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.  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}/../technotes/guides/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 final PriorityQueue<E> q = new PriorityQueue<E>();

    /**
     * Thread designated to wait for the element at the head of
     * the queue.  This variant of the Leader-Follower pattern
     * (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
     * minimize unnecessary timed waiting.  When a thread becomes
     * the leader, it waits only for the next delay to elapse, but
     * other threads await indefinitely.  The leader thread must
     * signal some other thread before returning from take() or
     * poll(...), unless some other thread becomes leader in the
     * interim.  Whenever the head of the queue is replaced with
     * an element with an earlier expiration time, the leader
     * field is invalidated by being reset to null, and some
     * waiting thread, but not necessarily the current leader, is
     * signalled.  So waiting threads must be prepared to acquire
     * and lose leadership while waiting.
     */
    private Thread leader = null;

    /**
     * Condition signalled when a newer element becomes available
     * at the head of the queue or a new thread may need to
     * become leader.
     */
    private final Condition available = lock.newCondition();

    /**
     * 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 {
            q.offer(e);
            if (q.peek() == e) {
                leader = null;
                available.signal();
            }
            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
                return q.poll();
        } 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)
                        return q.poll();
                    else if (leader != null)
                        available.await();
                    else {
                        Thread thisThread = Thread.currentThread();
                        leader = thisThread;
                        try {
                            available.awaitNanos(delay);
                        } finally {
                            if (leader == thisThread)
                                leader = null;
                        }
                    }
                }
            }
        } finally {
            if (leader == null && q.peek() != null)
                available.signal();
            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)
                        return q.poll();
                    if (nanos <= 0)
                        return null;
                    if (nanos < delay || leader != null)
                        nanos = available.awaitNanos(nanos);
                    else {
                        Thread thisThread = Thread.currentThread();
                        leader = thisThread;
                        try {
                            long timeLeft = available.awaitNanos(delay);
                            nanos -= delay - timeLeft;
                        } finally {
                            if (leader == thisThread)
                                leader = null;
                        }
                    }
                }
            }
        } finally {
            if (leader == null && q.peek() != null)
                available.signal();
            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;
            }
            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;
            }
            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
     * <tt>Iterator</tt> is a "weakly consistent" iterator that will
     * never throw {@link ConcurrentModificationException}, and
     * guarantees to traverse elements as they existed upon
     * construction of the iterator, and may (but is not guaranteed
     * to) reflect any modifications subsequent to construction.
     *
     * @return an iterator over the elements in this queue
     */
    public Iterator<E> iterator() {
        return new Itr(toArray());
    }

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

        @SuppressWarnings("unchecked")
        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:	1.50
Committed:	Mon May 19 01:14:25 2008 UTC (16 years ago) by jsr166
Branch:	MAIN
Changes since 1.49:	+1 -0 lines
Log Message:	Sync with OpenJDK; 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.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. Even though unexpired elements cannot be
21	* removed using <tt>take</tt> or <tt>poll</tt>, they are otherwise
22	* treated as normal elements. For example, the <tt>size</tt> method
23	* returns the count of both expired and unexpired elements.
24	* This queue does not permit null elements.
25	*
26	* <p>This class and its iterator implement all of the
27	* <em>optional</em> methods of the {@link Collection} and {@link
28	* Iterator} interfaces.
29	*
30	* <p>This class is a member of the
31	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
32	* Java Collections Framework</a>.
33	*
34	* @since 1.5
35	* @author Doug Lea
36	* @param <E> the type of elements held in this collection
37	*/
38
39	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
40	implements BlockingQueue<E> {
41
42	private transient final ReentrantLock lock = new ReentrantLock();
43	private final PriorityQueue<E> q = new PriorityQueue<E>();
44
45	/**
46	* Thread designated to wait for the element at the head of
47	* the queue. This variant of the Leader-Follower pattern
48	* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
49	* minimize unnecessary timed waiting. When a thread becomes
50	* the leader, it waits only for the next delay to elapse, but
51	* other threads await indefinitely. The leader thread must
52	* signal some other thread before returning from take() or
53	* poll(...), unless some other thread becomes leader in the
54	* interim. Whenever the head of the queue is replaced with
55	* an element with an earlier expiration time, the leader
56	* field is invalidated by being reset to null, and some
57	* waiting thread, but not necessarily the current leader, is
58	* signalled. So waiting threads must be prepared to acquire
59	* and lose leadership while waiting.
