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 = null;

    /**
     * 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();
                    else 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;
                    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:	1.3
Committed:	Fri Jan 18 04:23:27 2013 UTC (11 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.2:	+1 -1 lines
Log Message:	use blessed modifier order
#	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			import static java.util.concurrent.TimeUnit.NANOSECONDS;
9			import java.util.concurrent.locks.Condition;
10			import java.util.concurrent.locks.ReentrantLock;
11			import java.util.*;
12
13			/**
14			* An unbounded {@linkplain BlockingQueue blocking queue} of
15	jsr166	1.2	* {@code Delayed} elements, in which an element can only be taken
16	dl	1.1	* when its delay has expired. The <em>head</em> of the queue is that
17	jsr166	1.2	* {@code Delayed} element whose delay expired furthest in the
18			* past. If no delay has expired there is no head and {@code poll}
19			* will return {@code null}. Expiration occurs when an element's
20			* {@code getDelay(TimeUnit.NANOSECONDS)} method returns a value less
21	dl	1.1	* than or equal to zero. Even though unexpired elements cannot be
22	jsr166	1.2	* removed using {@code take} or {@code poll}, they are otherwise
23			* treated as normal elements. For example, the {@code size} method
24	dl	1.1	* returns the count of both expired and unexpired elements.
25			* This queue does not permit null elements.
26			*
27			* <p>This class and its iterator implement all of the
28			* <em>optional</em> methods of the {@link Collection} and {@link
29			* Iterator} interfaces. The Iterator provided in method {@link
30			* #iterator()} is <em>not</em> guaranteed to traverse the elements of
31			* the DelayQueue in any particular order.
32			*
33			* <p>This class is a member of the
34			* <a href="{@docRoot}/../technotes/guides/collections/index.html">
35			* Java Collections Framework</a>.
36			*
37			* @since 1.5
38			* @author Doug Lea
39			* @param <E> the type of elements held in this collection
40			*/
41			public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
42			implements BlockingQueue<E> {
43
44	jsr166	1.3	private final transient ReentrantLock lock = new ReentrantLock();
45	dl	1.1	private final PriorityQueue<E> q = new PriorityQueue<E>();
46
47			/**
48			* Thread designated to wait for the element at the head of
49			* the queue. This variant of the Leader-Follower pattern
50			* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
51			* minimize unnecessary timed waiting. When a thread becomes
52			* the leader, it waits only for the next delay to elapse, but
53			* other threads await indefinitely. The leader thread must
54			* signal some other thread before returning from take() or
55			* poll(...), unless some other thread becomes leader in the
56			* interim. Whenever the head of the queue is replaced with
57			* an element with an earlier expiration time, the leader
58			* field is invalidated by being reset to null, and some
59			* waiting thread, but not necessarily the current leader, is
60			* signalled. So waiting threads must be prepared to acquire
61			* and lose leadership while waiting.
62			*/
63			private Thread leader = null;
64
65			/**
66			* Condition signalled when a newer element becomes available
67			* at the head of the queue or a new thread may need to
68			* become leader.
69			*/
70			private final Condition available = lock.newCondition();
71
72			/**
73	jsr166	1.2	* Creates a new {@code DelayQueue} that is initially empty.
74	dl	1.1	*/
75			public DelayQueue() {}
76
77			/**
78	jsr166	1.2	* Creates a {@code DelayQueue} initially containing the elements of the
79	dl	1.1	* given collection of {@link Delayed} instances.
80			*
81			* @param c the collection of elements to initially contain
82			* @throws NullPointerException if the specified collection or any
83			* of its elements are null
84			*/
85			public DelayQueue(Collection<? extends E> c) {
86			this.addAll(c);
87			}
88
89			/**
90			* Inserts the specified element into this delay queue.
91			*
92			* @param e the element to add
93	jsr166	1.2	* @return {@code true} (as specified by {@link Collection#add})
94	dl	1.1	* @throws NullPointerException if the specified element is null
95			*/
96			public boolean add(E e) {
97			return offer(e);
98			}
99
100			/**
101			* Inserts the specified element into this delay queue.
