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 {
        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(TimeUnit.NANOSECONDS);
                    if (delay > 0) {
                        if (nanos <= 0)
                            return null;
                        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.
     *
     * @return an iterator over the elements in this queue
     */
    public Iterator<E> iterator() {
        return new Itr<E>(toArray());
    }

    /**
     * Snapshot iterator that works off copy of underlying q array.
     */
    private class Itr<E> 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;
        }

        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();
            Object x = array[lastRet];
            lastRet = -1;
            // Traverse underlying queue to find == element,
            // not just a .equals element.
            lock.lock();
            try {
                for (Iterator it = q.iterator(); it.hasNext(); ) {
                    if (it.next() == x) {
                        it.remove();
                        return;
                    }
                }
            } finally {
                lock.unlock();
            }
        }
    }

}
Revision:	1.43
Committed:	Wed Nov 23 05:33:03 2005 UTC (18 years, 6 months ago) by jsr166
Branch:	MAIN
Changes since 1.42:	+3 -3 lines
Log Message:	whitespace
#	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	long nanos = unit.toNanos(timeout);
193	final ReentrantLock lock = this.lock;
194	lock.lockInterruptibly();
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 (nanos <= 0)
207	return null;
208	if (delay > nanos)
209	delay = nanos;
210	long timeLeft = available.awaitNanos(delay);
211	nanos -= delay - timeLeft;
212	} else {
213	E x = q.poll();
214	assert x != null;
215	if (q.size() != 0)
216	available.signalAll();
217	return x;
218	}
219	}
220	}
221	} finally {
222	lock.unlock();
223	}
224	}
225
226	/**
227	* Retrieves, but does not remove, the head of this queue, or
228	* returns <tt>null</tt> if this queue is empty. Unlike
229	* <tt>poll</tt>, if no expired elements are available in the queue,
230	* this method returns the element that will expire next,
231	* if one exists.
232	*
233	* @return the head of this queue, or <tt>null</tt> if this
234	* queue is empty.
235	*/
236	public E peek() {
237	final ReentrantLock lock = this.lock;
238	lock.lock();
239	try {
240	return q.peek();
241	} finally {
242	lock.unlock();
243	}
244	}
245
246	public int size() {
247	final ReentrantLock lock = this.lock;
248	lock.lock();
249	try {
250	return q.size();
251	} finally {
252	lock.unlock();
253	}
254	}
255
256	/**
257	* @throws UnsupportedOperationException {@inheritDoc}
258	* @throws ClassCastException {@inheritDoc}
259	* @throws NullPointerException {@inheritDoc}
260	* @throws IllegalArgumentException {@inheritDoc}
261	*/
262	public int drainTo(Collection<? super E> c) {
263	if (c == null)
264	throw new NullPointerException();
265	if (c == this)
266	throw new IllegalArgumentException();
267	final ReentrantLock lock = this.lock;
268	lock.lock();
269	try {
270	int n = 0;
271	for (;;) {
272	E first = q.peek();
273	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
274	break;
275	c.add(q.poll());
276	++n;
277	}
278	if (n > 0)
279	available.signalAll();
280	return n;
281	} finally {
282	lock.unlock();
283	}
284	}
285
286	/**
287	* @throws UnsupportedOperationException {@inheritDoc}
288	* @throws ClassCastException {@inheritDoc}
289	* @throws NullPointerException {@inheritDoc}
290	* @throws IllegalArgumentException {@inheritDoc}
291	*/
292	public int drainTo(Collection<? super E> c, int maxElements) {
293	if (c == null)
294	throw new NullPointerException();
295	if (c == this)
296	throw new IllegalArgumentException();
297	if (maxElements <= 0)
298	return 0;
299	final ReentrantLock lock = this.lock;
300	lock.lock();
301	try {
302	int n = 0;
303	while (n < maxElements) {
304	E first = q.peek();
305	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
306	break;
307	c.add(q.poll());
308	++n;
309	}
310	if (n > 0)
311	available.signalAll();
312	return n;
313	} finally {
314	lock.unlock();
315	}
316	}
317
318	/**
319	* Atomically removes all of the elements from this delay queue.
320	* The queue will be empty after this call returns.
321	* Elements with an unexpired delay are not waited for; they are
322	* simply discarded from the queue.
323	*/
324	public void clear() {
325	final ReentrantLock lock = this.lock;
326	lock.lock();
327	try {
328	q.clear();
329	} finally {
330	lock.unlock();
331	}
