util/concurrent/DelayQueue.java

/*
 * 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.*;

/**
 * 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.
 *
 * <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 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;
        }
    }

}
Revision:	1.7
Committed:	Sun Jan 18 20:17:32 2015 UTC (9 years, 4 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.6:	+1 -0 lines
Log Message:	exactly one blank line before and after package statements
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/publicdomain/zero/1.0/
5			*/
6
7			package java.util.concurrent;
8	jsr166	1.7
9	dl	1.1	import static java.util.concurrent.TimeUnit.NANOSECONDS;
10			import java.util.concurrent.locks.Condition;
11			import java.util.concurrent.locks.ReentrantLock;
12			import java.util.*;
13
14			/**
15			* An unbounded {@linkplain BlockingQueue blocking queue} of
16	jsr166	1.2	* {@code Delayed} elements, in which an element can only be taken
17	dl	1.1	* when its delay has expired. The <em>head</em> of the queue is that
18	jsr166	1.2	* {@code Delayed} element whose delay expired furthest in the
19			* past. If no delay has expired there is no head and {@code poll}
20			* will return {@code null}. Expiration occurs when an element's
21			* {@code getDelay(TimeUnit.NANOSECONDS)} method returns a value less
22	dl	1.1	* than or equal to zero. Even though unexpired elements cannot be
23	jsr166	1.2	* removed using {@code take} or {@code poll}, they are otherwise
24			* treated as normal elements. For example, the {@code size} method
25	dl	1.1	* returns the count of both expired and unexpired elements.
26			* This queue does not permit null elements.
27			*
28			* <p>This class and its iterator implement all of the
29			* <em>optional</em> methods of the {@link Collection} and {@link
30			* Iterator} interfaces. The Iterator provided in method {@link
31			* #iterator()} is <em>not</em> guaranteed to traverse the elements of
32			* the DelayQueue in any particular order.
33			*
34			* <p>This class is a member of the
35			* <a href="{@docRoot}/../technotes/guides/collections/index.html">
36			* Java Collections Framework</a>.
37			*
38			* @since 1.5
39			* @author Doug Lea
40			* @param <E> the type of elements held in this collection
41			*/
42			public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
43			implements BlockingQueue<E> {
44
45	jsr166	1.3	private final transient ReentrantLock lock = new ReentrantLock();
46	dl	1.1	private final PriorityQueue<E> q = new PriorityQueue<E>();
47
48			/**
49			* Thread designated to wait for the element at the head of
50			* the queue. This variant of the Leader-Follower pattern
51			* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
52			* minimize unnecessary timed waiting. When a thread becomes
53			* the leader, it waits only for the next delay to elapse, but
54			* other threads await indefinitely. The leader thread must
55			* signal some other thread before returning from take() or
56			* poll(...), unless some other thread becomes leader in the
57			* interim. Whenever the head of the queue is replaced with
58			* an element with an earlier expiration time, the leader
59			* field is invalidated by being reset to null, and some
60			* waiting thread, but not necessarily the current leader, is
61			* signalled. So waiting threads must be prepared to acquire
62			* and lose leadership while waiting.
63			*/
64	jsr166	1.6	private Thread leader;
65	dl	1.1
66			/**
67			* Condition signalled when a newer element becomes available
68			* at the head of the queue or a new thread may need to
69			* become leader.
70			*/
71			private final Condition available = lock.newCondition();
72
73			/**
74	jsr166	1.2	* Creates a new {@code DelayQueue} that is initially empty.
75	dl	1.1	*/
76			public DelayQueue() {}
77
78			/**
79	jsr166	1.2	* Creates a {@code DelayQueue} initially containing the elements of the
80	dl	1.1	* given collection of {@link Delayed} instances.
81			*
82			* @param c the collection of elements to initially contain
83			* @throws NullPointerException if the specified collection or any
84			* of its elements are null
85			*/
86			public DelayQueue(Collection<? extends E> c) {
87			this.addAll(c);
88			}
89
90			/**
91			* Inserts the specified element into this delay queue.
92			*
93			* @param e the element to add
94	jsr166	1.2	* @return {@code true} (as specified by {@link Collection#add})
95	dl	1.1	* @throws NullPointerException if the specified element is null
96			*/
97			public boolean add(E e) {
98			return offer(e);
99			}
100
101			/**
102			* Inserts the specified element into this delay queue.