102			*
103			* @param e the element to add
104	jsr166	1.2	* @return {@code true}
105	dl	1.1	* @throws NullPointerException if the specified element is null
106			*/
107			public boolean offer(E e) {
108			final ReentrantLock lock = this.lock;
109			lock.lock();
110			try {
111			q.offer(e);
112			if (q.peek() == e) {
113			leader = null;
114			available.signal();
115			}
116			return true;
117			} finally {
118			lock.unlock();
119			}
120			}
121
122			/**
123			* Inserts the specified element into this delay queue. As the queue is
124			* unbounded this method will never block.
125			*
126			* @param e the element to add
127			* @throws NullPointerException {@inheritDoc}
128			*/
129			public void put(E e) {
130			offer(e);
131			}
132
133			/**
134			* Inserts the specified element into this delay queue. As the queue is
135			* unbounded this method will never block.
136			*
137			* @param e the element to add
138			* @param timeout This parameter is ignored as the method never blocks
139			* @param unit This parameter is ignored as the method never blocks
140	jsr166	1.2	* @return {@code true}
141	dl	1.1	* @throws NullPointerException {@inheritDoc}
142			*/
143			public boolean offer(E e, long timeout, TimeUnit unit) {
144			return offer(e);
145			}
146
147			/**
148	jsr166	1.2	* Retrieves and removes the head of this queue, or returns {@code null}
149	dl	1.1	* if this queue has no elements with an expired delay.
150			*
151	jsr166	1.2	* @return the head of this queue, or {@code null} if this
152	dl	1.1	* queue has no elements with an expired delay
153			*/
154			public E poll() {
155			final ReentrantLock lock = this.lock;
156			lock.lock();
157			try {
158			E first = q.peek();
159			if (first == null \|\| first.getDelay(NANOSECONDS) > 0)
160			return null;
161			else
162			return q.poll();
163			} finally {
164			lock.unlock();
165			}
166			}
167
168			/**
169			* Retrieves and removes the head of this queue, waiting if necessary
170			* until an element with an expired delay is available on this queue.
171			*
172			* @return the head of this queue
173			* @throws InterruptedException {@inheritDoc}
174			*/
175			public E take() throws InterruptedException {
176			final ReentrantLock lock = this.lock;
177			lock.lockInterruptibly();
178			try {
179			for (;;) {
180			E first = q.peek();
181			if (first == null)
182			available.await();
183			else {
184			long delay = first.getDelay(NANOSECONDS);
185			if (delay <= 0)
186			return q.poll();
187			else if (leader != null)
188			available.await();
189			else {
190			Thread thisThread = Thread.currentThread();
191			leader = thisThread;
192			try {
193			available.awaitNanos(delay);
194			} finally {
195			if (leader == thisThread)
196			leader = null;
197			}
198			}
199			}
200			}
201			} finally {
202			if (leader == null && q.peek() != null)
203			available.signal();
204			lock.unlock();
205			}
206			}
207
208			/**
209			* Retrieves and removes the head of this queue, waiting if necessary
210			* until an element with an expired delay is available on this queue,
211			* or the specified wait time expires.
212			*
213	jsr166	1.2	* @return the head of this queue, or {@code null} if the
214	dl	1.1	* specified waiting time elapses before an element with
215			* an expired delay becomes available
216			* @throws InterruptedException {@inheritDoc}
217			*/
218			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
219			long nanos = unit.toNanos(timeout);
220			final ReentrantLock lock = this.lock;
221			lock.lockInterruptibly();
222			try {
223			for (;;) {
224			E first = q.peek();
225			if (first == null) {
226			if (nanos <= 0)
227			return null;
228			else
229			nanos = available.awaitNanos(nanos);
230			} else {
231			long delay = first.getDelay(NANOSECONDS);
232			if (delay <= 0)
233			return q.poll();
234			if (nanos <= 0)
235			return null;
236			if (nanos < delay \|\| leader != null)
237			nanos = available.awaitNanos(nanos);
238			else {
239			Thread thisThread = Thread.currentThread();
240			leader = thisThread;
241			try {
242			long timeLeft = available.awaitNanos(delay);
243			nanos -= delay - timeLeft;
244			} finally {
245			if (leader == thisThread)
246			leader = null;
247			}
248			}
249			}
250			}
251			} finally {
252			if (leader == null && q.peek() != null)
253			available.signal();
254			lock.unlock();
255			}
256			}
257
258			/**
259			* Retrieves, but does not remove, the head of this queue, or
260	jsr166	1.2	* returns {@code null} if this queue is empty. Unlike
261			* {@code poll}, if no expired elements are available in the queue,
262	dl	1.1	* this method returns the element that will expire next,
263			* if one exists.
