util/concurrent/DelayQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;
import static java.util.concurrent.TimeUnit.NANOSECONDS;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.*;

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

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

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

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

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

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

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

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

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

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

    /**
     * Retrieves and removes the head of this queue, or returns {@code null}
     * if this queue has no elements with an expired delay.
     *
     * @return the head of this queue, or {@code null} if this
     *         queue has no elements with an expired delay
     */
    public E poll() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            E first = q.peek();
            if (first == null || first.getDelay(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(NANOSECONDS);
                    if (delay <= 0)
                        return q.poll();
                    first = null; // don't retain ref while waiting
                    if (leader != null)
                        available.await();
                    else {
                        Thread thisThread = Thread.currentThread();
                        leader = thisThread;
                        try {
                            available.awaitNanos(delay);
                        } finally {
                            if (leader == thisThread)
                                leader = null;
                        }
                    }
                }
            }
        } finally {
            if (leader == null && q.peek() != null)
                available.signal();
            lock.unlock();
        }
    }

    /**
     * Retrieves and removes the head of this queue, waiting if necessary
     * until an element with an expired delay is available on this queue,
     * or the specified wait time expires.
     *
     * @return the head of this queue, or {@code null} if the
     *         specified waiting time elapses before an element with
     *         an expired delay becomes available
     * @throws InterruptedException {@inheritDoc}
     */
    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
        long nanos = unit.toNanos(timeout);
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            for (;;) {
                E first = q.peek();
                if (first == null) {
                    if (nanos <= 0)
                        return null;
                    else
                        nanos = available.awaitNanos(nanos);
                } else {
                    long delay = first.getDelay(NANOSECONDS);
                    if (delay <= 0)
                        return q.poll();
                    if (nanos <= 0)
                        return null;
                    first = null; // don't retain ref while waiting
                    if (nanos < delay || leader != null)
                        nanos = available.awaitNanos(nanos);
                    else {
                        Thread thisThread = Thread.currentThread();
                        leader = thisThread;
                        try {
                            long timeLeft = available.awaitNanos(delay);
                            nanos -= delay - timeLeft;
                        } finally {
                            if (leader == thisThread)
                                leader = null;
                        }
                    }
                }
            }
        } finally {
            if (leader == null && q.peek() != null)
                available.signal();
            lock.unlock();
        }
    }

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

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

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

    /**
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    public int drainTo(Collection<? super E> c) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            int n = 0;
            for (E e; (e = peekExpired()) != null;) {
                c.add(e);       // In this order, in case add() throws.
                q.poll();
                ++n;
            }
            return n;
        } finally {
            lock.unlock();
        }
    }

    /**
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    public int drainTo(Collection<? super E> c, int maxElements) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        if (maxElements <= 0)
            return 0;
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            int n = 0;
            for (E e; n < maxElements && (e = peekExpired()) != null;) {
                c.add(e);       // In this order, in case add() throws.
                q.poll();
                ++n;
            }
            return n;
        } finally {
            lock.unlock();
        }
    }

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

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

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

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

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

    /**
     * Identity-based version for use in Itr.remove
     */
    void removeEQ(Object o) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
                if (o == it.next()) {
                    it.remove();
                    break;
                }
            }
        } finally {
            lock.unlock();
        }
    }

    /**
     * Returns an iterator over all the elements (both expired and
     * unexpired) in this queue. The iterator does not return the
     * elements in any particular order.
     *
     * <p>The returned iterator is
     * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
     *
     * @return an iterator over the elements in this queue
     */
    public Iterator<E> iterator() {
        return new Itr(toArray());
    }

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

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

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

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

        public void remove() {
            if (lastRet < 0)
                throw new IllegalStateException();
            removeEQ(array[lastRet]);
            lastRet = -1;
        }
    }

