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	/*
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	/*
	* This file is available under and governed by the GNU General Public
	* License version 2 only, as published by the Free Software Foundation.
	* However, the following notice accompanied the original version of this
	* file:
	*
	* Written by Doug Lea with assistance from members of JCP JSR-166
	* Expert Group and released to the public domain, as explained at
	* http://creativecommons.org/publicdomain/zero/1.0/
	*/

	package java.util.concurrent.locks;

	import java.util.ArrayList;
	import java.util.Collection;
	import java.util.Date;
	import java.util.concurrent.TimeUnit;
	import java.util.concurrent.ForkJoinPool;
	import java.util.concurrent.RejectedExecutionException;
	import jdk.internal.misc.Unsafe;

	/**
	* A version of {@link AbstractQueuedSynchronizer} in
	* which synchronization state is maintained as a {@code long}.
	* This class has exactly the same structure, properties, and methods
	* as {@code AbstractQueuedSynchronizer} with the exception
	* that all state-related parameters and results are defined
	* as {@code long} rather than {@code int}. This class
	* may be useful when creating synchronizers such as
	* multilevel locks and barriers that require
	* 64 bits of state.
	*
	* <p>See {@link AbstractQueuedSynchronizer} for usage
	* notes and examples.
	*
	* @since 1.6
	* @author Doug Lea
	*/
	public abstract class AbstractQueuedLongSynchronizer
	extends AbstractOwnableSynchronizer
	implements java.io.Serializable {

	private static final long serialVersionUID = 7373984972572414692L;

	/**
	* Constructor for subclasses to call.
	*/
	public AbstractQueuedLongSynchronizer() {}

	/*
	* To keep sources in sync, the remainder of this source file is
	* exactly cloned from AbstractQueuedSynchronizer, replacing class
	* name and changing ints related with sync state to longs. Please
	* keep it that way.
	*/

	// Node status bits, also used as argument and return values
	static final int WAITING = 1; // must be 1
	static final int CANCELLED = 0x80000000; // must be negative
	static final int COND = 2; // in a condition wait

	/** CLH Nodes */
	abstract static class Node {
	volatile Node prev; // initially attached via casTail
	volatile Node next; // visibly nonnull when signallable
	Thread waiter; // visibly nonnull when enqueued
	volatile int status; // written by owner, atomic bit ops by others

	// methods for atomic operations
	final boolean casPrev(Node c, Node v) { // for cleanQueue
	return U.weakCompareAndSetReference(this, PREV, c, v);
	}
	final boolean casNext(Node c, Node v) { // for cleanQueue
	return U.weakCompareAndSetReference(this, NEXT, c, v);
	}
	final int getAndUnsetStatus(int v) { // for signalling
	return U.getAndBitwiseAndInt(this, STATUS, ~v);
	}
	final void setPrevRelaxed(Node p) { // for off-queue assignment
	U.putReference(this, PREV, p);
	}
	final void setStatusRelaxed(int s) { // for off-queue assignment
	U.putInt(this, STATUS, s);
	}
	final void clearStatus() { // for reducing unneeded signals
	U.putIntOpaque(this, STATUS, 0);
	}

	private static final long STATUS
	= U.objectFieldOffset(Node.class, "status");
	private static final long NEXT
	= U.objectFieldOffset(Node.class, "next");
	private static final long PREV
	= U.objectFieldOffset(Node.class, "prev");
	}

	// Concrete classes tagged by type
	static final class ExclusiveNode extends Node { }
	static final class SharedNode extends Node { }

	static final class ConditionNode extends Node
	implements ForkJoinPool.ManagedBlocker {
	ConditionNode nextWaiter; // link to next waiting node

	/**
	* Allows Conditions to be used in ForkJoinPools without
	* risking fixed pool exhaustion. This is usable only for
	* untimed Condition waits, not timed versions.
	*/
	public final boolean isReleasable() {
	return status <= 1 \|\| Thread.currentThread().isInterrupted();
	}

	public final boolean block() {
	while (!isReleasable()) LockSupport.park();
	return true;
	}
	}

	/**
	* Head of the wait queue, lazily initialized.
	*/
	private transient volatile Node head;

	/**
	* Tail of the wait queue. After initialization, modified only via casTail.
	*/
	private transient volatile Node tail;

	/**
	* The synchronization state.
	*/
	private volatile long state;

	/**
	* Returns the current value of synchronization state.
	* This operation has memory semantics of a {@code volatile} read.
	* @return current state value
	*/
	protected final long getState() {
	return state;
	}

	/**
	* Sets the value of synchronization state.
	* This operation has memory semantics of a {@code volatile} write.
	* @param newState the new state value
	*/
	protected final void setState(long newState) {
	state = newState;
	}

	/**
	* Atomically sets synchronization state to the given updated
	* value if the current state value equals the expected value.
	* This operation has memory semantics of a {@code volatile} read
	* and write.
	*
	* @param expect the expected value
	* @param update the new value
	* @return {@code true} if successful. False return indicates that the actual
	* value was not equal to the expected value.
	*/
	protected final boolean compareAndSetState(long expect, long update) {
	return U.compareAndSetLong(this, STATE, expect, update);
	}

	// Queuing utilities

	private boolean casTail(Node c, Node v) {
	return U.compareAndSetReference(this, TAIL, c, v);
	}

	/** tries once to CAS a new dummy node for head */
	private void tryInitializeHead() {
	Node h = new ExclusiveNode();
	if (U.compareAndSetReference(this, HEAD, null, h))
	tail = h;
	}

	/**
	* Enqueues the node unless null. (Currently used only for
	* ConditionNodes; other cases are interleaved with acquires.)
	*/
	final void enqueue(Node node) {
	if (node != null) {
	for (;;) {
	Node t = tail;
	node.setPrevRelaxed(t); // avoid unnecessary fence
	if (t == null) // initialize
	tryInitializeHead();
	else if (casTail(t, node)) {
	t.next = node;
	if (t.status < 0) // wake up to clean link
	LockSupport.unpark(node.waiter);
	break;
	}
	}
	}
	}

