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 <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>, 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:	1.37
Committed:	Mon Jul 18 00:25:25 2005 UTC (18 years, 10 months ago) by jsr166
Branch:	MAIN
Changes since 1.36:	+4 -4 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 <tt>null</tt>
26	* elements.
27	*
28	* <p>This class and its iterator implement all of the
29	* <em>optional</em> methods of the {@link Collection} and {@link
30	* Iterator} interfaces.
31	*
32	* <p>This class is a member of the
33	* <a href="{@docRoot}/../guide/collections/index.html">
34	* Java Collections Framework</a>.
35	*
36	* @since 1.5
37	* @author Doug Lea
38	* @param <E> the type of elements held in this collection
39	*/
40
41	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
42	implements BlockingQueue<E> {
43
44	private transient final ReentrantLock lock = new ReentrantLock();
45	private transient final Condition available = lock.newCondition();
46	private final PriorityQueue<E> q = new PriorityQueue<E>();
47
48	/**
49	* Creates a new <tt>DelayQueue</tt> that is initially empty.
50	*/
51	public DelayQueue() {}
52
53	/**
54	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
55	* given collection of {@link Delayed} instances.
56	*
57	* @param c the collection of elements to initially contain
58	* @throws NullPointerException if the specified collection or any
59	* of its elements are null
60	*/
61	public DelayQueue(Collection<? extends E> c) {
62	this.addAll(c);
63	}
64
65	/**
66	* Inserts the specified element into this delay queue.
67	*
68	* @param e the element to add
69	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
70	* @throws NullPointerException if the specified element is null
71	*/
72	public boolean add(E e) {
73	return offer(e);
74	}
75
76	/**
77	* Inserts the specified element into this delay queue.
78	*
79	* @param e the element to add
80	* @return <tt>true</tt>
81	* @throws NullPointerException if the specified element is null
82	*/
83	public boolean offer(E e) {
84	final ReentrantLock lock = this.lock;
85	lock.lock();
86	try {
87	E first = q.peek();
88	q.offer(e);
89	if (first == null \|\| e.compareTo(first) < 0)
90	available.signalAll();
91	return true;
92	} finally {
93	lock.unlock();
94	}
95	}
96
97	/**
98	* Inserts the specified element into this delay queue. As the queue is
99	* unbounded this method will never block.
100	*
101	* @param e the element to add
102	* @throws NullPointerException {@inheritDoc}
103	*/
104	public void put(E e) {
105	offer(e);
106	}
107
108	/**
109	* Inserts the specified element into this delay queue. As the queue is
110	* unbounded this method will never block.
111	*
112	* @param e the element to add
113	* @param timeout This parameter is ignored as the method never blocks
114	* @param unit This parameter is ignored as the method never blocks
115	* @return <tt>true</tt>
116	* @throws NullPointerException {@inheritDoc}
117	*/
118	public boolean offer(E e, long timeout, TimeUnit unit) {
119	return offer(e);
120	}
121
122	/**
123	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
124	* if this queue has no elements with an expired delay.
125	*
126	* @return the head of this queue, or <tt>null</tt> if this
127	* queue has no elements with an expired delay
128	*/
129	public E poll() {
130	final ReentrantLock lock = this.lock;
131	lock.lock();
132	try {
133	E first = q.peek();
134	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
135	return null;
136	else {
137	E x = q.poll();
138	assert x != null;
139	if (q.size() != 0)
140	available.signalAll();
141	return x;
142	}
143	} finally {
144	lock.unlock();
145	}
146	}
147
148	/**
149	* Retrieves and removes the head of this queue, waiting if necessary
150	* until an element with an expired delay is available on this queue.
151	*
152	* @return the head of this queue
153	* @throws InterruptedException {@inheritDoc}
154	*/
155	public E take() throws InterruptedException {
156	final ReentrantLock lock = this.lock;
157	lock.lockInterruptibly();
158	try {
159	for (;;) {
160	E first = q.peek();
161	if (first == null) {
162	available.await();
163	} else {
164	long delay = first.getDelay(TimeUnit.NANOSECONDS);
165	if (delay > 0) {
166	long tl = available.awaitNanos(delay);
167	} else {
168	E x = q.poll();
169	assert x != null;
170	if (q.size() != 0)
171	available.signalAll(); // wake up other takers
172	return x;
173
174	}
175	}
176	}
177	} finally {
178	lock.unlock();
179	}
180	}
181
182	/**
183	* Retrieves and removes the head of this queue, waiting if necessary
184	* until an element with an expired delay is available on this queue,
185	* or the specified wait time expires.
