util/concurrent/DelayQueue.java

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

package java.util.concurrent;
import java.util.concurrent.locks.*;
import java.util.*;

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

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

    private transient final ReentrantLock lock = new ReentrantLock();
    private final PriorityQueue<E> q = new PriorityQueue<E>();

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

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

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

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

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

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

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

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

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

    /**
     * Retrieves and removes the head of this queue, waiting if necessary
     * until an element with an expired delay is available on this queue.
     *
     * @return the head of this queue
     * @throws InterruptedException {@inheritDoc}
     */
    public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            for (;;) {
                E first = q.peek();
                if (first == null)
                    available.await();
                else {
                    long delay = first.getDelay(TimeUnit.NANOSECONDS);
                    if (delay <= 0)
                        return q.poll();
                    else if (leader != null)
                        available.await();
                    else {
                        Thread thisThread = Thread.currentThread();
                        leader = thisThread;
                        try {
                            available.awaitNanos(delay);
                        } finally {
                            if (leader == thisThread)
                                leader = null;
                        }
                    }
                }
            }
        } finally {
            if (leader == null && q.peek() != null)
                available.signal();
            lock.unlock();
        }
    }

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

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

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

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

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

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

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

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

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

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

    /**
     * Returns an iterator over all the elements (both expired and
     * unexpired) in this queue. The iterator does not return the
     * elements in any particular order.  The returned
     * <tt>Iterator</tt> is a "weakly consistent" iterator that will
     * never throw {@link ConcurrentModificationException}, and
     * guarantees to traverse elements as they existed upon
     * construction of the iterator, and may (but is not guaranteed
     * to) reflect any modifications subsequent to construction.
     *
     * @return an iterator over the elements in this queue
     */
    public Iterator<E> iterator() {
        return new Itr(toArray());
    }

    /**
     * Snapshot iterator that works off copy of underlying q array.
     */
    private class Itr implements Iterator<E> {
        final Object[] array; // Array of all elements
        int cursor;           // index of next element to return;
        int lastRet;          // index of last element, or -1 if no such

        Itr(Object[] array) {
            lastRet = -1;
            this.array = array;
        }

        public boolean hasNext() {
            return cursor < array.length;
        }

        @SuppressWarnings("unchecked")
        public E next() {
            if (cursor >= array.length)
                throw new NoSuchElementException();
            lastRet = cursor;
            return (E)array[cursor++];
        }

        public void remove() {
            if (lastRet < 0)
                throw new IllegalStateException();
            Object x = array[lastRet];
            lastRet = -1;
            // Traverse underlying queue to find == element,
            // not just a .equals element.
            lock.lock();
            try {
                for (Iterator it = q.iterator(); it.hasNext(); ) {
                    if (it.next() == x) {
                        it.remove();
                        return;
                    }
                }
            } finally {
                lock.unlock();
            }
        }
    }

