util/concurrent/PriorityBlockingQueue.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} based on a
 * {@link PriorityQueue}, obeying its ordering rules and
 * implementation characteristics.  While this queue is logically
 * unbounded, attempted additions may fail due to resource exhaustion
 * (causing <tt>OutOfMemoryError</tt>). A priority queue does not
 * permit <tt>null</tt> elements.  A priority queue relying on natural
 * ordering also does not permit insertion of non-comparable objects
 * (doing so results in <tt>ClassCastException</tt>).
 *
 * <p>This class implements all of the <em>optional</em> methods
 * of the {@link Collection} and {@link Iterator} interfaces.
 * <p>The Iterator provided in method {@link #iterator()} is
 * <em>not</em> guaranteed to traverse the elements of the
 * PriorityBlockingQueue in any particular order. If you need ordered
 * traversal, consider using <tt>Arrays.sort(pq.toArray())</tt>.
 *
 * @since 1.5
 * @author Doug Lea
*/
public class PriorityBlockingQueue<E> extends AbstractQueue<E>
    implements BlockingQueue<E>, java.io.Serializable {
    private static final long serialVersionUID = 5595510919245408276L;

    private final PriorityQueue<E> q;
    private final ReentrantLock lock = new ReentrantLock(true);
    private final Condition notEmpty = lock.newCondition();

    /**
     * Creates a <tt>PriorityBlockingQueue</tt> with the default initial 
     * capacity
     * (11) that orders its elements according to their natural
     * ordering (using <tt>Comparable</tt>).
     */
    public PriorityBlockingQueue() {
        q = new PriorityQueue<E>();
    }

    /**
     * Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
     * capacity
     * that orders its elements according to their natural ordering
     * (using <tt>Comparable</tt>).
     *
     * @param initialCapacity the initial capacity for this priority queue.
     * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
     * than 1
     */
    public PriorityBlockingQueue(int initialCapacity) {
        q = new PriorityQueue<E>(initialCapacity, null);
    }

    /**
     * Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
     * capacity
     * that orders its elements according to the specified comparator.
     *
     * @param initialCapacity the initial capacity for this priority queue.
     * @param comparator the comparator used to order this priority queue.
     * If <tt>null</tt> then the order depends on the elements' natural
     * ordering.
     * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
     * than 1
     */
    public PriorityBlockingQueue(int initialCapacity,
                                 Comparator<? super E> comparator) {
        q = new PriorityQueue<E>(initialCapacity, comparator);
    }

    /**
     * Creates a <tt>PriorityBlockingQueue</tt> containing the elements
     * in the specified collection.  The priority queue has an initial
     * capacity of 110% of the size of the specified collection. If
     * the specified collection is a {@link SortedSet} or a {@link
     * PriorityQueue}, this priority queue will be sorted according to
     * the same comparator, or according to its elements' natural
     * order if the collection is sorted according to its elements'
     * natural order.  Otherwise, this priority queue is ordered
     * according to its elements' natural order.
     *
     * @param c the collection whose elements are to be placed
     *        into this priority queue.
     * @throws ClassCastException if elements of the specified collection
     *         cannot be compared to one another according to the priority
     *         queue's ordering.
     * @throws NullPointerException if <tt>c</tt> or any element within it
     * is <tt>null</tt>
     */
    public PriorityBlockingQueue(Collection<? extends E> c) {
        q = new PriorityQueue<E>(c);
    }


    // these first few override just to update doc comments

    /**
     * Adds the specified element to this queue.
     * @return <tt>true</tt> (as per the general contract of
     * <tt>Collection.add</tt>).
     *
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     * @throws ClassCastException if the specified element cannot be compared
     * with elements currently in the priority queue according
     * to the priority queue's ordering.
     */
    public boolean add(E o) {
        return super.add(o);
    }

    /**
     * Returns the comparator used to order this collection, or <tt>null</tt>
     * if this collection is sorted according to its elements natural ordering
     * (using <tt>Comparable</tt>).
     *
     * @return the comparator used to order this collection, or <tt>null</tt>
     * if this collection is sorted according to its elements natural ordering.
     */
    public Comparator comparator() {
        return q.comparator();
    }

    /**
     * Inserts the specified element into this priority queue.
     *
     * @param o the element to add
     * @return <tt>true</tt>
     * @throws ClassCastException if the specified element cannot be compared
     * with elements currently in the priority queue according
     * to the priority queue's ordering.
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     */
    public boolean offer(E o) {
        if (o == null) throw new NullPointerException();
        lock.lock();
        try {
            boolean ok = q.offer(o);
            assert ok;
            notEmpty.signal();
            return true;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Adds the specified element to this priority queue. As the queue is
     * unbounded this method will never block.
     * @param o the element to add
     * @throws ClassCastException if the element cannot be compared
     * with elements currently in the priority queue according
     * to the priority queue's ordering.
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     */
    public void put(E o) {
        offer(o); // never need to block
    }

