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.
 * @since 1.5
 * @author Doug Lea
*/

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);
    }

    /**
     * Add the specified element to this delay queue.
     *
     * @return <tt>true</tt>
     * @throws NullPointerException {@inheritDoc}
     */
    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.
     * @throws NullPointerException {@inheritDoc}
     */
    public void put(E o) {
        offer(o);
    }

    /**
     * Adds the specified element to this priority queue. As the queue is
     * unbounded this method will never block.
     * @param o {@inheritDoc}
     * @param timeout This parameter is ignored as the method never blocks
     * @param unit This parameter is ignored as the method never blocks
     * @throws NullPointerException {@inheritDoc}
     * @return <tt>true</tt>
     */
    public boolean offer(E o, long time, TimeUnit unit) {
        return offer(o);
    }

    /**
     * Adds the specified element to this queue.
     * @return <tt>true</tt> (as per the general contract of
     * <tt>Collection.add</tt>).
     *
     * @throws NullPointerException {@inheritDoc}
     */
    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)
                        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();
        }
    }

    /**
     * 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();
        }
    }

    /**
     * Removes a single instance of the specified element from this
     * queue, if it is present.  More formally,
     * removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
     * o.equals(e))</tt>, if the queue contains one or more such
     * elements.  Returns <tt>true</tt> if the queue contained the
     * specified element (or equivalently, if the queue changed as a
     * result of the call).
     *
     * <p>This implementation iterates over the queue looking for the
     * specified element.  If it finds the element, it removes the element
     * from the queue using the iterator's remove method.<p>
     *
     */
    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 "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:	1.10
Committed:	Wed Aug 6 16:08:49 2003 UTC (20 years, 10 months ago) by dl
Branch:	MAIN
Changes since 1.9:	+0 -1 lines
Log Message:	Misc doc touch-ups
#	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	* @since 1.5
20	* @author Doug Lea
21	*/
22
23	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
24	implements BlockingQueue<E> {
25
26	private transient final ReentrantLock lock = new ReentrantLock();
27	private transient final Condition available = lock.newCondition();
28	private final PriorityQueue<E> q = new PriorityQueue<E>();
29
30	/**
31	* Creates a new <tt>DelayQueue</tt> that is initially empty.
32	*/
33	public DelayQueue() {}
34
35	/**
36	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
37	* given collection of {@link Delayed} instances.
38	*
39	* @throws NullPointerException if <tt>c</tt> or any element within it
40	* is <tt>null</tt>
41	*
42	*/
43	public DelayQueue(Collection<? extends E> c) {
44	this.addAll(c);
45	}
46
47	/**
48	* Add the specified element to this delay queue.
49	*
50	* @return <tt>true</tt>
51	* @throws NullPointerException {@inheritDoc}
52	*/
53	public boolean offer(E o) {
54	lock.lock();
55	try {
56	E first = q.peek();
57	q.offer(o);
58	if (first == null \|\| o.compareTo(first) < 0)
59	available.signalAll();
60	return true;
61	}
62	finally {
63	lock.unlock();
64	}
65	}
66
67
68	/**
69	* Adds the specified element to this delay queue. As the queue is
70	* unbounded this method will never block.
71	* @throws NullPointerException {@inheritDoc}
72	*/
73	public void put(E o) {
74	offer(o);
75	}
76
77	/**
78	* Adds the specified element to this priority queue. As the queue is
79	* unbounded this method will never block.
80	* @param o {@inheritDoc}
81	* @param timeout This parameter is ignored as the method never blocks
82	* @param unit This parameter is ignored as the method never blocks
83	* @throws NullPointerException {@inheritDoc}
84	* @return <tt>true</tt>
85	*/
86	public boolean offer(E o, long time, TimeUnit unit) {
87	return offer(o);
88	}
89
90	/**
91	* Adds the specified element to this queue.
92	* @return <tt>true</tt> (as per the general contract of
93	* <tt>Collection.add</tt>).
94	*
95	* @throws NullPointerException {@inheritDoc}
96	*/