}
Revision:	1.49
Committed:	Sun May 18 23:47:56 2008 UTC (16 years ago) by jsr166
Branch:	MAIN
Changes since 1.48:	+41 -41 lines
Log Message:	Sync with OpenJDK; untabify
#	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	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
43	tim	1.1
44	dl	1.4	/**
45	jsr166	1.48	* Thread designated to wait for the element at the head of
46			* the queue. This variant of the Leader-Follower pattern
47			* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
48			* minimize unnecessary timed waiting. When a thread becomes
49			* the leader, it waits only for the next delay to elapse, but
50			* other threads await indefinitely. The leader thread must
51			* signal some other thread before returning from take() or
52			* poll(...), unless some other thread becomes leader in the
53			* interim. Whenever the head of the queue is replaced with
54			* an element with an earlier expiration time, the leader
55			* field is invalidated by being reset to null, and some
56			* waiting thread, but not necessarily the current leader, is
57			* signalled. So waiting threads must be prepared to acquire
58			* and lose leadership while waiting.
59			*/
60			private Thread leader = null;
61
62			/**
63			* Condition signalled when a newer element becomes available
64			* at the head of the queue or a new thread may need to
65			* become leader.
66			*/
67			private final Condition available = lock.newCondition();
68
69			/**
70	dholmes	1.7	* Creates a new <tt>DelayQueue</tt> that is initially empty.
71	dl	1.4	*/
72	tim	1.1	public DelayQueue() {}
73
74	tim	1.6	/**
75	tim	1.9	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
76	dholmes	1.7	* given collection of {@link Delayed} instances.
77			*
78	jsr166	1.32	* @param c the collection of elements to initially contain
79			* @throws NullPointerException if the specified collection or any
80			* of its elements are null
81	tim	1.6	*/
82			public DelayQueue(Collection<? extends E> c) {
83			this.addAll(c);
84			}
85
86	dholmes	1.7	/**
87	dl	1.16	* Inserts the specified element into this delay queue.
88	dholmes	1.7	*
89	jsr166	1.30	* @param e the element to add
90	jsr166	1.38	* @return <tt>true</tt> (as specified by {@link Collection#add})
91	jsr166	1.32	* @throws NullPointerException if the specified element is null
92			*/
93			public boolean add(E e) {
94			return offer(e);
95			}
96
97			/**
98			* Inserts the specified element into this delay queue.
99			*
100			* @param e the element to add
101	dholmes	1.7	* @return <tt>true</tt>
102	jsr166	1.32	* @throws NullPointerException if the specified element is null
103	dholmes	1.7	*/
104	jsr166	1.30	public boolean offer(E e) {
105	dl	1.21	final ReentrantLock lock = this.lock;
106	dl	1.2	lock.lock();
107			try {
108	jsr166	1.30	q.offer(e);
109	jsr166	1.48	if (q.peek() == e) {
110	jsr166	1.49	leader = null;
111	jsr166	1.48	available.signal();
112	jsr166	1.49	}
113	dl	1.2	return true;
114	tim	1.13	} finally {
115	dl	1.2	lock.unlock();
116			}
117			}
118
119	dholmes	1.7	/**
120	jsr166	1.32	* Inserts the specified element into this delay queue. As the queue is
121	dholmes	1.7	* unbounded this method will never block.
122	jsr166	1.32	*
123	jsr166	1.30	* @param e the element to add
124	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
125	dholmes	1.7	*/
126	jsr166	1.30	public void put(E e) {
127			offer(e);
128	dl	1.2	}
129
130	dholmes	1.7	/**
131	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
132	dholmes	1.7	* unbounded this method will never block.
133	jsr166	1.32	*
134	jsr166	1.30	* @param e the element to add
135	dl	1.14	* @param timeout This parameter is ignored as the method never blocks
136	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
137			* @return <tt>true</tt>
138	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
139	dholmes	1.7	*/
140	jsr166	1.30	public boolean offer(E e, long timeout, TimeUnit unit) {
141			return offer(e);
142	dl	1.2	}
143
144	dholmes	1.7	/**
