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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 and Martin Buchholz with assistance from members of
	* JCP JSR-166 Expert Group and released to the public domain, as explained
	* at http://creativecommons.org/publicdomain/zero/1.0/
	*/

	package java.util.concurrent;

	import java.util.AbstractQueue;
	import java.util.ArrayList;
	import java.util.Collection;
	import java.util.Iterator;
	import java.util.NoSuchElementException;
	import java.util.Queue;
	import java.util.Spliterator;
	import java.util.Spliterators;
	import java.util.function.Consumer;

	/**
	* An unbounded thread-safe {@linkplain Queue queue} based on linked nodes.
	* This queue orders elements FIFO (first-in-first-out).
	* The <em>head</em> of the queue is that element that has been on the
	* queue the longest time.
	* The <em>tail</em> of the queue is that element that has been on the
	* queue the shortest time. New elements
	* are inserted at the tail of the queue, and the queue retrieval
	* operations obtain elements at the head of the queue.
	* A {@code ConcurrentLinkedQueue} is an appropriate choice when
	* many threads will share access to a common collection.
	* Like most other concurrent collection implementations, this class
	* does not permit the use of {@code null} elements.
	*
	* <p>This implementation employs an efficient <em>non-blocking</em>
	* algorithm based on one described in <a
	* href="http://www.cs.rochester.edu/u/michael/PODC96.html"> Simple,
	* Fast, and Practical Non-Blocking and Blocking Concurrent Queue
	* Algorithms</a> by Maged M. Michael and Michael L. Scott.
	*
	* <p>Iterators are <i>weakly consistent</i>, returning elements
	* reflecting the state of the queue at some point at or since the
	* creation of the iterator. They do <em>not</em> throw {@link
	* java.util.ConcurrentModificationException}, and may proceed concurrently
	* with other operations. Elements contained in the queue since the creation
	* of the iterator will be returned exactly once.
	*
	* <p>Beware that, unlike in most collections, the {@code size} method
	* is <em>NOT</em> a constant-time operation. Because of the
	* asynchronous nature of these queues, determining the current number
	* of elements requires a traversal of the elements, and so may report
	* inaccurate results if this collection is modified during traversal.
	* Additionally, the bulk operations {@code addAll},
	* {@code removeAll}, {@code retainAll}, {@code containsAll},
	* {@code equals}, and {@code toArray} are <em>not</em> guaranteed
	* to be performed atomically. For example, an iterator operating
	* concurrently with an {@code addAll} operation might view only some
	* of the added elements.
	*
	* <p>This class and its iterator implement all of the <em>optional</em>
	* methods of the {@link Queue} and {@link Iterator} interfaces.
	*
	* <p>Memory consistency effects: As with other concurrent
	* collections, actions in a thread prior to placing an object into a
	* {@code ConcurrentLinkedQueue}
	* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
	* actions subsequent to the access or removal of that element from
	* the {@code ConcurrentLinkedQueue} in another thread.
	*
	* <p>This class is a member of the
	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
	* Java Collections Framework</a>.
	*
	* @since 1.5
	* @author Doug Lea
	* @param <E> the type of elements held in this collection
	*/
	public class ConcurrentLinkedQueue<E> extends AbstractQueue<E>
	implements Queue<E>, java.io.Serializable {
	private static final long serialVersionUID = 196745693267521676L;

