--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/util/concurrent/ForkJoinTask.java Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,1527 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package java.util.concurrent;
+
+import java.io.Serializable;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.WeakReference;
+import java.lang.reflect.Constructor;
+import java.util.Collection;
+import java.util.List;
+import java.util.RandomAccess;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * Abstract base class for tasks that run within a {@link ForkJoinPool}.
+ * A {@code ForkJoinTask} is a thread-like entity that is much
+ * lighter weight than a normal thread. Huge numbers of tasks and
+ * subtasks may be hosted by a small number of actual threads in a
+ * ForkJoinPool, at the price of some usage limitations.
+ *
+ * <p>A "main" {@code ForkJoinTask} begins execution when it is
+ * explicitly submitted to a {@link ForkJoinPool}, or, if not already
+ * engaged in a ForkJoin computation, commenced in the {@link
+ * ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or
+ * related methods. Once started, it will usually in turn start other
+ * subtasks. As indicated by the name of this class, many programs
+ * using {@code ForkJoinTask} employ only methods {@link #fork} and
+ * {@link #join}, or derivatives such as {@link
+ * #invokeAll(ForkJoinTask...) invokeAll}. However, this class also
+ * provides a number of other methods that can come into play in
+ * advanced usages, as well as extension mechanics that allow support
+ * of new forms of fork/join processing.
+ *
+ * <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
+ * The efficiency of {@code ForkJoinTask}s stems from a set of
+ * restrictions (that are only partially statically enforceable)
+ * reflecting their main use as computational tasks calculating pure
+ * functions or operating on purely isolated objects. The primary
+ * coordination mechanisms are {@link #fork}, that arranges
+ * asynchronous execution, and {@link #join}, that doesn't proceed
+ * until the task's result has been computed. Computations should
+ * ideally avoid {@code synchronized} methods or blocks, and should
+ * minimize other blocking synchronization apart from joining other
+ * tasks or using synchronizers such as Phasers that are advertised to
+ * cooperate with fork/join scheduling. Subdividable tasks should also
+ * not perform blocking I/O, and should ideally access variables that
+ * are completely independent of those accessed by other running
+ * tasks. These guidelines are loosely enforced by not permitting
+ * checked exceptions such as {@code IOExceptions} to be
+ * thrown. However, computations may still encounter unchecked
+ * exceptions, that are rethrown to callers attempting to join
+ * them. These exceptions may additionally include {@link
+ * RejectedExecutionException} stemming from internal resource
+ * exhaustion, such as failure to allocate internal task
+ * queues. Rethrown exceptions behave in the same way as regular
+ * exceptions, but, when possible, contain stack traces (as displayed
+ * for example using {@code ex.printStackTrace()}) of both the thread
+ * that initiated the computation as well as the thread actually
+ * encountering the exception; minimally only the latter.
+ *
+ * <p>It is possible to define and use ForkJoinTasks that may block,
+ * but doing so requires three further considerations: (1) Completion
+ * of few if any <em>other</em> tasks should be dependent on a task
+ * that blocks on external synchronization or I/O. Event-style async
+ * tasks that are never joined (for example, those subclassing {@link
+ * CountedCompleter}) often fall into this category. (2) To minimize
+ * resource impact, tasks should be small; ideally performing only the
+ * (possibly) blocking action. (3) Unless the {@link
+ * ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
+ * blocked tasks is known to be less than the pool's {@link
+ * ForkJoinPool#getParallelism} level, the pool cannot guarantee that
+ * enough threads will be available to ensure progress or good
+ * performance.
+ *
+ * <p>The primary method for awaiting completion and extracting
+ * results of a task is {@link #join}, but there are several variants:
+ * The {@link Future#get} methods support interruptible and/or timed
+ * waits for completion and report results using {@code Future}
+ * conventions. Method {@link #invoke} is semantically
+ * equivalent to {@code fork(); join()} but always attempts to begin
+ * execution in the current thread. The "<em>quiet</em>" forms of
+ * these methods do not extract results or report exceptions. These
+ * may be useful when a set of tasks are being executed, and you need
+ * to delay processing of results or exceptions until all complete.
+ * Method {@code invokeAll} (available in multiple versions)
+ * performs the most common form of parallel invocation: forking a set
+ * of tasks and joining them all.
+ *
+ * <p>In the most typical usages, a fork-join pair act like a call
+ * (fork) and return (join) from a parallel recursive function. As is
+ * the case with other forms of recursive calls, returns (joins)
+ * should be performed innermost-first. For example, {@code a.fork();
+ * b.fork(); b.join(); a.join();} is likely to be substantially more
+ * efficient than joining {@code a} before {@code b}.
+ *
+ * <p>The execution status of tasks may be queried at several levels
+ * of detail: {@link #isDone} is true if a task completed in any way
+ * (including the case where a task was cancelled without executing);
+ * {@link #isCompletedNormally} is true if a task completed without
+ * cancellation or encountering an exception; {@link #isCancelled} is
+ * true if the task was cancelled (in which case {@link #getException}
+ * returns a {@link CancellationException}); and
+ * {@link #isCompletedAbnormally} is true if a task was either
+ * cancelled or encountered an exception, in which case {@link
+ * #getException} will return either the encountered exception or
+ * {@link CancellationException}.
+ *
+ * <p>The ForkJoinTask class is not usually directly subclassed.
+ * Instead, you subclass one of the abstract classes that support a
+ * particular style of fork/join processing, typically {@link
+ * RecursiveAction} for most computations that do not return results,
+ * {@link RecursiveTask} for those that do, and {@link
+ * CountedCompleter} for those in which completed actions trigger
+ * other actions. Normally, a concrete ForkJoinTask subclass declares
+ * fields comprising its parameters, established in a constructor, and
+ * then defines a {@code compute} method that somehow uses the control
+ * methods supplied by this base class.
+ *
+ * <p>Method {@link #join} and its variants are appropriate for use
+ * only when completion dependencies are acyclic; that is, the
+ * parallel computation can be described as a directed acyclic graph
+ * (DAG). Otherwise, executions may encounter a form of deadlock as
+ * tasks cyclically wait for each other. However, this framework
+ * supports other methods and techniques (for example the use of
+ * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
+ * may be of use in constructing custom subclasses for problems that
+ * are not statically structured as DAGs. To support such usages, a
+ * ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
+ * value using {@link #setForkJoinTaskTag} or {@link
+ * #compareAndSetForkJoinTaskTag} and checked using {@link
+ * #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
+ * these {@code protected} methods or tags for any purpose, but they
+ * may be of use in the construction of specialized subclasses. For
+ * example, parallel graph traversals can use the supplied methods to
+ * avoid revisiting nodes/tasks that have already been processed.
