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/licenses/publicdomain
 */


package java.util.concurrent;
import java.util.concurrent.*; // for javadoc (till 6280605 is fixed)
import java.util.concurrent.locks.*;
import java.util.*;

/**
 * An unbounded {@linkplain BlockingQueue blocking queue} of
 * <tt>Delayed</tt> elements, in which an element can only be taken
 * when its delay has expired.  The <em>head</em> of the queue is that
 * <tt>Delayed</tt> element whose delay expired furthest in the
 * past.  If no delay has expired there is no head and <tt>poll</tt>
 * will return <tt>null</tt>. Expiration occurs when an element's
 * <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less
 * than or equal to zero.  Even though unexpired elements cannot be
 * removed using <tt>take</tt> or <tt>poll</tt>, they are otherwise
 * treated as normal elements. For example, the <tt>size</tt> 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.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../guide/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 transient final ReentrantLock lock = new ReentrantLock();
    private transient final Condition available = lock.newCondition();
    private final PriorityQueue<E> q = new PriorityQueue<E>();

    /**
     * Creates a new <tt>DelayQueue</tt> that is initially empty.
     */
    public DelayQueue() {}

    /**
     * Creates a <tt>DelayQueue</tt> 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 <tt>true</tt> (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 <tt>true</tt>
     * @throws NullPointerException if the specified element is null
     */
    public boolean offer(E e) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            E first = q.peek();
            q.offer(e);
            if (first == null || e.compareTo(first) < 0)
                available.signalAll();
            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 <tt>true</tt>
     * @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 <tt>null</tt>
     * if this queue has no elements with an expired delay.
     *
     * @return the head of this queue, or <tt>null</tt> 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(TimeUnit.NANOSECONDS) > 0)
                return null;
            else {
                E x = q.poll();
                assert x != null;
                if (q.size() != 0)
                    available.signalAll();
                return x;
            }
        } 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(TimeUnit.NANOSECONDS);
                    if (delay > 0) {
                        long tl = available.awaitNanos(delay);
                    } else {
                        E x = q.poll();
                        assert x != null;
                        if (q.size() != 0)
                            available.signalAll(); // wake up other takers
                        return x;

                    }
                }
            }
        } 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,
     * or the specified wait time expires.
     *
     * @return the head of this queue, or <tt>null</tt> 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 {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        long nanos = unit.toNanos(timeout);
        try {
            for (;;) {
                E first = q.peek();
                if (first == null) {
                    if (nanos <= 0)
                        return null;
                    else
                        nanos = available.awaitNanos(nanos);
                } else {
                    long delay =  first.getDelay(TimeUnit.NANOSECONDS);
                    if (delay > 0) {
                        if (delay > nanos)
                            delay = nanos;
                        long timeLeft = available.awaitNanos(delay);
                        nanos -= delay - timeLeft;
                    } else {
                        E x = q.poll();
                        assert x != null;
                        if (q.size() != 0)
                            available.signalAll();
                        return x;
                    }
                }
            }
        } finally {
            lock.unlock();
        }
    }

    /**
     * Retrieves, but does not remove, the head of this queue, or
     * returns <tt>null</tt> if this queue is empty.  Unlike
     * <tt>poll</tt>, 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 <tt>null</tt> 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();
        }
    }

    /**
     * @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 first = q.peek();
                if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0)
                    break;
                c.add(q.poll());
                ++n;
            }
            if (n > 0)
                available.signalAll();
            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;
            while (n < maxElements) {
                E first = q.peek();
                if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0)
                    break;
                c.add(q.poll());
                ++n;
            }
            if (n > 0)
                available.signalAll();
            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 <tt>Integer.MAX_VALUE</tt> because
     * a <tt>DelayQueue</tt> is not capacity constrained.
     *
     * @return <tt>Integer.MAX_VALUE</tt>
     */
    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
     * <tt>null</tt>.
     *
     * <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 <tt>Delayed</tt>:
     *
     * <pre>
     *     Delayed[] a = q.toArray(new Delayed[0]);</pre>
     *
     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
     * <tt>toArray()</tt>.
     *
     * @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();
        }
    }

    /**
     * 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. The returned
     * iterator is a thread-safe "fast-fail" iterator that will throw
     * {@link ConcurrentModificationException} upon detected
     * interference.
     *
     * @return an iterator over the elements in this queue
     */
    public Iterator<E> iterator() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return new Itr<E>(q.iterator());
        } finally {
            lock.unlock();
        }
    }

    private class Itr<E> implements Iterator<E> {
        private final Iterator<E> iter;
        Itr(Iterator<E> i) {
            iter = i;
        }

        public boolean hasNext() {
            return iter.hasNext();
        }

        public E next() {
            final ReentrantLock lock = DelayQueue.this.lock;
            lock.lock();
            try {
                return iter.next();
            } finally {
                lock.unlock();
            }
        }

        public void remove() {
            final ReentrantLock lock = DelayQueue.this.lock;
            lock.lock();
            try {
                iter.remove();
            } finally {
                lock.unlock();
            }
        }
    }

