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 time 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:	1.11
Committed:	Wed Aug 6 18:22:09 2003 UTC (20 years, 10 months ago) by tim
Branch:	MAIN
CVS Tags:	JSR166_CR1
Changes since 1.10:	+1 -1 lines
Log Message:	Fixes to minor errors found by DocCheck
#	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			* 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	dl	1.2	lock.lock();
55			try {
56	dl	1.3	E first = q.peek();
57	dholmes	1.7	q.offer(o);
58			if (first == null \|\| o.compareTo(first) < 0)
59	dl	1.4	available.signalAll();
60	dl	1.2	return true;
61			}
62			finally {
63			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			* @throws NullPointerException {@inheritDoc}
72			*/
73			public void put(E o) {
74			offer(o);
75	dl	1.2	}
76
77	dholmes	1.7	/**
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	tim	1.11	* @param time This parameter is ignored as the method never blocks
82	dholmes	1.7	* @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	dl	1.2	}
89
90	dholmes	1.7	/**
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	dl	1.2	}
100
101	dl	1.3	public E take() throws InterruptedException {
102	dl	1.2	lock.lockInterruptibly();
103			try {
104			for (;;) {
105	dl	1.3	E first = q.peek();
106	dl	1.2	if (first == null)
107	dl	1.4	available.await();
108	dl	1.2	else {
109			long delay = first.getDelay(TimeUnit.NANOSECONDS);
110			if (delay > 0)
111	dl	1.4	available.awaitNanos(delay);
112	dl	1.2	else {
113	dl	1.3	E x = q.poll();
114	dl	1.2	assert x != null;
115			if (q.size() != 0)
116	dl	1.4	available.signalAll(); // wake up other takers
117	dl	1.2	return x;
118	tim	1.6
119	dl	1.2	}
120			}
121			}
122			}
123			finally {
124			lock.unlock();
125			}
126			}
127
128	dl	1.3	public E poll(long time, TimeUnit unit) throws InterruptedException {
129	dl	1.2	lock.lockInterruptibly();
130			long nanos = unit.toNanos(time);
131			try {
132			for (;;) {
133	dl	1.3	E first = q.peek();
134	dl	1.2	if (first == null) {
135			if (nanos <= 0)
136			return null;
137			else
138	dl	1.4	nanos = available.awaitNanos(nanos);
139	dl	1.2	}
140			else {
141			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			}
148			else {
149	dl	1.3	E x = q.poll();
150	dl	1.2	assert x != null;
151			if (q.size() != 0)
152	tim	1.6	available.signalAll();
153	dl	1.2	return x;
154			}
155			}
156			}
157			}
158			finally {
159			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			}
178			finally {
179			lock.unlock();
180			}
181			}
182
183	dl	1.3	public E peek() {
184	dl	1.2	lock.lock();
185			try {
186			return q.peek();
187			}
188			finally {
189			lock.unlock();
190			}
191	tim	1.1	}
192
193	dl	1.2	public int size() {
194			lock.lock();
195			try {
196			return q.size();
197			}
198			finally {
199			lock.unlock();
200			}
201			}
202
203	dholmes	1.7	/**
204			* Atomically removes all of the elements from this delay queue.
205			* The queue will be empty after this call returns.
206			*/
207	dl	1.2	public void clear() {
208			lock.lock();
209			try {
210			q.clear();
211			}
212			finally {
213			lock.unlock();
214			}
215			}
216	tim	1.1
217	dholmes	1.7	/**
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	dl	1.2	public int remainingCapacity() {
223			return Integer.MAX_VALUE;
224	tim	1.1	}
225	dl	1.2
226			public Object[] toArray() {
227			lock.lock();
228			try {
229			return q.toArray();
230			}
231			finally {
232			lock.unlock();
233			}
234	tim	1.1	}
235	dl	1.2
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	tim	1.1	}
245
246	dholmes	1.7	/**
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	dl	1.2	lock.lock();
262			try {
263	dholmes	1.7	return q.remove(o);
264	dl	1.2	}
265			finally {
266			lock.unlock();
267			}
268			}
269
270	dholmes	1.7	/**
271			* Returns an iterator over the elements in this queue. The iterator
272	dl	1.8	* 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	dholmes	1.7	*
277			* @return an iterator over the elements in this queue.
278			*/
279	dl	1.3	public Iterator<E> iterator() {
280	dl	1.2	lock.lock();
281			try {
282			return new Itr(q.iterator());
283			}
284			finally {
285			lock.unlock();
286			}
287			}
288
289	dl	1.3	private class Itr<E> implements Iterator<E> {
290			private final Iterator<E> iter;
291	tim	1.6	Itr(Iterator<E> i) {
292			iter = i;
293	dl	1.2	}
294
295	tim	1.6	public boolean hasNext() {
296	dl	1.2	return iter.hasNext();
297	tim	1.6	}
298
299			public E next() {
300	dl	1.2	lock.lock();
301			try {
302			return iter.next();
303			}
304			finally {
305			lock.unlock();
306			}
307	tim	1.6	}
308
309			public void remove() {
310	dl	1.2	lock.lock();
311			try {
312			iter.remove();
313			}
314			finally {
315			lock.unlock();
316			}
317	tim	1.6	}
318	tim	1.1	}
319
320			}