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>).
 * @since 1.5
 * @author Doug Lea
*/
public class PriorityBlockingQueue<E> extends AbstractQueue<E>
    implements BlockingQueue<E>, java.io.Serializable {

    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 {@inheritDoc}
     * @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);
    }

    /**
     * Adds all of the elements in the specified collection to this queue.
     * The behavior of this operation is undefined if
     * the specified collection is modified while the operation is in
     * progress.  (This implies that the behavior of this call is undefined if
     * the specified collection is this queue, and this queue is nonempty.)
     * <p>
     * This implementation iterates over the specified collection, and adds
     * each object returned by the iterator to this collection, in turn.
     * @throws NullPointerException {@inheritDoc}
     * @throws ClassCastException if any element cannot be compared
     * with elements currently in the priority queue according
     * to the priority queue's ordering.
     */
    public boolean addAll(Collection<? extends E> c) {
        return super.addAll(c);
    }

    /**
     * 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();
    }

    /**
     * Adds the specified element to this priority queue.
     *
     * @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 {@inheritDoc}
     */
    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.
     * @throws ClassCastException if the element cannot be compared
     * with elements currently in the priority queue according
     * to the priority queue's ordering.
     * @throws NullPointerException {@inheritDoc}
     */
    public void put(E o) {
        offer(o); // never need to block
    }

    /**
     * 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 ClassCastException if the element cannot be compared
     * with elements currently in the priority queue according
     * to the priority queue's ordering.
     * @throws NullPointerException {@inheritDoc}
     * @return <tt>true</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;
    }

    /**
     * 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();
        }
    }

