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
#	Content
1	/*
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	package java.util.concurrent;
9	import java.util.concurrent.locks.*;
10	import java.util.*;
11
12	/**
13	* An unbounded {@linkplain BlockingQueue blocking queue} of <tt>Delayed</tt>
14	* 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	* <p>This class implements all of the <em>optional</em> methods
20	* of the {@link Collection} and {@link Iterator} interfaces.
21	* @since 1.5
22	* @author Doug Lea
23	* @param <E> the type of elements held in this collection
24	*/
25
26	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
27	implements BlockingQueue<E> {
28
29	private transient final ReentrantLock lock = new ReentrantLock();
30	private transient final ReentrantLock.ConditionObject available = lock.newCondition();
31	private final PriorityQueue<E> q = new PriorityQueue<E>();
32
33	/**
34	* Creates a new <tt>DelayQueue</tt> that is initially empty.
35	*/
36	public DelayQueue() {}
37
38	/**
39	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
40	* 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	*
45	*/
46	public DelayQueue(Collection<? extends E> c) {
47	this.addAll(c);
48	}
49
50	/**
51	* Inserts the specified element into this delay queue.
52	*
53	* @param o the element to add
54	* @return <tt>true</tt>
55	* @throws NullPointerException if the specified element is <tt>null</tt>.
56	*/
57	public boolean offer(E o) {
58	lock.lock();
59	try {
60	E first = q.peek();
61	q.offer(o);
62	if (first == null \|\| o.compareTo(first) < 0)
63	available.signalAll();
64	return true;
65	} finally {
66	lock.unlock();
67	}
68	}
69
70
71	/**
72	* Adds the specified element to this delay queue. As the queue is
73	* unbounded this method will never block.
74	* @param o the element to add
75	* @throws NullPointerException if the specified element is <tt>null</tt>.
76	*/
77	public void put(E o) {
78	offer(o);
79	}
80
81	/**
82	* Inserts the specified element into this delay queue. As the queue is
83	* unbounded this method will never block.
84	* @param o the element to add
85	* @param timeout This parameter is ignored as the method never blocks
86	* @param unit This parameter is ignored as the method never blocks
87	* @return <tt>true</tt>
88	* @throws NullPointerException if the specified element is <tt>null</tt>.
89	*/
90	public boolean offer(E o, long timeout, TimeUnit unit) {
91	return offer(o);
92	}
93
94	/**
95	* Adds the specified element to this queue.
96	* @param o the element to add
97	* @return <tt>true</tt> (as per the general contract of
98	* <tt>Collection.add</tt>).
99	*
100	* @throws NullPointerException if the specified element is <tt>null</tt>.
101	*/
102	public boolean add(E o) {
103	return offer(o);
104	}
105
106	public E take() throws InterruptedException {
107	lock.lockInterruptibly();
108	try {
109	for (;;) {
110	E first = q.peek();
111	if (first == null) {
112	available.await();
113	} else {
114	long delay = first.getDelay(TimeUnit.NANOSECONDS);
115	if (delay > 0) {
116	long tl = available.awaitNanos(delay);
117	} else {
118	E x = q.poll();
119	assert x != null;
120	if (q.size() != 0)
121	available.signalAll(); // wake up other takers
122	return x;
123
124	}
125	}
126	}
127	} finally {
128	lock.unlock();
129	}
130	}
131
132	public E poll(long time, TimeUnit unit) throws InterruptedException {
133	lock.lockInterruptibly();
134	long nanos = unit.toNanos(time);
135	try {
136	for (;;) {
137	E first = q.peek();
138	if (first == null) {
139	if (nanos <= 0)
140	return null;
141	else
142	nanos = available.awaitNanos(nanos);
143	} else {
144	long delay = first.getDelay(TimeUnit.NANOSECONDS);
145	if (delay > 0) {
146	if (delay > nanos)
147	delay = nanos;
148	long timeLeft = available.awaitNanos(delay);
149	nanos -= delay - timeLeft;
150	} else {
151	E x = q.poll();
152	assert x != null;
153	if (q.size() != 0)
154	available.signalAll();
155	return x;
156	}
157	}
158	}
159	} finally {
160	lock.unlock();
161	}
162	}
163
164
165	public E poll() {
166	lock.lock();
167	try {
168	E first = q.peek();
169	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
170	return null;
171	else {
172	E x = q.poll();
173	assert x != null;
174	if (q.size() != 0)
175	available.signalAll();
176	return x;
177	}
178	} finally {
179	lock.unlock();
180	}
181	}
182
183	public E peek() {
184	lock.lock();
185	try {
186	return q.peek();
187	} finally {
188	lock.unlock();
189	}
190	}
191
192	public int size() {
193	lock.lock();
194	try {
195	return q.size();
196	} finally {
197	lock.unlock();
198	}
199	}
200
201	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	/**
250	* Atomically removes all of the elements from this delay queue.
251	* The queue will be empty after this call returns.
252	*/
253	public void clear() {
254	lock.lock();
255	try {
256	q.clear();
257	} finally {
258	lock.unlock();
259	}
260	}
261
262	/**
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	public int remainingCapacity() {
268	return Integer.MAX_VALUE;
269	}
270
271	public Object[] toArray() {
272	lock.lock();
273	try {
274	return q.toArray();
275	} finally {
276	lock.unlock();
277	}
278	}
279
280	public <T> T[] toArray(T[] array) {
281	lock.lock();
282	try {
283	return q.toArray(array);
284	} finally {
285	lock.unlock();
286	}
287	}
288
289	public boolean remove(Object o) {
290	lock.lock();
291	try {
292	return q.remove(o);
293	} finally {
294	lock.unlock();
295	}
296	}
297
298	/**
299	* Returns an iterator over the elements in this queue. The iterator
300	* does not return the elements in any particular order. The
301	* returned iterator is a thread-safe "fast-fail" iterator that will
302	* throw {@link java.util.ConcurrentModificationException}
303	* upon detected interference.
304	*
305	* @return an iterator over the elements in this queue.
306	*/
307	public Iterator<E> iterator() {
308	lock.lock();
309	try {
310	return new Itr(q.iterator());
311	} finally {
312	lock.unlock();
313	}
314	}
315
316	private class Itr<E> implements Iterator<E> {
317	private final Iterator<E> iter;
318	Itr(Iterator<E> i) {
319	iter = i;
320	}
321
322	public boolean hasNext() {
323	return iter.hasNext();
324	}
325
326	public E next() {
327	lock.lock();
328	try {
329	return iter.next();
330	} finally {
331	lock.unlock();
332	}
333	}
334
335	public void remove() {
336	lock.lock();
337	try {
338	iter.remove();
339	} finally {
340	lock.unlock();
341	}
342	}
343	}
344
345	}