	/*
	* This is a modification of the Michael & Scott algorithm,
	* adapted for a garbage-collected environment, with support for
	* interior node deletion (to support remove(Object)). For
	* explanation, read the paper.
	*
	* Note that like most non-blocking algorithms in this package,
	* this implementation relies on the fact that in garbage
	* collected systems, there is no possibility of ABA problems due
	* to recycled nodes, so there is no need to use "counted
	* pointers" or related techniques seen in versions used in
	* non-GC'ed settings.
	*
	* The fundamental invariants are:
	* - There is exactly one (last) Node with a null next reference,
	* which is CASed when enqueueing. This last Node can be
	* reached in O(1) time from tail, but tail is merely an
	* optimization - it can always be reached in O(N) time from
	* head as well.
	* - The elements contained in the queue are the non-null items in
	* Nodes that are reachable from head. CASing the item
	* reference of a Node to null atomically removes it from the
	* queue. Reachability of all elements from head must remain
	* true even in the case of concurrent modifications that cause
	* head to advance. A dequeued Node may remain in use
	* indefinitely due to creation of an Iterator or simply a
	* poll() that has lost its time slice.
	*
	* The above might appear to imply that all Nodes are GC-reachable
	* from a predecessor dequeued Node. That would cause two problems:
	* - allow a rogue Iterator to cause unbounded memory retention
	* - cause cross-generational linking of old Nodes to new Nodes if
	* a Node was tenured while live, which generational GCs have a
	* hard time dealing with, causing repeated major collections.
	* However, only non-deleted Nodes need to be reachable from
	* dequeued Nodes, and reachability does not necessarily have to
	* be of the kind understood by the GC. We use the trick of
	* linking a Node that has just been dequeued to itself. Such a
	* self-link implicitly means to advance to head.
	*
	* Both head and tail are permitted to lag. In fact, failing to
	* update them every time one could is a significant optimization
	* (fewer CASes). As with LinkedTransferQueue (see the internal
	* documentation for that class), we use a slack threshold of two;
	* that is, we update head/tail when the current pointer appears
	* to be two or more steps away from the first/last node.
	*
	* Since head and tail are updated concurrently and independently,
	* it is possible for tail to lag behind head (why not)?
	*
	* CASing a Node's item reference to null atomically removes the
	* element from the queue. Iterators skip over Nodes with null
	* items. Prior implementations of this class had a race between
	* poll() and remove(Object) where the same element would appear
	* to be successfully removed by two concurrent operations. The
	* method remove(Object) also lazily unlinks deleted Nodes, but
	* this is merely an optimization.
	*
	* When constructing a Node (before enqueuing it) we avoid paying
	* for a volatile write to item by using Unsafe.putObject instead
	* of a normal write. This allows the cost of enqueue to be
	* "one-and-a-half" CASes.
	*
	* Both head and tail may or may not point to a Node with a
	* non-null item. If the queue is empty, all items must of course
	* be null. Upon creation, both head and tail refer to a dummy
	* Node with null item. Both head and tail are only updated using
	* CAS, so they never regress, although again this is merely an
	* optimization.
	*/

	private static class Node<E> {
	volatile E item;
	volatile Node<E> next;

	/**
	* Constructs a new node. Uses relaxed write because item can
	* only be seen after publication via casNext.
	*/
	Node(E item) {
	UNSAFE.putObject(this, itemOffset, item);
	}

	boolean casItem(E cmp, E val) {
	return UNSAFE.compareAndSwapObject(this, itemOffset, cmp, val);
	}

	void lazySetNext(Node<E> val) {
	UNSAFE.putOrderedObject(this, nextOffset, val);
	}

	boolean casNext(Node<E> cmp, Node<E> val) {
	return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val);
	}

	// Unsafe mechanics

	private static final sun.misc.Unsafe UNSAFE;
	private static final long itemOffset;
	private static final long nextOffset;

	static {
	try {
	UNSAFE = sun.misc.Unsafe.getUnsafe();
	Class<?> k = Node.class;
	itemOffset = UNSAFE.objectFieldOffset
	(k.getDeclaredField("item"));
	nextOffset = UNSAFE.objectFieldOffset
	(k.getDeclaredField("next"));
	} catch (Exception e) {
	throw new Error(e);
	}
	}
	}

	/**
	* A node from which the first live (non-deleted) node (if any)
	* can be reached in O(1) time.
	* Invariants:
	* - all live nodes are reachable from head via succ()
	* - head != null
	* - (tmp = head).next != tmp \|\| tmp != head
	* Non-invariants:
	* - head.item may or may not be null.
	* - it is permitted for tail to lag behind head, that is, for tail
	* to not be reachable from head!
	*/
	private transient volatile Node<E> head;