    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 "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:	1.19
Committed:	Fri Aug 8 20:05:07 2003 UTC (20 years, 10 months ago) by tim
Branch:	MAIN
Changes since 1.18:	+18 -36 lines
Log Message:	Scrunched catch, finally, else clauses.
#	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},
15	* obeying its ordering rules and implementation characteristics.
16	* While this queue is logically unbounded,
17	* attempted additions may fail due to resource exhaustion (causing
18	* <tt>OutOfMemoryError</tt>).
19	* @since 1.5
20	* @author Doug Lea
21	*/
22	public class PriorityBlockingQueue<E> extends AbstractQueue<E>
23	implements BlockingQueue<E>, java.io.Serializable {
24
25	private final PriorityQueue<E> q;
26	private final ReentrantLock lock = new ReentrantLock(true);
27	private final Condition notEmpty = lock.newCondition();
28
29	/**
30	* Creates a <tt>PriorityBlockingQueue</tt> with the default initial
31	* capacity
32	* (11) that orders its elements according to their natural
33	* ordering (using <tt>Comparable</tt>).
34	*/
35	public PriorityBlockingQueue() {
36	q = new PriorityQueue<E>();
37	}
38
39	/**
40	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
41	* capacity
42	* that orders its elements according to their natural ordering
43	* (using <tt>Comparable</tt>).
44	*
45	* @param initialCapacity the initial capacity for this priority queue.
46	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
47	* than 1
48	*/
49	public PriorityBlockingQueue(int initialCapacity) {
50	q = new PriorityQueue<E>(initialCapacity, null);
51	}
52
53	/**
54	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
55	* capacity
56	* that orders its elements according to the specified comparator.
57	*
58	* @param initialCapacity the initial capacity for this priority queue.
59	* @param comparator the comparator used to order this priority queue.
60	* If <tt>null</tt> then the order depends on the elements' natural
61	* ordering.
62	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
63	* than 1
64	*/
65	public PriorityBlockingQueue(int initialCapacity,
66	Comparator<? super E> comparator) {
67	q = new PriorityQueue<E>(initialCapacity, comparator);
68	}
69
70	/**
71	* Creates a <tt>PriorityBlockingQueue</tt> containing the elements
72	* in the specified collection. The priority queue has an initial
73	* capacity of 110% of the size of the specified collection. If
74	* the specified collection is a {@link SortedSet} or a {@link
75	* PriorityQueue}, this priority queue will be sorted according to
76	* the same comparator, or according to its elements' natural
77	* order if the collection is sorted according to its elements'
78	* natural order. Otherwise, this priority queue is ordered
79	* according to its elements' natural order.
80	*
81	* @param c the collection whose elements are to be placed
82	* into this priority queue.
83	* @throws ClassCastException if elements of the specified collection
84	* cannot be compared to one another according to the priority
85	* queue's ordering.
86	* @throws NullPointerException if <tt>c</tt> or any element within it
87	* is <tt>null</tt>
88	*/
89	public PriorityBlockingQueue(Collection<? extends E> c) {
90	q = new PriorityQueue<E>(c);
91	}
92
93
94	// these first few override just to update doc comments
95
96	/**
97	* Adds the specified element to this queue.
98	* @return <tt>true</tt> (as per the general contract of
99	* <tt>Collection.add</tt>).
100	*
101	* @throws NullPointerException {@inheritDoc}
102	* @throws ClassCastException if the specified element cannot be compared
103	* with elements currently in the priority queue according
104	* to the priority queue's ordering.
105	*/
106	public boolean add(E o) {
107	return super.add(o);
108	}
109
110	/**
111	* Adds all of the elements in the specified collection to this queue.
112	* The behavior of this operation is undefined if
113	* the specified collection is modified while the operation is in
114	* progress. (This implies that the behavior of this call is undefined if
115	* the specified collection is this queue, and this queue is nonempty.)
116	* <p>
117	* This implementation iterates over the specified collection, and adds
118	* each object returned by the iterator to this collection, in turn.
119	* @throws NullPointerException {@inheritDoc}
120	* @throws ClassCastException if any element cannot be compared
121	* with elements currently in the priority queue according
122	* to the priority queue's ordering.
123	*/
124	public boolean addAll(Collection<? extends E> c) {
125	return super.addAll(c);
126	}
127
128	/**
129	* Returns the comparator used to order this collection, or <tt>null</tt>
130	* if this collection is sorted according to its elements natural ordering
131	* (using <tt>Comparable</tt>).
132	*
133	* @return the comparator used to order this collection, or <tt>null</tt>
134	* if this collection is sorted according to its elements natural ordering.
135	*/
136	public Comparator comparator() {
137	return q.comparator();
138	}
139
140	/**
141	* Adds the specified element to this priority queue.
142	*
143	* @return <tt>true</tt>
144	* @throws ClassCastException if the specified element cannot be compared
145	* with elements currently in the priority queue according
146	* to the priority queue's ordering.
147	* @throws NullPointerException {@inheritDoc}
148	*/
149	public boolean offer(E o) {
150	if (o == null) throw new NullPointerException();
151	lock.lock();
152	try {
153	boolean ok = q.offer(o);
154	assert ok;
155	notEmpty.signal();
156	return true;
157	} finally {
158	lock.unlock();
159	}
160	}
161
162	/**
163	* Adds the specified element to this priority queue. As the queue is
164	* unbounded this method will never block.
