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 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.  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(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> {@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();
        }
    }

    /**
     * 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<E> it = q.iterator(); it.hasNext(); ) {
                    if (it.next() == x) {
                        it.remove();
                        return;
                    }
                }
            } finally {
                lock.unlock();
            }
        }
    }

}
Revision:	1.55
Committed:	Thu Jun 9 07:48:43 2011 UTC (12 years, 11 months ago) by jsr166
Branch:	MAIN
Changes since 1.54:	+1 -2 lines
Log Message:	consistent style for code snippets
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.23	* Expert Group and released to the public domain, as explained at
4	jsr166	1.52	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.2	*/
6
7	jsr166	1.50
8	tim	1.1	package java.util.concurrent;
9	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	dl	1.53	* Iterator} interfaces. The Iterator provided in method {@link
29			* #iterator()} is <em>not</em> guaranteed to traverse the elements of
30			* the DelayQueue in any particular order.
31	dl	1.26	*
32	dl	1.25	* <p>This class is a member of the
33	jsr166	1.46	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
34	dl	1.25	* Java Collections Framework</a>.
35			*
36	dl	1.4	* @since 1.5
37			* @author Doug Lea
38	dl	1.20	* @param <E> the type of elements held in this collection
39	dl	1.19	*/
40	tim	1.1
41	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
42			implements BlockingQueue<E> {
43	tim	1.6
44	dl	1.2	private transient final ReentrantLock lock = new ReentrantLock();
45	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
46	tim	1.1
47	dl	1.4	/**
48	jsr166	1.48	* Thread designated to wait for the element at the head of
49			* the queue. This variant of the Leader-Follower pattern
50			* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
51			* minimize unnecessary timed waiting. When a thread becomes
52			* the leader, it waits only for the next delay to elapse, but
53			* other threads await indefinitely. The leader thread must
54			* signal some other thread before returning from take() or
55			* poll(...), unless some other thread becomes leader in the
56			* interim. Whenever the head of the queue is replaced with
57			* an element with an earlier expiration time, the leader
58			* field is invalidated by being reset to null, and some
59			* waiting thread, but not necessarily the current leader, is
60			* signalled. So waiting threads must be prepared to acquire
61			* and lose leadership while waiting.
62			*/
63			private Thread leader = null;
64
65			/**
66			* Condition signalled when a newer element becomes available
67			* at the head of the queue or a new thread may need to
68			* become leader.
69			*/
70			private final Condition available = lock.newCondition();
71
72			/**
73	dholmes	1.7	* Creates a new <tt>DelayQueue</tt> that is initially empty.
74	dl	1.4	*/
75	tim	1.1	public DelayQueue() {}
76
77	tim	1.6	/**
78	tim	1.9	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
79	dholmes	1.7	* given collection of {@link Delayed} instances.
80			*
81	jsr166	1.32	* @param c the collection of elements to initially contain
82			* @throws NullPointerException if the specified collection or any
83			* of its elements are null
84	tim	1.6	*/
85			public DelayQueue(Collection<? extends E> c) {
86			this.addAll(c);
87			}
88
89	dholmes	1.7	/**
90	dl	1.16	* Inserts the specified element into this delay queue.
91	dholmes	1.7	*
92	jsr166	1.30	* @param e the element to add
93	jsr166	1.38	* @return <tt>true</tt> (as specified by {@link Collection#add})
94	jsr166	1.32	* @throws NullPointerException if the specified element is null
95			*/
96			public boolean add(E e) {
97			return offer(e);
98			}
99
100			/**
101			* Inserts the specified element into this delay queue.
102			*
103			* @param e the element to add
104	dholmes	1.7	* @return <tt>true</tt>
105	jsr166	1.32	* @throws NullPointerException if the specified element is null
106	dholmes	1.7	*/
107	jsr166	1.30	public boolean offer(E e) {
108	dl	1.21	final ReentrantLock lock = this.lock;
109	dl	1.2	lock.lock();
110			try {
111	jsr166	1.30	q.offer(e);
112	jsr166	1.48	if (q.peek() == e) {
113	jsr166	1.49	leader = null;
114	jsr166	1.48	available.signal();
115	jsr166	1.49	}
116	dl	1.2	return true;
117	tim	1.13	} finally {
118	dl	1.2	lock.unlock();
119			}
120			}
121
122	dholmes	1.7	/**
123	jsr166	1.32	* Inserts the specified element into this delay queue. As the queue is
124	dholmes	1.7	* unbounded this method will never block.
125	jsr166	1.32	*
126	jsr166	1.30	* @param e the element to add
127	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
128	dholmes	1.7	*/
129	jsr166	1.30	public void put(E e) {
130			offer(e);
131	dl	1.2	}
132
133	dholmes	1.7	/**
134	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
135	dholmes	1.7	* unbounded this method will never block.