60	*/
61	private Thread leader = null;
62
63	/**
64	* Condition signalled when a newer element becomes available
65	* at the head of the queue or a new thread may need to
66	* become leader.
67	*/
68	private final Condition available = lock.newCondition();
69
70	/**
71	* Creates a new <tt>DelayQueue</tt> that is initially empty.
72	*/
73	public DelayQueue() {}
74
75	/**
76	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
77	* given collection of {@link Delayed} instances.
78	*
79	* @param c the collection of elements to initially contain
80	* @throws NullPointerException if the specified collection or any
81	* of its elements are null
82	*/
83	public DelayQueue(Collection<? extends E> c) {
84	this.addAll(c);
85	}
86
87	/**
88	* Inserts the specified element into this delay queue.
89	*
90	* @param e the element to add
91	* @return <tt>true</tt> (as specified by {@link Collection#add})
92	* @throws NullPointerException if the specified element is null
93	*/
94	public boolean add(E e) {
95	return offer(e);
96	}
97
98	/**
99	* Inserts the specified element into this delay queue.
100	*
101	* @param e the element to add
102	* @return <tt>true</tt>
103	* @throws NullPointerException if the specified element is null
104	*/
105	public boolean offer(E e) {
106	final ReentrantLock lock = this.lock;
107	lock.lock();
108	try {
109	q.offer(e);
110	if (q.peek() == e) {
111	leader = null;
112	available.signal();
113	}
114	return true;
115	} finally {
116	lock.unlock();
117	}
118	}
119
120	/**
121	* Inserts the specified element into this delay queue. As the queue is
122	* unbounded this method will never block.
123	*
124	* @param e the element to add
125	* @throws NullPointerException {@inheritDoc}
126	*/
127	public void put(E e) {
128	offer(e);
129	}
130
131	/**
132	* Inserts the specified element into this delay queue. As the queue is
133	* unbounded this method will never block.
134	*
135	* @param e the element to add
136	* @param timeout This parameter is ignored as the method never blocks
137	* @param unit This parameter is ignored as the method never blocks
138	* @return <tt>true</tt>
139	* @throws NullPointerException {@inheritDoc}
140	*/
141	public boolean offer(E e, long timeout, TimeUnit unit) {
142	return offer(e);
143	}
144
145	/**
146	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
147	* if this queue has no elements with an expired delay.
148	*
149	* @return the head of this queue, or <tt>null</tt> if this
150	* queue has no elements with an expired delay
151	*/
152	public E poll() {
153	final ReentrantLock lock = this.lock;
154	lock.lock();
155	try {
156	E first = q.peek();
157	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
158	return null;
159	else
160	return q.poll();
161	} finally {
162	lock.unlock();
163	}
164	}
165
166	/**
167	* Retrieves and removes the head of this queue, waiting if necessary
168	* until an element with an expired delay is available on this queue.
169	*
170	* @return the head of this queue
171	* @throws InterruptedException {@inheritDoc}
172	*/
173	public E take() throws InterruptedException {
174	final ReentrantLock lock = this.lock;
175	lock.lockInterruptibly();
176	try {
177	for (;;) {
178	E first = q.peek();
179	if (first == null)
180	available.await();
181	else {
182	long delay = first.getDelay(TimeUnit.NANOSECONDS);
183	if (delay <= 0)
184	return q.poll();
185	else if (leader != null)
186	available.await();
187	else {
188	Thread thisThread = Thread.currentThread();
189	leader = thisThread;
190	try {
191	available.awaitNanos(delay);
192	} finally {
193	if (leader == thisThread)
194	leader = null;
195	}
196	}
197	}
198	}
199	} finally {
200	if (leader == null && q.peek() != null)
201	available.signal();
202	lock.unlock();
203	}
204	}
205
206	/**
207	* Retrieves and removes the head of this queue, waiting if necessary
208	* until an element with an expired delay is available on this queue,
209	* or the specified wait time expires.
