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();
        }
    }

    /**
     * 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 <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:	1.59
Committed:	Tue Feb 21 01:54:03 2012 UTC (12 years, 3 months ago) by jsr166
Branch:	MAIN
Changes since 1.58:	+1 -1 lines
Log Message:	use third person in javadoc first sentence
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.23	* Expert Group and released to the public domain, as explained at
4	jsr166	1.52	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.2	*/
6
7	tim	1.1	package java.util.concurrent;
8	jsr166	1.56	import static java.util.concurrent.TimeUnit.NANOSECONDS;
9			import java.util.concurrent.locks.Condition;
10			import java.util.concurrent.locks.ReentrantLock;
11	tim	1.1	import java.util.*;
12
13			/**
14	dl	1.27	* An unbounded {@linkplain BlockingQueue blocking queue} of
15			* <tt>Delayed</tt> elements, in which an element can only be taken
16			* when its delay has expired. The <em>head</em> of the queue is that
17			* <tt>Delayed</tt> element whose delay expired furthest in the
18	jsr166	1.32	* past. If no delay has expired there is no head and <tt>poll</tt>
19	dl	1.27	* will return <tt>null</tt>. Expiration occurs when an element's
20			* <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less
21	dl	1.36	* than or equal to zero. Even though unexpired elements cannot be
22			* removed using <tt>take</tt> or <tt>poll</tt>, they are otherwise
23			* treated as normal elements. For example, the <tt>size</tt> method
24			* returns the count of both expired and unexpired elements.
25	jsr166	1.39	* This queue does not permit null elements.
26	dl	1.25	*
27	dl	1.26	* <p>This class and its iterator implement all of the
28			* <em>optional</em> methods of the {@link Collection} and {@link
29	dl	1.53	* Iterator} interfaces. The Iterator provided in method {@link
30			* #iterator()} is <em>not</em> guaranteed to traverse the elements of
31			* the DelayQueue in any particular order.
32	dl	1.26	*
33	dl	1.25	* <p>This class is a member of the
34	jsr166	1.46	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
35	dl	1.25	* Java Collections Framework</a>.
36			*
37	dl	1.4	* @since 1.5
38			* @author Doug Lea
39	dl	1.20	* @param <E> the type of elements held in this collection
40	dl	1.19	*/
41	tim	1.1
42	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
43			implements BlockingQueue<E> {
44	tim	1.6
45	dl	1.2	private transient final ReentrantLock lock = new ReentrantLock();
46	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
47	tim	1.1
48	dl	1.4	/**
49	jsr166	1.48	* Thread designated to wait for the element at the head of
50			* the queue. This variant of the Leader-Follower pattern
51			* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
52			* minimize unnecessary timed waiting. When a thread becomes
53			* the leader, it waits only for the next delay to elapse, but
54			* other threads await indefinitely. The leader thread must
55			* signal some other thread before returning from take() or
56			* poll(...), unless some other thread becomes leader in the
57			* interim. Whenever the head of the queue is replaced with
58			* an element with an earlier expiration time, the leader
59			* field is invalidated by being reset to null, and some
60			* waiting thread, but not necessarily the current leader, is
61			* signalled. So waiting threads must be prepared to acquire
62			* and lose leadership while waiting.
63			*/
64			private Thread leader = null;
65
66			/**
67			* Condition signalled when a newer element becomes available
68			* at the head of the queue or a new thread may need to
69			* become leader.
70			*/
71			private final Condition available = lock.newCondition();
72
73			/**
74	dholmes	1.7	* Creates a new <tt>DelayQueue</tt> that is initially empty.
75	dl	1.4	*/
76	tim	1.1	public DelayQueue() {}
77
78	tim	1.6	/**
79	tim	1.9	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
80	dholmes	1.7	* given collection of {@link Delayed} instances.
81			*
82	jsr166	1.32	* @param c the collection of elements to initially contain
83			* @throws NullPointerException if the specified collection or any
84			* of its elements are null
85	tim	1.6	*/
86			public DelayQueue(Collection<? extends E> c) {
87			this.addAll(c);
88			}
89
90	dholmes	1.7	/**
91	dl	1.16	* Inserts the specified element into this delay queue.
