luni/src/main/java/java/util/concurrent/DelayQueue.java - platform/libcore - Git at Google

 /*
  * 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 static java.util.concurrent.TimeUnit.NANOSECONDS;
 import java.util.concurrent.locks.Condition;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.*;

 // BEGIN android-note
 // removed link to collections framework docs
 // END android-note

 /**
  * An unbounded {@linkplain BlockingQueue blocking queue} of
  * {@code Delayed} elements, in which an element can only be taken
  * when its delay has expired.  The <em>head</em> of the queue is that
  * {@code Delayed} element whose delay expired furthest in the
  * past.  If no delay has expired there is no head and {@code poll}
  * will return {@code null}. Expiration occurs when an element's
  * {@code getDelay(TimeUnit.NANOSECONDS)} method returns a value less
  * than or equal to zero.  Even though unexpired elements cannot be
  * removed using {@code take} or {@code poll}, they are otherwise
  * treated as normal elements. For example, the {@code size} method
  * returns the count of both expired and unexpired elements.
  * This queue does not permit null elements.
  *
  * <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 DelayQueue in any particular order.
  *
  * @since 1.5
  * @author Doug Lea
  * @param <E> the type of elements held in this collection
  */
 public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
     implements BlockingQueue<E> {

     private final transient ReentrantLock lock = new ReentrantLock();
     private final PriorityQueue<E> q = new PriorityQueue<E>();

     /**
      * Thread designated to wait for the element at the head of
      * the queue.  This variant of the Leader-Follower pattern
      * (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
      * minimize unnecessary timed waiting.  When a thread becomes
      * the leader, it waits only for the next delay to elapse, but
      * other threads await indefinitely.  The leader thread must
      * signal some other thread before returning from take() or
      * poll(...), unless some other thread becomes leader in the
      * interim.  Whenever the head of the queue is replaced with
      * an element with an earlier expiration time, the leader
      * field is invalidated by being reset to null, and some
      * waiting thread, but not necessarily the current leader, is
      * signalled.  So waiting threads must be prepared to acquire
      * and lose leadership while waiting.
      */
     private Thread leader;

     /**
      * Condition signalled when a newer element becomes available
      * at the head of the queue or a new thread may need to
      * become leader.
      */
     private final Condition available = lock.newCondition();

     /**
      * Creates a new {@code DelayQueue} that is initially empty.
      */
     public DelayQueue() {}

     /**
      * Creates a {@code DelayQueue} initially containing the elements of the
      * given collection of {@link Delayed} instances.
      *
      * @param c the collection of elements to initially contain
      * @throws NullPointerException if the specified collection or any
      *         of its elements are null
      */
     public DelayQueue(Collection<? extends E> c) {
         this.addAll(c);
     }

     /**
      * Inserts the specified element into this delay queue.
      *
      * @param e the element to add
      * @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);
     }

     /**
      * Inserts the specified element into this delay queue.
      *
      * @param e the element to add
      * @return {@code true}
      * @throws NullPointerException if the specified element is null
      */
     public boolean offer(E e) {
         final ReentrantLock lock = this.lock;
         lock.lock();
         try {
             q.offer(e);
             if (q.peek() == e) {
                 leader = null;
                 available.signal();
             }
             return true;
         } finally {
             lock.unlock();
         }
     }

     /**
      * Inserts the specified element into this delay queue. As the queue is
      * unbounded this method will never block.
      *
      * @param e the element to add
      * @throws NullPointerException {@inheritDoc}
      */
     public void put(E e) {
         offer(e);
     }

     /**
      * Inserts the specified element into this delay queue. As the queue is
      * unbounded this method will never block.
      *
      * @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}
      * @throws NullPointerException {@inheritDoc}
      */
     public boolean offer(E e, long timeout, TimeUnit unit) {
         return offer(e);
     }

     /**
      * Retrieves and removes the head of this queue, or returns {@code null}
      * if this queue has no elements with an expired delay.
      *
      * @return the head of this queue, or {@code null} if this
      *         queue has no elements with an expired delay
      */
     public E poll() {
         final ReentrantLock lock = this.lock;
         lock.lock();
         try {
             E first = q.peek();
             if (first == null || first.getDelay(NANOSECONDS) > 0)
                 return null;
             else
                 return q.poll();
         } finally {
             lock.unlock();
         }
     }

