content: /**
   * This file is part of Aion-Lightning <aion-lightning.org>.
   *
   *  Aion-Lightning is free software: you can redistribute it and/or modify
   *  it under the terms of the GNU General Public License as published by
   *  the Free Software Foundation, either version 3 of the License, or
   *  (at your option) any later version.
   *
   *  Aion-Lightning is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *  GNU General Public License for more details. *
   *  You should have received a copy of the GNU General Public License
   *  along with Aion-Lightning.
   *  If not, see <http://www.gnu.org/licenses/>.
   */
  
  /*
   * 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 com.aionemu.commons.utils.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.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.
   *
   * <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 java.util.concurrent.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
  
  		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 (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) {
  				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(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;
  		}
  		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
  	 */
  	@Override
  	public boolean cancel(boolean mayInterruptIfRunning) {
  		return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
  	}
  
  	@Override
  	public final boolean isDone() {
  		return status < 0;
  	}
  
  	@Override
  	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
  	 */
  	@Override
  	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
  	 */
  	@Override
  	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
  		}
  
  		@Override
  		public final T getRawResult() {
  			return result;
  		}
  
  		@Override
  		public final void setRawResult(T v) {
  			result = v;
  		}
  
  		@Override
  		public final boolean exec() {
  			runnable.run();
  			return true;
  		}
  
  		@Override
  		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;
  		}
  
  		@Override
  		public final Void getRawResult() {
  			return null;
  		}
  
  		@Override
  		public final void setRawResult(Void v) {
  		}
  
  		@Override
  		public final boolean exec() {
  			runnable.run();
  			return true;
  		}
  
  		@Override
  		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;
  		}
  
  		@Override
  		public final T getRawResult() {
  			return result;
  		}
  
  		@Override
  		public final void setRawResult(T v) {
  			result = v;
  		}
  
  		@Override
  		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);
  			}
  		}
  
  		@Override
  		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>() {
  						@Override
  						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());
  		}
  	}
  }
  