92	dholmes	1.7	*
93	jsr166	1.30	* @param e the element to add
94	jsr166	1.38	* @return <tt>true</tt> (as specified by {@link Collection#add})
95	jsr166	1.32	* @throws NullPointerException if the specified element is null
96			*/
97			public boolean add(E e) {
98			return offer(e);
99			}
100
101			/**
102			* Inserts the specified element into this delay queue.
103			*
104			* @param e the element to add
105	dholmes	1.7	* @return <tt>true</tt>
106	jsr166	1.32	* @throws NullPointerException if the specified element is null
107	dholmes	1.7	*/
108	jsr166	1.30	public boolean offer(E e) {
109	dl	1.21	final ReentrantLock lock = this.lock;
110	dl	1.2	lock.lock();
111			try {
112	jsr166	1.30	q.offer(e);
113	jsr166	1.48	if (q.peek() == e) {
114	jsr166	1.49	leader = null;
115	jsr166	1.48	available.signal();
116	jsr166	1.49	}
117	dl	1.2	return true;
118	tim	1.13	} finally {
119	dl	1.2	lock.unlock();
120			}
121			}
122
123	dholmes	1.7	/**
124	jsr166	1.32	* Inserts the specified element into this delay queue. As the queue is
125	dholmes	1.7	* unbounded this method will never block.
126	jsr166	1.32	*
127	jsr166	1.30	* @param e the element to add
128	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
129	dholmes	1.7	*/
130	jsr166	1.30	public void put(E e) {
131			offer(e);
132	dl	1.2	}
133
134	dholmes	1.7	/**
135	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
136	dholmes	1.7	* unbounded this method will never block.
137	jsr166	1.32	*
138	jsr166	1.30	* @param e the element to add
139	dl	1.14	* @param timeout This parameter is ignored as the method never blocks
140	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
141			* @return <tt>true</tt>
142	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
143	dholmes	1.7	*/
144	jsr166	1.30	public boolean offer(E e, long timeout, TimeUnit unit) {
145			return offer(e);
146	dl	1.2	}
147
148	dholmes	1.7	/**
149	jsr166	1.32	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
150			* if this queue has no elements with an expired delay.
151	dholmes	1.7	*
152	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
153			* queue has no elements with an expired delay
154	dholmes	1.7	*/
155	jsr166	1.32	public E poll() {
156			final ReentrantLock lock = this.lock;
157			lock.lock();
158			try {
159			E first = q.peek();
160	jsr166	1.56	if (first == null \|\| first.getDelay(NANOSECONDS) > 0)
161	jsr166	1.32	return null;
162	jsr166	1.48	else
163			return q.poll();
164	jsr166	1.32	} finally {
165			lock.unlock();
166			}
167	dl	1.2	}
168
169	dl	1.27	/**
170	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
171			* until an element with an expired delay is available on this queue.
172			*
173	dl	1.27	* @return the head of this queue
174	jsr166	1.32	* @throws InterruptedException {@inheritDoc}
175	dl	1.27	*/
176	dl	1.3	public E take() throws InterruptedException {
177	dl	1.21	final ReentrantLock lock = this.lock;
178	dl	1.2	lock.lockInterruptibly();
179			try {
180			for (;;) {
181	dl	1.3	E first = q.peek();
182	jsr166	1.48	if (first == null)
183	dl	1.4	available.await();
184	jsr166	1.49	else {
185	jsr166	1.56	long delay = first.getDelay(NANOSECONDS);
186	jsr166	1.49	if (delay <= 0)
187			return q.poll();
188			else if (leader != null)
189			available.await();
190			else {
191			Thread thisThread = Thread.currentThread();
192			leader = thisThread;
193			try {
194			available.awaitNanos(delay);
195			} finally {
196			if (leader == thisThread)
197			leader = null;
198			}
199	dl	1.2	}
200			}
201			}
202	tim	1.13	} finally {
203	jsr166	1.49	if (leader == null && q.peek() != null)
204			available.signal();
205	dl	1.2	lock.unlock();
206			}
207			}
208
209	dl	1.27	/**
210	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
211			* until an element with an expired delay is available on this queue,
212			* or the specified wait time expires.