210	*
211	* @return the head of this queue, or <tt>null</tt> if the
212	* specified waiting time elapses before an element with
213	* an expired delay becomes available
214	* @throws InterruptedException {@inheritDoc}
215	*/
216	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
217	long nanos = unit.toNanos(timeout);
218	final ReentrantLock lock = this.lock;
219	lock.lockInterruptibly();
220	try {
221	for (;;) {
222	E first = q.peek();
223	if (first == null) {
224	if (nanos <= 0)
225	return null;
226	else
227	nanos = available.awaitNanos(nanos);
228	} else {
229	long delay = first.getDelay(TimeUnit.NANOSECONDS);
230	if (delay <= 0)
231	return q.poll();
232	if (nanos <= 0)
233	return null;
234	if (nanos < delay \|\| leader != null)
235	nanos = available.awaitNanos(nanos);
236	else {
237	Thread thisThread = Thread.currentThread();
238	leader = thisThread;
239	try {
240	long timeLeft = available.awaitNanos(delay);
241	nanos -= delay - timeLeft;
242	} finally {
243	if (leader == thisThread)
244	leader = null;
245	}
246	}
247	}
248	}
249	} finally {
250	if (leader == null && q.peek() != null)
251	available.signal();
252	lock.unlock();
253	}
254	}
255
256	/**
257	* Retrieves, but does not remove, the head of this queue, or
258	* returns <tt>null</tt> if this queue is empty. Unlike
259	* <tt>poll</tt>, if no expired elements are available in the queue,
260	* this method returns the element that will expire next,
261	* if one exists.
262	*
263	* @return the head of this queue, or <tt>null</tt> if this
264	* queue is empty.
265	*/
266	public E peek() {
267	final ReentrantLock lock = this.lock;
268	lock.lock();
269	try {
270	return q.peek();
271	} finally {
272	lock.unlock();
273	}
274	}
275
276	public int size() {
277	final ReentrantLock lock = this.lock;
278	lock.lock();
279	try {
280	return q.size();
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) {
293	if (c == null)
294	throw new NullPointerException();
295	if (c == this)
296	throw new IllegalArgumentException();
297	final ReentrantLock lock = this.lock;
298	lock.lock();
299	try {
300	int n = 0;
301	for (;;) {
302	E first = q.peek();
303	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
304	break;
305	c.add(q.poll());
306	++n;
307	}
308	return n;
309	} finally {
310	lock.unlock();
311	}
312	}
313
314	/**
315	* @throws UnsupportedOperationException {@inheritDoc}
316	* @throws ClassCastException {@inheritDoc}
317	* @throws NullPointerException {@inheritDoc}
318	* @throws IllegalArgumentException {@inheritDoc}
319	*/
320	public int drainTo(Collection<? super E> c, int maxElements) {
321	if (c == null)
322	throw new NullPointerException();
323	if (c == this)
324	throw new IllegalArgumentException();
325	if (maxElements <= 0)
326	return 0;
327	final ReentrantLock lock = this.lock;
328	lock.lock();
329	try {
330	int n = 0;
331	while (n < maxElements) {
332	E first = q.peek();
333	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
334	break;
335	c.add(q.poll());
336	++n;
337	}
338	return n;
339	} finally {
340	lock.unlock();
341	}
342	}
343
344	/**
345	* Atomically removes all of the elements from this delay queue.
346	* The queue will be empty after this call returns.
347	* Elements with an unexpired delay are not waited for; they are
348	* simply discarded from the queue.
349	*/
350	public void clear() {
351	final ReentrantLock lock = this.lock;
352	lock.lock();
353	try {
354	q.clear();
355	} finally {
356	lock.unlock();
357	}
358	}
359
360	/**
361	* Always returns <tt>Integer.MAX_VALUE</tt> because
362	* a <tt>DelayQueue</tt> is not capacity constrained.
363	*
364	* @return <tt>Integer.MAX_VALUE</tt>
365	*/
366	public int remainingCapacity() {
367	return Integer.MAX_VALUE;
368	}
369
370	/**
371	* Returns an array containing all of the elements in this queue.
372	* The returned array elements are in no particular order.
373	*
374	* <p>The returned array will be "safe" in that no references to it are
375	* maintained by this queue. (In other words, this method must allocate
376	* a new array). The caller is thus free to modify the returned array.
