util/concurrent/DelayQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */


package java.util.concurrent;
import java.util.concurrent.*; // for javadoc (till 6280605 is fixed)
import java.util.concurrent.locks.*;
import java.util.*;

/**
 * An unbounded {@linkplain BlockingQueue blocking queue} of
 * <tt>Delayed</tt> elements, in which an element can only be taken
 * when its delay has expired.  The <em>head</em> of the queue is that
 * <tt>Delayed</tt> element whose delay expired furthest in the
 * past.  If no delay has expired there is no head and <tt>poll</tt>
 * will return <tt>null</tt>. Expiration occurs when an element's
 * <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less
 * than or equal to zero.  Even though unexpired elements cannot be
 * removed using <tt>take</tt> or <tt>poll</tt>, they are otherwise
 * treated as normal elements. For example, the <tt>size</tt> method
 * returns the count of both expired and unexpired elements.
 * This queue does not permit null elements.
 *
 * <p>This class and its iterator implement all of the
 * <em>optional</em> methods of the {@link Collection} and {@link
 * Iterator} interfaces.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */

public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
    implements BlockingQueue<E> {

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    /**
     * Returns an iterator over all the elements (both expired and
     * unexpired) in this queue. The iterator does not
     * return the elements in any particular order. The returned
     * iterator is a thread-safe "fast-fail" iterator that will throw
     * {@link ConcurrentModificationException} upon detected
     * interference.
     *
     * @return an iterator over the elements in this queue
     */
    public Iterator<E> iterator() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return new Itr<E>(q.iterator());
        } finally {
            lock.unlock();
        }
    }

    private class Itr<E> implements Iterator<E> {
        private final Iterator<E> iter;
        Itr(Iterator<E> i) {
            iter = i;
        }

        public boolean hasNext() {
            return iter.hasNext();
        }

        public E next() {
            final ReentrantLock lock = DelayQueue.this.lock;
            lock.lock();
            try {
                return iter.next();
            } finally {
                lock.unlock();
            }
        }

        public void remove() {
            final ReentrantLock lock = DelayQueue.this.lock;
            lock.lock();
            try {
                iter.remove();
            } finally {
                lock.unlock();
            }
        }
    }