165	* @throws ClassCastException if the element cannot be compared
166	* with elements currently in the priority queue according
167	* to the priority queue's ordering.
168	* @throws NullPointerException {@inheritDoc}
169	*/
170	public void put(E o) {
171	offer(o); // never need to block
172	}
173
174	/**
175	* Adds the specified element to this priority queue. As the queue is
176	* unbounded this method will never block.
177	* @param o {@inheritDoc}
178	* @param timeout This parameter is ignored as the method never blocks
179	* @param unit This parameter is ignored as the method never blocks
180	* @throws ClassCastException if the element cannot be compared
181	* with elements currently in the priority queue according
182	* to the priority queue's ordering.
183	* @throws NullPointerException {@inheritDoc}
184	* @return <tt>true</tt>
185	*/
186	public boolean offer(E o, long timeout, TimeUnit unit) {
187	return offer(o); // never need to block
188	}
189
190	public E take() throws InterruptedException {
191	lock.lockInterruptibly();
192	try {
193	try {
194	while (q.size() == 0)
195	notEmpty.await();
196	} catch (InterruptedException ie) {
197	notEmpty.signal(); // propagate to non-interrupted thread
198	throw ie;
199	}
200	E x = q.poll();
201	assert x != null;
202	return x;
203	} finally {
204	lock.unlock();
205	}
206	}
207
208
209	public E poll() {
210	lock.lock();
211	try {
212	return q.poll();
213	} finally {
214	lock.unlock();
215	}
216	}
217
218	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
219	long nanos = unit.toNanos(timeout);
220	lock.lockInterruptibly();
221	try {
222	for (;;) {
223	E x = q.poll();
224	if (x != null)
225	return x;
226	if (nanos <= 0)
227	return null;
228	try {
229	nanos = notEmpty.awaitNanos(nanos);
230	} catch (InterruptedException ie) {
231	notEmpty.signal(); // propagate to non-interrupted thread
232	throw ie;
233	}
234	}
235	} finally {
236	lock.unlock();
237	}
238	}
239
240	public E peek() {
241	lock.lock();
242	try {
243	return q.peek();
244	} finally {
245	lock.unlock();
246	}
247	}
248
249	public int size() {
250	lock.lock();
251	try {
252	return q.size();
253	} finally {
254	lock.unlock();
255	}
256	}
257
258	/**
259	* Always returns <tt>Integer.MAX_VALUE</tt> because
260	* a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
261	* @return <tt>Integer.MAX_VALUE</tt>
262	*/
263	public int remainingCapacity() {
264	return Integer.MAX_VALUE;
265	}
266
267	/**
268	* Removes a single instance of the specified element from this
269	* queue, if it is present. More formally,
270	* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
271	* o.equals(e))</tt>, if the queue contains one or more such
272	* elements. Returns <tt>true</tt> if the queue contained the
273	* specified element (or equivalently, if the queue changed as a
274	* result of the call).
275	*
276	* <p>This implementation iterates over the queue looking for the
277	* specified element. If it finds the element, it removes the element
278	* from the queue using the iterator's remove method.<p>
279	*
280	*/
281	public boolean remove(Object o) {
282	lock.lock();
283	try {
284	return q.remove(o);
285	} finally {
286	lock.unlock();
287	}
288	}
289
290	public boolean contains(Object o) {
291	lock.lock();
292	try {
293	return q.contains(o);
294	} finally {
295	lock.unlock();
296	}
297	}
298
299	public Object[] toArray() {
300	lock.lock();
301	try {
302	return q.toArray();
303	} finally {
304	lock.unlock();
305	}
306	}
307
308
309	public String toString() {
310	lock.lock();
311	try {
312	return q.toString();
313	} finally {
314	lock.unlock();
315	}
316	}
317
318	/**
319	* Atomically removes all of the elements from this delay queue.
320	* The queue will be empty after this call returns.
321	*/
322	public void clear() {
323	lock.lock();
324	try {
325	q.clear();
326	} finally {
327	lock.unlock();
328	}
329	}
330
331	public <T> T[] toArray(T[] a) {
332	lock.lock();
333	try {
334	return q.toArray(a);
335	} finally {
336	lock.unlock();
337	}
338	}
339
340	/**
341	* Returns an iterator over the elements in this queue. The iterator
342	* does not return the elements in any particular order.
343	* The
344	* returned iterator is a "fast-fail" iterator that will
345	* throw {@link java.util.ConcurrentModificationException}
346	* upon detected interference.
347	*
348	* @return an iterator over the elements in this queue.
349	*/
350	public Iterator<E> iterator() {
351	lock.lock();
352	try {
353	return new Itr(q.iterator());
354	} finally {
355	lock.unlock();
356	}
357	}
358
359	private class Itr<E> implements Iterator<E> {
360	private final Iterator<E> iter;
361	Itr(Iterator<E> i) {
362	iter = i;
363	}
364
365	public boolean hasNext() {
366	/*
367	* No sync -- we rely on underlying hasNext to be
368	* stateless, in which case we can return true by mistake
369	* only when next() willl subsequently throw
370	* ConcurrentModificationException.
371	*/
372	return iter.hasNext();
373	}
374
375	public E next() {
376	lock.lock();
377	try {
378	return iter.next();
379	} finally {
380	lock.unlock();
381	}
382	}
383
384	public void remove() {
385	lock.lock();
386	try {
387	iter.remove();
388	} finally {
389	lock.unlock();
390	}
391	}
392	}
393
394	/**
395	* Save the state to a stream (that is, serialize it). This
396	* merely wraps default serialization within lock. The
397	* serialization strategy for items is left to underlying
398	* Queue. Note that locking is not needed on deserialization, so
399	* readObject is not defined, just relying on default.
400	*/
401	private void writeObject(java.io.ObjectOutputStream s)
402	throws java.io.IOException {
403	lock.lock();
404	try {
405	s.defaultWriteObject();
406	} finally {
407	lock.unlock();
408	}
409	}
410
411	}