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.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}/../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:	1.69
Committed:	Wed Dec 31 07:54:13 2014 UTC (9 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.68:	+3 -2 lines
Log Message:	standardize import statement order
#	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			import java.util.PriorityQueue;
16	jsr166	1.69	import java.util.concurrent.locks.Condition;
17			import java.util.concurrent.locks.ReentrantLock;
18	tim	1.1
19			/**
20	dl	1.27	* An unbounded {@linkplain BlockingQueue blocking queue} of
21	jsr166	1.61	* {@code Delayed} elements, in which an element can only be taken
22	dl	1.27	* when its delay has expired. The <em>head</em> of the queue is that
23	jsr166	1.61	* {@code Delayed} element whose delay expired furthest in the
24			* past. If no delay has expired there is no head and {@code poll}
25			* will return {@code null}. Expiration occurs when an element's
26			* {@code getDelay(TimeUnit.NANOSECONDS)} method returns a value less
27	dl	1.36	* than or equal to zero. Even though unexpired elements cannot be
28	jsr166	1.61	* removed using {@code take} or {@code poll}, they are otherwise
29			* treated as normal elements. For example, the {@code size} method
30	dl	1.36	* returns the count of both expired and unexpired elements.
31	jsr166	1.39	* This queue does not permit null elements.
32	dl	1.25	*
33	dl	1.26	* <p>This class and its iterator implement all of the
34			* <em>optional</em> methods of the {@link Collection} and {@link
35	dl	1.53	* Iterator} interfaces. The Iterator provided in method {@link
36			* #iterator()} is <em>not</em> guaranteed to traverse the elements of
37			* the DelayQueue in any particular order.
38	dl	1.26	*
39	dl	1.25	* <p>This class is a member of the
40	jsr166	1.46	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
41	dl	1.25	* Java Collections Framework</a>.
42			*
43	dl	1.4	* @since 1.5
44			* @author Doug Lea
45	jsr166	1.67	* @param <E> the type of elements held in this queue
46	dl	1.19	*/
47	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
48			implements BlockingQueue<E> {
49	tim	1.6
50	jsr166	1.62	private final transient ReentrantLock lock = new ReentrantLock();
51	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
52	tim	1.1
53	dl	1.4	/**
54	jsr166	1.48	* Thread designated to wait for the element at the head of
55			* the queue. This variant of the Leader-Follower pattern
56			* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
57			* minimize unnecessary timed waiting. When a thread becomes
58			* the leader, it waits only for the next delay to elapse, but
59			* other threads await indefinitely. The leader thread must
60			* signal some other thread before returning from take() or
61			* poll(...), unless some other thread becomes leader in the
62			* interim. Whenever the head of the queue is replaced with
63			* an element with an earlier expiration time, the leader
64			* field is invalidated by being reset to null, and some
65			* waiting thread, but not necessarily the current leader, is
66			* signalled. So waiting threads must be prepared to acquire
67			* and lose leadership while waiting.
68			*/
69	jsr166	1.66	private Thread leader;
70	jsr166	1.48
71			/**
72			* Condition signalled when a newer element becomes available
73			* at the head of the queue or a new thread may need to
74			* become leader.
75			*/
76			private final Condition available = lock.newCondition();
77
78			/**
79	jsr166	1.61	* Creates a new {@code DelayQueue} that is initially empty.
80	dl	1.4	*/
81	tim	1.1	public DelayQueue() {}
82
83	tim	1.6	/**
84	jsr166	1.61	* Creates a {@code DelayQueue} initially containing the elements of the
85	dholmes	1.7	* given collection of {@link Delayed} instances.
86			*
87	jsr166	1.32	* @param c the collection of elements to initially contain
88			* @throws NullPointerException if the specified collection or any
89			* of its elements are null
90	tim	1.6	*/
91			public DelayQueue(Collection<? extends E> c) {
92			this.addAll(c);
93			}
94
95	dholmes	1.7	/**
96	dl	1.16	* Inserts the specified element into this delay queue.