}
Revision:	1.41
Committed:	Fri Sep 23 18:08:35 2005 UTC (18 years, 8 months ago) by jsr166
Branch:	MAIN
Changes since 1.40:	+2 -2 lines
Log Message:	hold locks only when necessary
#	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
8	tim	1.1	package java.util.concurrent;
9	jsr166	1.37	import java.util.concurrent.*; // for javadoc (till 6280605 is fixed)
10	dl	1.5	import java.util.concurrent.locks.*;
11	tim	1.1	import java.util.*;
12
13			/**
14	dl	1.27	* An unbounded {@linkplain BlockingQueue blocking queue} of
15			* <tt>Delayed</tt> elements, in which an element can only be taken
16			* when its delay has expired. The <em>head</em> of the queue is that
17			* <tt>Delayed</tt> element whose delay expired furthest in the
18	jsr166	1.32	* past. If no delay has expired there is no head and <tt>poll</tt>
19	dl	1.27	* will return <tt>null</tt>. Expiration occurs when an element's
20			* <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less
21	dl	1.36	* than or equal to zero. Even though unexpired elements cannot be
22			* removed using <tt>take</tt> or <tt>poll</tt>, they are otherwise
23			* treated as normal elements. For example, the <tt>size</tt> method
24			* returns the count of both expired and unexpired elements.
25	jsr166	1.39	* This queue does not permit null elements.
26	dl	1.25	*
27	dl	1.26	* <p>This class and its iterator implement all of the
28			* <em>optional</em> methods of the {@link Collection} and {@link
29	jsr166	1.29	* Iterator} interfaces.
30	dl	1.26	*
31	dl	1.25	* <p>This class is a member of the
32			* <a href="{@docRoot}/../guide/collections/index.html">
33			* Java Collections Framework</a>.
34			*
35	dl	1.4	* @since 1.5
36			* @author Doug Lea
37	dl	1.20	* @param <E> the type of elements held in this collection
38	dl	1.19	*/
39	tim	1.1
40	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
41			implements BlockingQueue<E> {
42	tim	1.6
43	dl	1.2	private transient final ReentrantLock lock = new ReentrantLock();
44	dl	1.22	private transient final Condition available = lock.newCondition();
45	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
46	tim	1.1
47	dl	1.4	/**
48	dholmes	1.7	* Creates a new <tt>DelayQueue</tt> that is initially empty.
49	dl	1.4	*/
50	tim	1.1	public DelayQueue() {}
51
52	tim	1.6	/**
53	tim	1.9	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
54	dholmes	1.7	* given collection of {@link Delayed} instances.
55			*
56	jsr166	1.32	* @param c the collection of elements to initially contain
57			* @throws NullPointerException if the specified collection or any
58			* of its elements are null
59	tim	1.6	*/
60			public DelayQueue(Collection<? extends E> c) {
61			this.addAll(c);
62			}
63
64	dholmes	1.7	/**
65	dl	1.16	* Inserts the specified element into this delay queue.
66	dholmes	1.7	*
67	jsr166	1.30	* @param e the element to add
68	jsr166	1.38	* @return <tt>true</tt> (as specified by {@link Collection#add})
69	jsr166	1.32	* @throws NullPointerException if the specified element is null
70			*/
71			public boolean add(E e) {
72			return offer(e);
73			}
74
75			/**
76			* Inserts the specified element into this delay queue.
77			*
78			* @param e the element to add
79	dholmes	1.7	* @return <tt>true</tt>
80	jsr166	1.32	* @throws NullPointerException if the specified element is null
81	dholmes	1.7	*/
82	jsr166	1.30	public boolean offer(E e) {
83	dl	1.21	final ReentrantLock lock = this.lock;
84	dl	1.2	lock.lock();
85			try {
86	dl	1.3	E first = q.peek();
87	jsr166	1.30	q.offer(e);
88			if (first == null \|\| e.compareTo(first) < 0)
89	dl	1.4	available.signalAll();
90	dl	1.2	return true;
91	tim	1.13	} finally {
92	dl	1.2	lock.unlock();
93			}
94			}
95
96	dholmes	1.7	/**
97	jsr166	1.32	* Inserts the specified element into this delay queue. As the queue is
98	dholmes	1.7	* unbounded this method will never block.
99	jsr166	1.32	*
100	jsr166	1.30	* @param e the element to add
101	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
