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/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import static java.util.concurrent.TimeUnit.NANOSECONDS;

import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.PriorityQueue;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

/**
 * An unbounded {@linkplain BlockingQueue blocking queue} of
 * {@code Delayed} elements, in which an element can only be taken
 * when its delay has expired.  The <em>head</em> of the queue is that
 * {@code Delayed} element whose delay expired furthest in the
 * past.  If no delay has expired there is no head and {@code poll}
 * will return {@code null}. Expiration occurs when an element's
 * {@code getDelay(TimeUnit.NANOSECONDS)} method returns a value less
 * than or equal to zero.  Even though unexpired elements cannot be
 * removed using {@code take} or {@code poll}, they are otherwise
 * treated as normal elements. For example, the {@code size} 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.  The Iterator provided in method {@link
 * #iterator()} is <em>not</em> guaranteed to traverse the elements of
 * the DelayQueue in any particular order.
 *
 * <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 queue
 */
public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
    implements BlockingQueue<E> {

    private final transient 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;

    /**
     * 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 {@code DelayQueue} that is initially empty.
     */
    public DelayQueue() {}

    /**
     * Creates a {@code DelayQueue} 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 {@code true} (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 {@code true}
     * @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 {@code true}
     * @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 {@code null}
     * if this queue has no elements with an expired delay.
     *
     * @return the head of this queue, or {@code null} 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();
            return (first == null || first.getDelay(NANOSECONDS) > 0)
                ? null
                : 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(NANOSECONDS);
                    if (delay <= 0L)
                        return q.poll();
                    first = null; // don't retain ref while waiting
                    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 {@code null} 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 <= 0L)
                        return null;
                    else
                        nanos = available.awaitNanos(nanos);
                } else {
                    long delay = first.getDelay(NANOSECONDS);
                    if (delay <= 0L)
                        return q.poll();
                    if (nanos <= 0L)
                        return null;
                    first = null; // don't retain ref while waiting
                    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 {@code null} if this queue is empty.  Unlike
     * {@code poll}, 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 {@code null} 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();
        }
    }

    /**
     * Returns first element only if it is expired.
     * Used only by drainTo.  Call only when holding lock.
     */
    private E peekExpired() {
        // assert lock.isHeldByCurrentThread();
        E first = q.peek();
        return (first == null || first.getDelay(NANOSECONDS) > 0) ?
            null : first;
    }

    /**
     * @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 e; (e = peekExpired()) != null;) {
                c.add(e);       // In this order, in case add() throws.
                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;
            for (E e; n < maxElements && (e = peekExpired()) != null;) {
                c.add(e);       // In this order, in case add() throws.
                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 {@code Integer.MAX_VALUE} because
     * a {@code DelayQueue} is not capacity constrained.
     *
     * @return {@code Integer.MAX_VALUE}
     */
    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
     * {@code null}.
     *
     * <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 {@code Delayed}:
     *
     * <pre> {@code Delayed[] a = q.toArray(new Delayed[0]);}</pre>
     *
     * Note that {@code toArray(new Object[0])} is identical in function to
     * {@code toArray()}.
     *
     * @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();
        }
    }

    /**
     * Identity-based version for use in Itr.remove.
     */
    void removeEQ(Object o) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
                if (o == it.next()) {
                    it.remove();
                    break;
                }
            }
        } 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.
     *
     * <p>The returned iterator is
     * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
     *
     * @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();
            removeEQ(array[lastRet]);
            lastRet = -1;
        }
    }

