1 /* 2 * Written by Doug Lea with assistance from members of JCP JSR-166 3 * Expert Group and released to the public domain, as explained at 4 * http://creativecommons.org/publicdomain/zero/1.0/ 5 */ 6 7 package java.util.concurrent; 8 9 import java.io.Serializable; 10 import java.util.Collection; 11 import java.util.List; 12 import java.util.RandomAccess; 13 import java.lang.ref.WeakReference; 14 import java.lang.ref.ReferenceQueue; 15 import java.util.concurrent.Callable; 16 import java.util.concurrent.CancellationException; 17 import java.util.concurrent.ExecutionException; 18 import java.util.concurrent.Future; 19 import java.util.concurrent.RejectedExecutionException; 20 import java.util.concurrent.RunnableFuture; 21 import java.util.concurrent.TimeUnit; 22 import java.util.concurrent.TimeoutException; 23 import java.util.concurrent.locks.ReentrantLock; 24 import java.lang.reflect.Constructor; 25 26 /** 27 * Abstract base class for tasks that run within a {@link ForkJoinPool}. 28 * A {@code ForkJoinTask} is a thread-like entity that is much 29 * lighter weight than a normal thread. Huge numbers of tasks and 30 * subtasks may be hosted by a small number of actual threads in a 31 * ForkJoinPool, at the price of some usage limitations. 32 * 33 * <p>A "main" {@code ForkJoinTask} begins execution when it is 34 * explicitly submitted to a {@link ForkJoinPool}, or, if not already 35 * engaged in a ForkJoin computation, commenced in the {@link 36 * ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or 37 * related methods. Once started, it will usually in turn start other 38 * subtasks. As indicated by the name of this class, many programs 39 * using {@code ForkJoinTask} employ only methods {@link #fork} and 40 * {@link #join}, or derivatives such as {@link 41 * #invokeAll(ForkJoinTask...) invokeAll}. However, this class also 42 * provides a number of other methods that can come into play in 43 * advanced usages, as well as extension mechanics that allow support 44 * of new forms of fork/join processing. 45 * 46 * <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}. 47 * The efficiency of {@code ForkJoinTask}s stems from a set of 48 * restrictions (that are only partially statically enforceable) 49 * reflecting their main use as computational tasks calculating pure 50 * functions or operating on purely isolated objects. The primary 51 * coordination mechanisms are {@link #fork}, that arranges 52 * asynchronous execution, and {@link #join}, that doesn't proceed 53 * until the task's result has been computed. Computations should 54 * ideally avoid {@code synchronized} methods or blocks, and should 55 * minimize other blocking synchronization apart from joining other 56 * tasks or using synchronizers such as Phasers that are advertised to 57 * cooperate with fork/join scheduling. Subdividable tasks should also 58 * not perform blocking I/O, and should ideally access variables that 59 * are completely independent of those accessed by other running 60 * tasks. These guidelines are loosely enforced by not permitting 61 * checked exceptions such as {@code IOExceptions} to be 62 * thrown. However, computations may still encounter unchecked 63 * exceptions, that are rethrown to callers attempting to join 64 * them. These exceptions may additionally include {@link 65 * RejectedExecutionException} stemming from internal resource 66 * exhaustion, such as failure to allocate internal task 67 * queues. Rethrown exceptions behave in the same way as regular 68 * exceptions, but, when possible, contain stack traces (as displayed 69 * for example using {@code ex.printStackTrace()}) of both the thread 70 * that initiated the computation as well as the thread actually 71 * encountering the exception; minimally only the latter. 72 * 73 * <p>It is possible to define and use ForkJoinTasks that may block, 74 * but doing do requires three further considerations: (1) Completion 75 * of few if any <em>other</em> tasks should be dependent on a task 76 * that blocks on external synchronization or I/O. Event-style async 77 * tasks that are never joined (for example, those subclassing {@link 78 * CountedCompleter}) often fall into this category. (2) To minimize 79 * resource impact, tasks should be small; ideally performing only the 80 * (possibly) blocking action. (3) Unless the {@link 81 * ForkJoinPool.ManagedBlocker} API is used, or the number of possibly 82 * blocked tasks is known to be less than the pool's {@link 83 * ForkJoinPool#getParallelism} level, the pool cannot guarantee that 84 * enough threads will be available to ensure progress or good 85 * performance. 86 * 87 * <p>The primary method for awaiting completion and extracting 88 * results of a task is {@link #join}, but there are several variants: 89 * The {@link Future#get} methods support interruptible and/or timed 90 * waits for completion and report results using {@code Future} 91 * conventions. Method {@link #invoke} is semantically 92 * equivalent to {@code fork(); join()} but always attempts to begin 93 * execution in the current thread. The "<em>quiet</em>" forms of 94 * these methods do not extract results or report exceptions. These 95 * may be useful when a set of tasks are being executed, and you need 96 * to delay processing of results or exceptions until all complete. 97 * Method {@code invokeAll} (available in multiple versions) 98 * performs the most common form of parallel invocation: forking a set 99 * of tasks and joining them all. 100 * 101 * <p>In the most typical usages, a fork-join pair act like a call 102 * (fork) and return (join) from a parallel recursive function. As is 103 * the case with other forms of recursive calls, returns (joins) 104 * should be performed innermost-first. For example, {@code a.fork(); 105 * b.fork(); b.join(); a.join();} is likely to be substantially more 106 * efficient than joining {@code a} before {@code b}. 107 * 108 * <p>The execution status of tasks may be queried at several levels 109 * of detail: {@link #isDone} is true if a task completed in any way 110 * (including the case where a task was cancelled without executing); 111 * {@link #isCompletedNormally} is true if a task completed without 112 * cancellation or encountering an exception; {@link #isCancelled} is 113 * true if the task was cancelled (in which case {@link #getException} 114 * returns a {@link java.util.concurrent.CancellationException}); and 115 * {@link #isCompletedAbnormally} is true if a task was either 116 * cancelled or encountered an exception, in which case {@link 117 * #getException} will return either the encountered exception or 118 * {@link java.util.concurrent.CancellationException}. 119 * 120 * <p>The ForkJoinTask class is not usually directly subclassed. 