145	jsr166	1.32	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
146			* if this queue has no elements with an expired delay.
147	dholmes	1.7	*
148	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
149			* queue has no elements with an expired delay
150	dholmes	1.7	*/
151	jsr166	1.32	public E poll() {
152			final ReentrantLock lock = this.lock;
153			lock.lock();
154			try {
155			E first = q.peek();
156			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
157			return null;
158	jsr166	1.48	else
159			return q.poll();
160	jsr166	1.32	} finally {
161			lock.unlock();
162			}
163	dl	1.2	}
164
165	dl	1.27	/**
166	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
167			* until an element with an expired delay is available on this queue.
168			*
169	dl	1.27	* @return the head of this queue
170	jsr166	1.32	* @throws InterruptedException {@inheritDoc}
171	dl	1.27	*/
172	dl	1.3	public E take() throws InterruptedException {
173	dl	1.21	final ReentrantLock lock = this.lock;
174	dl	1.2	lock.lockInterruptibly();
175			try {
176			for (;;) {
177	dl	1.3	E first = q.peek();
178	jsr166	1.48	if (first == null)
179	dl	1.4	available.await();
180	jsr166	1.49	else {
181	jsr166	1.48	long delay = first.getDelay(TimeUnit.NANOSECONDS);
182	jsr166	1.49	if (delay <= 0)
183			return q.poll();
184			else if (leader != null)
185			available.await();
186			else {
187			Thread thisThread = Thread.currentThread();
188			leader = thisThread;
189			try {
190			available.awaitNanos(delay);
191			} finally {
192			if (leader == thisThread)
193			leader = null;
194			}
195	dl	1.2	}
196			}
197			}
198	tim	1.13	} finally {
199	jsr166	1.49	if (leader == null && q.peek() != null)
200			available.signal();
201	dl	1.2	lock.unlock();
202			}
203			}
204
205	dl	1.27	/**
206	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
207			* until an element with an expired delay is available on this queue,
208			* or the specified wait time expires.
209			*
210	dl	1.27	* @return the head of this queue, or <tt>null</tt> if the
211	jsr166	1.32	* specified waiting time elapses before an element with
212			* an expired delay becomes available
213			* @throws InterruptedException {@inheritDoc}
214	dl	1.27	*/
215			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
216	jsr166	1.41	long nanos = unit.toNanos(timeout);
217	dl	1.21	final ReentrantLock lock = this.lock;
218	dl	1.2	lock.lockInterruptibly();
219			try {
220			for (;;) {
221	dl	1.3	E first = q.peek();
222	dl	1.2	if (first == null) {
223			if (nanos <= 0)
224			return null;
225			else
226	dl	1.4	nanos = available.awaitNanos(nanos);
227	tim	1.13	} else {
228	jsr166	1.41	long delay = first.getDelay(TimeUnit.NANOSECONDS);
229	jsr166	1.49	if (delay <= 0)
230			return q.poll();
231			if (nanos <= 0)
232			return null;
233			if (nanos < delay \|\| leader != null)
234			nanos = available.awaitNanos(nanos);
235			else {
236			Thread thisThread = Thread.currentThread();
237			leader = thisThread;
238			try {
239			long timeLeft = available.awaitNanos(delay);
240			nanos -= delay - timeLeft;
241			} finally {
242			if (leader == thisThread)
243			leader = null;
244			}
245			}
246	dl	1.2	}
247			}
248	tim	1.13	} finally {
249	jsr166	1.49	if (leader == null && q.peek() != null)
250			available.signal();
251	dl	1.2	lock.unlock();
252			}
253			}
254
255	dl	1.27	/**
256	dl	1.36	* Retrieves, but does not remove, the head of this queue, or
257			* returns <tt>null</tt> if this queue is empty. Unlike
258			* <tt>poll</tt>, if no expired elements are available in the queue,
259			* this method returns the element that will expire next,
260			* if one exists.
261	dl	1.27	*
262	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
263	dl	1.35	* queue is empty.
264	dl	1.27	*/
265	dl	1.3	public E peek() {
266	dl	1.21	final ReentrantLock lock = this.lock;
267	dl	1.2	lock.lock();
268			try {
269			return q.peek();
270	tim	1.13	} finally {
271	dl	1.2	lock.unlock();
272			}
273	tim	1.1	}
274
275	dl	1.2	public int size() {
276	dl	1.21	final ReentrantLock lock = this.lock;
