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    This artifact provides a single jar that contains all classes required to use remote Jakarta Enterprise Beans and Jakarta Messaging, including all dependencies. It is intended for use by those not using maven, maven users should just import the Jakarta Enterprise Beans and Jakarta Messaging BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

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    /*
 * Copyright 2013 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

/*
 * 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 io.netty.util.internal.chmv8;

import java.io.Serializable;
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.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.Phaser;
import java.util.concurrent.RecursiveAction;
import java.util.concurrent.RecursiveTask;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.RunnableFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
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.
 *
 * 
    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.
 *
 * 
    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.
 *
 * 
    It is possible to define and use ForkJoinTasks that may block,
 * but doing do requires three further considerations: (1) Completion
 * of few if any other 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.
 *
 * 
    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 "quiet" 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.
 *
 * 
    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}.
 *
 * 
    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 java.util.concurrent.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 java.util.concurrent.CancellationException}.
 *
 * 
    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.
 *
 * 
    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 tagged 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.)
 *
 * 
    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.
 *
 * 
    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.
 *
 * 
    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 asyncMode.
 *
 * 
    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
 */
@SuppressWarnings("all")
public abstract class ForkJoinTask implements Future, 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 (U.compareAndSwapInt(this, STATUS, 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;
    }

    /**
     * Tries to set SIGNAL status unless already completed. Used by
     * ForkJoinPool. Other variants are directly incorporated into
     * externalAwaitDone etc.
     *
     * @return true if successful
     */
    final boolean trySetSignal() {
        int s = status;
        return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL);
    }

    /**
     * Blocks a non-worker-thread until completion.
     * @return status upon completion
     */
    private int externalAwaitDone() {
        int s;
        ForkJoinPool cp = ForkJoinPool.common;
        if ((s = status) >= 0) {
            if (cp != null) {
                if (this instanceof CountedCompleter)
                    s = cp.externalHelpComplete((CountedCompleter)this);
                else if (cp.tryExternalUnpush(this))
                    s = doExec();
            }
            if (s >= 0 && (s = status) >= 0) {
                boolean interrupted = false;
                do {
                    if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
                        synchronized (this) {
                            if (status >= 0) {
                                try {
                                    wait();
                                } 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;
        ForkJoinPool cp = ForkJoinPool.common;
        if (Thread.interrupted())
            throw new InterruptedException();
        if ((s = status) >= 0 && cp != null) {
            if (this instanceof CountedCompleter)
                cp.externalHelpComplete((CountedCompleter)this);
            else if (cp.tryExternalUnpush(this))
                doExec();
        }
        while ((s = status) >= 0) {
            if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
                synchronized (this) {
                    if (status >= 0)
                        wait();
                    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) :
                        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) :
                        externalAwaitDone();
    }

    // Exception table support

    /**
     * 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.
     *
     * Note: These statics are initialized below in static block.
     */
    private static final ExceptionNode[] exceptionTable;
    private static final ReentrantLock exceptionTableLock;
    private static final ReferenceQueue exceptionTableRefQueue;

    /**
     * Fixed capacity for exceptionTable.
     */
    private static final int EXCEPTION_MAP_CAPACITY = 32;

    /**
     * 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> {
        final Throwable ex;
        ExceptionNode next;
        final long thrower;  // use id not ref to avoid weak cycles
        ExceptionNode(ForkJoinTask task, Throwable ex, ExceptionNode next) {
            super(task, exceptionTableRefQueue);
            this.ex = ex;
            this.next = next;
            this.thrower = Thread.currentThread().getId();
        }
    }

    /**
     * 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]);
                        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 the given 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() {
        if ((status & DONE_MASK) != EXCEPTIONAL)
            return null;
        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 (false && e.thrower != Thread.currentThread().getId()) {
            Class ec = ex.getClass();
            try {
                Constructor noArgCtor = null;
                Constructor[] cs = ec.getConstructors();// public ctors only
                for (int i = 0; i < cs.length; ++i) {
                    Constructor c = cs[i];
                    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;
    }

