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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;

	import java.util.concurrent.locks.Condition;
	import java.util.concurrent.locks.ReentrantLock;
	import java.util.AbstractQueue;
	import java.util.Arrays;
	import java.util.Collection;
	import java.util.Comparator;
	import java.util.Iterator;
	import java.util.NoSuchElementException;
	import java.util.PriorityQueue;
	import java.util.Queue;
	import java.util.SortedSet;
	import java.util.Spliterator;
	import java.util.function.Consumer;
	import sun.misc.SharedSecrets;

	/**
	* An unbounded {@linkplain BlockingQueue blocking queue} that uses
	* the same ordering rules as class {@link PriorityQueue} and supplies
	* blocking retrieval operations. While this queue is logically
	* unbounded, attempted additions may fail due to resource exhaustion
	* (causing {@code OutOfMemoryError}). This class does not permit
	* {@code null} elements. A priority queue relying on {@linkplain
	* Comparable natural ordering} also does not permit insertion of
	* non-comparable objects (doing so results in
	* {@code ClassCastException}).
	*
	* <p>This class and its iterator implement all of the
	* <em>optional</em> methods of the {@link Collection} and {@link
	* Iterator} interfaces. The Iterator provided in method {@link
	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
	* the PriorityBlockingQueue in any particular order. If you need
	* ordered traversal, consider using
	* {@code Arrays.sort(pq.toArray())}. Also, method {@code drainTo}
	* can be used to <em>remove</em> some or all elements in priority
	* order and place them in another collection.
	*
	* <p>Operations on this class make no guarantees about the ordering
	* of elements with equal priority. If you need to enforce an
	* ordering, you can define custom classes or comparators that use a
	* secondary key to break ties in primary priority values. For
	* example, here is a class that applies first-in-first-out
	* tie-breaking to comparable elements. To use it, you would insert a
	* {@code new FIFOEntry(anEntry)} instead of a plain entry object.
	*
	* <pre> {@code
	* class FIFOEntry<E extends Comparable<? super E>>
	* implements Comparable<FIFOEntry<E>> {
	* static final AtomicLong seq = new AtomicLong(0);
	* final long seqNum;
	* final E entry;
	* public FIFOEntry(E entry) {
	* seqNum = seq.getAndIncrement();
	* this.entry = entry;
	* }
	* public E getEntry() { return entry; }
	* public int compareTo(FIFOEntry<E> other) {
	* int res = entry.compareTo(other.entry);
	* if (res == 0 && other.entry != this.entry)
	* res = (seqNum < other.seqNum ? -1 : 1);
	* return res;
	* }
	* }}</pre>
	*
	* <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
	*/
	@SuppressWarnings("unchecked")
	public class PriorityBlockingQueue<E> extends AbstractQueue<E>
	implements BlockingQueue<E>, java.io.Serializable {
	private static final long serialVersionUID = 5595510919245408276L;

	/*
	* The implementation uses an array-based binary heap, with public
	* operations protected with a single lock. However, allocation
	* during resizing uses a simple spinlock (used only while not
	* holding main lock) in order to allow takes to operate
	* concurrently with allocation. This avoids repeated
	* postponement of waiting consumers and consequent element
	* build-up. The need to back away from lock during allocation
	* makes it impossible to simply wrap delegated
	* java.util.PriorityQueue operations within a lock, as was done
	* in a previous version of this class. To maintain
	* interoperability, a plain PriorityQueue is still used during
	* serialization, which maintains compatibility at the expense of
	* transiently doubling overhead.
	*/

	/**
	* Default array capacity.
	*/
	private static final int DEFAULT_INITIAL_CAPACITY = 11;

	/**
	* The maximum size of array to allocate.
	* Some VMs reserve some header words in an array.
	* Attempts to allocate larger arrays may result in
	* OutOfMemoryError: Requested array size exceeds VM limit
	*/
	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

	/**
	* Priority queue represented as a balanced binary heap: the two
	* children of queue[n] are queue[2n+1] and queue[2(n+1)]. The
	* priority queue is ordered by comparator, or by the elements'
	* natural ordering, if comparator is null: For each node n in the
	* heap and each descendant d of n, n <= d. The element with the
	* lowest value is in queue[0], assuming the queue is nonempty.
	*/
	private transient Object[] queue;

	/**
	* The number of elements in the priority queue.
	*/
	private transient int size;