277	dl	1.2	lock.lock();
278			try {
279			return q.size();
280	tim	1.13	} finally {
281	dl	1.2	lock.unlock();
282			}
283			}
284
285	jsr166	1.32	/**
286			* @throws UnsupportedOperationException {@inheritDoc}
287			* @throws ClassCastException {@inheritDoc}
288			* @throws NullPointerException {@inheritDoc}
289			* @throws IllegalArgumentException {@inheritDoc}
290			*/
291	dl	1.17	public int drainTo(Collection<? super E> c) {
292			if (c == null)
293			throw new NullPointerException();
294			if (c == this)
295			throw new IllegalArgumentException();
296	dl	1.21	final ReentrantLock lock = this.lock;
297	dl	1.17	lock.lock();
298			try {
299			int n = 0;
300			for (;;) {
301			E first = q.peek();
302			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
303			break;
304			c.add(q.poll());
305			++n;
306			}
307			return n;
308			} finally {
309			lock.unlock();
310			}
311			}
312
313	jsr166	1.32	/**
314			* @throws UnsupportedOperationException {@inheritDoc}
315			* @throws ClassCastException {@inheritDoc}
316			* @throws NullPointerException {@inheritDoc}
317			* @throws IllegalArgumentException {@inheritDoc}
318			*/
319	dl	1.17	public int drainTo(Collection<? super E> c, int maxElements) {
320			if (c == null)
321			throw new NullPointerException();
322			if (c == this)
323			throw new IllegalArgumentException();
324			if (maxElements <= 0)
325			return 0;
326	dl	1.21	final ReentrantLock lock = this.lock;
327	dl	1.17	lock.lock();
328			try {
329			int n = 0;
330			while (n < maxElements) {
331			E first = q.peek();
332			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
333			break;
334			c.add(q.poll());
335			++n;
336			}
337			return n;
338			} finally {
339			lock.unlock();
340			}
341			}
342
343	dholmes	1.7	/**
344			* Atomically removes all of the elements from this delay queue.
345			* The queue will be empty after this call returns.
346	jsr166	1.32	* Elements with an unexpired delay are not waited for; they are
347			* simply discarded from the queue.
348	dholmes	1.7	*/
349	dl	1.2	public void clear() {
350	dl	1.21	final ReentrantLock lock = this.lock;
351	dl	1.2	lock.lock();
352			try {
353			q.clear();
354	tim	1.13	} finally {
355	dl	1.2	lock.unlock();
356			}
357			}
358	tim	1.1
359	dholmes	1.7	/**
360			* Always returns <tt>Integer.MAX_VALUE</tt> because
361			* a <tt>DelayQueue</tt> is not capacity constrained.
362	jsr166	1.32	*
363	dholmes	1.7	* @return <tt>Integer.MAX_VALUE</tt>
364			*/
365	dl	1.2	public int remainingCapacity() {
366			return Integer.MAX_VALUE;
367	tim	1.1	}
368	dl	1.2
369	jsr166	1.32	/**
370			* Returns an array containing all of the elements in this queue.
371			* The returned array elements are in no particular order.
372			*
373			* <p>The returned array will be "safe" in that no references to it are
374			* maintained by this queue. (In other words, this method must allocate
375			* a new array). The caller is thus free to modify the returned array.
376	jsr166	1.33	*
377	jsr166	1.32	* <p>This method acts as bridge between array-based and collection-based
378			* APIs.
379			*
380			* @return an array containing all of the elements in this queue
381			*/
382	dl	1.2	public Object[] toArray() {
383	dl	1.21	final ReentrantLock lock = this.lock;
384	dl	1.2	lock.lock();
385			try {
386			return q.toArray();
387	tim	1.13	} finally {
388	dl	1.2	lock.unlock();
389			}
390	tim	1.1	}
391	dl	1.2
392	jsr166	1.32	/**
393			* Returns an array containing all of the elements in this queue; the
394			* runtime type of the returned array is that of the specified array.
395			* The returned array elements are in no particular order.
396			* If the queue fits in the specified array, it is returned therein.
397			* Otherwise, a new array is allocated with the runtime type of the
398			* specified array and the size of this queue.
399			*
400			* <p>If this queue fits in the specified array with room to spare
401			* (i.e., the array has more elements than this queue), the element in
