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/licenses/publicdomain
 */


package java.util.concurrent;
import java.util.concurrent.locks.*;
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.
 *
 * <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(TimeUnit.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(TimeUnit.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(TimeUnit.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();
        }
    }

    /**
     * @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 first = q.peek();
                if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0)
                    break;
                c.add(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;
            while (n < maxElements) {
                E first = q.peek();
                if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0)
                    break;
                c.add(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>
     *     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();
        }
    }

    /**
     * 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();
            Object x = array[lastRet];
            lastRet = -1;
            // Traverse underlying queue to find == element,
            // not just a .equals element.
            lock.lock();
            try {
                for (Iterator it = q.iterator(); it.hasNext(); ) {
                    if (it.next() == x) {
                        it.remove();
                        return;
                    }
                }
            } finally {
                lock.unlock();
            }
        }
    }

}
Revision:	1.51
Committed:	Fri Nov 19 08:02:09 2010 UTC (13 years, 6 months ago) by jsr166
Branch:	MAIN
Changes since 1.50:	+8 -6 lines
Log Message:	make iterator weakly consistent specs more consistent
#	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			* http://creativecommons.org/licenses/publicdomain
5	dl	1.2	*/
6
7	jsr166	1.50
8	tim	1.1	package java.util.concurrent;
9	dl	1.5	import java.util.concurrent.locks.*;
10	tim	1.1	import java.util.*;
11
12			/**
13	dl	1.27	* An unbounded {@linkplain BlockingQueue blocking queue} of
14			* <tt>Delayed</tt> elements, in which an element can only be taken
15			* when its delay has expired. The <em>head</em> of the queue is that
16			* <tt>Delayed</tt> element whose delay expired furthest in the
17	jsr166	1.32	* past. If no delay has expired there is no head and <tt>poll</tt>
18	dl	1.27	* will return <tt>null</tt>. Expiration occurs when an element's
19			* <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less
20	dl	1.36	* than or equal to zero. Even though unexpired elements cannot be
21			* removed using <tt>take</tt> or <tt>poll</tt>, they are otherwise
22			* treated as normal elements. For example, the <tt>size</tt> method
23			* returns the count of both expired and unexpired elements.
24	jsr166	1.39	* This queue does not permit null elements.
25	dl	1.25	*
26	dl	1.26	* <p>This class and its iterator implement all of the
27			* <em>optional</em> methods of the {@link Collection} and {@link
28	jsr166	1.29	* Iterator} interfaces.
29	dl	1.26	*
30	dl	1.25	* <p>This class is a member of the
31	jsr166	1.46	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
32	dl	1.25	* Java Collections Framework</a>.
33			*
34	dl	1.4	* @since 1.5
35			* @author Doug Lea
36	dl	1.20	* @param <E> the type of elements held in this collection
37	dl	1.19	*/
38	tim	1.1
39	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
40			implements BlockingQueue<E> {
41	tim	1.6
42	dl	1.2	private transient final ReentrantLock lock = new ReentrantLock();
43	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
44	tim	1.1
45	dl	1.4	/**
46	jsr166	1.48	* Thread designated to wait for the element at the head of
47			* the queue. This variant of the Leader-Follower pattern
48			* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
49			* minimize unnecessary timed waiting. When a thread becomes
50			* the leader, it waits only for the next delay to elapse, but
51			* other threads await indefinitely. The leader thread must
52			* signal some other thread before returning from take() or
53			* poll(...), unless some other thread becomes leader in the
54			* interim. Whenever the head of the queue is replaced with
55			* an element with an earlier expiration time, the leader
56			* field is invalidated by being reset to null, and some
57			* waiting thread, but not necessarily the current leader, is
58			* signalled. So waiting threads must be prepared to acquire
59			* and lose leadership while waiting.
60			*/
61			private Thread leader = null;
62
63			/**
64			* Condition signalled when a newer element becomes available
65			* at the head of the queue or a new thread may need to
66			* become leader.