	/**
	* The comparator, or null if priority queue uses elements'
	* natural ordering.
	*/
	private transient Comparator<? super E> comparator;

	/**
	* Lock used for all public operations
	*/
	private final ReentrantLock lock;

	/**
	* Condition for blocking when empty
	*/
	private final Condition notEmpty;

	/**
	* Spinlock for allocation, acquired via CAS.
	*/
	private transient volatile int allocationSpinLock;

	/**
	* A plain PriorityQueue used only for serialization,
	* to maintain compatibility with previous versions
	* of this class. Non-null only during serialization/deserialization.
	*/
	private PriorityQueue<E> q;

	/**
	* Creates a {@code PriorityBlockingQueue} with the default
	* initial capacity (11) that orders its elements according to
	* their {@linkplain Comparable natural ordering}.
	*/
	public PriorityBlockingQueue() {
	this(DEFAULT_INITIAL_CAPACITY, null);
	}

	/**
	* Creates a {@code PriorityBlockingQueue} with the specified
	* initial capacity that orders its elements according to their
	* {@linkplain Comparable natural ordering}.
	*
	* @param initialCapacity the initial capacity for this priority queue
	* @throws IllegalArgumentException if {@code initialCapacity} is less
	* than 1
	*/
	public PriorityBlockingQueue(int initialCapacity) {
	this(initialCapacity, null);
	}

	/**
	* Creates a {@code PriorityBlockingQueue} with the specified initial
	* capacity that orders its elements according to the specified
	* comparator.
	*
	* @param initialCapacity the initial capacity for this priority queue
	* @param comparator the comparator that will be used to order this
	* priority queue. If {@code null}, the {@linkplain Comparable
	* natural ordering} of the elements will be used.
	* @throws IllegalArgumentException if {@code initialCapacity} is less
	* than 1
	*/
	public PriorityBlockingQueue(int initialCapacity,
	Comparator<? super E> comparator) {
	if (initialCapacity < 1)
	throw new IllegalArgumentException();
	this.lock = new ReentrantLock();
	this.notEmpty = lock.newCondition();
	this.comparator = comparator;
	this.queue = new Object[initialCapacity];
	}

	/**
	* Creates a {@code PriorityBlockingQueue} containing the elements
	* in the specified collection. If the specified collection is a
	* {@link SortedSet} or a {@link PriorityQueue}, this
	* priority queue will be ordered according to the same ordering.
	* Otherwise, this priority queue will be ordered according to the
	* {@linkplain Comparable natural ordering} of its elements.
	*
	* @param c the collection whose elements are to be placed
	* into this priority queue
	* @throws ClassCastException if elements of the specified collection
	* cannot be compared to one another according to the priority
	* queue's ordering
	* @throws NullPointerException if the specified collection or any
	* of its elements are null
	*/
	public PriorityBlockingQueue(Collection<? extends E> c) {
	this.lock = new ReentrantLock();
	this.notEmpty = lock.newCondition();
	boolean heapify = true; // true if not known to be in heap order
	boolean screen = true; // true if must screen for nulls
	if (c instanceof SortedSet<?>) {
	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
	this.comparator = (Comparator<? super E>) ss.comparator();
	heapify = false;
	}
	else if (c instanceof PriorityBlockingQueue<?>) {
	PriorityBlockingQueue<? extends E> pq =
	(PriorityBlockingQueue<? extends E>) c;
	this.comparator = (Comparator<? super E>) pq.comparator();
	screen = false;
	if (pq.getClass() == PriorityBlockingQueue.class) // exact match
	heapify = false;
	}
	Object[] a = c.toArray();
	int n = a.length;
	if (c.getClass() != java.util.ArrayList.class)
	a = Arrays.copyOf(a, n, Object[].class);
	if (screen && (n == 1 \|\| this.comparator != null)) {
	for (int i = 0; i < n; ++i)
	if (a[i] == null)
	throw new NullPointerException();
	}
	this.queue = a;
	this.size = n;
	if (heapify)
	heapify();
	}