103			*
104			* @param e the element to add
105	jsr166	1.2	* @return {@code true}
106	dl	1.1	* @throws NullPointerException if the specified element is null
107			*/
108			public boolean offer(E e) {
109			final ReentrantLock lock = this.lock;
110			lock.lock();
111			try {
112			q.offer(e);
113			if (q.peek() == e) {
114			leader = null;
115			available.signal();
116			}
117			return true;
118			} finally {
119			lock.unlock();
120			}
121			}
122
123			/**
124			* Inserts the specified element into this delay queue. As the queue is
125			* unbounded this method will never block.
126			*
127			* @param e the element to add
128			* @throws NullPointerException {@inheritDoc}
129			*/
130			public void put(E e) {
131			offer(e);
132			}
133
134			/**
135			* Inserts the specified element into this delay queue. As the queue is
136			* unbounded this method will never block.
137			*
138			* @param e the element to add
139			* @param timeout This parameter is ignored as the method never blocks
140			* @param unit This parameter is ignored as the method never blocks
141	jsr166	1.2	* @return {@code true}
142	dl	1.1	* @throws NullPointerException {@inheritDoc}
143			*/
144			public boolean offer(E e, long timeout, TimeUnit unit) {
145			return offer(e);
146			}
147
148			/**
149	jsr166	1.2	* Retrieves and removes the head of this queue, or returns {@code null}
150	dl	1.1	* if this queue has no elements with an expired delay.
151			*
152	jsr166	1.2	* @return the head of this queue, or {@code null} if this
153	dl	1.1	* queue has no elements with an expired delay
154			*/
155			public E poll() {
156			final ReentrantLock lock = this.lock;
157			lock.lock();
158			try {
159			E first = q.peek();
160			if (first == null \|\| first.getDelay(NANOSECONDS) > 0)
161			return null;
162			else
163			return q.poll();
164			} finally {
165			lock.unlock();
166			}
167			}
168
169			/**
170			* Retrieves and removes the head of this queue, waiting if necessary
171			* until an element with an expired delay is available on this queue.
172			*
173			* @return the head of this queue
174			* @throws InterruptedException {@inheritDoc}
175			*/
176			public E take() throws InterruptedException {
177			final ReentrantLock lock = this.lock;
178			lock.lockInterruptibly();
179			try {
180			for (;;) {
181			E first = q.peek();
182			if (first == null)
183			available.await();
184			else {
185			long delay = first.getDelay(NANOSECONDS);
186			if (delay <= 0)
187			return q.poll();
188	jsr166	1.5	first = null; // don't retain ref while waiting
189			if (leader != null)
190	dl	1.1	available.await();
191			else {
192			Thread thisThread = Thread.currentThread();
193			leader = thisThread;
194			try {
195			available.awaitNanos(delay);
196			} finally {
197			if (leader == thisThread)
198			leader = null;
199			}
200			}
201			}
202			}
203			} finally {
204			if (leader == null && q.peek() != null)
205			available.signal();
206			lock.unlock();
207			}
208			}
209
210			/**
211			* Retrieves and removes the head of this queue, waiting if necessary
212			* until an element with an expired delay is available on this queue,
213			* or the specified wait time expires.
214			*
215	jsr166	1.2	* @return the head of this queue, or {@code null} if the
216	dl	1.1	* specified waiting time elapses before an element with
217			* an expired delay becomes available
218			* @throws InterruptedException {@inheritDoc}
219			*/
220			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
221			long nanos = unit.toNanos(timeout);
222			final ReentrantLock lock = this.lock;
223			lock.lockInterruptibly();
224			try {
225			for (;;) {
226			E first = q.peek();
227			if (first == null) {
228			if (nanos <= 0)
229			return null;
230			else
231			nanos = available.awaitNanos(nanos);
232			} else {
233			long delay = first.getDelay(NANOSECONDS);
234			if (delay <= 0)
235			return q.poll();
236			if (nanos <= 0)
237			return null;
238	jsr166	1.5	first = null; // don't retain ref while waiting
239	dl	1.1	if (nanos < delay \|\| leader != null)
240			nanos = available.awaitNanos(nanos);
241			else {
242			Thread thisThread = Thread.currentThread();
243			leader = thisThread;
244			try {
245			long timeLeft = available.awaitNanos(delay);
246			nanos -= delay - timeLeft;
247			} finally {
248			if (leader == thisThread)
249			leader = null;
250			}
251			}
252			}
253			}
254			} finally {
255			if (leader == null && q.peek() != null)
256			available.signal();
257			lock.unlock();
258			}
259			}
260
261			/**
262			* Retrieves, but does not remove, the head of this queue, or
263	jsr166	1.2	* returns {@code null} if this queue is empty. Unlike
264			* {@code poll}, if no expired elements are available in the queue,
265	dl	1.1	* this method returns the element that will expire next,
266			* if one exists.