	/** Returns true if node is found in traversal from tail */
	final boolean isEnqueued(Node node) {
	for (Node t = tail; t != null; t = t.prev)
	if (t == node)
	return true;
	return false;
	}

	/**
	* Wakes up the successor of given node, if one exists, and unsets its
	* WAITING status to avoid park race. This may fail to wake up an
	* eligible thread when one or more have been cancelled, but
	* cancelAcquire ensures liveness.
	*/
	private static void signalNext(Node h) {
	Node s;
	if (h != null && (s = h.next) != null && s.status != 0) {
	s.getAndUnsetStatus(WAITING);
	LockSupport.unpark(s.waiter);
	}
	}

	/** Wakes up the given node if in shared mode */
	private static void signalNextIfShared(Node h) {
	Node s;
	if (h != null && (s = h.next) != null &&
	(s instanceof SharedNode) && s.status != 0) {
	s.getAndUnsetStatus(WAITING);
	LockSupport.unpark(s.waiter);
	}
	}

	/**
	* Main acquire method, invoked by all exported acquire methods.
	*
	* @param node null unless a reacquiring Condition
	* @param arg the acquire argument
	* @param shared true if shared mode else exclusive
	* @param interruptible if abort and return negative on interrupt
	* @param timed if true use timed waits
	* @param time if timed, the System.nanoTime value to timeout
	* @return positive if acquired, 0 if timed out, negative if interrupted
	*/
	final int acquire(Node node, long arg, boolean shared,
	boolean interruptible, boolean timed, long time) {
	Thread current = Thread.currentThread();
	byte spins = 0, postSpins = 0; // retries upon unpark of first thread
	boolean interrupted = false, first = false;
	Node pred = null; // predecessor of node when enqueued

	/*
	* Repeatedly:
	* Check if node now first
	* if so, ensure head stable, else ensure valid predecessor
	* if node is first or not yet enqueued, try acquiring
	* else if node not yet created, create it
	* else if not yet enqueued, try once to enqueue
	* else if woken from park, retry (up to postSpins times)
	* else if WAITING status not set, set and retry
	* else park and clear WAITING status, and check cancellation
	*/

	for (;;) {
	if (!first && (pred = (node == null) ? null : node.prev) != null &&
	!(first = (head == pred))) {
	if (pred.status < 0) {
	cleanQueue(); // predecessor cancelled
	continue;
	} else if (pred.prev == null) {
	Thread.onSpinWait(); // ensure serialization
	continue;
	}
	}
	if (first \|\| pred == null) {
	boolean acquired;
	try {
	if (shared)
	acquired = (tryAcquireShared(arg) >= 0);
	else
	acquired = tryAcquire(arg);
	} catch (Throwable ex) {
	cancelAcquire(node, interrupted, false);
	throw ex;
	}
	if (acquired) {
	if (first) {
	node.prev = null;
	head = node;
	pred.next = null;
	node.waiter = null;
	if (shared)
	signalNextIfShared(node);
	if (interrupted)
	current.interrupt();
	}
	return 1;
	}
	}
	if (node == null) { // allocate; retry before enqueue
	if (shared)
	node = new SharedNode();
	else
	node = new ExclusiveNode();
	} else if (pred == null) { // try to enqueue
	node.waiter = current;
	Node t = tail;
	node.setPrevRelaxed(t); // avoid unnecessary fence
	if (t == null)
	tryInitializeHead();
	else if (!casTail(t, node))
	node.setPrevRelaxed(null); // back out
	else
	t.next = node;
	} else if (first && spins != 0) {
	--spins; // reduce unfairness on rewaits
	Thread.onSpinWait();
	} else if (node.status == 0) {
	node.status = WAITING; // enable signal and recheck
	} else {
	long nanos;
	spins = postSpins = (byte)((postSpins << 1) \| 1);
	if (!timed)
	LockSupport.park(this);
	else if ((nanos = time - System.nanoTime()) > 0L)
	LockSupport.parkNanos(this, nanos);
	else
	break;
	node.clearStatus();
	if ((interrupted \|= Thread.interrupted()) && interruptible)
	break;
	}
	}
	return cancelAcquire(node, interrupted, interruptible);
	}

	/**
	* Possibly repeatedly traverses from tail, unsplicing cancelled
	* nodes until none are found.
	*/
	private void cleanQueue() {
	for (;;) { // restart point
	for (Node q = tail, s = null, p, n;;) { // (p, q, s) triples
	if (q == null \|\| (p = q.prev) == null)
	return; // end of list
	if (s == null ? tail != q : (s.prev != q \|\| s.status < 0))
	break; // inconsistent
	if (q.status < 0) { // cancelled
	if ((s == null ? casTail(q, p) : s.casPrev(q, p)) &&
	q.prev == p) {
	p.casNext(q, s); // OK if fails
	if (p.prev == null)
	signalNext(p);
	}
	break;
	}
	if ((n = p.next) != q) { // help finish
	if (n != null && q.prev == p) {
	p.casNext(n, q);
	if (p.prev == null)
	signalNext(p);
	}
	break;
	}
	s = q;
	q = q.prev;
	}
	}
	}

	/**
	* Cancels an ongoing attempt to acquire.
	*
	* @param node the node (may be null if cancelled before enqueuing)
	* @param interrupted true if thread interrupted
	* @param interruptible if should report interruption vs reset
	*/
	private int cancelAcquire(Node node, boolean interrupted,
	boolean interruptible) {
	if (node != null) {
	node.waiter = null;
	node.status = CANCELLED;
	if (node.prev != null)
	cleanQueue();
	}
	if (interrupted) {
	if (interruptible)
	return CANCELLED;
	else
	Thread.currentThread().interrupt();
	}
	return 0;
	}