}
Revision:	1.39
Committed:	Sat Aug 20 07:41:47 2005 UTC (18 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.38:	+1 -2 lines
Log Message:	doc fixes
#	Content
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/licenses/publicdomain
5	*/
6
7
8	package java.util.concurrent;
9	import java.util.concurrent.*; // for javadoc (till 6280605 is fixed)
10	import java.util.concurrent.locks.*;
11	import java.util.*;
12
13	/**
14	* An unbounded {@linkplain BlockingQueue blocking queue} of
15	* <tt>Delayed</tt> elements, in which an element can only be taken
16	* when its delay has expired. The <em>head</em> of the queue is that
17	* <tt>Delayed</tt> element whose delay expired furthest in the
18	* past. If no delay has expired there is no head and <tt>poll</tt>
19	* will return <tt>null</tt>. Expiration occurs when an element's
20	* <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less
21	* than or equal to zero. Even though unexpired elements cannot be
22	* removed using <tt>take</tt> or <tt>poll</tt>, they are otherwise
23	* treated as normal elements. For example, the <tt>size</tt> method
24	* 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.
30	*
31	* <p>This class is a member of the
32	* <a href="{@docRoot}/../guide/collections/index.html">
33	* Java Collections Framework</a>.
34	*
35	* @since 1.5
36	* @author Doug Lea
37	* @param <E> the type of elements held in this collection
38	*/
39
40	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
41	implements BlockingQueue<E> {
42
43	private transient final ReentrantLock lock = new ReentrantLock();
44	private transient final Condition available = lock.newCondition();
45	private final PriorityQueue<E> q = new PriorityQueue<E>();
46
47	/**
48	* Creates a new <tt>DelayQueue</tt> that is initially empty.
49	*/
50	public DelayQueue() {}
51
52	/**
53	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
54	* given collection of {@link Delayed} instances.
55	*
56	* @param c the collection of elements to initially contain
57	* @throws NullPointerException if the specified collection or any
58	* of its elements are null
59	*/
60	public DelayQueue(Collection<? extends E> c) {
61	this.addAll(c);
62	}
63
64	/**
65	* Inserts the specified element into this delay queue.
66	*
67	* @param e the element to add
68	* @return <tt>true</tt> (as specified by {@link Collection#add})
69	* @throws NullPointerException if the specified element is null
70	*/
71	public boolean add(E e) {
72	return offer(e);
73	}
74
75	/**
76	* Inserts the specified element into this delay queue.
77	*
78	* @param e the element to add
79	* @return <tt>true</tt>
80	* @throws NullPointerException if the specified element is null
81	*/
82	public boolean offer(E e) {
83	final ReentrantLock lock = this.lock;
84	lock.lock();
85	try {
86	E first = q.peek();
87	q.offer(e);
88	if (first == null \|\| e.compareTo(first) < 0)
89	available.signalAll();
90	return true;
91	} finally {
92	lock.unlock();
93	}
94	}
95
96	/**
97	* Inserts the specified element into this delay queue. As the queue is
98	* unbounded this method will never block.
99	*
100	* @param e the element to add
101	* @throws NullPointerException {@inheritDoc}
102	*/
103	public void put(E e) {
104	offer(e);
105	}
106
107	/**
108	* Inserts the specified element into this delay queue. As the queue is
109	* unbounded this method will never block.
110	*
111	* @param e the element to add
112	* @param timeout This parameter is ignored as the method never blocks
113	* @param unit This parameter is ignored as the method never blocks
114	* @return <tt>true</tt>
115	* @throws NullPointerException {@inheritDoc}
116	*/
117	public boolean offer(E e, long timeout, TimeUnit unit) {
118	return offer(e);
119	}
120
121	/**
122	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
123	* if this queue has no elements with an expired delay.
124	*
125	* @return the head of this queue, or <tt>null</tt> if this
126	* queue has no elements with an expired delay
127	*/
128	public E poll() {
129	final ReentrantLock lock = this.lock;
130	lock.lock();
131	try {
132	E first = q.peek();
133	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
134	return null;
135	else {
136	E x = q.poll();
137	assert x != null;
138	if (q.size() != 0)
139	available.signalAll();
140	return x;
141	}
142	} finally {
143	lock.unlock();
144	}
145	}
146
147	/**
148	* Retrieves and removes the head of this queue, waiting if necessary
