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> initialy 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>
     *
     * @fixme Should the body be wrapped with try-lock-finally-unlock?
     */
    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.
     *
     * @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:	1.7
Committed:	Wed Aug 6 01:57:53 2003 UTC (20 years, 10 months ago) by dholmes
Branch:	MAIN
Changes since 1.6:	+80 -16 lines
Log Message:	Final major updates to Collection related classes.
#	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	dholmes	1.7	* 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	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	dholmes	1.7	* Creates a <tt>DelayQueue</tt> initialy 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	tim	1.6	*
42			* @fixme Should the body be wrapped with try-lock-finally-unlock?
43			*/
44			public DelayQueue(Collection<? extends E> c) {
45			this.addAll(c);
46			}
47
48	dholmes	1.7	/**
49			* Add the specified element to this delay queue.
50			*
51			* @return <tt>true</tt>
52			* @throws NullPointerException {@inheritDoc}
53			*/
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			}
63			finally {
64			lock.unlock();
65			}
66			}
67
68	dholmes	1.7
69			/**
70			* Adds the specified element to this delay queue. As the queue is
71			* unbounded this method will never block.
72			* @throws NullPointerException {@inheritDoc}
73			*/
74			public void put(E o) {
75			offer(o);
76	dl	1.2	}
77
78	dholmes	1.7	/**
79			* Adds the specified element to this priority queue. As the queue is
80			* unbounded this method will never block.
81			* @param o {@inheritDoc}
82			* @param timeout This parameter is ignored as the method never blocks
83			* @param unit This parameter is ignored as the method never blocks
84			* @throws NullPointerException {@inheritDoc}
85			* @return <tt>true</tt>
86			*/
87			public boolean offer(E o, long time, TimeUnit unit) {
88			return offer(o);
89	dl	1.2	}
90
91	dholmes	1.7	/**
92			* Adds the specified element to this queue.
93			* @return <tt>true</tt> (as per the general contract of
94			* <tt>Collection.add</tt>).
95			*
96			* @throws NullPointerException {@inheritDoc}
97			*/
98			public boolean add(E o) {
99			return offer(o);
100	dl	1.2	}
101
102	dl	1.3	public E take() throws InterruptedException {
103	dl	1.2	lock.lockInterruptibly();
104			try {
105			for (;;) {
106	dl	1.3	E first = q.peek();
107	dl	1.2	if (first == null)
108	dl	1.4	available.await();
109	dl	1.2	else {
110			long delay = first.getDelay(TimeUnit.NANOSECONDS);
111			if (delay > 0)
112	dl	1.4	available.awaitNanos(delay);
113	dl	1.2	else {
114	dl	1.3	E x = q.poll();
115	dl	1.2	assert x != null;
116			if (q.size() != 0)
117	dl	1.4	available.signalAll(); // wake up other takers
118	dl	1.2	return x;
119	tim	1.6
120	dl	1.2	}
121			}
122			}
123			}
124			finally {
125			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	dl	1.2	}
141			else {
142			long delay = first.getDelay(TimeUnit.NANOSECONDS);
143			if (delay > 0) {
144			if (delay > nanos)
145			delay = nanos;
146	dl	1.4	long timeLeft = available.awaitNanos(delay);
147	dl	1.2	nanos -= delay - timeLeft;
148			}
149			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			}
159			finally {
160			lock.unlock();
161			}
162			}
163
164
165	dl	1.3	public E poll() {
166	dl	1.2	lock.lock();
167			try {
168	dl	1.3	E first = q.peek();
169	dl	1.2	if (first == null \|\| first.getDelay(TimeUnit.NANOSECONDS) > 0)
170			return null;
171			else {
172	dl	1.3	E x = q.poll();
173	dl	1.2	assert x != null;
174			if (q.size() != 0)
175	tim	1.6	available.signalAll();
176	dl	1.2	return x;
177			}
178			}
179			finally {
180			lock.unlock();
181			}
182			}
183
184	dl	1.3	public E peek() {
185	dl	1.2	lock.lock();
186			try {
187			return q.peek();
188			}
189			finally {
190			lock.unlock();
191			}
192	tim	1.1	}
193
194	dl	1.2	public int size() {
195			lock.lock();
196			try {
197			return q.size();
198			}
199			finally {
200			lock.unlock();
201			}
202			}
203
204	dholmes	1.7	/**
205			* Atomically removes all of the elements from this delay queue.
206			* The queue will be empty after this call returns.
207			*/
208	dl	1.2	public void clear() {
209			lock.lock();
210			try {
211			q.clear();
212			}
213			finally {
214			lock.unlock();
215			}
216			}
217	tim	1.1
218	dholmes	1.7	/**
219			* Always returns <tt>Integer.MAX_VALUE</tt> because
220			* a <tt>DelayQueue</tt> is not capacity constrained.
221			* @return <tt>Integer.MAX_VALUE</tt>
222			*/
223	dl	1.2	public int remainingCapacity() {
224			return Integer.MAX_VALUE;
225	tim	1.1	}
226	dl	1.2
227			public Object[] toArray() {
228			lock.lock();
229			try {
230			return q.toArray();
231			}
232			finally {
233			lock.unlock();
234			}
235	tim	1.1	}
236	dl	1.2
237			public <T> T[] toArray(T[] array) {
238			lock.lock();
239			try {
240			return q.toArray(array);
241			}
242			finally {
243			lock.unlock();
244			}
245	tim	1.1	}
246
247	dholmes	1.7	/**
248			* Removes a single instance of the specified element from this
249			* queue, if it is present. More formally,
250			* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
251			* o.equals(e))</tt>, if the queue contains one or more such
252			* elements. Returns <tt>true</tt> if the queue contained the
253			* specified element (or equivalently, if the queue changed as a
254			* result of the call).
255			*
256			* <p>This implementation iterates over the queue looking for the
257			* specified element. If it finds the element, it removes the element
258			* from the queue using the iterator's remove method.<p>
259			*
260			*/
261			public boolean remove(Object o) {
262	dl	1.2	lock.lock();
263			try {
264	dholmes	1.7	return q.remove(o);
265	dl	1.2	}
266			finally {
267			lock.unlock();
268			}
269			}
270
271	dholmes	1.7	/**
272			* Returns an iterator over the elements in this queue. The iterator
273			* does not return the elements in any particular order.
274			*
275			* @return an iterator over the elements in this queue.
276			*/
277	dl	1.3	public Iterator<E> iterator() {
278	dl	1.2	lock.lock();
279			try {
280			return new Itr(q.iterator());
281			}
282			finally {
283			lock.unlock();
284			}
285			}
286
287	dl	1.3	private class Itr<E> implements Iterator<E> {
288			private final Iterator<E> iter;
289	tim	1.6	Itr(Iterator<E> i) {
290			iter = i;
291	dl	1.2	}
292
293	tim	1.6	public boolean hasNext() {
294	dl	1.2	return iter.hasNext();
295	tim	1.6	}
296
297			public E next() {
298	dl	1.2	lock.lock();
299			try {
300			return iter.next();
301			}
302			finally {
303			lock.unlock();
304			}
305	tim	1.6	}
306
307			public void remove() {
308	dl	1.2	lock.lock();
309			try {
310			iter.remove();
311			}
312			finally {
313			lock.unlock();
314			}
315	tim	1.6	}
316	tim	1.1	}
317
318			}