	// Main exported methods

	/**
	* Attempts to acquire in exclusive mode. This method should query
	* if the state of the object permits it to be acquired in the
	* exclusive mode, and if so to acquire it.
	*
	* <p>This method is always invoked by the thread performing
	* acquire. If this method reports failure, the acquire method
	* may queue the thread, if it is not already queued, until it is
	* signalled by a release from some other thread. This can be used
	* to implement method {@link Lock#tryLock()}.
	*
	* <p>The default
	* implementation throws {@link UnsupportedOperationException}.
	*
	* @param arg the acquire argument. This value is always the one
	* passed to an acquire method, or is the value saved on entry
	* to a condition wait. The value is otherwise uninterpreted
	* and can represent anything you like.
	* @return {@code true} if successful. Upon success, this object has
	* been acquired.
	* @throws IllegalMonitorStateException if acquiring would place this
	* synchronizer in an illegal state. This exception must be
	* thrown in a consistent fashion for synchronization to work
	* correctly.
	* @throws UnsupportedOperationException if exclusive mode is not supported
	*/
	protected boolean tryAcquire(long arg) {
	throw new UnsupportedOperationException();
	}

	/**
	* Attempts to set the state to reflect a release in exclusive
	* mode.
	*
	* <p>This method is always invoked by the thread performing release.
	*
	* <p>The default implementation throws
	* {@link UnsupportedOperationException}.
	*
	* @param arg the release argument. This value is always the one
	* passed to a release method, or the current state value upon
	* entry to a condition wait. The value is otherwise
	* uninterpreted and can represent anything you like.
	* @return {@code true} if this object is now in a fully released
	* state, so that any waiting threads may attempt to acquire;
	* and {@code false} otherwise.
	* @throws IllegalMonitorStateException if releasing would place this
	* synchronizer in an illegal state. This exception must be
	* thrown in a consistent fashion for synchronization to work
	* correctly.
	* @throws UnsupportedOperationException if exclusive mode is not supported
	*/
	protected boolean tryRelease(long arg) {
	throw new UnsupportedOperationException();
	}

	/**
	* Attempts to acquire in shared mode. This method should query if
	* the state of the object permits it to be acquired in the shared
	* mode, and if so to acquire it.
	*
	* <p>This method is always invoked by the thread performing
	* acquire. If this method reports failure, the acquire method
	* may queue the thread, if it is not already queued, until it is
	* signalled by a release from some other thread.
	*
	* <p>The default implementation throws {@link
	* UnsupportedOperationException}.
	*
	* @param arg the acquire argument. This value is always the one
	* passed to an acquire method, or is the value saved on entry
	* to a condition wait. The value is otherwise uninterpreted
	* and can represent anything you like.
	* @return a negative value on failure; zero if acquisition in shared
	* mode succeeded but no subsequent shared-mode acquire can
	* succeed; and a positive value if acquisition in shared
	* mode succeeded and subsequent shared-mode acquires might
	* also succeed, in which case a subsequent waiting thread
	* must check availability. (Support for three different
	* return values enables this method to be used in contexts
	* where acquires only sometimes act exclusively.) Upon
	* success, this object has been acquired.
	* @throws IllegalMonitorStateException if acquiring would place this
	* synchronizer in an illegal state. This exception must be
	* thrown in a consistent fashion for synchronization to work
	* correctly.
	* @throws UnsupportedOperationException if shared mode is not supported
	*/
	protected long tryAcquireShared(long arg) {
	throw new UnsupportedOperationException();
	}

	/**
	* Attempts to set the state to reflect a release in shared mode.
	*
	* <p>This method is always invoked by the thread performing release.
	*
	* <p>The default implementation throws
	* {@link UnsupportedOperationException}.
	*
	* @param arg the release argument. This value is always the one
	* passed to a release method, or the current state value upon
	* entry to a condition wait. The value is otherwise
	* uninterpreted and can represent anything you like.
	* @return {@code true} if this release of shared mode may permit a
	* waiting acquire (shared or exclusive) to succeed; and
	* {@code false} otherwise
	* @throws IllegalMonitorStateException if releasing would place this
	* synchronizer in an illegal state. This exception must be
	* thrown in a consistent fashion for synchronization to work
	* correctly.
	* @throws UnsupportedOperationException if shared mode is not supported
	*/
	protected boolean tryReleaseShared(long arg) {
	throw new UnsupportedOperationException();
	}

	/**
	* Returns {@code true} if synchronization is held exclusively with
	* respect to the current (calling) thread. This method is invoked
	* upon each call to a {@link ConditionObject} method.
	*
	* <p>The default implementation throws {@link
	* UnsupportedOperationException}. This method is invoked
	* internally only within {@link ConditionObject} methods, so need
	* not be defined if conditions are not used.
	*
	* @return {@code true} if synchronization is held exclusively;
	* {@code false} otherwise
	* @throws UnsupportedOperationException if conditions are not supported
	*/
	protected boolean isHeldExclusively() {
	throw new UnsupportedOperationException();
	}

	/**
	* Acquires in exclusive mode, ignoring interrupts. Implemented
	* by invoking at least once {@link #tryAcquire},
	* returning on success. Otherwise the thread is queued, possibly
	* repeatedly blocking and unblocking, invoking {@link
	* #tryAcquire} until success. This method can be used
	* to implement method {@link Lock#lock}.
	*
	* @param arg the acquire argument. This value is conveyed to
	* {@link #tryAcquire} but is otherwise uninterpreted and
	* can represent anything you like.
	*/
	public final void acquire(long arg) {
	if (!tryAcquire(arg))
	acquire(null, arg, false, false, false, 0L);
	}