}
Revision:	1.1
Committed:	Sat Mar 26 06:22:50 2016 UTC (8 years, 1 month ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	fork jdk8 maintenance branch for source and jtreg tests
#	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/publicdomain/zero/1.0/
5	*/
6
7	package java.util.concurrent;
8
9	import static java.util.concurrent.TimeUnit.NANOSECONDS;
10
11	import java.util.AbstractQueue;
12	import java.util.Collection;
13	import java.util.Iterator;
14	import java.util.NoSuchElementException;
15	import java.util.PriorityQueue;
16	import java.util.concurrent.locks.Condition;
17	import java.util.concurrent.locks.ReentrantLock;
18
19	/**
20	* An unbounded {@linkplain BlockingQueue blocking queue} of
21	* {@code Delayed} elements, in which an element can only be taken
22	* when its delay has expired. The <em>head</em> of the queue is that
23	* {@code Delayed} element whose delay expired furthest in the
24	* past. If no delay has expired there is no head and {@code poll}
25	* will return {@code null}. Expiration occurs when an element's
26	* {@code getDelay(TimeUnit.NANOSECONDS)} method returns a value less
27	* than or equal to zero. Even though unexpired elements cannot be
28	* removed using {@code take} or {@code poll}, they are otherwise
29	* treated as normal elements. For example, the {@code size} method
30	* returns the count of both expired and unexpired elements.
31	* This queue does not permit null elements.
32	*
33	* <p>This class and its iterator implement all of the
34	* <em>optional</em> methods of the {@link Collection} and {@link
35	* Iterator} interfaces. The Iterator provided in method {@link
36	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
37	* the DelayQueue in any particular order.
38	*
39	* <p>This class is a member of the
40	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
41	* Java Collections Framework</a>.
42	*
43	* @since 1.5
44	* @author Doug Lea
45	* @param <E> the type of elements held in this queue
46	*/
47	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
48	implements BlockingQueue<E> {
49
50	private final transient ReentrantLock lock = new ReentrantLock();
51	private final PriorityQueue<E> q = new PriorityQueue<E>();
52
53	/**
54	* Thread designated to wait for the element at the head of
55	* the queue. This variant of the Leader-Follower pattern
56	* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
57	* minimize unnecessary timed waiting. When a thread becomes
58	* the leader, it waits only for the next delay to elapse, but
59	* other threads await indefinitely. The leader thread must
60	* signal some other thread before returning from take() or
61	* poll(...), unless some other thread becomes leader in the
62	* interim. Whenever the head of the queue is replaced with
63	* an element with an earlier expiration time, the leader
64	* field is invalidated by being reset to null, and some
65	* waiting thread, but not necessarily the current leader, is
66	* signalled. So waiting threads must be prepared to acquire
67	* and lose leadership while waiting.
68	*/
69	private Thread leader;
70
71	/**
72	* Condition signalled when a newer element becomes available
73	* at the head of the queue or a new thread may need to
74	* become leader.
75	*/
76	private final Condition available = lock.newCondition();
77
78	/**
79	* Creates a new {@code DelayQueue} that is initially empty.
80	*/
81	public DelayQueue() {}
82
83	/**
84	* Creates a {@code DelayQueue} initially containing the elements of the
85	* given collection of {@link Delayed} instances.
86	*
87	* @param c the collection of elements to initially contain
88	* @throws NullPointerException if the specified collection or any
89	* of its elements are null
90	*/
91	public DelayQueue(Collection<? extends E> c) {
92	this.addAll(c);
93	}
94
95	/**
96	* Inserts the specified element into this delay queue.
97	*
98	* @param e the element to add
99	* @return {@code true} (as specified by {@link Collection#add})
