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 transient final Condition available = lock.newCondition();
    private final PriorityQueue<E> q = new PriorityQueue<E>();

    /**
     * Creates a new <tt>DelayQueue</tt> that is initially empty.
     */
    public DelayQueue() {}

    /**
     * Creates a <tt>DelayQueue</tt> initially containing the elements of the
     * given collection of {@link Delayed} instances.
     *
     * @param c the collection of elements to initially contain
     * @throws NullPointerException if the specified collection or any
     *         of its elements are null
     */
    public DelayQueue(Collection<? extends E> c) {
        this.addAll(c);
    }

    /**
     * Inserts the specified element into this delay queue.
     *
     * @param e the element to add
     * @return <tt>true</tt> (as specified by {@link Collection#add})
     * @throws NullPointerException if the specified element is null
     */
    public boolean add(E e) {
        return offer(e);
    }

    /**
     * Inserts the specified element into this delay queue.
     *
     * @param e the element to add
     * @return <tt>true</tt>
     * @throws NullPointerException if the specified element is null
     */
    public boolean offer(E e) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            E first = q.peek();
            q.offer(e);
            if (first == null || e.compareTo(first) < 0)
                available.signalAll();
            return true;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Inserts the specified element into this delay queue. As the queue is
     * unbounded this method will never block.
     *
     * @param e the element to add
     * @throws NullPointerException {@inheritDoc}
     */
    public void put(E e) {
        offer(e);
    }

    /**
     * Inserts the specified element into this delay queue. As the queue is
     * unbounded this method will never block.
     *
     * @param e the element to add
     * @param timeout This parameter is ignored as the method never blocks
     * @param unit This parameter is ignored as the method never blocks
     * @return <tt>true</tt>
     * @throws NullPointerException {@inheritDoc}
     */
    public boolean offer(E e, long timeout, TimeUnit unit) {
        return offer(e);
    }

    /**
     * Retrieves and removes the head of this queue, or returns <tt>null</tt>
     * if this queue has no elements with an expired delay.
     *
     * @return the head of this queue, or <tt>null</tt> if this
     *         queue has no elements with an expired delay
     */
    public E poll() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            E first = q.peek();
            if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0)
                return null;
            else {
                E x = q.poll();
                assert x != null;
                if (q.size() != 0)
                    available.signalAll();
                return x;
            }
        } finally {
            lock.unlock();
        }
    }

    /**
     * Retrieves and removes the head of this queue, waiting if necessary
     * until an element with an expired delay is available on this queue.
     *
     * @return the head of this queue
     * @throws InterruptedException {@inheritDoc}
     */
    public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            for (;;) {
                E first = q.peek();
                if (first == null) {
                    available.await();
                } else {
                    long delay =  first.getDelay(TimeUnit.NANOSECONDS);
                    if (delay > 0) {
                        long tl = available.awaitNanos(delay);
                    } else {
                        E x = q.poll();
                        assert x != null;
                        if (q.size() != 0)
                            available.signalAll(); // wake up other takers
                        return x;

                    }
                }
            }
        } finally {
            lock.unlock();
        }
    }

    /**
     * Retrieves and removes the head of this queue, waiting if necessary
     * until an element with an expired delay is available on this queue,
     * or the specified wait time expires.
     *
     * @return the head of this queue, or <tt>null</tt> if the
     *         specified waiting time elapses before an element with
     *         an expired delay becomes available
     * @throws InterruptedException {@inheritDoc}
     */
    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
        long nanos = unit.toNanos(timeout);
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            for (;;) {
                E first = q.peek();
                if (first == null) {
                    if (nanos <= 0)
                        return null;
                    else
                        nanos = available.awaitNanos(nanos);
                } else {
                    long delay = first.getDelay(TimeUnit.NANOSECONDS);
                    if (delay > 0) {
                        if (nanos <= 0)
                            return null;
                        if (delay > nanos)
                            delay = nanos;
                        long timeLeft = available.awaitNanos(delay);
                        nanos -= delay - timeLeft;
                    } else {
                        E x = q.poll();
                        assert x != null;
                        if (q.size() != 0)
                            available.signalAll();
                        return x;
                    }
                }
            }
        } finally {
            lock.unlock();
        }
    }

