util/concurrent/DelayQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */


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>.
 * This queue does not permit <tt>null</tt> elements.
 * <p>This class implements all of the <em>optional</em> methods
 * of the {@link Collection} and {@link Iterator} interfaces.
 * @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 transient final ReentrantLock.ConditionObject available = lock.newCondition();
    private final PriorityQueue<E> q = new PriorityQueue<E>();

    /**
     * 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.
     *
     * @throws NullPointerException if <tt>c</tt> or any element within it
     * is <tt>null</tt>
     *
     */
    public DelayQueue(Collection<? extends E> c) {
        this.addAll(c);
    }

    /**
     * Inserts the specified element into this delay queue.
     *
     * @param o the element to add
     * @return <tt>true</tt>
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     */
    public boolean offer(E o) {
        lock.lock();
        try {
            E first = q.peek();
            q.offer(o);
            if (first == null || o.compareTo(first) < 0)
                available.signalAll();
            return true;
        } finally {
            lock.unlock();
        }
    }


    /**
     * Adds the specified element to this delay queue. As the queue is
     * unbounded this method will never block.
     * @param o the element to add
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     */
    public void put(E o) {
        offer(o);
    }

    /**
     * Inserts the specified element into this delay queue. As the queue is
     * unbounded this method will never block.
     * @param o 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 if the specified element is <tt>null</tt>.
     */
    public boolean offer(E o, long timeout, TimeUnit unit) {
        return offer(o);
    }

    /**
     * Adds the specified element to this queue.
     * @param o the element to add
     * @return <tt>true</tt> (as per the general contract of
     * <tt>Collection.add</tt>).
     *
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     */
    public boolean add(E o) {
        return offer(o);
    }

    public E take() throws InterruptedException {
        lock.lockInterruptibly();
        try {
            for (;;) {
                E first = q.peek();
                if (first == null) {
                    available.await();
                } else {
                    long delay =  first.getDelay(TimeUnit.NANOSECONDS);
                    if (delay > 0) {
                        long tl = available.awaitNanos(delay);
                    } else {
                        E x = q.poll();
                        assert x != null;
                        if (q.size() != 0)
                            available.signalAll(); // wake up other takers
                        return x;

                    }
                }
            }
        } finally {
            lock.unlock();
        }
    }

    public E poll(long time, TimeUnit unit) throws InterruptedException {
        lock.lockInterruptibly();
        long nanos = unit.toNanos(time);
        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) {
                        if (delay > nanos)
                            delay = nanos;
                        long timeLeft = available.awaitNanos(delay);
                        nanos -= delay - timeLeft;
                    } else {
                        E x = q.poll();
                        assert x != null;
                        if (q.size() != 0)
                            available.signalAll();
                        return x;
                    }
                }
            }
        } finally {
            lock.unlock();
        }
    }


    public E poll() {
        lock.lock();
        try {
            E first = q.peek();
            if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0)
                return null;
            else {
                E x = q.poll();
                assert x != null;
                if (q.size() != 0)
                    available.signalAll();
                return x;
            }
        } finally {
            lock.unlock();
        }
    }

    public E peek() {
        lock.lock();
        try {
            return q.peek();
        } finally {
            lock.unlock();
        }
    }

    public int size() {
        lock.lock();
        try {
            return q.size();
        } finally {
            lock.unlock();
        }
    }

    public int drainTo(Collection<? super E> c) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        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;
            }
            if (n > 0)
                available.signalAll();
            return n;
        } finally {
            lock.unlock();
        }
    }

    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;
        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;
            }
            if (n > 0)
                available.signalAll();
            return n;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Atomically removes all of the elements from this delay queue.
     * The queue will be empty after this call returns.
     */
    public void clear() {
        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;
    }

    public Object[] toArray() {
        lock.lock();
        try {
            return q.toArray();
        } finally {
            lock.unlock();
        }
    }

    public <T> T[] toArray(T[] array) {
        lock.lock();
        try {
            return q.toArray(array);
        } finally {
            lock.unlock();
        }
    }

    public boolean remove(Object o) {
        lock.lock();
        try {
            return q.remove(o);
        } finally {
            lock.unlock();
        }
    }

