util/concurrent/PriorityBlockingQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

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 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();
        final ReentrantLock lock = this.lock;
        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 {
        final ReentrantLock lock = this.lock;
        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() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.poll();
        } finally {
            lock.unlock();
        }
    }

    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
        long nanos = unit.toNanos(timeout);
        final ReentrantLock lock = this.lock;
        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() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.peek();
        } finally {
            lock.unlock();
        }
    }

    public int size() {
        final ReentrantLock lock = this.lock;
        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) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.remove(o);
        } finally {
            lock.unlock();
        }
    }

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

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


    public String toString() {
        final ReentrantLock lock = this.lock;
        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();
        final ReentrantLock lock = this.lock;
        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;
        final ReentrantLock lock = this.lock;
        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() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            q.clear();
        } finally {
            lock.unlock();
        }
    }

    public <T> T[] toArray(T[] a) {
        final ReentrantLock lock = this.lock;
        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() {
        final ReentrantLock lock = this.lock;
        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() {
            ReentrantLock lock = PriorityBlockingQueue.this.lock;
            lock.lock();
            try {
                return iter.next();
            } finally {
                lock.unlock();
            }
        }

        public void remove() {
            ReentrantLock lock = PriorityBlockingQueue.this.lock;
            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:	1.33
Committed:	Sat Dec 27 19:26:26 2003 UTC (20 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.32:	+2 -2 lines
Log Message:	Headers reference Creative Commons
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/licenses/publicdomain
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 Condition 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	final ReentrantLock lock = this.lock;
147	lock.lock();
148	try {
149	boolean ok = q.offer(o);
150	assert ok;
151	notEmpty.signal();
152	return true;
153	} finally {
154	lock.unlock();
155	}
156	}
157
158	/**
159	* Adds the specified element to this priority queue. As the queue is
160	* unbounded this method will never block.
161	* @param o the element to add
162	* @throws ClassCastException if the element cannot be compared
163	* with elements currently in the priority queue according
164	* to the priority queue's ordering.
165	* @throws NullPointerException if the specified element is <tt>null</tt>.
166	*/
167	public void put(E o) {
168	offer(o); // never need to block
169	}
170
171	/**
172	* Inserts the specified element into this priority queue. As the queue is
173	* unbounded this method will never block.
174	* @param o the element to add
175	* @param timeout This parameter is ignored as the method never blocks
176	* @param unit This parameter is ignored as the method never blocks
177	* @return <tt>true</tt>
178	* @throws ClassCastException if the element cannot be compared
179	* with elements currently in the priority queue according
180	* to the priority queue's ordering.
181	* @throws NullPointerException if the specified element is <tt>null</tt>.
182	*/
183	public boolean offer(E o, long timeout, TimeUnit unit) {
184	return offer(o); // never need to block
185	}
186
187	public E take() throws InterruptedException {
188	final ReentrantLock lock = this.lock;
189	lock.lockInterruptibly();
190	try {
191	try {
192	while (q.size() == 0)
193	notEmpty.await();
194	} catch (InterruptedException ie) {
195	notEmpty.signal(); // propagate to non-interrupted thread
196	throw ie;
197	}
198	E x = q.poll();
199	assert x != null;
200	return x;
201	} finally {
202	lock.unlock();
203	}
204	}
205
206
207	public E poll() {
208	final ReentrantLock lock = this.lock;
209	lock.lock();
210	try {
211	return q.poll();
212	} finally {
213	lock.unlock();