+ * (Method names for tagging are bulky in part to encourage definition
+ * of methods that reflect their usage patterns.)
+ *
+ * <p>Most base support methods are {@code final}, to prevent
+ * overriding of implementations that are intrinsically tied to the
+ * underlying lightweight task scheduling framework. Developers
+ * creating new basic styles of fork/join processing should minimally
+ * implement {@code protected} methods {@link #exec}, {@link
+ * #setRawResult}, and {@link #getRawResult}, while also introducing
+ * an abstract computational method that can be implemented in its
+ * subclasses, possibly relying on other {@code protected} methods
+ * provided by this class.
+ *
+ * <p>ForkJoinTasks should perform relatively small amounts of
+ * computation. Large tasks should be split into smaller subtasks,
+ * usually via recursive decomposition. As a very rough rule of thumb,
+ * a task should perform more than 100 and less than 10000 basic
+ * computational steps, and should avoid indefinite looping. If tasks
+ * are too big, then parallelism cannot improve throughput. If too
+ * small, then memory and internal task maintenance overhead may
+ * overwhelm processing.
+ *
+ * <p>This class provides {@code adapt} methods for {@link Runnable}
+ * and {@link Callable}, that may be of use when mixing execution of
+ * {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
+ * of this form, consider using a pool constructed in <em>asyncMode</em>.
+ *
+ * <p>ForkJoinTasks are {@code Serializable}, which enables them to be
+ * used in extensions such as remote execution frameworks. It is
+ * sensible to serialize tasks only before or after, but not during,
+ * execution. Serialization is not relied on during execution itself.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
+
+ /*
+ * See the internal documentation of class ForkJoinPool for a
+ * general implementation overview. ForkJoinTasks are mainly
+ * responsible for maintaining their "status" field amidst relays
+ * to methods in ForkJoinWorkerThread and ForkJoinPool.
+ *
+ * The methods of this class are more-or-less layered into
+ * (1) basic status maintenance
+ * (2) execution and awaiting completion
+ * (3) user-level methods that additionally report results.
+ * This is sometimes hard to see because this file orders exported
+ * methods in a way that flows well in javadocs.
+ */
+
+ /*
+ * The status field holds run control status bits packed into a
+ * single int to minimize footprint and to ensure atomicity (via
+ * CAS). Status is initially zero, and takes on nonnegative
+ * values until completed, upon which status (anded with
+ * DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks
+ * undergoing blocking waits by other threads have the SIGNAL bit
+ * set. Completion of a stolen task with SIGNAL set awakens any
+ * waiters via notifyAll. Even though suboptimal for some
+ * purposes, we use basic builtin wait/notify to take advantage of
+ * "monitor inflation" in JVMs that we would otherwise need to
+ * emulate to avoid adding further per-task bookkeeping overhead.
+ * We want these monitors to be "fat", i.e., not use biasing or
+ * thin-lock techniques, so use some odd coding idioms that tend
+ * to avoid them, mainly by arranging that every synchronized
+ * block performs a wait, notifyAll or both.
+ *
+ * These control bits occupy only (some of) the upper half (16
+ * bits) of status field. The lower bits are used for user-defined
+ * tags.
+ */
+
+ /** The run status of this task */
+ volatile int status; // accessed directly by pool and workers
+ static final int DONE_MASK = 0xf0000000; // mask out non-completion bits
+ static final int NORMAL = 0xf0000000; // must be negative
+ static final int CANCELLED = 0xc0000000; // must be < NORMAL
+ static final int EXCEPTIONAL = 0x80000000; // must be < CANCELLED
+ static final int SIGNAL = 0x00010000; // must be >= 1 << 16
+ static final int SMASK = 0x0000ffff; // short bits for tags
+
+ /**
+ * Marks completion and wakes up threads waiting to join this
+ * task.
+ *
+ * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
+ * @return completion status on exit
+ */
+ private int setCompletion(int completion) {
+ for (int s;;) {
+ if ((s = status) < 0)
+ return s;
+ if (STATUS.compareAndSet(this, s, s | completion)) {
+ if ((s >>> 16) != 0)
+ synchronized (this) { notifyAll(); }
+ return completion;
+ }
+ }
+ }
+
+ /**
+ * Primary execution method for stolen tasks. Unless done, calls
+ * exec and records status if completed, but doesn't wait for
+ * completion otherwise.
+ *
+ * @return status on exit from this method
+ */
+ final int doExec() {
+ int s; boolean completed;
+ if ((s = status) >= 0) {
+ try {
+ completed = exec();
+ } catch (Throwable rex) {
+ return setExceptionalCompletion(rex);
+ }
+ if (completed)
+ s = setCompletion(NORMAL);
+ }
+ return s;
+ }
+
+ /**
+ * If not done, sets SIGNAL status and performs Object.wait(timeout).
+ * This task may or may not be done on exit. Ignores interrupts.
+ *
+ * @param timeout using Object.wait conventions.
+ */
+ final void internalWait(long timeout) {
+ int s;
+ if ((s = status) >= 0 && // force completer to issue notify
+ STATUS.compareAndSet(this, s, s | SIGNAL)) {
+ synchronized (this) {
+ if (status >= 0)
+ try { wait(timeout); } catch (InterruptedException ie) { }
+ else
+ notifyAll();
+ }
+ }
+ }
+
+ /**
+ * Blocks a non-worker-thread until completion.
+ * @return status upon completion
+ */
+ private int externalAwaitDone() {
+ int s = ((this instanceof CountedCompleter) ? // try helping
+ ForkJoinPool.common.externalHelpComplete(
+ (CountedCompleter<?>)this, 0) :
+ ForkJoinPool.common.tryExternalUnpush(this) ? doExec() : 0);
+ if (s >= 0 && (s = status) >= 0) {
+ boolean interrupted = false;
+ do {
+ if (STATUS.compareAndSet(this, s, s | SIGNAL)) {
+ synchronized (this) {
+ if (status >= 0) {
+ try {
+ wait(0L);
+ } catch (InterruptedException ie) {
+ interrupted = true;
+ }
+ }
+ else
+ notifyAll();
+ }
+ }
+ } while ((s = status) >= 0);
+ if (interrupted)
+ Thread.currentThread().interrupt();
+ }
+ return s;
+ }
+
+ /**
+ * Blocks a non-worker-thread until completion or interruption.
