util/concurrent/DelayQueue.java

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

package java.util.concurrent;

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

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

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

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

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

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

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

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

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

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

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

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

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

    /**
     * Retrieves and removes the head of this queue, waiting if necessary
     * until an element with an expired delay is available on this queue.
     *
     * @return the head of this queue
     * @throws InterruptedException {@inheritDoc}
     */
    public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            for (;;) {
                E first = q.peek();
                if (first == null)
                    available.await();
                else {
                    long delay = first.getDelay(NANOSECONDS);
                    if (delay <= 0L)
                        return q.poll();
                    first = null; // don't retain ref while waiting
                    if (leader != null)
                        available.await();
                    else {
                        Thread thisThread = Thread.currentThread();
                        leader = thisThread;
                        try {
                            available.awaitNanos(delay);
                        } finally {
                            if (leader == thisThread)
                                leader = null;
                        }
                    }
                }
            }
        } finally {
            if (leader == null && q.peek() != null)
                available.signal();
            lock.unlock();
        }
    }

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

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

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

    /**
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    public int drainTo(Collection<? super E> c) {
        return drainTo(c, Integer.MAX_VALUE);
    }

    /**
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    public int drainTo(Collection<? super E> c, int maxElements) {
        Objects.requireNonNull(c);
        if (c == this)
            throw new IllegalArgumentException();
        if (maxElements <= 0)
            return 0;
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            int n = 0;
            for (E first;
                 n < maxElements
                     && (first = q.peek()) != null
                     && first.getDelay(NANOSECONDS) <= 0;) {
                c.add(first);   // 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();
            return (E)array[lastRet = cursor++];
        }