67			*/
68			private final Condition available = lock.newCondition();
69
70			/**
71	dholmes	1.7	* Creates a new <tt>DelayQueue</tt> that is initially empty.
72	dl	1.4	*/
73	tim	1.1	public DelayQueue() {}
74
75	tim	1.6	/**
76	tim	1.9	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
77	dholmes	1.7	* given collection of {@link Delayed} instances.
78			*
79	jsr166	1.32	* @param c the collection of elements to initially contain
80			* @throws NullPointerException if the specified collection or any
81			* of its elements are null
82	tim	1.6	*/
83			public DelayQueue(Collection<? extends E> c) {
84			this.addAll(c);
85			}
86
87	dholmes	1.7	/**
88	dl	1.16	* Inserts the specified element into this delay queue.
89	dholmes	1.7	*
90	jsr166	1.30	* @param e the element to add
91	jsr166	1.38	* @return <tt>true</tt> (as specified by {@link Collection#add})
92	jsr166	1.32	* @throws NullPointerException if the specified element is null
93			*/
94			public boolean add(E e) {
95			return offer(e);
96			}
97
98			/**
99			* Inserts the specified element into this delay queue.
100			*
101			* @param e the element to add
102	dholmes	1.7	* @return <tt>true</tt>
103	jsr166	1.32	* @throws NullPointerException if the specified element is null
104	dholmes	1.7	*/
105	jsr166	1.30	public boolean offer(E e) {
106	dl	1.21	final ReentrantLock lock = this.lock;
107	dl	1.2	lock.lock();
108			try {
109	jsr166	1.30	q.offer(e);
110	jsr166	1.48	if (q.peek() == e) {
111	jsr166	1.49	leader = null;
112	jsr166	1.48	available.signal();
113	jsr166	1.49	}
114	dl	1.2	return true;
115	tim	1.13	} finally {
116	dl	1.2	lock.unlock();
117			}
118			}
119
120	dholmes	1.7	/**
121	jsr166	1.32	* Inserts the specified element into this delay queue. As the queue is
122	dholmes	1.7	* unbounded this method will never block.
123	jsr166	1.32	*
124	jsr166	1.30	* @param e the element to add
125	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
126	dholmes	1.7	*/
127	jsr166	1.30	public void put(E e) {
128			offer(e);
129	dl	1.2	}
130
131	dholmes	1.7	/**
132	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
133	dholmes	1.7	* unbounded this method will never block.
134	jsr166	1.32	*
135	jsr166	1.30	* @param e the element to add
136	dl	1.14	* @param timeout This parameter is ignored as the method never blocks
137	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
138			* @return <tt>true</tt>
139	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
140	dholmes	1.7	*/
141	jsr166	1.30	public boolean offer(E e, long timeout, TimeUnit unit) {
142			return offer(e);
143	dl	1.2	}
144
145	dholmes	1.7	/**
146	jsr166	1.32	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
147			* if this queue has no elements with an expired delay.
148	dholmes	1.7	*
149	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
150			* queue has no elements with an expired delay
151	dholmes	1.7	*/
152	jsr166	1.32	public E poll() {
153			final ReentrantLock lock = this.lock;
154			lock.lock();
155			try {
156			E first = q.peek();
157			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
158			return null;
159	jsr166	1.48	else
160			return q.poll();
161	jsr166	1.32	} finally {
162			lock.unlock();
163			}
164	dl	1.2	}
165
166	dl	1.27	/**
167	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
168			* until an element with an expired delay is available on this queue.