	/**
	* A node from which the last node on list (that is, the unique
	* node with node.next == null) can be reached in O(1) time.
	* Invariants:
	* - the last node is always reachable from tail via succ()
	* - tail != null
	* Non-invariants:
	* - tail.item may or may not be null.
	* - it is permitted for tail to lag behind head, that is, for tail
	* to not be reachable from head!
	* - tail.next may or may not be self-pointing to tail.
	*/
	private transient volatile Node<E> tail;

	/**
	* Creates a {@code ConcurrentLinkedQueue} that is initially empty.
	*/
	public ConcurrentLinkedQueue() {
	head = tail = new Node<E>(null);
	}

	/**
	* Creates a {@code ConcurrentLinkedQueue}
	* initially containing the elements of the given collection,
	* added in traversal order of the collection's iterator.
	*
	* @param c the collection of elements to initially contain
	* @throws NullPointerException if the specified collection or any
	* of its elements are null
	*/
	public ConcurrentLinkedQueue(Collection<? extends E> c) {
	Node<E> h = null, t = null;
	for (E e : c) {
	checkNotNull(e);
	Node<E> newNode = new Node<E>(e);
	if (h == null)
	h = t = newNode;
	else {
	t.lazySetNext(newNode);
	t = newNode;
	}
	}
	if (h == null)
	h = t = new Node<E>(null);
	head = h;
	tail = t;
	}

	// Have to override just to update the javadoc

	/**
	* Inserts the specified element at the tail of this queue.
	* As the queue is unbounded, this method will never throw
	* {@link IllegalStateException} or return {@code false}.
	*
	* @return {@code true} (as specified by {@link Collection#add})
	* @throws NullPointerException if the specified element is null
	*/
	public boolean add(E e) {
	return offer(e);
	}

	/**
	* Tries to CAS head to p. If successful, repoint old head to itself
	* as sentinel for succ(), below.
	*/
	final void updateHead(Node<E> h, Node<E> p) {
	if (h != p && casHead(h, p))
	h.lazySetNext(h);
	}

	/**
	* Returns the successor of p, or the head node if p.next has been
	* linked to self, which will only be true if traversing with a
	* stale pointer that is now off the list.
	*/
	final Node<E> succ(Node<E> p) {
	Node<E> next = p.next;
	return (p == next) ? head : next;
	}

	/**
	* Inserts the specified element at the tail of this queue.
	* As the queue is unbounded, this method will never return {@code false}.
	*
	* @return {@code true} (as specified by {@link Queue#offer})
	* @throws NullPointerException if the specified element is null
	*/
	public boolean offer(E e) {
	checkNotNull(e);
	final Node<E> newNode = new Node<E>(e);

	for (Node<E> t = tail, p = t;;) {
	Node<E> q = p.next;
	if (q == null) {
	// p is last node
	if (p.casNext(null, newNode)) {
	// Successful CAS is the linearization point
	// for e to become an element of this queue,
	// and for newNode to become "live".
	if (p != t) // hop two nodes at a time
	casTail(t, newNode); // Failure is OK.
	return true;
	}
	// Lost CAS race to another thread; re-read next
	}
	else if (p == q)
	// We have fallen off list. If tail is unchanged, it
	// will also be off-list, in which case we need to
	// jump to head, from which all live nodes are always
	// reachable. Else the new tail is a better bet.
	p = (t != (t = tail)) ? t : head;
	else
	// Check for tail updates after two hops.
	p = (p != t && t != (t = tail)) ? t : q;
	}
	}

	public E poll() {
	restartFromHead:
	for (;;) {
	for (Node<E> h = head, p = h, q;;) {
	E item = p.item;

	if (item != null && p.casItem(item, null)) {
	// Successful CAS is the linearization point
	// for item to be removed from this queue.
	if (p != h) // hop two nodes at a time
	updateHead(h, ((q = p.next) != null) ? q : p);
	return item;
	}
	else if ((q = p.next) == null) {
	updateHead(h, p);
	return null;
	}
	else if (p == q)
	continue restartFromHead;
	else
	p = q;
	}
	}
	}

	public E peek() {
	restartFromHead:
	for (;;) {
	for (Node<E> h = head, p = h, q;;) {
	E item = p.item;
	if (item != null \|\| (q = p.next) == null) {
	updateHead(h, p);
	return item;
	}
	else if (p == q)
	continue restartFromHead;
	else
	p = q;
	}
	}
	}

