Imported Upstream version 1.0.3upstream/1.0.3

1 files changed, 1509 insertions, 0 deletions

diff --git a/src/main/java/jsr166y/ForkJoinTask.java b/src/main/java/jsr166y/ForkJoinTask.java
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+++ b/src/main/java/jsr166y/ForkJoinTask.java
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+/*
+ * 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 jsr166y;
+
+import java.io.Serializable;
+import java.util.Collection;
+import java.util.List;
+import java.util.RandomAccess;
+import java.lang.ref.WeakReference;
+import java.lang.ref.ReferenceQueue;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
+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;
+import java.lang.reflect.Constructor;
+
+/**
+ * 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 do 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 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}.
+ *
+ * <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 (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.externalHelpJoin(this);
+        boolean interrupted = false;
+        while ((s = status) >= 0) {
+            if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
+                synchronized (this) {
+                    if (status >= 0) {
+                        try {
+                            wait();
+                        } catch (InterruptedException ie) {
+                            interrupted = true;
+                        }
+                    }
+                    else
+                        notifyAll();
+                }
+            }
+        }
+        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();
+        ForkJoinPool.externalHelpJoin(this);
+        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<Object> 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<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) {
+            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]);
+                        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<? extends Throwable> 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) {
+                int hashCode = ((ExceptionNode)x).hashCode;
+                ExceptionNode[] t = exceptionTable;
+                int i = 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, 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(final Throwable ex) {
+        if (ex != null) {
+            if (ex instanceof Error)
+                throw (Error)ex;
+            if (ex instanceof RuntimeException)
+                throw (RuntimeException)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
+    }
+
+    /**
+     * 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 {@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 <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
+     * @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}.
+     *
+     * @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);
+        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
+                ForkJoinPool.externalHelpJoin(this);
+            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())
+                            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.
+     *
+     * <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 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.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 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<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;
+    }
+
+    /**
+     * Adaptor 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;
+    }
+
+    /**
+     * Adaptor 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 (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 <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
+     * @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).
+     *
+     * @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<Object>();
+        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<sun.misc.Unsafe>() {
+                public sun.misc.Unsafe run() throws Exception {
+                    Class<sun.misc.Unsafe> 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());
+        }
+    }
+}