97	public boolean add(E o) {
98	return offer(o);
99	}
100
101	public E take() throws InterruptedException {
102	lock.lockInterruptibly();
103	try {
104	for (;;) {
105	E first = q.peek();
106	if (first == null)
107	available.await();
108	else {
109	long delay = first.getDelay(TimeUnit.NANOSECONDS);
110	if (delay > 0)
111	available.awaitNanos(delay);
112	else {
113	E x = q.poll();
114	assert x != null;
115	if (q.size() != 0)
116	available.signalAll(); // wake up other takers
117	return x;
118
119	}
120	}
121	}
122	}
123	finally {
124	lock.unlock();
125	}
126	}
127
128	public E poll(long time, TimeUnit unit) throws InterruptedException {
129	lock.lockInterruptibly();
130	long nanos = unit.toNanos(time);
131	try {
132	for (;;) {
133	E first = q.peek();
134	if (first == null) {
135	if (nanos <= 0)
136	return null;
137	else
138	nanos = available.awaitNanos(nanos);
139	}
140	else {
141	long delay = first.getDelay(TimeUnit.NANOSECONDS);
142	if (delay > 0) {
143	if (delay > nanos)
144	delay = nanos;
145	long timeLeft = available.awaitNanos(delay);
146	nanos -= delay - timeLeft;
147	}
148	else {
149	E x = q.poll();
150	assert x != null;
151	if (q.size() != 0)
152	available.signalAll();
153	return x;
154	}
155	}
156	}
157	}
158	finally {
159	lock.unlock();
160	}
161	}
162
163
164	public E poll() {
165	lock.lock();
166	try {
167	E first = q.peek();
168	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
169	return null;
170	else {
171	E x = q.poll();
172	assert x != null;
173	if (q.size() != 0)
174	available.signalAll();
175	return x;
176	}
177	}
178	finally {
179	lock.unlock();
180	}
181	}
182
183	public E peek() {
184	lock.lock();
185	try {
186	return q.peek();
187	}
188	finally {
189	lock.unlock();
190	}
191	}
192
193	public int size() {
194	lock.lock();
195	try {
196	return q.size();
197	}
198	finally {
199	lock.unlock();
200	}
201	}
202
203	/**
204	* Atomically removes all of the elements from this delay queue.
205	* The queue will be empty after this call returns.
206	*/
207	public void clear() {
208	lock.lock();
209	try {
210	q.clear();
211	}
212	finally {
213	lock.unlock();
214	}
215	}
216
217	/**
218	* Always returns <tt>Integer.MAX_VALUE</tt> because
219	* a <tt>DelayQueue</tt> is not capacity constrained.
220	* @return <tt>Integer.MAX_VALUE</tt>
221	*/
222	public int remainingCapacity() {
223	return Integer.MAX_VALUE;
224	}
225
226	public Object[] toArray() {
227	lock.lock();
228	try {
229	return q.toArray();
230	}
231	finally {
232	lock.unlock();
233	}
234	}
235
236	public <T> T[] toArray(T[] array) {
237	lock.lock();
238	try {
239	return q.toArray(array);
240	}
241	finally {
242	lock.unlock();
243	}
244	}
245
246	/**
247	* Removes a single instance of the specified element from this
248	* queue, if it is present. More formally,
249	* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
250	* o.equals(e))</tt>, if the queue contains one or more such
251	* elements. Returns <tt>true</tt> if the queue contained the
252	* specified element (or equivalently, if the queue changed as a
253	* result of the call).
254	*
255	* <p>This implementation iterates over the queue looking for the
256	* specified element. If it finds the element, it removes the element
257	* from the queue using the iterator's remove method.<p>
258	*
259	*/
260	public boolean remove(Object o) {
261	lock.lock();
262	try {
263	return q.remove(o);
264	}
265	finally {
266	lock.unlock();
267	}
268	}
269
270	/**
271	* Returns an iterator over the elements in this queue. The iterator
272	* does not return the elements in any particular order. The
273	* returned iterator is a "fast-fail" iterator that will
274	* throw {@link java.util.ConcurrentModificationException}
275	* upon detected interference.
276	*
277	* @return an iterator over the elements in this queue.
278	*/
279	public Iterator<E> iterator() {
280	lock.lock();
281	try {
282	return new Itr(q.iterator());
283	}
284	finally {
285	lock.unlock();
286	}
287	}
288
289	private class Itr<E> implements Iterator<E> {
290	private final Iterator<E> iter;
291	Itr(Iterator<E> i) {
292	iter = i;
293	}
294
295	public boolean hasNext() {
296	return iter.hasNext();
297	}
298
299	public E next() {
300	lock.lock();
301	try {
302	return iter.next();
303	}
304	finally {
305	lock.unlock();
306	}
307	}
308
309	public void remove() {
310	lock.lock();
311	try {
312	iter.remove();
313	}
314	finally {
315	lock.unlock();
316	}
317	}
318	}
319
320	}