}
Revision:	1.67
Committed:	Tue Dec 2 05:48:28 2014 UTC (9 years, 6 months ago) by jsr166
Branch:	MAIN
Changes since 1.66:	+1 -1 lines
Log Message:	this collection => this XXX
#	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	jsr166	1.52	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.2	*/
6
7	tim	1.1	package java.util.concurrent;
8	jsr166	1.56	import static java.util.concurrent.TimeUnit.NANOSECONDS;
9			import java.util.concurrent.locks.Condition;
10			import java.util.concurrent.locks.ReentrantLock;
11	tim	1.1	import java.util.*;
12
13			/**
14	dl	1.27	* An unbounded {@linkplain BlockingQueue blocking queue} of
15	jsr166	1.61	* {@code Delayed} elements, in which an element can only be taken
16	dl	1.27	* when its delay has expired. The <em>head</em> of the queue is that
17	jsr166	1.61	* {@code Delayed} element whose delay expired furthest in the
18			* past. If no delay has expired there is no head and {@code poll}
19			* will return {@code null}. Expiration occurs when an element's
20			* {@code getDelay(TimeUnit.NANOSECONDS)} method returns a value less
21	dl	1.36	* than or equal to zero. Even though unexpired elements cannot be
22	jsr166	1.61	* removed using {@code take} or {@code poll}, they are otherwise
23			* treated as normal elements. For example, the {@code size} method
24	dl	1.36	* 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	dl	1.53	* Iterator} interfaces. The Iterator provided in method {@link
30			* #iterator()} is <em>not</em> guaranteed to traverse the elements of
31			* the DelayQueue in any particular order.
32	dl	1.26	*
33	dl	1.25	* <p>This class is a member of the
34	jsr166	1.46	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
35	dl	1.25	* Java Collections Framework</a>.
36			*
37	dl	1.4	* @since 1.5
38			* @author Doug Lea
39	jsr166	1.67	* @param <E> the type of elements held in this queue
40	dl	1.19	*/
41	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
42			implements BlockingQueue<E> {
43	tim	1.6
44	jsr166	1.62	private final transient ReentrantLock lock = new ReentrantLock();
45	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
46	tim	1.1
47	dl	1.4	/**
48	jsr166	1.48	* Thread designated to wait for the element at the head of
49			* the queue. This variant of the Leader-Follower pattern
50			* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
51			* minimize unnecessary timed waiting. When a thread becomes
52			* the leader, it waits only for the next delay to elapse, but
53			* other threads await indefinitely. The leader thread must
54			* signal some other thread before returning from take() or
55			* poll(...), unless some other thread becomes leader in the
56			* interim. Whenever the head of the queue is replaced with
57			* an element with an earlier expiration time, the leader
58			* field is invalidated by being reset to null, and some
59			* waiting thread, but not necessarily the current leader, is
60			* signalled. So waiting threads must be prepared to acquire
61			* and lose leadership while waiting.
62			*/
63	jsr166	1.66	private Thread leader;
64	jsr166	1.48
65			/**
66			* Condition signalled when a newer element becomes available
67			* at the head of the queue or a new thread may need to
68			* become leader.
69			*/
70			private final Condition available = lock.newCondition();
71
72			/**
73	jsr166	1.61	* Creates a new {@code DelayQueue} that is initially empty.
74	dl	1.4	*/
75	tim	1.1	public DelayQueue() {}
76
77	tim	1.6	/**
78	jsr166	1.61	* Creates a {@code DelayQueue} initially containing the elements of the
79	dholmes	1.7	* given collection of {@link Delayed} instances.
80			*
81	jsr166	1.32	* @param c the collection of elements to initially contain