149	* until an element with an expired delay is available on this queue.
150	*
151	* @return the head of this queue
152	* @throws InterruptedException {@inheritDoc}
153	*/
154	public E take() throws InterruptedException {
155	final ReentrantLock lock = this.lock;
156	lock.lockInterruptibly();
157	try {
158	for (;;) {
159	E first = q.peek();
160	if (first == null) {
161	available.await();
162	} else {
163	long delay = first.getDelay(TimeUnit.NANOSECONDS);
164	if (delay > 0) {
165	long tl = available.awaitNanos(delay);
166	} else {
167	E x = q.poll();
168	assert x != null;
169	if (q.size() != 0)
170	available.signalAll(); // wake up other takers
171	return x;
172
173	}
174	}
175	}
176	} finally {
177	lock.unlock();
178	}
179	}
180
181	/**
182	* Retrieves and removes the head of this queue, waiting if necessary
183	* until an element with an expired delay is available on this queue,
184	* or the specified wait time expires.
185	*
186	* @return the head of this queue, or <tt>null</tt> if the
187	* specified waiting time elapses before an element with
188	* an expired delay becomes available
189	* @throws InterruptedException {@inheritDoc}
190	*/
191	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
192	final ReentrantLock lock = this.lock;
193	lock.lockInterruptibly();
194	long nanos = unit.toNanos(timeout);
195	try {
196	for (;;) {
197	E first = q.peek();
198	if (first == null) {
199	if (nanos <= 0)
200	return null;
201	else
202	nanos = available.awaitNanos(nanos);
203	} else {
204	long delay = first.getDelay(TimeUnit.NANOSECONDS);
205	if (delay > 0) {
206	if (delay > nanos)
207	delay = nanos;
208	long timeLeft = available.awaitNanos(delay);
209	nanos -= delay - timeLeft;
210	} else {
211	E x = q.poll();
212	assert x != null;
213	if (q.size() != 0)
214	available.signalAll();
215	return x;
216	}
217	}
218	}
219	} finally {
220	lock.unlock();
221	}
222	}
223
224	/**
225	* Retrieves, but does not remove, the head of this queue, or
226	* returns <tt>null</tt> if this queue is empty. Unlike
227	* <tt>poll</tt>, if no expired elements are available in the queue,
228	* this method returns the element that will expire next,
229	* if one exists.
230	*
231	* @return the head of this queue, or <tt>null</tt> if this
232	* queue is empty.
233	*/
234	public E peek() {
235	final ReentrantLock lock = this.lock;
236	lock.lock();
237	try {
238	return q.peek();
239	} finally {
240	lock.unlock();
241	}
242	}
243
244	public int size() {
245	final ReentrantLock lock = this.lock;
246	lock.lock();
247	try {
248	return q.size();
249	} finally {
250	lock.unlock();
251	}
252	}
253
254	/**
255	* @throws UnsupportedOperationException {@inheritDoc}
256	* @throws ClassCastException {@inheritDoc}
257	* @throws NullPointerException {@inheritDoc}
258	* @throws IllegalArgumentException {@inheritDoc}
259	*/
260	public int drainTo(Collection<? super E> c) {
261	if (c == null)
262	throw new NullPointerException();
263	if (c == this)
264	throw new IllegalArgumentException();
265	final ReentrantLock lock = this.lock;
266	lock.lock();
267	try {
268	int n = 0;
269	for (;;) {
270	E first = q.peek();
271	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
272	break;
273	c.add(q.poll());
274	++n;
275	}
276	if (n > 0)
277	available.signalAll();
278	return n;
279	} finally {
280	lock.unlock();
281	}
282	}
283
284	/**
285	* @throws UnsupportedOperationException {@inheritDoc}
286	* @throws ClassCastException {@inheritDoc}
287	* @throws NullPointerException {@inheritDoc}
288	* @throws IllegalArgumentException {@inheritDoc}
289	*/
290	public int drainTo(Collection<? super E> c, int maxElements) {
291	if (c == null)
292	throw new NullPointerException();
293	if (c == this)
294	throw new IllegalArgumentException();
295	if (maxElements <= 0)
296	return 0;
297	final ReentrantLock lock = this.lock;
298	lock.lock();
299	try {
300	int n = 0;
301	while (n < maxElements) {
302	E first = q.peek();
303	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
304	break;
305	c.add(q.poll());
306	++n;
307	}
308	if (n > 0)
309	available.signalAll();
310	return n;
311	} finally {
312	lock.unlock();
313	}
314	}
315
316	/**
317	* Atomically removes all of the elements from this delay queue.
318	* The queue will be empty after this call returns.
319	* Elements with an unexpired delay are not waited for; they are
320	* simply discarded from the queue.
321	*/
322	public void clear() {
323	final ReentrantLock lock = this.lock;
324	lock.lock();
325	try {