100	* @throws NullPointerException if the specified element is null
101	*/
102	public boolean add(E e) {
103	return offer(e);
104	}
105
106	/**
107	* Inserts the specified element into this delay queue.
108	*
109	* @param e the element to add
110	* @return {@code true}
111	* @throws NullPointerException if the specified element is null
112	*/
113	public boolean offer(E e) {
114	final ReentrantLock lock = this.lock;
115	lock.lock();
116	try {
117	q.offer(e);
118	if (q.peek() == e) {
119	leader = null;
120	available.signal();
121	}
122	return true;
123	} finally {
124	lock.unlock();
125	}
126	}
127
128	/**
129	* Inserts the specified element into this delay queue. As the queue is
130	* unbounded this method will never block.
131	*
132	* @param e the element to add
133	* @throws NullPointerException {@inheritDoc}
134	*/
135	public void put(E e) {
136	offer(e);
137	}
138
139	/**
140	* Inserts the specified element into this delay queue. As the queue is
141	* unbounded this method will never block.
142	*
143	* @param e the element to add
144	* @param timeout This parameter is ignored as the method never blocks
145	* @param unit This parameter is ignored as the method never blocks
146	* @return {@code true}
147	* @throws NullPointerException {@inheritDoc}
148	*/
149	public boolean offer(E e, long timeout, TimeUnit unit) {
150	return offer(e);
151	}
152
153	/**
154	* Retrieves and removes the head of this queue, or returns {@code null}
155	* if this queue has no elements with an expired delay.
156	*
157	* @return the head of this queue, or {@code null} if this
158	* queue has no elements with an expired delay
159	*/
160	public E poll() {
161	final ReentrantLock lock = this.lock;
162	lock.lock();
163	try {
164	E first = q.peek();
165	return (first == null \|\| first.getDelay(NANOSECONDS) > 0)
166	? null
167	: q.poll();
168	} finally {
169	lock.unlock();
170	}
171	}
172
173	/**
174	* Retrieves and removes the head of this queue, waiting if necessary
175	* until an element with an expired delay is available on this queue.
176	*
177	* @return the head of this queue
178	* @throws InterruptedException {@inheritDoc}
179	*/
180	public E take() throws InterruptedException {
181	final ReentrantLock lock = this.lock;
182	lock.lockInterruptibly();
183	try {
184	for (;;) {
185	E first = q.peek();
186	if (first == null)
187	available.await();
188	else {
189	long delay = first.getDelay(NANOSECONDS);
190	if (delay <= 0L)
191	return q.poll();
192	first = null; // don't retain ref while waiting
193	if (leader != null)
194	available.await();
195	else {
196	Thread thisThread = Thread.currentThread();
197	leader = thisThread;
198	try {
199	available.awaitNanos(delay);
200	} finally {
201	if (leader == thisThread)
202	leader = null;
203	}
204	}
205	}
206	}
207	} finally {
208	if (leader == null && q.peek() != null)
209	available.signal();
210	lock.unlock();
211	}
212	}
213
214	/**
215	* Retrieves and removes the head of this queue, waiting if necessary
216	* until an element with an expired delay is available on this queue,
217	* or the specified wait time expires.
218	*
219	* @return the head of this queue, or {@code null} if the
220	* specified waiting time elapses before an element with
221	* an expired delay becomes available
222	* @throws InterruptedException {@inheritDoc}
223	*/
224	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
225	long nanos = unit.toNanos(timeout);
226	final ReentrantLock lock = this.lock;
227	lock.lockInterruptibly();
228	try {
229	for (;;) {
230	E first = q.peek();
231	if (first == null) {
232	if (nanos <= 0L)
233	return null;
234	else
235	nanos = available.awaitNanos(nanos);
236	} else {
237	long delay = first.getDelay(NANOSECONDS);
238	if (delay <= 0L)
239	return q.poll();
240	if (nanos <= 0L)
241	return null;
242	first = null; // don't retain ref while waiting
243	if (nanos < delay \|\| leader != null)
244	nanos = available.awaitNanos(nanos);
245	else {
246	Thread thisThread = Thread.currentThread();
