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>).
 *
 * <p>The Iterator provided in method {@link #iterator()} is
 * <em>not</em> guaranteed to traverse the elements of the
 * PriorityBlockingQueue in any particular order. If you need ordered
 * traversal, consider using <tt>Arrays.sort(pq.toArray())</tt>.
 *
 * @since 1.5
 * @author Doug Lea
*/
public class PriorityBlockingQueue<E> extends AbstractQueue<E>
    implements BlockingQueue<E>, java.io.Serializable {

    private 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:	1.20
Committed:	Sun Aug 24 23:32:25 2003 UTC (20 years, 9 months ago) by dl
Branch:	MAIN
Changes since 1.19:	+6 -0 lines
Log Message:	Kill ScheduledExecutor Date methods; Documentation clarifications
#	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	1.20	*
20			* <p>The Iterator provided in method {@link #iterator()} is
21			* <em>not</em> guaranteed to traverse the elements of the
22			* PriorityBlockingQueue in any particular order. If you need ordered
23			* traversal, consider using <tt>Arrays.sort(pq.toArray())</tt>.
24			*
25	dl	1.6	* @since 1.5
26			* @author Doug Lea
27	dholmes	1.14	*/
28	dl	1.5	public class PriorityBlockingQueue<E> extends AbstractQueue<E>
29	dl	1.15	implements BlockingQueue<E>, java.io.Serializable {
30	tim	1.1
31	dl	1.5	private final PriorityQueue<E> q;
32	dl	1.9	private final ReentrantLock lock = new ReentrantLock(true);
33	dl	1.5	private final Condition notEmpty = lock.newCondition();
34
35	dl	1.2	/**
36	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> with the default initial
37	dholmes	1.14	* capacity
38	dholmes	1.10	* (11) that orders its elements according to their natural
39	tim	1.18	* ordering (using <tt>Comparable</tt>).
40	dl	1.2	*/
41			public PriorityBlockingQueue() {
42	dl	1.5	q = new PriorityQueue<E>();
43	dl	1.2	}
44
45			/**
46	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
47	dholmes	1.10	* capacity
48			* that orders its elements according to their natural ordering
49	tim	1.18	* (using <tt>Comparable</tt>).
50	dl	1.2	*
51			* @param initialCapacity the initial capacity for this priority queue.
52	dholmes	1.16	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
53			* than 1
54	dl	1.2	*/
55			public PriorityBlockingQueue(int initialCapacity) {
56	dl	1.5	q = new PriorityQueue<E>(initialCapacity, null);
57	dl	1.2	}
58
59			/**
60	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
61	dholmes	1.10	* capacity
62	dl	1.2	* that orders its elements according to the specified comparator.
63			*
64			* @param initialCapacity the initial capacity for this priority queue.
65			* @param comparator the comparator used to order this priority queue.
66	dholmes	1.10	* If <tt>null</tt> then the order depends on the elements' natural
67			* ordering.
68	dholmes	1.16	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
69			* than 1
70	dl	1.2	*/
71	tim	1.13	public PriorityBlockingQueue(int initialCapacity,
72	dholmes	1.14	Comparator<? super E> comparator) {
73	dl	1.5	q = new PriorityQueue<E>(initialCapacity, comparator);
74	dl	1.2	}
75
76			/**
77	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> containing the elements
78	dl	1.15	* in the specified collection. The priority queue has an initial
79			* capacity of 110% of the size of the specified collection. If
80			* the specified collection is a {@link SortedSet} or a {@link
81			* PriorityQueue}, this priority queue will be sorted according to
82			* the same comparator, or according to its elements' natural
83			* order if the collection is sorted according to its elements'
84			* natural order. Otherwise, this priority queue is ordered
85			* according to its elements' natural order.
86	dl	1.2	*
87	dholmes	1.14	* @param c the collection whose elements are to be placed
88	dl	1.2	* into this priority queue.
89			* @throws ClassCastException if elements of the specified collection
90			* cannot be compared to one another according to the priority
91			* queue's ordering.
92	dholmes	1.14	* @throws NullPointerException if <tt>c</tt> or any element within it
93			* is <tt>null</tt>
94	dl	1.2	*/
95	dholmes	1.14	public PriorityBlockingQueue(Collection<? extends E> c) {
96			q = new PriorityQueue<E>(c);
97	dl	1.7	}
98
99	dholmes	1.10
100	dholmes	1.16	// these first few override just to update doc comments
101	dholmes	1.10
102			/**
103	dholmes	1.16	* Adds the specified element to this queue.
104			* @return <tt>true</tt> (as per the general contract of
105			* <tt>Collection.add</tt>).
106			*
107	dholmes	1.14	* @throws NullPointerException {@inheritDoc}
108	dholmes	1.16	* @throws ClassCastException if the specified element cannot be compared
109			* with elements currently in the priority queue according
110			* to the priority queue's ordering.