	/**
	* Returns the first live (non-deleted) node on list, or null if none.
	* This is yet another variant of poll/peek; here returning the
	* first node, not element. We could make peek() a wrapper around
	* first(), but that would cost an extra volatile read of item,
	* and the need to add a retry loop to deal with the possibility
	* of losing a race to a concurrent poll().
	*/
	Node<E> first() {
	restartFromHead:
	for (;;) {
	for (Node<E> h = head, p = h, q;;) {
	boolean hasItem = (p.item != null);
	if (hasItem \|\| (q = p.next) == null) {
	updateHead(h, p);
	return hasItem ? p : null;
	}
	else if (p == q)
	continue restartFromHead;
	else
	p = q;
	}
	}
	}

	/**
	* Returns {@code true} if this queue contains no elements.
	*
	* @return {@code true} if this queue contains no elements
	*/
	public boolean isEmpty() {
	return first() == null;
	}

	/**
	* Returns the number of elements in this queue. If this queue
	* contains more than {@code Integer.MAX_VALUE} elements, returns
	* {@code Integer.MAX_VALUE}.
	*
	* <p>Beware that, unlike in most collections, this method is
	* <em>NOT</em> a constant-time operation. Because of the
	* asynchronous nature of these queues, determining the current
	* number of elements requires an O(n) traversal.
	* Additionally, if elements are added or removed during execution
	* of this method, the returned result may be inaccurate. Thus,
	* this method is typically not very useful in concurrent
	* applications.
	*
	* @return the number of elements in this queue
	*/
	public int size() {
	int count = 0;
	for (Node<E> p = first(); p != null; p = succ(p))
	if (p.item != null)
	// Collection.size() spec says to max out
	if (++count == Integer.MAX_VALUE)
	break;
	return count;
	}

	/**
	* Returns {@code true} if this queue contains the specified element.
	* More formally, returns {@code true} if and only if this queue contains
	* at least one element {@code e} such that {@code o.equals(e)}.
	*
	* @param o object to be checked for containment in this queue
	* @return {@code true} if this queue contains the specified element
	*/
	public boolean contains(Object o) {
	if (o == null) return false;
	for (Node<E> p = first(); p != null; p = succ(p)) {
	E item = p.item;
	if (item != null && o.equals(item))
	return true;
	}
	return false;
	}

	/**
	* Removes a single instance of the specified element from this queue,
	* if it is present. More formally, removes an element {@code e} such
	* that {@code o.equals(e)}, if this queue contains one or more such
	* elements.
	* Returns {@code true} if this queue contained the specified element
	* (or equivalently, if this queue changed as a result of the call).
	*
	* @param o element to be removed from this queue, if present
	* @return {@code true} if this queue changed as a result of the call
	*/
	public boolean remove(Object o) {
	if (o != null) {
	Node<E> next, pred = null;
	for (Node<E> p = first(); p != null; pred = p, p = next) {
	boolean removed = false;
	E item = p.item;
	if (item != null) {
	if (!o.equals(item)) {
	next = succ(p);
	continue;
	}
	removed = p.casItem(item, null);
	}

	next = succ(p);
	if (pred != null && next != null) // unlink
	pred.casNext(p, next);
	if (removed)
	return true;
	}
	}
	return false;
	}

	/**
	* Appends all of the elements in the specified collection to the end of
	* this queue, in the order that they are returned by the specified
	* collection's iterator. Attempts to {@code addAll} of a queue to
	* itself result in {@code IllegalArgumentException}.
	*
	* @param c the elements to be inserted into this queue
	* @return {@code true} if this queue changed as a result of the call
	* @throws NullPointerException if the specified collection or any
	* of its elements are null
	* @throws IllegalArgumentException if the collection is this queue
	*/
	public boolean addAll(Collection<? extends E> c) {
	if (c == this)
	// As historically specified in AbstractQueue#addAll
	throw new IllegalArgumentException();

