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>.
 * 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 Condition 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) {
        final ReentrantLock lock = this.lock;
        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 {
        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) {
                        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 {
        final ReentrantLock lock = this.lock;
        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() {
        final ReentrantLock lock = this.lock;
        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() {
        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();
        }
    }

    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;
            }
            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;
        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;
            }
            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() {
        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;
    }

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

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

    public boolean remove(Object o) {
        final ReentrantLock lock = this.lock;
        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() {
        final ReentrantLock lock = this.lock;
        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() {
            final ReentrantLock lock = DelayQueue.this.lock;
            lock.lock();
            try {
                return iter.next();
            } finally {
                lock.unlock();
            }
        }

        public void remove() {
            final ReentrantLock lock = DelayQueue.this.lock;
            lock.lock();
            try {
                iter.remove();
            } finally {
                lock.unlock();
            }
        }
    }

}
Revision:	1.23
Committed:	Sat Dec 27 19:26:25 2003 UTC (20 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.22:	+2 -2 lines
Log Message:	Headers reference Creative Commons
#	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
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	1.22	private transient final Condition 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	1.21	final ReentrantLock lock = this.lock;
59	dl	1.2	lock.lock();
60			try {
61	dl	1.3	E first = q.peek();
62	dholmes	1.7	q.offer(o);
63			if (first == null \|\| o.compareTo(first) < 0)
64	dl	1.4	available.signalAll();
65	dl	1.2	return true;
66	tim	1.13	} finally {
67	dl	1.2	lock.unlock();
68			}
69			}
70
71	dholmes	1.7
72			/**
73			* Adds the specified element to this delay queue. As the queue is
74			* unbounded this method will never block.
75	dl	1.14	* @param o the element to add
76			* @throws NullPointerException if the specified element is <tt>null</tt>.
77	dholmes	1.7	*/
78			public void put(E o) {
79			offer(o);
80	dl	1.2	}
81
82	dholmes	1.7	/**
83	dl	1.16	* Inserts the specified element into this delay queue. As the queue is
84	dholmes	1.7	* unbounded this method will never block.
85	dl	1.14	* @param o the element to add
86			* @param timeout This parameter is ignored as the method never blocks
87	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
88			* @return <tt>true</tt>
89	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
90	dholmes	1.7	*/
91	dl	1.14	public boolean offer(E o, long timeout, TimeUnit unit) {
92	dholmes	1.7	return offer(o);
93	dl	1.2	}
94
95	dholmes	1.7	/**
96			* Adds the specified element to this queue.
97	dl	1.14	* @param o the element to add
98	dholmes	1.7	* @return <tt>true</tt> (as per the general contract of
99			* <tt>Collection.add</tt>).
100			*
101	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
102	dholmes	1.7	*/
103			public boolean add(E o) {
104			return offer(o);
105	dl	1.2	}
106
107	dl	1.3	public E take() throws InterruptedException {
108	dl	1.21	final ReentrantLock lock = this.lock;
109	dl	1.2	lock.lockInterruptibly();
110			try {
111			for (;;) {
112	dl	1.3	E first = q.peek();
113	dl	1.12	if (first == null) {
114	dl	1.4	available.await();
115	tim	1.13	} else {
116	dl	1.2	long delay = first.getDelay(TimeUnit.NANOSECONDS);
117	dl	1.12	if (delay > 0) {
118			long tl = available.awaitNanos(delay);
119	tim	1.13	} else {
120	dl	1.3	E x = q.poll();
121	dl	1.2	assert x != null;
122			if (q.size() != 0)
123	dl	1.4	available.signalAll(); // wake up other takers
124	dl	1.2	return x;
125	tim	1.6
126	dl	1.2	}
127			}
128			}
129	tim	1.13	} finally {
130	dl	1.2	lock.unlock();
131			}
132			}
133
134	dl	1.3	public E poll(long time, TimeUnit unit) throws InterruptedException {
135	dl	1.21	final ReentrantLock lock = this.lock;
136	dl	1.2	lock.lockInterruptibly();
137			long nanos = unit.toNanos(time);
138			try {
139			for (;;) {
140	dl	1.3	E first = q.peek();
141	dl	1.2	if (first == null) {
142			if (nanos <= 0)
143			return null;
144			else
145	dl	1.4	nanos = available.awaitNanos(nanos);
146	tim	1.13	} else {
147	dl	1.2	long delay = first.getDelay(TimeUnit.NANOSECONDS);
148			if (delay > 0) {
149			if (delay > nanos)
150			delay = nanos;