    /**
     * Poll stale refs and remove them. Call only while holding lock.
     */
    private static void expungeStaleExceptions() {
        for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
            if (x instanceof ExceptionNode) {
                ForkJoinTask key = ((ExceptionNode)x).get();
                ExceptionNode[] t = exceptionTable;
                int i = System.identityHashCode(key) & (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, poll stale refs and remove 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) {
        if (ex != null)
            ForkJoinTask.uncheckedThrow(ex);
    }

    /**
     * The sneaky part of sneaky throw, relying on generics
     * limitations to evade compiler complaints about rethrowing
     * unchecked exceptions
     */
    @SuppressWarnings("unchecked") static 
    void uncheckedThrow(Throwable t) throws T {
        throw (T)t; // rely on vacuous cast
    }

    /**
     * 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 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 {@link #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 not 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
     * @return the tasks argument, to simplify usage
     * @throws NullPointerException if tasks or any element are null
     */
    public static > Collection invokeAll(Collection tasks) {
        if (!(tasks instanceof RandomAccess) || !(tasks instanceof List)) {
            invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()]));
            return tasks;
        }
        @SuppressWarnings("unchecked")
        List> ts =
                (List>) 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}.
     *
     * 
    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.
     *
     * 
    This method is designed to be invoked by other
     * 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();
        Throwable ex;
        if ((s &= DONE_MASK) == CANCELLED)
            throw new CancellationException();
        if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
            throw new ExecutionException(ex);
        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 {
        if (Thread.interrupted())
            throw new InterruptedException();
        // Messy in part because we measure in nanosecs, but wait in millisecs
        int s; long ms;
        long ns = unit.toNanos(timeout);
        ForkJoinPool cp;
        if ((s = status) >= 0 && ns > 0L) {
            long deadline = System.nanoTime() + ns;
            ForkJoinPool p = null;
            ForkJoinPool.WorkQueue w = null;
            Thread t = Thread.currentThread();
            if (t instanceof ForkJoinWorkerThread) {
                ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
                p = wt.pool;
                w = wt.workQueue;
                p.helpJoinOnce(w, this); // no retries on failure
            }
            else if ((cp = ForkJoinPool.common) != null) {
                if (this instanceof CountedCompleter)
                    cp.externalHelpComplete((CountedCompleter)this);
                else if (cp.tryExternalUnpush(this))
                    doExec();
            }
            boolean canBlock = false;
            boolean interrupted = false;
            try {
                while ((s = status) >= 0) {
                    if (w != null && w.qlock < 0)
                        cancelIgnoringExceptions(this);
                    else if (!canBlock) {
                        if (p == null || p.tryCompensate(p.ctl))
                            canBlock = true;
                    }
                    else {
                        if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
                                U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
                            synchronized (this) {
                                if (status >= 0) {
                                    try {
                                        wait(ms);
                                    } catch (InterruptedException ie) {
                                        if (p == null)
                                            interrupted = true;
                                    }
                                }
                                else
                                    notifyAll();
                            }
                        }
                        if ((s = status) < 0 || interrupted ||
                                (ns = deadline - System.nanoTime()) <= 0L)
                            break;
                    }
                }
            } finally {
                if (p != null && canBlock)
                    p.incrementActiveCount();
            }
            if (interrupted)
                throw new InterruptedException();
        }
        if ((s &= DONE_MASK) != NORMAL) {
            Throwable ex;
            if (s == CANCELLED)
                throw new CancellationException();
            if (s != EXCEPTIONAL)
                throw new TimeoutException();
            if ((ex = getThrowableException()) != null)
                throw new ExecutionException(ex);
        }
        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
     * {@link 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.
     *
     * 
    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 task execution, or null
     * if this task is executing outside of any ForkJoinPool.
     *
     * @see #inForkJoinPool
     * @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;
    }