121 * Instead, you subclass one of the abstract classes that support a 122 * particular style of fork/join processing, typically {@link 123 * RecursiveAction} for most computations that do not return results, 124 * {@link RecursiveTask} for those that do, and {@link 125 * CountedCompleter} for those in which completed actions trigger 126 * other actions. Normally, a concrete ForkJoinTask subclass declares 127 * fields comprising its parameters, established in a constructor, and 128 * then defines a {@code compute} method that somehow uses the control 129 * methods supplied by this base class. 130 * 131 * <p>Method {@link #join} and its variants are appropriate for use 132 * only when completion dependencies are acyclic; that is, the 133 * parallel computation can be described as a directed acyclic graph 134 * (DAG). Otherwise, executions may encounter a form of deadlock as 135 * tasks cyclically wait for each other. However, this framework 136 * supports other methods and techniques (for example the use of 137 * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that 138 * may be of use in constructing custom subclasses for problems that 139 * are not statically structured as DAGs. To support such usages a 140 * ForkJoinTask may be atomically <em>tagged</em> with a {@code short} 141 * value using {@link #setForkJoinTaskTag} or {@link 142 * #compareAndSetForkJoinTaskTag} and checked using {@link 143 * #getForkJoinTaskTag}. The ForkJoinTask implementation does not use 144 * these {@code protected} methods or tags for any purpose, but they 145 * may be of use in the construction of specialized subclasses. For 146 * example, parallel graph traversals can use the supplied methods to 147 * avoid revisiting nodes/tasks that have already been processed. 148 * (Method names for tagging are bulky in part to encourage definition 149 * of methods that reflect their usage patterns.) 150 * 151 * <p>Most base support methods are {@code final}, to prevent 152 * overriding of implementations that are intrinsically tied to the 153 * underlying lightweight task scheduling framework. Developers 154 * creating new basic styles of fork/join processing should minimally 155 * implement {@code protected} methods {@link #exec}, {@link 156 * #setRawResult}, and {@link #getRawResult}, while also introducing 157 * an abstract computational method that can be implemented in its 158 * subclasses, possibly relying on other {@code protected} methods 159 * provided by this class. 160 * 161 * <p>ForkJoinTasks should perform relatively small amounts of 162 * computation. Large tasks should be split into smaller subtasks, 163 * usually via recursive decomposition. As a very rough rule of thumb, 164 * a task should perform more than 100 and less than 10000 basic 165 * computational steps, and should avoid indefinite looping. If tasks 166 * are too big, then parallelism cannot improve throughput. If too 167 * small, then memory and internal task maintenance overhead may 168 * overwhelm processing. 169 * 170 * <p>This class provides {@code adapt} methods for {@link Runnable} 171 * and {@link Callable}, that may be of use when mixing execution of 172 * {@code ForkJoinTasks} with other kinds of tasks. When all tasks are 173 * of this form, consider using a pool constructed in <em>asyncMode</em>. 174 * 175 * <p>ForkJoinTasks are {@code Serializable}, which enables them to be 176 * used in extensions such as remote execution frameworks. It is 177 * sensible to serialize tasks only before or after, but not during, 178 * execution. Serialization is not relied on during execution itself. 179 * 180 * @since 1.7 181 * @hide 182 * @author Doug Lea 183 */ 184 public abstract class ForkJoinTask<V> implements Future<V>, Serializable { 185 186 /* 187 * See the internal documentation of class ForkJoinPool for a 188 * general implementation overview. ForkJoinTasks are mainly 189 * responsible for maintaining their "status" field amidst relays 190 * to methods in ForkJoinWorkerThread and ForkJoinPool. 191 * 192 * The methods of this class are more-or-less layered into 193 * (1) basic status maintenance 194 * (2) execution and awaiting completion 195 * (3) user-level methods that additionally report results. 196 * This is sometimes hard to see because this file orders exported 197 * methods in a way that flows well in javadocs. 198 */ 199 200 /* 201 * The status field holds run control status bits packed into a 202 * single int to minimize footprint and to ensure atomicity (via 203 * CAS). Status is initially zero, and takes on nonnegative 204 * values until completed, upon which status (anded with 205 * DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks 206 * undergoing blocking waits by other threads have the SIGNAL bit 207 * set. Completion of a stolen task with SIGNAL set awakens any 208 * waiters via notifyAll. Even though suboptimal for some 209 * purposes, we use basic builtin wait/notify to take advantage of 210 * "monitor inflation" in JVMs that we would otherwise need to 211 * emulate to avoid adding further per-task bookkeeping overhead. 212 * We want these monitors to be "fat", i.e., not use biasing or 213 * thin-lock techniques, so use some odd coding idioms that tend 214 * to avoid them, mainly by arranging that every synchronized 215 * block performs a wait, notifyAll or both. 216 * 217 * These control bits occupy only (some of) the upper half (16 218 * bits) of status field. The lower bits are used for user-defined 219 * tags. 220 */ 221 222 /** The run status of this task */ 223 volatile int status; // accessed directly by pool and workers 224 static final int DONE_MASK = 0xf0000000; // mask out non-completion bits 225 static final int NORMAL = 0xf0000000; // must be negative 226 static final int CANCELLED = 0xc0000000; // must be < NORMAL 227 static final int EXCEPTIONAL = 0x80000000; // must be < CANCELLED 228 static final int SIGNAL = 0x00010000; // must be >= 1 << 16 229 static final int SMASK = 0x0000ffff; // short bits for tags 230 231 /** 232 * Marks completion and wakes up threads waiting to join this 233 * task. 234 * 235 * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL 236 * @return completion status on exit 237 */ 238 private int setCompletion(int completion) { 239 for (int s;;) { 240 if ((s = status) < 0) 241 return s; 242 if (U.compareAndSwapInt(this, STATUS, s, s | completion)) { 243 if ((s >>> 16) != 0) 244 synchronized (this) { notifyAll(); } 245 return completion; 246 } 247 } 248 } 249 250 /** 251 * Primary execution method for stolen tasks. Unless done, calls 252 * exec and records status if completed, but doesn't wait for 253 * completion otherwise. 