    /**
     * Retrieves, but does not remove, the head of this queue, or
     * returns <tt>null</tt> if this queue is empty.  Unlike
     * <tt>poll</tt>, if no expired elements are available in the queue,
     * this method returns the element that will expire next,
     * if one exists.
     *
     * @return the head of this queue, or <tt>null</tt> if this
     *         queue is empty.
     */
    public E peek() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.peek();
        } finally {
            lock.unlock();
        }
    }

    public int size() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.size();
        } finally {
            lock.unlock();
        }
    }

    /**
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    public int drainTo(Collection<? super E> c) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            int n = 0;
            for (;;) {
                E first = q.peek();
                if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0)
                    break;
                c.add(q.poll());
                ++n;
            }
            if (n > 0)
                available.signalAll();
            return n;
        } finally {
            lock.unlock();
        }
    }

    /**
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    public int drainTo(Collection<? super E> c, int maxElements) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        if (maxElements <= 0)
            return 0;
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            int n = 0;
            while (n < maxElements) {
                E first = q.peek();
                if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0)
                    break;
                c.add(q.poll());
                ++n;
            }
            if (n > 0)
                available.signalAll();
            return n;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Atomically removes all of the elements from this delay queue.
     * The queue will be empty after this call returns.
     * Elements with an unexpired delay are not waited for; they are
     * simply discarded from the queue.
     */
    public void clear() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            q.clear();
        } finally {
            lock.unlock();
        }
    }

    /**
     * Always returns <tt>Integer.MAX_VALUE</tt> because
     * a <tt>DelayQueue</tt> is not capacity constrained.
     *
     * @return <tt>Integer.MAX_VALUE</tt>
     */
    public int remainingCapacity() {
        return Integer.MAX_VALUE;
    }

    /**
     * Returns an array containing all of the elements in this queue.
     * The returned array elements are in no particular order.
     *
     * <p>The returned array will be "safe" in that no references to it are
     * maintained by this queue.  (In other words, this method must allocate
     * a new array).  The caller is thus free to modify the returned array.
     *
     * <p>This method acts as bridge between array-based and collection-based
     * APIs.
     *
     * @return an array containing all of the elements in this queue
     */
    public Object[] toArray() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.toArray();
        } finally {
            lock.unlock();
        }
    }

    /**
     * Returns an array containing all of the elements in this queue; the
     * runtime type of the returned array is that of the specified array.
     * The returned array elements are in no particular order.
     * If the queue fits in the specified array, it is returned therein.
     * Otherwise, a new array is allocated with the runtime type of the
     * specified array and the size of this queue.
     *
     * <p>If this queue fits in the specified array with room to spare
     * (i.e., the array has more elements than this queue), the element in
     * the array immediately following the end of the queue is set to
     * <tt>null</tt>.
     *
     * <p>Like the {@link #toArray()} method, this method acts as bridge between
     * array-based and collection-based APIs.  Further, this method allows
     * precise control over the runtime type of the output array, and may,
     * under certain circumstances, be used to save allocation costs.
     *
     * <p>The following code can be used to dump a delay queue into a newly
     * allocated array of <tt>Delayed</tt>:
     *
     * <pre>
     *     Delayed[] a = q.toArray(new Delayed[0]);</pre>
     *
     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
     * <tt>toArray()</tt>.
     *
     * @param a the array into which the elements of the queue are to
     *          be stored, if it is big enough; otherwise, a new array of the
     *          same runtime type is allocated for this purpose
     * @return an array containing all of the elements in this queue
     * @throws ArrayStoreException if the runtime type of the specified array
     *         is not a supertype of the runtime type of every element in
     *         this queue
     * @throws NullPointerException if the specified array is null
     */
    public <T> T[] toArray(T[] a) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.toArray(a);
        } finally {
            lock.unlock();
        }
    }

    /**
     * Removes a single instance of the specified element from this
     * queue, if it is present, whether or not it has expired.
     */
    public boolean remove(Object o) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.remove(o);
        } finally {
            lock.unlock();
        }
    }

    /**
     * Returns an iterator over all the elements (both expired and
     * unexpired) in this queue. The iterator does not return the
     * elements in any particular order.  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;
        }