213			*
214	dl	1.27	* @return the head of this queue, or <tt>null</tt> if the
215	jsr166	1.32	* specified waiting time elapses before an element with
216			* an expired delay becomes available
217			* @throws InterruptedException {@inheritDoc}
218	dl	1.27	*/
219			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
220	jsr166	1.41	long nanos = unit.toNanos(timeout);
221	dl	1.21	final ReentrantLock lock = this.lock;
222	dl	1.2	lock.lockInterruptibly();
223			try {
224			for (;;) {
225	dl	1.3	E first = q.peek();
226	dl	1.2	if (first == null) {
227			if (nanos <= 0)
228			return null;
229			else
230	dl	1.4	nanos = available.awaitNanos(nanos);
231	tim	1.13	} else {
232	jsr166	1.56	long delay = first.getDelay(NANOSECONDS);
233	jsr166	1.49	if (delay <= 0)
234			return q.poll();
235			if (nanos <= 0)
236			return null;
237			if (nanos < delay \|\| leader != null)
238			nanos = available.awaitNanos(nanos);
239			else {
240			Thread thisThread = Thread.currentThread();
241			leader = thisThread;
242			try {
243			long timeLeft = available.awaitNanos(delay);
244			nanos -= delay - timeLeft;
245			} finally {
246			if (leader == thisThread)
247			leader = null;
248			}
249			}
250	dl	1.2	}
251			}
252	tim	1.13	} finally {
253	jsr166	1.49	if (leader == null && q.peek() != null)
254			available.signal();
255	dl	1.2	lock.unlock();
256			}
257			}
258
259	dl	1.27	/**
260	dl	1.36	* Retrieves, but does not remove, the head of this queue, or
261			* returns <tt>null</tt> if this queue is empty. Unlike
262			* <tt>poll</tt>, if no expired elements are available in the queue,
263			* this method returns the element that will expire next,
264			* if one exists.
265	dl	1.27	*
266	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
267	dl	1.35	* queue is empty.
268	dl	1.27	*/
269	dl	1.3	public E peek() {
270	dl	1.21	final ReentrantLock lock = this.lock;
271	dl	1.2	lock.lock();
272			try {
273			return q.peek();
274	tim	1.13	} finally {
275	dl	1.2	lock.unlock();
276			}
277	tim	1.1	}
278
279	dl	1.2	public int size() {
280	dl	1.21	final ReentrantLock lock = this.lock;
281	dl	1.2	lock.lock();
282			try {
283			return q.size();
284	tim	1.13	} finally {
285	dl	1.2	lock.unlock();
286			}
287			}
288
289	jsr166	1.32	/**
290	jsr166	1.59	* Returns first element only if it is expired.
291	jsr166	1.56	* Used only by drainTo. Call only when holding lock.
292			*/
293			private E peekExpired() {
294			// assert lock.isHeldByCurrentThread();
295			E first = q.peek();
296			return (first == null \|\| first.getDelay(NANOSECONDS) > 0) ?
297			null : first;
298			}
299
300			/**
301	jsr166	1.32	* @throws UnsupportedOperationException {@inheritDoc}
302			* @throws ClassCastException {@inheritDoc}
303			* @throws NullPointerException {@inheritDoc}
304			* @throws IllegalArgumentException {@inheritDoc}
305			*/
306	dl	1.17	public int drainTo(Collection<? super E> c) {
307			if (c == null)
308			throw new NullPointerException();
309			if (c == this)
310			throw new IllegalArgumentException();
311	dl	1.21	final ReentrantLock lock = this.lock;
312	dl	1.17	lock.lock();
313			try {
314			int n = 0;
315	jsr166	1.56	for (E e; (e = peekExpired()) != null;) {
316			c.add(e); // In this order, in case add() throws.