	/**
	* Acquires in exclusive mode, aborting if interrupted.
	* Implemented by first checking interrupt status, then invoking
	* at least once {@link #tryAcquire}, returning on
	* success. Otherwise the thread is queued, possibly repeatedly
	* blocking and unblocking, invoking {@link #tryAcquire}
	* until success or the thread is interrupted. This method can be
	* used to implement method {@link Lock#lockInterruptibly}.
	*
	* @param arg the acquire argument. This value is conveyed to
	* {@link #tryAcquire} but is otherwise uninterpreted and
	* can represent anything you like.
	* @throws InterruptedException if the current thread is interrupted
	*/
	public final void acquireInterruptibly(long arg)
	throws InterruptedException {
	if (Thread.interrupted() \|\|
	(!tryAcquire(arg) && acquire(null, arg, false, true, false, 0L) < 0))
	throw new InterruptedException();
	}

	/**
	* Attempts to acquire in exclusive mode, aborting if interrupted,
	* and failing if the given timeout elapses. Implemented by first
	* checking interrupt status, then invoking at least once {@link
	* #tryAcquire}, returning on success. Otherwise, the thread is
	* queued, possibly repeatedly blocking and unblocking, invoking
	* {@link #tryAcquire} until success or the thread is interrupted
	* or the timeout elapses. This method can be used to implement
	* method {@link Lock#tryLock(long, TimeUnit)}.
	*
	* @param arg the acquire argument. This value is conveyed to
	* {@link #tryAcquire} but is otherwise uninterpreted and
	* can represent anything you like.
	* @param nanosTimeout the maximum number of nanoseconds to wait
	* @return {@code true} if acquired; {@code false} if timed out
	* @throws InterruptedException if the current thread is interrupted
	*/
	public final boolean tryAcquireNanos(long arg, long nanosTimeout)
	throws InterruptedException {
	if (!Thread.interrupted()) {
	if (tryAcquire(arg))
	return true;
	if (nanosTimeout <= 0L)
	return false;
	int stat = acquire(null, arg, false, true, true,
	System.nanoTime() + nanosTimeout);
	if (stat > 0)
	return true;
	if (stat == 0)
	return false;
	}
	throw new InterruptedException();
	}

	/**
	* Releases in exclusive mode. Implemented by unblocking one or
	* more threads if {@link #tryRelease} returns true.
	* This method can be used to implement method {@link Lock#unlock}.
	*
	* @param arg the release argument. This value is conveyed to
	* {@link #tryRelease} but is otherwise uninterpreted and
	* can represent anything you like.
	* @return the value returned from {@link #tryRelease}
	*/
	public final boolean release(long arg) {
	if (tryRelease(arg)) {
	signalNext(head);
	return true;
	}
	return false;
	}

	/**
	* Acquires in shared mode, ignoring interrupts. Implemented by
	* first invoking at least once {@link #tryAcquireShared},
	* returning on success. Otherwise the thread is queued, possibly
	* repeatedly blocking and unblocking, invoking {@link
	* #tryAcquireShared} until success.
	*
	* @param arg the acquire argument. This value is conveyed to
	* {@link #tryAcquireShared} but is otherwise uninterpreted
	* and can represent anything you like.
	*/
	public final void acquireShared(long arg) {
	if (tryAcquireShared(arg) < 0)
	acquire(null, arg, true, false, false, 0L);
	}

	/**
	* Acquires in shared mode, aborting if interrupted. Implemented
	* by first checking interrupt status, then invoking at least once
	* {@link #tryAcquireShared}, returning on success. Otherwise the
	* thread is queued, possibly repeatedly blocking and unblocking,
	* invoking {@link #tryAcquireShared} until success or the thread
	* is interrupted.
	* @param arg the acquire argument.
	* This value is conveyed to {@link #tryAcquireShared} but is
	* otherwise uninterpreted and can represent anything
	* you like.
	* @throws InterruptedException if the current thread is interrupted
	*/
	public final void acquireSharedInterruptibly(long arg)
	throws InterruptedException {
	if (Thread.interrupted() \|\|
	(tryAcquireShared(arg) < 0 &&
	acquire(null, arg, true, true, false, 0L) < 0))
	throw new InterruptedException();
	}

	/**
	* Attempts to acquire in shared mode, aborting if interrupted, and
	* failing if the given timeout elapses. Implemented by first
	* checking interrupt status, then invoking at least once {@link
	* #tryAcquireShared}, returning on success. Otherwise, the
	* thread is queued, possibly repeatedly blocking and unblocking,
	* invoking {@link #tryAcquireShared} until success or the thread
	* is interrupted or the timeout elapses.
	*
	* @param arg the acquire argument. This value is conveyed to
	* {@link #tryAcquireShared} but is otherwise uninterpreted
	* and can represent anything you like.
	* @param nanosTimeout the maximum number of nanoseconds to wait
	* @return {@code true} if acquired; {@code false} if timed out
	* @throws InterruptedException if the current thread is interrupted
	*/
	public final boolean tryAcquireSharedNanos(long arg, long nanosTimeout)
	throws InterruptedException {
	if (!Thread.interrupted()) {
	if (tryAcquireShared(arg) >= 0)
	return true;
	if (nanosTimeout <= 0L)
	return false;
	int stat = acquire(null, arg, true, true, true,
	System.nanoTime() + nanosTimeout);
	if (stat > 0)
	return true;
	if (stat == 0)
	return false;
	}
	throw new InterruptedException();
	}

	/**
	* Releases in shared mode. Implemented by unblocking one or more
	* threads if {@link #tryReleaseShared} returns true.
	*
	* @param arg the release argument. This value is conveyed to
	* {@link #tryReleaseShared} but is otherwise uninterpreted
	* and can represent anything you like.
	* @return the value returned from {@link #tryReleaseShared}
	*/
	public final boolean releaseShared(long arg) {
	if (tryReleaseShared(arg)) {
	signalNext(head);
	return true;
	}
	return false;
	}

	// Queue inspection methods

	/**
	* Queries whether any threads are waiting to acquire. Note that
	* because cancellations due to interrupts and timeouts may occur
	* at any time, a {@code true} return does not guarantee that any
	* other thread will ever acquire.
	*
	* @return {@code true} if there may be other threads waiting to acquire
	*/
	public final boolean hasQueuedThreads() {
	for (Node p = tail, h = head; p != h && p != null; p = p.prev)
	if (p.status >= 0)
	return true;
	return false;
	}