151	dl	1.4	long timeLeft = available.awaitNanos(delay);
152	dl	1.2	nanos -= delay - timeLeft;
153	tim	1.13	} else {
154	dl	1.3	E x = q.poll();
155	dl	1.2	assert x != null;
156			if (q.size() != 0)
157	tim	1.6	available.signalAll();
158	dl	1.2	return x;
159			}
160			}
161			}
162	tim	1.13	} finally {
163	dl	1.2	lock.unlock();
164			}
165			}
166
167
168	dl	1.3	public E poll() {
169	dl	1.21	final ReentrantLock lock = this.lock;
170	dl	1.2	lock.lock();
171			try {
172	dl	1.3	E first = q.peek();
173	dl	1.2	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
174			return null;
175			else {
176	dl	1.3	E x = q.poll();
177	dl	1.2	assert x != null;
178			if (q.size() != 0)
179	tim	1.6	available.signalAll();
180	dl	1.2	return x;
181			}
182	tim	1.13	} finally {
183	dl	1.2	lock.unlock();
184			}
185			}
186
187	dl	1.3	public E peek() {
188	dl	1.21	final ReentrantLock lock = this.lock;
189	dl	1.2	lock.lock();
190			try {
191			return q.peek();
192	tim	1.13	} finally {
193	dl	1.2	lock.unlock();
194			}
195	tim	1.1	}
196
197	dl	1.2	public int size() {
198	dl	1.21	final ReentrantLock lock = this.lock;
199	dl	1.2	lock.lock();
200			try {
201			return q.size();
202	tim	1.13	} finally {
203	dl	1.2	lock.unlock();
204			}
205			}
206
207	dl	1.17	public int drainTo(Collection<? super E> c) {
208			if (c == null)
209			throw new NullPointerException();
210			if (c == this)
211			throw new IllegalArgumentException();
212	dl	1.21	final ReentrantLock lock = this.lock;
213	dl	1.17	lock.lock();
214			try {
215			int n = 0;
216			for (;;) {
217			E first = q.peek();
218			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
219			break;
220			c.add(q.poll());
221			++n;
222			}
223			if (n > 0)
224			available.signalAll();
225			return n;
226			} finally {
227			lock.unlock();
228			}
229			}
230
231			public int drainTo(Collection<? super E> c, int maxElements) {
232			if (c == null)
233			throw new NullPointerException();
234			if (c == this)
235			throw new IllegalArgumentException();
236			if (maxElements <= 0)
237			return 0;
238	dl	1.21	final ReentrantLock lock = this.lock;
239	dl	1.17	lock.lock();
240			try {
241			int n = 0;
242			while (n < maxElements) {
243			E first = q.peek();
244			if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
245			break;
246			c.add(q.poll());
247			++n;
248			}
249			if (n > 0)
250			available.signalAll();
251			return n;
252			} finally {
253			lock.unlock();
254			}
255			}
256
257	dholmes	1.7	/**
258			* Atomically removes all of the elements from this delay queue.
259			* The queue will be empty after this call returns.
260			*/
261	dl	1.2	public void clear() {
262	dl	1.21	final ReentrantLock lock = this.lock;
263	dl	1.2	lock.lock();
264			try {
265			q.clear();
266	tim	1.13	} finally {
267	dl	1.2	lock.unlock();
268			}
269			}
270	tim	1.1
271	dholmes	1.7	/**
272			* Always returns <tt>Integer.MAX_VALUE</tt> because
273			* a <tt>DelayQueue</tt> is not capacity constrained.
274			* @return <tt>Integer.MAX_VALUE</tt>
275			*/
276	dl	1.2	public int remainingCapacity() {
277			return Integer.MAX_VALUE;
278	tim	1.1	}
279	dl	1.2
280			public Object[] toArray() {
281	dl	1.21	final ReentrantLock lock = this.lock;
282	dl	1.2	lock.lock();
283			try {
284			return q.toArray();
285	tim	1.13	} finally {
286	dl	1.2	lock.unlock();
287			}
288	tim	1.1	}
289	dl	1.2
290			public <T> T[] toArray(T[] array) {
291	dl	1.21	final ReentrantLock lock = this.lock;
292	dl	1.2	lock.lock();
293			try {
294			return q.toArray(array);
295	tim	1.13	} finally {
296	dl	1.2	lock.unlock();
297			}
298	tim	1.1	}
299
300	dholmes	1.7	public boolean remove(Object o) {
301	dl	1.21	final ReentrantLock lock = this.lock;
302	dl	1.2	lock.lock();
303			try {
304	dholmes	1.7	return q.remove(o);
305	tim	1.13	} finally {
306	dl	1.2	lock.unlock();
307			}
308			}
309
310	dholmes	1.7	/**
311			* Returns an iterator over the elements in this queue. The iterator
312	dl	1.8	* does not return the elements in any particular order. The
313	dl	1.15	* returned iterator is a thread-safe "fast-fail" iterator that will
314	dl	1.8	* throw {@link java.util.ConcurrentModificationException}
315			* upon detected interference.
316	dholmes	1.7	*
317			* @return an iterator over the elements in this queue.
318			*/
319	dl	1.3	public Iterator<E> iterator() {
320	dl	1.21	final ReentrantLock lock = this.lock;
321	dl	1.2	lock.lock();
322			try {
323			return new Itr(q.iterator());
324	tim	1.13	} finally {
325	dl	1.2	lock.unlock();
326			}
327			}
328
329	dl	1.3	private class Itr<E> implements Iterator<E> {
330			private final Iterator<E> iter;
331	tim	1.6	Itr(Iterator<E> i) {
332			iter = i;
333	dl	1.2	}
334
335	tim	1.6	public boolean hasNext() {
336	dl	1.2	return iter.hasNext();
337	tim	1.6	}
338
339			public E next() {
340	dl	1.21	final ReentrantLock lock = DelayQueue.this.lock;
341	dl	1.2	lock.lock();
342			try {
343			return iter.next();
344	tim	1.13	} finally {
345	dl	1.2	lock.unlock();
346			}
347	tim	1.6	}
348
349			public void remove() {
350	dl	1.21	final ReentrantLock lock = DelayQueue.this.lock;
351	dl	1.2	lock.lock();
352			try {
353			iter.remove();
354	tim	1.13	} finally {
355	dl	1.2	lock.unlock();
356			}
357	tim	1.6	}
358	tim	1.1	}
359
360			}