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.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.  This queue does not permit <tt>null</tt>
 * 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 per the spec for {@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>, this method can be used to inspect
     * elements that have not yet expired.
     *
     * @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>Suppose <tt>x</tt> is a queue known to contain only strings.
     * The following code can be used to dump the queue into a newly
     * allocated array of <tt>String</tt>:
     *
     * <pre>
     *     String[] y = x.toArray(new String[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.
     */
    public boolean remove(Object o) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.remove(o);
        } finally {
            lock.unlock();
        }
    }

    /**
     * Returns an iterator over the elements 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:	1.35
Committed:	Fri Jun 10 18:12:59 2005 UTC (19 years ago) by dl
Branch:	MAIN
Changes since 1.34:	+4 -3 lines
Log Message:	Fix peek spec
#	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.locks.*;
10	import java.util.*;
11
12	/**
13	* An unbounded {@linkplain BlockingQueue blocking queue} of
14	* <tt>Delayed</tt> elements, in which an element can only be taken
15	* when its delay has expired. The <em>head</em> of the queue is that
16	* <tt>Delayed</tt> element whose delay expired furthest in the
17	* past. If no delay has expired there is no head and <tt>poll</tt>
18	* will return <tt>null</tt>. Expiration occurs when an element's
19	* <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less
20	* than or equal to zero. This queue does not permit <tt>null</tt>
21	* elements.
22	*
23	* <p>This class and its iterator implement all of the
24	* <em>optional</em> methods of the {@link Collection} and {@link
25	* Iterator} interfaces.
26	*
27	* <p>This class is a member of the
28	* <a href="{@docRoot}/../guide/collections/index.html">
29	* Java Collections Framework</a>.
30	*
31	* @since 1.5
32	* @author Doug Lea
33	* @param <E> the type of elements held in this collection
34	*/
35
36	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
37	implements BlockingQueue<E> {
38
39	private transient final ReentrantLock lock = new ReentrantLock();
40	private transient final Condition available = lock.newCondition();
41	private final PriorityQueue<E> q = new PriorityQueue<E>();
42
43	/**
44	* Creates a new <tt>DelayQueue</tt> that is initially empty.
45	*/
46	public DelayQueue() {}
47
48	/**
49	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
50	* given collection of {@link Delayed} instances.
51	*
52	* @param c the collection of elements to initially contain
53	* @throws NullPointerException if the specified collection or any
54	* of its elements are null
55	*/
56	public DelayQueue(Collection<? extends E> c) {
57	this.addAll(c);
58	}
59
60	/**
61	* Inserts the specified element into this delay queue.
62	*
63	* @param e the element to add
64	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
65	* @throws NullPointerException if the specified element is null
66	*/
67	public boolean add(E e) {
68	return offer(e);
69	}
70
71	/**
72	* Inserts the specified element into this delay queue.
73	*
74	* @param e the element to add
75	* @return <tt>true</tt>
76	* @throws NullPointerException if the specified element is null
77	*/
78	public boolean offer(E e) {
79	final ReentrantLock lock = this.lock;
80	lock.lock();
81	try {
82	E first = q.peek();
83	q.offer(e);
84	if (first == null \|\| e.compareTo(first) < 0)
85	available.signalAll();
86	return true;
87	} finally {
88	lock.unlock();
89	}
90	}
91
92	/**
93	* Inserts the specified element into this delay queue. As the queue is
94	* unbounded this method will never block.
95	*
96	* @param e the element to add
97	* @throws NullPointerException {@inheritDoc}
98	*/
99	public void put(E e) {
100	offer(e);
101	}
102
103	/**
104	* Inserts the specified element into this delay queue. As the queue is
105	* unbounded this method will never block.
106	*
107	* @param e the element to add
108	* @param timeout This parameter is ignored as the method never blocks
109	* @param unit This parameter is ignored as the method never blocks
110	* @return <tt>true</tt>
111	* @throws NullPointerException {@inheritDoc}
112	*/
113	public boolean offer(E e, long timeout, TimeUnit unit) {
114	return offer(e);
115	}
116
117	/**
118	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
119	* if this queue has no elements with an expired delay.
120	*
121	* @return the head of this queue, or <tt>null</tt> if this
122	* queue has no elements with an expired delay
123	*/
124	public E poll() {
125	final ReentrantLock lock = this.lock;
126	lock.lock();
127	try {
128	E first = q.peek();
129	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
130	return null;
131	else {
132	E x = q.poll();
133	assert x != null;
134	if (q.size() != 0)
135	available.signalAll();
136	return x;
137	}
138	} finally {
139	lock.unlock();
140	}
141	}
142
143	/**
144	* Retrieves and removes the head of this queue, waiting if necessary
145	* until an element with an expired delay is available on this queue.