    /**
     * Inserts the specified element into this priority 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 ClassCastException if the element cannot be compared
     * with elements currently in the priority queue according
     * to the priority queue's ordering.
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     */
    public boolean offer(E o, long timeout, TimeUnit unit) {
        return offer(o); // never need to block
    }

    public E take() throws InterruptedException {
        lock.lockInterruptibly();
        try {
            try {
                while (q.size() == 0)
                    notEmpty.await();
            } catch (InterruptedException ie) {
                notEmpty.signal(); // propagate to non-interrupted thread
                throw ie;
            }
            E x = q.poll();
            assert x != null;
            return x;
        } finally {
            lock.unlock();
        }
    }


    public E poll() {
        lock.lock();
        try {
            return q.poll();
        } finally {
            lock.unlock();
        }
    }

    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
        long nanos = unit.toNanos(timeout);
        lock.lockInterruptibly();
        try {
            for (;;) {
                E x = q.poll();
                if (x != null)
                    return x;
                if (nanos <= 0)
                    return null;
                try {
                    nanos = notEmpty.awaitNanos(nanos);
                } catch (InterruptedException ie) {
                    notEmpty.signal(); // propagate to non-interrupted thread
                    throw ie;
                }
            }
        } 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();
        }
    }

    /**
     * Always returns <tt>Integer.MAX_VALUE</tt> because
     * a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
     * @return <tt>Integer.MAX_VALUE</tt>
     */
    public int remainingCapacity() {
        return Integer.MAX_VALUE;
    }

    public boolean remove(Object o) {
        lock.lock();
        try {
            return q.remove(o);
        } finally {
            lock.unlock();
        }
    }

    public boolean contains(Object o) {
        lock.lock();
        try {
            return q.contains(o);
        } finally {
            lock.unlock();
        }
    }

    public Object[] toArray() {
        lock.lock();
        try {
            return q.toArray();
        } finally {
            lock.unlock();
        }
    }


    public String toString() {
        lock.lock();
        try {
            return q.toString();
        } 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();
        }
    }

    public <T> T[] toArray(T[] a) {
        lock.lock();
        try {
            return q.toArray(a);
        } 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() {
            /*
             * No sync -- we rely on underlying hasNext to be
             * stateless, in which case we can return true by mistake
             * only when next() willl subsequently throw
             * ConcurrentModificationException.
             */
            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();
            }
        }
    }

    /**
     * Save the state to a stream (that is, serialize it).  This
     * merely wraps default serialization within lock.  The
     * serialization strategy for items is left to underlying
     * Queue. Note that locking is not needed on deserialization, so
     * readObject is not defined, just relying on default.
     */
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        lock.lock();
        try {
            s.defaultWriteObject();
        } finally {
            lock.unlock();
        }
    }

