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 {@linkplain
 * Comparable natural ordering} also does not permit insertion of
 * non-comparable objects (doing so results in
 * <tt>ClassCastException</tt>).
 *
 * <p>This class and its iterator implement all of the
 * <em>optional</em> methods of the {@link Collection} and {@link
 * Iterator} interfaces.  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>.  Also, method <tt>drainTo</tt>
 * can be used to <em>remove</em> some or all elements in priority
 * order and place them in another collection.
 *
 * <p>Operations on this class make no guarantees about the ordering
 * of elements with equal priority. If you need to enforce an
 * ordering, you can define custom classes or comparators that use a
 * secondary key to break ties in primary priority values.  For
 * example, here is a class that applies first-in-first-out
 * tie-breaking to comparable elements. To use it, you would insert a
 * <tt>new FIFOEntry(anEntry)</tt> instead of a plain entry object.
 *
 *  <pre> {@code
 * class FIFOEntry<E extends Comparable<? super E>>
 *     implements Comparable<FIFOEntry<E>> {
 *   final static AtomicLong seq = new AtomicLong();
 *   final long seqNum;
 *   final E entry;
 *   public FIFOEntry(E entry) {
 *     seqNum = seq.getAndIncrement();
 *     this.entry = entry;
 *   }
 *   public E getEntry() { return entry; }
 *   public int compareTo(FIFOEntry<E> other) {
 *     int res = entry.compareTo(other.entry);
 *     if (res == 0 && other.entry != this.entry)
 *       res = (seqNum < other.seqNum ? -1 : 1);
 *     return res;
 *   }
 * }}</pre>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @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;

    final PriorityQueue<E> q;
    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 {@linkplain Comparable natural ordering}.
     */
    public PriorityBlockingQueue() {
        q = new PriorityQueue<E>();
    }

    /**
     * Creates a <tt>PriorityBlockingQueue</tt> with the specified
     * initial capacity that orders its elements according to their
     * {@linkplain Comparable natural ordering}.
     *
     * @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 that will be used to order this
     *         priority queue.  If {@code null}, the {@linkplain Comparable
     *         natural ordering} of the elements will be used.
     * @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.  If the specified collection is a
     * {@link SortedSet} or a {@link PriorityQueue},  this
     * priority queue will be ordered according to the same ordering.
     * Otherwise, this priority queue will be ordered according to the
     * {@linkplain Comparable natural ordering} of its elements.
     *
     * @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 the specified collection or any
     *         of its elements are null
     */
    public PriorityBlockingQueue(Collection<? extends E> c) {
        q = new PriorityQueue<E>(c);
    }

    /**
     * Inserts the specified element into this priority queue.
     *
     * @param e the element to add
     * @return <tt>true</tt> (as specified by {@link Collection#add})
     * @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 null
     */
    public boolean add(E e) {
        return offer(e);
    }

    /**
     * Inserts the specified element into this priority queue.
     *
     * @param e the element to add
     * @return <tt>true</tt> (as specified by {@link Queue#offer})
     * @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 null
     */
    public boolean offer(E e) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            boolean ok = q.offer(e);
            assert ok;
            notEmpty.signal();
            return true;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Inserts the specified element into this priority queue. As the queue is
     * unbounded this method will never block.
     *
     * @param e the element to add
     * @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 null
     */
    public void put(E e) {
        offer(e); // never need to block
    }

    /**
     * Inserts the specified element into this priority queue. As the queue is
     * unbounded this method will never block.
     *
     * @param e 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 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 null
     */
    public boolean offer(E e, long timeout, TimeUnit unit) {
        return offer(e); // never need to block
    }

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

    public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            E x;
            while ( (x = q.poll()) == null)
                notEmpty.await();
            return x;
        } 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 {
            E x;
            while ( (x = q.poll()) == null) {
                if (nanos <= 0)
                    return null;
                nanos = notEmpty.awaitNanos(nanos);
            }
            return x;
        } finally {
            lock.unlock();
        }
    }

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

    /**
     * Returns the comparator used to order the elements in this queue,
     * or <tt>null</tt> if this queue uses the {@linkplain Comparable
     * natural ordering} of its elements.
     *
     * @return the comparator used to order the elements in this queue,
     *         or <tt>null</tt> if this queue uses the natural
     *         ordering of its elements
     */
    public Comparator<? super E> comparator() {
        return q.comparator();
    }

    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;
    }

    /**
     * Removes a single instance of the specified element from this queue,
     * if it is present.  More formally, removes an element {@code e} such
     * that {@code o.equals(e)}, if this queue contains one or more such
     * elements.  Returns {@code true} if and only if this queue contained
     * the specified element (or equivalently, if this queue changed as a
     * result of the call).
     *
     * @param o element to be removed from this queue, if present
     * @return <tt>true</tt> if this queue changed as a result of the call
     */
    public boolean remove(Object o) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.remove(o);
        } finally {
            lock.unlock();
        }
    }