+ */
+ private int externalInterruptibleAwaitDone() throws InterruptedException {
+ int s;
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ if ((s = status) >= 0 &&
+ (s = ((this instanceof CountedCompleter) ?
+ ForkJoinPool.common.externalHelpComplete(
+ (CountedCompleter<?>)this, 0) :
+ ForkJoinPool.common.tryExternalUnpush(this) ? doExec() :
+ 0)) >= 0) {
+ while ((s = status) >= 0) {
+ if (STATUS.compareAndSet(this, s, s | SIGNAL)) {
+ synchronized (this) {
+ if (status >= 0)
+ wait(0L);
+ else
+ notifyAll();
+ }
+ }
+ }
+ }
+ return s;
+ }
+
+ /**
+ * Implementation for join, get, quietlyJoin. Directly handles
+ * only cases of already-completed, external wait, and
+ * unfork+exec. Others are relayed to ForkJoinPool.awaitJoin.
+ *
+ * @return status upon completion
+ */
+ private int doJoin() {
+ int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
+ return (s = status) < 0 ? s :
+ ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
+ (w = (wt = (ForkJoinWorkerThread)t).workQueue).
+ tryUnpush(this) && (s = doExec()) < 0 ? s :
+ wt.pool.awaitJoin(w, this, 0L) :
+ externalAwaitDone();
+ }
+
+ /**
+ * Implementation for invoke, quietlyInvoke.
+ *
+ * @return status upon completion
+ */
+ private int doInvoke() {
+ int s; Thread t; ForkJoinWorkerThread wt;
+ return (s = doExec()) < 0 ? s :
+ ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
+ (wt = (ForkJoinWorkerThread)t).pool.
+ awaitJoin(wt.workQueue, this, 0L) :
+ externalAwaitDone();
+ }
+
+ // Exception table support
+
+ /**
+ * Hash table of exceptions thrown by tasks, to enable reporting
+ * by callers. Because exceptions are rare, we don't directly keep
+ * them with task objects, but instead use a weak ref table. Note
+ * that cancellation exceptions don't appear in the table, but are
+ * instead recorded as status values.
+ *
+ * The exception table has a fixed capacity.
+ */
+ private static final ExceptionNode[] exceptionTable
+ = new ExceptionNode[32];
+
+ /** Lock protecting access to exceptionTable. */
+ private static final ReentrantLock exceptionTableLock
+ = new ReentrantLock();
+
+ /** Reference queue of stale exceptionally completed tasks. */
+ private static final ReferenceQueue<ForkJoinTask<?>> exceptionTableRefQueue
+ = new ReferenceQueue<>();
+
+ /**
+ * Key-value nodes for exception table. The chained hash table
+ * uses identity comparisons, full locking, and weak references
+ * for keys. The table has a fixed capacity because it only
+ * maintains task exceptions long enough for joiners to access
+ * them, so should never become very large for sustained
+ * periods. However, since we do not know when the last joiner
+ * completes, we must use weak references and expunge them. We do
+ * so on each operation (hence full locking). Also, some thread in
+ * any ForkJoinPool will call helpExpungeStaleExceptions when its
+ * pool becomes isQuiescent.
+ */
+ static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
+ final Throwable ex;
+ ExceptionNode next;
+ final long thrower; // use id not ref to avoid weak cycles
+ final int hashCode; // store task hashCode before weak ref disappears
+ ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next,
+ ReferenceQueue<ForkJoinTask<?>> exceptionTableRefQueue) {
+ super(task, exceptionTableRefQueue);
+ this.ex = ex;
+ this.next = next;
+ this.thrower = Thread.currentThread().getId();
+ this.hashCode = System.identityHashCode(task);
+ }
+ }
+
+ /**
+ * Records exception and sets status.
+ *
+ * @return status on exit
+ */
+ final int recordExceptionalCompletion(Throwable ex) {
+ int s;
+ if ((s = status) >= 0) {
+ int h = System.identityHashCode(this);
+ final ReentrantLock lock = exceptionTableLock;
+ lock.lock();
+ try {
+ expungeStaleExceptions();
+ ExceptionNode[] t = exceptionTable;
+ int i = h & (t.length - 1);
+ for (ExceptionNode e = t[i]; ; e = e.next) {
+ if (e == null) {
+ t[i] = new ExceptionNode(this, ex, t[i],
+ exceptionTableRefQueue);
+ break;
+ }
+ if (e.get() == this) // already present
+ break;
+ }
+ } finally {
+ lock.unlock();
+ }
+ s = setCompletion(EXCEPTIONAL);
+ }
+ return s;
+ }
+
+ /**
+ * Records exception and possibly propagates.
+ *
+ * @return status on exit
+ */
+ private int setExceptionalCompletion(Throwable ex) {
+ int s = recordExceptionalCompletion(ex);
+ if ((s & DONE_MASK) == EXCEPTIONAL)
+ internalPropagateException(ex);
+ return s;
+ }
+
+ /**
+ * Hook for exception propagation support for tasks with completers.
+ */
+ void internalPropagateException(Throwable ex) {
+ }
+
+ /**
+ * Cancels, ignoring any exceptions thrown by cancel. Used during
+ * worker and pool shutdown. Cancel is spec'ed not to throw any
+ * exceptions, but if it does anyway, we have no recourse during
+ * shutdown, so guard against this case.
+ */
+ static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
+ if (t != null && t.status >= 0) {
+ try {
+ t.cancel(false);
+ } catch (Throwable ignore) {
+ }
+ }
+ }
+
+ /**
+ * Removes exception node and clears status.
+ */
+ private void clearExceptionalCompletion() {
+ int h = System.identityHashCode(this);
+ final ReentrantLock lock = exceptionTableLock;
+ lock.lock();
+ try {
+ ExceptionNode[] t = exceptionTable;
+ int i = h & (t.length - 1);
+ ExceptionNode e = t[i];
+ ExceptionNode pred = null;
+ while (e != null) {
+ ExceptionNode next = e.next;
+ if (e.get() == this) {
+ if (pred == null)
+ t[i] = next;
+ else
+ pred.next = next;
+ break;
+ }
+ pred = e;
+ e = next;
+ }
+ expungeStaleExceptions();
+ status = 0;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * Returns a rethrowable exception for this task, if available.
+ * To provide accurate stack traces, if the exception was not
+ * thrown by the current thread, we try to create a new exception
+ * of the same type as the one thrown, but with the recorded
+ * exception as its cause. If there is no such constructor, we
+ * instead try to use a no-arg constructor, followed by initCause,
+ * to the same effect. If none of these apply, or any fail due to
+ * other exceptions, we return the recorded exception, which is
+ * still correct, although it may contain a misleading stack
+ * trace.