102	dholmes	1.7	*/
103	jsr166	1.30	public void put(E e) {
104			offer(e);
105	dl	1.2	}
106
107	dholmes	1.7	/**
108	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
109	dholmes	1.7	* unbounded this method will never block.
110	jsr166	1.32	*
111	jsr166	1.30	* @param e the element to add
112	dl	1.14	* @param timeout This parameter is ignored as the method never blocks
113	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
114			* @return <tt>true</tt>
115	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
116	dholmes	1.7	*/
117	jsr166	1.30	public boolean offer(E e, long timeout, TimeUnit unit) {
118			return offer(e);
119	dl	1.2	}
120
121	dholmes	1.7	/**
122	jsr166	1.32	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
123			* if this queue has no elements with an expired delay.
124	dholmes	1.7	*
125	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
126			* queue has no elements with an expired delay
127	dholmes	1.7	*/
128	jsr166	1.32	public E poll() {
129			final ReentrantLock lock = this.lock;
130			lock.lock();
131			try {
132			E first = q.peek();
133			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
134			return null;
135			else {
136			E x = q.poll();
137			assert x != null;
138			if (q.size() != 0)
139			available.signalAll();
140			return x;
141			}
142			} finally {
143			lock.unlock();
144			}
145	dl	1.2	}
146
147	dl	1.27	/**
148	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
149			* until an element with an expired delay is available on this queue.
150			*
151	dl	1.27	* @return the head of this queue
152	jsr166	1.32	* @throws InterruptedException {@inheritDoc}
153	dl	1.27	*/
154	dl	1.3	public E take() throws InterruptedException {
155	dl	1.21	final ReentrantLock lock = this.lock;
156	dl	1.2	lock.lockInterruptibly();
157			try {
158			for (;;) {
159	dl	1.3	E first = q.peek();
160	dl	1.12	if (first == null) {
161	dl	1.4	available.await();
162	tim	1.13	} else {
163	dl	1.2	long delay = first.getDelay(TimeUnit.NANOSECONDS);
164	dl	1.12	if (delay > 0) {
165			long tl = available.awaitNanos(delay);
166	tim	1.13	} else {
167	dl	1.3	E x = q.poll();
168	dl	1.2	assert x != null;
169			if (q.size() != 0)
170	dl	1.4	available.signalAll(); // wake up other takers
171	dl	1.2	return x;
172	tim	1.6
173	dl	1.2	}
174			}
175			}
176	tim	1.13	} finally {
177	dl	1.2	lock.unlock();
178			}
179			}
180
181	dl	1.27	/**
182	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
183			* until an element with an expired delay is available on this queue,
184			* or the specified wait time expires.
185			*
186	dl	1.27	* @return the head of this queue, or <tt>null</tt> if the
187	jsr166	1.32	* specified waiting time elapses before an element with
188			* an expired delay becomes available
189			* @throws InterruptedException {@inheritDoc}
190	dl	1.27	*/
191			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
192	jsr166	1.41	long nanos = unit.toNanos(timeout);
193	dl	1.21	final ReentrantLock lock = this.lock;
194	dl	1.2	lock.lockInterruptibly();
195			try {
196			for (;;) {
197	dl	1.3	E first = q.peek();
198	dl	1.2	if (first == null) {
199			if (nanos <= 0)
200			return null;
201			else
202	dl	1.4	nanos = available.awaitNanos(nanos);
203	tim	1.13	} else {
204	jsr166	1.41	long delay = first.getDelay(TimeUnit.NANOSECONDS);
205	dl	1.2	if (delay > 0) {
206	dl	1.40	if (nanos <= 0)
207			return null;
208	dl	1.2	if (delay > nanos)
209			delay = nanos;
210	dl	1.4	long timeLeft = available.awaitNanos(delay);
211	dl	1.2	nanos -= delay - timeLeft;
212	tim	1.13	} else {
213	dl	1.3	E x = q.poll();
214	dl	1.2	assert x != null;
215			if (q.size() != 0)
216	tim	1.6	available.signalAll();
217	dl	1.2	return x;
218			}
219			}
220			}
221	tim	1.13	} finally {
222	dl	1.2	lock.unlock();
223			}
224			}
225
226	dl	1.27	/**
227	dl	1.36	* Retrieves, but does not remove, the head of this queue, or
228			* returns <tt>null</tt> if this queue is empty. Unlike