317			q.poll();
318	dl	1.17	++n;
319			}
320			return n;
321			} finally {
322			lock.unlock();
323			}
324			}
325
326	jsr166	1.32	/**
327			* @throws UnsupportedOperationException {@inheritDoc}
328			* @throws ClassCastException {@inheritDoc}
329			* @throws NullPointerException {@inheritDoc}
330			* @throws IllegalArgumentException {@inheritDoc}
331			*/
332	dl	1.17	public int drainTo(Collection<? super E> c, int maxElements) {
333			if (c == null)
334			throw new NullPointerException();
335			if (c == this)
336			throw new IllegalArgumentException();
337			if (maxElements <= 0)
338			return 0;
339	dl	1.21	final ReentrantLock lock = this.lock;
340	dl	1.17	lock.lock();
341			try {
342			int n = 0;
343	jsr166	1.56	for (E e; n < maxElements && (e = peekExpired()) != null;) {
344			c.add(e); // In this order, in case add() throws.
345			q.poll();
346	dl	1.17	++n;
347			}
348			return n;
349			} finally {
350			lock.unlock();
351			}
352			}
353
354	dholmes	1.7	/**
355			* Atomically removes all of the elements from this delay queue.
356			* The queue will be empty after this call returns.
357	jsr166	1.32	* Elements with an unexpired delay are not waited for; they are
358			* simply discarded from the queue.
359	dholmes	1.7	*/
360	dl	1.2	public void clear() {
361	dl	1.21	final ReentrantLock lock = this.lock;
362	dl	1.2	lock.lock();
363			try {
364			q.clear();
365	tim	1.13	} finally {
366	dl	1.2	lock.unlock();
367			}
368			}
369	tim	1.1
370	dholmes	1.7	/**
371			* Always returns <tt>Integer.MAX_VALUE</tt> because
372			* a <tt>DelayQueue</tt> is not capacity constrained.
373	jsr166	1.32	*
374	dholmes	1.7	* @return <tt>Integer.MAX_VALUE</tt>
375			*/
376	dl	1.2	public int remainingCapacity() {
377			return Integer.MAX_VALUE;
378	tim	1.1	}
379	dl	1.2
380	jsr166	1.32	/**
381			* Returns an array containing all of the elements in this queue.
382			* The returned array elements are in no particular order.
383			*
384			* <p>The returned array will be "safe" in that no references to it are
385			* maintained by this queue. (In other words, this method must allocate
386			* a new array). The caller is thus free to modify the returned array.
387	jsr166	1.33	*
388	jsr166	1.32	* <p>This method acts as bridge between array-based and collection-based
389			* APIs.
390			*
391			* @return an array containing all of the elements in this queue
392			*/
393	dl	1.2	public Object[] toArray() {
394	dl	1.21	final ReentrantLock lock = this.lock;
395	dl	1.2	lock.lock();
396			try {
397			return q.toArray();
398	tim	1.13	} finally {
399	dl	1.2	lock.unlock();
400			}
401	tim	1.1	}
402	dl	1.2
403	jsr166	1.32	/**
404			* Returns an array containing all of the elements in this queue; the
405			* runtime type of the returned array is that of the specified array.
406			* The returned array elements are in no particular order.
407			* If the queue fits in the specified array, it is returned therein.
408			* Otherwise, a new array is allocated with the runtime type of the
409			* specified array and the size of this queue.
410			*
411			* <p>If this queue fits in the specified array with room to spare
412			* (i.e., the array has more elements than this queue), the element in
413			* the array immediately following the end of the queue is set to
414			* <tt>null</tt>.
415			*
416			* <p>Like the {@link #toArray()} method, this method acts as bridge between
417			* array-based and collection-based APIs. Further, this method allows
418			* precise control over the runtime type of the output array, and may,
419			* under certain circumstances, be used to save allocation costs.
