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} that uses
 * the same ordering rules as class {@link PriorityQueue} and supplies
 * blocking retrieval operations.  While this queue is logically
 * unbounded, attempted additions may fail due to resource exhaustion
 * (causing <tt>OutOfMemoryError</tt>). This class 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
 * @param <E> the type of elements held in this collection
 */
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 ReentrantLock.ConditionObject 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();
        }
    }

    public int drainTo(Collection<? super E> c) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        lock.lock();
        try {
            int n = 0;
            E e;
            while ( (e = q.poll()) != null) {
                c.add(e);
                ++n;
            }
            return n;
        } finally {
            lock.unlock();
        }
    }

    public int drainTo(Collection<? super E> c, int maxElements) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        if (maxElements <= 0)
            return 0;
        lock.lock();
        try {
            int n = 0;
            E e;
            while (n < maxElements && (e = q.poll()) != null) {
                c.add(e);
                ++n;
            }
            return n;
        } 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() will 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:	1.30
Committed:	Wed Nov 12 01:04:24 2003 UTC (20 years, 6 months ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_DEC9_PRE_ES_SUBMIT, JSR166_DEC9_POST_ES_SUBMIT
Changes since 1.29:	+1 -1 lines
Log Message:	fixed typos; avoided some casts
#	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} that uses
14	* the same ordering rules as class {@link PriorityQueue} and supplies
15	* blocking retrieval operations. While this queue is logically
16	* unbounded, attempted additions may fail due to resource exhaustion
17	* (causing <tt>OutOfMemoryError</tt>). This class does not permit
18	* <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	* @param <E> the type of elements held in this collection
32	*/
33	public class PriorityBlockingQueue<E> extends AbstractQueue<E>
34	implements BlockingQueue<E>, java.io.Serializable {
35	private static final long serialVersionUID = 5595510919245408276L;
36
37	private final PriorityQueue<E> q;
38	private final ReentrantLock lock = new ReentrantLock(true);
39	private final ReentrantLock.ConditionObject notEmpty = lock.newCondition();
40
41	/**
42	* Creates a <tt>PriorityBlockingQueue</tt> with the default initial
43	* capacity
44	* (11) that orders its elements according to their natural
45	* ordering (using <tt>Comparable</tt>).
46	*/
47	public PriorityBlockingQueue() {
48	q = new PriorityQueue<E>();
49	}
50
51	/**
52	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
53	* capacity
54	* that orders its elements according to their natural ordering
55	* (using <tt>Comparable</tt>).
56	*
57	* @param initialCapacity the initial capacity for this priority queue.
58	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
59	* than 1
60	*/
61	public PriorityBlockingQueue(int initialCapacity) {
62	q = new PriorityQueue<E>(initialCapacity, null);
63	}
64
65	/**
66	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
67	* capacity
68	* that orders its elements according to the specified comparator.
69	*
70	* @param initialCapacity the initial capacity for this priority queue.
71	* @param comparator the comparator used to order this priority queue.
72	* If <tt>null</tt> then the order depends on the elements' natural
73	* ordering.
74	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
75	* than 1
76	*/
77	public PriorityBlockingQueue(int initialCapacity,
78	Comparator<? super E> comparator) {
79	q = new PriorityQueue<E>(initialCapacity, comparator);
80	}
81
82	/**
83	* Creates a <tt>PriorityBlockingQueue</tt> containing the elements
84	* in the specified collection. The priority queue has an initial
85	* capacity of 110% of the size of the specified collection. If
86	* the specified collection is a {@link SortedSet} or a {@link
87	* PriorityQueue}, this priority queue will be sorted according to
88	* the same comparator, or according to its elements' natural
89	* order if the collection is sorted according to its elements'
90	* natural order. Otherwise, this priority queue is ordered
91	* according to its elements' natural order.
92	*
93	* @param c the collection whose elements are to be placed
94	* into this priority queue.
95	* @throws ClassCastException if elements of the specified collection
96	* cannot be compared to one another according to the priority
97	* queue's ordering.