136	jsr166	1.32	*
137	jsr166	1.30	* @param e the element to add
138	dl	1.14	* @param timeout This parameter is ignored as the method never blocks
139	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
140			* @return <tt>true</tt>
141	jsr166	1.32	* @throws NullPointerException {@inheritDoc}
142	dholmes	1.7	*/
143	jsr166	1.30	public boolean offer(E e, long timeout, TimeUnit unit) {
144			return offer(e);
145	dl	1.2	}
146
147	dholmes	1.7	/**
148	jsr166	1.32	* Retrieves and removes the head of this queue, or returns <tt>null</tt>
149			* if this queue has no elements with an expired delay.
150	dholmes	1.7	*
151	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
152			* queue has no elements with an expired delay
153	dholmes	1.7	*/
154	jsr166	1.32	public E poll() {
155			final ReentrantLock lock = this.lock;
156			lock.lock();
157			try {
158			E first = q.peek();
159			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
160			return null;
161	jsr166	1.48	else
162			return q.poll();
163	jsr166	1.32	} finally {
164			lock.unlock();
165			}
166	dl	1.2	}
167
168	dl	1.27	/**
169	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
170			* until an element with an expired delay is available on this queue.
171			*
172	dl	1.27	* @return the head of this queue
173	jsr166	1.32	* @throws InterruptedException {@inheritDoc}
174	dl	1.27	*/
175	dl	1.3	public E take() throws InterruptedException {
176	dl	1.21	final ReentrantLock lock = this.lock;
177	dl	1.2	lock.lockInterruptibly();
178			try {
179			for (;;) {
180	dl	1.3	E first = q.peek();
181	jsr166	1.48	if (first == null)
182	dl	1.4	available.await();
183	jsr166	1.49	else {
184	jsr166	1.48	long delay = first.getDelay(TimeUnit.NANOSECONDS);
185	jsr166	1.49	if (delay <= 0)
186			return q.poll();
187			else if (leader != null)
188			available.await();
189			else {
190			Thread thisThread = Thread.currentThread();
191			leader = thisThread;
192			try {
193			available.awaitNanos(delay);
194			} finally {
195			if (leader == thisThread)
196			leader = null;
197			}
198	dl	1.2	}
199			}
200			}
201	tim	1.13	} finally {
202	jsr166	1.49	if (leader == null && q.peek() != null)
203			available.signal();
204	dl	1.2	lock.unlock();
205			}
206			}
207
208	dl	1.27	/**
209	jsr166	1.32	* Retrieves and removes the head of this queue, waiting if necessary
210			* until an element with an expired delay is available on this queue,
211			* or the specified wait time expires.
212			*
213	dl	1.27	* @return the head of this queue, or <tt>null</tt> if the
214	jsr166	1.32	* specified waiting time elapses before an element with
215			* an expired delay becomes available
216			* @throws InterruptedException {@inheritDoc}
217	dl	1.27	*/
218			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
219	jsr166	1.41	long nanos = unit.toNanos(timeout);
220	dl	1.21	final ReentrantLock lock = this.lock;
221	dl	1.2	lock.lockInterruptibly();
222			try {
223			for (;;) {
224	dl	1.3	E first = q.peek();
225	dl	1.2	if (first == null) {
226			if (nanos <= 0)
227			return null;
228			else
229	dl	1.4	nanos = available.awaitNanos(nanos);
230	tim	1.13	} else {
231	jsr166	1.41	long delay = first.getDelay(TimeUnit.NANOSECONDS);
232	jsr166	1.49	if (delay <= 0)
233			return q.poll();
234			if (nanos <= 0)
235			return null;
236			if (nanos < delay \|\| leader != null)
237			nanos = available.awaitNanos(nanos);
238			else {
239			Thread thisThread = Thread.currentThread();
240			leader = thisThread;
241			try {
242			long timeLeft = available.awaitNanos(delay);
243			nanos -= delay - timeLeft;
244			} finally {
245			if (leader == thisThread)
246			leader = null;
247			}
248			}
249	dl	1.2	}
250			}
251	tim	1.13	} finally {
252	jsr166	1.49	if (leader == null && q.peek() != null)
253			available.signal();
254	dl	1.2	lock.unlock();
255			}
256			}
257
258	dl	1.27	/**
259	dl	1.36	* Retrieves, but does not remove, the head of this queue, or
260			* returns <tt>null</tt> if this queue is empty. Unlike
261			* <tt>poll</tt>, if no expired elements are available in the queue,
262			* this method returns the element that will expire next,
263			* if one exists.