	/**
	* Tries to grow array to accommodate at least one more element
	* (but normally expand by about 50%), giving up (allowing retry)
	* on contention (which we expect to be rare). Call only while
	* holding lock.
	*
	* @param array the heap array
	* @param oldCap the length of the array
	*/
	private void tryGrow(Object[] array, int oldCap) {
	lock.unlock(); // must release and then re-acquire main lock
	Object[] newArray = null;
	if (allocationSpinLock == 0 &&
	UNSAFE.compareAndSwapInt(this, allocationSpinLockOffset,
	0, 1)) {
	try {
	int newCap = oldCap + ((oldCap < 64) ?
	(oldCap + 2) : // grow faster if small
	(oldCap >> 1));
	if (newCap - MAX_ARRAY_SIZE > 0) { // possible overflow
	int minCap = oldCap + 1;
	if (minCap < 0 \|\| minCap > MAX_ARRAY_SIZE)
	throw new OutOfMemoryError();
	newCap = MAX_ARRAY_SIZE;
	}
	if (newCap > oldCap && queue == array)
	newArray = new Object[newCap];
	} finally {
	allocationSpinLock = 0;
	}
	}
	if (newArray == null) // back off if another thread is allocating
	Thread.yield();
	lock.lock();
	if (newArray != null && queue == array) {
	queue = newArray;
	System.arraycopy(array, 0, newArray, 0, oldCap);
	}
	}

	/**
	* Mechanics for poll(). Call only while holding lock.
	*/
	private E dequeue() {
	int n = size - 1;
	if (n < 0)
	return null;
	else {
	Object[] array = queue;
	E result = (E) array[0];
	E x = (E) array[n];
	array[n] = null;
	Comparator<? super E> cmp = comparator;
	if (cmp == null)
	siftDownComparable(0, x, array, n);
	else
	siftDownUsingComparator(0, x, array, n, cmp);
	size = n;
	return result;
	}
	}

	/**
	* Inserts item x at position k, maintaining heap invariant by
	* promoting x up the tree until it is greater than or equal to
	* its parent, or is the root.
	*
	* To simplify and speed up coercions and comparisons. the
	* Comparable and Comparator versions are separated into different
	* methods that are otherwise identical. (Similarly for siftDown.)
	* These methods are static, with heap state as arguments, to
	* simplify use in light of possible comparator exceptions.
	*
	* @param k the position to fill
	* @param x the item to insert
	* @param array the heap array
	*/
	private static <T> void siftUpComparable(int k, T x, Object[] array) {
	Comparable<? super T> key = (Comparable<? super T>) x;
	while (k > 0) {
	int parent = (k - 1) >>> 1;
	Object e = array[parent];
	if (key.compareTo((T) e) >= 0)
	break;
	array[k] = e;
	k = parent;
	}
	array[k] = key;
	}

	private static <T> void siftUpUsingComparator(int k, T x, Object[] array,
	Comparator<? super T> cmp) {
	while (k > 0) {
	int parent = (k - 1) >>> 1;
	Object e = array[parent];
	if (cmp.compare(x, (T) e) >= 0)
	break;
	array[k] = e;
	k = parent;
	}
	array[k] = x;
	}

	/**
	* Inserts item x at position k, maintaining heap invariant by
	* demoting x down the tree repeatedly until it is less than or
	* equal to its children or is a leaf.
	*
	* @param k the position to fill
	* @param x the item to insert
	* @param array the heap array
	* @param n heap size
	*/
	private static <T> void siftDownComparable(int k, T x, Object[] array,
	int n) {
	if (n > 0) {
	Comparable<? super T> key = (Comparable<? super T>)x;
	int half = n >>> 1; // loop while a non-leaf
	while (k < half) {
	int child = (k << 1) + 1; // assume left child is least
	Object c = array[child];
	int right = child + 1;
	if (right < n &&
	((Comparable<? super T>) c).compareTo((T) array[right]) > 0)
	c = array[child = right];
	if (key.compareTo((T) c) <= 0)
	break;
	array[k] = c;
	k = child;
	}
	array[k] = key;
	}
	}

	private static <T> void siftDownUsingComparator(int k, T x, Object[] array,
	int n,
	Comparator<? super T> cmp) {
	if (n > 0) {
	int half = n >>> 1;
	while (k < half) {
	int child = (k << 1) + 1;
	Object c = array[child];
	int right = child + 1;
	if (right < n && cmp.compare((T) c, (T) array[right]) > 0)
	c = array[child = right];
	if (cmp.compare(x, (T) c) <= 0)
	break;
	array[k] = c;
	k = child;
	}
	array[k] = x;
	}
	}