	/**
	* Queries whether any threads have ever contended to acquire this
	* synchronizer; that is, if an acquire method has ever blocked.
	*
	* <p>In this implementation, this operation returns in
	* constant time.
	*
	* @return {@code true} if there has ever been contention
	*/
	public final boolean hasContended() {
	return head != null;
	}

	/**
	* Returns the first (longest-waiting) thread in the queue, or
	* {@code null} if no threads are currently queued.
	*
	* <p>In this implementation, this operation normally returns in
	* constant time, but may iterate upon contention if other threads are
	* concurrently modifying the queue.
	*
	* @return the first (longest-waiting) thread in the queue, or
	* {@code null} if no threads are currently queued
	*/
	public final Thread getFirstQueuedThread() {
	Thread first = null, w; Node h, s;
	if ((h = head) != null && ((s = h.next) == null \|\|
	(first = s.waiter) == null \|\|
	s.prev == null)) {
	// traverse from tail on stale reads
	for (Node p = tail, q; p != null && (q = p.prev) != null; p = q)
	if ((w = p.waiter) != null)
	first = w;
	}
	return first;
	}

	/**
	* Returns true if the given thread is currently queued.
	*
	* <p>This implementation traverses the queue to determine
	* presence of the given thread.
	*
	* @param thread the thread
	* @return {@code true} if the given thread is on the queue
	* @throws NullPointerException if the thread is null
	*/
	public final boolean isQueued(Thread thread) {
	if (thread == null)
	throw new NullPointerException();
	for (Node p = tail; p != null; p = p.prev)
	if (p.waiter == thread)
	return true;
	return false;
	}

	/**
	* Returns {@code true} if the apparent first queued thread, if one
	* exists, is waiting in exclusive mode. If this method returns
	* {@code true}, and the current thread is attempting to acquire in
	* shared mode (that is, this method is invoked from {@link
	* #tryAcquireShared}) then it is guaranteed that the current thread
	* is not the first queued thread. Used only as a heuristic in
	* ReentrantReadWriteLock.
	*/
	final boolean apparentlyFirstQueuedIsExclusive() {
	Node h, s;
	return (h = head) != null && (s = h.next) != null &&
	!(s instanceof SharedNode) && s.waiter != null;
	}

	/**
	* Queries whether any threads have been waiting to acquire longer
	* than the current thread.
	*
	* <p>An invocation of this method is equivalent to (but may be
	* more efficient than):
	* <pre> {@code
	* getFirstQueuedThread() != Thread.currentThread()
	* && hasQueuedThreads()}</pre>
	*
	* <p>Note that because cancellations due to interrupts and
	* timeouts may occur at any time, a {@code true} return does not
	* guarantee that some other thread will acquire before the current
	* thread. Likewise, it is possible for another thread to win a
	* race to enqueue after this method has returned {@code false},
	* due to the queue being empty.
	*
	* <p>This method is designed to be used by a fair synchronizer to
	* avoid <a href="AbstractQueuedSynchronizer.html#barging">barging</a>.
	* Such a synchronizer's {@link #tryAcquire} method should return
	* {@code false}, and its {@link #tryAcquireShared} method should
	* return a negative value, if this method returns {@code true}
	* (unless this is a reentrant acquire). For example, the {@code
	* tryAcquire} method for a fair, reentrant, exclusive mode
	* synchronizer might look like this:
	*
	* <pre> {@code
	* protected boolean tryAcquire(long arg) {
	* if (isHeldExclusively()) {
	* // A reentrant acquire; increment hold count
	* return true;
	* } else if (hasQueuedPredecessors()) {
	* return false;
	* } else {
	* // try to acquire normally
	* }
	* }}</pre>
	*
	* @return {@code true} if there is a queued thread preceding the
	* current thread, and {@code false} if the current thread
	* is at the head of the queue or the queue is empty
	* @since 1.7
	*/
	public final boolean hasQueuedPredecessors() {
	Thread first = null; Node h, s;
	if ((h = head) != null && ((s = h.next) == null \|\|
	(first = s.waiter) == null \|\|
	s.prev == null))
	first = getFirstQueuedThread(); // retry via getFirstQueuedThread
	return first != null && first != Thread.currentThread();
	}

	// Instrumentation and monitoring methods

	/**
	* Returns an estimate of the number of threads waiting to
	* acquire. The value is only an estimate because the number of
	* threads may change dynamically while this method traverses
	* internal data structures. This method is designed for use in
	* monitoring system state, not for synchronization control.
	*
	* @return the estimated number of threads waiting to acquire
	*/
	public final int getQueueLength() {
	int n = 0;
	for (Node p = tail; p != null; p = p.prev) {
	if (p.waiter != null)
	++n;
	}
	return n;
	}

	/**
	* Returns a collection containing threads that may be waiting to
	* acquire. Because the actual set of threads may change
	* dynamically while constructing this result, the returned
	* collection is only a best-effort estimate. The elements of the
	* returned collection are in no particular order. This method is
	* designed to facilitate construction of subclasses that provide
	* more extensive monitoring facilities.
	*
	* @return the collection of threads
	*/
	public final Collection<Thread> getQueuedThreads() {
	ArrayList<Thread> list = new ArrayList<>();
	for (Node p = tail; p != null; p = p.prev) {
	Thread t = p.waiter;
	if (t != null)
	list.add(t);
	}
	return list;
	}

	/**
	* Returns a collection containing threads that may be waiting to
	* acquire in exclusive mode. This has the same properties
	* as {@link #getQueuedThreads} except that it only returns
	* those threads waiting due to an exclusive acquire.
	*
	* @return the collection of threads
	*/
	public final Collection<Thread> getExclusiveQueuedThreads() {
	ArrayList<Thread> list = new ArrayList<>();
	for (Node p = tail; p != null; p = p.prev) {
	if (!(p instanceof SharedNode)) {
	Thread t = p.waiter;
	if (t != null)
	list.add(t);
	}
	}
	return list;
	}