111	dholmes	1.10	*/
112	dholmes	1.16	public boolean add(E o) {
113			return super.add(o);
114	dholmes	1.10	}
115
116	tim	1.13	/**
117	dholmes	1.16	* Adds all of the elements in the specified collection to this queue.
118			* The behavior of this operation is undefined if
119			* the specified collection is modified while the operation is in
120			* progress. (This implies that the behavior of this call is undefined if
121			* the specified collection is this queue, and this queue is nonempty.)
122			* <p>
123			* This implementation iterates over the specified collection, and adds
124			* each object returned by the iterator to this collection, in turn.
125	dholmes	1.14	* @throws NullPointerException {@inheritDoc}
126	dholmes	1.16	* @throws ClassCastException if any element cannot be compared
127			* with elements currently in the priority queue according
128			* to the priority queue's ordering.
129	tim	1.13	*/
130			public boolean addAll(Collection<? extends E> c) {
131			return super.addAll(c);
132			}
133	dholmes	1.10
134	dholmes	1.16	/**
135			* Returns the comparator used to order this collection, or <tt>null</tt>
136			* if this collection is sorted according to its elements natural ordering
137	tim	1.18	* (using <tt>Comparable</tt>).
138	dholmes	1.16	*
139			* @return the comparator used to order this collection, or <tt>null</tt>
140			* if this collection is sorted according to its elements natural ordering.
141			*/
142	dl	1.7	public Comparator comparator() {
143			return q.comparator();
144	dl	1.5	}
145
146	dholmes	1.16	/**
147			* Adds the specified element to this priority queue.
148			*
149			* @return <tt>true</tt>
150			* @throws ClassCastException if the specified element cannot be compared
151			* with elements currently in the priority queue according
152			* to the priority queue's ordering.
153			* @throws NullPointerException {@inheritDoc}
154			*/
155	dholmes	1.14	public boolean offer(E o) {
156			if (o == null) throw new NullPointerException();
157	dl	1.5	lock.lock();
158			try {
159	dholmes	1.14	boolean ok = q.offer(o);
160	dl	1.5	assert ok;
161			notEmpty.signal();
162			return true;
163	tim	1.19	} finally {
164	tim	1.13	lock.unlock();
165	dl	1.5	}
166			}
167
168	dholmes	1.16	/**
169			* Adds the specified element to this priority queue. As the queue is
170			* unbounded this method will never block.
171			* @throws ClassCastException if the element cannot be compared
172			* with elements currently in the priority queue according
173			* to the priority queue's ordering.
174			* @throws NullPointerException {@inheritDoc}
175			*/
176			public void put(E o) {
177	dholmes	1.14	offer(o); // never need to block
178	dl	1.5	}
179
180	dholmes	1.16	/**
181			* Adds the specified element to this priority queue. As the queue is
182			* unbounded this method will never block.
183			* @param o {@inheritDoc}
184			* @param timeout This parameter is ignored as the method never blocks
185			* @param unit This parameter is ignored as the method never blocks
186			* @throws ClassCastException if the element cannot be compared
187			* with elements currently in the priority queue according
188			* to the priority queue's ordering.
189			* @throws NullPointerException {@inheritDoc}
190			* @return <tt>true</tt>
191			*/
192			public boolean offer(E o, long timeout, TimeUnit unit) {
193	dholmes	1.14	return offer(o); // never need to block
194	dl	1.5	}
195
196			public E take() throws InterruptedException {
197			lock.lockInterruptibly();
198			try {
199			try {
200			while (q.size() == 0)
201			notEmpty.await();
202	tim	1.19	} catch (InterruptedException ie) {
203	dl	1.5	notEmpty.signal(); // propagate to non-interrupted thread
204			throw ie;
205			}
206			E x = q.poll();
207			assert x != null;
208			return x;
209	tim	1.19	} finally {
210	dl	1.5	lock.unlock();
211			}
212			}
213
214
215			public E poll() {
216			lock.lock();
217			try {
218			return q.poll();
219	tim	1.19	} finally {
220	tim	1.13	lock.unlock();
221	dl	1.5	}
222			}
223
224			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
225	dholmes	1.10	long nanos = unit.toNanos(timeout);
226	dl	1.5	lock.lockInterruptibly();
227			try {
228			for (;;) {
229			E x = q.poll();
230	tim	1.13	if (x != null)
231	dl	1.5	return x;
232			if (nanos <= 0)
233			return null;
234			try {
235			nanos = notEmpty.awaitNanos(nanos);
236	tim	1.19	} catch (InterruptedException ie) {
237	dl	1.5	notEmpty.signal(); // propagate to non-interrupted thread
238			throw ie;
239			}
240			}
241	tim	1.19	} finally {
242	dl	1.5	lock.unlock();
243			}
244			}
245
246			public E peek() {
247			lock.lock();
248			try {
249			return q.peek();
250	tim	1.19	} finally {
251	tim	1.13	lock.unlock();
252	dl	1.5	}
253			}
254
255			public int size() {
256			lock.lock();
257			try {
258			return q.size();
259	tim	1.19	} finally {
260	dl	1.5	lock.unlock();
261			}
262			}
263
264			/**
265			* Always returns <tt>Integer.MAX_VALUE</tt> because
266	dholmes	1.16	* a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
267	dl	1.5	* @return <tt>Integer.MAX_VALUE</tt>
268			*/
269			public int remainingCapacity() {
270			return Integer.MAX_VALUE;
271			}
272
273	dholmes	1.16	/**
274			* Removes a single instance of the specified element from this
275			* queue, if it is present. More formally,
276			* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
277			* o.equals(e))</tt>, if the queue contains one or more such
278			* elements. Returns <tt>true</tt> if the queue contained the
279			* specified element (or equivalently, if the queue changed as a
280			* result of the call).