    // 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.
     *
     * @param tag the tag value
     * @return the previous value of the tag
     * @since 1.8
     */
    public final short setForkJoinTaskTag(short tag) {
        for (int s;;) {
            if (U.compareAndSwapInt(this, STATUS, s = status,
                    (s & ~SMASK) | (tag & 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 e the expected tag value
     * @param tag the new tag value
     * @return {@code true} if successful; i.e., the current value was
     * equal to e and is now tag.
     * @since 1.8
     */
    public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
        for (int s;;) {
            if ((short)(s = status) != e)
                return false;
            if (U.compareAndSwapInt(this, STATUS, s,
                    (s & ~SMASK) | (tag & SMASK)))
                return true;
        }
    }

    /**
     * Adaptor for Runnables. This implements RunnableFuture
     * to be compliant with AbstractExecutorService constraints
     * when used in ForkJoinPool.
     */
    static final class AdaptedRunnable extends ForkJoinTask
            implements RunnableFuture {
        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;
    }

    /**
     * Adaptor for Runnables without results
     */
    static final class AdaptedRunnableAction extends ForkJoinTask
            implements RunnableFuture {
        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;
    }

    /**
     * Adaptor for Runnables in which failure forces worker exception
     */
    static final class RunnableExecuteAction extends ForkJoinTask {
        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;
    }

    /**
     * Adaptor for Callables
     */
    static final class AdaptedCallable extends ForkJoinTask
            implements RunnableFuture {
        final Callable callable;
        T result;
        AdaptedCallable(Callable 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 (Error err) {
                throw err;
            } 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
     * @return the task
     */
    public static  ForkJoinTask adapt(Runnable runnable, T result) {
        return new AdaptedRunnable(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
     * @return the task
     */
    public static  ForkJoinTask adapt(Callable callable) {
        return new AdaptedCallable(callable);
    }

    // Serialization support

    private static final long serialVersionUID = -7721805057305804111L;

    /**
     * Saves this task to a stream (that is, serializes it).
     *
     * @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).
     */
    private void readObject(java.io.ObjectInputStream s)
            throws java.io.IOException, ClassNotFoundException {
        s.defaultReadObject();
        Object ex = s.readObject();
        if (ex != null)
            setExceptionalCompletion((Throwable)ex);
    }

    // Unsafe mechanics
    private static final sun.misc.Unsafe U;
    private static final long STATUS;

    static {
        exceptionTableLock = new ReentrantLock();
        exceptionTableRefQueue = new ReferenceQueue();
        exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
        try {
            U = getUnsafe();
            Class k = ForkJoinTask.class;
            STATUS = U.objectFieldOffset
                    (k.getDeclaredField("status"));
        } catch (Exception e) {
            throw new Error(e);
        }
    }

    /**
     * Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
     * Replace with a simple call to Unsafe.getUnsafe when integrating
     * into a jdk.
     *
     * @return a sun.misc.Unsafe
     */
    private static sun.misc.Unsafe getUnsafe() {
        try {
            return sun.misc.Unsafe.getUnsafe();
        } catch (SecurityException tryReflectionInstead) {}
        try {
            return java.security.AccessController.doPrivileged
                    (new java.security.PrivilegedExceptionAction() {
                        public sun.misc.Unsafe run() throws Exception {
                            Class k = sun.misc.Unsafe.class;
                            for (java.lang.reflect.Field f : k.getDeclaredFields()) {
                                f.setAccessible(true);
                                Object x = f.get(null);
                                if (k.isInstance(x))
                                    return k.cast(x);
                            }
                            throw new NoSuchFieldError("the Unsafe");
                        }});
        } catch (java.security.PrivilegedActionException e) {
            throw new RuntimeException("Could not initialize intrinsics",
                    e.getCause());
        }
    }
}
    
    
    
    

    




    
    
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