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

}
Revision:	1.77
Committed:	Sat May 6 06:49:46 2017 UTC (7 years ago) by jsr166
Branch:	MAIN
Changes since 1.76:	+1 -1 lines
Log Message:	8177789: fix collections framework links to point to java.util package doc
#	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	1.68
9	jsr166	1.56	import static java.util.concurrent.TimeUnit.NANOSECONDS;
10	jsr166	1.69
11	jsr166	1.68	import java.util.AbstractQueue;
12			import java.util.Collection;
13			import java.util.Iterator;
14			import java.util.NoSuchElementException;
15	jsr166	1.74	import java.util.Objects;
16	jsr166	1.68	import java.util.PriorityQueue;
17	jsr166	1.69	import java.util.concurrent.locks.Condition;
18			import java.util.concurrent.locks.ReentrantLock;
19	tim	1.1
20			/**
21	dl	1.27	* An unbounded {@linkplain BlockingQueue blocking queue} of
22	jsr166	1.61	* {@code Delayed} elements, in which an element can only be taken
23	dl	1.27	* when its delay has expired. The <em>head</em> of the queue is that
24	jsr166	1.61	* {@code Delayed} element whose delay expired furthest in the
25			* past. If no delay has expired there is no head and {@code poll}
26			* will return {@code null}. Expiration occurs when an element's
27			* {@code getDelay(TimeUnit.NANOSECONDS)} method returns a value less
28	dl	1.36	* than or equal to zero. Even though unexpired elements cannot be
29	jsr166	1.61	* removed using {@code take} or {@code poll}, they are otherwise
30			* treated as normal elements. For example, the {@code size} method
31	dl	1.36	* returns the count of both expired and unexpired elements.
32	jsr166	1.39	* This queue does not permit null elements.
33	dl	1.25	*
34	jsr166	1.75	* <p>This class and its iterator implement all of the <em>optional</em>
35			* methods of the {@link Collection} and {@link Iterator} interfaces.
36			* The Iterator provided in method {@link #iterator()} is <em>not</em>
37			* guaranteed to traverse the elements of the DelayQueue in any
38			* particular order.
39	dl	1.26	*
40	dl	1.25	* <p>This class is a member of the
41	jsr166	1.77	* <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
42	dl	1.25	* Java Collections Framework</a>.
43			*
44	dl	1.4	* @since 1.5
45			* @author Doug Lea
46	jsr166	1.67	* @param <E> the type of elements held in this queue
47	dl	1.19	*/
48	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
49			implements BlockingQueue<E> {
50	tim	1.6
51	jsr166	1.62	private final transient ReentrantLock lock = new ReentrantLock();
52	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
53	tim	1.1
54	dl	1.4	/**
55	jsr166	1.48	* Thread designated to wait for the element at the head of
56			* the queue. This variant of the Leader-Follower pattern
57			* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
58			* minimize unnecessary timed waiting. When a thread becomes
59			* the leader, it waits only for the next delay to elapse, but
60			* other threads await indefinitely. The leader thread must
61			* signal some other thread before returning from take() or
62			* poll(...), unless some other thread becomes leader in the
63			* interim. Whenever the head of the queue is replaced with
64			* an element with an earlier expiration time, the leader
65			* field is invalidated by being reset to null, and some
66			* waiting thread, but not necessarily the current leader, is
67			* signalled. So waiting threads must be prepared to acquire
68			* and lose leadership while waiting.
69			*/
70	jsr166	1.66	private Thread leader;
71	jsr166	1.48
72			/**
73			* Condition signalled when a newer element becomes available
74			* at the head of the queue or a new thread may need to
75			* become leader.
76			*/
77			private final Condition available = lock.newCondition();
78
79			/**
80	jsr166	1.61	* Creates a new {@code DelayQueue} that is initially empty.
81	dl	1.4	*/
82	tim	1.1	public DelayQueue() {}
83
84	tim	1.6	/**
85	jsr166	1.61	* Creates a {@code DelayQueue} initially containing the elements of the
86	dholmes	1.7	* given collection of {@link Delayed} instances.
87			*
88	jsr166	1.32	* @param c the collection of elements to initially contain
89			* @throws NullPointerException if the specified collection or any
90			* of its elements are null
91	tim	1.6	*/
92			public DelayQueue(Collection<? extends E> c) {
93			this.addAll(c);
94			}
95
96	dholmes	1.7	/**
97	dl	1.16	* Inserts the specified element into this delay queue.
98	dholmes	1.7	*
99	jsr166	1.30	* @param e the element to add
100	jsr166	1.61	* @return {@code true} (as specified by {@link Collection#add})
