util/concurrent/PriorityBlockingQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;

import java.util.concurrent.locks.*;
import java.util.*;

/**
 * An unbounded {@linkplain BlockingQueue blocking queue} that uses
 * the same ordering rules as class {@link PriorityQueue} and supplies
 * blocking retrieval operations.  While this queue is logically
 * unbounded, attempted additions may fail due to resource exhaustion
 * (causing <tt>OutOfMemoryError</tt>). This class does not permit
 * <tt>null</tt> elements.  A priority queue relying on natural
 * ordering also does not permit insertion of non-comparable objects
 * (doing so results in <tt>ClassCastException</tt>).
 *
 * <p>This class implements all of the <em>optional</em> methods
 * of the {@link Collection} and {@link Iterator} interfaces.
 * <p>The Iterator provided in method {@link #iterator()} is
 * <em>not</em> guaranteed to traverse the elements of the
 * PriorityBlockingQueue in any particular order. If you need ordered
 * traversal, consider using <tt>Arrays.sort(pq.toArray())</tt>.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public class PriorityBlockingQueue<E> extends AbstractQueue<E>
    implements BlockingQueue<E>, java.io.Serializable {
    private static final long serialVersionUID = 5595510919245408276L;

    private final PriorityQueue<E> q;
    private final ReentrantLock lock = new ReentrantLock(true);
    private final ReentrantLock.ConditionObject notEmpty = lock.newCondition();

    /**
     * Creates a <tt>PriorityBlockingQueue</tt> with the default initial 
     * capacity
     * (11) that orders its elements according to their natural
     * ordering (using <tt>Comparable</tt>).
     */
    public PriorityBlockingQueue() {
        q = new PriorityQueue<E>();
    }

    /**
     * Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
     * capacity
     * that orders its elements according to their natural ordering
     * (using <tt>Comparable</tt>).
     *
     * @param initialCapacity the initial capacity for this priority queue.
     * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
     * than 1
     */
    public PriorityBlockingQueue(int initialCapacity) {
        q = new PriorityQueue<E>(initialCapacity, null);
    }

    /**
     * Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
     * capacity
     * that orders its elements according to the specified comparator.
     *
     * @param initialCapacity the initial capacity for this priority queue.
     * @param comparator the comparator used to order this priority queue.
     * If <tt>null</tt> then the order depends on the elements' natural
     * ordering.
     * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
     * than 1
     */
    public PriorityBlockingQueue(int initialCapacity,
                                 Comparator<? super E> comparator) {
        q = new PriorityQueue<E>(initialCapacity, comparator);
    }

    /**
     * Creates a <tt>PriorityBlockingQueue</tt> containing the elements
     * in the specified collection.  The priority queue has an initial
     * capacity of 110% of the size of the specified collection. If
     * the specified collection is a {@link SortedSet} or a {@link
     * PriorityQueue}, this priority queue will be sorted according to
     * the same comparator, or according to its elements' natural
     * order if the collection is sorted according to its elements'
     * natural order.  Otherwise, this priority queue is ordered
     * according to its elements' natural order.
     *
     * @param c the collection whose elements are to be placed
     *        into this priority queue.
     * @throws ClassCastException if elements of the specified collection
     *         cannot be compared to one another according to the priority
     *         queue's ordering.
     * @throws NullPointerException if <tt>c</tt> or any element within it
     * is <tt>null</tt>
     */
    public PriorityBlockingQueue(Collection<? extends E> c) {
        q = new PriorityQueue<E>(c);
    }


    // these first few override just to update doc comments

    /**
     * Adds the specified element to this queue.
     * @return <tt>true</tt> (as per the general contract of
     * <tt>Collection.add</tt>).
     *
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     * @throws ClassCastException if the specified element cannot be compared
     * with elements currently in the priority queue according
     * to the priority queue's ordering.
     */
    public boolean add(E o) {
        return super.add(o);
    }

    /**
     * Returns the comparator used to order this collection, or <tt>null</tt>
     * if this collection is sorted according to its elements natural ordering
     * (using <tt>Comparable</tt>).
     *
     * @return the comparator used to order this collection, or <tt>null</tt>
     * if this collection is sorted according to its elements natural ordering.
     */
    public Comparator comparator() {
        return q.comparator();
    }