}
Revision:	1.24
Committed:	Mon Sep 15 12:02:46 2003 UTC (20 years, 8 months ago) by dl
Branch:	MAIN
Changes since 1.23:	+9 -29 lines
Log Message:	Fix some javadoc inconsistencies
#	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	package java.util.concurrent;
8
9	import java.util.concurrent.locks.*;
10	import java.util.*;
11
12	/**
13	* An unbounded {@linkplain BlockingQueue blocking queue} based on a
14	* {@link PriorityQueue}, obeying its ordering rules and
15	* implementation characteristics. While this queue is logically
16	* unbounded, attempted additions may fail due to resource exhaustion
17	* (causing <tt>OutOfMemoryError</tt>). A priority queue does not
18	* permit <tt>null</tt> elements. A priority queue relying on natural
19	* ordering also does not permit insertion of non-comparable objects
20	* (doing so results in <tt>ClassCastException</tt>).
21	*
22	* <p>This class implements all of the <em>optional</em> methods
23	* of the {@link Collection} and {@link Iterator} interfaces.
24	* <p>The Iterator provided in method {@link #iterator()} is
25	* <em>not</em> guaranteed to traverse the elements of the
26	* PriorityBlockingQueue in any particular order. If you need ordered
27	* traversal, consider using <tt>Arrays.sort(pq.toArray())</tt>.
28	*
29	* @since 1.5
30	* @author Doug Lea
31	*/
32	public class PriorityBlockingQueue<E> extends AbstractQueue<E>
33	implements BlockingQueue<E>, java.io.Serializable {
34	private static final long serialVersionUID = 5595510919245408276L;
35
36	private final PriorityQueue<E> q;
37	private final ReentrantLock lock = new ReentrantLock(true);
38	private final Condition notEmpty = lock.newCondition();
39
40	/**
41	* Creates a <tt>PriorityBlockingQueue</tt> with the default initial
42	* capacity
43	* (11) that orders its elements according to their natural
44	* ordering (using <tt>Comparable</tt>).
45	*/
46	public PriorityBlockingQueue() {
47	q = new PriorityQueue<E>();
48	}
49
50	/**
51	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
52	* capacity
53	* that orders its elements according to their natural ordering
54	* (using <tt>Comparable</tt>).
55	*
56	* @param initialCapacity the initial capacity for this priority queue.
57	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
58	* than 1
59	*/
60	public PriorityBlockingQueue(int initialCapacity) {
61	q = new PriorityQueue<E>(initialCapacity, null);
62	}
63
64	/**
65	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
66	* capacity
67	* that orders its elements according to the specified comparator.
68	*
69	* @param initialCapacity the initial capacity for this priority queue.
70	* @param comparator the comparator used to order this priority queue.
71	* If <tt>null</tt> then the order depends on the elements' natural
72	* ordering.
73	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
74	* than 1
75	*/
76	public PriorityBlockingQueue(int initialCapacity,
77	Comparator<? super E> comparator) {
78	q = new PriorityQueue<E>(initialCapacity, comparator);
79	}
80
81	/**
82	* Creates a <tt>PriorityBlockingQueue</tt> containing the elements
83	* in the specified collection. The priority queue has an initial
84	* capacity of 110% of the size of the specified collection. If
85	* the specified collection is a {@link SortedSet} or a {@link
86	* PriorityQueue}, this priority queue will be sorted according to
87	* the same comparator, or according to its elements' natural
88	* order if the collection is sorted according to its elements'
89	* natural order. Otherwise, this priority queue is ordered
90	* according to its elements' natural order.
91	*
92	* @param c the collection whose elements are to be placed
93	* into this priority queue.
94	* @throws ClassCastException if elements of the specified collection
95	* cannot be compared to one another according to the priority
96	* queue's ordering.
97	* @throws NullPointerException if <tt>c</tt> or any element within it
98	* is <tt>null</tt>
99	*/
100	public PriorityBlockingQueue(Collection<? extends E> c) {
101	q = new PriorityQueue<E>(c);
102	}
103
104
105	// these first few override just to update doc comments
106
107	/**
108	* Adds the specified element to this queue.
109	* @return <tt>true</tt> (as per the general contract of
110	* <tt>Collection.add</tt>).
111	*
112	* @throws NullPointerException if the specified element is <tt>null</tt>.
113	* @throws ClassCastException if the specified element cannot be compared
114	* with elements currently in the priority queue according
115	* to the priority queue's ordering.
116	*/
117	public boolean add(E o) {
118	return super.add(o);
119	}
120
121	/**
122	* Returns the comparator used to order this collection, or <tt>null</tt>
123	* if this collection is sorted according to its elements natural ordering
124	* (using <tt>Comparable</tt>).
125	*
126	* @return the comparator used to order this collection, or <tt>null</tt>
127	* if this collection is sorted according to its elements natural ordering.
128	*/
129	public Comparator comparator() {
130	return q.comparator();
131	}
132
133	/**
134	* Inserts the specified element into this priority queue.
135	*
136	* @param o the element to add
137	* @return <tt>true</tt>
138	* @throws ClassCastException if the specified element cannot be compared
139	* with elements currently in the priority queue according
140	* to the priority queue's ordering.
141	* @throws NullPointerException if the specified element is <tt>null</tt>.
142	*/
143	public boolean offer(E o) {
144	if (o == null) throw new NullPointerException();