     /**
      * Retrieves and removes the head of this queue, waiting if necessary
      * until an element with an expired delay is available on this queue.
      *
      * @return the head of this queue
      * @throws InterruptedException {@inheritDoc}
      */
     public E take() throws InterruptedException {
         final ReentrantLock lock = this.lock;
         lock.lockInterruptibly();
         try {
             for (;;) {
                 E first = q.peek();
                 if (first == null)
                     available.await();
                 else {
                     long delay = first.getDelay(NANOSECONDS);
                     if (delay <= 0)
                         return q.poll();
                     first = null; // don't retain ref while waiting
                     if (leader != null)
                         available.await();
                     else {
                         Thread thisThread = Thread.currentThread();
                         leader = thisThread;
                         try {
                             available.awaitNanos(delay);
                         } finally {
                             if (leader == thisThread)
                                 leader = null;
                         }
                     }
                 }
             }
         } finally {
             if (leader == null && q.peek() != null)
                 available.signal();
             lock.unlock();
         }
     }

     /**
      * Retrieves and removes the head of this queue, waiting if necessary
      * until an element with an expired delay is available on this queue,
      * or the specified wait time expires.
      *
      * @return the head of this queue, or {@code null} if the
      *         specified waiting time elapses before an element with
      *         an expired delay becomes available
      * @throws InterruptedException {@inheritDoc}
      */
     public E poll(long timeout, TimeUnit unit) throws InterruptedException {
         long nanos = unit.toNanos(timeout);
         final ReentrantLock lock = this.lock;
         lock.lockInterruptibly();
         try {
             for (;;) {
                 E first = q.peek();
                 if (first == null) {
                     if (nanos <= 0)
                         return null;
                     else
                         nanos = available.awaitNanos(nanos);
                 } else {
                     long delay = first.getDelay(NANOSECONDS);
                     if (delay <= 0)
                         return q.poll();
                     if (nanos <= 0)
                         return null;
                     first = null; // don't retain ref while waiting
                     if (nanos < delay || leader != null)
                         nanos = available.awaitNanos(nanos);
                     else {
                         Thread thisThread = Thread.currentThread();
                         leader = thisThread;
                         try {
                             long timeLeft = available.awaitNanos(delay);
                             nanos -= delay - timeLeft;
                         } finally {
                             if (leader == thisThread)
                                 leader = null;
                         }
                     }
                 }
             }
         } finally {
             if (leader == null && q.peek() != null)
                 available.signal();
             lock.unlock();
         }
     }

     /**
      * Retrieves, but does not remove, the head of this queue, or
      * returns {@code null} if this queue is empty.  Unlike
      * {@code poll}, if no expired elements are available in the queue,
      * this method returns the element that will expire next,
      * if one exists.
      *
      * @return the head of this queue, or {@code null} if this
      *         queue is empty
      */
     public E peek() {
         final ReentrantLock lock = this.lock;
         lock.lock();
         try {
             return q.peek();
         } finally {
             lock.unlock();
         }
     }

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

     /**
      * Returns first element only if it is expired.
      * Used only by drainTo.  Call only when holding lock.
      */
     private E peekExpired() {
         // assert lock.isHeldByCurrentThread();
         E first = q.peek();
         return (first == null || first.getDelay(NANOSECONDS) > 0) ?
             null : first;
     }

     /**
      * @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;
             for (E e; (e = peekExpired()) != null;) {
                 c.add(e);       // In this order, in case add() throws.
                 q.poll();
                 ++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;
             for (E e; n < maxElements && (e = peekExpired()) != null;) {
                 c.add(e);       // In this order, in case add() throws.
                 q.poll();
                 ++n;
             }
             return n;
         } finally {
             lock.unlock();
         }
     }

     /**
      * Atomically removes all of the elements from this delay queue.
      * The queue will be empty after this call returns.
      * Elements with an unexpired delay are not waited for; they are
      * simply discarded from the queue.
      */
     public void clear() {
         final ReentrantLock lock = this.lock;
         lock.lock();
         try {
             q.clear();
         } finally {
             lock.unlock();
         }
     }

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

     /**
      * 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 q.toArray();
         } 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>The following code can be used to dump a delay queue into a newly
      * allocated array of {@code Delayed}:
      *
      * <pre> {@code Delayed[] a = q.toArray(new Delayed[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 {
             return q.toArray(a);
         } finally {
             lock.unlock();
         }
     }

     /**
      * Removes a single instance of the specified element from this
      * queue, if it is present, whether or not it has expired.
      */
     public boolean remove(Object o) {
         final ReentrantLock lock = this.lock;
         lock.lock();
         try {
             return q.remove(o);
         } finally {
             lock.unlock();
         }
     }

     /**
      * Identity-based version for use in Itr.remove
      */
     void removeEQ(Object o) {
         final ReentrantLock lock = this.lock;
         lock.lock();
         try {
             for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
                 if (o == it.next()) {
                     it.remove();
                     break;
                 }
             }
         } finally {
             lock.unlock();
         }
     }