        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:	1.47
Committed:	Wed Aug 8 16:08:40 2007 UTC (16 years, 10 months ago) by jsr166
Branch:	MAIN
Changes since 1.46:	+0 -1 lines
Log Message:	whitespace
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.23	* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/licenses/publicdomain
5	dl	1.2	*/
6
7	tim	1.1	package java.util.concurrent;
8	dl	1.5	import java.util.concurrent.locks.*;
9	tim	1.1	import java.util.*;
10
11			/**
12	dl	1.27	* An unbounded {@linkplain BlockingQueue blocking queue} of
13			* <tt>Delayed</tt> elements, in which an element can only be taken
14			* when its delay has expired. The <em>head</em> of the queue is that
15			* <tt>Delayed</tt> element whose delay expired furthest in the
16	jsr166	1.32	* past. If no delay has expired there is no head and <tt>poll</tt>
17	dl	1.27	* will return <tt>null</tt>. Expiration occurs when an element's
18			* <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less
19	dl	1.36	* than or equal to zero. Even though unexpired elements cannot be
20			* removed using <tt>take</tt> or <tt>poll</tt>, they are otherwise
21			* treated as normal elements. For example, the <tt>size</tt> method
22			* returns the count of both expired and unexpired elements.
23	jsr166	1.39	* This queue does not permit null elements.
24	dl	1.25	*
25	dl	1.26	* <p>This class and its iterator implement all of the
26			* <em>optional</em> methods of the {@link Collection} and {@link
27	jsr166	1.29	* Iterator} interfaces.
28	dl	1.26	*
29	dl	1.25	* <p>This class is a member of the
30	jsr166	1.46	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
31	dl	1.25	* Java Collections Framework</a>.
32			*
33	dl	1.4	* @since 1.5
34			* @author Doug Lea
35	dl	1.20	* @param <E> the type of elements held in this collection
36	dl	1.19	*/
37	tim	1.1
38	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
39			implements BlockingQueue<E> {
40	tim	1.6
41	dl	1.2	private transient final ReentrantLock lock = new ReentrantLock();
42	dl	1.22	private transient final Condition available = lock.newCondition();
43	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
44	tim	1.1
45	dl	1.4	/**
46	dholmes	1.7	* Creates a new <tt>DelayQueue</tt> that is initially empty.
47	dl	1.4	*/
48	tim	1.1	public DelayQueue() {}
49
50	tim	1.6	/**
51	tim	1.9	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
52	dholmes	1.7	* given collection of {@link Delayed} instances.
53			*
54	jsr166	1.32	* @param c the collection of elements to initially contain
55			* @throws NullPointerException if the specified collection or any
56			* of its elements are null
57	tim	1.6	*/
58			public DelayQueue(Collection<? extends E> c) {
59			this.addAll(c);
60			}
61
62	dholmes	1.7	/**
63	dl	1.16	* Inserts the specified element into this delay queue.
64	dholmes	1.7	*
65	jsr166	1.30	* @param e the element to add
66	jsr166	1.38	* @return <tt>true</tt> (as specified by {@link Collection#add})
67	jsr166	1.32	* @throws NullPointerException if the specified element is null
68			*/
69			public boolean add(E e) {
70			return offer(e);
71			}
72
73			/**
74			* Inserts the specified element into this delay queue.
75			*
76			* @param e the element to add
77	dholmes	1.7	* @return <tt>true</tt>
78	jsr166	1.32	* @throws NullPointerException if the specified element is null
79	dholmes	1.7	*/
80	jsr166	1.30	public boolean offer(E e) {
81	dl	1.21	final ReentrantLock lock = this.lock;
82	dl	1.2	lock.lock();
83			try {
84	dl	1.3	E first = q.peek();
85	jsr166	1.30	q.offer(e);
86			if (first == null \|\| e.compareTo(first) < 0)
87	dl	1.4	available.signalAll();
88	dl	1.2	return true;
89	tim	1.13	} finally {
90	dl	1.2	lock.unlock();
91			}
92			}
93
94	dholmes	1.7	/**
95	jsr166	1.32	* Inserts the specified element into this delay queue. As the queue is
96	dholmes	1.7	* unbounded this method will never block.
97	jsr166	1.32	*
98	jsr166	1.30	* @param e the element to add
99	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
100	dholmes	1.7	*/
101	jsr166	1.30	public void put(E e) {
102			offer(e);
103	dl	1.2	}
104