267			*
268	jsr166	1.2	* @return the head of this queue, or {@code null} if this
269	jsr166	1.4	* queue is empty
270	dl	1.1	*/
271			public E peek() {
272			final ReentrantLock lock = this.lock;
273			lock.lock();
274			try {
275			return q.peek();
276			} finally {
277			lock.unlock();
278			}
279			}
280
281			public int size() {
282			final ReentrantLock lock = this.lock;
283			lock.lock();
284			try {
285			return q.size();
286			} finally {
287			lock.unlock();
288			}
289			}
290
291			/**
292			* Returns first element only if it is expired.
293			* Used only by drainTo. Call only when holding lock.
294			*/
295			private E peekExpired() {
296			// assert lock.isHeldByCurrentThread();
297			E first = q.peek();
298			return (first == null \|\| first.getDelay(NANOSECONDS) > 0) ?
299			null : first;
300			}
301
302			/**
303			* @throws UnsupportedOperationException {@inheritDoc}
304			* @throws ClassCastException {@inheritDoc}
305			* @throws NullPointerException {@inheritDoc}
306			* @throws IllegalArgumentException {@inheritDoc}
307			*/
308			public int drainTo(Collection<? super E> c) {
309			if (c == null)
310			throw new NullPointerException();
311			if (c == this)
312			throw new IllegalArgumentException();
313			final ReentrantLock lock = this.lock;
314			lock.lock();
315			try {
316			int n = 0;
317			for (E e; (e = peekExpired()) != null;) {
318			c.add(e); // In this order, in case add() throws.
319			q.poll();
320			++n;
321			}
322			return n;
323			} finally {
324			lock.unlock();
325			}
326			}
327
328			/**
329			* @throws UnsupportedOperationException {@inheritDoc}
330			* @throws ClassCastException {@inheritDoc}
331			* @throws NullPointerException {@inheritDoc}
332			* @throws IllegalArgumentException {@inheritDoc}
333			*/
334			public int drainTo(Collection<? super E> c, int maxElements) {
335			if (c == null)
336			throw new NullPointerException();
337			if (c == this)
338			throw new IllegalArgumentException();
339			if (maxElements <= 0)
340			return 0;
341			final ReentrantLock lock = this.lock;
342			lock.lock();
343			try {
344			int n = 0;
345			for (E e; n < maxElements && (e = peekExpired()) != null;) {
346			c.add(e); // In this order, in case add() throws.
347			q.poll();
348			++n;
349			}
350			return n;
351			} finally {
352			lock.unlock();
353			}
354			}
355
356			/**
357			* Atomically removes all of the elements from this delay queue.
358			* The queue will be empty after this call returns.
359			* Elements with an unexpired delay are not waited for; they are
360			* simply discarded from the queue.
361			*/
362			public void clear() {
363			final ReentrantLock lock = this.lock;
364			lock.lock();
365			try {
366			q.clear();
367			} finally {
368			lock.unlock();
369			}
370			}
371
372			/**
373	jsr166	1.2	* Always returns {@code Integer.MAX_VALUE} because
374			* a {@code DelayQueue} is not capacity constrained.
375	dl	1.1	*
376	jsr166	1.2	* @return {@code Integer.MAX_VALUE}
377	dl	1.1	*/
378			public int remainingCapacity() {
379			return Integer.MAX_VALUE;
380			}
381
382			/**
383			* Returns an array containing all of the elements in this queue.
384			* The returned array elements are in no particular order.
385			*
386			* <p>The returned array will be "safe" in that no references to it are
387			* maintained by this queue. (In other words, this method must allocate
388			* a new array). The caller is thus free to modify the returned array.
389			*
390			* <p>This method acts as bridge between array-based and collection-based
391			* APIs.