82			* @throws NullPointerException if the specified collection or any
83			* of its elements are null
84	tim	1.6	*/
85			public DelayQueue(Collection<? extends E> c) {
86			this.addAll(c);
87			}
88
89	dholmes	1.7	/**
90	dl	1.16	* Inserts the specified element into this delay queue.
91	dholmes	1.7	*
92	jsr166	1.30	* @param e the element to add
93	jsr166	1.61	* @return {@code true} (as specified by {@link Collection#add})
94	jsr166	1.32	* @throws NullPointerException if the specified element is null
95			*/
96			public boolean add(E e) {
97			return offer(e);
98			}
99
100			/**
101			* Inserts the specified element into this delay queue.
102			*
103			* @param e the element to add
104	jsr166	1.61	* @return {@code true}
105	jsr166	1.32	* @throws NullPointerException if the specified element is null
106	dholmes	1.7	*/
107	jsr166	1.30	public boolean offer(E e) {
108	dl	1.21	final ReentrantLock lock = this.lock;
109	dl	1.2	lock.lock();
110			try {
111	jsr166	1.30	q.offer(e);
112	jsr166	1.48	if (q.peek() == e) {
113	jsr166	1.49	leader = null;
114	jsr166	1.48	available.signal();
115	jsr166	1.49	}
116	dl	1.2	return true;
117	tim	1.13	} finally {
118	dl	1.2	lock.unlock();
119			}
120			}
121
122	dholmes	1.7	/**
123	jsr166	1.32	* Inserts the specified element into this delay queue. As the queue is
124	dholmes	1.7	* unbounded this method will never block.
125	jsr166	1.32	*
126	jsr166	1.30	* @param e the element to add
127	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
128	dholmes	1.7	*/
129	jsr166	1.30	public void put(E e) {
130			offer(e);
131	dl	1.2	}
132
133	dholmes	1.7	/**
134	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
135	dholmes	1.7	* unbounded this method will never block.
136	jsr166	1.32	*
137	jsr166	1.30	* @param e the element to add
138	dl	1.14	* @param timeout This parameter is ignored as the method never blocks
139	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
140	jsr166	1.61	* @return {@code true}
141	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
142	dholmes	1.7	*/
143	jsr166	1.30	public boolean offer(E e, long timeout, TimeUnit unit) {
144			return offer(e);
145	dl	1.2	}
146
147	dholmes	1.7	/**
148	jsr166	1.61	* Retrieves and removes the head of this queue, or returns {@code null}
149	jsr166	1.32	* if this queue has no elements with an expired delay.
150	dholmes	1.7	*
151	jsr166	1.61	* @return the head of this queue, or {@code null} if this
152	jsr166	1.32	* queue has no elements with an expired delay
153	dholmes	1.7	*/
154	jsr166	1.32	public E poll() {
155			final ReentrantLock lock = this.lock;
156			lock.lock();
157			try {
158			E first = q.peek();
159	jsr166	1.56	if (first == null \|\| first.getDelay(NANOSECONDS) > 0)
160	jsr166	1.32	return null;
161	jsr166	1.48	else
162			return q.poll();
163	jsr166	1.32	} finally {
164			lock.unlock();
165			}
166	dl	1.2	}
167
168	dl	1.27	/**
169	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
170			* until an element with an expired delay is available on this queue.
171			*
172	dl	1.27	* @return the head of this queue
173	jsr166	1.32	* @throws InterruptedException {@inheritDoc}
174	dl	1.27	*/
175	dl	1.3	public E take() throws InterruptedException {
176	dl	1.21	final ReentrantLock lock = this.lock;
177	dl	1.2	lock.lockInterruptibly();
178			try {
179			for (;;) {
180	dl	1.3	E first = q.peek();
181	jsr166	1.48	if (first == null)
182	dl	1.4	available.await();
183	jsr166	1.49	else {
184	jsr166	1.56	long delay = first.getDelay(NANOSECONDS);
185	jsr166	1.49	if (delay <= 0)
186			return q.poll();
187	jsr166	1.64	first = null; // don't retain ref while waiting
188			if (leader != null)
189	jsr166	1.49	available.await();