420			*
421	jsr166	1.37	* <p>The following code can be used to dump a delay queue into a newly
422			* allocated array of <tt>Delayed</tt>:
423	jsr166	1.32	*
424	jsr166	1.55	* <pre> {@code Delayed[] a = q.toArray(new Delayed[0]);}</pre>
425	jsr166	1.32	*
426			* Note that <tt>toArray(new Object[0])</tt> is identical in function to
427			* <tt>toArray()</tt>.
428			*
429			* @param a the array into which the elements of the queue are to
430			* be stored, if it is big enough; otherwise, a new array of the
431			* same runtime type is allocated for this purpose
432			* @return an array containing all of the elements in this queue
433			* @throws ArrayStoreException if the runtime type of the specified array
434			* is not a supertype of the runtime type of every element in
435			* this queue
436			* @throws NullPointerException if the specified array is null
437			*/
438			public <T> T[] toArray(T[] a) {
439	dl	1.21	final ReentrantLock lock = this.lock;
440	dl	1.2	lock.lock();
441			try {
442	jsr166	1.32	return q.toArray(a);
443	tim	1.13	} finally {
444	dl	1.2	lock.unlock();
445			}
446	tim	1.1	}
447
448	dl	1.26	/**
449			* Removes a single instance of the specified element from this
450	dl	1.36	* queue, if it is present, whether or not it has expired.
451	dl	1.26	*/
452	dholmes	1.7	public boolean remove(Object o) {
453	dl	1.21	final ReentrantLock lock = this.lock;
454	dl	1.2	lock.lock();
455			try {
456	dholmes	1.7	return q.remove(o);
457	tim	1.13	} finally {
458	dl	1.2	lock.unlock();
459			}
460			}
461
462	dholmes	1.7	/**
463	jsr166	1.57	* Identity-based version for use in Itr.remove
464			*/
465			void removeEQ(Object o) {
466			final ReentrantLock lock = this.lock;
467			lock.lock();
468			try {
469			for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
470			if (o == it.next()) {
471			it.remove();
472			break;
473			}
474			}
475			} finally {
476			lock.unlock();
477			}
478			}
479
480			/**
481	dl	1.36	* Returns an iterator over all the elements (both expired and
482	dl	1.44	* unexpired) in this queue. The iterator does not return the
483	jsr166	1.51	* elements in any particular order.
484			*
485			* <p>The returned iterator is a "weakly consistent" iterator that
486			* will never throw {@link java.util.ConcurrentModificationException
487			* ConcurrentModificationException}, and guarantees to traverse
488			* elements as they existed upon construction of the iterator, and
489			* may (but is not guaranteed to) reflect any modifications
490			* subsequent to construction.
491	dholmes	1.7	*
492	jsr166	1.32	* @return an iterator over the elements in this queue
493	dholmes	1.7	*/
494	dl	1.3	public Iterator<E> iterator() {
495	dl	1.44	return new Itr(toArray());
496	dl	1.2	}
497
498	dl	1.42	/**
499			* Snapshot iterator that works off copy of underlying q array.
500			*/
501	dl	1.44	private class Itr implements Iterator<E> {
502	dl	1.42	final Object[] array; // Array of all elements
503	jsr166	1.57	int cursor; // index of next element to return
504	jsr166	1.49	int lastRet; // index of last element, or -1 if no such
505	jsr166	1.43
506	dl	1.42	Itr(Object[] array) {
507			lastRet = -1;
508			this.array = array;
509	dl	1.2	}
510
511	tim	1.6	public boolean hasNext() {
512	dl	1.42	return cursor < array.length;
513	tim	1.6	}
514
515	jsr166	1.49	@SuppressWarnings("unchecked")
516	tim	1.6	public E next() {
517	dl	1.42	if (cursor >= array.length)
518			throw new NoSuchElementException();
519			lastRet = cursor;
520			return (E)array[cursor++];
521	tim	1.6	}
522
523			public void remove() {
524	jsr166	1.43	if (lastRet < 0)
525	jsr166	1.49	throw new IllegalStateException();
526	jsr166	1.57	removeEQ(array[lastRet]);
527	dl	1.42	lastRet = -1;
528	tim	1.6	}
529	tim	1.1	}
530
531			}