169			*
170	dl	1.27	* @return the head of this queue
171	jsr166	1.32	* @throws InterruptedException {@inheritDoc}
172	dl	1.27	*/
173	dl	1.3	public E take() throws InterruptedException {
174	dl	1.21	final ReentrantLock lock = this.lock;
175	dl	1.2	lock.lockInterruptibly();
176			try {
177			for (;;) {
178	dl	1.3	E first = q.peek();
179	jsr166	1.48	if (first == null)
180	dl	1.4	available.await();
181	jsr166	1.49	else {
182	jsr166	1.48	long delay = first.getDelay(TimeUnit.NANOSECONDS);
183	jsr166	1.49	if (delay <= 0)
184			return q.poll();
185			else if (leader != null)
186			available.await();
187			else {
188			Thread thisThread = Thread.currentThread();
189			leader = thisThread;
190			try {
191			available.awaitNanos(delay);
192			} finally {
193			if (leader == thisThread)
194			leader = null;
195			}
196	dl	1.2	}
197			}
198			}
199	tim	1.13	} finally {
200	jsr166	1.49	if (leader == null && q.peek() != null)
201			available.signal();
202	dl	1.2	lock.unlock();
203			}
204			}
205
206	dl	1.27	/**
207	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
208			* until an element with an expired delay is available on this queue,
209			* or the specified wait time expires.
210			*
211	dl	1.27	* @return the head of this queue, or <tt>null</tt> if the
212	jsr166	1.32	* specified waiting time elapses before an element with
213			* an expired delay becomes available
214			* @throws InterruptedException {@inheritDoc}
215	dl	1.27	*/
216			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
217	jsr166	1.41	long nanos = unit.toNanos(timeout);
218	dl	1.21	final ReentrantLock lock = this.lock;
219	dl	1.2	lock.lockInterruptibly();
220			try {
221			for (;;) {
222	dl	1.3	E first = q.peek();
223	dl	1.2	if (first == null) {
224			if (nanos <= 0)
225			return null;
226			else
227	dl	1.4	nanos = available.awaitNanos(nanos);
228	tim	1.13	} else {
229	jsr166	1.41	long delay = first.getDelay(TimeUnit.NANOSECONDS);
230	jsr166	1.49	if (delay <= 0)
231			return q.poll();
232			if (nanos <= 0)
233			return null;
234			if (nanos < delay \|\| leader != null)
235			nanos = available.awaitNanos(nanos);
236			else {
237			Thread thisThread = Thread.currentThread();
238			leader = thisThread;
239			try {
240			long timeLeft = available.awaitNanos(delay);
241			nanos -= delay - timeLeft;
242			} finally {
243			if (leader == thisThread)
244			leader = null;
245			}
246			}
247	dl	1.2	}
248			}
249	tim	1.13	} finally {
250	jsr166	1.49	if (leader == null && q.peek() != null)
251			available.signal();
252	dl	1.2	lock.unlock();
253			}
254			}
255
256	dl	1.27	/**
257	dl	1.36	* Retrieves, but does not remove, the head of this queue, or
258			* returns <tt>null</tt> if this queue is empty. Unlike
259			* <tt>poll</tt>, if no expired elements are available in the queue,
260			* this method returns the element that will expire next,
261			* if one exists.
262	dl	1.27	*
263	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
264	dl	1.35	* queue is empty.
265	dl	1.27	*/
266	dl	1.3	public E peek() {
267	dl	1.21	final ReentrantLock lock = this.lock;
268	dl	1.2	lock.lock();
269			try {
270			return q.peek();
271	tim	1.13	} finally {
272	dl	1.2	lock.unlock();
273			}
274	tim	1.1	}
275
276	dl	1.2	public int size() {
277	dl	1.21	final ReentrantLock lock = this.lock;
278	dl	1.2	lock.lock();
279			try {
280			return q.size();
281	tim	1.13	} finally {
282	dl	1.2	lock.unlock();
283			}
284			}
285
286	jsr166	1.32	/**
287			* @throws UnsupportedOperationException {@inheritDoc}
288			* @throws ClassCastException {@inheritDoc}
289			* @throws NullPointerException {@inheritDoc}
290			* @throws IllegalArgumentException {@inheritDoc}
291			*/
292	dl	1.17	public int drainTo(Collection<? super E> c) {
293			if (c == null)
294			throw new NullPointerException();
295			if (c == this)
296			throw new IllegalArgumentException();