214	}
215	}
216
217	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
218	long nanos = unit.toNanos(timeout);
219	final ReentrantLock lock = this.lock;
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	final ReentrantLock lock = this.lock;
242	lock.lock();
243	try {
244	return q.peek();
245	} finally {
246	lock.unlock();
247	}
248	}
249
250	public int size() {
251	final ReentrantLock lock = this.lock;
252	lock.lock();
253	try {
254	return q.size();
255	} finally {
256	lock.unlock();
257	}
258	}
259
260	/**
261	* Always returns <tt>Integer.MAX_VALUE</tt> because
262	* a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
263	* @return <tt>Integer.MAX_VALUE</tt>
264	*/
265	public int remainingCapacity() {
266	return Integer.MAX_VALUE;
267	}
268
269	public boolean remove(Object o) {
270	final ReentrantLock lock = this.lock;
271	lock.lock();
272	try {
273	return q.remove(o);
274	} finally {
275	lock.unlock();
276	}
277	}
278
279	public boolean contains(Object o) {
280	final ReentrantLock lock = this.lock;
281	lock.lock();
282	try {
283	return q.contains(o);
284	} finally {
285	lock.unlock();
286	}
287	}
288
289	public Object[] toArray() {
290	final ReentrantLock lock = this.lock;
291	lock.lock();
292	try {
293	return q.toArray();
294	} finally {
295	lock.unlock();
296	}
297	}
298
299
300	public String toString() {
301	final ReentrantLock lock = this.lock;
302	lock.lock();
303	try {
304	return q.toString();
305	} finally {
306	lock.unlock();
307	}
308	}
309
310	public int drainTo(Collection<? super E> c) {
311	if (c == null)
312	throw new NullPointerException();
313	if (c == this)
314	throw new IllegalArgumentException();
315	final ReentrantLock lock = this.lock;
316	lock.lock();
317	try {
318	int n = 0;
319	E e;
320	while ( (e = q.poll()) != null) {
321	c.add(e);
322	++n;
323	}
324	return n;
325	} finally {
326	lock.unlock();
327	}
328	}
329
330	public int drainTo(Collection<? super E> c, int maxElements) {
331	if (c == null)
332	throw new NullPointerException();
333	if (c == this)
334	throw new IllegalArgumentException();
335	if (maxElements <= 0)
336	return 0;
337	final ReentrantLock lock = this.lock;
338	lock.lock();
339	try {
340	int n = 0;
341	E e;
342	while (n < maxElements && (e = q.poll()) != null) {
343	c.add(e);
344	++n;
345	}
346	return n;
347	} finally {
348	lock.unlock();
349	}
350	}
351
352	/**
353	* Atomically removes all of the elements from this delay queue.
354	* The queue will be empty after this call returns.
355	*/
356	public void clear() {
357	final ReentrantLock lock = this.lock;
358	lock.lock();
359	try {
360	q.clear();
361	} finally {
362	lock.unlock();
363	}
364	}
365
366	public <T> T[] toArray(T[] a) {
367	final ReentrantLock lock = this.lock;
368	lock.lock();
369	try {
370	return q.toArray(a);
371	} finally {
372	lock.unlock();
373	}
374	}
375
376	/**
377	* Returns an iterator over the elements in this queue. The
378	* iterator does not return the elements in any particular order.
379	* The returned iterator is a thread-safe "fast-fail" iterator
380	* that will throw {@link
381	* java.util.ConcurrentModificationException} upon detected
382	* interference.
383	*
384	* @return an iterator over the elements in this queue.
385	*/
386	public Iterator<E> iterator() {
387	final ReentrantLock lock = this.lock;
388	lock.lock();
389	try {
390	return new Itr(q.iterator());
391	} finally {
392	lock.unlock();
393	}
394	}
395
396	private class Itr<E> implements Iterator<E> {
397	private final Iterator<E> iter;
398	Itr(Iterator<E> i) {
399	iter = i;
400	}
401
402	public boolean hasNext() {
403	/*
404	* No sync -- we rely on underlying hasNext to be
405	* stateless, in which case we can return true by mistake
406	* only when next() will subsequently throw
407	* ConcurrentModificationException.
408	*/
409	return iter.hasNext();
410	}
411
412	public E next() {
413	ReentrantLock lock = PriorityBlockingQueue.this.lock;
414	lock.lock();
415	try {
416	return iter.next();
417	} finally {
418	lock.unlock();
419	}
420	}
421
422	public void remove() {
423	ReentrantLock lock = PriorityBlockingQueue.this.lock;
424	lock.lock();
425	try {
426	iter.remove();
427	} finally {
428	lock.unlock();
429	}
430	}
431	}
432
433	/**
434	* Save the state to a stream (that is, serialize it). This
435	* merely wraps default serialization within lock. The
436	* serialization strategy for items is left to underlying
437	* Queue. Note that locking is not needed on deserialization, so
438	* readObject is not defined, just relying on default.
439	*/
440	private void writeObject(java.io.ObjectOutputStream s)
441	throws java.io.IOException {
442	lock.lock();
443	try {
444	s.defaultWriteObject();
445	} finally {
446	lock.unlock();
447	}
448	}
449
450	}