    /**
     * Returns {@code true} if this queue contains the specified element.
     * More formally, returns {@code true} if and only if this queue contains
     * at least one element {@code e} such that {@code o.equals(e)}.
     *
     * @param o object to be checked for containment in this queue
     * @return <tt>true</tt> if this queue contains the specified element
     */
    public boolean contains(Object o) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return q.contains(o);
        } finally {
            lock.unlock();
        }
    }

    /**
     * Returns an array containing all of the elements in this queue.
     * The returned array elements are in no particular order.
     *
     * <p>The returned array will be "safe" in that no references to it are
     * maintained by this queue.  (In other words, this method must allocate
     * a new array).  The caller is thus free to modify the returned array.
     *
     * <p>This method acts as bridge between array-based and collection-based
     * APIs.
     *
     * @return an array containing all of the elements in this queue
     */
    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();
        }
    }

    /**
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    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();
        }
    }

    /**
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    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 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();
        }
    }

    /**
     * Returns an array containing all of the elements in this queue; the
     * runtime type of the returned array is that of the specified array.
     * The returned array elements are in no particular order.
     * If the queue fits in the specified array, it is returned therein.
     * Otherwise, a new array is allocated with the runtime type of the
     * specified array and the size of this queue.
     *
     * <p>If this queue fits in the specified array with room to spare
     * (i.e., the array has more elements than this queue), the element in
     * the array immediately following the end of the queue is set to
     * <tt>null</tt>.
     *
     * <p>Like the {@link #toArray()} method, this method acts as bridge between
     * array-based and collection-based APIs.  Further, this method allows
     * precise control over the runtime type of the output array, and may,
     * under certain circumstances, be used to save allocation costs.
     *
     * <p>Suppose <tt>x</tt> is a queue known to contain only strings.
     * The following code can be used to dump the queue into a newly
     * allocated array of <tt>String</tt>:
     *
     * <pre>
     *     String[] y = x.toArray(new String[0]);</pre>
     *
     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
     * <tt>toArray()</tt>.
     *
     * @param a the array into which the elements of the queue are to
     *          be stored, if it is big enough; otherwise, a new array of the
     *          same runtime type is allocated for this purpose
     * @return an array containing all of the elements in this queue
     * @throws ArrayStoreException if the runtime type of the specified array
     *         is not a supertype of the runtime type of every element in
     *         this queue
     * @throws NullPointerException if the specified array is null
     */
    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 <tt>Iterator</tt> is a "weakly consistent"
     * iterator that will never throw {@link
     * ConcurrentModificationException}, and guarantees to traverse
     * elements as they existed upon construction of the iterator, and
     * may (but is not guaranteed to) reflect any modifications
     * subsequent to construction.
     *
     * @return an iterator over the elements in this queue
     */
    public Iterator<E> iterator() {
        return new Itr(toArray());
    }

    /**
     * Snapshot iterator that works off copy of underlying q array.
     */
    private class Itr implements Iterator<E> {
        final Object[] array; // Array of all elements
        int cursor;           // index of next element to return;
        int lastRet;          // index of last element, or -1 if no such

        Itr(Object[] array) {
            lastRet = -1;
            this.array = array;
        }

        public boolean hasNext() {
            return cursor < array.length;
        }

        public E next() {
            if (cursor >= array.length)
                throw new NoSuchElementException();
            lastRet = cursor;
            return (E)array[cursor++];
        }

        public void remove() {
            if (lastRet < 0)
                throw new IllegalStateException();
            Object x = array[lastRet];
            lastRet = -1;
            // Traverse underlying queue to find == element,
            // not just a .equals element.
            lock.lock();
            try {
                for (Iterator it = q.iterator(); it.hasNext(); ) {
                    if (it.next() == x) {
                        it.remove();
                        return;
                    }
                }
            } finally {
                lock.unlock();
            }
        }
    }