281			*
282			* <p>This implementation iterates over the queue looking for the
283			* specified element. If it finds the element, it removes the element
284			* from the queue using the iterator's remove method.<p>
285			*
286			*/
287	dholmes	1.14	public boolean remove(Object o) {
288	dl	1.5	lock.lock();
289			try {
290	dholmes	1.14	return q.remove(o);
291	tim	1.19	} finally {
292	dl	1.5	lock.unlock();
293			}
294			}
295
296	dholmes	1.14	public boolean contains(Object o) {
297	dl	1.5	lock.lock();
298			try {
299	dholmes	1.14	return q.contains(o);
300	tim	1.19	} finally {
301	dl	1.5	lock.unlock();
302			}
303			}
304
305			public Object[] toArray() {
306			lock.lock();
307			try {
308			return q.toArray();
309	tim	1.19	} finally {
310	dl	1.5	lock.unlock();
311			}
312			}
313
314
315			public String toString() {
316			lock.lock();
317			try {
318			return q.toString();
319	tim	1.19	} finally {
320	dl	1.5	lock.unlock();
321			}
322			}
323
324	dl	1.17	/**
325			* Atomically removes all of the elements from this delay queue.
326			* The queue will be empty after this call returns.
327			*/
328			public void clear() {
329			lock.lock();
330			try {
331			q.clear();
332	tim	1.19	} finally {
333	dl	1.17	lock.unlock();
334			}
335			}
336
337	dl	1.5	public <T> T[] toArray(T[] a) {
338			lock.lock();
339			try {
340			return q.toArray(a);
341	tim	1.19	} finally {
342	dl	1.5	lock.unlock();
343			}
344			}
345
346	dholmes	1.16	/**
347			* Returns an iterator over the elements in this queue. The iterator
348			* does not return the elements in any particular order.
349	dl	1.17	* The
350			* returned iterator is a "fast-fail" iterator that will
351			* throw {@link java.util.ConcurrentModificationException}
352			* upon detected interference.
353	dholmes	1.16	*
354			* @return an iterator over the elements in this queue.
355			*/
356	dl	1.5	public Iterator<E> iterator() {
357			lock.lock();
358			try {
359			return new Itr(q.iterator());
360	tim	1.19	} finally {
361	dl	1.5	lock.unlock();
362			}
363			}
364
365			private class Itr<E> implements Iterator<E> {
366			private final Iterator<E> iter;
367	tim	1.13	Itr(Iterator<E> i) {
368			iter = i;
369	dl	1.5	}
370
371	tim	1.13	public boolean hasNext() {
372	dl	1.5	/*
373			* No sync -- we rely on underlying hasNext to be
374			* stateless, in which case we can return true by mistake
375			* only when next() willl subsequently throw
376			* ConcurrentModificationException.
377			*/
378			return iter.hasNext();
379	tim	1.13	}
380
381			public E next() {
382	dl	1.5	lock.lock();
383			try {
384			return iter.next();
385	tim	1.19	} finally {
386	dl	1.5	lock.unlock();
387			}
388	tim	1.13	}
389
390			public void remove() {
391	dl	1.5	lock.lock();
392			try {
393			iter.remove();
394	tim	1.19	} finally {
395	dl	1.5	lock.unlock();
396			}
397	tim	1.13	}
398	dl	1.5	}
399
400			/**
401			* Save the state to a stream (that is, serialize it). This
402			* merely wraps default serialization within lock. The
403			* serialization strategy for items is left to underlying
404			* Queue. Note that locking is not needed on deserialization, so
405			* readObject is not defined, just relying on default.
406			*/
407			private void writeObject(java.io.ObjectOutputStream s)
408			throws java.io.IOException {
409			lock.lock();
410			try {
411			s.defaultWriteObject();
412	tim	1.19	} finally {
413	dl	1.5	lock.unlock();
414			}
415	tim	1.1	}
416
417			}