402			* the array immediately following the end of the queue is set to
403			* <tt>null</tt>.
404			*
405			* <p>Like the {@link #toArray()} method, this method acts as bridge between
406			* array-based and collection-based APIs. Further, this method allows
407			* precise control over the runtime type of the output array, and may,
408			* under certain circumstances, be used to save allocation costs.
409			*
410	jsr166	1.37	* <p>The following code can be used to dump a delay queue into a newly
411			* allocated array of <tt>Delayed</tt>:
412	jsr166	1.32	*
413			* <pre>
414	jsr166	1.37	* Delayed[] a = q.toArray(new Delayed[0]);</pre>
415	jsr166	1.32	*
416			* Note that <tt>toArray(new Object[0])</tt> is identical in function to
417			* <tt>toArray()</tt>.
418			*
419			* @param a the array into which the elements of the queue are to
420			* be stored, if it is big enough; otherwise, a new array of the
421			* same runtime type is allocated for this purpose
422			* @return an array containing all of the elements in this queue
423			* @throws ArrayStoreException if the runtime type of the specified array
424			* is not a supertype of the runtime type of every element in
425			* this queue
426			* @throws NullPointerException if the specified array is null
427			*/
428			public <T> T[] toArray(T[] a) {
429	dl	1.21	final ReentrantLock lock = this.lock;
430	dl	1.2	lock.lock();
431			try {
432	jsr166	1.32	return q.toArray(a);
433	tim	1.13	} finally {
434	dl	1.2	lock.unlock();
435			}
436	tim	1.1	}
437
438	dl	1.26	/**
439			* Removes a single instance of the specified element from this
440	dl	1.36	* queue, if it is present, whether or not it has expired.
441	dl	1.26	*/
442	dholmes	1.7	public boolean remove(Object o) {
443	dl	1.21	final ReentrantLock lock = this.lock;
444	dl	1.2	lock.lock();
445			try {
446	dholmes	1.7	return q.remove(o);
447	tim	1.13	} finally {
448	dl	1.2	lock.unlock();
449			}
450			}
451
452	dholmes	1.7	/**
453	dl	1.36	* Returns an iterator over all the elements (both expired and
454	dl	1.44	* unexpired) in this queue. The iterator does not return the
455			* elements in any particular order. The returned
456			* <tt>Iterator</tt> is a "weakly consistent" iterator that will
457			* never throw {@link ConcurrentModificationException}, and
458			* guarantees to traverse elements as they existed upon
459			* construction of the iterator, and may (but is not guaranteed
460			* to) reflect any modifications subsequent to construction.
461	dholmes	1.7	*
462	jsr166	1.32	* @return an iterator over the elements in this queue
463	dholmes	1.7	*/
464	dl	1.3	public Iterator<E> iterator() {
465	dl	1.44	return new Itr(toArray());
466	dl	1.2	}
467
468	dl	1.42	/**
469			* Snapshot iterator that works off copy of underlying q array.
470			*/
471	dl	1.44	private class Itr implements Iterator<E> {
472	dl	1.42	final Object[] array; // Array of all elements
473	jsr166	1.49	int cursor; // index of next element to return;
474			int lastRet; // index of last element, or -1 if no such
475	jsr166	1.43
476	dl	1.42	Itr(Object[] array) {
477			lastRet = -1;
478			this.array = array;
479	dl	1.2	}
480
481	tim	1.6	public boolean hasNext() {
482	dl	1.42	return cursor < array.length;
483	tim	1.6	}
484
485	jsr166	1.49	@SuppressWarnings("unchecked")
486	tim	1.6	public E next() {
487	dl	1.42	if (cursor >= array.length)
488			throw new NoSuchElementException();
489			lastRet = cursor;
490			return (E)array[cursor++];
491	tim	1.6	}
492
493			public void remove() {
494	jsr166	1.43	if (lastRet < 0)
495	jsr166	1.49	throw new IllegalStateException();
496	dl	1.42	Object x = array[lastRet];
497			lastRet = -1;
498			// Traverse underlying queue to find == element,
499			// not just a .equals element.
500	dl	1.2	lock.lock();
501			try {
502	dl	1.42	for (Iterator it = q.iterator(); it.hasNext(); ) {
503			if (it.next() == x) {
504			it.remove();
505			return;
506			}
507			}
508	tim	1.13	} finally {
509	dl	1.2	lock.unlock();
510			}
511	tim	1.6	}
512	tim	1.1	}
513
514			}