105	dholmes	1.7	/**
106	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
107	dholmes	1.7	* unbounded this method will never block.
108	jsr166	1.32	*
109	jsr166	1.30	* @param e the element to add
110	dl	1.14	* @param timeout This parameter is ignored as the method never blocks
111	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
112			* @return <tt>true</tt>
113	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
114	dholmes	1.7	*/
115	jsr166	1.30	public boolean offer(E e, long timeout, TimeUnit unit) {
116			return offer(e);
117	dl	1.2	}
118
119	dholmes	1.7	/**
120	jsr166	1.32	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
121			* if this queue has no elements with an expired delay.
122	dholmes	1.7	*
123	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
124			* queue has no elements with an expired delay
125	dholmes	1.7	*/
126	jsr166	1.32	public E poll() {
127			final ReentrantLock lock = this.lock;
128			lock.lock();
129			try {
130			E first = q.peek();
131			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
132			return null;
133			else {
134			E x = q.poll();
135			assert x != null;
136			if (q.size() != 0)
137			available.signalAll();
138			return x;
139			}
140			} finally {
141			lock.unlock();
142			}
143	dl	1.2	}
144
145	dl	1.27	/**
146	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
147			* until an element with an expired delay is available on this queue.
148			*
149	dl	1.27	* @return the head of this queue
150	jsr166	1.32	* @throws InterruptedException {@inheritDoc}
151	dl	1.27	*/
152	dl	1.3	public E take() throws InterruptedException {
153	dl	1.21	final ReentrantLock lock = this.lock;
154	dl	1.2	lock.lockInterruptibly();
155			try {
156			for (;;) {
157	dl	1.3	E first = q.peek();
158	dl	1.12	if (first == null) {
159	dl	1.4	available.await();
160	tim	1.13	} else {
161	dl	1.2	long delay = first.getDelay(TimeUnit.NANOSECONDS);
162	dl	1.12	if (delay > 0) {
163			long tl = available.awaitNanos(delay);
164	tim	1.13	} else {
165	dl	1.3	E x = q.poll();
166	dl	1.2	assert x != null;
167			if (q.size() != 0)
168	dl	1.4	available.signalAll(); // wake up other takers
169	dl	1.2	return x;
170	tim	1.6
171	dl	1.2	}
172			}
173			}
174	tim	1.13	} finally {
175	dl	1.2	lock.unlock();
176			}
177			}
178
179	dl	1.27	/**
180	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
181			* until an element with an expired delay is available on this queue,
182			* or the specified wait time expires.
183			*
184	dl	1.27	* @return the head of this queue, or <tt>null</tt> if the
185	jsr166	1.32	* specified waiting time elapses before an element with
186			* an expired delay becomes available
187			* @throws InterruptedException {@inheritDoc}
188	dl	1.27	*/
189			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
190	jsr166	1.41	long nanos = unit.toNanos(timeout);
191	dl	1.21	final ReentrantLock lock = this.lock;
192	dl	1.2	lock.lockInterruptibly();
193			try {
194			for (;;) {
195	dl	1.3	E first = q.peek();
196	dl	1.2	if (first == null) {
197			if (nanos <= 0)
198			return null;
199			else
200	dl	1.4	nanos = available.awaitNanos(nanos);
201	tim	1.13	} else {
202	jsr166	1.41	long delay = first.getDelay(TimeUnit.NANOSECONDS);
203	dl	1.2	if (delay > 0) {
204	dl	1.40	if (nanos <= 0)
205			return null;
206	dl	1.2	if (delay > nanos)
207			delay = nanos;
208	dl	1.4	long timeLeft = available.awaitNanos(delay);
209	dl	1.2	nanos -= delay - timeLeft;
210	tim	1.13	} else {
211	dl	1.3	E x = q.poll();
212	dl	1.2	assert x != null;
213			if (q.size() != 0)
214	tim	1.6	available.signalAll();
215	dl	1.2	return x;
216			}
217			}
218			}
219	tim	1.13	} finally {
220	dl	1.2	lock.unlock();
221			}
222			}
223
224	dl	1.27	/**
225	dl	1.36	* Retrieves, but does not remove, the head of this queue, or
226			* returns <tt>null</tt> if this queue is empty. Unlike
227			* <tt>poll</tt>, if no expired elements are available in the queue,
228			* this method returns the element that will expire next,
229			* if one exists.
230	dl	1.27	*
231	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
232	dl	1.35	* queue is empty.
233	dl	1.27	*/
