209 */ 1210 protected static ForkJoinTask<?> pollNextLocalTask() { 1211 Thread t; 1212 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? 1213 ((ForkJoinWorkerThread)t).workQueue.nextLocalTask() : null); 1214 } 1215 1216 /** 1217 * If the current thread is operating in a ForkJoinPool, 1218 * unschedules and returns, without executing, the next task 1219 * queued by the current thread but not yet executed, if one is 1220 * available, or if not available, a task that was forked by some 1221 * other thread, if available. Availability may be transient, so a 1222 * {@code null} result does not necessarily imply quiescence of 1223 * the pool this task is operating in. This method is designed 1224 * primarily to support extensions, and is unlikely to be useful 1225 * otherwise. 1226 * 1227 * @return a task, or {@code null} if none are available 1228 */ 1229 protected static ForkJoinTask<?> pollTask() { 1230 Thread t; ForkJoinWorkerThread w; 1231 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? 1232 (w = (ForkJoinWorkerThread)t).pool.nextTaskFor(w.workQueue) : 1233 null); 1234 } 1235 1236 /** 1237 * If the current thread is operating in a ForkJoinPool, 1238 * unschedules and returns, without executing, a task externally 1239 * submitted to the pool, if one is available. Availability may be 1240 * transient, so a {@code null} result does not necessarily imply 1241 * quiescence of the pool. This method is designed primarily to 1242 * support extensions, and is unlikely to be useful otherwise. 1243 * 1244 * @return a task, or {@code null} if none are available 1245 * @since 9 1246 */ 1247 protected static ForkJoinTask<?> pollSubmission() { 1248 Thread t; 1249 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? 1250 ((ForkJoinWorkerThread)t).pool.pollSubmission() : null); 1251 } 1252 1253 // tag operations 1254 1255 /** 1256 * Returns the tag for this task. 1257 * 1258 * @return the tag for this task 1259 * @since 1.8 1260 */ 1261 public final short getForkJoinTaskTag() { 1262 return (short)status; 1263 } 1264 1265 /** 1266 * Atomically sets the tag value for this task and returns the old value. 1267 * 1268 * @param newValue the new tag value 1269 * @return the previous value of the tag 1270 * @since 1.8 1271 */ 1272 public final short setForkJoinTaskTag(short newValue) { 1273 for (int s;;) { 1274 if (casStatus(s = status, (s & ~SMASK) | (newValue & SMASK))) 1275 return (short)s; 1276 } 1277 } 1278 1279 /** 1280 * Atomically conditionally sets the tag value for this task. 1281 * Among other applications, tags can be used as visit markers 1282 * in tasks operating on graphs, as in methods that check: {@code 1283 * if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))} 1284 * before processing, otherwise exiting because the node has 1285 * already been visited. 1286 * 1287 * @param expect the expected tag value 1288 * @param update the new tag value 1289 * @return {@code true} if successful; i.e., the current value was 1290 * equal to {@code expect} and was changed to {@code update}. 1291 * @since 1.8 1292 */ 1293 public final boolean compareAndSetForkJoinTaskTag(short expect, short update) { 1294 for (int s;;) { 1295 if ((short)(s = status) != expect) 1296 return false; 1297 if (casStatus(s, (s & ~SMASK) | (update & SMASK))) 1298 return true; 1299 } 1300 } 1301 1302 /** 1303 * Adapter for Runnables. This implements RunnableFuture 1304 * to be compliant with AbstractExecutorService constraints 1305 * when used in ForkJoinPool. 1306 */ 1307 static final class AdaptedRunnable<T> extends ForkJoinTask<T> 1308 implements RunnableFuture<T> { 1309 @SuppressWarnings("serial") // Conditionally serializable 1310 final Runnable runnable; 1311 @SuppressWarnings("serial") // Conditionally serializable 1312 T result; 1313 AdaptedRunnable(Runnable runnable, T result) { 1314 if (runnable == null) throw new NullPointerException(); 1315 this.runnable = runnable; 1316 this.result = result; // OK to set this even before completion 1317 } 1318 public final T getRawResult() { return result; } 1319 public final void setRawResult(T v) { result = v; } 1320 public final boolean exec() { runnable.run(); return true; } 1321 public final void run() { invoke(); } 1322 public String toString() { 1323 return super.toString() + "[Wrapped task = " + runnable + "]"; 1324 } 1325 private static final long serialVersionUID = 5232453952276885070L; 1326 } 1327 1328 /** 1329 * Adapter for Runnables without results. 