190			else {
191			Thread thisThread = Thread.currentThread();
192			leader = thisThread;
193			try {
194			available.awaitNanos(delay);
195			} finally {
196			if (leader == thisThread)
197			leader = null;
198			}
199	dl	1.2	}
200			}
201			}
202	tim	1.13	} finally {
203	jsr166	1.49	if (leader == null && q.peek() != null)
204			available.signal();
205	dl	1.2	lock.unlock();
206			}
207			}
208
209	dl	1.27	/**
210	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
211			* until an element with an expired delay is available on this queue,
212			* or the specified wait time expires.
213			*
214	jsr166	1.61	* @return the head of this queue, or {@code null} if the
215	jsr166	1.32	* specified waiting time elapses before an element with
216			* an expired delay becomes available
217			* @throws InterruptedException {@inheritDoc}
218	dl	1.27	*/
219			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
220	jsr166	1.41	long nanos = unit.toNanos(timeout);
221	dl	1.21	final ReentrantLock lock = this.lock;
222	dl	1.2	lock.lockInterruptibly();
223			try {
224			for (;;) {
225	dl	1.3	E first = q.peek();
226	dl	1.2	if (first == null) {
227			if (nanos <= 0)
228			return null;
229			else
230	dl	1.4	nanos = available.awaitNanos(nanos);
231	tim	1.13	} else {
232	jsr166	1.56	long delay = first.getDelay(NANOSECONDS);
233	jsr166	1.49	if (delay <= 0)
234			return q.poll();
235			if (nanos <= 0)
236			return null;
237	jsr166	1.64	first = null; // don't retain ref while waiting
238	jsr166	1.49	if (nanos < delay \|\| leader != null)
239			nanos = available.awaitNanos(nanos);
240			else {
241			Thread thisThread = Thread.currentThread();
242			leader = thisThread;
243			try {
244			long timeLeft = available.awaitNanos(delay);
245			nanos -= delay - timeLeft;
246			} finally {
247			if (leader == thisThread)
248			leader = null;
249			}
250			}
251	dl	1.2	}
252			}
253	tim	1.13	} finally {
254	jsr166	1.49	if (leader == null && q.peek() != null)
255			available.signal();
256	dl	1.2	lock.unlock();
257			}
258			}
259
260	dl	1.27	/**
261	dl	1.36	* Retrieves, but does not remove, the head of this queue, or
262	jsr166	1.61	* returns {@code null} if this queue is empty. Unlike
263			* {@code poll}, if no expired elements are available in the queue,
264	dl	1.36	* this method returns the element that will expire next,
265			* if one exists.
266	dl	1.27	*
267	jsr166	1.61	* @return the head of this queue, or {@code null} if this
268	jsr166	1.63	* queue is empty
269	dl	1.27	*/
270	dl	1.3	public E peek() {
271	dl	1.21	final ReentrantLock lock = this.lock;
272	dl	1.2	lock.lock();
273			try {
274			return q.peek();
275	tim	1.13	} finally {
276	dl	1.2	lock.unlock();
277			}
278	tim	1.1	}
279
280	dl	1.2	public int size() {
281	dl	1.21	final ReentrantLock lock = this.lock;
282	dl	1.2	lock.lock();
283			try {
284			return q.size();
285	tim	1.13	} finally {
286	dl	1.2	lock.unlock();
287			}
288			}
289
290	jsr166	1.32	/**
291	jsr166	1.59	* Returns first element only if it is expired.
292	jsr166	1.56	* Used only by drainTo. Call only when holding lock.
293			*/
294			private E peekExpired() {
295			// assert lock.isHeldByCurrentThread();
296			E first = q.peek();
297			return (first == null \|\| first.getDelay(NANOSECONDS) > 0) ?
298			null : first;
299			}
300
301			/**
302	jsr166	1.32	* @throws UnsupportedOperationException {@inheritDoc}
303			* @throws ClassCastException {@inheritDoc}
304			* @throws NullPointerException {@inheritDoc}
305			* @throws IllegalArgumentException {@inheritDoc}
306			*/
307	dl	1.17	public int drainTo(Collection<? super E> c) {
308			if (c == null)
309			throw new NullPointerException();
310			if (c == this)
311			throw new IllegalArgumentException();