254 * 255 * @return status on exit from this method 256 */ 257 final int doExec() { 258 int s; boolean completed; 259 if ((s = status) >= 0) { 260 try { 261 completed = exec(); 262 } catch (Throwable rex) { 263 return setExceptionalCompletion(rex); 264 } 265 if (completed) 266 s = setCompletion(NORMAL); 267 } 268 return s; 269 } 270 271 /** 272 * Tries to set SIGNAL status unless already completed. Used by 273 * ForkJoinPool. Other variants are directly incorporated into 274 * externalAwaitDone etc. 275 * 276 * @return true if successful 277 */ 278 final boolean trySetSignal() { 279 int s = status; 280 return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL); 281 } 282 283 /** 284 * Blocks a non-worker-thread until completion. 285 * @return status upon completion 286 */ 287 private int externalAwaitDone() { 288 int s; 289 ForkJoinPool.externalHelpJoin(this); 290 boolean interrupted = false; 291 while ((s = status) >= 0) { 292 if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { 293 synchronized (this) { 294 if (status >= 0) { 295 try { 296 wait(); 297 } catch (InterruptedException ie) { 298 interrupted = true; 299 } 300 } 301 else 302 notifyAll(); 303 } 304 } 305 } 306 if (interrupted) 307 Thread.currentThread().interrupt(); 308 return s; 309 } 310 311 /** 312 * Blocks a non-worker-thread until completion or interruption. 313 */ 314 private int externalInterruptibleAwaitDone() throws InterruptedException { 315 int s; 316 if (Thread.interrupted()) 317 throw new InterruptedException(); 318 ForkJoinPool.externalHelpJoin(this); 319 while ((s = status) >= 0) { 320 if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { 321 synchronized (this) { 322 if (status >= 0) 323 wait(); 324 else 325 notifyAll(); 326 } 327 } 328 } 329 return s; 330 } 331 332 333 /** 334 * Implementation for join, get, quietlyJoin. Directly handles 335 * only cases of already-completed, external wait, and 336 * unfork+exec. Others are relayed to ForkJoinPool.awaitJoin. 337 * 338 * @return status upon completion 339 */ 340 private int doJoin() { 341 int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w; 342 return (s = status) < 0 ? s : 343 ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? 344 (w = (wt = (ForkJoinWorkerThread)t).workQueue). 345 tryUnpush(this) && (s = doExec()) < 0 ? s : 346 wt.pool.awaitJoin(w, this) : 347 externalAwaitDone(); 348 } 349 350 /** 351 * Implementation for invoke, quietlyInvoke. 352 * 353 * @return status upon completion 354 */ 355 private int doInvoke() { 356 int s; Thread t; ForkJoinWorkerThread wt; 357 return (s = doExec()) < 0 ? s : 358 ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? 359 (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, this) : 360 externalAwaitDone(); 361 } 362 363 // Exception table support 364 365 /** 366 * Table of exceptions thrown by tasks, to enable reporting by 367 * callers. Because exceptions are rare, we don't directly keep 368 * them with task objects, but instead use a weak ref table. Note 369 * that cancellation exceptions don't appear in the table, but are 370 * instead recorded as status values. 371 * 372 * Note: These statics are initialized below in static block. 373 */ 374 private static final ExceptionNode[] exceptionTable; 375 private static final ReentrantLock exceptionTableLock; 376 private static final ReferenceQueue<Object> exceptionTableRefQueue; 377 378 /** 379 * Fixed capacity for exceptionTable. 380 */ 381 private static final int EXCEPTION_MAP_CAPACITY = 32; 382 383 /** 384 * Key-value nodes for exception table. The chained hash table 385 * uses identity comparisons, full locking, and weak references 386 * for keys. The table has a fixed capacity because it only 387 * maintains task exceptions long enough for joiners to access 388 * them, so should never become very large for sustained 389 * periods. However, since we do not know when the last joiner 390 * completes, we must use weak references and expunge them. We do 391 * so on each operation (hence full locking). Also, some thread in 392 * any ForkJoinPool will call helpExpungeStaleExceptions when its 393 * pool becomes isQuiescent. 394 */ 395 static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> { 396 final Throwable ex; 397 ExceptionNode next; 398 final long thrower; // use id not ref to avoid weak cycles 399 ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) { 400 super(task, exceptionTableRefQueue); 401 this.ex = ex; 402 this.next = next; 403 this.thrower = Thread.currentThread().getId(); 404 } 405 } 406 407 /** 408 * Records exception and sets status. 409 * 410 * @return status on exit 411 */ 412 final int recordExceptionalCompletion(Throwable ex) { 413 int s; 414 if ((s = status) >= 0) { 415 int h = System.identityHashCode(this); 416 final ReentrantLock lock = exceptionTableLock; 417 lock.lock(); 418 try { 419 expungeStaleExceptions(); 420 ExceptionNode[] t = exceptionTable; 421 int i = h & (t.length - 1); 422 for (ExceptionNode e = t[i]; ; e = e.next) { 423 if (e == null) { 424 t[i] = new ExceptionNode(this, ex, t[i]); 425 break; 426 } 427 if (e.get() == this) // already present 428 break; 429 } 430 } finally { 431 lock.unlock(); 432 } 433 s = setCompletion(EXCEPTIONAL); 434 } 435 return s; 436 } 437 438 /** 439 * Records exception and possibly propagates. 440 * 441 * @return status on exit 442 */ 443 private int setExceptionalCompletion(Throwable ex) { 444 int s = recordExceptionalCompletion(ex); 445 if ((s & DONE_MASK) == EXCEPTIONAL) 446 internalPropagateException(ex); 447 return s; 448 } 449 450 /** 451 * Hook for exception propagation support for tasks with completers. 452 */ 453 void internalPropagateException(Throwable ex) { 454 } 455 456 /** 457 * Cancels, ignoring any exceptions thrown by cancel. Used during 458 * worker and pool shutdown. Cancel is spec'ed not to throw any 459 * exceptions, but if it does anyway, we have no recourse during 460 * shutdown, so guard against this case. 461 */ 462 static final void cancelIgnoringExceptions(ForkJoinTask<?> t) { 463 if (t != null && t.status >= 0) { 464 try { 465 t.cancel(false); 466 } catch (Throwable ignore) { 467 } 468 } 469 } 470 471 /** 472 * Removes exception node and clears status. 473 */ 474 private void clearExceptionalCompletion() { 475 int h = System.identityHashCode(this); 476 final ReentrantLock lock = exceptionTableLock; 477 lock.lock(); 478 try { 479 ExceptionNode[] t = exceptionTable; 480 int i = h & (t.length - 1); 481 ExceptionNode e = t[i]; 482 ExceptionNode pred = null; 483 while (e != null) { 484 ExceptionNode next = e.next; 485 if (e.get() == this) { 486 if (pred == null) 487 t[i] = next; 488 else 489 pred.next = next; 490 break; 491 } 492 pred = e; 493 e = next; 494 } 495 expungeStaleExceptions(); 496 status = 0; 497 } finally { 498 lock.unlock(); 499 } 500 } 501 502 /** 503 * Returns a rethrowable exception for the given task, if 504 * available. To provide accurate stack traces, if the exception 505 * was not thrown by the current thread, we try to create a new 506 * exception of the same type as the one thrown, but with the 507 * recorded exception as its cause. If there is no such 508 * constructor, we instead try to use a no-arg constructor, 509 * followed by initCause, to the same effect. If none of these 510 * apply, or any fail due to other exceptions, we return the 511 * recorded exception, which is still correct, although it may 512 * contain a misleading stack trace. 