    /**
     * Inserts the specified element into this priority queue.
     *
     * @param o the element to add
     * @return <tt>true</tt>
     * @throws ClassCastException if the specified element cannot be compared
     * with elements currently in the priority queue according
     * to the priority queue's ordering.
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     */
    public boolean offer(E o) {
        if (o == null) throw new NullPointerException();
        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:	1.31
Committed:	Tue Dec 23 19:38:09 2003 UTC (20 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.30:	+17 -0 lines
Log Message:	cache finals across volatiles; avoid readResolve; doc improvments; timed invokeAll interleaves
#	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	dl	1.25	* 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	dl	1.24	* unbounded, attempted additions may fail due to resource exhaustion
17	dl	1.25	* (causing <tt>OutOfMemoryError</tt>). This class does not permit
18			* <tt>null</tt> elements. A priority queue relying on natural
19	dl	1.24	* ordering also does not permit insertion of non-comparable objects
20			* (doing so results in <tt>ClassCastException</tt>).
21	dl	1.20	*
22	dl	1.23	* <p>This class implements all of the <em>optional</em> methods
23			* of the {@link Collection} and {@link Iterator} interfaces.
24	dl	1.20	* <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	dl	1.6	* @since 1.5
30			* @author Doug Lea
31	dl	1.29	* @param <E> the type of elements held in this collection
32	dl	1.28	*/
33	dl	1.5	public class PriorityBlockingQueue<E> extends AbstractQueue<E>
34	dl	1.15	implements BlockingQueue<E>, java.io.Serializable {
35	dl	1.21	private static final long serialVersionUID = 5595510919245408276L;
36	tim	1.1
37	dl	1.5	private final PriorityQueue<E> q;
38	dl	1.9	private final ReentrantLock lock = new ReentrantLock(true);
39	dl	1.27	private final ReentrantLock.ConditionObject notEmpty = lock.newCondition();
40	dl	1.5
41	dl	1.2	/**
42	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> with the default initial
43	dholmes	1.14	* capacity
44	dholmes	1.10	* (11) that orders its elements according to their natural
45	tim	1.18	* ordering (using <tt>Comparable</tt>).
46	dl	1.2	*/
47			public PriorityBlockingQueue() {
48	dl	1.5	q = new PriorityQueue<E>();
49	dl	1.2	}
50
51			/**
52	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
53	dholmes	1.10	* capacity
54			* that orders its elements according to their natural ordering
55	tim	1.18	* (using <tt>Comparable</tt>).
56	dl	1.2	*
57			* @param initialCapacity the initial capacity for this priority queue.
58	dholmes	1.16	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
59			* than 1
60	dl	1.2	*/
61			public PriorityBlockingQueue(int initialCapacity) {
62	dl	1.5	q = new PriorityQueue<E>(initialCapacity, null);
63	dl	1.2	}
64
65			/**
66	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
67	dholmes	1.10	* capacity
68	dl	1.2	* 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	dholmes	1.10	* If <tt>null</tt> then the order depends on the elements' natural
73			* ordering.
74	dholmes	1.16	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
75			* than 1
76	dl	1.2	*/
77	tim	1.13	public PriorityBlockingQueue(int initialCapacity,
78	dholmes	1.14	Comparator<? super E> comparator) {
79	dl	1.5	q = new PriorityQueue<E>(initialCapacity, comparator);
80	dl	1.2	}
81
82			/**
83	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> containing the elements
84	dl	1.15	* 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	dl	1.2	*
93	dholmes	1.14	* @param c the collection whose elements are to be placed
94	dl	1.2	* 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	dholmes	1.14	* @throws NullPointerException if <tt>c</tt> or any element within it