377	*
378	* <p>This method acts as bridge between array-based and collection-based
379	* APIs.
380	*
381	* @return an array containing all of the elements in this queue
382	*/
383	public Object[] toArray() {
384	final ReentrantLock lock = this.lock;
385	lock.lock();
386	try {
387	return q.toArray();
388	} finally {
389	lock.unlock();
390	}
391	}
392
393	/**
394	* Returns an array containing all of the elements in this queue; the
395	* runtime type of the returned array is that of the specified array.
396	* The returned array elements are in no particular order.
397	* If the queue fits in the specified array, it is returned therein.
398	* Otherwise, a new array is allocated with the runtime type of the
399	* specified array and the size of this queue.
400	*
401	* <p>If this queue fits in the specified array with room to spare
402	* (i.e., the array has more elements than this queue), the element in
403	* the array immediately following the end of the queue is set to
404	* <tt>null</tt>.
405	*
406	* <p>Like the {@link #toArray()} method, this method acts as bridge between
407	* array-based and collection-based APIs. Further, this method allows
408	* precise control over the runtime type of the output array, and may,
409	* under certain circumstances, be used to save allocation costs.
410	*
411	* <p>The following code can be used to dump a delay queue into a newly
412	* allocated array of <tt>Delayed</tt>:
413	*
414	* <pre>
415	* Delayed[] a = q.toArray(new Delayed[0]);</pre>
416	*
417	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
418	* <tt>toArray()</tt>.
419	*
420	* @param a the array into which the elements of the queue are to
421	* be stored, if it is big enough; otherwise, a new array of the
422	* same runtime type is allocated for this purpose
423	* @return an array containing all of the elements in this queue
424	* @throws ArrayStoreException if the runtime type of the specified array
425	* is not a supertype of the runtime type of every element in
426	* this queue
427	* @throws NullPointerException if the specified array is null
428	*/
429	public <T> T[] toArray(T[] a) {
430	final ReentrantLock lock = this.lock;
431	lock.lock();
432	try {
433	return q.toArray(a);
434	} finally {
435	lock.unlock();
436	}
437	}
438
439	/**
440	* Removes a single instance of the specified element from this
441	* queue, if it is present, whether or not it has expired.
442	*/
443	public boolean remove(Object o) {
444	final ReentrantLock lock = this.lock;
445	lock.lock();
446	try {
447	return q.remove(o);
448	} finally {
449	lock.unlock();
450	}
451	}
452
453	/**
454	* Returns an iterator over all the elements (both expired and
455	* unexpired) in this queue. The iterator does not return the
456	* elements in any particular order. The returned
457	* <tt>Iterator</tt> is a "weakly consistent" iterator that will
458	* never throw {@link ConcurrentModificationException}, and
459	* guarantees to traverse elements as they existed upon
460	* construction of the iterator, and may (but is not guaranteed
461	* to) reflect any modifications subsequent to construction.
462	*
463	* @return an iterator over the elements in this queue
464	*/
465	public Iterator<E> iterator() {
466	return new Itr(toArray());
467	}
468
469	/**
470	* Snapshot iterator that works off copy of underlying q array.
471	*/
472	private class Itr implements Iterator<E> {
473	final Object[] array; // Array of all elements
474	int cursor; // index of next element to return;
475	int lastRet; // index of last element, or -1 if no such
476
477	Itr(Object[] array) {
478	lastRet = -1;
479	this.array = array;
480	}
481
482	public boolean hasNext() {
483	return cursor < array.length;
484	}
485
486	@SuppressWarnings("unchecked")
487	public E next() {
488	if (cursor >= array.length)
489	throw new NoSuchElementException();
490	lastRet = cursor;
491	return (E)array[cursor++];
492	}
493
494	public void remove() {
495	if (lastRet < 0)
496	throw new IllegalStateException();
497	Object x = array[lastRet];
498	lastRet = -1;
499	// Traverse underlying queue to find == element,
500	// not just a .equals element.
501	lock.lock();
502	try {
503	for (Iterator it = q.iterator(); it.hasNext(); ) {
504	if (it.next() == x) {
505	it.remove();
506	return;
507	}
508	}
509	} finally {
510	lock.unlock();
511	}
512	}
513	}
514
515	}