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);
    }

    /**
     * Inserts the specified element to 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);
    }

    /**
     * Adds the specified element to 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();
        }
    }

    /**
     * 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 "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:	1.14
Committed:	Fri Sep 12 15:40:10 2003 UTC (20 years, 8 months ago) by dl
Branch:	MAIN
Changes since 1.13:	+12 -23 lines
Log Message:	Adapt AbstractQueue changes; Conditionalize CancellableTask.reset; new TimeUnit methods
#	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	1.4	* @since 1.5
20			* @author Doug Lea
21			*/
22	tim	1.1
23	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
24			implements BlockingQueue<E> {
25	tim	1.6
26	dl	1.2	private transient final ReentrantLock lock = new ReentrantLock();
27	dl	1.4	private transient final Condition available = lock.newCondition();
28	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
29	tim	1.1
30	dl	1.4	/**
31	dholmes	1.7	* Creates a new <tt>DelayQueue</tt> that is initially empty.
32	dl	1.4	*/
33	tim	1.1	public DelayQueue() {}
34
35	tim	1.6	/**
36	tim	1.9	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
37	dholmes	1.7	* 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	tim	1.6	*
42			*/
43			public DelayQueue(Collection<? extends E> c) {
44			this.addAll(c);
45			}
46
47	dholmes	1.7	/**
48	dl	1.14	* Inserts the specified element to this delay queue.
49	dholmes	1.7	*
50	dl	1.14	* @param o the element to add
51	dholmes	1.7	* @return <tt>true</tt>
52	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
53	dholmes	1.7	*/
54			public boolean offer(E o) {
55	dl	1.2	lock.lock();
56			try {
57	dl	1.3	E first = q.peek();
58	dholmes	1.7	q.offer(o);
59			if (first == null \|\| o.compareTo(first) < 0)
60	dl	1.4	available.signalAll();
61	dl	1.2	return true;
62	tim	1.13	} finally {
63	dl	1.2	lock.unlock();
64			}
65			}
66
67	dholmes	1.7
68			/**
69			* Adds the specified element to this delay queue. As the queue is
70			* unbounded this method will never block.
71	dl	1.14	* @param o the element to add
72			* @throws NullPointerException if the specified element is <tt>null</tt>.
73	dholmes	1.7	*/
74			public void put(E o) {
75			offer(o);
76	dl	1.2	}
77
78	dholmes	1.7	/**
79	dl	1.14	* Adds the specified element to this delay queue. As the queue is
80	dholmes	1.7	* unbounded this method will never block.
81	dl	1.14	* @param o the element to add
82			* @param timeout This parameter is ignored as the method never blocks
83	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
84			* @return <tt>true</tt>
85	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
86	dholmes	1.7	*/
87	dl	1.14	public boolean offer(E o, long timeout, TimeUnit unit) {
88	dholmes	1.7	return offer(o);
89	dl	1.2	}
90
91	dholmes	1.7	/**
92			* Adds the specified element to this queue.
93	dl	1.14	* @param o the element to add
94	dholmes	1.7	* @return <tt>true</tt> (as per the general contract of
95			* <tt>Collection.add</tt>).
96			*
97	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
98	dholmes	1.7	*/
99			public boolean add(E o) {
100			return offer(o);
101	dl	1.2	}
102
103	dl	1.3	public E take() throws InterruptedException {
104	dl	1.2	lock.lockInterruptibly();
105			try {
106			for (;;) {
107	dl	1.3	E first = q.peek();
108	dl	1.12	if (first == null) {
109	dl	1.4	available.await();
110	tim	1.13	} else {
111	dl	1.2	long delay = first.getDelay(TimeUnit.NANOSECONDS);
112	dl	1.12	if (delay > 0) {
113			long tl = available.awaitNanos(delay);
114	tim	1.13	} else {
115	dl	1.3	E x = q.poll();
116	dl	1.2	assert x != null;
117			if (q.size() != 0)
118	dl	1.4	available.signalAll(); // wake up other takers
119	dl	1.2	return x;
120	tim	1.6
121	dl	1.2	}
122			}
123			}
124	tim	1.13	} finally {
125	dl	1.2	lock.unlock();
126			}
127			}