326	q.clear();
327	} finally {
328	lock.unlock();
329	}
330	}
331
332	/**
333	* Always returns <tt>Integer.MAX_VALUE</tt> because
334	* a <tt>DelayQueue</tt> is not capacity constrained.
335	*
336	* @return <tt>Integer.MAX_VALUE</tt>
337	*/
338	public int remainingCapacity() {
339	return Integer.MAX_VALUE;
340	}
341
342	/**
343	* Returns an array containing all of the elements in this queue.
344	* The returned array elements are in no particular order.
345	*
346	* <p>The returned array will be "safe" in that no references to it are
347	* maintained by this queue. (In other words, this method must allocate
348	* a new array). The caller is thus free to modify the returned array.
349	*
350	* <p>This method acts as bridge between array-based and collection-based
351	* APIs.
352	*
353	* @return an array containing all of the elements in this queue
354	*/
355	public Object[] toArray() {
356	final ReentrantLock lock = this.lock;
357	lock.lock();
358	try {
359	return q.toArray();
360	} finally {
361	lock.unlock();
362	}
363	}
364
365	/**
366	* Returns an array containing all of the elements in this queue; the
367	* runtime type of the returned array is that of the specified array.
368	* The returned array elements are in no particular order.
369	* If the queue fits in the specified array, it is returned therein.
370	* Otherwise, a new array is allocated with the runtime type of the
371	* specified array and the size of this queue.
372	*
373	* <p>If this queue fits in the specified array with room to spare
374	* (i.e., the array has more elements than this queue), the element in
375	* the array immediately following the end of the queue is set to
376	* <tt>null</tt>.
377	*
378	* <p>Like the {@link #toArray()} method, this method acts as bridge between
379	* array-based and collection-based APIs. Further, this method allows
380	* precise control over the runtime type of the output array, and may,
381	* under certain circumstances, be used to save allocation costs.
382	*
383	* <p>The following code can be used to dump a delay queue into a newly
384	* allocated array of <tt>Delayed</tt>:
385	*
386	* <pre>
387	* Delayed[] a = q.toArray(new Delayed[0]);</pre>
388	*
389	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
390	* <tt>toArray()</tt>.
391	*
392	* @param a the array into which the elements of the queue are to
393	* be stored, if it is big enough; otherwise, a new array of the
394	* same runtime type is allocated for this purpose
395	* @return an array containing all of the elements in this queue
396	* @throws ArrayStoreException if the runtime type of the specified array
397	* is not a supertype of the runtime type of every element in
398	* this queue
399	* @throws NullPointerException if the specified array is null
400	*/
401	public <T> T[] toArray(T[] a) {
402	final ReentrantLock lock = this.lock;
403	lock.lock();
404	try {
405	return q.toArray(a);
406	} finally {
407	lock.unlock();
408	}
409	}
410
411	/**
412	* Removes a single instance of the specified element from this
413	* queue, if it is present, whether or not it has expired.
414	*/
415	public boolean remove(Object o) {
416	final ReentrantLock lock = this.lock;
417	lock.lock();
418	try {
419	return q.remove(o);
420	} finally {
421	lock.unlock();
422	}
423	}
424
425	/**
426	* Returns an iterator over all the elements (both expired and
427	* unexpired) in this queue. The iterator does not
428	* return the elements in any particular order. The returned
429	* iterator is a thread-safe "fast-fail" iterator that will throw
430	* {@link ConcurrentModificationException} upon detected
431	* interference.
432	*
433	* @return an iterator over the elements in this queue
434	*/
435	public Iterator<E> iterator() {
436	final ReentrantLock lock = this.lock;
437	lock.lock();
438	try {
439	return new Itr<E>(q.iterator());
440	} finally {
441	lock.unlock();
442	}
443	}
444
445	private class Itr<E> implements Iterator<E> {
446	private final Iterator<E> iter;
447	Itr(Iterator<E> i) {
448	iter = i;
449	}
450
451	public boolean hasNext() {
452	return iter.hasNext();
453	}
454
455	public E next() {
456	final ReentrantLock lock = DelayQueue.this.lock;
457	lock.lock();
458	try {
459	return iter.next();
460	} finally {
461	lock.unlock();
462	}
463	}
464
465	public void remove() {
466	final ReentrantLock lock = DelayQueue.this.lock;
467	lock.lock();
468	try {
469	iter.remove();
470	} finally {
471	lock.unlock();
472	}
473	}
474	}
475
476	}