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, 9 months ago) by tim
Branch:	MAIN
Changes since 1.18:	+18 -36 lines
Log Message:	Scrunched catch, finally, else clauses.
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5			*/
6
7	tim	1.1	package java.util.concurrent;
8	tim	1.13
9	dl	1.8	import java.util.concurrent.locks.*;
10	tim	1.1	import java.util.*;
11
12			/**
13	dholmes	1.16	* 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	dl	1.15	* attempted additions may fail due to resource exhaustion (causing
18	dholmes	1.16	* <tt>OutOfMemoryError</tt>).
19	dl	1.6	* @since 1.5
20			* @author Doug Lea
21	dholmes	1.14	*/
22	dl	1.5	public class PriorityBlockingQueue<E> extends AbstractQueue<E>
23	dl	1.15	implements BlockingQueue<E>, java.io.Serializable {
24	tim	1.1
25	dl	1.5	private final PriorityQueue<E> q;
26	dl	1.9	private final ReentrantLock lock = new ReentrantLock(true);
27	dl	1.5	private final Condition notEmpty = lock.newCondition();
28
29	dl	1.2	/**
30	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> with the default initial
31	dholmes	1.14	* capacity
32	dholmes	1.10	* (11) that orders its elements according to their natural
33	tim	1.18	* ordering (using <tt>Comparable</tt>).
34	dl	1.2	*/
35			public PriorityBlockingQueue() {
36	dl	1.5	q = new PriorityQueue<E>();
37	dl	1.2	}
38
39			/**
40	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
41	dholmes	1.10	* capacity
42			* that orders its elements according to their natural ordering
43	tim	1.18	* (using <tt>Comparable</tt>).
44	dl	1.2	*
45			* @param initialCapacity the initial capacity for this priority queue.
46	dholmes	1.16	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
47			* than 1
48	dl	1.2	*/
49			public PriorityBlockingQueue(int initialCapacity) {
50	dl	1.5	q = new PriorityQueue<E>(initialCapacity, null);
51	dl	1.2	}
52
53			/**
54	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
55	dholmes	1.10	* capacity
56	dl	1.2	* 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	dholmes	1.10	* If <tt>null</tt> then the order depends on the elements' natural
61			* ordering.
62	dholmes	1.16	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
63			* than 1
64	dl	1.2	*/
65	tim	1.13	public PriorityBlockingQueue(int initialCapacity,
66	dholmes	1.14	Comparator<? super E> comparator) {
67	dl	1.5	q = new PriorityQueue<E>(initialCapacity, comparator);
68	dl	1.2	}
69
70			/**
71	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> containing the elements
72	dl	1.15	* 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	dl	1.2	*
81	dholmes	1.14	* @param c the collection whose elements are to be placed
82	dl	1.2	* 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	dholmes	1.14	* @throws NullPointerException if <tt>c</tt> or any element within it
87			* is <tt>null</tt>
88	dl	1.2	*/
89	dholmes	1.14	public PriorityBlockingQueue(Collection<? extends E> c) {
90			q = new PriorityQueue<E>(c);
91	dl	1.7	}
92
93	dholmes	1.10
94	dholmes	1.16	// these first few override just to update doc comments
95	dholmes	1.10
96			/**
97	dholmes	1.16	* 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	dholmes	1.14	* @throws NullPointerException {@inheritDoc}
102	dholmes	1.16	* @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	dholmes	1.10	*/
106	dholmes	1.16	public boolean add(E o) {
107			return super.add(o);
108	dholmes	1.10	}
109
110	tim	1.13	/**
111	dholmes	1.16	* 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	dholmes	1.14	* @throws NullPointerException {@inheritDoc}
120	dholmes	1.16	* @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	tim	1.13	*/
124			public boolean addAll(Collection<? extends E> c) {
125			return super.addAll(c);
126			}
127	dholmes	1.10
128	dholmes	1.16	/**
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	tim	1.18	* (using <tt>Comparable</tt>).