264			*
265	jsr166	1.2	* @return the head of this queue, or {@code null} if this
266	dl	1.1	* queue is empty.
267			*/
268			public E peek() {
269			final ReentrantLock lock = this.lock;
270			lock.lock();
271			try {
272			return q.peek();
273			} finally {
274			lock.unlock();
275			}
276			}
277
278			public int size() {
279			final ReentrantLock lock = this.lock;
280			lock.lock();
281			try {
282			return q.size();
283			} finally {
284			lock.unlock();
285			}
286			}
287
288			/**
289			* Returns first element only if it is expired.
290			* Used only by drainTo. Call only when holding lock.
291			*/
292			private E peekExpired() {
293			// assert lock.isHeldByCurrentThread();
294			E first = q.peek();
295			return (first == null \|\| first.getDelay(NANOSECONDS) > 0) ?
296			null : first;
297			}
298
299			/**
300			* @throws UnsupportedOperationException {@inheritDoc}
301			* @throws ClassCastException {@inheritDoc}
302			* @throws NullPointerException {@inheritDoc}
303			* @throws IllegalArgumentException {@inheritDoc}
304			*/
305			public int drainTo(Collection<? super E> c) {
306			if (c == null)
307			throw new NullPointerException();
308			if (c == this)
309			throw new IllegalArgumentException();
310			final ReentrantLock lock = this.lock;
311			lock.lock();
312			try {
313			int n = 0;
314			for (E e; (e = peekExpired()) != null;) {
315			c.add(e); // In this order, in case add() throws.
316			q.poll();
317			++n;
318			}
319			return n;
320			} finally {
321			lock.unlock();
322			}
323			}
324
325			/**
326			* @throws UnsupportedOperationException {@inheritDoc}
327			* @throws ClassCastException {@inheritDoc}
328			* @throws NullPointerException {@inheritDoc}
329			* @throws IllegalArgumentException {@inheritDoc}
330			*/
331			public int drainTo(Collection<? super E> c, int maxElements) {
332			if (c == null)
333			throw new NullPointerException();
334			if (c == this)
335			throw new IllegalArgumentException();
336			if (maxElements <= 0)
337			return 0;
338			final ReentrantLock lock = this.lock;
339			lock.lock();
340			try {
341			int n = 0;
342			for (E e; n < maxElements && (e = peekExpired()) != null;) {
343			c.add(e); // In this order, in case add() throws.
344			q.poll();
345			++n;
346			}
347			return n;
348			} finally {
349			lock.unlock();
350			}
351			}
352
353			/**
354			* Atomically removes all of the elements from this delay queue.
355			* The queue will be empty after this call returns.
356			* Elements with an unexpired delay are not waited for; they are
357			* simply discarded from the queue.
358			*/
359			public void clear() {
360			final ReentrantLock lock = this.lock;
361			lock.lock();
362			try {
363			q.clear();
364			} finally {
365			lock.unlock();
366			}
367			}
368
369			/**
370	jsr166	1.2	* Always returns {@code Integer.MAX_VALUE} because
371			* a {@code DelayQueue} is not capacity constrained.
372	dl	1.1	*
373	jsr166	1.2	* @return {@code Integer.MAX_VALUE}
374	dl	1.1	*/
375			public int remainingCapacity() {
376			return Integer.MAX_VALUE;
377			}
378
379			/**
380			* Returns an array containing all of the elements in this queue.
381			* The returned array elements are in no particular order.
382			*
383			* <p>The returned array will be "safe" in that no references to it are
384			* maintained by this queue. (In other words, this method must allocate
385			* a new array). The caller is thus free to modify the returned array.
386			*
387			* <p>This method acts as bridge between array-based and collection-based
388			* APIs.