297	dl	1.21	final ReentrantLock lock = this.lock;
298	dl	1.17	lock.lock();
299			try {
300			int n = 0;
301			for (;;) {
302			E first = q.peek();
303			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
304			break;
305			c.add(q.poll());
306			++n;
307			}
308			return n;
309			} finally {
310			lock.unlock();
311			}
312			}
313
314	jsr166	1.32	/**
315			* @throws UnsupportedOperationException {@inheritDoc}
316			* @throws ClassCastException {@inheritDoc}
317			* @throws NullPointerException {@inheritDoc}
318			* @throws IllegalArgumentException {@inheritDoc}
319			*/
320	dl	1.17	public int drainTo(Collection<? super E> c, int maxElements) {
321			if (c == null)
322			throw new NullPointerException();
323			if (c == this)
324			throw new IllegalArgumentException();
325			if (maxElements <= 0)
326			return 0;
327	dl	1.21	final ReentrantLock lock = this.lock;
328	dl	1.17	lock.lock();
329			try {
330			int n = 0;
331			while (n < maxElements) {
332			E first = q.peek();
333			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
334			break;
335			c.add(q.poll());
336			++n;
337			}
338			return n;
339			} finally {
340			lock.unlock();
341			}
342			}
343
344	dholmes	1.7	/**
345			* Atomically removes all of the elements from this delay queue.
346			* The queue will be empty after this call returns.
347	jsr166	1.32	* Elements with an unexpired delay are not waited for; they are
348			* simply discarded from the queue.
349	dholmes	1.7	*/
350	dl	1.2	public void clear() {
351	dl	1.21	final ReentrantLock lock = this.lock;
352	dl	1.2	lock.lock();
353			try {
354			q.clear();
355	tim	1.13	} finally {
356	dl	1.2	lock.unlock();
357			}
358			}
359	tim	1.1
360	dholmes	1.7	/**
361			* Always returns <tt>Integer.MAX_VALUE</tt> because
362			* a <tt>DelayQueue</tt> is not capacity constrained.
363	jsr166	1.32	*
364	dholmes	1.7	* @return <tt>Integer.MAX_VALUE</tt>
365			*/
366	dl	1.2	public int remainingCapacity() {
367			return Integer.MAX_VALUE;
368	tim	1.1	}
369	dl	1.2
370	jsr166	1.32	/**
371			* Returns an array containing all of the elements in this queue.
372			* The returned array elements are in no particular order.
373			*
374			* <p>The returned array will be "safe" in that no references to it are
375			* maintained by this queue. (In other words, this method must allocate
376			* a new array). The caller is thus free to modify the returned array.
377	jsr166	1.33	*
378	jsr166	1.32	* <p>This method acts as bridge between array-based and collection-based
379			* APIs.
380			*
381			* @return an array containing all of the elements in this queue
382			*/
383	dl	1.2	public Object[] toArray() {
384	dl	1.21	final ReentrantLock lock = this.lock;
385	dl	1.2	lock.lock();
386			try {
387			return q.toArray();
388	tim	1.13	} finally {
389	dl	1.2	lock.unlock();
390			}
391	tim	1.1	}
392	dl	1.2
393	jsr166	1.32	/**
394			* Returns an array containing all of the elements in this queue; the
395			* runtime type of the returned array is that of the specified array.
396			* The returned array elements are in no particular order.
397			* If the queue fits in the specified array, it is returned therein.
398			* Otherwise, a new array is allocated with the runtime type of the
399			* specified array and the size of this queue.
400			*
401			* <p>If this queue fits in the specified array with room to spare
402			* (i.e., the array has more elements than this queue), the element in
403			* the array immediately following the end of the queue is set to
404			* <tt>null</tt>.
405			*
406			* <p>Like the {@link #toArray()} method, this method acts as bridge between
407			* array-based and collection-based APIs. Further, this method allows
408			* precise control over the runtime type of the output array, and may,
409			* under certain circumstances, be used to save allocation costs.