101	jsr166	1.32	* @throws NullPointerException if the specified element is null
102			*/
103			public boolean add(E e) {
104			return offer(e);
105			}
106
107			/**
108			* Inserts the specified element into this delay queue.
109			*
110			* @param e the element to add
111	jsr166	1.61	* @return {@code true}
112	jsr166	1.32	* @throws NullPointerException if the specified element is null
113	dholmes	1.7	*/
114	jsr166	1.30	public boolean offer(E e) {
115	dl	1.21	final ReentrantLock lock = this.lock;
116	dl	1.2	lock.lock();
117			try {
118	jsr166	1.30	q.offer(e);
119	jsr166	1.48	if (q.peek() == e) {
120	jsr166	1.49	leader = null;
121	jsr166	1.48	available.signal();
122	jsr166	1.49	}
123	dl	1.2	return true;
124	tim	1.13	} finally {
125	dl	1.2	lock.unlock();
126			}
127			}
128
129	dholmes	1.7	/**
130	jsr166	1.32	* Inserts the specified element into this delay queue. As the queue is
131	dholmes	1.7	* unbounded this method will never block.
132	jsr166	1.32	*
133	jsr166	1.30	* @param e the element to add
134	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
135	dholmes	1.7	*/
136	jsr166	1.30	public void put(E e) {
137			offer(e);
138	dl	1.2	}
139
140	dholmes	1.7	/**
141	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
142	dholmes	1.7	* unbounded this method will never block.
143	jsr166	1.32	*
144	jsr166	1.30	* @param e the element to add
145	dl	1.14	* @param timeout This parameter is ignored as the method never blocks
146	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
147	jsr166	1.61	* @return {@code true}
148	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
149	dholmes	1.7	*/
150	jsr166	1.30	public boolean offer(E e, long timeout, TimeUnit unit) {
151			return offer(e);
152	dl	1.2	}
153
154	dholmes	1.7	/**
155	jsr166	1.61	* Retrieves and removes the head of this queue, or returns {@code null}
156	jsr166	1.32	* if this queue has no elements with an expired delay.
157	dholmes	1.7	*
158	jsr166	1.61	* @return the head of this queue, or {@code null} if this
159	jsr166	1.32	* queue has no elements with an expired delay
160	dholmes	1.7	*/
161	jsr166	1.32	public E poll() {
162			final ReentrantLock lock = this.lock;
163			lock.lock();
164			try {
165			E first = q.peek();
166	jsr166	1.70	return (first == null \|\| first.getDelay(NANOSECONDS) > 0)
167			? null
168			: q.poll();
169	jsr166	1.32	} finally {
170			lock.unlock();
171			}
172	dl	1.2	}
173
174	dl	1.27	/**
175	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
176			* until an element with an expired delay is available on this queue.
177			*
178	dl	1.27	* @return the head of this queue
179	jsr166	1.32	* @throws InterruptedException {@inheritDoc}
180	dl	1.27	*/
181	dl	1.3	public E take() throws InterruptedException {
182	dl	1.21	final ReentrantLock lock = this.lock;
183	dl	1.2	lock.lockInterruptibly();
184			try {
185			for (;;) {
186	dl	1.3	E first = q.peek();
187	jsr166	1.48	if (first == null)
188	dl	1.4	available.await();
189	jsr166	1.49	else {
190	jsr166	1.56	long delay = first.getDelay(NANOSECONDS);
191	jsr166	1.72	if (delay <= 0L)
192	jsr166	1.49	return q.poll();
193	jsr166	1.64	first = null; // don't retain ref while waiting
194			if (leader != null)
195	jsr166	1.49	available.await();
196			else {
197			Thread thisThread = Thread.currentThread();
198			leader = thisThread;
199			try {
200			available.awaitNanos(delay);
201			} finally {
202			if (leader == thisThread)
203			leader = null;
204			}
205	dl	1.2	}
206			}
207			}
208	tim	1.13	} finally {
209	jsr166	1.49	if (leader == null && q.peek() != null)
210			available.signal();
211	dl	1.2	lock.unlock();
212			}
213			}
214
215	dl	1.27	/**
216	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
217			* until an element with an expired delay is available on this queue,
218			* or the specified wait time expires.
219			*
220	jsr166	1.61	* @return the head of this queue, or {@code null} if the
221	jsr166	1.32	* specified waiting time elapses before an element with
222			* an expired delay becomes available
223			* @throws InterruptedException {@inheritDoc}
224	dl	1.27	*/
225			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
226	jsr166	1.41	long nanos = unit.toNanos(timeout);
227	dl	1.21	final ReentrantLock lock = this.lock;
228	dl	1.2	lock.lockInterruptibly();
229			try {
230			for (;;) {
231	dl	1.3	E first = q.peek();
232	dl	1.2	if (first == null) {
233	jsr166	1.72	if (nanos <= 0L)
234	dl	1.2	return null;
235			else
236	dl	1.4	nanos = available.awaitNanos(nanos);
237	tim	1.13	} else {
238	jsr166	1.56	long delay = first.getDelay(NANOSECONDS);