234	dl	1.3	public E peek() {
235	dl	1.21	final ReentrantLock lock = this.lock;
236	dl	1.2	lock.lock();
237			try {
238			return q.peek();
239	tim	1.13	} finally {
240	dl	1.2	lock.unlock();
241			}
242	tim	1.1	}
243
244	dl	1.2	public int size() {
245	dl	1.21	final ReentrantLock lock = this.lock;
246	dl	1.2	lock.lock();
247			try {
248			return q.size();
249	tim	1.13	} finally {
250	dl	1.2	lock.unlock();
251			}
252			}
253
254	jsr166	1.32	/**
255			* @throws UnsupportedOperationException {@inheritDoc}
256			* @throws ClassCastException {@inheritDoc}
257			* @throws NullPointerException {@inheritDoc}
258			* @throws IllegalArgumentException {@inheritDoc}
259			*/
260	dl	1.17	public int drainTo(Collection<? super E> c) {
261			if (c == null)
262			throw new NullPointerException();
263			if (c == this)
264			throw new IllegalArgumentException();
265	dl	1.21	final ReentrantLock lock = this.lock;
266	dl	1.17	lock.lock();
267			try {
268			int n = 0;
269			for (;;) {
270			E first = q.peek();
271			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
272			break;
273			c.add(q.poll());
274			++n;
275			}
276			if (n > 0)
277			available.signalAll();
278			return n;
279			} finally {
280			lock.unlock();
281			}
282			}
283
284	jsr166	1.32	/**
285			* @throws UnsupportedOperationException {@inheritDoc}
286			* @throws ClassCastException {@inheritDoc}
287			* @throws NullPointerException {@inheritDoc}
288			* @throws IllegalArgumentException {@inheritDoc}
289			*/
290	dl	1.17	public int drainTo(Collection<? super E> c, int maxElements) {
291			if (c == null)
292			throw new NullPointerException();
293			if (c == this)
294			throw new IllegalArgumentException();
295			if (maxElements <= 0)
296			return 0;
297	dl	1.21	final ReentrantLock lock = this.lock;
298	dl	1.17	lock.lock();
299			try {
300			int n = 0;
301			while (n < maxElements) {
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			if (n > 0)
309			available.signalAll();
310			return n;
311			} finally {
312			lock.unlock();
313			}
314			}
315
316	dholmes	1.7	/**
317			* Atomically removes all of the elements from this delay queue.
318			* The queue will be empty after this call returns.
319	jsr166	1.32	* Elements with an unexpired delay are not waited for; they are
320			* simply discarded from the queue.
321	dholmes	1.7	*/
322	dl	1.2	public void clear() {
323	dl	1.21	final ReentrantLock lock = this.lock;
324	dl	1.2	lock.lock();
325			try {
326			q.clear();
327	tim	1.13	} finally {
328	dl	1.2	lock.unlock();
329			}
330			}
331	tim	1.1
332	dholmes	1.7	/**
333			* Always returns <tt>Integer.MAX_VALUE</tt> because
334			* a <tt>DelayQueue</tt> is not capacity constrained.
335	jsr166	1.32	*
336	dholmes	1.7	* @return <tt>Integer.MAX_VALUE</tt>
337			*/
338	dl	1.2	public int remainingCapacity() {
339			return Integer.MAX_VALUE;
340	tim	1.1	}
341	dl	1.2
342	jsr166	1.32	/**
343			* Returns an array containing all of the elements in this queue.
344			* The returned array elements are in no particular order.
345			*
346			* <p>The returned array will be "safe" in that no references to it are
347			* maintained by this queue. (In other words, this method must allocate
348			* a new array). The caller is thus free to modify the returned array.
349	jsr166	1.33	*
350	jsr166	1.32	* <p>This method acts as bridge between array-based and collection-based
351			* APIs.
352			*
353			* @return an array containing all of the elements in this queue
354			*/
355	dl	1.2	public Object[] toArray() {
356	dl	1.21	final ReentrantLock lock = this.lock;
357	dl	1.2	lock.lock();
358			try {
359			return q.toArray();
360	tim	1.13	} finally {
361	dl	1.2	lock.unlock();
362			}
363	tim	1.1	}
364	dl	1.2
365	jsr166	1.32	/**
366			* Returns an array containing all of the elements in this queue; the
367			* runtime type of the returned array is that of the specified array.
368			* The returned array elements are in no particular order.
369			* If the queue fits in the specified array, it is returned therein.
370			* Otherwise, a new array is allocated with the runtime type of the
371			* specified array and the size of this queue.