229			* <tt>poll</tt>, if no expired elements are available in the queue,
230			* this method returns the element that will expire next,
231			* if one exists.
232	dl	1.27	*
233	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
234	dl	1.35	* queue is empty.
235	dl	1.27	*/
236	dl	1.3	public E peek() {
237	dl	1.21	final ReentrantLock lock = this.lock;
238	dl	1.2	lock.lock();
239			try {
240			return q.peek();
241	tim	1.13	} finally {
242	dl	1.2	lock.unlock();
243			}
244	tim	1.1	}
245
246	dl	1.2	public int size() {
247	dl	1.21	final ReentrantLock lock = this.lock;
248	dl	1.2	lock.lock();
249			try {
250			return q.size();
251	tim	1.13	} finally {
252	dl	1.2	lock.unlock();
253			}
254			}
255
256	jsr166	1.32	/**
257			* @throws UnsupportedOperationException {@inheritDoc}
258			* @throws ClassCastException {@inheritDoc}
259			* @throws NullPointerException {@inheritDoc}
260			* @throws IllegalArgumentException {@inheritDoc}
261			*/
262	dl	1.17	public int drainTo(Collection<? super E> c) {
263			if (c == null)
264			throw new NullPointerException();
265			if (c == this)
266			throw new IllegalArgumentException();
267	dl	1.21	final ReentrantLock lock = this.lock;
268	dl	1.17	lock.lock();
269			try {
270			int n = 0;
271			for (;;) {
272			E first = q.peek();
273			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
274			break;
275			c.add(q.poll());
276			++n;
277			}
278			if (n > 0)
279			available.signalAll();
280			return n;
281			} finally {
282			lock.unlock();
283			}
284			}
285
286	jsr166	1.32	/**
287			* @throws UnsupportedOperationException {@inheritDoc}
288			* @throws ClassCastException {@inheritDoc}
289			* @throws NullPointerException {@inheritDoc}
290			* @throws IllegalArgumentException {@inheritDoc}
291			*/
292	dl	1.17	public int drainTo(Collection<? super E> c, int maxElements) {
293			if (c == null)
294			throw new NullPointerException();
295			if (c == this)
296			throw new IllegalArgumentException();
297			if (maxElements <= 0)
298			return 0;
299	dl	1.21	final ReentrantLock lock = this.lock;
300	dl	1.17	lock.lock();
301			try {
302			int n = 0;
303			while (n < maxElements) {
304			E first = q.peek();
305			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
306			break;
307			c.add(q.poll());
308			++n;
309			}
310			if (n > 0)
311			available.signalAll();
312			return n;
313			} finally {
314			lock.unlock();
315			}
316			}
317
318	dholmes	1.7	/**
319			* Atomically removes all of the elements from this delay queue.
320			* The queue will be empty after this call returns.
321	jsr166	1.32	* Elements with an unexpired delay are not waited for; they are
322			* simply discarded from the queue.
323	dholmes	1.7	*/
324	dl	1.2	public void clear() {
325	dl	1.21	final ReentrantLock lock = this.lock;
326	dl	1.2	lock.lock();
327			try {
328			q.clear();
329	tim	1.13	} finally {
330	dl	1.2	lock.unlock();
331			}
332			}
333	tim	1.1
334	dholmes	1.7	/**
335			* Always returns <tt>Integer.MAX_VALUE</tt> because
336			* a <tt>DelayQueue</tt> is not capacity constrained.
337	jsr166	1.32	*
338	dholmes	1.7	* @return <tt>Integer.MAX_VALUE</tt>
339			*/
340	dl	1.2	public int remainingCapacity() {
341			return Integer.MAX_VALUE;
342	tim	1.1	}
343	dl	1.2
344	jsr166	1.32	/**
345			* Returns an array containing all of the elements in this queue.
346			* The returned array elements are in no particular order.
347			*
348			* <p>The returned array will be "safe" in that no references to it are
349			* maintained by this queue. (In other words, this method must allocate
350			* a new array). The caller is thus free to modify the returned array.
351	jsr166	1.33	*
352	jsr166	1.32	* <p>This method acts as bridge between array-based and collection-based
353			* APIs.
354			*
355			* @return an array containing all of the elements in this queue
356			*/
357	dl	1.2	public Object[] toArray() {
358	dl	1.21	final ReentrantLock lock = this.lock;
359	dl	1.2	lock.lock();
360			try {
361			return q.toArray();