+ *
+ * @return the exception, or null if none
+ */
+ private Throwable getThrowableException() {
+ int h = System.identityHashCode(this);
+ ExceptionNode e;
+ final ReentrantLock lock = exceptionTableLock;
+ lock.lock();
+ try {
+ expungeStaleExceptions();
+ ExceptionNode[] t = exceptionTable;
+ e = t[h & (t.length - 1)];
+ while (e != null && e.get() != this)
+ e = e.next;
+ } finally {
+ lock.unlock();
+ }
+ Throwable ex;
+ if (e == null || (ex = e.ex) == null)
+ return null;
+ if (e.thrower != Thread.currentThread().getId()) {
+ try {
+ Constructor<?> noArgCtor = null;
+ // public ctors only
+ for (Constructor<?> c : ex.getClass().getConstructors()) {
+ Class<?>[] ps = c.getParameterTypes();
+ if (ps.length == 0)
+ noArgCtor = c;
+ else if (ps.length == 1 && ps[0] == Throwable.class)
+ return (Throwable)c.newInstance(ex);
+ }
+ if (noArgCtor != null) {
+ Throwable wx = (Throwable)noArgCtor.newInstance();
+ wx.initCause(ex);
+ return wx;
+ }
+ } catch (Exception ignore) {
+ }
+ }
+ return ex;
+ }
+
+ /**
+ * Polls stale refs and removes them. Call only while holding lock.
+ */
+ private static void expungeStaleExceptions() {
+ for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
+ if (x instanceof ExceptionNode) {
+ ExceptionNode[] t = exceptionTable;
+ int i = ((ExceptionNode)x).hashCode & (t.length - 1);
+ ExceptionNode e = t[i];
+ ExceptionNode pred = null;
+ while (e != null) {
+ ExceptionNode next = e.next;
+ if (e == x) {
+ if (pred == null)
+ t[i] = next;
+ else
+ pred.next = next;
+ break;
+ }
+ pred = e;
+ e = next;
+ }
+ }
+ }
+ }
+
+ /**
+ * If lock is available, polls stale refs and removes them.
+ * Called from ForkJoinPool when pools become quiescent.
+ */
+ static final void helpExpungeStaleExceptions() {
+ final ReentrantLock lock = exceptionTableLock;
+ if (lock.tryLock()) {
+ try {
+ expungeStaleExceptions();
+ } finally {
+ lock.unlock();
+ }
+ }
+ }
+
+ /**
+ * A version of "sneaky throw" to relay exceptions.
+ */
+ static void rethrow(Throwable ex) {
+ ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
+ }
+
+ /**
+ * The sneaky part of sneaky throw, relying on generics
+ * limitations to evade compiler complaints about rethrowing
+ * unchecked exceptions.
+ */
+ @SuppressWarnings("unchecked") static <T extends Throwable>
+ void uncheckedThrow(Throwable t) throws T {
+ if (t != null)
+ throw (T)t; // rely on vacuous cast
+ else
+ throw new Error("Unknown Exception");
+ }
+
+ /**
+ * Throws exception, if any, associated with the given status.
+ */
+ private void reportException(int s) {
+ if (s == CANCELLED)
+ throw new CancellationException();
+ if (s == EXCEPTIONAL)
+ rethrow(getThrowableException());
+ }
+
+ // public methods
+
+ /**
+ * Arranges to asynchronously execute this task in the pool the
+ * current task is running in, if applicable, or using the {@link
+ * ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. While
+ * it is not necessarily enforced, it is a usage error to fork a
+ * task more than once unless it has completed and been
+ * reinitialized. Subsequent modifications to the state of this
+ * task or any data it operates on are not necessarily
+ * consistently observable by any thread other than the one
+ * executing it unless preceded by a call to {@link #join} or
+ * related methods, or a call to {@link #isDone} returning {@code
+ * true}.
+ *
+ * @return {@code this}, to simplify usage
+ */
+ public final ForkJoinTask<V> fork() {
+ Thread t;
+ if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
+ ((ForkJoinWorkerThread)t).workQueue.push(this);
+ else
+ ForkJoinPool.common.externalPush(this);
+ return this;
+ }
+
+ /**
+ * Returns the result of the computation when it
+ * {@linkplain #isDone is done}.
+ * This method differs from {@link #get()} in that abnormal
+ * completion results in {@code RuntimeException} or {@code Error},
+ * not {@code ExecutionException}, and that interrupts of the
+ * calling thread do <em>not</em> cause the method to abruptly
+ * return by throwing {@code InterruptedException}.
+ *
+ * @return the computed result
+ */
+ public final V join() {
+ int s;
+ if ((s = doJoin() & DONE_MASK) != NORMAL)
+ reportException(s);
+ return getRawResult();
+ }
+
+ /**
+ * Commences performing this task, awaits its completion if
+ * necessary, and returns its result, or throws an (unchecked)
+ * {@code RuntimeException} or {@code Error} if the underlying
+ * computation did so.
+ *
+ * @return the computed result
+ */
+ public final V invoke() {
+ int s;
+ if ((s = doInvoke() & DONE_MASK) != NORMAL)
+ reportException(s);
+ return getRawResult();
+ }
+
+ /**
+ * Forks the given tasks, returning when {@code isDone} holds for
+ * each task or an (unchecked) exception is encountered, in which
+ * case the exception is rethrown. If more than one task
+ * encounters an exception, then this method throws any one of
+ * these exceptions. If any task encounters an exception, the
+ * other may be cancelled. However, the execution status of
+ * individual tasks is not guaranteed upon exceptional return. The
+ * status of each task may be obtained using {@link
+ * #getException()} and related methods to check if they have been
+ * cancelled, completed normally or exceptionally, or left
+ * unprocessed.
+ *
+ * @param t1 the first task
+ * @param t2 the second task
+ * @throws NullPointerException if any task is null
+ */
+ public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
+ int s1, s2;
+ t2.fork();
+ if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
+ t1.reportException(s1);
+ if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
+ t2.reportException(s2);
+ }
+
+ /**
+ * Forks the given tasks, returning when {@code isDone} holds for
+ * each task or an (unchecked) exception is encountered, in which
+ * case the exception is rethrown. If more than one task
+ * encounters an exception, then this method throws any one of
+ * these exceptions. If any task encounters an exception, others
+ * may be cancelled. However, the execution status of individual
+ * tasks is not guaranteed upon exceptional return. The status of
+ * each task may be obtained using {@link #getException()} and
+ * related methods to check if they have been cancelled, completed
+ * normally or exceptionally, or left unprocessed.