513 * 514 * @return the exception, or null if none 515 */ 516 private Throwable getThrowableException() { 517 if ((status & DONE_MASK) != EXCEPTIONAL) 518 return null; 519 int h = System.identityHashCode(this); 520 ExceptionNode e; 521 final ReentrantLock lock = exceptionTableLock; 522 lock.lock(); 523 try { 524 expungeStaleExceptions(); 525 ExceptionNode[] t = exceptionTable; 526 e = t[h & (t.length - 1)]; 527 while (e != null && e.get() != this) 528 e = e.next; 529 } finally { 530 lock.unlock(); 531 } 532 Throwable ex; 533 if (e == null || (ex = e.ex) == null) 534 return null; 535 if (false && e.thrower != Thread.currentThread().getId()) { 536 Class<? extends Throwable> ec = ex.getClass(); 537 try { 538 Constructor<?> noArgCtor = null; 539 Constructor<?>[] cs = ec.getConstructors();// public ctors only 540 for (int i = 0; i < cs.length; ++i) { 541 Constructor<?> c = cs[i]; 542 Class<?>[] ps = c.getParameterTypes(); 543 if (ps.length == 0) 544 noArgCtor = c; 545 else if (ps.length == 1 && ps[0] == Throwable.class) 546 return (Throwable)(c.newInstance(ex)); 547 } 548 if (noArgCtor != null) { 549 Throwable wx = (Throwable)(noArgCtor.newInstance()); 550 wx.initCause(ex); 551 return wx; 552 } 553 } catch (Exception ignore) { 554 } 555 } 556 return ex; 557 } 558 559 /** 560 * Poll stale refs and remove them. Call only while holding lock. 561 */ 562 private static void expungeStaleExceptions() { 563 for (Object x; (x = exceptionTableRefQueue.poll()) != null;) { 564 if (x instanceof ExceptionNode) { 565 ForkJoinTask<?> key = ((ExceptionNode)x).get(); 566 ExceptionNode[] t = exceptionTable; 567 int i = System.identityHashCode(key) & (t.length - 1); 568 ExceptionNode e = t[i]; 569 ExceptionNode pred = null; 570 while (e != null) { 571 ExceptionNode next = e.next; 572 if (e == x) { 573 if (pred == null) 574 t[i] = next; 575 else 576 pred.next = next; 577 break; 578 } 579 pred = e; 580 e = next; 581 } 582 } 583 } 584 } 585 586 /** 587 * If lock is available, poll stale refs and remove them. 588 * Called from ForkJoinPool when pools become quiescent. 589 */ 590 static final void helpExpungeStaleExceptions() { 591 final ReentrantLock lock = exceptionTableLock; 592 if (lock.tryLock()) { 593 try { 594 expungeStaleExceptions(); 595 } finally { 596 lock.unlock(); 597 } 598 } 599 } 600 601 /** 602 * A version of "sneaky throw" to relay exceptions 603 */ 604 static void rethrow(final Throwable ex) { 605 if (ex != null) { 606 if (ex instanceof Error) 607 throw (Error)ex; 608 if (ex instanceof RuntimeException) 609 throw (RuntimeException)ex; 610 throw uncheckedThrowable(ex, RuntimeException.class); 611 } 612 } 613 614 /** 615 * The sneaky part of sneaky throw, relying on generics 616 * limitations to evade compiler complaints about rethrowing 617 * unchecked exceptions 618 */ 619 @SuppressWarnings("unchecked") static <T extends Throwable> 620 T uncheckedThrowable(final Throwable t, final Class<T> c) { 621 return (T)t; // rely on vacuous cast 622 } 623 624 /** 625 * Throws exception, if any, associated with the given status. 626 */ 627 private void reportException(int s) { 628 if (s == CANCELLED) 629 throw new CancellationException(); 630 if (s == EXCEPTIONAL) 631 rethrow(getThrowableException()); 632 } 633 634 // public methods 635 636 /** 637 * Arranges to asynchronously execute this task in the pool the 638 * current task is running in, if applicable, or using the {@link 639 * ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. While 640 * it is not necessarily enforced, it is a usage error to fork a 641 * task more than once unless it has completed and been 642 * reinitialized. Subsequent modifications to the state of this 643 * task or any data it operates on are not necessarily 644 * consistently observable by any thread other than the one 645 * executing it unless preceded by a call to {@link #join} or 646 * related methods, or a call to {@link #isDone} returning {@code 647 * true}. 648 * 649 * @return {@code this}, to simplify usage 650 */ 651 public final ForkJoinTask<V> fork() { 652 Thread t; 653 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) 654 ((ForkJoinWorkerThread)t).workQueue.push(this); 655 else 656 ForkJoinPool.commonPool.externalPush(this); 657 return this; 658 } 659 660 /** 661 * Returns the result of the computation when it {@link #isDone is 662 * done}. This method differs from {@link #get()} in that 663 * abnormal completion results in {@code RuntimeException} or 664 * {@code Error}, not {@code ExecutionException}, and that 665 * interrupts of the calling thread do <em>not</em> cause the 666 * method to abruptly return by throwing {@code 667 * InterruptedException}. 668 * 669 * @return the computed result 670 */ 671 public final V join() { 672 int s; 673 if ((s = doJoin() & DONE_MASK) != NORMAL) 674 reportException(s); 675 return getRawResult(); 676 } 677 678 /** 679 * Commences performing this task, awaits its completion if 680 * necessary, and returns its result, or throws an (unchecked) 681 * {@code RuntimeException} or {@code Error} if the underlying 682 * computation did so. 683 * 684 * @return the computed result 685 */ 686 public final V invoke() { 687 int s; 688 if ((s = doInvoke() & DONE_MASK) != NORMAL) 689 reportException(s); 690 return getRawResult(); 691 } 692 693 /** 694 * Forks the given tasks, returning when {@code isDone} holds for 695 * each task or an (unchecked) exception is encountered, in which 696 * case the exception is rethrown. If more than one task 697 * encounters an exception, then this method throws any one of 698 * these exceptions. If any task encounters an exception, the 699 * other may be cancelled. However, the execution status of 700 * individual tasks is not guaranteed upon exceptional return. The 701 * status of each task may be obtained using {@link 702 * #getException()} and related methods to check if they have been 703 * cancelled, completed normally or exceptionally, or left 704 * unprocessed. 