	// Copy c into a private chain of Nodes
	Node<E> beginningOfTheEnd = null, last = null;
	for (E e : c) {
	checkNotNull(e);
	Node<E> newNode = new Node<E>(e);
	if (beginningOfTheEnd == null)
	beginningOfTheEnd = last = newNode;
	else {
	last.lazySetNext(newNode);
	last = newNode;
	}
	}
	if (beginningOfTheEnd == null)
	return false;

	// Atomically append the chain at the tail of this collection
	for (Node<E> t = tail, p = t;;) {
	Node<E> q = p.next;
	if (q == null) {
	// p is last node
	if (p.casNext(null, beginningOfTheEnd)) {
	// Successful CAS is the linearization point
	// for all elements to be added to this queue.
	if (!casTail(t, last)) {
	// Try a little harder to update tail,
	// since we may be adding many elements.
	t = tail;
	if (last.next == null)
	casTail(t, last);
	}
	return true;
	}
	// Lost CAS race to another thread; re-read next
	}
	else if (p == q)
	// We have fallen off list. If tail is unchanged, it
	// will also be off-list, in which case we need to
	// jump to head, from which all live nodes are always
	// reachable. Else the new tail is a better bet.
	p = (t != (t = tail)) ? t : head;
	else
	// Check for tail updates after two hops.
	p = (p != t && t != (t = tail)) ? t : q;
	}
	}

	/**
	* Returns an array containing all of the elements in this queue, in
	* proper sequence.
	*
	* <p>The returned array will be "safe" in that no references to it are
	* maintained by this queue. (In other words, this method must allocate
	* a new array). The caller is thus free to modify the returned array.
	*
	* <p>This method acts as bridge between array-based and collection-based
	* APIs.
	*
	* @return an array containing all of the elements in this queue
	*/
	public Object[] toArray() {
	// Use ArrayList to deal with resizing.
	ArrayList<E> al = new ArrayList<E>();
	for (Node<E> p = first(); p != null; p = succ(p)) {
	E item = p.item;
	if (item != null)
	al.add(item);
	}
	return al.toArray();
	}

	/**
	* Returns an array containing all of the elements in this queue, in
	* proper sequence; the runtime type of the returned array is that of
	* the specified array. If the queue fits in the specified array, it
	* is returned therein. Otherwise, a new array is allocated with the
	* runtime type of the specified array and the size of this queue.
	*
	* <p>If this queue fits in the specified array with room to spare
	* (i.e., the array has more elements than this queue), the element in
	* the array immediately following the end of the queue is set to
	* {@code null}.
	*
	* <p>Like the {@link #toArray()} method, this method acts as bridge between
	* array-based and collection-based APIs. Further, this method allows
	* precise control over the runtime type of the output array, and may,
	* under certain circumstances, be used to save allocation costs.
	*
	* <p>Suppose {@code x} is a queue known to contain only strings.
	* The following code can be used to dump the queue into a newly
	* allocated array of {@code String}:
	*
	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
	*
	* Note that {@code toArray(new Object[0])} is identical in function to
	* {@code toArray()}.
	*
	* @param a the array into which the elements of the queue are to
	* be stored, if it is big enough; otherwise, a new array of the
	* same runtime type is allocated for this purpose
	* @return an array containing all of the elements in this queue
	* @throws ArrayStoreException if the runtime type of the specified array
	* is not a supertype of the runtime type of every element in
	* this queue
	* @throws NullPointerException if the specified array is null
	*/
	@SuppressWarnings("unchecked")
	public <T> T[] toArray(T[] a) {
	// try to use sent-in array
	int k = 0;
	Node<E> p;
	for (p = first(); p != null && k < a.length; p = succ(p)) {
	E item = p.item;
	if (item != null)
	a[k++] = (T)item;
	}
	if (p == null) {
	if (k < a.length)
	a[k] = null;
	return a;
	}