1330 */ 1331 static final class AdaptedRunnableAction extends ForkJoinTask<Void> 1332 implements RunnableFuture<Void> { 1333 @SuppressWarnings("serial") // Conditionally serializable 1334 final Runnable runnable; 1335 AdaptedRunnableAction(Runnable runnable) { 1336 if (runnable == null) throw new NullPointerException(); 1337 this.runnable = runnable; 1338 } 1339 public final Void getRawResult() { return null; } 1340 public final void setRawResult(Void v) { } 1341 public final boolean exec() { runnable.run(); return true; } 1342 public final void run() { invoke(); } 1343 public String toString() { 1344 return super.toString() + "[Wrapped task = " + runnable + "]"; 1345 } 1346 private static final long serialVersionUID = 5232453952276885070L; 1347 } 1348 1349 /** 1350 * Adapter for Runnables in which failure forces worker exception. 1351 */ 1352 static final class RunnableExecuteAction extends ForkJoinTask<Void> { 1353 @SuppressWarnings("serial") // Conditionally serializable 1354 final Runnable runnable; 1355 RunnableExecuteAction(Runnable runnable) { 1356 if (runnable == null) throw new NullPointerException(); 1357 this.runnable = runnable; 1358 } 1359 public final Void getRawResult() { return null; } 1360 public final void setRawResult(Void v) { } 1361 public final boolean exec() { runnable.run(); return true; } 1362 int trySetException(Throwable ex) { // if a handler, invoke it 1363 int s; Thread t; java.lang.Thread.UncaughtExceptionHandler h; 1364 if (isExceptionalStatus(s = trySetThrown(ex)) && 1365 (h = ((t = Thread.currentThread()). 1366 getUncaughtExceptionHandler())) != null) { 1367 try { 1368 h.uncaughtException(t, ex); 1369 } catch (Throwable ignore) { 1370 } 1371 } 1372 return s; 1373 } 1374 private static final long serialVersionUID = 5232453952276885070L; 1375 } 1376 1377 /** 1378 * Adapter for Callables. 1379 */ 1380 static final class AdaptedCallable<T> extends ForkJoinTask<T> 1381 implements RunnableFuture<T> { 1382 @SuppressWarnings("serial") // Conditionally serializable 1383 final Callable<? extends T> callable; 1384 @SuppressWarnings("serial") // Conditionally serializable 1385 T result; 1386 AdaptedCallable(Callable<? extends T> callable) { 1387 if (callable == null) throw new NullPointerException(); 1388 this.callable = callable; 1389 } 1390 public final T getRawResult() { return result; } 1391 public final void setRawResult(T v) { result = v; } 1392 public final boolean exec() { 1393 try { 1394 result = callable.call(); 1395 return true; 1396 } catch (RuntimeException rex) { 1397 throw rex; 1398 } catch (Exception ex) { 1399 throw new RuntimeException(ex); 1400 } 1401 } 1402 public final void run() { invoke(); } 1403 public String toString() { 1404 return super.toString() + "[Wrapped task = " + callable + "]"; 1405 } 1406 private static final long serialVersionUID = 2838392045355241008L; 1407 } 1408 1409 static final class AdaptedInterruptibleCallable<T> extends ForkJoinTask<T> 1410 implements RunnableFuture<T> { 1411 @SuppressWarnings("serial") // Conditionally serializable 1412 final Callable<? extends T> callable; 1413 @SuppressWarnings("serial") // Conditionally serializable 1414 transient volatile Thread runner; 1415 T result; 1416 AdaptedInterruptibleCallable(Callable<? extends T> callable) { 1417 if (callable == null) throw new NullPointerException(); 1418 this.callable = callable; 1419 } 1420 public final T getRawResult() { return result; } 1421 public final void setRawResult(T v) { result = v; } 1422 public final boolean exec() { 1423 Thread.interrupted(); 1424 runner = Thread.currentThread(); 1425 try { 1426 if (!isDone()) // recheck 1427 result = callable.call(); 1428 return true; 1429 } catch (RuntimeException rex) { 1430 throw rex; 1431 } catch (Exception ex) { 1432 throw new RuntimeException(ex); 1433 } finally { 1434 runner = null; 1435 Thread.interrupted(); 1436 } 1437 } 1438 public final void run() { invoke(); } 1439 public final boolean cancel(boolean mayInterruptIfRunning) { 1440 Thread t; 1441 boolean stat = super.cancel(false); 1442 if (mayInterruptIfRunning && (t = runner) != null) { 1443 try { 1444 t.interrupt(); 1445 } catch (Throwable ignore) { 1446 } 1447 } 1448 return stat; 1449 } 1450 public String toString() { 1451 return super.toString() + "[Wrapped task = " + callable + "]"; 1452 } 1453 private static final long serialVersionUID = 2838392045355241008L; 1454 } 1455 1456 /** 1457 * Returns a new {@code ForkJoinTask} that performs the {@code run} 1458 * method of the given {@code Runnable} as its action, and returns 1459 * a null result upon {@link #join}. 