98	* @throws NullPointerException if <tt>c</tt> or any element within it
99	* is <tt>null</tt>
100	*/
101	public PriorityBlockingQueue(Collection<? extends E> c) {
102	q = new PriorityQueue<E>(c);
103	}
104
105
106	// these first few override just to update doc comments
107
108	/**
109	* Adds the specified element to this queue.
110	* @return <tt>true</tt> (as per the general contract of
111	* <tt>Collection.add</tt>).
112	*
113	* @throws NullPointerException if the specified element is <tt>null</tt>.
114	* @throws ClassCastException if the specified element cannot be compared
115	* with elements currently in the priority queue according
116	* to the priority queue's ordering.
117	*/
118	public boolean add(E o) {
119	return super.add(o);
120	}
121
122	/**
123	* Returns the comparator used to order this collection, or <tt>null</tt>
124	* if this collection is sorted according to its elements natural ordering
125	* (using <tt>Comparable</tt>).
126	*
127	* @return the comparator used to order this collection, or <tt>null</tt>
128	* if this collection is sorted according to its elements natural ordering.
129	*/
130	public Comparator comparator() {
131	return q.comparator();
132	}
133
134	/**
135	* Inserts the specified element into this priority queue.
136	*
137	* @param o the element to add
138	* @return <tt>true</tt>
139	* @throws ClassCastException if the specified element cannot be compared
140	* with elements currently in the priority queue according
141	* to the priority queue's ordering.
142	* @throws NullPointerException if the specified element is <tt>null</tt>.
143	*/
144	public boolean offer(E o) {
145	if (o == null) throw new NullPointerException();
146	lock.lock();
147	try {
148	boolean ok = q.offer(o);
149	assert ok;
150	notEmpty.signal();
151	return true;
152	} finally {
153	lock.unlock();
154	}
155	}
156
157	/**
158	* Adds the specified element to this priority queue. As the queue is
159	* unbounded this method will never block.
160	* @param o the element to add
161	* @throws ClassCastException if the element cannot be compared
162	* with elements currently in the priority queue according
163	* to the priority queue's ordering.
164	* @throws NullPointerException if the specified element is <tt>null</tt>.
165	*/
166	public void put(E o) {
167	offer(o); // never need to block
168	}
169
170	/**
171	* Inserts the specified element into this priority queue. As the queue is
172	* unbounded this method will never block.
173	* @param o the element to add
174	* @param timeout This parameter is ignored as the method never blocks
175	* @param unit This parameter is ignored as the method never blocks
176	* @return <tt>true</tt>
177	* @throws ClassCastException if the element cannot be compared
178	* with elements currently in the priority queue according
179	* to the priority queue's ordering.
180	* @throws NullPointerException if the specified element is <tt>null</tt>.
181	*/
182	public boolean offer(E o, long timeout, TimeUnit unit) {
183	return offer(o); // never need to block
184	}
185
186	public E take() throws InterruptedException {
187	lock.lockInterruptibly();
188	try {
189	try {
190	while (q.size() == 0)
191	notEmpty.await();
192	} catch (InterruptedException ie) {
193	notEmpty.signal(); // propagate to non-interrupted thread
194	throw ie;
195	}
196	E x = q.poll();
197	assert x != null;
198	return x;
199	} finally {
200	lock.unlock();
201	}
202	}
203
204
205	public E poll() {
206	lock.lock();
207	try {
208	return q.poll();
209	} finally {
210	lock.unlock();
211	}
212	}
213
214	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
215	long nanos = unit.toNanos(timeout);
216	lock.lockInterruptibly();
217	try {
218	for (;;) {
219	E x = q.poll();
220	if (x != null)
221	return x;
222	if (nanos <= 0)
223	return null;
224	try {
225	nanos = notEmpty.awaitNanos(nanos);
226	} catch (InterruptedException ie) {
227	notEmpty.signal(); // propagate to non-interrupted thread
228	throw ie;
229	}
230	}
231	} finally {