	// If won't fit, use ArrayList version
	ArrayList<E> al = new ArrayList<E>();
	for (Node<E> q = first(); q != null; q = succ(q)) {
	E item = q.item;
	if (item != null)
	al.add(item);
	}
	return al.toArray(a);
	}

	/**
	* Returns an iterator over the elements in this queue in proper sequence.
	* The elements will be returned in order from first (head) to last (tail).
	*
	* <p>The returned iterator is
	* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
	*
	* @return an iterator over the elements in this queue in proper sequence
	*/
	public Iterator<E> iterator() {
	return new Itr();
	}

	private class Itr implements Iterator<E> {
	/**
	* Next node to return item for.
	*/
	private Node<E> nextNode;

	/**
	* nextItem holds on to item fields because once we claim
	* that an element exists in hasNext(), we must return it in
	* the following next() call even if it was in the process of
	* being removed when hasNext() was called.
	*/
	private E nextItem;

	/**
	* Node of the last returned item, to support remove.
	*/
	private Node<E> lastRet;

	Itr() {
	advance();
	}

	/**
	* Moves to next valid node and returns item to return for
	* next(), or null if no such.
	*/
	private E advance() {
	lastRet = nextNode;
	E x = nextItem;

	Node<E> pred, p;
	if (nextNode == null) {
	p = first();
	pred = null;
	} else {
	pred = nextNode;
	p = succ(nextNode);
	}

	for (;;) {
	if (p == null) {
	nextNode = null;
	nextItem = null;
	return x;
	}
	E item = p.item;
	if (item != null) {
	nextNode = p;
	nextItem = item;
	return x;
	} else {
	// skip over nulls
	Node<E> next = succ(p);
	if (pred != null && next != null)
	pred.casNext(p, next);
	p = next;
	}
	}
	}

	public boolean hasNext() {
	return nextNode != null;
	}

	public E next() {
	if (nextNode == null) throw new NoSuchElementException();
	return advance();
	}

	public void remove() {
	Node<E> l = lastRet;
	if (l == null) throw new IllegalStateException();
	// rely on a future traversal to relink.
	l.item = null;
	lastRet = null;
	}
	}

	/**
	* Saves this queue to a stream (that is, serializes it).
	*
	* @param s the stream
	* @throws java.io.IOException if an I/O error occurs
	* @serialData All of the elements (each an {@code E}) in
	* the proper order, followed by a null
	*/
	private void writeObject(java.io.ObjectOutputStream s)
	throws java.io.IOException {

	// Write out any hidden stuff
	s.defaultWriteObject();

	// Write out all elements in the proper order.
	for (Node<E> p = first(); p != null; p = succ(p)) {
	Object item = p.item;
	if (item != null)
	s.writeObject(item);
	}

	// Use trailing null as sentinel
	s.writeObject(null);
	}

	/**
	* Reconstitutes this queue from a stream (that is, deserializes it).
	* @param s the stream
	* @throws ClassNotFoundException if the class of a serialized object
	* could not be found
	* @throws java.io.IOException if an I/O error occurs
	*/
	private void readObject(java.io.ObjectInputStream s)
	throws java.io.IOException, ClassNotFoundException {
	s.defaultReadObject();

	// Read in elements until trailing null sentinel found
	Node<E> h = null, t = null;
	Object item;
	while ((item = s.readObject()) != null) {
	@SuppressWarnings("unchecked")
	Node<E> newNode = new Node<E>((E) item);
	if (h == null)
	h = t = newNode;
	else {
	t.lazySetNext(newNode);
	t = newNode;
	}
	}
	if (h == null)
	h = t = new Node<E>(null);
	head = h;
	tail = t;
	}

