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
 * <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.  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 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(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();
                    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(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();
        }
    }

    /**
     * Return 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 <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> {@code 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();
        }
    }

    /**
     * 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 "weakly consistent" iterator that
     * will never throw {@link java.util.ConcurrentModificationException
     * 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();
            removeEQ(array[lastRet]);
            lastRet = -1;
        }
    }

}
Revision:	1.57
Committed:	Sun Jul 3 06:04:06 2011 UTC (12 years, 11 months ago) by jsr166
Branch:	MAIN
Changes since 1.56:	+20 -15 lines
Log Message:	Introduce removeEQ as in PriorityBlockingQueue
#	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	jsr166	1.50
8	tim	1.1	package java.util.concurrent;
9	jsr166	1.56	import static java.util.concurrent.TimeUnit.NANOSECONDS;
10			import java.util.concurrent.locks.Condition;
11			import java.util.concurrent.locks.ReentrantLock;
12	tim	1.1	import java.util.*;
13
14			/**
15	dl	1.27	* An unbounded {@linkplain BlockingQueue blocking queue} of
16			* <tt>Delayed</tt> elements, in which an element can only be taken
17			* when its delay has expired. The <em>head</em> of the queue is that
18			* <tt>Delayed</tt> element whose delay expired furthest in the
19	jsr166	1.32	* past. If no delay has expired there is no head and <tt>poll</tt>
20	dl	1.27	* will return <tt>null</tt>. Expiration occurs when an element's
21			* <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less
22	dl	1.36	* than or equal to zero. Even though unexpired elements cannot be
23			* removed using <tt>take</tt> or <tt>poll</tt>, they are otherwise
24			* treated as normal elements. For example, the <tt>size</tt> method
25			* returns the count of both expired and unexpired elements.
26	jsr166	1.39	* This queue does not permit null elements.
27	dl	1.25	*
28	dl	1.26	* <p>This class and its iterator implement all of the
29			* <em>optional</em> methods of the {@link Collection} and {@link
30	dl	1.53	* Iterator} interfaces. The Iterator provided in method {@link
31			* #iterator()} is <em>not</em> guaranteed to traverse the elements of
32			* the DelayQueue in any particular order.
33	dl	1.26	*
34	dl	1.25	* <p>This class is a member of the
35	jsr166	1.46	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
36	dl	1.25	* Java Collections Framework</a>.
37			*
38	dl	1.4	* @since 1.5
39			* @author Doug Lea
40	dl	1.20	* @param <E> the type of elements held in this collection
41	dl	1.19	*/
42	tim	1.1
43	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
44			implements BlockingQueue<E> {
45	tim	1.6
46	dl	1.2	private transient final ReentrantLock lock = new ReentrantLock();
47	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
48	tim	1.1
49	dl	1.4	/**
50	jsr166	1.48	* Thread designated to wait for the element at the head of
51			* the queue. This variant of the Leader-Follower pattern
52			* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
53			* minimize unnecessary timed waiting. When a thread becomes
54			* the leader, it waits only for the next delay to elapse, but
55			* other threads await indefinitely. The leader thread must
56			* signal some other thread before returning from take() or
57			* poll(...), unless some other thread becomes leader in the
58			* interim. Whenever the head of the queue is replaced with
59			* an element with an earlier expiration time, the leader
60			* field is invalidated by being reset to null, and some
61			* waiting thread, but not necessarily the current leader, is
62			* signalled. So waiting threads must be prepared to acquire
63			* and lose leadership while waiting.
64			*/
65			private Thread leader = null;
66
67			/**
68			* Condition signalled when a newer element becomes available
69			* at the head of the queue or a new thread may need to
70			* become leader.
71			*/
72			private final Condition available = lock.newCondition();
73
74			/**
75	dholmes	1.7	* Creates a new <tt>DelayQueue</tt> that is initially empty.
76	dl	1.4	*/
77	tim	1.1	public DelayQueue() {}
78
79	tim	1.6	/**
80	tim	1.9	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
81	dholmes	1.7	* given collection of {@link Delayed} instances.