146	*
147	* @return the head of this queue
148	* @throws InterruptedException {@inheritDoc}
149	*/
150	public E take() throws InterruptedException {
151	final ReentrantLock lock = this.lock;
152	lock.lockInterruptibly();
153	try {
154	for (;;) {
155	E first = q.peek();
156	if (first == null) {
157	available.await();
158	} else {
159	long delay = first.getDelay(TimeUnit.NANOSECONDS);
160	if (delay > 0) {
161	long tl = available.awaitNanos(delay);
162	} else {
163	E x = q.poll();
164	assert x != null;
165	if (q.size() != 0)
166	available.signalAll(); // wake up other takers
167	return x;
168
169	}
170	}
171	}
172	} finally {
173	lock.unlock();
174	}
175	}
176
177	/**
178	* Retrieves and removes the head of this queue, waiting if necessary
179	* until an element with an expired delay is available on this queue,
180	* or the specified wait time expires.
181	*
182	* @return the head of this queue, or <tt>null</tt> if the
183	* specified waiting time elapses before an element with
184	* an expired delay becomes available
185	* @throws InterruptedException {@inheritDoc}
186	*/
187	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
188	final ReentrantLock lock = this.lock;
189	lock.lockInterruptibly();
190	long nanos = unit.toNanos(timeout);
191	try {
192	for (;;) {
193	E first = q.peek();
194	if (first == null) {
195	if (nanos <= 0)
196	return null;
197	else
198	nanos = available.awaitNanos(nanos);
199	} else {
200	long delay = first.getDelay(TimeUnit.NANOSECONDS);
201	if (delay > 0) {
202	if (delay > nanos)
203	delay = nanos;
204	long timeLeft = available.awaitNanos(delay);
205	nanos -= delay - timeLeft;
206	} else {
207	E x = q.poll();
208	assert x != null;
209	if (q.size() != 0)
210	available.signalAll();
211	return x;
212	}
213	}
214	}
215	} finally {
216	lock.unlock();
217	}
218	}
219
220	/**
221	* Retrieves, but does not remove, the head of this queue,
222	* or returns <tt>null</tt> if this queue is empty.
223	* Unlike <tt>poll</tt>, this method can be used to inspect
224	* elements that have not yet expired.
225	*
226	* @return the head of this queue, or <tt>null</tt> if this
227	* queue is empty.
228	*/
229	public E peek() {
230	final ReentrantLock lock = this.lock;
231	lock.lock();
232	try {
233	return q.peek();
234	} finally {
235	lock.unlock();
236	}
237	}
238
239	public int size() {
240	final ReentrantLock lock = this.lock;
241	lock.lock();
242	try {
243	return q.size();
244	} finally {
245	lock.unlock();
246	}
247	}
248
249	/**
250	* @throws UnsupportedOperationException {@inheritDoc}
251	* @throws ClassCastException {@inheritDoc}
252	* @throws NullPointerException {@inheritDoc}
253	* @throws IllegalArgumentException {@inheritDoc}
254	*/
255	public int drainTo(Collection<? super E> c) {
256	if (c == null)
257	throw new NullPointerException();
258	if (c == this)
259	throw new IllegalArgumentException();
260	final ReentrantLock lock = this.lock;
261	lock.lock();
262	try {
263	int n = 0;
264	for (;;) {
265	E first = q.peek();
266	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
267	break;
268	c.add(q.poll());
269	++n;
270	}
271	if (n > 0)
272	available.signalAll();
273	return n;
274	} finally {
275	lock.unlock();
276	}
277	}
278
279	/**
280	* @throws UnsupportedOperationException {@inheritDoc}
281	* @throws ClassCastException {@inheritDoc}
282	* @throws NullPointerException {@inheritDoc}
283	* @throws IllegalArgumentException {@inheritDoc}
284	*/
285	public int drainTo(Collection<? super E> c, int maxElements) {
286	if (c == null)
287	throw new NullPointerException();
288	if (c == this)
289	throw new IllegalArgumentException();
290	if (maxElements <= 0)
291	return 0;
292	final ReentrantLock lock = this.lock;
293	lock.lock();
294	try {
295	int n = 0;
296	while (n < maxElements) {
297	E first = q.peek();
298	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
299	break;
300	c.add(q.poll());
301	++n;
302	}
303	if (n > 0)
304	available.signalAll();
305	return n;
306	} finally {
307	lock.unlock();
308	}
309	}
310
311	/**
312	* Atomically removes all of the elements from this delay queue.
313	* The queue will be empty after this call returns.