+ *
+ * @param tasks the tasks
+ * @throws NullPointerException if any task is null
+ */
+ public static void invokeAll(ForkJoinTask<?>... tasks) {
+ Throwable ex = null;
+ int last = tasks.length - 1;
+ for (int i = last; i >= 0; --i) {
+ ForkJoinTask<?> t = tasks[i];
+ if (t == null) {
+ if (ex == null)
+ ex = new NullPointerException();
+ }
+ else if (i != 0)
+ t.fork();
+ else if (t.doInvoke() < NORMAL && ex == null)
+ ex = t.getException();
+ }
+ for (int i = 1; i <= last; ++i) {
+ ForkJoinTask<?> t = tasks[i];
+ if (t != null) {
+ if (ex != null)
+ t.cancel(false);
+ else if (t.doJoin() < NORMAL)
+ ex = t.getException();
+ }
+ }
+ if (ex != null)
+ rethrow(ex);
+ }
+
+ /**
+ * Forks all tasks in the specified collection, returning when
+ * {@code isDone} holds for each task or an (unchecked) exception
+ * is encountered, in which case the exception is rethrown. If
+ * more than one task encounters an exception, then this method
+ * throws any one of these exceptions. If any task encounters an
+ * exception, others may be cancelled. However, the execution
+ * status of individual tasks is not guaranteed upon exceptional
+ * return. The status of each task may be obtained using {@link
+ * #getException()} and related methods to check if they have been
+ * cancelled, completed normally or exceptionally, or left
+ * unprocessed.
+ *
+ * @param tasks the collection of tasks
+ * @param <T> the type of the values returned from the tasks
+ * @return the tasks argument, to simplify usage
+ * @throws NullPointerException if tasks or any element are null
+ */
+ public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
+ if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
+ invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
+ return tasks;
+ }
+ @SuppressWarnings("unchecked")
+ List<? extends ForkJoinTask<?>> ts =
+ (List<? extends ForkJoinTask<?>>) tasks;
+ Throwable ex = null;
+ int last = ts.size() - 1;
+ for (int i = last; i >= 0; --i) {
+ ForkJoinTask<?> t = ts.get(i);
+ if (t == null) {
+ if (ex == null)
+ ex = new NullPointerException();
+ }
+ else if (i != 0)
+ t.fork();
+ else if (t.doInvoke() < NORMAL && ex == null)
+ ex = t.getException();
+ }
+ for (int i = 1; i <= last; ++i) {
+ ForkJoinTask<?> t = ts.get(i);
+ if (t != null) {
+ if (ex != null)
+ t.cancel(false);
+ else if (t.doJoin() < NORMAL)
+ ex = t.getException();
+ }
+ }
+ if (ex != null)
+ rethrow(ex);
+ return tasks;
+ }
+
+ /**
+ * Attempts to cancel execution of this task. This attempt will
+ * fail if the task has already completed or could not be
+ * cancelled for some other reason. If successful, and this task
+ * has not started when {@code cancel} is called, execution of
+ * this task is suppressed. After this method returns
+ * successfully, unless there is an intervening call to {@link
+ * #reinitialize}, subsequent calls to {@link #isCancelled},
+ * {@link #isDone}, and {@code cancel} will return {@code true}
+ * and calls to {@link #join} and related methods will result in
+ * {@code CancellationException}.
+ *
+ * <p>This method may be overridden in subclasses, but if so, must
+ * still ensure that these properties hold. In particular, the
+ * {@code cancel} method itself must not throw exceptions.
+ *
+ * <p>This method is designed to be invoked by <em>other</em>
+ * tasks. To terminate the current task, you can just return or
+ * throw an unchecked exception from its computation method, or
+ * invoke {@link #completeExceptionally(Throwable)}.
+ *
+ * @param mayInterruptIfRunning this value has no effect in the
+ * default implementation because interrupts are not used to
+ * control cancellation.
+ *
+ * @return {@code true} if this task is now cancelled
+ */
+ public boolean cancel(boolean mayInterruptIfRunning) {
+ return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
+ }
+
+ public final boolean isDone() {
+ return status < 0;
+ }
+
+ public final boolean isCancelled() {
+ return (status & DONE_MASK) == CANCELLED;
+ }
+
+ /**
+ * Returns {@code true} if this task threw an exception or was cancelled.
+ *
+ * @return {@code true} if this task threw an exception or was cancelled
+ */
+ public final boolean isCompletedAbnormally() {
+ return status < NORMAL;
+ }
+
+ /**
+ * Returns {@code true} if this task completed without throwing an
+ * exception and was not cancelled.
+ *
+ * @return {@code true} if this task completed without throwing an
+ * exception and was not cancelled
+ */
+ public final boolean isCompletedNormally() {
+ return (status & DONE_MASK) == NORMAL;
+ }
+
+ /**
+ * Returns the exception thrown by the base computation, or a
+ * {@code CancellationException} if cancelled, or {@code null} if
+ * none or if the method has not yet completed.
+ *
+ * @return the exception, or {@code null} if none
+ */
+ public final Throwable getException() {
+ int s = status & DONE_MASK;
+ return ((s >= NORMAL) ? null :
+ (s == CANCELLED) ? new CancellationException() :
+ getThrowableException());
+ }
+
+ /**
+ * Completes this task abnormally, and if not already aborted or
+ * cancelled, causes it to throw the given exception upon
+ * {@code join} and related operations. This method may be used
+ * to induce exceptions in asynchronous tasks, or to force
+ * completion of tasks that would not otherwise complete. Its use
+ * in other situations is discouraged. This method is
+ * overridable, but overridden versions must invoke {@code super}
+ * implementation to maintain guarantees.
+ *
+ * @param ex the exception to throw. If this exception is not a
+ * {@code RuntimeException} or {@code Error}, the actual exception
+ * thrown will be a {@code RuntimeException} with cause {@code ex}.
+ */
+ public void completeExceptionally(Throwable ex) {
+ setExceptionalCompletion((ex instanceof RuntimeException) ||
+ (ex instanceof Error) ? ex :
+ new RuntimeException(ex));
+ }
+
+ /**
+ * Completes this task, and if not already aborted or cancelled,
+ * returning the given value as the result of subsequent
+ * invocations of {@code join} and related operations. This method
+ * may be used to provide results for asynchronous tasks, or to
+ * provide alternative handling for tasks that would not otherwise
+ * complete normally. Its use in other situations is
+ * discouraged. This method is overridable, but overridden
+ * versions must invoke {@code super} implementation to maintain
+ * guarantees.