	/** A customized variant of Spliterators.IteratorSpliterator */
	static final class CLQSpliterator<E> implements Spliterator<E> {
	static final int MAX_BATCH = 1 << 25; // max batch array size;
	final ConcurrentLinkedQueue<E> queue;
	Node<E> current; // current node; null until initialized
	int batch; // batch size for splits
	boolean exhausted; // true when no more nodes
	CLQSpliterator(ConcurrentLinkedQueue<E> queue) {
	this.queue = queue;
	}

	public Spliterator<E> trySplit() {
	Node<E> p;
	final ConcurrentLinkedQueue<E> q = this.queue;
	int b = batch;
	int n = (b <= 0) ? 1 : (b >= MAX_BATCH) ? MAX_BATCH : b + 1;
	if (!exhausted &&
	((p = current) != null \|\| (p = q.first()) != null) &&
	p.next != null) {
	Object[] a = new Object[n];
	int i = 0;
	do {
	if ((a[i] = p.item) != null)
	++i;
	if (p == (p = p.next))
	p = q.first();
	} while (p != null && i < n);
	if ((current = p) == null)
	exhausted = true;
	if (i > 0) {
	batch = i;
	return Spliterators.spliterator
	(a, 0, i, Spliterator.ORDERED \| Spliterator.NONNULL \|
	Spliterator.CONCURRENT);
	}
	}
	return null;
	}

	public void forEachRemaining(Consumer<? super E> action) {
	Node<E> p;
	if (action == null) throw new NullPointerException();
	final ConcurrentLinkedQueue<E> q = this.queue;
	if (!exhausted &&
	((p = current) != null \|\| (p = q.first()) != null)) {
	exhausted = true;
	do {
	E e = p.item;
	if (p == (p = p.next))
	p = q.first();
	if (e != null)
	action.accept(e);
	} while (p != null);
	}
	}

	public boolean tryAdvance(Consumer<? super E> action) {
	Node<E> p;
	if (action == null) throw new NullPointerException();
	final ConcurrentLinkedQueue<E> q = this.queue;
	if (!exhausted &&
	((p = current) != null \|\| (p = q.first()) != null)) {
	E e;
	do {
	e = p.item;
	if (p == (p = p.next))
	p = q.first();
	} while (e == null && p != null);
	if ((current = p) == null)
	exhausted = true;
	if (e != null) {
	action.accept(e);
	return true;
	}
	}
	return false;
	}

	public long estimateSize() { return Long.MAX_VALUE; }

	public int characteristics() {
	return Spliterator.ORDERED \| Spliterator.NONNULL \|
	Spliterator.CONCURRENT;
	}
	}

	/**
	* Returns a {@link Spliterator} over the elements in this queue.
	*
	* <p>The returned spliterator is
	* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
	*
	* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
	* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}.
	*
	* @implNote
	* The {@code Spliterator} implements {@code trySplit} to permit limited
	* parallelism.
	*
	* @return a {@code Spliterator} over the elements in this queue
	* @since 1.8
	*/
	@Override
	public Spliterator<E> spliterator() {
	return new CLQSpliterator<E>(this);
	}

	/**
	* Throws NullPointerException if argument is null.
	*
	* @param v the element
	*/
	private static void checkNotNull(Object v) {
	if (v == null)
	throw new NullPointerException();
	}

	private boolean casTail(Node<E> cmp, Node<E> val) {
	return UNSAFE.compareAndSwapObject(this, tailOffset, cmp, val);
	}

	private boolean casHead(Node<E> cmp, Node<E> val) {
	return UNSAFE.compareAndSwapObject(this, headOffset, cmp, val);
	}

	// Unsafe mechanics

	private static final sun.misc.Unsafe UNSAFE;
	private static final long headOffset;
	private static final long tailOffset;
	static {
	try {
	UNSAFE = sun.misc.Unsafe.getUnsafe();
	Class<?> k = ConcurrentLinkedQueue.class;
	headOffset = UNSAFE.objectFieldOffset
	(k.getDeclaredField("head"));
	tailOffset = UNSAFE.objectFieldOffset
	(k.getDeclaredField("tail"));
	} catch (Exception e) {
	throw new Error(e);
	}
	}
	}

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