	/**
	* Establishes the heap invariant (described above) in the entire tree,
	* assuming nothing about the order of the elements prior to the call.
	*/
	private void heapify() {
	Object[] array = queue;
	int n = size;
	int half = (n >>> 1) - 1;
	Comparator<? super E> cmp = comparator;
	if (cmp == null) {
	for (int i = half; i >= 0; i--)
	siftDownComparable(i, (E) array[i], array, n);
	}
	else {
	for (int i = half; i >= 0; i--)
	siftDownUsingComparator(i, (E) array[i], array, n, cmp);
	}
	}

	/**
	* Inserts the specified element into this priority queue.
	*
	* @param e the element to add
	* @return {@code true} (as specified by {@link Collection#add})
	* @throws ClassCastException if the specified element cannot be compared
	* with elements currently in the priority queue according to the
	* priority queue's ordering
	* @throws NullPointerException if the specified element is null
	*/
	public boolean add(E e) {
	return offer(e);
	}

	/**
	* Inserts the specified element into this priority queue.
	* As the queue is unbounded, this method will never return {@code false}.
	*
	* @param e the element to add
	* @return {@code true} (as specified by {@link Queue#offer})
	* @throws ClassCastException if the specified element cannot be compared
	* with elements currently in the priority queue according to the
	* priority queue's ordering
	* @throws NullPointerException if the specified element is null
	*/
	public boolean offer(E e) {
	if (e == null)
	throw new NullPointerException();
	final ReentrantLock lock = this.lock;
	lock.lock();
	int n, cap;
	Object[] array;
	while ((n = size) >= (cap = (array = queue).length))
	tryGrow(array, cap);
	try {
	Comparator<? super E> cmp = comparator;
	if (cmp == null)
	siftUpComparable(n, e, array);
	else
	siftUpUsingComparator(n, e, array, cmp);
	size = n + 1;
	notEmpty.signal();
	} finally {
	lock.unlock();
	}
	return true;
	}

	/**
	* Inserts the specified element into this priority queue.
	* As the queue is unbounded, this method will never block.
	*
	* @param e the element to add
	* @throws ClassCastException if the specified element cannot be compared
	* with elements currently in the priority queue according to the
	* priority queue's ordering
	* @throws NullPointerException if the specified element is null
	*/
	public void put(E e) {
	offer(e); // never need to block
	}

	/**
	* Inserts the specified element into this priority queue.
	* As the queue is unbounded, this method will never block or
	* return {@code false}.
	*
	* @param e the element to add
	* @param timeout This parameter is ignored as the method never blocks
	* @param unit This parameter is ignored as the method never blocks
	* @return {@code true} (as specified by
	* {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer})
	* @throws ClassCastException if the specified element cannot be compared
	* with elements currently in the priority queue according to the
	* priority queue's ordering
	* @throws NullPointerException if the specified element is null
	*/
	public boolean offer(E e, long timeout, TimeUnit unit) {
	return offer(e); // never need to block
	}

	public E poll() {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	return dequeue();
	} finally {
	lock.unlock();
	}
	}

	public E take() throws InterruptedException {
	final ReentrantLock lock = this.lock;
	lock.lockInterruptibly();
	E result;
	try {
	while ( (result = dequeue()) == null)
	notEmpty.await();
	} finally {
	lock.unlock();
	}
	return result;
	}

	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
	long nanos = unit.toNanos(timeout);
	final ReentrantLock lock = this.lock;
	lock.lockInterruptibly();
	E result;
	try {
	while ( (result = dequeue()) == null && nanos > 0)
	nanos = notEmpty.awaitNanos(nanos);
	} finally {
	lock.unlock();
	}
	return result;
	}

	public E peek() {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	return (size == 0) ? null : (E) queue[0];
	} finally {
	lock.unlock();
	}
	}

	/**
	* Returns the comparator used to order the elements in this queue,
	* or {@code null} if this queue uses the {@linkplain Comparable
	* natural ordering} of its elements.
	*
	* @return the comparator used to order the elements in this queue,
	* or {@code null} if this queue uses the natural
	* ordering of its elements
	*/
	public Comparator<? super E> comparator() {
	return comparator;
	}

	public int size() {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	return size;
	} finally {
	lock.unlock();
	}
	}