+ *
+ * @param value the result value for this task
+ */
+ public void complete(V value) {
+ try {
+ setRawResult(value);
+ } catch (Throwable rex) {
+ setExceptionalCompletion(rex);
+ return;
+ }
+ setCompletion(NORMAL);
+ }
+
+ /**
+ * Completes this task normally without setting a value. The most
+ * recent value established by {@link #setRawResult} (or {@code
+ * null} by default) will be returned as the result of subsequent
+ * invocations of {@code join} and related operations.
+ *
+ * @since 1.8
+ */
+ public final void quietlyComplete() {
+ setCompletion(NORMAL);
+ }
+
+ /**
+ * Waits if necessary for the computation to complete, and then
+ * retrieves its result.
+ *
+ * @return the computed result
+ * @throws CancellationException if the computation was cancelled
+ * @throws ExecutionException if the computation threw an
+ * exception
+ * @throws InterruptedException if the current thread is not a
+ * member of a ForkJoinPool and was interrupted while waiting
+ */
+ public final V get() throws InterruptedException, ExecutionException {
+ int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
+ doJoin() : externalInterruptibleAwaitDone();
+ if ((s &= DONE_MASK) == CANCELLED)
+ throw new CancellationException();
+ if (s == EXCEPTIONAL)
+ throw new ExecutionException(getThrowableException());
+ return getRawResult();
+ }
+
+ /**
+ * Waits if necessary for at most the given time for the computation
+ * to complete, and then retrieves its result, if available.
+ *
+ * @param timeout the maximum time to wait
+ * @param unit the time unit of the timeout argument
+ * @return the computed result
+ * @throws CancellationException if the computation was cancelled
+ * @throws ExecutionException if the computation threw an
+ * exception
+ * @throws InterruptedException if the current thread is not a
+ * member of a ForkJoinPool and was interrupted while waiting
+ * @throws TimeoutException if the wait timed out
+ */
+ public final V get(long timeout, TimeUnit unit)
+ throws InterruptedException, ExecutionException, TimeoutException {
+ int s;
+ long nanos = unit.toNanos(timeout);
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ if ((s = status) >= 0 && nanos > 0L) {
+ long d = System.nanoTime() + nanos;
+ long deadline = (d == 0L) ? 1L : d; // avoid 0
+ Thread t = Thread.currentThread();
+ if (t instanceof ForkJoinWorkerThread) {
+ ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
+ s = wt.pool.awaitJoin(wt.workQueue, this, deadline);
+ }
+ else if ((s = ((this instanceof CountedCompleter) ?
+ ForkJoinPool.common.externalHelpComplete(
+ (CountedCompleter<?>)this, 0) :
+ ForkJoinPool.common.tryExternalUnpush(this) ?
+ doExec() : 0)) >= 0) {
+ long ns, ms; // measure in nanosecs, but wait in millisecs
+ while ((s = status) >= 0 &&
+ (ns = deadline - System.nanoTime()) > 0L) {
+ if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
+ STATUS.compareAndSet(this, s, s | SIGNAL)) {
+ synchronized (this) {
+ if (status >= 0)
+ wait(ms); // OK to throw InterruptedException
+ else
+ notifyAll();
+ }
+ }
+ }
+ }
+ }
+ if (s >= 0)
+ s = status;
+ if ((s &= DONE_MASK) != NORMAL) {
+ if (s == CANCELLED)
+ throw new CancellationException();
+ if (s != EXCEPTIONAL)
+ throw new TimeoutException();
+ throw new ExecutionException(getThrowableException());
+ }
+ return getRawResult();
+ }
+
+ /**
+ * Joins this task, without returning its result or throwing its
+ * exception. This method may be useful when processing
+ * collections of tasks when some have been cancelled or otherwise
+ * known to have aborted.
+ */
+ public final void quietlyJoin() {
+ doJoin();
+ }
+
+ /**
+ * Commences performing this task and awaits its completion if
+ * necessary, without returning its result or throwing its
+ * exception.
+ */
+ public final void quietlyInvoke() {
+ doInvoke();
+ }
+
+ /**
+ * Possibly executes tasks until the pool hosting the current task
+ * {@linkplain ForkJoinPool#isQuiescent is quiescent}. This
+ * method may be of use in designs in which many tasks are forked,
+ * but none are explicitly joined, instead executing them until
+ * all are processed.
+ */
+ public static void helpQuiesce() {
+ Thread t;
+ if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
+ ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
+ wt.pool.helpQuiescePool(wt.workQueue);
+ }
+ else
+ ForkJoinPool.quiesceCommonPool();
+ }
+
+ /**
+ * Resets the internal bookkeeping state of this task, allowing a
+ * subsequent {@code fork}. This method allows repeated reuse of
+ * this task, but only if reuse occurs when this task has either
+ * never been forked, or has been forked, then completed and all
+ * outstanding joins of this task have also completed. Effects
+ * under any other usage conditions are not guaranteed.
+ * This method may be useful when executing
+ * pre-constructed trees of subtasks in loops.
+ *
+ * <p>Upon completion of this method, {@code isDone()} reports
+ * {@code false}, and {@code getException()} reports {@code
+ * null}. However, the value returned by {@code getRawResult} is
+ * unaffected. To clear this value, you can invoke {@code
+ * setRawResult(null)}.
+ */
+ public void reinitialize() {
+ if ((status & DONE_MASK) == EXCEPTIONAL)
+ clearExceptionalCompletion();
+ else
+ status = 0;
+ }
+
+ /**
+ * Returns the pool hosting the current thread, or {@code null}
+ * if the current thread is executing outside of any ForkJoinPool.
+ *
+ * <p>This method returns {@code null} if and only if {@link
+ * #inForkJoinPool} returns {@code false}.
+ *
+ * @return the pool, or {@code null} if none
+ */
+ public static ForkJoinPool getPool() {
+ Thread t = Thread.currentThread();
+ return (t instanceof ForkJoinWorkerThread) ?
+ ((ForkJoinWorkerThread) t).pool : null;
+ }
+
+ /**
+ * Returns {@code true} if the current thread is a {@link
+ * ForkJoinWorkerThread} executing as a ForkJoinPool computation.