99			* is <tt>null</tt>
100	dl	1.2	*/
101	dholmes	1.14	public PriorityBlockingQueue(Collection<? extends E> c) {
102			q = new PriorityQueue<E>(c);
103	dl	1.7	}
104
105	dholmes	1.10
106	dholmes	1.16	// these first few override just to update doc comments
107	dholmes	1.10
108			/**
109	dholmes	1.16	* 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	dl	1.22	* @throws NullPointerException if the specified element is <tt>null</tt>.
114	dholmes	1.16	* @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	dholmes	1.10	*/
118	dholmes	1.16	public boolean add(E o) {
119			return super.add(o);
120	dholmes	1.10	}
121
122	tim	1.13	/**
123	dholmes	1.16	* 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	tim	1.18	* (using <tt>Comparable</tt>).
126	dholmes	1.16	*
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	dl	1.7	public Comparator comparator() {
131			return q.comparator();
132	dl	1.5	}
133
134	dholmes	1.16	/**
135	dl	1.24	* Inserts the specified element into this priority queue.
136	dholmes	1.16	*
137	dl	1.22	* @param o the element to add
138	dholmes	1.16	* @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	dl	1.22	* @throws NullPointerException if the specified element is <tt>null</tt>.
143	dholmes	1.16	*/
144	dholmes	1.14	public boolean offer(E o) {
145			if (o == null) throw new NullPointerException();
146	dl	1.31	final ReentrantLock lock = this.lock;
147	dl	1.5	lock.lock();
148			try {
149	dholmes	1.14	boolean ok = q.offer(o);
150	dl	1.5	assert ok;
151			notEmpty.signal();
152			return true;
153	tim	1.19	} finally {
154	tim	1.13	lock.unlock();
155	dl	1.5	}
156			}
157
158	dholmes	1.16	/**
159			* Adds the specified element to this priority queue. As the queue is
160			* unbounded this method will never block.
161	dl	1.22	* @param o the element to add
162	dholmes	1.16	* @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	dl	1.22	* @throws NullPointerException if the specified element is <tt>null</tt>.
166	dholmes	1.16	*/
167			public void put(E o) {
168	dholmes	1.14	offer(o); // never need to block
169	dl	1.5	}
170
171	dholmes	1.16	/**
172	dl	1.24	* Inserts the specified element into this priority queue. As the queue is
173	dholmes	1.16	* unbounded this method will never block.
174	dl	1.22	* @param o the element to add
175	dholmes	1.16	* @param timeout This parameter is ignored as the method never blocks
176			* @param unit This parameter is ignored as the method never blocks
177	dl	1.22	* @return <tt>true</tt>
178	dholmes	1.16	* @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	dl	1.22	* @throws NullPointerException if the specified element is <tt>null</tt>.
182	dholmes	1.16	*/
183			public boolean offer(E o, long timeout, TimeUnit unit) {
184	dholmes	1.14	return offer(o); // never need to block
185	dl	1.5	}
186
187			public E take() throws InterruptedException {
188	dl	1.31	final ReentrantLock lock = this.lock;
189	dl	1.5	lock.lockInterruptibly();
190			try {
191			try {
192			while (q.size() == 0)
193			notEmpty.await();
194	tim	1.19	} catch (InterruptedException ie) {
195	dl	1.5	notEmpty.signal(); // propagate to non-interrupted thread
196			throw ie;
197			}
198			E x = q.poll();
199			assert x != null;
200			return x;
201	tim	1.19	} finally {
202	dl	1.5	lock.unlock();
203			}
204			}
205
206
207			public E poll() {
208	dl	1.31	final ReentrantLock lock = this.lock;
209	dl	1.5	lock.lock();
210			try {
211			return q.poll();
212	tim	1.19	} finally {
213	tim	1.13	lock.unlock();
214	dl	1.5	}
215			}
216
217			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
218	dholmes	1.10	long nanos = unit.toNanos(timeout);
219	dl	1.31	final ReentrantLock lock = this.lock;
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	dl	1.31	final ReentrantLock lock = this.lock;
242	dl	1.5	lock.lock();
243			try {
244			return q.peek();
245	tim	1.19	} finally {