239	jsr166	1.72	if (delay <= 0L)
240	jsr166	1.49	return q.poll();
241	jsr166	1.72	if (nanos <= 0L)
242	jsr166	1.49	return null;
243	jsr166	1.64	first = null; // don't retain ref while waiting
244	jsr166	1.49	if (nanos < delay \|\| leader != null)
245			nanos = available.awaitNanos(nanos);
246			else {
247			Thread thisThread = Thread.currentThread();
248			leader = thisThread;
249			try {
250			long timeLeft = available.awaitNanos(delay);
251			nanos -= delay - timeLeft;
252			} finally {
253			if (leader == thisThread)
254			leader = null;
255			}
256			}
257	dl	1.2	}
258			}
259	tim	1.13	} finally {
260	jsr166	1.49	if (leader == null && q.peek() != null)
261			available.signal();
262	dl	1.2	lock.unlock();
263			}
264			}
265
266	dl	1.27	/**
267	dl	1.36	* Retrieves, but does not remove, the head of this queue, or
268	jsr166	1.61	* returns {@code null} if this queue is empty. Unlike
269			* {@code poll}, if no expired elements are available in the queue,
270	dl	1.36	* this method returns the element that will expire next,
271			* if one exists.
272	dl	1.27	*
273	jsr166	1.61	* @return the head of this queue, or {@code null} if this
274	jsr166	1.63	* queue is empty
275	dl	1.27	*/
276	dl	1.3	public E peek() {
277	dl	1.21	final ReentrantLock lock = this.lock;
278	dl	1.2	lock.lock();
279			try {
280			return q.peek();
281	tim	1.13	} finally {
282	dl	1.2	lock.unlock();
283			}
284	tim	1.1	}
285
286	dl	1.2	public int size() {
287	dl	1.21	final ReentrantLock lock = this.lock;
288	dl	1.2	lock.lock();
289			try {
290			return q.size();
291	tim	1.13	} finally {
292	dl	1.2	lock.unlock();
293			}
294			}
295
296	jsr166	1.32	/**
297			* @throws UnsupportedOperationException {@inheritDoc}
298			* @throws ClassCastException {@inheritDoc}
299			* @throws NullPointerException {@inheritDoc}
300			* @throws IllegalArgumentException {@inheritDoc}
301			*/
302	dl	1.17	public int drainTo(Collection<? super E> c) {
303	jsr166	1.76	return drainTo(c, Integer.MAX_VALUE);
304	dl	1.17	}
305
306	jsr166	1.32	/**
307			* @throws UnsupportedOperationException {@inheritDoc}
308			* @throws ClassCastException {@inheritDoc}
309			* @throws NullPointerException {@inheritDoc}
310			* @throws IllegalArgumentException {@inheritDoc}
311			*/
312	dl	1.17	public int drainTo(Collection<? super E> c, int maxElements) {
313	jsr166	1.74	Objects.requireNonNull(c);
314	dl	1.17	if (c == this)
315			throw new IllegalArgumentException();
316			if (maxElements <= 0)
317			return 0;
318	dl	1.21	final ReentrantLock lock = this.lock;
319	dl	1.17	lock.lock();
320			try {
321			int n = 0;
322	jsr166	1.76	for (E first;
323			n < maxElements
324			&& (first = q.peek()) != null
325			&& first.getDelay(NANOSECONDS) <= 0;) {
326			c.add(first); // In this order, in case add() throws.
327	jsr166	1.56	q.poll();
328	dl	1.17	++n;
329			}
330			return n;
331			} finally {
332			lock.unlock();
333			}
334			}
335
336	dholmes	1.7	/**
337			* Atomically removes all of the elements from this delay queue.
338			* The queue will be empty after this call returns.
339	jsr166	1.32	* Elements with an unexpired delay are not waited for; they are
340			* simply discarded from the queue.
341	dholmes	1.7	*/
342	dl	1.2	public void clear() {
343	dl	1.21	final ReentrantLock lock = this.lock;
344	dl	1.2	lock.lock();
345			try {
346			q.clear();
347	tim	1.13	} finally {
348	dl	1.2	lock.unlock();
349			}
350			}
351	tim	1.1
352	dholmes	1.7	/**
353	jsr166	1.61	* Always returns {@code Integer.MAX_VALUE} because
354			* a {@code DelayQueue} is not capacity constrained.
355	jsr166	1.32	*
356	jsr166	1.61	* @return {@code Integer.MAX_VALUE}
357	dholmes	1.7	*/
358	dl	1.2	public int remainingCapacity() {
359			return Integer.MAX_VALUE;
360	tim	1.1	}
361	dl	1.2
362	jsr166	1.32	/**
363			* Returns an array containing all of the elements in this queue.
364			* The returned array elements are in no particular order.
365			*
366			* <p>The returned array will be "safe" in that no references to it are
367			* maintained by this queue. (In other words, this method must allocate
368			* a new array). The caller is thus free to modify the returned array.
369	jsr166	1.33	*
370	jsr166	1.32	* <p>This method acts as bridge between array-based and collection-based
371			* APIs.
372			*
373			* @return an array containing all of the elements in this queue
374			*/
375	dl	1.2	public Object[] toArray() {
376	dl	1.21	final ReentrantLock lock = this.lock;
377	dl	1.2	lock.lock();
378			try {
379			return q.toArray();
380	tim	1.13	} finally {
381	dl	1.2	lock.unlock();