82			*
83	jsr166	1.32	* @param c the collection of elements to initially contain
84			* @throws NullPointerException if the specified collection or any
85			* of its elements are null
86	tim	1.6	*/
87			public DelayQueue(Collection<? extends E> c) {
88			this.addAll(c);
89			}
90
91	dholmes	1.7	/**
92	dl	1.16	* Inserts the specified element into this delay queue.
93	dholmes	1.7	*
94	jsr166	1.30	* @param e the element to add
95	jsr166	1.38	* @return <tt>true</tt> (as specified by {@link Collection#add})
96	jsr166	1.32	* @throws NullPointerException if the specified element is null
97			*/
98			public boolean add(E e) {
99			return offer(e);
100			}
101
102			/**
103			* Inserts the specified element into this delay queue.
104			*
105			* @param e the element to add
106	dholmes	1.7	* @return <tt>true</tt>
107	jsr166	1.32	* @throws NullPointerException if the specified element is null
108	dholmes	1.7	*/
109	jsr166	1.30	public boolean offer(E e) {
110	dl	1.21	final ReentrantLock lock = this.lock;
111	dl	1.2	lock.lock();
112			try {
113	jsr166	1.30	q.offer(e);
114	jsr166	1.48	if (q.peek() == e) {
115	jsr166	1.49	leader = null;
116	jsr166	1.48	available.signal();
117	jsr166	1.49	}
118	dl	1.2	return true;
119	tim	1.13	} finally {
120	dl	1.2	lock.unlock();
121			}
122			}
123
124	dholmes	1.7	/**
125	jsr166	1.32	* Inserts the specified element into this delay queue. As the queue is
126	dholmes	1.7	* unbounded this method will never block.
127	jsr166	1.32	*
128	jsr166	1.30	* @param e the element to add
129	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
130	dholmes	1.7	*/
131	jsr166	1.30	public void put(E e) {
132			offer(e);
133	dl	1.2	}
134
135	dholmes	1.7	/**
136	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
137	dholmes	1.7	* unbounded this method will never block.
138	jsr166	1.32	*
139	jsr166	1.30	* @param e the element to add
140	dl	1.14	* @param timeout This parameter is ignored as the method never blocks
141	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
142			* @return <tt>true</tt>
143	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
144	dholmes	1.7	*/
145	jsr166	1.30	public boolean offer(E e, long timeout, TimeUnit unit) {
146			return offer(e);
147	dl	1.2	}
148
149	dholmes	1.7	/**
150	jsr166	1.32	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
151			* if this queue has no elements with an expired delay.
152	dholmes	1.7	*
153	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
154			* queue has no elements with an expired delay
155	dholmes	1.7	*/
156	jsr166	1.32	public E poll() {
157			final ReentrantLock lock = this.lock;
158			lock.lock();
159			try {
160			E first = q.peek();
161	jsr166	1.56	if (first == null \|\| first.getDelay(NANOSECONDS) > 0)
162	jsr166	1.32	return null;
163	jsr166	1.48	else
164			return q.poll();
165	jsr166	1.32	} finally {
166			lock.unlock();
167			}
168	dl	1.2	}
169
170	dl	1.27	/**
171	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
172			* until an element with an expired delay is available on this queue.
173			*
174	dl	1.27	* @return the head of this queue
175	jsr166	1.32	* @throws InterruptedException {@inheritDoc}
176	dl	1.27	*/
177	dl	1.3	public E take() throws InterruptedException {
178	dl	1.21	final ReentrantLock lock = this.lock;
179	dl	1.2	lock.lockInterruptibly();
180			try {
181			for (;;) {
182	dl	1.3	E first = q.peek();
183	jsr166	1.48	if (first == null)
184	dl	1.4	available.await();
185	jsr166	1.49	else {
186	jsr166	1.56	long delay = first.getDelay(NANOSECONDS);
187	jsr166	1.49	if (delay <= 0)
188			return q.poll();
189			else if (leader != null)
190			available.await();
191			else {
192			Thread thisThread = Thread.currentThread();
193			leader = thisThread;
194			try {
195			available.awaitNanos(delay);
196			} finally {
197			if (leader == thisThread)
198			leader = null;
199			}
200	dl	1.2	}
201			}
202			}
203	tim	1.13	} finally {
204	jsr166	1.49	if (leader == null && q.peek() != null)
205			available.signal();
206	dl	1.2	lock.unlock();
207			}
208			}
209
210	dl	1.27	/**
211	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
212			* until an element with an expired delay is available on this queue,
213			* or the specified wait time expires.