    /**
     * Returns an iterator over the elements in this queue. The iterator
     * does not return the elements in any particular order. The
     * returned iterator is a thread-safe "fast-fail" iterator that will
     * throw {@link java.util.ConcurrentModificationException}
     * upon detected interference.
     *
     * @return an iterator over the elements in this queue.
     */
    public Iterator<E> iterator() {
        lock.lock();
        try {
            return new Itr(q.iterator());
        } finally {
            lock.unlock();
        }
    }

    private class Itr<E> implements Iterator<E> {
        private final Iterator<E> iter;
        Itr(Iterator<E> i) {
            iter = i;
        }

        public boolean hasNext() {
            return iter.hasNext();
        }

        public E next() {
            lock.lock();
            try {
                return iter.next();
            } finally {
                lock.unlock();
            }
        }

        public void remove() {
            lock.lock();
            try {
                iter.remove();
            } finally {
                lock.unlock();
            }
        }
    }

}
Revision:	1.20
Committed:	Sun Oct 19 13:38:34 2003 UTC (20 years, 7 months ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_NOV3_FREEZE, JSR166_DEC9_PRE_ES_SUBMIT, JSR166_DEC9_POST_ES_SUBMIT
Changes since 1.19:	+1 -1 lines
Log Message:	Changed doc strings for generic params
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5			*/
6
7
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	tim	1.9	* An unbounded {@linkplain BlockingQueue blocking queue} of <tt>Delayed</tt>
14	dholmes	1.7	* elements, in which an element can only be taken when its delay has expired.
15			* The <em>head</em> of the queue is that <tt>Delayed</tt> element whose delay
16			* expired furthest in the past - if no delay has expired there is no head and
17			* <tt>poll</tt> will return <tt>null</tt>.
18			* This queue does not permit <tt>null</tt> elements.
19	dl	1.15	* <p>This class implements all of the <em>optional</em> methods
20			* of the {@link Collection} and {@link Iterator} interfaces.
21	dl	1.4	* @since 1.5
22			* @author Doug Lea
23	dl	1.20	* @param <E> the type of elements held in this collection
24	dl	1.19	*/
25	tim	1.1
26	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
27			implements BlockingQueue<E> {
28	tim	1.6
29	dl	1.2	private transient final ReentrantLock lock = new ReentrantLock();
30	dl	1.18	private transient final ReentrantLock.ConditionObject available = lock.newCondition();
31	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
32	tim	1.1
33	dl	1.4	/**
34	dholmes	1.7	* Creates a new <tt>DelayQueue</tt> that is initially empty.
35	dl	1.4	*/
36	tim	1.1	public DelayQueue() {}
37
38	tim	1.6	/**
39	tim	1.9	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
40	dholmes	1.7	* given collection of {@link Delayed} instances.
41			*
42			* @throws NullPointerException if <tt>c</tt> or any element within it
43			* is <tt>null</tt>
44	tim	1.6	*
45			*/
46			public DelayQueue(Collection<? extends E> c) {
47			this.addAll(c);
48			}
49
50	dholmes	1.7	/**
51	dl	1.16	* Inserts the specified element into this delay queue.
52	dholmes	1.7	*
53	dl	1.14	* @param o the element to add
54	dholmes	1.7	* @return <tt>true</tt>
55	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
56	dholmes	1.7	*/
57			public boolean offer(E o) {
58	dl	1.2	lock.lock();
59			try {
60	dl	1.3	E first = q.peek();
61	dholmes	1.7	q.offer(o);