389			*
390			* @return an array containing all of the elements in this queue
391			*/
392			public Object[] toArray() {
393			final ReentrantLock lock = this.lock;
394			lock.lock();
395			try {
396			return q.toArray();
397			} finally {
398			lock.unlock();
399			}
400			}
401
402			/**
403			* Returns an array containing all of the elements in this queue; the
404			* runtime type of the returned array is that of the specified array.
405			* The returned array elements are in no particular order.
406			* If the queue fits in the specified array, it is returned therein.
407			* Otherwise, a new array is allocated with the runtime type of the
408			* specified array and the size of this queue.
409			*
410			* <p>If this queue fits in the specified array with room to spare
411			* (i.e., the array has more elements than this queue), the element in
412			* the array immediately following the end of the queue is set to
413	jsr166	1.2	* {@code null}.
414	dl	1.1	*
415			* <p>Like the {@link #toArray()} method, this method acts as bridge between
416			* array-based and collection-based APIs. Further, this method allows
417			* precise control over the runtime type of the output array, and may,
418			* under certain circumstances, be used to save allocation costs.
419			*
420			* <p>The following code can be used to dump a delay queue into a newly
421	jsr166	1.2	* allocated array of {@code Delayed}:
422	dl	1.1	*
423			* <pre> {@code Delayed[] a = q.toArray(new Delayed[0]);}</pre>
424			*
425	jsr166	1.2	* Note that {@code toArray(new Object[0])} is identical in function to
426			* {@code toArray()}.
427	dl	1.1	*
428			* @param a the array into which the elements of the queue are to
429			* be stored, if it is big enough; otherwise, a new array of the
430			* same runtime type is allocated for this purpose
431			* @return an array containing all of the elements in this queue
432			* @throws ArrayStoreException if the runtime type of the specified array
433			* is not a supertype of the runtime type of every element in
434			* this queue
435			* @throws NullPointerException if the specified array is null
436			*/
437			public <T> T[] toArray(T[] a) {
438			final ReentrantLock lock = this.lock;
439			lock.lock();
440			try {
441			return q.toArray(a);
442			} finally {
443			lock.unlock();
444			}
445			}
446
447			/**
448			* Removes a single instance of the specified element from this
449			* queue, if it is present, whether or not it has expired.
450			*/
451			public boolean remove(Object o) {
452			final ReentrantLock lock = this.lock;
453			lock.lock();
454			try {
455			return q.remove(o);
456			} finally {
457			lock.unlock();
458			}
459			}
460
461			/**
462			* Identity-based version for use in Itr.remove
463			*/
464			void removeEQ(Object o) {
465			final ReentrantLock lock = this.lock;
466			lock.lock();
467			try {
468			for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
469			if (o == it.next()) {
470			it.remove();
471			break;
472			}
473			}
474			} finally {
475			lock.unlock();
476			}
477			}
478
479			/**
480			* Returns an iterator over all the elements (both expired and
481			* unexpired) in this queue. The iterator does not return the
482			* elements in any particular order.
483			*
484			* <p>The returned iterator is a "weakly consistent" iterator that
485			* will never throw {@link java.util.ConcurrentModificationException
486			* ConcurrentModificationException}, and guarantees to traverse
487			* elements as they existed upon construction of the iterator, and
488			* may (but is not guaranteed to) reflect any modifications
489			* subsequent to construction.
490			*
491			* @return an iterator over the elements in this queue
492			*/
493			public Iterator<E> iterator() {
494			return new Itr(toArray());
495			}
496
497			/**
498			* Snapshot iterator that works off copy of underlying q array.
499			*/
500			private class Itr implements Iterator<E> {
501			final Object[] array; // Array of all elements
502			int cursor; // index of next element to return
503			int lastRet; // index of last element, or -1 if no such
504
505			Itr(Object[] array) {
506			lastRet = -1;
507			this.array = array;
508			}
509
510			public boolean hasNext() {
511			return cursor < array.length;
512			}
513
514			@SuppressWarnings("unchecked")
515			public E next() {
516			if (cursor >= array.length)
517			throw new NoSuchElementException();
518			lastRet = cursor;
519			return (E)array[cursor++];
520			}
521
522			public void remove() {
523			if (lastRet < 0)
524			throw new IllegalStateException();
525			removeEQ(array[lastRet]);
526			lastRet = -1;
527			}
528			}
529
530			}