97	dholmes	1.7	*
98	jsr166	1.30	* @param e the element to add
99	jsr166	1.61	* @return {@code true} (as specified by {@link Collection#add})
100	jsr166	1.32	* @throws NullPointerException if the specified element is null
101			*/
102			public boolean add(E e) {
103			return offer(e);
104			}
105
106			/**
107			* Inserts the specified element into this delay queue.
108			*
109			* @param e the element to add
110	jsr166	1.61	* @return {@code true}
111	jsr166	1.32	* @throws NullPointerException if the specified element is null
112	dholmes	1.7	*/
113	jsr166	1.30	public boolean offer(E e) {
114	dl	1.21	final ReentrantLock lock = this.lock;
115	dl	1.2	lock.lock();
116			try {
117	jsr166	1.30	q.offer(e);
118	jsr166	1.48	if (q.peek() == e) {
119	jsr166	1.49	leader = null;
120	jsr166	1.48	available.signal();
121	jsr166	1.49	}
122	dl	1.2	return true;
123	tim	1.13	} finally {
124	dl	1.2	lock.unlock();
125			}
126			}
127
128	dholmes	1.7	/**
129	jsr166	1.32	* Inserts the specified element into this delay queue. As the queue is
130	dholmes	1.7	* unbounded this method will never block.
131	jsr166	1.32	*
132	jsr166	1.30	* @param e the element to add
133	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
134	dholmes	1.7	*/
135	jsr166	1.30	public void put(E e) {
136			offer(e);
137	dl	1.2	}
138
139	dholmes	1.7	/**
140	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
141	dholmes	1.7	* unbounded this method will never block.
142	jsr166	1.32	*
143	jsr166	1.30	* @param e the element to add
144	dl	1.14	* @param timeout This parameter is ignored as the method never blocks
145	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
146	jsr166	1.61	* @return {@code true}
147	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
148	dholmes	1.7	*/
149	jsr166	1.30	public boolean offer(E e, long timeout, TimeUnit unit) {
150			return offer(e);
151	dl	1.2	}
152
153	dholmes	1.7	/**
154	jsr166	1.61	* Retrieves and removes the head of this queue, or returns {@code null}
155	jsr166	1.32	* if this queue has no elements with an expired delay.
156	dholmes	1.7	*
157	jsr166	1.61	* @return the head of this queue, or {@code null} if this
158	jsr166	1.32	* queue has no elements with an expired delay
159	dholmes	1.7	*/
160	jsr166	1.32	public E poll() {
161			final ReentrantLock lock = this.lock;
162			lock.lock();
163			try {
164			E first = q.peek();
165	jsr166	1.56	if (first == null \|\| first.getDelay(NANOSECONDS) > 0)
166	jsr166	1.32	return null;
167	jsr166	1.48	else
168			return 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	1.49	if (delay <= 0)
192			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			if (nanos <= 0)
234			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	1.49	if (delay <= 0)
240			return q.poll();
241			if (nanos <= 0)
242			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	jsr166	1.59	* Returns first element only if it is expired.
298	jsr166	1.56	* Used only by drainTo. Call only when holding lock.
299			*/
300			private E peekExpired() {
301			// assert lock.isHeldByCurrentThread();
302			E first = q.peek();
303			return (first == null \|\| first.getDelay(NANOSECONDS) > 0) ?
304			null : first;
305			}
306
307			/**
308	jsr166	1.32	* @throws UnsupportedOperationException {@inheritDoc}
309			* @throws ClassCastException {@inheritDoc}
310			* @throws NullPointerException {@inheritDoc}
311			* @throws IllegalArgumentException {@inheritDoc}
312			*/
313	dl	1.17	public int drainTo(Collection<? super E> c) {
314			if (c == null)
315			throw new NullPointerException();
316			if (c == this)
317			throw new IllegalArgumentException();
318	dl	1.21	final ReentrantLock lock = this.lock;
319	dl	1.17	lock.lock();
320			try {
321			int n = 0;
322	jsr166	1.56	for (E e; (e = peekExpired()) != null;) {
323			c.add(e); // In this order, in case add() throws.