232	lock.unlock();
233	}
234	}
235
236	public E peek() {
237	lock.lock();
238	try {
239	return q.peek();
240	} finally {
241	lock.unlock();
242	}
243	}
244
245	public int size() {
246	lock.lock();
247	try {
248	return q.size();
249	} finally {
250	lock.unlock();
251	}
252	}
253
254	/**
255	* Always returns <tt>Integer.MAX_VALUE</tt> because
256	* a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
257	* @return <tt>Integer.MAX_VALUE</tt>
258	*/
259	public int remainingCapacity() {
260	return Integer.MAX_VALUE;
261	}
262
263	public boolean remove(Object o) {
264	lock.lock();
265	try {
266	return q.remove(o);
267	} finally {
268	lock.unlock();
269	}
270	}
271
272	public boolean contains(Object o) {
273	lock.lock();
274	try {
275	return q.contains(o);
276	} finally {
277	lock.unlock();
278	}
279	}
280
281	public Object[] toArray() {
282	lock.lock();
283	try {
284	return q.toArray();
285	} finally {
286	lock.unlock();
287	}
288	}
289
290
291	public String toString() {
292	lock.lock();
293	try {
294	return q.toString();
295	} finally {
296	lock.unlock();
297	}
298	}
299
300	public int drainTo(Collection<? super E> c) {
301	if (c == null)
302	throw new NullPointerException();
303	if (c == this)
304	throw new IllegalArgumentException();
305	lock.lock();
306	try {
307	int n = 0;
308	E e;
309	while ( (e = q.poll()) != null) {
310	c.add(e);
311	++n;
312	}
313	return n;
314	} finally {
315	lock.unlock();
316	}
317	}
318
319	public int drainTo(Collection<? super E> c, int maxElements) {
320	if (c == null)
321	throw new NullPointerException();
322	if (c == this)
323	throw new IllegalArgumentException();
324	if (maxElements <= 0)
325	return 0;
326	lock.lock();
327	try {
328	int n = 0;
329	E e;
330	while (n < maxElements && (e = q.poll()) != null) {
331	c.add(e);
332	++n;
333	}
334	return n;
335	} finally {
336	lock.unlock();
337	}
338	}
339
340	/**
341	* Atomically removes all of the elements from this delay queue.
342	* The queue will be empty after this call returns.
343	*/
344	public void clear() {
345	lock.lock();
346	try {
347	q.clear();
348	} finally {
349	lock.unlock();
350	}
351	}
352
353	public <T> T[] toArray(T[] a) {
354	lock.lock();
355	try {
356	return q.toArray(a);
357	} finally {
358	lock.unlock();
359	}
360	}
361
362	/**
363	* Returns an iterator over the elements in this queue. The
364	* iterator does not return the elements in any particular order.
365	* The returned iterator is a thread-safe "fast-fail" iterator
366	* that will throw {@link
367	* java.util.ConcurrentModificationException} upon detected
368	* interference.
369	*
370	* @return an iterator over the elements in this queue.
371	*/
372	public Iterator<E> iterator() {
373	lock.lock();
374	try {
375	return new Itr(q.iterator());
376	} finally {
377	lock.unlock();
378	}
379	}
380
381	private class Itr<E> implements Iterator<E> {
382	private final Iterator<E> iter;
383	Itr(Iterator<E> i) {
384	iter = i;
385	}
386
387	public boolean hasNext() {
388	/*
389	* No sync -- we rely on underlying hasNext to be
390	* stateless, in which case we can return true by mistake
391	* only when next() will subsequently throw
392	* ConcurrentModificationException.
393	*/
394	return iter.hasNext();
395	}
396
397	public E next() {
398	lock.lock();
399	try {
400	return iter.next();
401	} finally {
402	lock.unlock();
403	}
404	}
405
406	public void remove() {
407	lock.lock();
408	try {
409	iter.remove();
410	} finally {
411	lock.unlock();
412	}
413	}
414	}
415
416	/**
417	* Save the state to a stream (that is, serialize it). This
418	* merely wraps default serialization within lock. The
419	* serialization strategy for items is left to underlying
420	* Queue. Note that locking is not needed on deserialization, so
421	* readObject is not defined, just relying on default.
422	*/
423	private void writeObject(java.io.ObjectOutputStream s)
424	throws java.io.IOException {
425	lock.lock();
426	try {
427	s.defaultWriteObject();
428	} finally {
429	lock.unlock();
430	}
431	}
432
433	}