diff -r 000000000000 -r 212417b74b72 rt/emul/compact/src/main/java/java/util/concurrent/PriorityBlockingQueue.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rt/emul/compact/src/main/java/java/util/concurrent/PriorityBlockingQueue.java	Sat Mar 19 10:46:31 2016 +0100
@@ -0,0 +1,978 @@
+/*
+ * 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.*;
+import java.util.*;
+
+/**
+ * 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
+ */
+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 espense 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[2*n+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 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.toArray incorrectly doesn't return Object[], copy it.
+        if (a.getClass() != Object[].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 extract() {
+        E result;
+        int n = size - 1;
+        if (n < 0)
+            result = null;
+        else {
+            Object[] array = queue;
+            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
+     * @param n heap size
+     */
+    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) {
+        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) {
+        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();
+        E result;
+        try {
+            result = extract();
+        } finally {
+            lock.unlock();
+        }
+        return result;
+    }
+
+    public E take() throws InterruptedException {
+        final ReentrantLock lock = this.lock;
+        lock.lockInterruptibly();
+        E result;
+        try {
+            while ( (result = extract()) == 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 = extract()) == null && nanos > 0)
+                nanos = notEmpty.awaitNanos(nanos);
+        } finally {
+            lock.unlock();
+        }
+        return result;
+    }
+
+    public E peek() {
+        final ReentrantLock lock = this.lock;
+        lock.lock();
+        E result;
+        try {
+            result = size > 0 ? (E) queue[0] : null;
+        } finally {
+            lock.unlock();
+        }
+        return result;
+    }
+
+    /**
+     * 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) {
+        boolean removed = false;
+        final ReentrantLock lock = this.lock;
+        lock.lock();
+        try {
+            int i = indexOf(o);
+            if (i != -1) {
+                removeAt(i);
+                removed = true;
+            }
+        } finally {
+            lock.unlock();
+        }
+        return removed;
+    }
+
+
+    /**
+     * Identity-based version for use in Itr.remove
+     */
+    private void removeEQ(Object o) {
+        final ReentrantLock lock = this.lock;
+        lock.lock();
+        try {
+            Object[] array = queue;
+            int n = size;
+            for (int i = 0; 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) {
+        int index;
+        final ReentrantLock lock = this.lock;
+        lock.lock();
+        try {
+            index = indexOf(o);
+        } finally {
+            lock.unlock();
+        }
+        return index != -1;
+    }
+
+    /**
+     * 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) {
+                E e = (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) {
+        if (c == null)
+            throw new NullPointerException();
+        if (c == this)
+            throw new IllegalArgumentException();
+        final ReentrantLock lock = this.lock;
+        lock.lock();
+        try {
+            int n = 0;
+            E e;
+            while ( (e = extract()) != null) {
+                c.add(e);
+                ++n;
+            }
+            return n;
+        } finally {
+            lock.unlock();
+        }
+    }
+
+    /**
+     * @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 = 0;
+            E e;
+            while (n < maxElements && (e = extract()) != null) {
+                c.add(e);
+                ++n;
+            }
+            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>
+     *     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 "weakly consistent" iterator that
+     * will never throw {@link java.util.ConcurrentModificationException
+     * ConcurrentModificationException}, and guarantees to traverse
+     * elements as they existed upon construction of the iterator, and
+     * may (but is not guaranteed to) reflect any modifications
+     * subsequent to construction.
+     *
+     * @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 the state 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.
+     */
+    private void writeObject(java.io.ObjectOutputStream s)
+        throws java.io.IOException {
+        lock.lock();
+        try {
+            int n = size; // avoid zero capacity argument
+            q = new PriorityQueue<E>(n == 0 ? 1 : n, comparator);
+            q.addAll(this);
+            s.defaultWriteObject();
+        } finally {
+            q = null;
+            lock.unlock();
+        }
+    }
+
+    /**
+     * Reconstitutes the {@code PriorityBlockingQueue} instance from a stream
+     * (that is, deserializes it).
+     *
+     * @param s the stream
+     */
+    private void readObject(java.io.ObjectInputStream s)
+        throws java.io.IOException, ClassNotFoundException {
+        try {
+            s.defaultReadObject();
+            this.queue = new Object[q.size()];
+            comparator = q.comparator();
+            addAll(q);
+        } finally {
+            q = null;
+        }
+    }
+
+    // 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);
+        }
+    }
+}