62			if (first == null \|\| o.compareTo(first) < 0)
63	dl	1.4	available.signalAll();
64	dl	1.2	return true;
65	tim	1.13	} finally {
66	dl	1.2	lock.unlock();
67			}
68			}
69
70	dholmes	1.7
71			/**
72			* Adds the specified element to this delay queue. As the queue is
73			* unbounded this method will never block.
74	dl	1.14	* @param o the element to add
75			* @throws NullPointerException if the specified element is <tt>null</tt>.
76	dholmes	1.7	*/
77			public void put(E o) {
78			offer(o);
79	dl	1.2	}
80
81	dholmes	1.7	/**
82	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
83	dholmes	1.7	* unbounded this method will never block.
84	dl	1.14	* @param o the element to add
85			* @param timeout This parameter is ignored as the method never blocks
86	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
87			* @return <tt>true</tt>
88	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
89	dholmes	1.7	*/
90	dl	1.14	public boolean offer(E o, long timeout, TimeUnit unit) {
91	dholmes	1.7	return offer(o);
92	dl	1.2	}
93
94	dholmes	1.7	/**
95			* Adds the specified element to this queue.
96	dl	1.14	* @param o the element to add
97	dholmes	1.7	* @return <tt>true</tt> (as per the general contract of
98			* <tt>Collection.add</tt>).
99			*
100	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
101	dholmes	1.7	*/
102			public boolean add(E o) {
103			return offer(o);
104	dl	1.2	}
105
106	dl	1.3	public E take() throws InterruptedException {
107	dl	1.2	lock.lockInterruptibly();
108			try {
109			for (;;) {
110	dl	1.3	E first = q.peek();
111	dl	1.12	if (first == null) {
112	dl	1.4	available.await();
113	tim	1.13	} else {
114	dl	1.2	long delay = first.getDelay(TimeUnit.NANOSECONDS);
115	dl	1.12	if (delay > 0) {
116			long tl = available.awaitNanos(delay);
117	tim	1.13	} else {
118	dl	1.3	E x = q.poll();
119	dl	1.2	assert x != null;
120			if (q.size() != 0)
121	dl	1.4	available.signalAll(); // wake up other takers
122	dl	1.2	return x;
123	tim	1.6
124	dl	1.2	}
125			}
126			}
127	tim	1.13	} finally {
128	dl	1.2	lock.unlock();
129			}
130			}
131
132	dl	1.3	public E poll(long time, TimeUnit unit) throws InterruptedException {
133	dl	1.2	lock.lockInterruptibly();
134			long nanos = unit.toNanos(time);
135			try {
136			for (;;) {
137	dl	1.3	E first = q.peek();
138	dl	1.2	if (first == null) {
139			if (nanos <= 0)
140			return null;
141			else
142	dl	1.4	nanos = available.awaitNanos(nanos);
143	tim	1.13	} else {
144	dl	1.2	long delay = first.getDelay(TimeUnit.NANOSECONDS);
145			if (delay > 0) {
146			if (delay > nanos)
147			delay = nanos;
148	dl	1.4	long timeLeft = available.awaitNanos(delay);
149	dl	1.2	nanos -= delay - timeLeft;
150	tim	1.13	} else {
151	dl	1.3	E x = q.poll();
152	dl	1.2	assert x != null;
153			if (q.size() != 0)
154	tim	1.6	available.signalAll();
155	dl	1.2	return x;
156			}
157			}
158			}
159	tim	1.13	} finally {
160	dl	1.2	lock.unlock();
161			}
162			}
163
164
165	dl	1.3	public E poll() {
166	dl	1.2	lock.lock();
167			try {
168	dl	1.3	E first = q.peek();
169	dl	1.2	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
170			return null;
171			else {
172	dl	1.3	E x = q.poll();
173	dl	1.2	assert x != null;
174			if (q.size() != 0)
175	tim	1.6	available.signalAll();
176	dl	1.2	return x;
177			}
178	tim	1.13	} finally {
179	dl	1.2	lock.unlock();
180			}
181			}
182
183	dl	1.3	public E peek() {
184	dl	1.2	lock.lock();
185			try {
186			return q.peek();
187	tim	1.13	} finally {
188	dl	1.2	lock.unlock();
189			}
190	tim	1.1	}
191
192	dl	1.2	public int size() {
193			lock.lock();
194			try {