+ *
+ * @return {@code true} if the current thread is a {@link
+ * ForkJoinWorkerThread} executing as a ForkJoinPool computation,
+ * or {@code false} otherwise
+ */
+ public static boolean inForkJoinPool() {
+ return Thread.currentThread() instanceof ForkJoinWorkerThread;
+ }
+
+ /**
+ * Tries to unschedule this task for execution. This method will
+ * typically (but is not guaranteed to) succeed if this task is
+ * the most recently forked task by the current thread, and has
+ * not commenced executing in another thread. This method may be
+ * useful when arranging alternative local processing of tasks
+ * that could have been, but were not, stolen.
+ *
+ * @return {@code true} if unforked
+ */
+ public boolean tryUnfork() {
+ Thread t;
+ return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
+ ((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
+ ForkJoinPool.common.tryExternalUnpush(this));
+ }
+
+ /**
+ * Returns an estimate of the number of tasks that have been
+ * forked by the current worker thread but not yet executed. This
+ * value may be useful for heuristic decisions about whether to
+ * fork other tasks.
+ *
+ * @return the number of tasks
+ */
+ public static int getQueuedTaskCount() {
+ Thread t; ForkJoinPool.WorkQueue q;
+ if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
+ q = ((ForkJoinWorkerThread)t).workQueue;
+ else
+ q = ForkJoinPool.commonSubmitterQueue();
+ return (q == null) ? 0 : q.queueSize();
+ }
+
+ /**
+ * Returns an estimate of how many more locally queued tasks are
+ * held by the current worker thread than there are other worker
+ * threads that might steal them, or zero if this thread is not
+ * operating in a ForkJoinPool. This value may be useful for
+ * heuristic decisions about whether to fork other tasks. In many
+ * usages of ForkJoinTasks, at steady state, each worker should
+ * aim to maintain a small constant surplus (for example, 3) of
+ * tasks, and to process computations locally if this threshold is
+ * exceeded.
+ *
+ * @return the surplus number of tasks, which may be negative
+ */
+ public static int getSurplusQueuedTaskCount() {
+ return ForkJoinPool.getSurplusQueuedTaskCount();
+ }
+
+ // Extension methods
+
+ /**
+ * Returns the result that would be returned by {@link #join}, even
+ * if this task completed abnormally, or {@code null} if this task
+ * is not known to have been completed. This method is designed
+ * to aid debugging, as well as to support extensions. Its use in
+ * any other context is discouraged.
+ *
+ * @return the result, or {@code null} if not completed
+ */
+ public abstract V getRawResult();
+
+ /**
+ * Forces the given value to be returned as a result. This method
+ * is designed to support extensions, and should not in general be
+ * called otherwise.
+ *
+ * @param value the value
+ */
+ protected abstract void setRawResult(V value);
+
+ /**
+ * Immediately performs the base action of this task and returns
+ * true if, upon return from this method, this task is guaranteed
+ * to have completed normally. This method may return false
+ * otherwise, to indicate that this task is not necessarily
+ * complete (or is not known to be complete), for example in
+ * asynchronous actions that require explicit invocations of
+ * completion methods. This method may also throw an (unchecked)
+ * exception to indicate abnormal exit. This method is designed to
+ * support extensions, and should not in general be called
+ * otherwise.
+ *
+ * @return {@code true} if this task is known to have completed normally
+ */
+ protected abstract boolean exec();
+
+ /**
+ * Returns, but does not unschedule or execute, a task queued by
+ * the current thread but not yet executed, if one is immediately
+ * available. There is no guarantee that this task will actually
+ * be polled or executed next. Conversely, this method may return
+ * null even if a task exists but cannot be accessed without
+ * contention with other threads. This method is designed
+ * primarily to support extensions, and is unlikely to be useful
+ * otherwise.
+ *
+ * @return the next task, or {@code null} if none are available
+ */
+ protected static ForkJoinTask<?> peekNextLocalTask() {
+ Thread t; ForkJoinPool.WorkQueue q;
+ if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
+ q = ((ForkJoinWorkerThread)t).workQueue;
+ else
+ q = ForkJoinPool.commonSubmitterQueue();
+ return (q == null) ? null : q.peek();
+ }
+
+ /**
+ * Unschedules and returns, without executing, the next task
+ * queued by the current thread but not yet executed, if the
+ * current thread is operating in a ForkJoinPool. This method is
+ * designed primarily to support extensions, and is unlikely to be
+ * useful otherwise.
+ *
+ * @return the next task, or {@code null} if none are available
+ */
+ protected static ForkJoinTask<?> pollNextLocalTask() {
+ Thread t;
+ return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
+ ((ForkJoinWorkerThread)t).workQueue.nextLocalTask() :
+ null;
+ }
+
+ /**
+ * If the current thread is operating in a ForkJoinPool,
+ * unschedules and returns, without executing, the next task
+ * queued by the current thread but not yet executed, if one is
+ * available, or if not available, a task that was forked by some
+ * other thread, if available. Availability may be transient, so a
+ * {@code null} result does not necessarily imply quiescence of
+ * the pool this task is operating in. This method is designed
+ * primarily to support extensions, and is unlikely to be useful
+ * otherwise.
+ *
+ * @return a task, or {@code null} if none are available
+ */
+ protected static ForkJoinTask<?> pollTask() {
+ Thread t; ForkJoinWorkerThread wt;
+ return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
+ (wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) :
+ null;
+ }
+
+ /**
+ * If the current thread is operating in a ForkJoinPool,
+ * unschedules and returns, without executing, a task externally
+ * submitted to the pool, if one is available. Availability may be
+ * transient, so a {@code null} result does not necessarily imply
+ * quiescence of the pool. This method is designed primarily to
+ * support extensions, and is unlikely to be useful otherwise.
+ *
+ * @return a task, or {@code null} if none are available
+ * @since 9
+ */
+ protected static ForkJoinTask<?> pollSubmission() {
+ Thread t;
+ return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
+ ((ForkJoinWorkerThread)t).pool.pollSubmission() : null;
+ }
+
+ // tag operations
+
+ /**
+ * Returns the tag for this task.
+ *
+ * @return the tag for this task
+ * @since 1.8
+ */
+ public final short getForkJoinTaskTag() {
+ return (short)status;
+ }
+
+ /**
+ * Atomically sets the tag value for this task and returns the old value.