145	lock.lock();
146	try {
147	boolean ok = q.offer(o);
148	assert ok;
149	notEmpty.signal();
150	return true;
151	} finally {
152	lock.unlock();
153	}
154	}
155
156	/**
157	* Adds the specified element to this priority queue. As the queue is
158	* unbounded this method will never block.
159	* @param o the element to add
160	* @throws ClassCastException if the element cannot be compared
161	* with elements currently in the priority queue according
162	* to the priority queue's ordering.
163	* @throws NullPointerException if the specified element is <tt>null</tt>.
164	*/
165	public void put(E o) {
166	offer(o); // never need to block
167	}
168
169	/**
170	* Inserts the specified element into this priority queue. As the queue is
171	* unbounded this method will never block.
172	* @param o the element to add
173	* @param timeout This parameter is ignored as the method never blocks
174	* @param unit This parameter is ignored as the method never blocks
175	* @return <tt>true</tt>
176	* @throws ClassCastException if the element cannot be compared
177	* with elements currently in the priority queue according
178	* to the priority queue's ordering.
179	* @throws NullPointerException if the specified element is <tt>null</tt>.
180	*/
181	public boolean offer(E o, long timeout, TimeUnit unit) {
182	return offer(o); // never need to block
183	}
184
185	public E take() throws InterruptedException {
186	lock.lockInterruptibly();
187	try {
188	try {
189	while (q.size() == 0)
190	notEmpty.await();
191	} catch (InterruptedException ie) {
192	notEmpty.signal(); // propagate to non-interrupted thread
193	throw ie;
194	}
195	E x = q.poll();
196	assert x != null;
197	return x;
198	} finally {
199	lock.unlock();
200	}
201	}
202
203
204	public E poll() {
205	lock.lock();
206	try {
207	return q.poll();
208	} finally {
209	lock.unlock();
210	}
211	}
212
213	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
214	long nanos = unit.toNanos(timeout);
215	lock.lockInterruptibly();
216	try {
217	for (;;) {
218	E x = q.poll();
219	if (x != null)
220	return x;
221	if (nanos <= 0)
222	return null;
223	try {
224	nanos = notEmpty.awaitNanos(nanos);
225	} catch (InterruptedException ie) {
226	notEmpty.signal(); // propagate to non-interrupted thread
227	throw ie;
228	}
229	}
230	} finally {
231	lock.unlock();
232	}
233	}
234
235	public E peek() {
236	lock.lock();
237	try {
238	return q.peek();
239	} finally {
240	lock.unlock();
241	}
242	}
243
244	public int size() {
245	lock.lock();
246	try {
247	return q.size();
248	} finally {
249	lock.unlock();
250	}
251	}
252
253	/**
254	* Always returns <tt>Integer.MAX_VALUE</tt> because
255	* a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
256	* @return <tt>Integer.MAX_VALUE</tt>
257	*/
258	public int remainingCapacity() {
259	return Integer.MAX_VALUE;
260	}
261
262	public boolean remove(Object o) {
263	lock.lock();
264	try {
265	return q.remove(o);
266	} finally {
267	lock.unlock();
268	}
269	}
270
271	public boolean contains(Object o) {
272	lock.lock();
273	try {
274	return q.contains(o);
275	} finally {
276	lock.unlock();
277	}
278	}
279
280	public Object[] toArray() {
281	lock.lock();
282	try {
283	return q.toArray();
284	} finally {
285	lock.unlock();
286	}
287	}
288
289
290	public String toString() {
291	lock.lock();
292	try {
293	return q.toString();
294	} finally {
295	lock.unlock();
296	}
297	}
298
299	/**
300	* Atomically removes all of the elements from this delay queue.
301	* The queue will be empty after this call returns.
302	*/
303	public void clear() {
304	lock.lock();
305	try {
306	q.clear();
307	} finally {
308	lock.unlock();
309	}
310	}
311
312	public <T> T[] toArray(T[] a) {
313	lock.lock();
314	try {
315	return q.toArray(a);
316	} finally {
317	lock.unlock();
318	}
319	}
320
321	/**
322	* Returns an iterator over the elements in this queue. The
323	* iterator does not return the elements in any particular order.
324	* The returned iterator is a thread-safe "fast-fail" iterator
325	* that will throw {@link
326	* java.util.ConcurrentModificationException} upon detected
327	* interference.
328	*
329	* @return an iterator over the elements in this queue.
330	*/
331	public Iterator<E> iterator() {
332	lock.lock();
333	try {
334	return new Itr(q.iterator());
335	} finally {
336	lock.unlock();
337	}
338	}
339
340	private class Itr<E> implements Iterator<E> {
341	private final Iterator<E> iter;
342	Itr(Iterator<E> i) {
343	iter = i;
344	}
345
346	public boolean hasNext() {
347	/*
348	* No sync -- we rely on underlying hasNext to be
349	* stateless, in which case we can return true by mistake
350	* only when next() willl subsequently throw
351	* ConcurrentModificationException.
352	*/
353	return iter.hasNext();
354	}
355
356	public E next() {
357	lock.lock();
358	try {
359	return iter.next();
360	} finally {
361	lock.unlock();
362	}
363	}
364
365	public void remove() {
366	lock.lock();
367	try {
368	iter.remove();
369	} finally {
370	lock.unlock();
371	}
372	}
373	}
374
375	/**
376	* Save the state to a stream (that is, serialize it). This
377	* merely wraps default serialization within lock. The
378	* serialization strategy for items is left to underlying
379	* Queue. Note that locking is not needed on deserialization, so
380	* readObject is not defined, just relying on default.
381	*/
382	private void writeObject(java.io.ObjectOutputStream s)
383	throws java.io.IOException {
384	lock.lock();
385	try {
386	s.defaultWriteObject();
387	} finally {
388	lock.unlock();
389	}
390	}
391
392	}