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
*/

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 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:	1.15
Committed:	Sat Sep 13 18:51:11 2003 UTC (20 years, 9 months ago) by dl
Branch:	MAIN
Changes since 1.14:	+3 -1 lines
Log Message:	Proofreading pass -- many minor adjustments
#	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			*/
24	tim	1.1
25	dl	1.3	public class DelayQueue<E extends Delayed> extends AbstractQueue<E>
26			implements BlockingQueue<E> {
27	tim	1.6
28	dl	1.2	private transient final ReentrantLock lock = new ReentrantLock();
29	dl	1.4	private transient final Condition available = lock.newCondition();
30	dl	1.3	private final PriorityQueue<E> q = new PriorityQueue<E>();
31	tim	1.1
32	dl	1.4	/**
33	dholmes	1.7	* Creates a new <tt>DelayQueue</tt> that is initially empty.
34	dl	1.4	*/
35	tim	1.1	public DelayQueue() {}
36
37	tim	1.6	/**
38	tim	1.9	* Creates a <tt>DelayQueue</tt> initially containing the elements of the
39	dholmes	1.7	* given collection of {@link Delayed} instances.
40			*
41			* @throws NullPointerException if <tt>c</tt> or any element within it
42			* is <tt>null</tt>
43	tim	1.6	*
44			*/
45			public DelayQueue(Collection<? extends E> c) {
46			this.addAll(c);
47			}
48
49	dholmes	1.7	/**
50	dl	1.14	* Inserts the specified element to this delay queue.
51	dholmes	1.7	*
52	dl	1.14	* @param o the element to add
53	dholmes	1.7	* @return <tt>true</tt>
54	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
55	dholmes	1.7	*/
56			public boolean offer(E o) {
57	dl	1.2	lock.lock();
58			try {
59	dl	1.3	E first = q.peek();
60	dholmes	1.7	q.offer(o);
61			if (first == null \|\| o.compareTo(first) < 0)
62	dl	1.4	available.signalAll();
63	dl	1.2	return true;
64	tim	1.13	} finally {
65	dl	1.2	lock.unlock();
66			}
67			}
68
69	dholmes	1.7
70			/**
71			* Adds the specified element to this delay queue. As the queue is
72			* unbounded this method will never block.
73	dl	1.14	* @param o the element to add
74			* @throws NullPointerException if the specified element is <tt>null</tt>.
75	dholmes	1.7	*/
76			public void put(E o) {
77			offer(o);
78	dl	1.2	}
79
80	dholmes	1.7	/**
81	dl	1.14	* Adds the specified element to this delay queue. As the queue is
82	dholmes	1.7	* unbounded this method will never block.
83	dl	1.14	* @param o the element to add
84			* @param timeout This parameter is ignored as the method never blocks
85	dholmes	1.7	* @param unit This parameter is ignored as the method never blocks
86			* @return <tt>true</tt>
87	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
88	dholmes	1.7	*/
89	dl	1.14	public boolean offer(E o, long timeout, TimeUnit unit) {
90	dholmes	1.7	return offer(o);
91	dl	1.2	}
92
93	dholmes	1.7	/**
94			* Adds the specified element to this queue.
95	dl	1.14	* @param o the element to add
96	dholmes	1.7	* @return <tt>true</tt> (as per the general contract of
97			* <tt>Collection.add</tt>).
98			*
99	dl	1.14	* @throws NullPointerException if the specified element is <tt>null</tt>.