382			}
383	tim	1.1	}
384	dl	1.2
385	jsr166	1.32	/**
386			* Returns an array containing all of the elements in this queue; the
387			* runtime type of the returned array is that of the specified array.
388			* The returned array elements are in no particular order.
389			* If the queue fits in the specified array, it is returned therein.
390			* Otherwise, a new array is allocated with the runtime type of the
391			* specified array and the size of this queue.
392			*
393			* <p>If this queue fits in the specified array with room to spare
394			* (i.e., the array has more elements than this queue), the element in
395			* the array immediately following the end of the queue is set to
396	jsr166	1.61	* {@code null}.
397	jsr166	1.32	*
398			* <p>Like the {@link #toArray()} method, this method acts as bridge between
399			* array-based and collection-based APIs. Further, this method allows
400			* precise control over the runtime type of the output array, and may,
401			* under certain circumstances, be used to save allocation costs.
402			*
403	jsr166	1.37	* <p>The following code can be used to dump a delay queue into a newly
404	jsr166	1.61	* allocated array of {@code Delayed}:
405	jsr166	1.32	*
406	jsr166	1.55	* <pre> {@code Delayed[] a = q.toArray(new Delayed[0]);}</pre>
407	jsr166	1.32	*
408	jsr166	1.61	* Note that {@code toArray(new Object[0])} is identical in function to
409			* {@code toArray()}.
410	jsr166	1.32	*
411			* @param a the array into which the elements of the queue are to
412			* be stored, if it is big enough; otherwise, a new array of the
413			* same runtime type is allocated for this purpose
414			* @return an array containing all of the elements in this queue
415			* @throws ArrayStoreException if the runtime type of the specified array
416			* is not a supertype of the runtime type of every element in
417			* this queue
418			* @throws NullPointerException if the specified array is null
419			*/
420			public <T> T[] toArray(T[] a) {
421	dl	1.21	final ReentrantLock lock = this.lock;
422	dl	1.2	lock.lock();
423			try {
424	jsr166	1.32	return q.toArray(a);
425	tim	1.13	} finally {
426	dl	1.2	lock.unlock();
427			}
428	tim	1.1	}
429
430	dl	1.26	/**
431			* Removes a single instance of the specified element from this
432	dl	1.36	* queue, if it is present, whether or not it has expired.
433	dl	1.26	*/
434	dholmes	1.7	public boolean remove(Object o) {
435	dl	1.21	final ReentrantLock lock = this.lock;
436	dl	1.2	lock.lock();
437			try {
438	dholmes	1.7	return q.remove(o);
439	tim	1.13	} finally {
440	dl	1.2	lock.unlock();
441			}
442			}
443
444	dholmes	1.7	/**
445	jsr166	1.71	* Identity-based version for use in Itr.remove.
446	jsr166	1.57	*/
447			void removeEQ(Object o) {
448			final ReentrantLock lock = this.lock;
449			lock.lock();
450			try {
451			for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
452			if (o == it.next()) {
453			it.remove();
454			break;
455			}
456			}
457			} finally {
458			lock.unlock();
459			}
460			}
461
462			/**
463	dl	1.36	* Returns an iterator over all the elements (both expired and
464	dl	1.44	* unexpired) in this queue. The iterator does not return the
465	jsr166	1.51	* elements in any particular order.
466			*
467	jsr166	1.65	* <p>The returned iterator is
468			* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
469	dholmes	1.7	*
470	jsr166	1.32	* @return an iterator over the elements in this queue
471	dholmes	1.7	*/
472	dl	1.3	public Iterator<E> iterator() {
473	dl	1.44	return new Itr(toArray());
474	dl	1.2	}
475
476	dl	1.42	/**
477			* Snapshot iterator that works off copy of underlying q array.
478			*/
479	dl	1.44	private class Itr implements Iterator<E> {
480	dl	1.42	final Object[] array; // Array of all elements
481	jsr166	1.57	int cursor; // index of next element to return
482	jsr166	1.49	int lastRet; // index of last element, or -1 if no such
483	jsr166	1.43
484	dl	1.42	Itr(Object[] array) {
485			lastRet = -1;
486			this.array = array;
487	dl	1.2	}
488
489	tim	1.6	public boolean hasNext() {
490	dl	1.42	return cursor < array.length;
491	tim	1.6	}
492
493	jsr166	1.49	@SuppressWarnings("unchecked")
494	tim	1.6	public E next() {
495	dl	1.42	if (cursor >= array.length)
496			throw new NoSuchElementException();
497	jsr166	1.73	return (E)array[lastRet = cursor++];
498	tim	1.6	}
499
500			public void remove() {
501	jsr166	1.43	if (lastRet < 0)
502	jsr166	1.49	throw new IllegalStateException();
503	jsr166	1.57	removeEQ(array[lastRet]);
504	dl	1.42	lastRet = -1;
505	tim	1.6	}
506	tim	1.1	}
507
508			}