186	*
187	* @return the head of this queue, or <tt>null</tt> if the
188	* specified waiting time elapses before an element with
189	* an expired delay becomes available
190	* @throws InterruptedException {@inheritDoc}
191	*/
192	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
193	final ReentrantLock lock = this.lock;
194	lock.lockInterruptibly();
195	long nanos = unit.toNanos(timeout);
196	try {
197	for (;;) {
198	E first = q.peek();
199	if (first == null) {
200	if (nanos <= 0)
201	return null;
202	else
203	nanos = available.awaitNanos(nanos);
204	} else {
205	long delay = first.getDelay(TimeUnit.NANOSECONDS);
206	if (delay > 0) {
207	if (delay > nanos)
208	delay = nanos;
209	long timeLeft = available.awaitNanos(delay);
210	nanos -= delay - timeLeft;
211	} else {
212	E x = q.poll();
213	assert x != null;
214	if (q.size() != 0)
215	available.signalAll();
216	return x;
217	}
218	}
219	}
220	} finally {
221	lock.unlock();
222	}
223	}
224
225	/**
226	* Retrieves, but does not remove, the head of this queue, or
227	* returns <tt>null</tt> if this queue is empty. Unlike
228	* <tt>poll</tt>, if no expired elements are available in the queue,
229	* this method returns the element that will expire next,
230	* if one exists.
231	*
232	* @return the head of this queue, or <tt>null</tt> if this
233	* queue is empty.
234	*/
235	public E peek() {
236	final ReentrantLock lock = this.lock;
237	lock.lock();
238	try {
239	return q.peek();
240	} finally {
241	lock.unlock();
242	}
243	}
244
245	public int size() {
246	final ReentrantLock lock = this.lock;
247	lock.lock();
248	try {
249	return q.size();
250	} finally {
251	lock.unlock();
252	}
253	}
254
255	/**
256	* @throws UnsupportedOperationException {@inheritDoc}
257	* @throws ClassCastException {@inheritDoc}
258	* @throws NullPointerException {@inheritDoc}
259	* @throws IllegalArgumentException {@inheritDoc}
260	*/
261	public int drainTo(Collection<? super E> c) {
262	if (c == null)
263	throw new NullPointerException();
264	if (c == this)
265	throw new IllegalArgumentException();
266	final ReentrantLock lock = this.lock;
267	lock.lock();
268	try {
269	int n = 0;
270	for (;;) {
271	E first = q.peek();
272	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
273	break;
274	c.add(q.poll());
275	++n;
276	}
277	if (n > 0)
278	available.signalAll();
279	return n;
280	} finally {
281	lock.unlock();
282	}
283	}
284
285	/**
286	* @throws UnsupportedOperationException {@inheritDoc}
287	* @throws ClassCastException {@inheritDoc}
288	* @throws NullPointerException {@inheritDoc}
289	* @throws IllegalArgumentException {@inheritDoc}
290	*/
291	public int drainTo(Collection<? super E> c, int maxElements) {
292	if (c == null)
293	throw new NullPointerException();
294	if (c == this)
295	throw new IllegalArgumentException();
296	if (maxElements <= 0)
297	return 0;
298	final ReentrantLock lock = this.lock;
299	lock.lock();
300	try {
301	int n = 0;
302	while (n < maxElements) {
303	E first = q.peek();
304	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
305	break;
306	c.add(q.poll());
307	++n;
308	}
309	if (n > 0)
310	available.signalAll();
311	return n;
312	} finally {
313	lock.unlock();
314	}
315	}
316
317	/**
318	* Atomically removes all of the elements from this delay queue.
319	* The queue will be empty after this call returns.
320	* Elements with an unexpired delay are not waited for; they are
321	* simply discarded from the queue.
322	*/
323	public void clear() {
324	final ReentrantLock lock = this.lock;
325	lock.lock();
326	try {
327	q.clear();
328	} finally {
329	lock.unlock();
330	}
331	}
332
333	/**
334	* Always returns <tt>Integer.MAX_VALUE</tt> because
335	* a <tt>DelayQueue</tt> is not capacity constrained.