264	dl	1.27	*
265	jsr166	1.32	* @return the head of this queue, or <tt>null</tt> if this
266	dl	1.35	* queue is empty.
267	dl	1.27	*/
268	dl	1.3	public E peek() {
269	dl	1.21	final ReentrantLock lock = this.lock;
270	dl	1.2	lock.lock();
271			try {
272			return q.peek();
273	tim	1.13	} finally {
274	dl	1.2	lock.unlock();
275			}
276	tim	1.1	}
277
278	dl	1.2	public int size() {
279	dl	1.21	final ReentrantLock lock = this.lock;
280	dl	1.2	lock.lock();
281			try {
282			return q.size();
283	tim	1.13	} finally {
284	dl	1.2	lock.unlock();
285			}
286			}
287
288	jsr166	1.32	/**
289			* @throws UnsupportedOperationException {@inheritDoc}
290			* @throws ClassCastException {@inheritDoc}
291			* @throws NullPointerException {@inheritDoc}
292			* @throws IllegalArgumentException {@inheritDoc}
293			*/
294	dl	1.17	public int drainTo(Collection<? super E> c) {
295			if (c == null)
296			throw new NullPointerException();
297			if (c == this)
298			throw new IllegalArgumentException();
299	dl	1.21	final ReentrantLock lock = this.lock;
300	dl	1.17	lock.lock();
301			try {
302			int n = 0;
303			for (;;) {
304			E first = q.peek();
305			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
306			break;
307			c.add(q.poll());
308			++n;
309			}
310			return n;
311			} finally {
312			lock.unlock();
313			}
314			}
315
316	jsr166	1.32	/**
317			* @throws UnsupportedOperationException {@inheritDoc}
318			* @throws ClassCastException {@inheritDoc}
319			* @throws NullPointerException {@inheritDoc}
320			* @throws IllegalArgumentException {@inheritDoc}
321			*/
322	dl	1.17	public int drainTo(Collection<? super E> c, int maxElements) {
323			if (c == null)
324			throw new NullPointerException();
325			if (c == this)
326			throw new IllegalArgumentException();
327			if (maxElements <= 0)
328			return 0;
329	dl	1.21	final ReentrantLock lock = this.lock;
330	dl	1.17	lock.lock();
331			try {
332			int n = 0;
333			while (n < maxElements) {
334			E first = q.peek();
335			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
336			break;
337			c.add(q.poll());
338			++n;
339			}
340			return n;
341			} finally {
342			lock.unlock();
343			}
344			}
345
346	dholmes	1.7	/**
347			* Atomically removes all of the elements from this delay queue.
348			* The queue will be empty after this call returns.
349	jsr166	1.32	* Elements with an unexpired delay are not waited for; they are
350			* simply discarded from the queue.
351	dholmes	1.7	*/
352	dl	1.2	public void clear() {
353	dl	1.21	final ReentrantLock lock = this.lock;
354	dl	1.2	lock.lock();
355			try {
356			q.clear();
357	tim	1.13	} finally {
358	dl	1.2	lock.unlock();
359			}
360			}
361	tim	1.1
362	dholmes	1.7	/**
363			* Always returns <tt>Integer.MAX_VALUE</tt> because
364			* a <tt>DelayQueue</tt> is not capacity constrained.
365	jsr166	1.32	*
366	dholmes	1.7	* @return <tt>Integer.MAX_VALUE</tt>
367			*/
368	dl	1.2	public int remainingCapacity() {
369			return Integer.MAX_VALUE;
370	tim	1.1	}
371	dl	1.2
372	jsr166	1.32	/**
373			* Returns an array containing all of the elements in this queue.
374			* The returned array elements are in no particular order.
375			*
376			* <p>The returned array will be "safe" in that no references to it are
377			* maintained by this queue. (In other words, this method must allocate
378			* a new array). The caller is thus free to modify the returned array.
379	jsr166	1.33	*
380	jsr166	1.32	* <p>This method acts as bridge between array-based and collection-based
381			* APIs.
382			*
383			* @return an array containing all of the elements in this queue
384			*/
385	dl	1.2	public Object[] toArray() {
386	dl	1.21	final ReentrantLock lock = this.lock;
387	dl	1.2	lock.lock();
388			try {
389			return q.toArray();
390	tim	1.13	} finally {
391	dl	1.2	lock.unlock();
392			}
393	tim	1.1	}
394	dl	1.2
395	jsr166	1.32	/**
396			* Returns an array containing all of the elements in this queue; the
397			* runtime type of the returned array is that of the specified array.
398			* The returned array elements are in no particular order.
399			* If the queue fits in the specified array, it is returned therein.
400			* Otherwise, a new array is allocated with the runtime type of the
401			* specified array and the size of this queue.