195			return q.size();
196	tim	1.13	} finally {
197	dl	1.2	lock.unlock();
198			}
199			}
200
201	dl	1.17	public int drainTo(Collection<? super E> c) {
202			if (c == null)
203			throw new NullPointerException();
204			if (c == this)
205			throw new IllegalArgumentException();
206			lock.lock();
207			try {
208			int n = 0;
209			for (;;) {
210			E first = q.peek();
211			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
212			break;
213			c.add(q.poll());
214			++n;
215			}
216			if (n > 0)
217			available.signalAll();
218			return n;
219			} finally {
220			lock.unlock();
221			}
222			}
223
224			public int drainTo(Collection<? super E> c, int maxElements) {
225			if (c == null)
226			throw new NullPointerException();
227			if (c == this)
228			throw new IllegalArgumentException();
229			if (maxElements <= 0)
230			return 0;
231			lock.lock();
232			try {
233			int n = 0;
234			while (n < maxElements) {
235			E first = q.peek();
236			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
237			break;
238			c.add(q.poll());
239			++n;
240			}
241			if (n > 0)
242			available.signalAll();
243			return n;
244			} finally {
245			lock.unlock();
246			}
247			}
248
249	dholmes	1.7	/**
250			* Atomically removes all of the elements from this delay queue.
251			* The queue will be empty after this call returns.
252			*/
253	dl	1.2	public void clear() {
254			lock.lock();
255			try {
256			q.clear();
257	tim	1.13	} finally {
258	dl	1.2	lock.unlock();
259			}
260			}
261	tim	1.1
262	dholmes	1.7	/**
263			* Always returns <tt>Integer.MAX_VALUE</tt> because
264			* a <tt>DelayQueue</tt> is not capacity constrained.
265			* @return <tt>Integer.MAX_VALUE</tt>
266			*/
267	dl	1.2	public int remainingCapacity() {
268			return Integer.MAX_VALUE;
269	tim	1.1	}
270	dl	1.2
271			public Object[] toArray() {
272			lock.lock();
273			try {
274			return q.toArray();
275	tim	1.13	} finally {
276	dl	1.2	lock.unlock();
277			}
278	tim	1.1	}
279	dl	1.2
280			public <T> T[] toArray(T[] array) {
281			lock.lock();
282			try {
283			return q.toArray(array);
284	tim	1.13	} finally {
285	dl	1.2	lock.unlock();
286			}
287	tim	1.1	}
288
289	dholmes	1.7	public boolean remove(Object o) {
290	dl	1.2	lock.lock();
291			try {
292	dholmes	1.7	return q.remove(o);
293	tim	1.13	} finally {
294	dl	1.2	lock.unlock();
295			}
296			}
297
298	dholmes	1.7	/**
299			* Returns an iterator over the elements in this queue. The iterator
300	dl	1.8	* does not return the elements in any particular order. The
301	dl	1.15	* returned iterator is a thread-safe "fast-fail" iterator that will
302	dl	1.8	* throw {@link java.util.ConcurrentModificationException}
303			* upon detected interference.
304	dholmes	1.7	*
305			* @return an iterator over the elements in this queue.
306			*/
307	dl	1.3	public Iterator<E> iterator() {
308	dl	1.2	lock.lock();
309			try {
310			return new Itr(q.iterator());
311	tim	1.13	} finally {
312	dl	1.2	lock.unlock();
313			}
314			}
315
316	dl	1.3	private class Itr<E> implements Iterator<E> {
317			private final Iterator<E> iter;
318	tim	1.6	Itr(Iterator<E> i) {
319			iter = i;
320	dl	1.2	}
321
322	tim	1.6	public boolean hasNext() {
323	dl	1.2	return iter.hasNext();
324	tim	1.6	}
325
326			public E next() {
327	dl	1.2	lock.lock();
328			try {
329			return iter.next();
330	tim	1.13	} finally {
331	dl	1.2	lock.unlock();
332			}
333	tim	1.6	}
334
335			public void remove() {
336	dl	1.2	lock.lock();
337			try {
338			iter.remove();
339	tim	1.13	} finally {
340	dl	1.2	lock.unlock();
341			}
342	tim	1.6	}
343	tim	1.1	}
344
345			}