392			*
393			* @return an array containing all of the elements in this queue
394			*/
395			public Object[] toArray() {
396			final ReentrantLock lock = this.lock;
397			lock.lock();
398			try {
399			return q.toArray();
400			} finally {
401			lock.unlock();
402			}
403			}
404
405			/**
406			* Returns an array containing all of the elements in this queue; the
407			* runtime type of the returned array is that of the specified array.
408			* The returned array elements are in no particular order.
409			* If the queue fits in the specified array, it is returned therein.
410			* Otherwise, a new array is allocated with the runtime type of the
411			* specified array and the size of this queue.
412			*
413			* <p>If this queue fits in the specified array with room to spare
414			* (i.e., the array has more elements than this queue), the element in
415			* the array immediately following the end of the queue is set to
416	jsr166	1.2	* {@code null}.
417	dl	1.1	*
418			* <p>Like the {@link #toArray()} method, this method acts as bridge between
419			* array-based and collection-based APIs. Further, this method allows
420			* precise control over the runtime type of the output array, and may,
421			* under certain circumstances, be used to save allocation costs.
422			*
423			* <p>The following code can be used to dump a delay queue into a newly
424	jsr166	1.2	* allocated array of {@code Delayed}:
425	dl	1.1	*
426			* <pre> {@code Delayed[] a = q.toArray(new Delayed[0]);}</pre>
427			*
428	jsr166	1.2	* Note that {@code toArray(new Object[0])} is identical in function to
429			* {@code toArray()}.
430	dl	1.1	*
431			* @param a the array into which the elements of the queue are to
432			* be stored, if it is big enough; otherwise, a new array of the
433			* same runtime type is allocated for this purpose
434			* @return an array containing all of the elements in this queue
435			* @throws ArrayStoreException if the runtime type of the specified array
436			* is not a supertype of the runtime type of every element in
437			* this queue
438			* @throws NullPointerException if the specified array is null
439			*/
440			public <T> T[] toArray(T[] a) {
441			final ReentrantLock lock = this.lock;
442			lock.lock();
443			try {
444			return q.toArray(a);
445			} finally {
446			lock.unlock();
447			}
448			}
449
450			/**
451			* Removes a single instance of the specified element from this
452			* queue, if it is present, whether or not it has expired.
453			*/
454			public boolean remove(Object o) {
455			final ReentrantLock lock = this.lock;
456			lock.lock();
457			try {
458			return q.remove(o);
459			} finally {
460			lock.unlock();
461			}
462			}
463
464			/**
465			* Identity-based version for use in Itr.remove
466			*/
467			void removeEQ(Object o) {
468			final ReentrantLock lock = this.lock;
469			lock.lock();
470			try {
471			for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
472			if (o == it.next()) {
473			it.remove();
474			break;
475			}
476			}
477			} finally {
478			lock.unlock();
479			}
480			}
481
482			/**
483			* Returns an iterator over all the elements (both expired and
484			* unexpired) in this queue. The iterator does not return the
485			* elements in any particular order.
486			*
487			* <p>The returned iterator is a "weakly consistent" iterator that
488			* will never throw {@link java.util.ConcurrentModificationException
489			* ConcurrentModificationException}, and guarantees to traverse
490			* elements as they existed upon construction of the iterator, and
491			* may (but is not guaranteed to) reflect any modifications
492			* subsequent to construction.
493			*
494			* @return an iterator over the elements in this queue
495			*/
496			public Iterator<E> iterator() {
497			return new Itr(toArray());
498			}
499
500			/**
501			* Snapshot iterator that works off copy of underlying q array.
502			*/
503			private class Itr implements Iterator<E> {
504			final Object[] array; // Array of all elements
505			int cursor; // index of next element to return
506			int lastRet; // index of last element, or -1 if no such
507
508			Itr(Object[] array) {
509			lastRet = -1;
510			this.array = array;
511			}
512
513			public boolean hasNext() {
514			return cursor < array.length;
515			}
516
517			@SuppressWarnings("unchecked")
518			public E next() {
519			if (cursor >= array.length)
520			throw new NoSuchElementException();
521			lastRet = cursor;
522			return (E)array[cursor++];
523			}
524
525			public void remove() {
526			if (lastRet < 0)
527			throw new IllegalStateException();
528			removeEQ(array[lastRet]);
529			lastRet = -1;
530			}
531			}
532
533			}