402			*
403			* <p>If this queue fits in the specified array with room to spare
404			* (i.e., the array has more elements than this queue), the element in
405			* the array immediately following the end of the queue is set to
406			* <tt>null</tt>.
407			*
408			* <p>Like the {@link #toArray()} method, this method acts as bridge between
409			* array-based and collection-based APIs. Further, this method allows
410			* precise control over the runtime type of the output array, and may,
411			* under certain circumstances, be used to save allocation costs.
412			*
413	jsr166	1.37	* <p>The following code can be used to dump a delay queue into a newly
414			* allocated array of <tt>Delayed</tt>:
415	jsr166	1.32	*
416	jsr166	1.55	* <pre> {@code Delayed[] a = q.toArray(new Delayed[0]);}</pre>
417	jsr166	1.32	*
418			* Note that <tt>toArray(new Object[0])</tt> is identical in function to
419			* <tt>toArray()</tt>.
420			*
421			* @param a the array into which the elements of the queue are to
422			* be stored, if it is big enough; otherwise, a new array of the
423			* same runtime type is allocated for this purpose
424			* @return an array containing all of the elements in this queue
425			* @throws ArrayStoreException if the runtime type of the specified array
426			* is not a supertype of the runtime type of every element in
427			* this queue
428			* @throws NullPointerException if the specified array is null
429			*/
430			public <T> T[] toArray(T[] a) {
431	dl	1.21	final ReentrantLock lock = this.lock;
432	dl	1.2	lock.lock();
433			try {
434	jsr166	1.32	return q.toArray(a);
435	tim	1.13	} finally {
436	dl	1.2	lock.unlock();
437			}
438	tim	1.1	}
439
440	dl	1.26	/**
441			* Removes a single instance of the specified element from this
442	dl	1.36	* queue, if it is present, whether or not it has expired.
443	dl	1.26	*/
444	dholmes	1.7	public boolean remove(Object o) {
445	dl	1.21	final ReentrantLock lock = this.lock;
446	dl	1.2	lock.lock();
447			try {
448	dholmes	1.7	return q.remove(o);
449	tim	1.13	} finally {
450	dl	1.2	lock.unlock();
451			}
452			}
453
454	dholmes	1.7	/**
455	dl	1.36	* Returns an iterator over all the elements (both expired and
456	dl	1.44	* unexpired) in this queue. The iterator does not return the
457	jsr166	1.51	* elements in any particular order.
458			*
459			* <p>The returned iterator is a "weakly consistent" iterator that
460			* will never throw {@link java.util.ConcurrentModificationException
461			* ConcurrentModificationException}, and guarantees to traverse
462			* elements as they existed upon construction of the iterator, and
463			* may (but is not guaranteed to) reflect any modifications
464			* subsequent to construction.
465	dholmes	1.7	*
466	jsr166	1.32	* @return an iterator over the elements in this queue
467	dholmes	1.7	*/
468	dl	1.3	public Iterator<E> iterator() {
469	dl	1.44	return new Itr(toArray());
470	dl	1.2	}
471
472	dl	1.42	/**
473			* Snapshot iterator that works off copy of underlying q array.
474			*/
475	dl	1.44	private class Itr implements Iterator<E> {
476	dl	1.42	final Object[] array; // Array of all elements
477	jsr166	1.49	int cursor; // index of next element to return;
478			int lastRet; // index of last element, or -1 if no such
479	jsr166	1.43
480	dl	1.42	Itr(Object[] array) {
481			lastRet = -1;
482			this.array = array;
483	dl	1.2	}
484
485	tim	1.6	public boolean hasNext() {
486	dl	1.42	return cursor < array.length;
487	tim	1.6	}
488
489	jsr166	1.49	@SuppressWarnings("unchecked")
490	tim	1.6	public E next() {
491	dl	1.42	if (cursor >= array.length)
492			throw new NoSuchElementException();
493			lastRet = cursor;
494			return (E)array[cursor++];
495	tim	1.6	}
496
497			public void remove() {
498	jsr166	1.43	if (lastRet < 0)
499	jsr166	1.49	throw new IllegalStateException();
500	dl	1.42	Object x = array[lastRet];
501			lastRet = -1;
502			// Traverse underlying queue to find == element,
503			// not just a .equals element.
504	dl	1.2	lock.lock();
505			try {
506	jsr166	1.54	for (Iterator<E> it = q.iterator(); it.hasNext(); ) {
507	dl	1.42	if (it.next() == x) {
508			it.remove();
509			return;
510			}
511			}
512	tim	1.13	} finally {
513	dl	1.2	lock.unlock();
514			}
515	tim	1.6	}
516	tim	1.1	}
517
518			}