	/**
	* Returns a collection containing threads that may be waiting to
	* acquire in shared mode. This has the same properties
	* as {@link #getQueuedThreads} except that it only returns
	* those threads waiting due to a shared acquire.
	*
	* @return the collection of threads
	*/
	public final Collection<Thread> getSharedQueuedThreads() {
	ArrayList<Thread> list = new ArrayList<>();
	for (Node p = tail; p != null; p = p.prev) {
	if (p instanceof SharedNode) {
	Thread t = p.waiter;
	if (t != null)
	list.add(t);
	}
	}
	return list;
	}

	/**
	* Returns a string identifying this synchronizer, as well as its state.
	* The state, in brackets, includes the String {@code "State ="}
	* followed by the current value of {@link #getState}, and either
	* {@code "nonempty"} or {@code "empty"} depending on whether the
	* queue is empty.
	*
	* @return a string identifying this synchronizer, as well as its state
	*/
	public String toString() {
	return super.toString()
	+ "[State = " + getState() + ", "
	+ (hasQueuedThreads() ? "non" : "") + "empty queue]";
	}

	// Instrumentation methods for conditions

	/**
	* Queries whether the given ConditionObject
	* uses this synchronizer as its lock.
	*
	* @param condition the condition
	* @return {@code true} if owned
	* @throws NullPointerException if the condition is null
	*/
	public final boolean owns(ConditionObject condition) {
	return condition.isOwnedBy(this);
	}

	/**
	* Queries whether any threads are waiting on the given condition
	* associated with this synchronizer. Note that because timeouts
	* and interrupts may occur at any time, a {@code true} return
	* does not guarantee that a future {@code signal} will awaken
	* any threads. This method is designed primarily for use in
	* monitoring of the system state.
	*
	* @param condition the condition
	* @return {@code true} if there are any waiting threads
	* @throws IllegalMonitorStateException if exclusive synchronization
	* is not held
	* @throws IllegalArgumentException if the given condition is
	* not associated with this synchronizer
	* @throws NullPointerException if the condition is null
	*/
	public final boolean hasWaiters(ConditionObject condition) {
	if (!owns(condition))
	throw new IllegalArgumentException("Not owner");
	return condition.hasWaiters();
	}

	/**
	* Returns an estimate of the number of threads waiting on the
	* given condition associated with this synchronizer. Note that
	* because timeouts and interrupts may occur at any time, the
	* estimate serves only as an upper bound on the actual number of
	* waiters. This method is designed for use in monitoring system
	* state, not for synchronization control.
	*
	* @param condition the condition
	* @return the estimated number of waiting threads
	* @throws IllegalMonitorStateException if exclusive synchronization
	* is not held
	* @throws IllegalArgumentException if the given condition is
	* not associated with this synchronizer
	* @throws NullPointerException if the condition is null
	*/
	public final int getWaitQueueLength(ConditionObject condition) {
	if (!owns(condition))
	throw new IllegalArgumentException("Not owner");
	return condition.getWaitQueueLength();
	}

	/**
	* Returns a collection containing those threads that may be
	* waiting on the given condition associated with this
	* synchronizer. Because the actual set of threads may change
	* dynamically while constructing this result, the returned
	* collection is only a best-effort estimate. The elements of the
	* returned collection are in no particular order.
	*
	* @param condition the condition
	* @return the collection of threads
	* @throws IllegalMonitorStateException if exclusive synchronization
	* is not held
	* @throws IllegalArgumentException if the given condition is
	* not associated with this synchronizer
	* @throws NullPointerException if the condition is null
	*/
	public final Collection<Thread> getWaitingThreads(ConditionObject condition) {
	if (!owns(condition))
	throw new IllegalArgumentException("Not owner");
	return condition.getWaitingThreads();
	}

	/**
	* Condition implementation for a {@link AbstractQueuedLongSynchronizer}
	* serving as the basis of a {@link Lock} implementation.
	*
	* <p>Method documentation for this class describes mechanics,
	* not behavioral specifications from the point of view of Lock
	* and Condition users. Exported versions of this class will in
	* general need to be accompanied by documentation describing
	* condition semantics that rely on those of the associated
	* {@code AbstractQueuedLongSynchronizer}.
	*
	* <p>This class is Serializable, but all fields are transient,
	* so deserialized conditions have no waiters.
	*/
	public class ConditionObject implements Condition, java.io.Serializable {
	private static final long serialVersionUID = 1173984872572414699L;
	/** First node of condition queue. */
	private transient ConditionNode firstWaiter;
	/** Last node of condition queue. */
	private transient ConditionNode lastWaiter;

	/**
	* Creates a new {@code ConditionObject} instance.
	*/
	public ConditionObject() { }

	// Signalling methods

	/**
	* Removes and transfers one or all waiters to sync queue.
	*/
	private void doSignal(ConditionNode first, boolean all) {
	while (first != null) {
	ConditionNode next = first.nextWaiter;
	if ((firstWaiter = next) == null)
	lastWaiter = null;
	if ((first.getAndUnsetStatus(COND) & COND) != 0) {
	enqueue(first);
	if (!all)
	break;
	}
	first = next;
	}
	}

	/**
	* Moves the longest-waiting thread, if one exists, from the
	* wait queue for this condition to the wait queue for the
	* owning lock.
	*
	* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
	* returns {@code false}
	*/
	public final void signal() {
	ConditionNode first = firstWaiter;
	if (!isHeldExclusively())
	throw new IllegalMonitorStateException();
	if (first != null)
	doSignal(first, false);
	}

	/**
	* Moves all threads from the wait queue for this condition to
	* the wait queue for the owning lock.
	*
	* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
	* returns {@code false}
	*/
	public final void signalAll() {
	ConditionNode first = firstWaiter;
	if (!isHeldExclusively())
	throw new IllegalMonitorStateException();
	if (first != null)
	doSignal(first, true);
	}