705 * 706 * @param t1 the first task 707 * @param t2 the second task 708 * @throws NullPointerException if any task is null 709 */ 710 public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) { 711 int s1, s2; 712 t2.fork(); 713 if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL) 714 t1.reportException(s1); 715 if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL) 716 t2.reportException(s2); 717 } 718 719 /** 720 * Forks the given tasks, returning when {@code isDone} holds for 721 * each task or an (unchecked) exception is encountered, in which 722 * case the exception is rethrown. If more than one task 723 * encounters an exception, then this method throws any one of 724 * these exceptions. If any task encounters an exception, others 725 * may be cancelled. However, the execution status of individual 726 * tasks is not guaranteed upon exceptional return. The status of 727 * each task may be obtained using {@link #getException()} and 728 * related methods to check if they have been cancelled, completed 729 * normally or exceptionally, or left unprocessed. 730 * 731 * @param tasks the tasks 732 * @throws NullPointerException if any task is null 733 */ 734 public static void invokeAll(ForkJoinTask<?>... tasks) { 735 Throwable ex = null; 736 int last = tasks.length - 1; 737 for (int i = last; i >= 0; --i) { 738 ForkJoinTask<?> t = tasks[i]; 739 if (t == null) { 740 if (ex == null) 741 ex = new NullPointerException(); 742 } 743 else if (i != 0) 744 t.fork(); 745 else if (t.doInvoke() < NORMAL && ex == null) 746 ex = t.getException(); 747 } 748 for (int i = 1; i <= last; ++i) { 749 ForkJoinTask<?> t = tasks[i]; 750 if (t != null) { 751 if (ex != null) 752 t.cancel(false); 753 else if (t.doJoin() < NORMAL) 754 ex = t.getException(); 755 } 756 } 757 if (ex != null) 758 rethrow(ex); 759 } 760 761 /** 762 * Forks all tasks in the specified collection, returning when 763 * {@code isDone} holds for each task or an (unchecked) exception 764 * is encountered, in which case the exception is rethrown. If 765 * more than one task encounters an exception, then this method 766 * throws any one of these exceptions. If any task encounters an 767 * exception, others may be cancelled. However, the execution 768 * status of individual tasks is not guaranteed upon exceptional 769 * return. The status of each task may be obtained using {@link 770 * #getException()} and related methods to check if they have been 771 * cancelled, completed normally or exceptionally, or left 772 * unprocessed. 773 * 774 * @param tasks the collection of tasks 775 * @return the tasks argument, to simplify usage 776 * @throws NullPointerException if tasks or any element are null 777 778 * @hide 779 */ 780 public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) { 781 if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) { 782 invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()])); 783 return tasks; 784 } 785 @SuppressWarnings("unchecked") 786 List<? extends ForkJoinTask<?>> ts = 787 (List<? extends ForkJoinTask<?>>) tasks; 788 Throwable ex = null; 789 int last = ts.size() - 1; 790 for (int i = last; i >= 0; --i) { 791 ForkJoinTask<?> t = ts.get(i); 792 if (t == null) { 793 if (ex == null) 794 ex = new NullPointerException(); 795 } 796 else if (i != 0) 797 t.fork(); 798 else if (t.doInvoke() < NORMAL && ex == null) 799 ex = t.getException(); 800 } 801 for (int i = 1; i <= last; ++i) { 802 ForkJoinTask<?> t = ts.get(i); 803 if (t != null) { 804 if (ex != null) 805 t.cancel(false); 806 else if (t.doJoin() < NORMAL) 807 ex = t.getException(); 808 } 809 } 810 if (ex != null) 811 rethrow(ex); 812 return tasks; 813 } 814 815 /** 816 * Attempts to cancel execution of this task. This attempt will 817 * fail if the task has already completed or could not be 818 * cancelled for some other reason. If successful, and this task 819 * has not started when {@code cancel} is called, execution of 820 * this task is suppressed. After this method returns 821 * successfully, unless there is an intervening call to {@link 822 * #reinitialize}, subsequent calls to {@link #isCancelled}, 823 * {@link #isDone}, and {@code cancel} will return {@code true} 824 * and calls to {@link #join} and related methods will result in 825 * {@code CancellationException}. 826 * 827 * <p>This method may be overridden in subclasses, but if so, must 828 * still ensure that these properties hold. In particular, the 829 * {@code cancel} method itself must not throw exceptions. 830 * 831 * <p>This method is designed to be invoked by <em>other</em> 832 * tasks. To terminate the current task, you can just return or 833 * throw an unchecked exception from its computation method, or 834 * invoke {@link #completeExceptionally}. 835 * 836 * @param mayInterruptIfRunning this value has no effect in the 837 * default implementation because interrupts are not used to 838 * control cancellation. 839 * 840 * @return {@code true} if this task is now cancelled 841 */ 842 public boolean cancel(boolean mayInterruptIfRunning) { 843 return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED; 844 } 845 846 public final boolean isDone() { 847 return status < 0; 848 } 849 850 public final boolean isCancelled() { 851 return (status & DONE_MASK) == CANCELLED; 852 } 853 854 /** 855 * Returns {@code true} if this task threw an exception or was cancelled. 856 * 857 * @return {@code true} if this task threw an exception or was cancelled 858 */ 859 public final boolean isCompletedAbnormally() { 860 return status < NORMAL; 861 } 862 863 /** 864 * Returns {@code true} if this task completed without throwing an 865 * exception and was not cancelled. 866 * 867 * @return {@code true} if this task completed without throwing an 868 * exception and was not cancelled 869 */ 870 public final boolean isCompletedNormally() { 871 return (status & DONE_MASK) == NORMAL; 872 } 873 874 /** 875 * Returns the exception thrown by the base computation, or a 876 * {@code CancellationException} if cancelled, or {@code null} if 877 * none or if the method has not yet completed. 878 * 879 * @return the exception, or {@code null} if none 880 */ 881 public final Throwable getException() { 882 int s = status & DONE_MASK; 883 return ((s >= NORMAL) ? null : 884 (s == CANCELLED) ? new CancellationException() : 885 getThrowableException()); 886 } 887 888 /** 889 * Completes this task abnormally, and if not already aborted or 890 * cancelled, causes it to throw the given exception upon 891 * {@code join} and related operations. This method may be used 892 * to induce exceptions in asynchronous tasks, or to force 893 * completion of tasks that would not otherwise complete. Its use 894 * in other situations is discouraged. This method is 895 * overridable, but overridden versions must invoke {@code super} 896 * implementation to maintain guarantees. 897 * 898 * @param ex the exception to throw. If this exception is not a 899 * {@code RuntimeException} or {@code Error}, the actual exception 900 * thrown will be a {@code RuntimeException} with cause {@code ex}. 