246	tim	1.13	lock.unlock();
247	dl	1.5	}
248			}
249
250			public int size() {
251	dl	1.31	final ReentrantLock lock = this.lock;
252	dl	1.5	lock.lock();
253			try {
254			return q.size();
255	tim	1.19	} finally {
256	dl	1.5	lock.unlock();
257			}
258			}
259
260			/**
261			* Always returns <tt>Integer.MAX_VALUE</tt> because
262	dholmes	1.16	* a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
263	dl	1.5	* @return <tt>Integer.MAX_VALUE</tt>
264			*/
265			public int remainingCapacity() {
266			return Integer.MAX_VALUE;
267			}
268
269	dholmes	1.14	public boolean remove(Object o) {
270	dl	1.31	final ReentrantLock lock = this.lock;
271	dl	1.5	lock.lock();
272			try {
273	dholmes	1.14	return q.remove(o);
274	tim	1.19	} finally {
275	dl	1.5	lock.unlock();
276			}
277			}
278
279	dholmes	1.14	public boolean contains(Object o) {
280	dl	1.31	final ReentrantLock lock = this.lock;
281	dl	1.5	lock.lock();
282			try {
283	dholmes	1.14	return q.contains(o);
284	tim	1.19	} finally {
285	dl	1.5	lock.unlock();
286			}
287			}
288
289			public Object[] toArray() {
290	dl	1.31	final ReentrantLock lock = this.lock;
291	dl	1.5	lock.lock();
292			try {
293			return q.toArray();
294	tim	1.19	} finally {
295	dl	1.5	lock.unlock();
296			}
297			}
298
299
300			public String toString() {
301	dl	1.31	final ReentrantLock lock = this.lock;
302	dl	1.5	lock.lock();
303			try {
304			return q.toString();
305	tim	1.19	} finally {
306	dl	1.5	lock.unlock();
307			}
308			}
309
310	dl	1.26	public int drainTo(Collection<? super E> c) {
311			if (c == null)
312			throw new NullPointerException();
313			if (c == this)
314			throw new IllegalArgumentException();
315	dl	1.31	final ReentrantLock lock = this.lock;
316	dl	1.26	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	dl	1.31	final ReentrantLock lock = this.lock;
338	dl	1.26	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	dl	1.17	/**
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	dl	1.31	final ReentrantLock lock = this.lock;
358	dl	1.17	lock.lock();
359			try {
360			q.clear();
361	tim	1.19	} finally {
362	dl	1.17	lock.unlock();
363			}
364			}
365
366	dl	1.5	public <T> T[] toArray(T[] a) {
367	dl	1.31	final ReentrantLock lock = this.lock;
368	dl	1.5	lock.lock();
369			try {
370			return q.toArray(a);
371	tim	1.19	} finally {
372	dl	1.5	lock.unlock();
373			}
374			}
375
376	dholmes	1.16	/**
377	dl	1.23	* 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	dholmes	1.16	*
384			* @return an iterator over the elements in this queue.
385			*/
386	dl	1.5	public Iterator<E> iterator() {
387	dl	1.31	final ReentrantLock lock = this.lock;
388	dl	1.5	lock.lock();
389			try {
390			return new Itr(q.iterator());
391	tim	1.19	} finally {
392	dl	1.5	lock.unlock();
393			}
394			}
395
396			private class Itr<E> implements Iterator<E> {
397			private final Iterator<E> iter;
398	tim	1.13	Itr(Iterator<E> i) {
399			iter = i;
400	dl	1.5	}
401
402	tim	1.13	public boolean hasNext() {
403	dl	1.5	/*
404			* No sync -- we rely on underlying hasNext to be
405			* stateless, in which case we can return true by mistake
406	dl	1.30	* only when next() will subsequently throw
407	dl	1.5	* ConcurrentModificationException.
408			*/
409			return iter.hasNext();
410	tim	1.13	}
411
412			public E next() {
413	dl	1.31	ReentrantLock lock = PriorityBlockingQueue.this.lock;
414	dl	1.5	lock.lock();
415			try {
416			return iter.next();
417	tim	1.19	} finally {
418	dl	1.5	lock.unlock();
419			}
420	tim	1.13	}
421
422			public void remove() {
423	dl	1.31	ReentrantLock lock = PriorityBlockingQueue.this.lock;
424	dl	1.5	lock.lock();
425			try {
426			iter.remove();
427	tim	1.19	} finally {
428	dl	1.5	lock.unlock();
429			}
430	tim	1.13	}
431	dl	1.5	}
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	tim	1.19	} finally {
446	dl	1.5	lock.unlock();
447			}
448	tim	1.1	}
449
450			}