332	}
333
334	/**
335	* Always returns <tt>Integer.MAX_VALUE</tt> because
336	* a <tt>DelayQueue</tt> is not capacity constrained.
337	*
338	* @return <tt>Integer.MAX_VALUE</tt>
339	*/
340	public int remainingCapacity() {
341	return Integer.MAX_VALUE;
342	}
343
344	/**
345	* Returns an array containing all of the elements in this queue.
346	* The returned array elements are in no particular order.
347	*
348	* <p>The returned array will be "safe" in that no references to it are
349	* maintained by this queue. (In other words, this method must allocate
350	* a new array). The caller is thus free to modify the returned array.
351	*
352	* <p>This method acts as bridge between array-based and collection-based
353	* APIs.
354	*
355	* @return an array containing all of the elements in this queue
356	*/
357	public Object[] toArray() {
358	final ReentrantLock lock = this.lock;
359	lock.lock();
360	try {
361	return q.toArray();
362	} finally {
363	lock.unlock();
364	}
365	}
366
367	/**
368	* Returns an array containing all of the elements in this queue; the
369	* runtime type of the returned array is that of the specified array.
370	* The returned array elements are in no particular order.
371	* If the queue fits in the specified array, it is returned therein.
372	* Otherwise, a new array is allocated with the runtime type of the
373	* specified array and the size of this queue.
374	*
375	* <p>If this queue fits in the specified array with room to spare
376	* (i.e., the array has more elements than this queue), the element in
377	* the array immediately following the end of the queue is set to
378	* <tt>null</tt>.
379	*
380	* <p>Like the {@link #toArray()} method, this method acts as bridge between
381	* array-based and collection-based APIs. Further, this method allows
382	* precise control over the runtime type of the output array, and may,
383	* under certain circumstances, be used to save allocation costs.
384	*
385	* <p>The following code can be used to dump a delay queue into a newly
386	* allocated array of <tt>Delayed</tt>:
387	*
388	* <pre>
389	* Delayed[] a = q.toArray(new Delayed[0]);</pre>
390	*
391	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
392	* <tt>toArray()</tt>.
393	*
394	* @param a the array into which the elements of the queue are to
395	* be stored, if it is big enough; otherwise, a new array of the
396	* same runtime type is allocated for this purpose
397	* @return an array containing all of the elements in this queue
398	* @throws ArrayStoreException if the runtime type of the specified array
399	* is not a supertype of the runtime type of every element in
400	* this queue
401	* @throws NullPointerException if the specified array is null
402	*/
403	public <T> T[] toArray(T[] a) {
404	final ReentrantLock lock = this.lock;
405	lock.lock();
406	try {
407	return q.toArray(a);
408	} finally {
409	lock.unlock();
410	}
411	}
412
413	/**
414	* Removes a single instance of the specified element from this
415	* queue, if it is present, whether or not it has expired.
416	*/
417	public boolean remove(Object o) {
418	final ReentrantLock lock = this.lock;
419	lock.lock();
420	try {
421	return q.remove(o);
422	} finally {
423	lock.unlock();
424	}
425	}
426
427	/**
428	* Returns an iterator over all the elements (both expired and
429	* unexpired) in this queue. The iterator does not
430	* return the elements in any particular order.
431	*
432	* @return an iterator over the elements in this queue
433	*/
434	public Iterator<E> iterator() {
435	return new Itr<E>(toArray());
436	}
437
438	/**
439	* Snapshot iterator that works off copy of underlying q array.
440	*/
441	private class Itr<E> implements Iterator<E> {
442	final Object[] array; // Array of all elements
443	int cursor; // index of next element to return;
444	int lastRet; // index of last element, or -1 if no such
445
446	Itr(Object[] array) {
447	lastRet = -1;
448	this.array = array;
449	}
450
451	public boolean hasNext() {
452	return cursor < array.length;
453	}
454
455	public E next() {
456	if (cursor >= array.length)
457	throw new NoSuchElementException();
458	lastRet = cursor;
459	return (E)array[cursor++];
460	}
461
462	public void remove() {
463	if (lastRet < 0)
464	throw new IllegalStateException();
465	Object x = array[lastRet];
466	lastRet = -1;
467	// Traverse underlying queue to find == element,
468	// not just a .equals element.
469	lock.lock();
470	try {
471	for (Iterator it = q.iterator(); it.hasNext(); ) {
472	if (it.next() == x) {
473	it.remove();
474	return;
475	}
476	}
477	} finally {
478	lock.unlock();
479	}
480	}
481	}
482
483	}