100	dholmes	1.7	*/
101			public boolean add(E o) {
102			return offer(o);
103	dl	1.2	}
104
105	dl	1.3	public E take() throws InterruptedException {
106	dl	1.2	lock.lockInterruptibly();
107			try {
108			for (;;) {
109	dl	1.3	E first = q.peek();
110	dl	1.12	if (first == null) {
111	dl	1.4	available.await();
112	tim	1.13	} else {
113	dl	1.2	long delay = first.getDelay(TimeUnit.NANOSECONDS);
114	dl	1.12	if (delay > 0) {
115			long tl = available.awaitNanos(delay);
116	tim	1.13	} else {
117	dl	1.3	E x = q.poll();
118	dl	1.2	assert x != null;
119			if (q.size() != 0)
120	dl	1.4	available.signalAll(); // wake up other takers
121	dl	1.2	return x;
122	tim	1.6
123	dl	1.2	}
124			}
125			}
126	tim	1.13	} finally {
127	dl	1.2	lock.unlock();
128			}
129			}
130
131	dl	1.3	public E poll(long time, TimeUnit unit) throws InterruptedException {
132	dl	1.2	lock.lockInterruptibly();
133			long nanos = unit.toNanos(time);
134			try {
135			for (;;) {
136	dl	1.3	E first = q.peek();
137	dl	1.2	if (first == null) {
138			if (nanos <= 0)
139			return null;
140			else
141	dl	1.4	nanos = available.awaitNanos(nanos);
142	tim	1.13	} else {
143	dl	1.2	long delay = first.getDelay(TimeUnit.NANOSECONDS);
144			if (delay > 0) {
145			if (delay > nanos)
146			delay = nanos;
147	dl	1.4	long timeLeft = available.awaitNanos(delay);
148	dl	1.2	nanos -= delay - timeLeft;
149	tim	1.13	} else {
150	dl	1.3	E x = q.poll();
151	dl	1.2	assert x != null;
152			if (q.size() != 0)
153	tim	1.6	available.signalAll();
154	dl	1.2	return x;
155			}
156			}
157			}
158	tim	1.13	} finally {
159	dl	1.2	lock.unlock();
160			}
161			}
162
163
164	dl	1.3	public E poll() {
165	dl	1.2	lock.lock();
166			try {
167	dl	1.3	E first = q.peek();
168	dl	1.2	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
169			return null;
170			else {
171	dl	1.3	E x = q.poll();
172	dl	1.2	assert x != null;
173			if (q.size() != 0)
174	tim	1.6	available.signalAll();
175	dl	1.2	return x;
176			}
177	tim	1.13	} finally {
178	dl	1.2	lock.unlock();
179			}
180			}
181
182	dl	1.3	public E peek() {
183	dl	1.2	lock.lock();
184			try {
185			return q.peek();
186	tim	1.13	} finally {
187	dl	1.2	lock.unlock();
188			}
189	tim	1.1	}
190
191	dl	1.2	public int size() {
192			lock.lock();
193			try {
194			return q.size();
195	tim	1.13	} finally {
196	dl	1.2	lock.unlock();
197			}
198			}
199
200	dholmes	1.7	/**
201			* Atomically removes all of the elements from this delay queue.
202			* The queue will be empty after this call returns.
203			*/
204	dl	1.2	public void clear() {
205			lock.lock();
206			try {
207			q.clear();
208	tim	1.13	} finally {
209	dl	1.2	lock.unlock();
210			}
211			}
212	tim	1.1
213	dholmes	1.7	/**
214			* Always returns <tt>Integer.MAX_VALUE</tt> because
215			* a <tt>DelayQueue</tt> is not capacity constrained.
216			* @return <tt>Integer.MAX_VALUE</tt>
217			*/
218	dl	1.2	public int remainingCapacity() {
219			return Integer.MAX_VALUE;
220	tim	1.1	}
221	dl	1.2
222			public Object[] toArray() {
223			lock.lock();
224			try {
225			return q.toArray();
226	tim	1.13	} finally {
227	dl	1.2	lock.unlock();
228			}
229	tim	1.1	}
230	dl	1.2
231			public <T> T[] toArray(T[] array) {
232			lock.lock();
233			try {
234			return q.toArray(array);
235	tim	1.13	} finally {
236	dl	1.2	lock.unlock();
237			}
238	tim	1.1	}
239
240	dholmes	1.7	public boolean remove(Object o) {
241	dl	1.2	lock.lock();
242			try {
243	dholmes	1.7	return q.remove(o);
244	tim	1.13	} finally {
245	dl	1.2	lock.unlock();
246			}
247			}
248
249	dholmes	1.7	/**
250			* Returns an iterator over the elements in this queue. The iterator
251	dl	1.8	* does not return the elements in any particular order. The
252	dl	1.15	* returned iterator is a thread-safe "fast-fail" iterator that will
253	dl	1.8	* throw {@link java.util.ConcurrentModificationException}
254			* upon detected interference.
255	dholmes	1.7	*
256			* @return an iterator over the elements in this queue.
257			*/
258	dl	1.3	public Iterator<E> iterator() {
259	dl	1.2	lock.lock();
260			try {
261			return new Itr(q.iterator());
262	tim	1.13	} finally {
263	dl	1.2	lock.unlock();
264			}
265			}
266
267	dl	1.3	private class Itr<E> implements Iterator<E> {
268			private final Iterator<E> iter;
269	tim	1.6	Itr(Iterator<E> i) {
270			iter = i;
271	dl	1.2	}
272
273	tim	1.6	public boolean hasNext() {
274	dl	1.2	return iter.hasNext();
275	tim	1.6	}
276
277			public E next() {
278	dl	1.2	lock.lock();
279			try {
280			return iter.next();
281	tim	1.13	} finally {
282	dl	1.2	lock.unlock();
283			}
284	tim	1.6	}
285
286			public void remove() {
287	dl	1.2	lock.lock();
288			try {
289			iter.remove();
290	tim	1.13	} finally {
291	dl	1.2	lock.unlock();
292			}
293	tim	1.6	}
294	tim	1.1	}
295
296			}