214			*
215	dl	1.27	* @return the head of this queue, or <tt>null</tt> if the
216	jsr166	1.32	* specified waiting time elapses before an element with
217			* an expired delay becomes available
218			* @throws InterruptedException {@inheritDoc}
219	dl	1.27	*/
220			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
221	jsr166	1.41	long nanos = unit.toNanos(timeout);
222	dl	1.21	final ReentrantLock lock = this.lock;
223	dl	1.2	lock.lockInterruptibly();
224			try {
225			for (;;) {
226	dl	1.3	E first = q.peek();
227	dl	1.2	if (first == null) {
228			if (nanos <= 0)
229			return null;
230			else
231	dl	1.4	nanos = available.awaitNanos(nanos);
232	tim	1.13	} else {
233	jsr166	1.56	long delay = first.getDelay(NANOSECONDS);
234	jsr166	1.49	if (delay <= 0)
235			return q.poll();
236			if (nanos <= 0)
237			return null;
238			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			* returns <tt>null</tt> if this queue is empty. Unlike
263			* <tt>poll</tt>, if no expired elements are available in the queue,
264			* this method returns the element that will expire next,
265			* if one exists.
266	dl	1.27	*
267	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
268	dl	1.35	* 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	1.56	* Return first element only if it is expired.
292			* 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			* Always returns <tt>Integer.MAX_VALUE</tt> because
373			* a <tt>DelayQueue</tt> is not capacity constrained.
374	jsr166	1.32	*
375	dholmes	1.7	* @return <tt>Integer.MAX_VALUE</tt>
376			*/
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			* <tt>null</tt>.
416			*
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			* allocated array of <tt>Delayed</tt>:
424	jsr166	1.32	*
425	jsr166	1.55	* <pre> {@code Delayed[] a = q.toArray(new Delayed[0]);}</pre>
426	jsr166	1.32	*
427			* Note that <tt>toArray(new Object[0])</tt> is identical in function to
428			* <tt>toArray()</tt>.
429			*
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			* <p>The returned iterator is a "weakly consistent" iterator that
487			* will never throw {@link java.util.ConcurrentModificationException
488			* ConcurrentModificationException}, and guarantees to traverse
489			* elements as they existed upon construction of the iterator, and
490			* may (but is not guaranteed to) reflect any modifications
491			* subsequent to construction.
492	dholmes	1.7	*
493	jsr166	1.32	* @return an iterator over the elements in this queue
494	dholmes	1.7	*/
495	dl	1.3	public Iterator<E> iterator() {
496	dl	1.44	return new Itr(toArray());
497	dl	1.2	}
498
499	dl	1.42	/**
500			* Snapshot iterator that works off copy of underlying q array.
501			*/
502	dl	1.44	private class Itr implements Iterator<E> {
503	dl	1.42	final Object[] array; // Array of all elements
504	jsr166	1.57	int cursor; // index of next element to return
505	jsr166	1.49	int lastRet; // index of last element, or -1 if no such
506	jsr166	1.43
507	dl	1.42	Itr(Object[] array) {
508			lastRet = -1;
509			this.array = array;
510	dl	1.2	}
511
512	tim	1.6	public boolean hasNext() {
513	dl	1.42	return cursor < array.length;
514	tim	1.6	}
515
516	jsr166	1.49	@SuppressWarnings("unchecked")
517	tim	1.6	public E next() {
518	dl	1.42	if (cursor >= array.length)
519			throw new NoSuchElementException();
520			lastRet = cursor;
521			return (E)array[cursor++];
522	tim	1.6	}
523
524			public void remove() {
525	jsr166	1.43	if (lastRet < 0)
526	jsr166	1.49	throw new IllegalStateException();
527	jsr166	1.57	removeEQ(array[lastRet]);
528	dl	1.42	lastRet = -1;
529	tim	1.6	}
530	tim	1.1	}
531
532			}