901 */ 902 public void completeExceptionally(Throwable ex) { 903 setExceptionalCompletion((ex instanceof RuntimeException) || 904 (ex instanceof Error) ? ex : 905 new RuntimeException(ex)); 906 } 907 908 /** 909 * Completes this task, and if not already aborted or cancelled, 910 * returning the given value as the result of subsequent 911 * invocations of {@code join} and related operations. This method 912 * may be used to provide results for asynchronous tasks, or to 913 * provide alternative handling for tasks that would not otherwise 914 * complete normally. Its use in other situations is 915 * discouraged. This method is overridable, but overridden 916 * versions must invoke {@code super} implementation to maintain 917 * guarantees. 918 * 919 * @param value the result value for this task 920 */ 921 public void complete(V value) { 922 try { 923 setRawResult(value); 924 } catch (Throwable rex) { 925 setExceptionalCompletion(rex); 926 return; 927 } 928 setCompletion(NORMAL); 929 } 930 931 /** 932 * Completes this task normally without setting a value. The most 933 * recent value established by {@link #setRawResult} (or {@code 934 * null} by default) will be returned as the result of subsequent 935 * invocations of {@code join} and related operations. 936 * 937 * @since 1.8 938 * @hide 939 */ 940 public final void quietlyComplete() { 941 setCompletion(NORMAL); 942 } 943 944 /** 945 * Waits if necessary for the computation to complete, and then 946 * retrieves its result. 947 * 948 * @return the computed result 949 * @throws CancellationException if the computation was cancelled 950 * @throws ExecutionException if the computation threw an 951 * exception 952 * @throws InterruptedException if the current thread is not a 953 * member of a ForkJoinPool and was interrupted while waiting 954 */ 955 public final V get() throws InterruptedException, ExecutionException { 956 int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ? 957 doJoin() : externalInterruptibleAwaitDone(); 958 Throwable ex; 959 if ((s &= DONE_MASK) == CANCELLED) 960 throw new CancellationException(); 961 if (s == EXCEPTIONAL && (ex = getThrowableException()) != null) 962 throw new ExecutionException(ex); 963 return getRawResult(); 964 } 965 966 /** 967 * Waits if necessary for at most the given time for the computation 968 * to complete, and then retrieves its result, if available. 969 * 970 * @param timeout the maximum time to wait 971 * @param unit the time unit of the timeout argument 972 * @return the computed result 973 * @throws CancellationException if the computation was cancelled 974 * @throws ExecutionException if the computation threw an 975 * exception 976 * @throws InterruptedException if the current thread is not a 977 * member of a ForkJoinPool and was interrupted while waiting 978 * @throws TimeoutException if the wait timed out 979 */ 980 public final V get(long timeout, TimeUnit unit) 981 throws InterruptedException, ExecutionException, TimeoutException { 982 if (Thread.interrupted()) 983 throw new InterruptedException(); 984 // Messy in part because we measure in nanosecs, but wait in millisecs 985 int s; long ms; 986 long ns = unit.toNanos(timeout); 987 if ((s = status) >= 0 && ns > 0L) { 988 long deadline = System.nanoTime() + ns; 989 ForkJoinPool p = null; 990 ForkJoinPool.WorkQueue w = null; 991 Thread t = Thread.currentThread(); 992 if (t instanceof ForkJoinWorkerThread) { 993 ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; 994 p = wt.pool; 995 w = wt.workQueue; 996 p.helpJoinOnce(w, this); // no retries on failure 997 } 998 else 999 ForkJoinPool.externalHelpJoin(this); 1000 boolean canBlock = false; 1001 boolean interrupted = false; 1002 try { 1003 while ((s = status) >= 0) { 1004 if (w != null && w.qlock < 0) 1005 cancelIgnoringExceptions(this); 1006 else if (!canBlock) { 1007 if (p == null || p.tryCompensate()) 1008 canBlock = true; 1009 } 1010 else { 1011 if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L && 1012 U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { 1013 synchronized (this) { 1014 if (status >= 0) { 1015 try { 1016 wait(ms); 1017 } catch (InterruptedException ie) { 1018 if (p == null) 1019 interrupted = true; 1020 } 1021 } 1022 else 1023 notifyAll(); 1024 } 1025 } 1026 if ((s = status) < 0 || interrupted || 1027 (ns = deadline - System.nanoTime()) <= 0L) 1028 break; 1029 } 1030 } 1031 } finally { 1032 if (p != null && canBlock) 1033 p.incrementActiveCount(); 1034 } 1035 if (interrupted) 1036 throw new InterruptedException(); 1037 } 1038 if ((s &= DONE_MASK) != NORMAL) { 1039 Throwable ex; 1040 if (s == CANCELLED) 1041 throw new CancellationException(); 1042 if (s != EXCEPTIONAL) 1043 throw new TimeoutException(); 1044 if ((ex = getThrowableException()) != null) 1045 throw new ExecutionException(ex); 1046 } 1047 return getRawResult(); 1048 } 1049 1050 /** 1051 * Joins this task, without returning its result or throwing its 1052 * exception. This method may be useful when processing 1053 * collections of tasks when some have been cancelled or otherwise 1054 * known to have aborted. 1055 */ 1056 public final void quietlyJoin() { 1057 doJoin(); 1058 } 1059 1060 /** 1061 * Commences performing this task and awaits its completion if 1062 * necessary, without returning its result or throwing its 1063 * exception. 1064 */ 1065 public final void quietlyInvoke() { 1066 doInvoke(); 1067 } 1068 1069 /** 1070 * Possibly executes tasks until the pool hosting the current task 1071 * {@link ForkJoinPool#isQuiescent is quiescent}. This method may 1072 * be of use in designs in which many tasks are forked, but none 1073 * are explicitly joined, instead executing them until all are 1074 * processed. 1075 */ 1076 public static void helpQuiesce() { 1077 Thread t; 1078 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) { 1079 ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; 1080 wt.pool.helpQuiescePool(wt.workQueue); 1081 } 1082 else 1083 ForkJoinPool.externalHelpQuiescePool(); 1084 } 1085 1086 /** 1087 * Resets the internal bookkeeping state of this task, allowing a 1088 * subsequent {@code fork}. This method allows repeated reuse of 1089 * this task, but only if reuse occurs when this task has either 1090 * never been forked, or has been forked, then completed and all 1091 * outstanding joins of this task have also completed. Effects 1092 * under any other usage conditions are not guaranteed. 1093 * This method may be useful when executing 1094 * pre-constructed trees of subtasks in loops. 1095 * 1096 * <p>Upon completion of this method, {@code isDone()} reports 1097 * {@code false}, and {@code getException()} reports {@code 1098 * null}. However, the value returned by {@code getRawResult} is 1099 * unaffected. To clear this value, you can invoke {@code 1100 * setRawResult(null)}. 