+ *
+ * @param newValue the new tag value
+ * @return the previous value of the tag
+ * @since 1.8
+ */
+ public final short setForkJoinTaskTag(short newValue) {
+ for (int s;;) {
+ if (STATUS.compareAndSet(this, s = status,
+ (s & ~SMASK) | (newValue & SMASK)))
+ return (short)s;
+ }
+ }
+
+ /**
+ * Atomically conditionally sets the tag value for this task.
+ * Among other applications, tags can be used as visit markers
+ * in tasks operating on graphs, as in methods that check: {@code
+ * if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
+ * before processing, otherwise exiting because the node has
+ * already been visited.
+ *
+ * @param expect the expected tag value
+ * @param update the new tag value
+ * @return {@code true} if successful; i.e., the current value was
+ * equal to {@code expect} and was changed to {@code update}.
+ * @since 1.8
+ */
+ public final boolean compareAndSetForkJoinTaskTag(short expect, short update) {
+ for (int s;;) {
+ if ((short)(s = status) != expect)
+ return false;
+ if (STATUS.compareAndSet(this, s,
+ (s & ~SMASK) | (update & SMASK)))
+ return true;
+ }
+ }
+
+ /**
+ * Adapter for Runnables. This implements RunnableFuture
+ * to be compliant with AbstractExecutorService constraints
+ * when used in ForkJoinPool.
+ */
+ static final class AdaptedRunnable<T> extends ForkJoinTask<T>
+ implements RunnableFuture<T> {
+ final Runnable runnable;
+ T result;
+ AdaptedRunnable(Runnable runnable, T result) {
+ if (runnable == null) throw new NullPointerException();
+ this.runnable = runnable;
+ this.result = result; // OK to set this even before completion
+ }
+ public final T getRawResult() { return result; }
+ public final void setRawResult(T v) { result = v; }
+ public final boolean exec() { runnable.run(); return true; }
+ public final void run() { invoke(); }
+ private static final long serialVersionUID = 5232453952276885070L;
+ }
+
+ /**
+ * Adapter for Runnables without results.
+ */
+ static final class AdaptedRunnableAction extends ForkJoinTask<Void>
+ implements RunnableFuture<Void> {
+ final Runnable runnable;
+ AdaptedRunnableAction(Runnable runnable) {
+ if (runnable == null) throw new NullPointerException();
+ this.runnable = runnable;
+ }
+ public final Void getRawResult() { return null; }
+ public final void setRawResult(Void v) { }
+ public final boolean exec() { runnable.run(); return true; }
+ public final void run() { invoke(); }
+ private static final long serialVersionUID = 5232453952276885070L;
+ }
+
+ /**
+ * Adapter for Runnables in which failure forces worker exception.
+ */
+ static final class RunnableExecuteAction extends ForkJoinTask<Void> {
+ final Runnable runnable;
+ RunnableExecuteAction(Runnable runnable) {
+ if (runnable == null) throw new NullPointerException();
+ this.runnable = runnable;
+ }
+ public final Void getRawResult() { return null; }
+ public final void setRawResult(Void v) { }
+ public final boolean exec() { runnable.run(); return true; }
+ void internalPropagateException(Throwable ex) {
+ rethrow(ex); // rethrow outside exec() catches.
+ }
+ private static final long serialVersionUID = 5232453952276885070L;
+ }
+
+ /**
+ * Adapter for Callables.
+ */
+ static final class AdaptedCallable<T> extends ForkJoinTask<T>
+ implements RunnableFuture<T> {
+ final Callable<? extends T> callable;
+ T result;
+ AdaptedCallable(Callable<? extends T> callable) {
+ if (callable == null) throw new NullPointerException();
+ this.callable = callable;
+ }
+ public final T getRawResult() { return result; }
+ public final void setRawResult(T v) { result = v; }
+ public final boolean exec() {
+ try {
+ result = callable.call();
+ return true;
+ } catch (RuntimeException rex) {
+ throw rex;
+ } catch (Exception ex) {
+ throw new RuntimeException(ex);
+ }
+ }
+ public final void run() { invoke(); }
+ private static final long serialVersionUID = 2838392045355241008L;
+ }
+
+ /**
+ * Returns a new {@code ForkJoinTask} that performs the {@code run}
+ * method of the given {@code Runnable} as its action, and returns
+ * a null result upon {@link #join}.
+ *
+ * @param runnable the runnable action
+ * @return the task
+ */
+ public static ForkJoinTask<?> adapt(Runnable runnable) {
+ return new AdaptedRunnableAction(runnable);
+ }
+
+ /**
+ * Returns a new {@code ForkJoinTask} that performs the {@code run}
+ * method of the given {@code Runnable} as its action, and returns
+ * the given result upon {@link #join}.
+ *
+ * @param runnable the runnable action
+ * @param result the result upon completion
+ * @param <T> the type of the result
+ * @return the task
+ */
+ public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
+ return new AdaptedRunnable<T>(runnable, result);
+ }
+
+ /**
+ * Returns a new {@code ForkJoinTask} that performs the {@code call}
+ * method of the given {@code Callable} as its action, and returns
+ * its result upon {@link #join}, translating any checked exceptions
+ * encountered into {@code RuntimeException}.
+ *
+ * @param callable the callable action
+ * @param <T> the type of the callable's result
+ * @return the task
+ */
+ public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
+ return new AdaptedCallable<T>(callable);
+ }
+
+ // Serialization support
+
+ private static final long serialVersionUID = -7721805057305804111L;
+
+ /**
+ * Saves this task to a stream (that is, serializes it).
+ *
+ * @param s the stream
+ * @throws java.io.IOException if an I/O error occurs
+ * @serialData the current run status and the exception thrown
+ * during execution, or {@code null} if none
+ */
+ private void writeObject(java.io.ObjectOutputStream s)
+ throws java.io.IOException {
+ s.defaultWriteObject();
+ s.writeObject(getException());
+ }
+
+ /**
+ * Reconstitutes this task from a stream (that is, deserializes it).
+ * @param s the stream
+ * @throws ClassNotFoundException if the class of a serialized object
+ * could not be found
+ * @throws java.io.IOException if an I/O error occurs
+ */
+ private void readObject(java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ s.defaultReadObject();
+ Object ex = s.readObject();
+ if (ex != null)
+ setExceptionalCompletion((Throwable)ex);
+ }
+
+ // VarHandle mechanics
+ private static final VarHandle STATUS;
+ static {
+ try {
+ MethodHandles.Lookup l = MethodHandles.lookup();
+ STATUS = l.findVarHandle(ForkJoinTask.class, "status", int.class);
+ } catch (ReflectiveOperationException e) {
+ throw new Error(e);
+ }
+ }
+
+}