     /**
      * Returns an iterator over all the elements (both expired and
      * unexpired) 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.
      */
     private 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;
         }

         @SuppressWarnings("unchecked")
         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;
         }
     }

 }
	/*
	* 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 static java.util.concurrent.TimeUnit.NANOSECONDS;
	import java.util.concurrent.locks.Condition;
	import java.util.concurrent.locks.ReentrantLock;
	import java.util.*;

	// BEGIN android-note
	// removed link to collections framework docs
	// END android-note

	/**
	* An unbounded {@linkplain BlockingQueue blocking queue} of
	* {@code Delayed} elements, in which an element can only be taken
	* when its delay has expired. The <em>head</em> of the queue is that
	* {@code Delayed} element whose delay expired furthest in the
	* past. If no delay has expired there is no head and {@code poll}
	* will return {@code null}. Expiration occurs when an element's
	* {@code getDelay(TimeUnit.NANOSECONDS)} method returns a value less
	* than or equal to zero. Even though unexpired elements cannot be
	* removed using {@code take} or {@code poll}, they are otherwise
	* treated as normal elements. For example, the {@code size} method
	* returns the count of both expired and unexpired elements.
	* This queue does not permit null elements.
	*
	* <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 DelayQueue in any particular order.
	*
	* @since 1.5
	* @author Doug Lea
	* @param <E> the type of elements held in this collection
	*/
	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
	implements BlockingQueue<E> {

	private final transient ReentrantLock lock = new ReentrantLock();
	private final PriorityQueue<E> q = new PriorityQueue<E>();

	/**
	* Thread designated to wait for the element at the head of
	* the queue. This variant of the Leader-Follower pattern
	* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
	* minimize unnecessary timed waiting. When a thread becomes
	* the leader, it waits only for the next delay to elapse, but
	* other threads await indefinitely. The leader thread must
	* signal some other thread before returning from take() or
	* poll(...), unless some other thread becomes leader in the
	* interim. Whenever the head of the queue is replaced with
	* an element with an earlier expiration time, the leader
	* field is invalidated by being reset to null, and some
	* waiting thread, but not necessarily the current leader, is
	* signalled. So waiting threads must be prepared to acquire
	* and lose leadership while waiting.
	*/
	private Thread leader;

	/**
	* Condition signalled when a newer element becomes available
	* at the head of the queue or a new thread may need to
	* become leader.
	*/
	private final Condition available = lock.newCondition();

	/**
	* Creates a new {@code DelayQueue} that is initially empty.
	*/
	public DelayQueue() {}

	/**
	* Creates a {@code DelayQueue} initially containing the elements of the
	* given collection of {@link Delayed} instances.
	*
	* @param c the collection of elements to initially contain
	* @throws NullPointerException if the specified collection or any
	* of its elements are null
	*/
	public DelayQueue(Collection<? extends E> c) {
	this.addAll(c);
	}

	/**
	* Inserts the specified element into this delay queue.
	*
	* @param e the element to add
	* @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);
	}

	/**
	* Inserts the specified element into this delay queue.
	*
	* @param e the element to add
	* @return {@code true}
	* @throws NullPointerException if the specified element is null
	*/
	public boolean offer(E e) {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	q.offer(e);
	if (q.peek() == e) {
	leader = null;
	available.signal();
	}
	return true;
	} finally {
	lock.unlock();
	}
	}

	/**
	* Inserts the specified element into this delay queue. As the queue is
	* unbounded this method will never block.
	*
	* @param e the element to add
	* @throws NullPointerException {@inheritDoc}
	*/
	public void put(E e) {
	offer(e);
	}

	/**
	* Inserts the specified element into this delay queue. As the queue is
	* unbounded this method will never block.
	*
	* @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}
	* @throws NullPointerException {@inheritDoc}
	*/
	public boolean offer(E e, long timeout, TimeUnit unit) {
	return offer(e);
	}

	/**
	* Retrieves and removes the head of this queue, or returns {@code null}
	* if this queue has no elements with an expired delay.
	*
	* @return the head of this queue, or {@code null} if this
	* queue has no elements with an expired delay
	*/
	public E poll() {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	E first = q.peek();
	if (first == null \|\| first.getDelay(NANOSECONDS) > 0)
	return null;
	else
	return q.poll();
	} finally {
	lock.unlock();
	}
	}