324			q.poll();
325	dl	1.17	++n;
326			}
327			return n;
328			} finally {
329			lock.unlock();
330			}
331			}
332
333	jsr166	1.32	/**
334			* @throws UnsupportedOperationException {@inheritDoc}
335			* @throws ClassCastException {@inheritDoc}
336			* @throws NullPointerException {@inheritDoc}
337			* @throws IllegalArgumentException {@inheritDoc}
338			*/
339	dl	1.17	public int drainTo(Collection<? super E> c, int maxElements) {
340			if (c == null)
341			throw new NullPointerException();
342			if (c == this)
343			throw new IllegalArgumentException();
344			if (maxElements <= 0)
345			return 0;
346	dl	1.21	final ReentrantLock lock = this.lock;
347	dl	1.17	lock.lock();
348			try {
349			int n = 0;
350	jsr166	1.56	for (E e; n < maxElements && (e = peekExpired()) != null;) {
351			c.add(e); // In this order, in case add() throws.
352			q.poll();
353	dl	1.17	++n;
354			}
355			return n;
356			} finally {
357			lock.unlock();
358			}
359			}
360
361	dholmes	1.7	/**
362			* Atomically removes all of the elements from this delay queue.
363			* The queue will be empty after this call returns.
364	jsr166	1.32	* Elements with an unexpired delay are not waited for; they are
365			* simply discarded from the queue.
366	dholmes	1.7	*/
367	dl	1.2	public void clear() {
368	dl	1.21	final ReentrantLock lock = this.lock;
369	dl	1.2	lock.lock();
370			try {
371			q.clear();
372	tim	1.13	} finally {
373	dl	1.2	lock.unlock();
374			}
375			}
376	tim	1.1
377	dholmes	1.7	/**
378	jsr166	1.61	* Always returns {@code Integer.MAX_VALUE} because
379			* a {@code DelayQueue} is not capacity constrained.
380	jsr166	1.32	*
381	jsr166	1.61	* @return {@code Integer.MAX_VALUE}
382	dholmes	1.7	*/
383	dl	1.2	public int remainingCapacity() {
384			return Integer.MAX_VALUE;
385	tim	1.1	}
386	dl	1.2
387	jsr166	1.32	/**
388			* Returns an array containing all of the elements in this queue.
389			* The returned array elements are in no particular order.
390			*
391			* <p>The returned array will be "safe" in that no references to it are
392			* maintained by this queue. (In other words, this method must allocate
393			* a new array). The caller is thus free to modify the returned array.
394	jsr166	1.33	*
395	jsr166	1.32	* <p>This method acts as bridge between array-based and collection-based
396			* APIs.
397			*
398			* @return an array containing all of the elements in this queue
399			*/
400	dl	1.2	public Object[] toArray() {
401	dl	1.21	final ReentrantLock lock = this.lock;
402	dl	1.2	lock.lock();
403			try {
404			return q.toArray();
405	tim	1.13	} finally {
406	dl	1.2	lock.unlock();
407			}
408	tim	1.1	}
409	dl	1.2
410	jsr166	1.32	/**
411			* Returns an array containing all of the elements in this queue; the
412			* runtime type of the returned array is that of the specified array.
413			* The returned array elements are in no particular order.
414			* If the queue fits in the specified array, it is returned therein.
415			* Otherwise, a new array is allocated with the runtime type of the
416			* specified array and the size of this queue.
417			*
418			* <p>If this queue fits in the specified array with room to spare
419			* (i.e., the array has more elements than this queue), the element in
420			* the array immediately following the end of the queue is set to
421	jsr166	1.61	* {@code null}.
422	jsr166	1.32	*
423			* <p>Like the {@link #toArray()} method, this method acts as bridge between
424			* array-based and collection-based APIs. Further, this method allows
425			* precise control over the runtime type of the output array, and may,
426			* under certain circumstances, be used to save allocation costs.