	// Waiting methods

	/**
	* Adds node to condition list and releases lock.
	*
	* @param node the node
	* @return savedState to reacquire after wait
	*/
	private long enableWait(ConditionNode node) {
	if (isHeldExclusively()) {
	node.waiter = Thread.currentThread();
	node.setStatusRelaxed(COND \| WAITING);
	ConditionNode last = lastWaiter;
	if (last == null)
	firstWaiter = node;
	else
	last.nextWaiter = node;
	lastWaiter = node;
	long savedState = getState();
	if (release(savedState))
	return savedState;
	}
	node.status = CANCELLED; // lock not held or inconsistent
	throw new IllegalMonitorStateException();
	}

	/**
	* Returns true if a node that was initially placed on a condition
	* queue is now ready to reacquire on sync queue.
	* @param node the node
	* @return true if is reacquiring
	*/
	private boolean canReacquire(ConditionNode node) {
	// check links, not status to avoid enqueue race
	return node != null && node.prev != null && isEnqueued(node);
	}

	/**
	* Unlinks the given node and other non-waiting nodes from
	* condition queue unless already unlinked.
	*/
	private void unlinkCancelledWaiters(ConditionNode node) {
	if (node == null \|\| node.nextWaiter != null \|\| node == lastWaiter) {
	ConditionNode w = firstWaiter, trail = null;
	while (w != null) {
	ConditionNode next = w.nextWaiter;
	if ((w.status & COND) == 0) {
	w.nextWaiter = null;
	if (trail == null)
	firstWaiter = next;
	else
	trail.nextWaiter = next;
	if (next == null)
	lastWaiter = trail;
	} else
	trail = w;
	w = next;
	}
	}
	}

	/**
	* Implements uninterruptible condition wait.
	* <ol>
	* <li>Save lock state returned by {@link #getState}.
	* <li>Invoke {@link #release} with saved state as argument,
	* throwing IllegalMonitorStateException if it fails.
	* <li>Block until signalled.
	* <li>Reacquire by invoking specialized version of
	* {@link #acquire} with saved state as argument.
	* </ol>
	*/
	public final void awaitUninterruptibly() {
	ConditionNode node = new ConditionNode();
	long savedState = enableWait(node);
	LockSupport.setCurrentBlocker(this); // for back-compatibility
	boolean interrupted = false, rejected = false;
	while (!canReacquire(node)) {
	if (Thread.interrupted())
	interrupted = true;
	else if ((node.status & COND) != 0) {
	try {
	if (rejected)
	node.block();
	else
	ForkJoinPool.managedBlock(node);
	} catch (RejectedExecutionException ex) {
	rejected = true;
	} catch (InterruptedException ie) {
	interrupted = true;
	}
	} else
	Thread.onSpinWait(); // awoke while enqueuing
	}
	LockSupport.setCurrentBlocker(null);
	node.clearStatus();
	acquire(node, savedState, false, false, false, 0L);
	if (interrupted)
	Thread.currentThread().interrupt();
	}

	/**
	* Implements interruptible condition wait.
	* <ol>
	* <li>If current thread is interrupted, throw InterruptedException.
	* <li>Save lock state returned by {@link #getState}.
	* <li>Invoke {@link #release} with saved state as argument,
	* throwing IllegalMonitorStateException if it fails.
	* <li>Block until signalled or interrupted.
	* <li>Reacquire by invoking specialized version of
	* {@link #acquire} with saved state as argument.
	* <li>If interrupted while blocked in step 4, throw InterruptedException.
	* </ol>
	*/
	public final void await() throws InterruptedException {
	if (Thread.interrupted())
	throw new InterruptedException();
	ConditionNode node = new ConditionNode();
	long savedState = enableWait(node);
	LockSupport.setCurrentBlocker(this); // for back-compatibility
	boolean interrupted = false, cancelled = false, rejected = false;
	while (!canReacquire(node)) {
	if (interrupted \|= Thread.interrupted()) {
	if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0)
	break; // else interrupted after signal
	} else if ((node.status & COND) != 0) {
	try {
	if (rejected)
	node.block();
	else
	ForkJoinPool.managedBlock(node);
	} catch (RejectedExecutionException ex) {
	rejected = true;
	} catch (InterruptedException ie) {
	interrupted = true;
	}
	} else
	Thread.onSpinWait(); // awoke while enqueuing
	}
	LockSupport.setCurrentBlocker(null);
	node.clearStatus();
	acquire(node, savedState, false, false, false, 0L);
	if (interrupted) {
	if (cancelled) {
	unlinkCancelledWaiters(node);
	throw new InterruptedException();
	}
	Thread.currentThread().interrupt();
	}
	}

	/**
	* Implements timed condition wait.
	* <ol>
	* <li>If current thread is interrupted, throw InterruptedException.
	* <li>Save lock state returned by {@link #getState}.
	* <li>Invoke {@link #release} with saved state as argument,
	* throwing IllegalMonitorStateException if it fails.
	* <li>Block until signalled, interrupted, or timed out.
	* <li>Reacquire by invoking specialized version of
	* {@link #acquire} with saved state as argument.
	* <li>If interrupted while blocked in step 4, throw InterruptedException.
	* </ol>
	*/
	public final long awaitNanos(long nanosTimeout)
	throws InterruptedException {
	if (Thread.interrupted())
	throw new InterruptedException();
	ConditionNode node = new ConditionNode();
	long savedState = enableWait(node);
	long nanos = (nanosTimeout < 0L) ? 0L : nanosTimeout;
	long deadline = System.nanoTime() + nanos;
	boolean cancelled = false, interrupted = false;
	while (!canReacquire(node)) {
	if ((interrupted \|= Thread.interrupted()) \|\|
	(nanos = deadline - System.nanoTime()) <= 0L) {
	if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0)
	break;
	} else
	LockSupport.parkNanos(this, nanos);
	}
	node.clearStatus();
	acquire(node, savedState, false, false, false, 0L);
	if (cancelled) {
	unlinkCancelledWaiters(node);
	if (interrupted)
	throw new InterruptedException();
	} else if (interrupted)
	Thread.currentThread().interrupt();
	long remaining = deadline - System.nanoTime(); // avoid overflow
	return (remaining <= nanosTimeout) ? remaining : Long.MIN_VALUE;
	}