	/**
	* Retrieves and removes the head of this queue, waiting if necessary
	* until an element with an expired delay is available on this queue.
	*
	* @return the head of this queue
	* @throws InterruptedException {@inheritDoc}
	*/
	public E take() throws InterruptedException {
	final ReentrantLock lock = this.lock;
	lock.lockInterruptibly();
	try {
	for (;;) {
	E first = q.peek();
	if (first == null)
	available.await();
	else {
	long delay = first.getDelay(NANOSECONDS);
	if (delay <= 0)
	return q.poll();
	first = null; // don't retain ref while waiting
	if (leader != null)
	available.await();
	else {
	Thread thisThread = Thread.currentThread();
	leader = thisThread;
	try {
	available.awaitNanos(delay);
	} finally {
	if (leader == thisThread)
	leader = null;
	}
	}
	}
	}
	} finally {
	if (leader == null && q.peek() != null)
	available.signal();
	lock.unlock();
	}
	}

	/**
	* Retrieves and removes the head of this queue, waiting if necessary
	* until an element with an expired delay is available on this queue,
	* or the specified wait time expires.
	*
	* @return the head of this queue, or {@code null} if the
	* specified waiting time elapses before an element with
	* an expired delay becomes available
	* @throws InterruptedException {@inheritDoc}
	*/
	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
	long nanos = unit.toNanos(timeout);
	final ReentrantLock lock = this.lock;
	lock.lockInterruptibly();
	try {
	for (;;) {
	E first = q.peek();
	if (first == null) {
	if (nanos <= 0)
	return null;
	else
	nanos = available.awaitNanos(nanos);
	} else {
	long delay = first.getDelay(NANOSECONDS);
	if (delay <= 0)
	return q.poll();
	if (nanos <= 0)
	return null;
	first = null; // don't retain ref while waiting
	if (nanos < delay \|\| leader != null)
	nanos = available.awaitNanos(nanos);
	else {
	Thread thisThread = Thread.currentThread();
	leader = thisThread;
	try {
	long timeLeft = available.awaitNanos(delay);
	nanos -= delay - timeLeft;
	} finally {
	if (leader == thisThread)
	leader = null;
	}
	}
	}
	}
	} finally {
	if (leader == null && q.peek() != null)
	available.signal();
	lock.unlock();
	}
	}

	/**
	* Retrieves, but does not remove, the head of this queue, or
	* returns {@code null} if this queue is empty. Unlike
	* {@code poll}, if no expired elements are available in the queue,
	* this method returns the element that will expire next,
	* if one exists.
	*
	* @return the head of this queue, or {@code null} if this
	* queue is empty
	*/
	public E peek() {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	return q.peek();
	} finally {
	lock.unlock();
	}
	}

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

	/**
	* Returns first element only if it is expired.
	* Used only by drainTo. Call only when holding lock.
	*/
	private E peekExpired() {
	// assert lock.isHeldByCurrentThread();
	E first = q.peek();
	return (first == null \|\| first.getDelay(NANOSECONDS) > 0) ?
	null : first;
	}

	/**
	* @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;
	for (E e; (e = peekExpired()) != null;) {
	c.add(e); // In this order, in case add() throws.
	q.poll();
	++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;
	for (E e; n < maxElements && (e = peekExpired()) != null;) {
	c.add(e); // In this order, in case add() throws.
	q.poll();
	++n;
	}
	return n;
	} finally {
	lock.unlock();
	}
	}

	/**
	* Atomically removes all of the elements from this delay queue.
	* The queue will be empty after this call returns.
	* Elements with an unexpired delay are not waited for; they are
	* simply discarded from the queue.
	*/
	public void clear() {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	q.clear();
	} finally {
	lock.unlock();
	}
	}

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

	/**
	* 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 q.toArray();
	} 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>The following code can be used to dump a delay queue into a newly
	* allocated array of {@code Delayed}:
	*
	* <pre> {@code Delayed[] a = q.toArray(new Delayed[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 {
	return q.toArray(a);
	} finally {
	lock.unlock();
	}
	}

	/**
	* Removes a single instance of the specified element from this
	* queue, if it is present, whether or not it has expired.
	*/
	public boolean remove(Object o) {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	return q.remove(o);
	} finally {
	lock.unlock();
	}
	}

	/**
	* Identity-based version for use in Itr.remove
	*/
	void removeEQ(Object o) {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
	for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
	if (o == it.next()) {
	it.remove();
	break;
	}
	}
	} finally {
	lock.unlock();
	}
	}

	/**
	* Returns an iterator over all the elements (both expired and
	* unexpired) 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.
	*/
	private 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;
	}

	@SuppressWarnings("unchecked")
	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;
	}
	}

	}