	/**
	* Always returns {@code Integer.MAX_VALUE} because
	* a {@code PriorityBlockingQueue} is not capacity constrained.
	* @return {@code Integer.MAX_VALUE} always
	*/
	public int remainingCapacity() {
	return Integer.MAX_VALUE;
	}

	private int indexOf(Object o) {
	if (o != null) {
	Object[] array = queue;
	int n = size;
	for (int i = 0; i < n; i++)
	if (o.equals(array[i]))
	return i;
	}
	return -1;
	}

	/**
	* Removes the ith element from queue.
	*/
	private void removeAt(int i) {
	Object[] array = queue;
	int n = size - 1;
	if (n == i) // removed last element
	array[i] = null;
	else {
	E moved = (E) array[n];
	array[n] = null;
	Comparator<? super E> cmp = comparator;
	if (cmp == null)
	siftDownComparable(i, moved, array, n);
	else
	siftDownUsingComparator(i, moved, array, n, cmp);
	if (array[i] == moved) {
	if (cmp == null)
	siftUpComparable(i, moved, array);
	else
	siftUpUsingComparator(i, moved, array, cmp);
	}
	}
	size = n;
	}

	/**
	* 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 and only 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) {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	int i = indexOf(o);
	if (i == -1)
	return false;
	removeAt(i);
	return true;
	} finally {
	lock.unlock();
	}
	}

	/**
	* Identity-based version for use in Itr.remove
	*/
	void removeEQ(Object o) {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	Object[] array = queue;
	for (int i = 0, n = size; i < n; i++) {
	if (o == array[i]) {
	removeAt(i);
	break;
	}
	}
	} finally {
	lock.unlock();
	}
	}

	/**
	* 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) {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	return indexOf(o) != -1;
	} finally {
	lock.unlock();
	}
	}

	/**
	* Returns an array containing all of the elements in this queue.
	* The returned array elements are in no particular order.
	*
	* <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() {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	return Arrays.copyOf(queue, size);
	} finally {
	lock.unlock();
	}
	}

	public String toString() {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	int n = size;
	if (n == 0)
	return "[]";
	StringBuilder sb = new StringBuilder();
	sb.append('[');
	for (int i = 0; i < n; ++i) {
	Object e = queue[i];
	sb.append(e == this ? "(this Collection)" : e);
	if (i != n - 1)
	sb.append(',').append(' ');
	}
	return sb.append(']').toString();
	} finally {
	lock.unlock();
	}
	}

	/**
	* @throws UnsupportedOperationException {@inheritDoc}
	* @throws ClassCastException {@inheritDoc}
	* @throws NullPointerException {@inheritDoc}
	* @throws IllegalArgumentException {@inheritDoc}
	*/
	public int drainTo(Collection<? super E> c) {
	return drainTo(c, Integer.MAX_VALUE);
	}

	/**
	* @throws UnsupportedOperationException {@inheritDoc}
	* @throws ClassCastException {@inheritDoc}
	* @throws NullPointerException {@inheritDoc}
	* @throws IllegalArgumentException {@inheritDoc}
	*/
	public int drainTo(Collection<? super E> c, int maxElements) {
	if (c == null)
	throw new NullPointerException();
	if (c == this)
	throw new IllegalArgumentException();
	if (maxElements <= 0)
	return 0;
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	int n = Math.min(size, maxElements);
	for (int i = 0; i < n; i++) {
	c.add((E) queue[0]); // In this order, in case add() throws.
	dequeue();
	}
	return n;
	} finally {
	lock.unlock();
	}
	}

	/**
	* Atomically removes all of the elements from this queue.
	* The queue will be empty after this call returns.
	*/
	public void clear() {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	Object[] array = queue;
	int n = size;
	size = 0;
	for (int i = 0; i < n; i++)
	array[i] = null;
	} finally {
	lock.unlock();
	}
	}

	/**
	* Returns an array containing all of the elements in this queue; the
	* runtime type of the returned array is that of the specified array.
	* The returned array elements are in no particular order.
	* 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
	*/
	public <T> T[] toArray(T[] a) {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	int n = size;
	if (a.length < n)
	// Make a new array of a's runtime type, but my contents:
	return (T[]) Arrays.copyOf(queue, size, a.getClass());
	System.arraycopy(queue, 0, a, 0, n);
	if (a.length > n)
	a[n] = null;
	return a;
	} finally {
	lock.unlock();
	}
	}

	/**
	* Returns an iterator over the elements in this queue. The
	* iterator does not return the elements in any particular order.
	*
	* <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
	*/
	public Iterator<E> iterator() {
	return new Itr(toArray());
	}