1101 */ 1102 public void reinitialize() { 1103 if ((status & DONE_MASK) == EXCEPTIONAL) 1104 clearExceptionalCompletion(); 1105 else 1106 status = 0; 1107 } 1108 1109 /** 1110 * Returns the pool hosting the current task execution, or null 1111 * if this task is executing outside of any ForkJoinPool. 1112 * 1113 * @see #inForkJoinPool 1114 * @return the pool, or {@code null} if none 1115 */ 1116 public static ForkJoinPool getPool() { 1117 Thread t = Thread.currentThread(); 1118 return (t instanceof ForkJoinWorkerThread) ? 1119 ((ForkJoinWorkerThread) t).pool : null; 1120 } 1121 1122 /** 1123 * Returns {@code true} if the current thread is a {@link 1124 * ForkJoinWorkerThread} executing as a ForkJoinPool computation. 1125 * 1126 * @return {@code true} if the current thread is a {@link 1127 * ForkJoinWorkerThread} executing as a ForkJoinPool computation, 1128 * or {@code false} otherwise 1129 */ 1130 public static boolean inForkJoinPool() { 1131 return Thread.currentThread() instanceof ForkJoinWorkerThread; 1132 } 1133 1134 /** 1135 * Tries to unschedule this task for execution. This method will 1136 * typically (but is not guaranteed to) succeed if this task is 1137 * the most recently forked task by the current thread, and has 1138 * not commenced executing in another thread. This method may be 1139 * useful when arranging alternative local processing of tasks 1140 * that could have been, but were not, stolen. 1141 * 1142 * @return {@code true} if unforked 1143 */ 1144 public boolean tryUnfork() { 1145 Thread t; 1146 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? 1147 ((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) : 1148 ForkJoinPool.tryExternalUnpush(this)); 1149 } 1150 1151 /** 1152 * Returns an estimate of the number of tasks that have been 1153 * forked by the current worker thread but not yet executed. This 1154 * value may be useful for heuristic decisions about whether to 1155 * fork other tasks. 1156 * 1157 * @return the number of tasks 1158 */ 1159 public static int getQueuedTaskCount() { 1160 Thread t; ForkJoinPool.WorkQueue q; 1161 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) 1162 q = ((ForkJoinWorkerThread)t).workQueue; 1163 else 1164 q = ForkJoinPool.commonSubmitterQueue(); 1165 return (q == null) ? 0 : q.queueSize(); 1166 } 1167 1168 /** 1169 * Returns an estimate of how many more locally queued tasks are 1170 * held by the current worker thread than there are other worker 1171 * threads that might steal them, or zero if this thread is not 1172 * operating in a ForkJoinPool. This value may be useful for 1173 * heuristic decisions about whether to fork other tasks. In many 1174 * usages of ForkJoinTasks, at steady state, each worker should 1175 * aim to maintain a small constant surplus (for example, 3) of 1176 * tasks, and to process computations locally if this threshold is 1177 * exceeded. 1178 * 1179 * @return the surplus number of tasks, which may be negative 1180 */ 1181 public static int getSurplusQueuedTaskCount() { 1182 return ForkJoinPool.getSurplusQueuedTaskCount(); 1183 } 1184 1185 // Extension methods 1186 1187 /** 1188 * Returns the result that would be returned by {@link #join}, even 1189 * if this task completed abnormally, or {@code null} if this task 1190 * is not known to have been completed. This method is designed 1191 * to aid debugging, as well as to support extensions. Its use in 1192 * any other context is discouraged. 1193 * 1194 * @return the result, or {@code null} if not completed 1195 */ 1196 public abstract V getRawResult(); 1197 1198 /** 1199 * Forces the given value to be returned as a result. This method 1200 * is designed to support extensions, and should not in general be 1201 * called otherwise. 1202 * 1203 * @param value the value 1204 */ 1205 protected abstract void setRawResult(V value); 1206 1207 /** 1208 * Immediately performs the base action of this task and returns 1209 * true if, upon return from this method, this task is guaranteed 1210 * to have completed normally. This method may return false 1211 * otherwise, to indicate that this task is not necessarily 1212 * complete (or is not known to be complete), for example in 1213 * asynchronous actions that require explicit invocations of 1214 * completion methods. This method may also throw an (unchecked) 1215 * exception to indicate abnormal exit. This method is designed to 1216 * support extensions, and should not in general be called 1217 * otherwise. 1218 * 1219 * @return {@code true} if this task is known to have completed normally 1220 */ 1221 protected abstract boolean exec(); 1222 1223 /** 1224 * Returns, but does not unschedule or execute, a task queued by 1225 * the current thread but not yet executed, if one is immediately 1226 * available. There is no guarantee that this task will actually 1227 * be polled or executed next. Conversely, this method may return 1228 * null even if a task exists but cannot be accessed without 1229 * contention with other threads. This method is designed 1230 * primarily to support extensions, and is unlikely to be useful 1231 * otherwise. 1232 * 1233 * @return the next task, or {@code null} if none are available 1234 */ 1235 protected static ForkJoinTask<?> peekNextLocalTask() { 1236 Thread t; ForkJoinPool.WorkQueue q; 1237 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) 1238 q = ((ForkJoinWorkerThread)t).workQueue; 1239 else 1240 q = ForkJoinPool.commonSubmitterQueue(); 1241 return (q == null) ? null : q.peek(); 1242 } 1243 1244 /** 1245 * Unschedules and returns, without executing, the next task 1246 * queued by the current thread but not yet executed, if the 1247 * current thread is operating in a ForkJoinPool. This method is 1248 * designed primarily to support extensions, and is unlikely to be 1249 * useful otherwise. 1250 * 1251 * @return the next task, or {@code null} if none are available 1252 */ 1253 protected static ForkJoinTask<?> pollNextLocalTask() { 1254 Thread t; 1255 return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? 1256 ((ForkJoinWorkerThread)t).workQueue.nextLocalTask() : 1257 null; 1258 } 1259 1260 /** 1261 * If the current thread is operating in a ForkJoinPool, 1262 * unschedules and returns, without executing, the next task 1263 * queued by the current thread but not yet executed, if one is 1264 * available, or if not available, a task that was forked by some 1265 * other thread, if available. Availability may be transient, so a 1266 * {@code null} result does not necessarily imply quiescence of 1267 * the pool this task is operating in. This method is designed 1268 * primarily to support extensions, and is unlikely to be useful 1269 * otherwise. 1270 * 1271 * @return a task, or {@code null} if none are available 1272 */ 1273 protected static ForkJoinTask<?