312	dl	1.21	final ReentrantLock lock = this.lock;
313	dl	1.17	lock.lock();
314			try {
315			int n = 0;
316	jsr166	1.56	for (E e; (e = peekExpired()) != null;) {
317			c.add(e); // In this order, in case add() throws.
318			q.poll();
319	dl	1.17	++n;
320			}
321			return n;
322			} finally {
323			lock.unlock();
324			}
325			}
326
327	jsr166	1.32	/**
328			* @throws UnsupportedOperationException {@inheritDoc}
329			* @throws ClassCastException {@inheritDoc}
330			* @throws NullPointerException {@inheritDoc}
331			* @throws IllegalArgumentException {@inheritDoc}
332			*/
333	dl	1.17	public int drainTo(Collection<? super E> c, int maxElements) {
334			if (c == null)
335			throw new NullPointerException();
336			if (c == this)
337			throw new IllegalArgumentException();
338			if (maxElements <= 0)
339			return 0;
340	dl	1.21	final ReentrantLock lock = this.lock;
341	dl	1.17	lock.lock();
342			try {
343			int n = 0;
344	jsr166	1.56	for (E e; n < maxElements && (e = peekExpired()) != null;) {
345			c.add(e); // In this order, in case add() throws.
346			q.poll();
347	dl	1.17	++n;
348			}
349			return n;
350			} finally {
351			lock.unlock();
352			}
353			}
354
355	dholmes	1.7	/**
356			* Atomically removes all of the elements from this delay queue.
357			* The queue will be empty after this call returns.
358	jsr166	1.32	* Elements with an unexpired delay are not waited for; they are
359			* simply discarded from the queue.
360	dholmes	1.7	*/
361	dl	1.2	public void clear() {
362	dl	1.21	final ReentrantLock lock = this.lock;
363	dl	1.2	lock.lock();
364			try {
365			q.clear();
366	tim	1.13	} finally {
367	dl	1.2	lock.unlock();
368			}
369			}
370	tim	1.1
371	dholmes	1.7	/**
372	jsr166	1.61	* Always returns {@code Integer.MAX_VALUE} because
373			* a {@code DelayQueue} is not capacity constrained.
374	jsr166	1.32	*
375	jsr166	1.61	* @return {@code Integer.MAX_VALUE}
376	dholmes	1.7	*/
377	dl	1.2	public int remainingCapacity() {
378			return Integer.MAX_VALUE;
379	tim	1.1	}
380	dl	1.2
381	jsr166	1.32	/**
382			* Returns an array containing all of the elements in this queue.
383			* The returned array elements are in no particular order.
384			*
385			* <p>The returned array will be "safe" in that no references to it are
386			* maintained by this queue. (In other words, this method must allocate
387			* a new array). The caller is thus free to modify the returned array.
388	jsr166	1.33	*
389	jsr166	1.32	* <p>This method acts as bridge between array-based and collection-based
390			* APIs.
391			*
392			* @return an array containing all of the elements in this queue
393			*/
394	dl	1.2	public Object[] toArray() {
395	dl	1.21	final ReentrantLock lock = this.lock;
396	dl	1.2	lock.lock();
397			try {
398			return q.toArray();
399	tim	1.13	} finally {
400	dl	1.2	lock.unlock();
401			}
402	tim	1.1	}
403	dl	1.2
404	jsr166	1.32	/**
405			* Returns an array containing all of the elements in this queue; the
406			* runtime type of the returned array is that of the specified array.
407			* The returned array elements are in no particular order.
408			* If the queue fits in the specified array, it is returned therein.
409			* Otherwise, a new array is allocated with the runtime type of the
410			* specified array and the size of this queue.
411			*
412			* <p>If this queue fits in the specified array with room to spare
413			* (i.e., the array has more elements than this queue), the element in
414			* the array immediately following the end of the queue is set to
415	jsr166	1.61	* {@code null}.
416	jsr166	1.32	*
417			* <p>Like the {@link #toArray()} method, this method acts as bridge between