314	* Elements with an unexpired delay are not waited for; they are
315	* simply discarded from the queue.
316	*/
317	public void clear() {
318	final ReentrantLock lock = this.lock;
319	lock.lock();
320	try {
321	q.clear();
322	} finally {
323	lock.unlock();
324	}
325	}
326
327	/**
328	* Always returns <tt>Integer.MAX_VALUE</tt> because
329	* a <tt>DelayQueue</tt> is not capacity constrained.
330	*
331	* @return <tt>Integer.MAX_VALUE</tt>
332	*/
333	public int remainingCapacity() {
334	return Integer.MAX_VALUE;
335	}
336
337	/**
338	* Returns an array containing all of the elements in this queue.
339	* The returned array elements are in no particular order.
340	*
341	* <p>The returned array will be "safe" in that no references to it are
342	* maintained by this queue. (In other words, this method must allocate
343	* a new array). The caller is thus free to modify the returned array.
344	*
345	* <p>This method acts as bridge between array-based and collection-based
346	* APIs.
347	*
348	* @return an array containing all of the elements in this queue
349	*/
350	public Object[] toArray() {
351	final ReentrantLock lock = this.lock;
352	lock.lock();
353	try {
354	return q.toArray();
355	} finally {
356	lock.unlock();
357	}
358	}
359
360	/**
361	* Returns an array containing all of the elements in this queue; the
362	* runtime type of the returned array is that of the specified array.
363	* The returned array elements are in no particular order.
364	* If the queue fits in the specified array, it is returned therein.
365	* Otherwise, a new array is allocated with the runtime type of the
366	* specified array and the size of this queue.
367	*
368	* <p>If this queue fits in the specified array with room to spare
369	* (i.e., the array has more elements than this queue), the element in
370	* the array immediately following the end of the queue is set to
371	* <tt>null</tt>.
372	*
373	* <p>Like the {@link #toArray()} method, this method acts as bridge between
374	* array-based and collection-based APIs. Further, this method allows
375	* precise control over the runtime type of the output array, and may,
376	* under certain circumstances, be used to save allocation costs.
377	*
378	* <p>Suppose <tt>x</tt> is a queue known to contain only strings.
379	* The following code can be used to dump the queue into a newly
380	* allocated array of <tt>String</tt>:
381	*
382	* <pre>
383	* String[] y = x.toArray(new String[0]);</pre>
384	*
385	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
386	* <tt>toArray()</tt>.
387	*
388	* @param a the array into which the elements of the queue are to
389	* be stored, if it is big enough; otherwise, a new array of the
390	* same runtime type is allocated for this purpose
391	* @return an array containing all of the elements in this queue
392	* @throws ArrayStoreException if the runtime type of the specified array
393	* is not a supertype of the runtime type of every element in
394	* this queue
395	* @throws NullPointerException if the specified array is null
396	*/
397	public <T> T[] toArray(T[] a) {
398	final ReentrantLock lock = this.lock;
399	lock.lock();
400	try {
401	return q.toArray(a);
402	} finally {
403	lock.unlock();
404	}
405	}
406
407	/**
408	* Removes a single instance of the specified element from this
409	* queue, if it is present.
410	*/
411	public boolean remove(Object o) {
412	final ReentrantLock lock = this.lock;
413	lock.lock();
414	try {
415	return q.remove(o);
416	} finally {
417	lock.unlock();
418	}
419	}
420
421	/**
422	* Returns an iterator over the elements in this queue. The iterator
423	* does not return the elements in any particular order. The
424	* returned iterator is a thread-safe "fast-fail" iterator that will
425	* throw {@link ConcurrentModificationException}
426	* upon detected interference.
427	*
428	* @return an iterator over the elements in this queue
429	*/
430	public Iterator<E> iterator() {
431	final ReentrantLock lock = this.lock;
432	lock.lock();
433	try {
434	return new Itr<E>(q.iterator());
435	} finally {
436	lock.unlock();
437	}
438	}
439
440	private class Itr<E> implements Iterator<E> {
441	private final Iterator<E> iter;
442	Itr(Iterator<E> i) {
443	iter = i;
444	}
445
446	public boolean hasNext() {
447	return iter.hasNext();
448	}
449
450	public E next() {
451	final ReentrantLock lock = DelayQueue.this.lock;
452	lock.lock();
453	try {
454	return iter.next();
455	} finally {
456	lock.unlock();
457	}
458	}
459
460	public void remove() {
461	final ReentrantLock lock = DelayQueue.this.lock;
462	lock.lock();
463	try {
464	iter.remove();
465	} finally {
466	lock.unlock();
467	}
468	}
469	}
470
471	}