> pollTask() { 1274 Thread t; ForkJoinWorkerThread wt; 1275 return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? 1276 (wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) : 1277 null; 1278 } 1279 1280 // tag operations 1281 1282 /** 1283 * Returns the tag for this task. 1284 * 1285 * @return the tag for this task 1286 * @since 1.8 1287 * @hide 1288 */ 1289 public final short getForkJoinTaskTag() { 1290 return (short)status; 1291 } 1292 1293 /** 1294 * Atomically sets the tag value for this task. 1295 * 1296 * @param tag the tag value 1297 * @return the previous value of the tag 1298 * @since 1.8 1299 * @hide 1300 */ 1301 public final short setForkJoinTaskTag(short tag) { 1302 for (int s;;) { 1303 if (U.compareAndSwapInt(this, STATUS, s = status, 1304 (s & ~SMASK) | (tag & SMASK))) 1305 return (short)s; 1306 } 1307 } 1308 1309 /** 1310 * Atomically conditionally sets the tag value for this task. 1311 * Among other applications, tags can be used as visit markers 1312 * in tasks operating on graphs, as in methods that check: {@code 1313 * if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))} 1314 * before processing, otherwise exiting because the node has 1315 * already been visited. 1316 * 1317 * @param e the expected tag value 1318 * @param tag the new tag value 1319 * @return true if successful; i.e., the current value was 1320 * equal to e and is now tag. 1321 * @since 1.8 1322 * @hide 1323 */ 1324 public final boolean compareAndSetForkJoinTaskTag(short e, short tag) { 1325 for (int s;;) { 1326 if ((short)(s = status) != e) 1327 return false; 1328 if (U.compareAndSwapInt(this, STATUS, s, 1329 (s & ~SMASK) | (tag & SMASK))) 1330 return true; 1331 } 1332 } 1333 1334 /** 1335 * Adaptor for Runnables. This implements RunnableFuture 1336 * to be compliant with AbstractExecutorService constraints 1337 * when used in ForkJoinPool. 1338 */ 1339 static final class AdaptedRunnable<T> extends ForkJoinTask<T> 1340 implements RunnableFuture<T> { 1341 final Runnable runnable; 1342 T result; 1343 AdaptedRunnable(Runnable runnable, T result) { 1344 if (runnable == null) throw new NullPointerException(); 1345 this.runnable = runnable; 1346 this.result = result; // OK to set this even before completion 1347 } 1348 public final T getRawResult() { return result; } 1349 public final void setRawResult(T v) { result = v; } 1350 public final boolean exec() { runnable.run(); return true; } 1351 public final void run() { invoke(); } 1352 private static final long serialVersionUID = 5232453952276885070L; 1353 } 1354 1355 /** 1356 * Adaptor for Runnables without results 1357 */ 1358 static final class AdaptedRunnableAction extends ForkJoinTask<Void> 1359 implements RunnableFuture<Void> { 1360 final Runnable runnable; 1361 AdaptedRunnableAction(Runnable runnable) { 1362 if (runnable == null) throw new NullPointerException(); 1363 this.runnable = runnable; 1364 } 1365 public final Void getRawResult() { return null; } 1366 public final void setRawResult(Void v) { } 1367 public final boolean exec() { runnable.run(); return true; } 1368 public final void run() { invoke(); } 1369 private static final long serialVersionUID = 5232453952276885070L; 1370 } 1371 1372 /** 1373 * Adaptor for Callables 1374 */ 1375 static final class AdaptedCallable<T> extends ForkJoinTask<T> 1376 implements RunnableFuture<T> { 1377 final Callable<? extends T> callable; 1378 T result; 1379 AdaptedCallable(Callable<? extends T> callable) { 1380 if (callable == null) throw new NullPointerException(); 1381 this.callable = callable; 1382 } 1383 public final T getRawResult() { return result; } 1384 public final void setRawResult(T v) { result = v; } 1385 public final boolean exec() { 1386 try { 1387 result = callable.call(); 1388 return true; 1389 } catch (Error err) { 1390 throw err; 1391 } catch (RuntimeException rex) { 1392 throw rex; 1393 } catch (Exception ex) { 1394 throw new RuntimeException(ex); 1395 } 1396 } 1397 public final void run() { invoke(); } 1398 private static final long serialVersionUID = 2838392045355241008L; 1399 } 1400 1401 /** 1402 * Returns a new {@code ForkJoinTask} that performs the {@code run} 1403 * method of the given {@code Runnable} as its action, and returns 1404 * a null result upon {@link #join}. 1405 * 1406 * @param runnable the runnable action 1407 * @return the task 1408 */ 1409 public static ForkJoinTask<?> adapt(Runnable runnable) { 1410 return new AdaptedRunnableAction(runnable); 1411 } 1412 1413 /** 1414 * Returns a new {@code ForkJoinTask} that performs the {@code run} 1415 * method of the given {@code Runnable} as its action, and returns 1416 * the given result upon {@link #join}. 1417 * 1418 * @param runnable the runnable action 1419 * @param result the result upon completion 1420 * @return the task 1421 */ 1422 public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) { 1423 return new AdaptedRunnable<T>(runnable, result); 1424 } 1425 1426 /** 1427 * Returns a new {@code ForkJoinTask} that performs the {@code call} 1428 * method of the given {@code Callable} as its action, and returns 1429 * its result upon {@link #join}, translating any checked exceptions 1430 * encountered into {@code RuntimeException}. 1431 * 1432 * @param callable the callable action 1433 * @return the task 1434 */ 1435 public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) { 1436 return new AdaptedCallable<T>(callable); 1437 } 1438 1439 // Serialization support 1440 1441 private static final long serialVersionUID = -7721805057305804111L; 1442 1443 /** 1444 * Saves this task to a stream (that is, serializes it). 1445 * 1446 * @serialData the current run status and the exception thrown 1447 * during execution, or {@code null} if none 1448 */ 1449 private void writeObject(java.io.ObjectOutputStream s) 1450 throws java.io.IOException { 1451 s.defaultWriteObject(); 1452 s.writeObject(getException()); 1453 } 1454 1455 /** 1456 * Reconstitutes this task from a stream (that is, deserializes it). 1457 */ 1458 private void readObject(java.io.ObjectInputStream s) 1459 throws java.io.IOException, ClassNotFoundException { 1460 s.defaultReadObject(); 1461 Object ex = s.readObject(); 1462 if (ex != null) 1463 setExceptionalCompletion((Throwable)ex); 1464 } 1465 1466 // Unsafe mechanics 1467 private static final sun.misc.Unsafe U; 1468 private static final long STATUS; 1469 1470 static { 1471 exceptionTableLock = new ReentrantLock(); 1472 exceptionTableRefQueue = new ReferenceQueue<Object>(); 1473 exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY]; 1474 try { 1475 U = sun.misc.Unsafe.getUnsafe(); 1476 Class<?> k = ForkJoinTask.class; 1477 STATUS = U.objectFieldOffset 1478 (k.getDeclaredField("status")); 1479 } catch (Exception e) { 1480 throw new Error(e); 1481 } 1482 } 1483 1484 } 1485