336	*
337	* @return <tt>Integer.MAX_VALUE</tt>
338	*/
339	public int remainingCapacity() {
340	return Integer.MAX_VALUE;
341	}
342
343	/**
344	* Returns an array containing all of the elements in this queue.
345	* The returned array elements are in no particular order.
346	*
347	* <p>The returned array will be "safe" in that no references to it are
348	* maintained by this queue. (In other words, this method must allocate
349	* a new array). The caller is thus free to modify the returned array.
350	*
351	* <p>This method acts as bridge between array-based and collection-based
352	* APIs.
353	*
354	* @return an array containing all of the elements in this queue
355	*/
356	public Object[] toArray() {
357	final ReentrantLock lock = this.lock;
358	lock.lock();
359	try {
360	return q.toArray();
361	} finally {
362	lock.unlock();
363	}
364	}
365
366	/**
367	* Returns an array containing all of the elements in this queue; the
368	* runtime type of the returned array is that of the specified array.
369	* The returned array elements are in no particular order.
370	* If the queue fits in the specified array, it is returned therein.
371	* Otherwise, a new array is allocated with the runtime type of the
372	* specified array and the size of this queue.
373	*
374	* <p>If this queue fits in the specified array with room to spare
375	* (i.e., the array has more elements than this queue), the element in
376	* the array immediately following the end of the queue is set to
377	* <tt>null</tt>.
378	*
379	* <p>Like the {@link #toArray()} method, this method acts as bridge between
380	* array-based and collection-based APIs. Further, this method allows
381	* precise control over the runtime type of the output array, and may,
382	* under certain circumstances, be used to save allocation costs.
383	*
384	* <p>The following code can be used to dump a delay queue into a newly
385	* allocated array of <tt>Delayed</tt>:
386	*
387	* <pre>
388	* Delayed[] a = q.toArray(new Delayed[0]);</pre>
389	*
390	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
391	* <tt>toArray()</tt>.
392	*
393	* @param a the array into which the elements of the queue are to
394	* be stored, if it is big enough; otherwise, a new array of the
395	* same runtime type is allocated for this purpose
396	* @return an array containing all of the elements in this queue
397	* @throws ArrayStoreException if the runtime type of the specified array
398	* is not a supertype of the runtime type of every element in
399	* this queue
400	* @throws NullPointerException if the specified array is null
401	*/
402	public <T> T[] toArray(T[] a) {
403	final ReentrantLock lock = this.lock;
404	lock.lock();
405	try {
406	return q.toArray(a);
407	} finally {
408	lock.unlock();
409	}
410	}
411
412	/**
413	* Removes a single instance of the specified element from this
414	* queue, if it is present, whether or not it has expired.
415	*/
416	public boolean remove(Object o) {
417	final ReentrantLock lock = this.lock;
418	lock.lock();
419	try {
420	return q.remove(o);
421	} finally {
422	lock.unlock();
423	}
424	}
425
426	/**
427	* Returns an iterator over all the elements (both expired and
428	* unexpired) in this queue. The iterator does not
429	* return the elements in any particular order. The returned
430	* iterator is a thread-safe "fast-fail" iterator that will throw
431	* {@link ConcurrentModificationException} upon detected
432	* interference.
433	*
434	* @return an iterator over the elements in this queue
435	*/
436	public Iterator<E> iterator() {
437	final ReentrantLock lock = this.lock;
438	lock.lock();
439	try {
440	return new Itr<E>(q.iterator());
441	} finally {
442	lock.unlock();
443	}
444	}
445
446	private class Itr<E> implements Iterator<E> {
447	private final Iterator<E> iter;
448	Itr(Iterator<E> i) {
449	iter = i;
450	}
451
452	public boolean hasNext() {
453	return iter.hasNext();
454	}
455
456	public E next() {
457	final ReentrantLock lock = DelayQueue.this.lock;
458	lock.lock();
459	try {
460	return iter.next();
461	} finally {
462	lock.unlock();
463	}
464	}
465
466	public void remove() {
467	final ReentrantLock lock = DelayQueue.this.lock;
468	lock.lock();
469	try {
470	iter.remove();
471	} finally {
472	lock.unlock();
473	}
474	}
475	}
476
477	}