362	tim	1.13	} finally {
363	dl	1.2	lock.unlock();
364			}
365	tim	1.1	}
366	dl	1.2
367	jsr166	1.32	/**
368			* Returns an array containing all of the elements in this queue; the
369			* runtime type of the returned array is that of the specified array.
370			* The returned array elements are in no particular order.
371			* If the queue fits in the specified array, it is returned therein.
372			* Otherwise, a new array is allocated with the runtime type of the
373			* specified array and the size of this queue.
374			*
375			* <p>If this queue fits in the specified array with room to spare
376			* (i.e., the array has more elements than this queue), the element in
377			* the array immediately following the end of the queue is set to
378			* <tt>null</tt>.
379			*
380			* <p>Like the {@link #toArray()} method, this method acts as bridge between
381			* array-based and collection-based APIs. Further, this method allows
382			* precise control over the runtime type of the output array, and may,
383			* under certain circumstances, be used to save allocation costs.
384			*
385	jsr166	1.37	* <p>The following code can be used to dump a delay queue into a newly
386			* allocated array of <tt>Delayed</tt>:
387	jsr166	1.32	*
388			* <pre>
389	jsr166	1.37	* Delayed[] a = q.toArray(new Delayed[0]);</pre>
390	jsr166	1.32	*
391			* Note that <tt>toArray(new Object[0])</tt> is identical in function to
392			* <tt>toArray()</tt>.
393			*
394			* @param a the array into which the elements of the queue are to
395			* be stored, if it is big enough; otherwise, a new array of the
396			* same runtime type is allocated for this purpose
397			* @return an array containing all of the elements in this queue
398			* @throws ArrayStoreException if the runtime type of the specified array
399			* is not a supertype of the runtime type of every element in
400			* this queue
401			* @throws NullPointerException if the specified array is null
402			*/
403			public <T> T[] toArray(T[] a) {
404	dl	1.21	final ReentrantLock lock = this.lock;
405	dl	1.2	lock.lock();
406			try {
407	jsr166	1.32	return q.toArray(a);
408	tim	1.13	} finally {
409	dl	1.2	lock.unlock();
410			}
411	tim	1.1	}
412
413	dl	1.26	/**
414			* Removes a single instance of the specified element from this
415	dl	1.36	* queue, if it is present, whether or not it has expired.
416	dl	1.26	*/
417	dholmes	1.7	public boolean remove(Object o) {
418	dl	1.21	final ReentrantLock lock = this.lock;
419	dl	1.2	lock.lock();
420			try {
421	dholmes	1.7	return q.remove(o);
422	tim	1.13	} finally {
423	dl	1.2	lock.unlock();
424			}
425			}
426
427	dholmes	1.7	/**
428	dl	1.36	* Returns an iterator over all the elements (both expired and
429			* unexpired) in this queue. The iterator does not
430			* return the elements in any particular order. The returned
431			* iterator is a thread-safe "fast-fail" iterator that will throw
432			* {@link ConcurrentModificationException} upon detected
433			* interference.
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	1.21	final ReentrantLock lock = this.lock;
439	dl	1.2	lock.lock();
440			try {
441	dl	1.34	return new Itr<E>(q.iterator());
442	tim	1.13	} finally {
443	dl	1.2	lock.unlock();
444			}
445			}
446
447	dl	1.3	private class Itr<E> implements Iterator<E> {
448			private final Iterator<E> iter;
449	tim	1.6	Itr(Iterator<E> i) {
450			iter = i;
451	dl	1.2	}
452
453	tim	1.6	public boolean hasNext() {
454	dl	1.2	return iter.hasNext();
455	tim	1.6	}
456
457			public E next() {
458	dl	1.21	final ReentrantLock lock = DelayQueue.this.lock;
459	dl	1.2	lock.lock();
460			try {
461			return iter.next();
462	tim	1.13	} finally {
463	dl	1.2	lock.unlock();
464			}
465	tim	1.6	}
466
467			public void remove() {
468	dl	1.21	final ReentrantLock lock = DelayQueue.this.lock;
469	dl	1.2	lock.lock();
470			try {
471			iter.remove();
472	tim	1.13	} finally {
473	dl	1.2	lock.unlock();
474			}
475	tim	1.6	}
476	tim	1.1	}
477
478			}