410			*
411	jsr166	1.37	* <p>The following code can be used to dump a delay queue into a newly
412			* allocated array of <tt>Delayed</tt>:
413	jsr166	1.32	*
414			* <pre>
415	jsr166	1.37	* Delayed[] a = q.toArray(new Delayed[0]);</pre>
416	jsr166	1.32	*
417			* Note that <tt>toArray(new Object[0])</tt> is identical in function to
418			* <tt>toArray()</tt>.
419			*
420			* @param a the array into which the elements of the queue are to
421			* be stored, if it is big enough; otherwise, a new array of the
422			* same runtime type is allocated for this purpose
423			* @return an array containing all of the elements in this queue
424			* @throws ArrayStoreException if the runtime type of the specified array
425			* is not a supertype of the runtime type of every element in
426			* this queue
427			* @throws NullPointerException if the specified array is null
428			*/
429			public <T> T[] toArray(T[] a) {
430	dl	1.21	final ReentrantLock lock = this.lock;
431	dl	1.2	lock.lock();
432			try {
433	jsr166	1.32	return q.toArray(a);
434	tim	1.13	} finally {
435	dl	1.2	lock.unlock();
436			}
437	tim	1.1	}
438
439	dl	1.26	/**
440			* Removes a single instance of the specified element from this
441	dl	1.36	* queue, if it is present, whether or not it has expired.
442	dl	1.26	*/
443	dholmes	1.7	public boolean remove(Object o) {
444	dl	1.21	final ReentrantLock lock = this.lock;
445	dl	1.2	lock.lock();
446			try {
447	dholmes	1.7	return q.remove(o);
448	tim	1.13	} finally {
449	dl	1.2	lock.unlock();
450			}
451			}
452
453	dholmes	1.7	/**
454	dl	1.36	* Returns an iterator over all the elements (both expired and
455	dl	1.44	* unexpired) in this queue. The iterator does not return the
456	jsr166	1.51	* elements in any particular order.
457			*
458			* <p>The returned iterator is a "weakly consistent" iterator that
459			* will never throw {@link java.util.ConcurrentModificationException
460			* ConcurrentModificationException}, and guarantees to traverse
461			* elements as they existed upon construction of the iterator, and
462			* may (but is not guaranteed to) reflect any modifications
463			* subsequent to construction.
464	dholmes	1.7	*
465	jsr166	1.32	* @return an iterator over the elements in this queue
466	dholmes	1.7	*/
467	dl	1.3	public Iterator<E> iterator() {
468	dl	1.44	return new Itr(toArray());
469	dl	1.2	}
470
471	dl	1.42	/**
472			* Snapshot iterator that works off copy of underlying q array.
473			*/
474	dl	1.44	private class Itr implements Iterator<E> {
475	dl	1.42	final Object[] array; // Array of all elements
476	jsr166	1.49	int cursor; // index of next element to return;
477			int lastRet; // index of last element, or -1 if no such
478	jsr166	1.43
479	dl	1.42	Itr(Object[] array) {
480			lastRet = -1;
481			this.array = array;
482	dl	1.2	}
483
484	tim	1.6	public boolean hasNext() {
485	dl	1.42	return cursor < array.length;
486	tim	1.6	}
487
488	jsr166	1.49	@SuppressWarnings("unchecked")
489	tim	1.6	public E next() {
490	dl	1.42	if (cursor >= array.length)
491			throw new NoSuchElementException();
492			lastRet = cursor;
493			return (E)array[cursor++];
494	tim	1.6	}
495
496			public void remove() {
497	jsr166	1.43	if (lastRet < 0)
498	jsr166	1.49	throw new IllegalStateException();
499	dl	1.42	Object x = array[lastRet];
500			lastRet = -1;
501			// Traverse underlying queue to find == element,
502			// not just a .equals element.
503	dl	1.2	lock.lock();
504			try {
505	dl	1.42	for (Iterator it = q.iterator(); it.hasNext(); ) {
506			if (it.next() == x) {
507			it.remove();
508			return;
509			}
510			}
511	tim	1.13	} finally {
512	dl	1.2	lock.unlock();
513			}
514	tim	1.6	}
515	tim	1.1	}
516
517			}