247	leader = thisThread;
248	try {
249	long timeLeft = available.awaitNanos(delay);
250	nanos -= delay - timeLeft;
251	} finally {
252	if (leader == thisThread)
253	leader = null;
254	}
255	}
256	}
257	}
258	} finally {
259	if (leader == null && q.peek() != null)
260	available.signal();
261	lock.unlock();
262	}
263	}
264
265	/**
266	* Retrieves, but does not remove, the head of this queue, or
267	* returns {@code null} if this queue is empty. Unlike
268	* {@code poll}, if no expired elements are available in the queue,
269	* this method returns the element that will expire next,
270	* if one exists.
271	*
272	* @return the head of this queue, or {@code null} if this
273	* queue is empty
274	*/
275	public E peek() {
276	final ReentrantLock lock = this.lock;
277	lock.lock();
278	try {
279	return q.peek();
280	} finally {
281	lock.unlock();
282	}
283	}
284
285	public int size() {
286	final ReentrantLock lock = this.lock;
287	lock.lock();
288	try {
289	return q.size();
290	} finally {
291	lock.unlock();
292	}
293	}
294
295	/**
296	* Returns first element only if it is expired.
297	* Used only by drainTo. Call only when holding lock.
298	*/
299	private E peekExpired() {
300	// assert lock.isHeldByCurrentThread();
301	E first = q.peek();
302	return (first == null \|\| first.getDelay(NANOSECONDS) > 0) ?
303	null : first;
304	}
305
306	/**
307	* @throws UnsupportedOperationException {@inheritDoc}
308	* @throws ClassCastException {@inheritDoc}
309	* @throws NullPointerException {@inheritDoc}
310	* @throws IllegalArgumentException {@inheritDoc}
311	*/
312	public int drainTo(Collection<? super E> c) {
313	if (c == null)
314	throw new NullPointerException();
315	if (c == this)
316	throw new IllegalArgumentException();
317	final ReentrantLock lock = this.lock;
318	lock.lock();
319	try {
320	int n = 0;
321	for (E e; (e = peekExpired()) != null;) {
322	c.add(e); // In this order, in case add() throws.
323	q.poll();
324	++n;
325	}
326	return n;
327	} finally {
328	lock.unlock();
329	}
330	}
331
332	/**
333	* @throws UnsupportedOperationException {@inheritDoc}
334	* @throws ClassCastException {@inheritDoc}
335	* @throws NullPointerException {@inheritDoc}
336	* @throws IllegalArgumentException {@inheritDoc}
337	*/
338	public int drainTo(Collection<? super E> c, int maxElements) {
339	if (c == null)
340	throw new NullPointerException();
341	if (c == this)
342	throw new IllegalArgumentException();
343	if (maxElements <= 0)
344	return 0;
345	final ReentrantLock lock = this.lock;
346	lock.lock();
347	try {
348	int n = 0;
349	for (E e; n < maxElements && (e = peekExpired()) != null;) {
350	c.add(e); // In this order, in case add() throws.
351	q.poll();
352	++n;
353	}
354	return n;
355	} finally {
356	lock.unlock();
357	}
358	}
359
360	/**
361	* Atomically removes all of the elements from this delay queue.
362	* The queue will be empty after this call returns.
363	* Elements with an unexpired delay are not waited for; they are
364	* simply discarded from the queue.
365	*/
366	public void clear() {
367	final ReentrantLock lock = this.lock;
368	lock.lock();
369	try {
370	q.clear();
371	} finally {
372	lock.unlock();
373	}
374	}
375
376	/**
377	* Always returns {@code Integer.MAX_VALUE} because
378	* a {@code DelayQueue} is not capacity constrained.
379	*
380	* @return {@code Integer.MAX_VALUE}
381	*/
382	public int remainingCapacity() {
383	return Integer.MAX_VALUE;
384	}
385
386	/**
387	* Returns an array containing all of the elements in this queue.
388	* The returned array elements are in no particular order.
389	*
390	* <p>The returned array will be "safe" in that no references to it are
391	* maintained by this queue. (In other words, this method must allocate
392	* a new array). The caller is thus free to modify the returned array.
393	*
394	* <p>This method acts as bridge between array-based and collection-based
395	* APIs.
396	*
397	* @return an array containing all of the elements in this queue
398	*/
399	public Object[] toArray() {