128
129	dl	1.3	public E poll(long time, TimeUnit unit) throws InterruptedException {
130	dl	1.2	lock.lockInterruptibly();
131			long nanos = unit.toNanos(time);
132			try {
133			for (;;) {
134	dl	1.3	E first = q.peek();
135	dl	1.2	if (first == null) {
136			if (nanos <= 0)
137			return null;
138			else
139	dl	1.4	nanos = available.awaitNanos(nanos);
140	tim	1.13	} else {
141	dl	1.2	long delay = first.getDelay(TimeUnit.NANOSECONDS);
142			if (delay > 0) {
143			if (delay > nanos)
144			delay = nanos;
145	dl	1.4	long timeLeft = available.awaitNanos(delay);
146	dl	1.2	nanos -= delay - timeLeft;
147	tim	1.13	} else {
148	dl	1.3	E x = q.poll();
149	dl	1.2	assert x != null;
150			if (q.size() != 0)
151	tim	1.6	available.signalAll();
152	dl	1.2	return x;
153			}
154			}
155			}
156	tim	1.13	} finally {
157	dl	1.2	lock.unlock();
158			}
159			}
160
161
162	dl	1.3	public E poll() {
163	dl	1.2	lock.lock();
164			try {
165	dl	1.3	E first = q.peek();
166	dl	1.2	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
167			return null;
168			else {
169	dl	1.3	E x = q.poll();
170	dl	1.2	assert x != null;
171			if (q.size() != 0)
172	tim	1.6	available.signalAll();
173	dl	1.2	return x;
174			}
175	tim	1.13	} finally {
176	dl	1.2	lock.unlock();
177			}
178			}
179
180	dl	1.3	public E peek() {
181	dl	1.2	lock.lock();
182			try {
183			return q.peek();
184	tim	1.13	} finally {
185	dl	1.2	lock.unlock();
186			}
187	tim	1.1	}
188
189	dl	1.2	public int size() {
190			lock.lock();
191			try {
192			return q.size();
193	tim	1.13	} finally {
194	dl	1.2	lock.unlock();
195			}
196			}
197
198	dholmes	1.7	/**
199			* Atomically removes all of the elements from this delay queue.
200			* The queue will be empty after this call returns.
201			*/
202	dl	1.2	public void clear() {
203			lock.lock();
204			try {
205			q.clear();
206	tim	1.13	} finally {
207	dl	1.2	lock.unlock();
208			}
209			}
210	tim	1.1
211	dholmes	1.7	/**
212			* Always returns <tt>Integer.MAX_VALUE</tt> because
213			* a <tt>DelayQueue</tt> is not capacity constrained.
214			* @return <tt>Integer.MAX_VALUE</tt>
215			*/
216	dl	1.2	public int remainingCapacity() {
217			return Integer.MAX_VALUE;
218	tim	1.1	}
219	dl	1.2
220			public Object[] toArray() {
221			lock.lock();
222			try {
223			return q.toArray();
224	tim	1.13	} finally {
225	dl	1.2	lock.unlock();
226			}
227	tim	1.1	}
228	dl	1.2
229			public <T> T[] toArray(T[] array) {
230			lock.lock();
231			try {
232			return q.toArray(array);
233	tim	1.13	} finally {
234	dl	1.2	lock.unlock();
235			}
236	tim	1.1	}
237
238	dholmes	1.7	public boolean remove(Object o) {
239	dl	1.2	lock.lock();
240			try {
241	dholmes	1.7	return q.remove(o);
242	tim	1.13	} finally {
243	dl	1.2	lock.unlock();
244			}
245			}
246
247	dholmes	1.7	/**
248			* Returns an iterator over the elements in this queue. The iterator
249	dl	1.8	* does not return the elements in any particular order. The
250			* returned iterator is a "fast-fail" iterator that will
251			* throw {@link java.util.ConcurrentModificationException}
252			* upon detected interference.
253	dholmes	1.7	*
254			* @return an iterator over the elements in this queue.
255			*/
256	dl	1.3	public Iterator<E> iterator() {
257	dl	1.2	lock.lock();
258			try {
259			return new Itr(q.iterator());
260	tim	1.13	} finally {
261	dl	1.2	lock.unlock();
262			}
263			}
264
265	dl	1.3	private class Itr<E> implements Iterator<E> {
266			private final Iterator<E> iter;
267	tim	1.6	Itr(Iterator<E> i) {
268			iter = i;
269	dl	1.2	}
270
271	tim	1.6	public boolean hasNext() {
272	dl	1.2	return iter.hasNext();
273	tim	1.6	}
274
275			public E next() {
276	dl	1.2	lock.lock();
277			try {
278			return iter.next();
279	tim	1.13	} finally {
280	dl	1.2	lock.unlock();
281			}
282	tim	1.6	}
283
284			public void remove() {
285	dl	1.2	lock.lock();
286			try {
287			iter.remove();
288	tim	1.13	} finally {
289	dl	1.2	lock.unlock();
290			}
291	tim	1.6	}
292	tim	1.1	}
293
294			}