418			* array-based and collection-based APIs. Further, this method allows
419			* precise control over the runtime type of the output array, and may,
420			* under certain circumstances, be used to save allocation costs.
421			*
422	jsr166	1.37	* <p>The following code can be used to dump a delay queue into a newly
423	jsr166	1.61	* allocated array of {@code Delayed}:
424	jsr166	1.32	*
425	jsr166	1.55	* <pre> {@code Delayed[] a = q.toArray(new Delayed[0]);}</pre>
426	jsr166	1.32	*
427	jsr166	1.61	* Note that {@code toArray(new Object[0])} is identical in function to
428			* {@code toArray()}.
429	jsr166	1.32	*
430			* @param a the array into which the elements of the queue are to
431			* be stored, if it is big enough; otherwise, a new array of the
432			* same runtime type is allocated for this purpose
433			* @return an array containing all of the elements in this queue
434			* @throws ArrayStoreException if the runtime type of the specified array
435			* is not a supertype of the runtime type of every element in
436			* this queue
437			* @throws NullPointerException if the specified array is null
438			*/
439			public <T> T[] toArray(T[] a) {
440	dl	1.21	final ReentrantLock lock = this.lock;
441	dl	1.2	lock.lock();
442			try {
443	jsr166	1.32	return q.toArray(a);
444	tim	1.13	} finally {
445	dl	1.2	lock.unlock();
446			}
447	tim	1.1	}
448
449	dl	1.26	/**
450			* Removes a single instance of the specified element from this
451	dl	1.36	* queue, if it is present, whether or not it has expired.
452	dl	1.26	*/
453	dholmes	1.7	public boolean remove(Object o) {
454	dl	1.21	final ReentrantLock lock = this.lock;
455	dl	1.2	lock.lock();
456			try {
457	dholmes	1.7	return q.remove(o);
458	tim	1.13	} finally {
459	dl	1.2	lock.unlock();
460			}
461			}
462
463	dholmes	1.7	/**
464	jsr166	1.57	* Identity-based version for use in Itr.remove
465			*/
466			void removeEQ(Object o) {
467			final ReentrantLock lock = this.lock;
468			lock.lock();
469			try {
470			for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
471			if (o == it.next()) {
472			it.remove();
473			break;
474			}
475			}
476			} finally {
477			lock.unlock();
478			}
479			}
480
481			/**
482	dl	1.36	* Returns an iterator over all the elements (both expired and
483	dl	1.44	* unexpired) in this queue. The iterator does not return the
484	jsr166	1.51	* elements in any particular order.
485			*
486	jsr166	1.65	* <p>The returned iterator is
487			* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
488	dholmes	1.7	*
489	jsr166	1.32	* @return an iterator over the elements in this queue
490	dholmes	1.7	*/
491	dl	1.3	public Iterator<E> iterator() {
492	dl	1.44	return new Itr(toArray());
493	dl	1.2	}
494
495	dl	1.42	/**
496			* Snapshot iterator that works off copy of underlying q array.
497			*/
498	dl	1.44	private class Itr implements Iterator<E> {
499	dl	1.42	final Object[] array; // Array of all elements
500	jsr166	1.57	int cursor; // index of next element to return
501	jsr166	1.49	int lastRet; // index of last element, or -1 if no such
502	jsr166	1.43
503	dl	1.42	Itr(Object[] array) {
504			lastRet = -1;
505			this.array = array;
506	dl	1.2	}
507
508	tim	1.6	public boolean hasNext() {
509	dl	1.42	return cursor < array.length;
510	tim	1.6	}
511
512	jsr166	1.49	@SuppressWarnings("unchecked")
513	tim	1.6	public E next() {
514	dl	1.42	if (cursor >= array.length)
515			throw new NoSuchElementException();
516			lastRet = cursor;
517			return (E)array[cursor++];
518	tim	1.6	}
519
520			public void remove() {
521	jsr166	1.43	if (lastRet < 0)
522	jsr166	1.49	throw new IllegalStateException();
523	jsr166	1.57	removeEQ(array[lastRet]);
524	dl	1.42	lastRet = -1;
525	tim	1.6	}
526	tim	1.1	}
527
528			}