400	final ReentrantLock lock = this.lock;
401	lock.lock();
402	try {
403	return q.toArray();
404	} finally {
405	lock.unlock();
406	}
407	}
408
409	/**
410	* Returns an array containing all of the elements in this queue; the
411	* runtime type of the returned array is that of the specified array.
412	* The returned array elements are in no particular order.
413	* If the queue fits in the specified array, it is returned therein.
414	* Otherwise, a new array is allocated with the runtime type of the
415	* specified array and the size of this queue.
416	*
417	* <p>If this queue fits in the specified array with room to spare
418	* (i.e., the array has more elements than this queue), the element in
419	* the array immediately following the end of the queue is set to
420	* {@code null}.
421	*
422	* <p>Like the {@link #toArray()} method, this method acts as bridge between
423	* array-based and collection-based APIs. Further, this method allows
424	* precise control over the runtime type of the output array, and may,
425	* under certain circumstances, be used to save allocation costs.
426	*
427	* <p>The following code can be used to dump a delay queue into a newly
428	* allocated array of {@code Delayed}:
429	*
430	* <pre> {@code Delayed[] a = q.toArray(new Delayed[0]);}</pre>
431	*
432	* Note that {@code toArray(new Object[0])} is identical in function to
433	* {@code toArray()}.
434	*
435	* @param a the array into which the elements of the queue are to
436	* be stored, if it is big enough; otherwise, a new array of the
437	* same runtime type is allocated for this purpose
438	* @return an array containing all of the elements in this queue
439	* @throws ArrayStoreException if the runtime type of the specified array
440	* is not a supertype of the runtime type of every element in
441	* this queue
442	* @throws NullPointerException if the specified array is null
443	*/
444	public <T> T[] toArray(T[] a) {
445	final ReentrantLock lock = this.lock;
446	lock.lock();
447	try {
448	return q.toArray(a);
449	} finally {
450	lock.unlock();
451	}
452	}
453
454	/**
455	* Removes a single instance of the specified element from this
456	* queue, if it is present, whether or not it has expired.
457	*/
458	public boolean remove(Object o) {
459	final ReentrantLock lock = this.lock;
460	lock.lock();
461	try {
462	return q.remove(o);
463	} finally {
464	lock.unlock();
465	}
466	}
467
468	/**
469	* Identity-based version for use in Itr.remove.
470	*/
471	void removeEQ(Object o) {
472	final ReentrantLock lock = this.lock;
473	lock.lock();
474	try {
475	for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
476	if (o == it.next()) {
477	it.remove();
478	break;
479	}
480	}
481	} finally {
482	lock.unlock();
483	}
484	}
485
486	/**
487	* Returns an iterator over all the elements (both expired and
488	* unexpired) in this queue. The iterator does not return the
489	* elements in any particular order.
490	*
491	* <p>The returned iterator is
492	* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
493	*
494	* @return an iterator over the elements in this queue
495	*/
496	public Iterator<E> iterator() {
497	return new Itr(toArray());
498	}
499
500	/**
501	* Snapshot iterator that works off copy of underlying q array.
502	*/
503	private class Itr implements Iterator<E> {
504	final Object[] array; // Array of all elements
505	int cursor; // index of next element to return
506	int lastRet; // index of last element, or -1 if no such
507
508	Itr(Object[] array) {
509	lastRet = -1;
510	this.array = array;
511	}
512
513	public boolean hasNext() {
514	return cursor < array.length;
515	}
516
517	@SuppressWarnings("unchecked")
518	public E next() {
519	if (cursor >= array.length)
520	throw new NoSuchElementException();
521	lastRet = cursor;
522	return (E)array[cursor++];
523	}
524
525	public void remove() {
526	if (lastRet < 0)
527	throw new IllegalStateException();
528	removeEQ(array[lastRet]);
529	lastRet = -1;
530	}
531	}
532
533	}