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,
     * returning <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 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(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:	1.32
Committed:	Tue May 17 06:44:59 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.31:	+123 -63 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.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	* returning <tt>null</tt> if this queue has no elements with an
223	* expired delay.
224	*
225	* @return the head of this queue, or <tt>null</tt> if this
226	* queue has no elements with an expired delay
227	*/
228	public E peek() {
229	final ReentrantLock lock = this.lock;
230	lock.lock();
231	try {
232	return q.peek();
233	} finally {
234	lock.unlock();
235	}
236	}
237
238	public int size() {
239	final ReentrantLock lock = this.lock;
240	lock.lock();
241	try {
242	return q.size();
243	} finally {
244	lock.unlock();
245	}
246	}
247
248	/**
249	* @throws UnsupportedOperationException {@inheritDoc}
250	* @throws ClassCastException {@inheritDoc}
251	* @throws NullPointerException {@inheritDoc}
252	* @throws IllegalArgumentException {@inheritDoc}
253	*/
254	public int drainTo(Collection<? super E> c) {
255	if (c == null)
256	throw new NullPointerException();
257	if (c == this)
258	throw new IllegalArgumentException();
259	final ReentrantLock lock = this.lock;
260	lock.lock();
261	try {
262	int n = 0;
263	for (;;) {
264	E first = q.peek();
265	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
266	break;
267	c.add(q.poll());
268	++n;
269	}
270	if (n > 0)
271	available.signalAll();
272	return n;
273	} finally {
274	lock.unlock();
275	}
276	}
277
278	/**
279	* @throws UnsupportedOperationException {@inheritDoc}
280	* @throws ClassCastException {@inheritDoc}
281	* @throws NullPointerException {@inheritDoc}
282	* @throws IllegalArgumentException {@inheritDoc}
283	*/
284	public int drainTo(Collection<? super E> c, int maxElements) {
285	if (c == null)
286	throw new NullPointerException();
287	if (c == this)
288	throw new IllegalArgumentException();
289	if (maxElements <= 0)
290	return 0;
291	final ReentrantLock lock = this.lock;
292	lock.lock();
293	try {
294	int n = 0;
295	while (n < maxElements) {
296	E first = q.peek();
297	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
298	break;
299	c.add(q.poll());
300	++n;
301	}
302	if (n > 0)
303	available.signalAll();
304	return n;
305	} finally {
306	lock.unlock();
307	}
308	}
309
310	/**
311	* Atomically removes all of the elements from this delay queue.
312	* The queue will be empty after this call returns.
313	* Elements with an unexpired delay are not waited for; they are
314	* simply discarded from the queue.
315	*/
316	public void clear() {
317	final ReentrantLock lock = this.lock;
318	lock.lock();
319	try {
320	q.clear();
321	} finally {
322	lock.unlock();
323	}
324	}
325
326	/**
327	* Always returns <tt>Integer.MAX_VALUE</tt> because
328	* a <tt>DelayQueue</tt> is not capacity constrained.
329	*
330	* @return <tt>Integer.MAX_VALUE</tt>
331	*/
332	public int remainingCapacity() {
333	return Integer.MAX_VALUE;
334	}
335
336	/**
337	* Returns an array containing all of the elements in this queue.
338	* The returned array elements are in no particular order.
339	*
340	* <p>The returned array will be "safe" in that no references to it are
341	* maintained by this queue. (In other words, this method must allocate
342	* a new array). The caller is thus free to modify the returned array.
343	*
344	* <p>This method acts as bridge between array-based and collection-based
345	* APIs.
346	*
347	* @return an array containing all of the elements in this queue
348	*/
349	public Object[] toArray() {
350	final ReentrantLock lock = this.lock;
351	lock.lock();
352	try {
353	return q.toArray();
354	} finally {
355	lock.unlock();
356	}
357	}
358
359	/**
360	* Returns an array containing all of the elements in this queue; the
361	* runtime type of the returned array is that of the specified array.
362	* The returned array elements are in no particular order.
363	* If the queue fits in the specified array, it is returned therein.
364	* Otherwise, a new array is allocated with the runtime type of the
365	* specified array and the size of this queue.
366	*
367	* <p>If this queue fits in the specified array with room to spare
368	* (i.e., the array has more elements than this queue), the element in
369	* the array immediately following the end of the queue is set to
370	* <tt>null</tt>.
371	*
372	* <p>Like the {@link #toArray()} method, this method acts as bridge between
373	* array-based and collection-based APIs. Further, this method allows
374	* precise control over the runtime type of the output array, and may,
375	* under certain circumstances, be used to save allocation costs.
376	*
377	* <p>Suppose <tt>x</tt> is a queue known to contain only strings.
378	* The following code can be used to dump the queue into a newly
379	* allocated array of <tt>String</tt>:
380	*
381	* <pre>
382	* String[] y = x.toArray(new String[0]);</pre>
383	*
384	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
385	* <tt>toArray()</tt>.
386	*
387	* @param a the array into which the elements of the queue are to
388	* be stored, if it is big enough; otherwise, a new array of the
389	* same runtime type is allocated for this purpose
390	* @return an array containing all of the elements in this queue
391	* @throws ArrayStoreException if the runtime type of the specified array
392	* is not a supertype of the runtime type of every element in
393	* this queue
394	* @throws NullPointerException if the specified array is null
395	*/
396	public <T> T[] toArray(T[] a) {
397	final ReentrantLock lock = this.lock;
398	lock.lock();
399	try {
400	return q.toArray(a);
401	} finally {
402	lock.unlock();
403	}
404	}
405
406	/**
407	* Removes a single instance of the specified element from this
408	* queue, if it is present.
409	*/
410	public boolean remove(Object o) {
411	final ReentrantLock lock = this.lock;
412	lock.lock();
413	try {
414	return q.remove(o);
415	} finally {
416	lock.unlock();
417	}
418	}
419
420	/**
421	* Returns an iterator over the elements in this queue. The iterator
422	* does not return the elements in any particular order. The
423	* returned iterator is a thread-safe "fast-fail" iterator that will
424	* throw {@link ConcurrentModificationException}
425	* upon detected interference.
426	*
427	* @return an iterator over the elements in this queue
428	*/
429	public Iterator<E> iterator() {
430	final ReentrantLock lock = this.lock;
431	lock.lock();
432	try {
433	return new Itr(q.iterator());
434	} finally {
435	lock.unlock();
436	}
437	}
438
439	private class Itr<E> implements Iterator<E> {
440	private final Iterator<E> iter;
441	Itr(Iterator<E> i) {
442	iter = i;
443	}
444
445	public boolean hasNext() {
446	return iter.hasNext();
447	}
448
449	public E next() {
450	final ReentrantLock lock = DelayQueue.this.lock;
451	lock.lock();
452	try {
453	return iter.next();
454	} finally {
455	lock.unlock();
456	}
457	}
458
459	public void remove() {
460	final ReentrantLock lock = DelayQueue.this.lock;
461	lock.lock();
462	try {
463	iter.remove();
464	} finally {
465	lock.unlock();
466	}
467	}
468	}
469
470	}