	/**
	* Implements absolute timed condition wait.
	* <ol>
	* <li>If current thread is interrupted, throw InterruptedException.
	* <li>Save lock state returned by {@link #getState}.
	* <li>Invoke {@link #release} with saved state as argument,
	* throwing IllegalMonitorStateException if it fails.
	* <li>Block until signalled, interrupted, or timed out.
	* <li>Reacquire by invoking specialized version of
	* {@link #acquire} with saved state as argument.
	* <li>If interrupted while blocked in step 4, throw InterruptedException.
	* <li>If timed out while blocked in step 4, return false, else true.
	* </ol>
	*/
	public final boolean awaitUntil(Date deadline)
	throws InterruptedException {
	long abstime = deadline.getTime();
	if (Thread.interrupted())
	throw new InterruptedException();
	ConditionNode node = new ConditionNode();
	long savedState = enableWait(node);
	boolean cancelled = false, interrupted = false;
	while (!canReacquire(node)) {
	if ((interrupted \|= Thread.interrupted()) \|\|
	System.currentTimeMillis() >= abstime) {
	if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0)
	break;
	} else
	LockSupport.parkUntil(this, abstime);
	}
	node.clearStatus();
	acquire(node, savedState, false, false, false, 0L);
	if (cancelled) {
	unlinkCancelledWaiters(node);
	if (interrupted)
	throw new InterruptedException();
	} else if (interrupted)
	Thread.currentThread().interrupt();
	return !cancelled;
	}

	/**
	* Implements timed condition wait.
	* <ol>
	* <li>If current thread is interrupted, throw InterruptedException.
	* <li>Save lock state returned by {@link #getState}.
	* <li>Invoke {@link #release} with saved state as argument,
	* throwing IllegalMonitorStateException if it fails.
	* <li>Block until signalled, interrupted, or timed out.
	* <li>Reacquire by invoking specialized version of
	* {@link #acquire} with saved state as argument.
	* <li>If interrupted while blocked in step 4, throw InterruptedException.
	* <li>If timed out while blocked in step 4, return false, else true.
	* </ol>
	*/
	public final boolean await(long time, TimeUnit unit)
	throws InterruptedException {
	long nanosTimeout = unit.toNanos(time);
	if (Thread.interrupted())
	throw new InterruptedException();
	ConditionNode node = new ConditionNode();
	long savedState = enableWait(node);
	long nanos = (nanosTimeout < 0L) ? 0L : nanosTimeout;
	long deadline = System.nanoTime() + nanos;
	boolean cancelled = false, interrupted = false;
	while (!canReacquire(node)) {
	if ((interrupted \|= Thread.interrupted()) \|\|
	(nanos = deadline - System.nanoTime()) <= 0L) {
	if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0)
	break;
	} else
	LockSupport.parkNanos(this, nanos);
	}
	node.clearStatus();
	acquire(node, savedState, false, false, false, 0L);
	if (cancelled) {
	unlinkCancelledWaiters(node);
	if (interrupted)
	throw new InterruptedException();
	} else if (interrupted)
	Thread.currentThread().interrupt();
	return !cancelled;
	}

	// support for instrumentation

	/**
	* Returns true if this condition was created by the given
	* synchronization object.
	*
	* @return {@code true} if owned
	*/
	final boolean isOwnedBy(AbstractQueuedLongSynchronizer sync) {
	return sync == AbstractQueuedLongSynchronizer.this;
	}

	/**
	* Queries whether any threads are waiting on this condition.
	* Implements {@link AbstractQueuedLongSynchronizer#hasWaiters(ConditionObject)}.
	*
	* @return {@code true} if there are any waiting threads
	* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
	* returns {@code false}
	*/
	protected final boolean hasWaiters() {
	if (!isHeldExclusively())
	throw new IllegalMonitorStateException();
	for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) {
	if ((w.status & COND) != 0)
	return true;
	}
	return false;
	}

	/**
	* Returns an estimate of the number of threads waiting on
	* this condition.
	* Implements {@link AbstractQueuedLongSynchronizer#getWaitQueueLength(ConditionObject)}.
	*
	* @return the estimated number of waiting threads
	* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
	* returns {@code false}
	*/
	protected final int getWaitQueueLength() {
	if (!isHeldExclusively())
	throw new IllegalMonitorStateException();
	int n = 0;
	for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) {
	if ((w.status & COND) != 0)
	++n;
	}
	return n;
	}

	/**
	* Returns a collection containing those threads that may be
	* waiting on this Condition.
	* Implements {@link AbstractQueuedLongSynchronizer#getWaitingThreads(ConditionObject)}.
	*
	* @return the collection of threads
	* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
	* returns {@code false}
	*/
	protected final Collection<Thread> getWaitingThreads() {
	if (!isHeldExclusively())
	throw new IllegalMonitorStateException();
	ArrayList<Thread> list = new ArrayList<>();
	for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) {
	if ((w.status & COND) != 0) {
	Thread t = w.waiter;
	if (t != null)
	list.add(t);
	}
	}
	return list;
	}
	}

	// Unsafe
	private static final Unsafe U = Unsafe.getUnsafe();
	private static final long STATE
	= U.objectFieldOffset(AbstractQueuedLongSynchronizer.class, "state");
	private static final long HEAD
	= U.objectFieldOffset(AbstractQueuedLongSynchronizer.class, "head");
	private static final long TAIL
	= U.objectFieldOffset(AbstractQueuedLongSynchronizer.class, "tail");

	static {
	Class<?> ensureLoaded = LockSupport.class;
	}
	}

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