427			*
428	jsr166	1.37	* <p>The following code can be used to dump a delay queue into a newly
429	jsr166	1.61	* allocated array of {@code Delayed}:
430	jsr166	1.32	*
431	jsr166	1.55	* <pre> {@code Delayed[] a = q.toArray(new Delayed[0]);}</pre>
432	jsr166	1.32	*
433	jsr166	1.61	* Note that {@code toArray(new Object[0])} is identical in function to
434			* {@code toArray()}.
435	jsr166	1.32	*
436			* @param a the array into which the elements of the queue are to
437			* be stored, if it is big enough; otherwise, a new array of the
438			* same runtime type is allocated for this purpose
439			* @return an array containing all of the elements in this queue
440			* @throws ArrayStoreException if the runtime type of the specified array
441			* is not a supertype of the runtime type of every element in
442			* this queue
443			* @throws NullPointerException if the specified array is null
444			*/
445			public <T> T[] toArray(T[] a) {
446	dl	1.21	final ReentrantLock lock = this.lock;
447	dl	1.2	lock.lock();
448			try {
449	jsr166	1.32	return q.toArray(a);
450	tim	1.13	} finally {
451	dl	1.2	lock.unlock();
452			}
453	tim	1.1	}
454
455	dl	1.26	/**
456			* Removes a single instance of the specified element from this
457	dl	1.36	* queue, if it is present, whether or not it has expired.
458	dl	1.26	*/
459	dholmes	1.7	public boolean remove(Object o) {
460	dl	1.21	final ReentrantLock lock = this.lock;
461	dl	1.2	lock.lock();
462			try {
463	dholmes	1.7	return q.remove(o);
464	tim	1.13	} finally {
465	dl	1.2	lock.unlock();
466			}
467			}
468
469	dholmes	1.7	/**
470	jsr166	1.57	* Identity-based version for use in Itr.remove
471			*/
472			void removeEQ(Object o) {
473			final ReentrantLock lock = this.lock;
474			lock.lock();
475			try {
476			for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
477			if (o == it.next()) {
478			it.remove();
479			break;
480			}
481			}
482			} finally {
483			lock.unlock();
484			}
485			}
486
487			/**
488	dl	1.36	* Returns an iterator over all the elements (both expired and
489	dl	1.44	* unexpired) in this queue. The iterator does not return the
490	jsr166	1.51	* elements in any particular order.
491			*
492	jsr166	1.65	* <p>The returned iterator is
493			* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
494	dholmes	1.7	*
495	jsr166	1.32	* @return an iterator over the elements in this queue
496	dholmes	1.7	*/
497	dl	1.3	public Iterator<E> iterator() {
498	dl	1.44	return new Itr(toArray());
499	dl	1.2	}
500
501	dl	1.42	/**
502			* Snapshot iterator that works off copy of underlying q array.
503			*/
504	dl	1.44	private class Itr implements Iterator<E> {
505	dl	1.42	final Object[] array; // Array of all elements
506	jsr166	1.57	int cursor; // index of next element to return
507	jsr166	1.49	int lastRet; // index of last element, or -1 if no such
508	jsr166	1.43
509	dl	1.42	Itr(Object[] array) {
510			lastRet = -1;
511			this.array = array;
512	dl	1.2	}
513
514	tim	1.6	public boolean hasNext() {
515	dl	1.42	return cursor < array.length;
516	tim	1.6	}
517
518	jsr166	1.49	@SuppressWarnings("unchecked")
519	tim	1.6	public E next() {
520	dl	1.42	if (cursor >= array.length)
521			throw new NoSuchElementException();
522			lastRet = cursor;
523			return (E)array[cursor++];
524	tim	1.6	}
525
526			public void remove() {
527	jsr166	1.43	if (lastRet < 0)
528	jsr166	1.49	throw new IllegalStateException();
529	jsr166	1.57	removeEQ(array[lastRet]);
530	dl	1.42	lastRet = -1;
531	tim	1.6	}
532	tim	1.1	}
533
534			}