132	dholmes	1.16	*
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	dl	1.7	public Comparator comparator() {
137			return q.comparator();
138	dl	1.5	}
139
140	dholmes	1.16	/**
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	dholmes	1.14	public boolean offer(E o) {
150			if (o == null) throw new NullPointerException();
151	dl	1.5	lock.lock();
152			try {
153	dholmes	1.14	boolean ok = q.offer(o);
154	dl	1.5	assert ok;
155			notEmpty.signal();
156			return true;
157	tim	1.19	} finally {
158	tim	1.13	lock.unlock();
159	dl	1.5	}
160			}
161
162	dholmes	1.16	/**
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	dholmes	1.14	offer(o); // never need to block
172	dl	1.5	}
173
174	dholmes	1.16	/**
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	dholmes	1.14	return offer(o); // never need to block
188	dl	1.5	}
189
190			public E take() throws InterruptedException {
191			lock.lockInterruptibly();
192			try {
193			try {
194			while (q.size() == 0)
195			notEmpty.await();
196	tim	1.19	} catch (InterruptedException ie) {
197	dl	1.5	notEmpty.signal(); // propagate to non-interrupted thread
198			throw ie;
199			}
200			E x = q.poll();
201			assert x != null;
202			return x;
203	tim	1.19	} finally {
204	dl	1.5	lock.unlock();
205			}
206			}
207
208
209			public E poll() {
210			lock.lock();
211			try {
212			return q.poll();
213	tim	1.19	} finally {
214	tim	1.13	lock.unlock();
215	dl	1.5	}
216			}
217
218			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
219	dholmes	1.10	long nanos = unit.toNanos(timeout);
220	dl	1.5	lock.lockInterruptibly();
221			try {
222			for (;;) {
223			E x = q.poll();
224	tim	1.13	if (x != null)
225	dl	1.5	return x;
226			if (nanos <= 0)
227			return null;
228			try {
229			nanos = notEmpty.awaitNanos(nanos);
230	tim	1.19	} catch (InterruptedException ie) {
231	dl	1.5	notEmpty.signal(); // propagate to non-interrupted thread
232			throw ie;
233			}
234			}
235	tim	1.19	} finally {
236	dl	1.5	lock.unlock();
237			}
238			}
239
240			public E peek() {
241			lock.lock();
242			try {
243			return q.peek();
244	tim	1.19	} finally {
245	tim	1.13	lock.unlock();
246	dl	1.5	}
247			}
248
249			public int size() {
250			lock.lock();
251			try {
252			return q.size();
253	tim	1.19	} finally {
254	dl	1.5	lock.unlock();
255			}
256			}
257
258			/**
259			* Always returns <tt>Integer.MAX_VALUE</tt> because
260	dholmes	1.16	* a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
261	dl	1.5	* @return <tt>Integer.MAX_VALUE</tt>
262			*/
263			public int remainingCapacity() {
264			return Integer.MAX_VALUE;
265			}
266
267	dholmes	1.16	/**
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	dholmes	1.14	public boolean remove(Object o) {
282	dl	1.5	lock.lock();
283			try {
284	dholmes	1.14	return q.remove(o);
285	tim	1.19	} finally {
286	dl	1.5	lock.unlock();
287			}
288			}
289
290	dholmes	1.14	public boolean contains(Object o) {
291	dl	1.5	lock.lock();
292			try {
293	dholmes	1.14	return q.contains(o);
294	tim	1.19	} finally {
295	dl	1.5	lock.unlock();
296			}
297			}
298
299			public Object[] toArray() {
300			lock.lock();
301			try {
302			return q.toArray();
303	tim	1.19	} finally {
304	dl	1.5	lock.unlock();
305			}
306			}
307
308
309			public String toString() {
310			lock.lock();
311			try {
312			return q.toString();
313	tim	1.19	} finally {
314	dl	1.5	lock.unlock();
315			}
316			}
317
318	dl	1.17	/**
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	tim	1.19	} finally {
327	dl	1.17	lock.unlock();
328			}
329			}
330
331	dl	1.5	public <T> T[] toArray(T[] a) {
332			lock.lock();
333			try {
334			return q.toArray(a);
335	tim	1.19	} finally {
336	dl	1.5	lock.unlock();
337			}
338			}
339
340	dholmes	1.16	/**
341			* Returns an iterator over the elements in this queue. The iterator
342			* does not return the elements in any particular order.
343	dl	1.17	* The
344			* returned iterator is a "fast-fail" iterator that will
345			* throw {@link java.util.ConcurrentModificationException}
346			* upon detected interference.
347	dholmes	1.16	*
348			* @return an iterator over the elements in this queue.
349			*/
350	dl	1.5	public Iterator<E> iterator() {
351			lock.lock();
352			try {
353			return new Itr(q.iterator());
354	tim	1.19	} finally {
355	dl	1.5	lock.unlock();
356			}
357			}
358
359			private class Itr<E> implements Iterator<E> {
360			private final Iterator<E> iter;
361	tim	1.13	Itr(Iterator<E> i) {
362			iter = i;
363	dl	1.5	}
364
365	tim	1.13	public boolean hasNext() {
366	dl	1.5	/*
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	tim	1.13	}
374
375			public E next() {
376	dl	1.5	lock.lock();
377			try {
378			return iter.next();
379	tim	1.19	} finally {
380	dl	1.5	lock.unlock();
381			}
382	tim	1.13	}
383
384			public void remove() {
385	dl	1.5	lock.lock();
386			try {
387			iter.remove();
388	tim	1.19	} finally {
389	dl	1.5	lock.unlock();
390			}
391	tim	1.13	}
392	dl	1.5	}
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	tim	1.19	} finally {
407	dl	1.5	lock.unlock();
408			}
409	tim	1.1	}
410
411			}