372			*
373			* <p>If this queue fits in the specified array with room to spare
374			* (i.e., the array has more elements than this queue), the element in
375			* the array immediately following the end of the queue is set to
376			* <tt>null</tt>.
377			*
378			* <p>Like the {@link #toArray()} method, this method acts as bridge between
379			* array-based and collection-based APIs. Further, this method allows
380			* precise control over the runtime type of the output array, and may,
381			* under certain circumstances, be used to save allocation costs.
382			*
383	jsr166	1.37	* <p>The following code can be used to dump a delay queue into a newly
384			* allocated array of <tt>Delayed</tt>:
385	jsr166	1.32	*
386			* <pre>
387	jsr166	1.37	* Delayed[] a = q.toArray(new Delayed[0]);</pre>
388	jsr166	1.32	*
389			* Note that <tt>toArray(new Object[0])</tt> is identical in function to
390			* <tt>toArray()</tt>.
391			*
392			* @param a the array into which the elements of the queue are to
393			* be stored, if it is big enough; otherwise, a new array of the
394			* same runtime type is allocated for this purpose
395			* @return an array containing all of the elements in this queue
396			* @throws ArrayStoreException if the runtime type of the specified array
397			* is not a supertype of the runtime type of every element in
398			* this queue
399			* @throws NullPointerException if the specified array is null
400			*/
401			public <T> T[] toArray(T[] a) {
402	dl	1.21	final ReentrantLock lock = this.lock;
403	dl	1.2	lock.lock();
404			try {
405	jsr166	1.32	return q.toArray(a);
406	tim	1.13	} finally {
407	dl	1.2	lock.unlock();
408			}
409	tim	1.1	}
410
411	dl	1.26	/**
412			* Removes a single instance of the specified element from this
413	dl	1.36	* queue, if it is present, whether or not it has expired.
414	dl	1.26	*/
415	dholmes	1.7	public boolean remove(Object o) {
416	dl	1.21	final ReentrantLock lock = this.lock;
417	dl	1.2	lock.lock();
418			try {
419	dholmes	1.7	return q.remove(o);
420	tim	1.13	} finally {
421	dl	1.2	lock.unlock();
422			}
423			}
424
425	dholmes	1.7	/**
426	dl	1.36	* Returns an iterator over all the elements (both expired and
427	dl	1.44	* unexpired) in this queue. The iterator does not return the
428			* elements in any particular order. The returned
429			* <tt>Iterator</tt> is a "weakly consistent" iterator that will
430			* never throw {@link ConcurrentModificationException}, and
431			* guarantees to traverse elements as they existed upon
432			* construction of the iterator, and may (but is not guaranteed
433			* to) reflect any modifications subsequent to construction.
434	dholmes	1.7	*
435	jsr166	1.32	* @return an iterator over the elements in this queue
436	dholmes	1.7	*/
437	dl	1.3	public Iterator<E> iterator() {
438	dl	1.44	return new Itr(toArray());
439	dl	1.2	}
440
441	dl	1.42	/**
442			* Snapshot iterator that works off copy of underlying q array.
443			*/
444	dl	1.44	private class Itr implements Iterator<E> {
445	dl	1.42	final Object[] array; // Array of all elements
446			int cursor; // index of next element to return;
447			int lastRet; // index of last element, or -1 if no such
448	jsr166	1.43
449	dl	1.42	Itr(Object[] array) {
450			lastRet = -1;
451			this.array = array;
452	dl	1.2	}
453
454	tim	1.6	public boolean hasNext() {
455	dl	1.42	return cursor < array.length;
456	tim	1.6	}
457
458			public E next() {
459	dl	1.42	if (cursor >= array.length)
460			throw new NoSuchElementException();
461			lastRet = cursor;
462			return (E)array[cursor++];
463	tim	1.6	}
464
465			public void remove() {
466	jsr166	1.43	if (lastRet < 0)
467	dl	1.42	throw new IllegalStateException();
468			Object x = array[lastRet];
469			lastRet = -1;
470			// Traverse underlying queue to find == element,
471			// not just a .equals element.
472	dl	1.2	lock.lock();
473			try {
474	dl	1.42	for (Iterator it = q.iterator(); it.hasNext(); ) {
475			if (it.next() == x) {
476			it.remove();
477			return;
478			}
479			}
480	tim	1.13	} finally {
481	dl	1.2	lock.unlock();
482			}
483	tim	1.6	}
484	tim	1.1	}
485
486			}