	/**
	* Snapshot iterator that works off copy of underlying q array.
	*/
	final class Itr implements Iterator<E> {
	final Object[] array; // Array of all elements
	int cursor; // index of next element to return
	int lastRet; // index of last element, or -1 if no such

	Itr(Object[] array) {
	lastRet = -1;
	this.array = array;
	}

	public boolean hasNext() {
	return cursor < array.length;
	}

	public E next() {
	if (cursor >= array.length)
	throw new NoSuchElementException();
	lastRet = cursor;
	return (E)array[cursor++];
	}

	public void remove() {
	if (lastRet < 0)
	throw new IllegalStateException();
	removeEQ(array[lastRet]);
	lastRet = -1;
	}
	}

	/**
	* Saves this queue to a stream (that is, serializes it).
	*
	* For compatibility with previous version of this class, elements
	* are first copied to a java.util.PriorityQueue, which is then
	* serialized.
	*
	* @param s the stream
	* @throws java.io.IOException if an I/O error occurs
	*/
	private void writeObject(java.io.ObjectOutputStream s)
	throws java.io.IOException {
	lock.lock();
	try {
	// avoid zero capacity argument
	q = new PriorityQueue<E>(Math.max(size, 1), comparator);
	q.addAll(this);
	s.defaultWriteObject();
	} finally {
	q = null;
	lock.unlock();
	}
	}

	/**
	* 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 {
	try {
	s.defaultReadObject();
	int sz = q.size();
	SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, sz);
	this.queue = new Object[sz];
	comparator = q.comparator();
	addAll(q);
	} finally {
	q = null;
	}
	}

	// Similar to Collections.ArraySnapshotSpliterator but avoids
	// commitment to toArray until needed
	static final class PBQSpliterator<E> implements Spliterator<E> {
	final PriorityBlockingQueue<E> queue;
	Object[] array;
	int index;
	int fence;

	PBQSpliterator(PriorityBlockingQueue<E> queue, Object[] array,
	int index, int fence) {
	this.queue = queue;
	this.array = array;
	this.index = index;
	this.fence = fence;
	}

	final int getFence() {
	int hi;
	if ((hi = fence) < 0)
	hi = fence = (array = queue.toArray()).length;
	return hi;
	}

	public Spliterator<E> trySplit() {
	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
	return (lo >= mid) ? null :
	new PBQSpliterator<E>(queue, array, lo, index = mid);
	}

	@SuppressWarnings("unchecked")
	public void forEachRemaining(Consumer<? super E> action) {
	Object[] a; int i, hi; // hoist accesses and checks from loop
	if (action == null)
	throw new NullPointerException();
	if ((a = array) == null)
	fence = (a = queue.toArray()).length;
	if ((hi = fence) <= a.length &&
	(i = index) >= 0 && i < (index = hi)) {
	do { action.accept((E)a[i]); } while (++i < hi);
	}
	}

	public boolean tryAdvance(Consumer<? super E> action) {
	if (action == null)
	throw new NullPointerException();
	if (getFence() > index && index >= 0) {
	@SuppressWarnings("unchecked") E e = (E) array[index++];
	action.accept(e);
	return true;
	}
	return false;
	}

	public long estimateSize() { return (long)(getFence() - index); }

	public int characteristics() {
	return Spliterator.NONNULL \| Spliterator.SIZED \| Spliterator.SUBSIZED;
	}
	}

	/**
	* 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#SIZED} and
	* {@link Spliterator#NONNULL}.
	*
	* @implNote
	* The {@code Spliterator} additionally reports {@link Spliterator#SUBSIZED}.
	*
	* @return a {@code Spliterator} over the elements in this queue
	* @since 1.8
	*/
	public Spliterator<E> spliterator() {
	return new PBQSpliterator<E>(this, null, 0, -1);
	}

	// Unsafe mechanics
	private static final sun.misc.Unsafe UNSAFE;
	private static final long allocationSpinLockOffset;
	static {
	try {
	UNSAFE = sun.misc.Unsafe.getUnsafe();
	Class<?> k = PriorityBlockingQueue.class;
	allocationSpinLockOffset = UNSAFE.objectFieldOffset
	(k.getDeclaredField("allocationSpinLock"));
	} catch (Exception e) {
	throw new Error(e);
	}
	}
	}

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