1460 * 1461 * @param runnable the runnable action 1462 * @return the task 1463 */ 1464 public static ForkJoinTask<?> adapt(Runnable runnable) { 1465 return new AdaptedRunnableAction(runnable); 1466 } 1467 1468 /** 1469 * Returns a new {@code ForkJoinTask} that performs the {@code run} 1470 * method of the given {@code Runnable} as its action, and returns 1471 * the given result upon {@link #join}. 1472 * 1473 * @param runnable the runnable action 1474 * @param result the result upon completion 1475 * @param <T> the type of the result 1476 * @return the task 1477 */ 1478 public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) { 1479 return new AdaptedRunnable<T>(runnable, result); 1480 } 1481 1482 /** 1483 * Returns a new {@code ForkJoinTask} that performs the {@code call} 1484 * method of the given {@code Callable} as its action, and returns 1485 * its result upon {@link #join}, translating any checked exceptions 1486 * encountered into {@code RuntimeException}. 1487 * 1488 * @param callable the callable action 1489 * @param <T> the type of the callable's result 1490 * @return the task 1491 */ 1492 public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) { 1493 return new AdaptedCallable<T>(callable); 1494 } 1495 1496 /** 1497 * Returns a new {@code ForkJoinTask} that performs the {@code call} 1498 * method of the given {@code Callable} as its action, and returns 1499 * its result upon {@link #join}, translating any checked exceptions 1500 * encountered into {@code RuntimeException}. Additionally, 1501 * invocations of {@code cancel} with {@code mayInterruptIfRunning 1502 * true} will attempt to interrupt the thread performing the task. 1503 * 1504 * @param callable the callable action 1505 * @param <T> the type of the callable's result 1506 * @return the task 1507 * 1508 * @since 17 1509 */ 1510 // adaptInterruptible deferred to its own independent change 1511 // https://bugs.openjdk.java.net/browse/JDK-8246587 1512 /* TODO: public */ private static <T> ForkJoinTask<T> adaptInterruptible(Callable<? extends T> callable) { 1513 return new AdaptedInterruptibleCallable<T>(callable); 1514 } 1515 1516 // Serialization support 1517 1518 private static final long serialVersionUID = -7721805057305804111L; 1519 1520 /** 1521 * Saves this task to a stream (that is, serializes it). 1522 * 1523 * @param s the stream 1524 * @throws java.io.IOException if an I/O error occurs 1525 * @serialData the current run status and the exception thrown 1526 * during execution, or {@code null} if none 1527 */ 1528 private void writeObject(java.io.ObjectOutputStream s) 1529 throws java.io.IOException { 1530 Aux a; 1531 s.defaultWriteObject(); 1532 s.writeObject((a = aux) == null ? null : a.ex); 1533 } 1534 1535 /** 1536 * Reconstitutes this task from a stream (that is, deserializes it). 1537 * @param s the stream 1538 * @throws ClassNotFoundException if the class of a serialized object 1539 * could not be found 1540 * @throws java.io.IOException if an I/O error occurs 1541 */ 1542 private void readObject(java.io.ObjectInputStream s) 1543 throws java.io.IOException, ClassNotFoundException { 1544 s.defaultReadObject(); 1545 Object ex = s.readObject(); 1546 if (ex != null) 1547 trySetThrown((Throwable)ex); 1548 } 1549 1550 static { 1551 try { 1552 MethodHandles.Lookup l = MethodHandles.lookup(); 1553 STATUS = l.findVarHandle(ForkJoinTask.class, "status", int.class); 1554 AUX = l.findVarHandle(ForkJoinTask.class, "aux", Aux.class); 1555 } catch (ReflectiveOperationException e) { 1556 throw new ExceptionInInitializerError(e); 1557 } 1558 } 1559 1560 }