    /**
     * Saves the state to a stream (that is, serializes 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:	1.56
Committed:	Mon Sep 20 20:23:52 2010 UTC (13 years, 8 months ago) by jsr166
Branch:	MAIN
Changes since 1.55:	+7 -7 lines
Log Message:	Fix javadoc code samples to use <pre> {@code so that we can replace < with <, etc.
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.33	* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/licenses/publicdomain
5	dl	1.2	*/
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	jsr166	1.42	* <tt>null</tt> elements. A priority queue relying on {@linkplain
19			* Comparable natural ordering} also does not permit insertion of
20			* non-comparable objects (doing so results in
21			* <tt>ClassCastException</tt>).
22	dl	1.20	*
23	dl	1.38	* <p>This class and its iterator implement all of the
24			* <em>optional</em> methods of the {@link Collection} and {@link
25	dl	1.41	* Iterator} interfaces. The Iterator provided in method {@link
26			* #iterator()} is <em>not</em> guaranteed to traverse the elements of
27			* the PriorityBlockingQueue in any particular order. If you need
28			* ordered traversal, consider using
29			* <tt>Arrays.sort(pq.toArray())</tt>. Also, method <tt>drainTo</tt>
30			* can be used to <em>remove</em> some or all elements in priority
31			* order and place them in another collection.
32			*
33			* <p>Operations on this class make no guarantees about the ordering
34			* of elements with equal priority. If you need to enforce an
35			* ordering, you can define custom classes or comparators that use a
36			* secondary key to break ties in primary priority values. For
37			* example, here is a class that applies first-in-first-out
38			* tie-breaking to comparable elements. To use it, you would insert a
39			* <tt>new FIFOEntry(anEntry)</tt> instead of a plain entry object.
40			*
41	jsr166	1.56	* <pre> {@code
42			* class FIFOEntry<E extends Comparable<? super E>>
43			* implements Comparable<FIFOEntry<E>> {
44	jsr166	1.47	* final static AtomicLong seq = new AtomicLong();
45	dl	1.41	* final long seqNum;
46			* final E entry;
47			* public FIFOEntry(E entry) {
48			* seqNum = seq.getAndIncrement();
49			* this.entry = entry;
50			* }
51			* public E getEntry() { return entry; }
52	jsr166	1.56	* public int compareTo(FIFOEntry<E> other) {
53	dl	1.41	* int res = entry.compareTo(other.entry);
54	jsr166	1.56	* if (res == 0 && other.entry != this.entry)
55			* res = (seqNum < other.seqNum ? -1 : 1);
56	dl	1.41	* return res;
57			* }
58	jsr166	1.56	* }}</pre>
59	dl	1.20	*
60	dl	1.35	* <p>This class is a member of the
61	jsr166	1.53	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
62	dl	1.35	* Java Collections Framework</a>.
63			*
64	dl	1.6	* @since 1.5
65			* @author Doug Lea
66	dl	1.29	* @param <E> the type of elements held in this collection
67	dl	1.28	*/
68	dl	1.5	public class PriorityBlockingQueue<E> extends AbstractQueue<E>
69	dl	1.15	implements BlockingQueue<E>, java.io.Serializable {
70	dl	1.21	private static final long serialVersionUID = 5595510919245408276L;
71	tim	1.1
72	jsr166	1.55	final PriorityQueue<E> q;
73			final ReentrantLock lock = new ReentrantLock(true);
74	dl	1.32	private final Condition notEmpty = lock.newCondition();
75	dl	1.5
76	dl	1.2	/**
77	jsr166	1.42	* Creates a <tt>PriorityBlockingQueue</tt> with the default
78			* initial capacity (11) that orders its elements according to
79			* their {@linkplain Comparable natural ordering}.
80	dl	1.2	*/
81			public PriorityBlockingQueue() {
82	dl	1.5	q = new PriorityQueue<E>();
83	dl	1.2	}
84
85			/**
86	jsr166	1.42	* Creates a <tt>PriorityBlockingQueue</tt> with the specified
87			* initial capacity that orders its elements according to their
88			* {@linkplain Comparable natural ordering}.
89	dl	1.2	*
90	jsr166	1.42	* @param initialCapacity the initial capacity for this priority queue
91	dholmes	1.16	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
92	jsr166	1.52	* than 1
93	dl	1.2	*/
94			public PriorityBlockingQueue(int initialCapacity) {
95	dl	1.5	q = new PriorityQueue<E>(initialCapacity, null);
96	dl	1.2	}
97
98			/**
99	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
100	jsr166	1.39	* capacity that orders its elements according to the specified
101			* comparator.
102	dl	1.2	*
103	jsr166	1.42	* @param initialCapacity the initial capacity for this priority queue
104	jsr166	1.52	* @param comparator the comparator that will be used to order this
105			* priority queue. If {@code null}, the {@linkplain Comparable
106			* natural ordering} of the elements will be used.
107	dholmes	1.16	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
108	jsr166	1.52	* than 1
109	dl	1.2	*/
110	tim	1.13	public PriorityBlockingQueue(int initialCapacity,
111	dholmes	1.14	Comparator<? super E> comparator) {
112	dl	1.5	q = new PriorityQueue<E>(initialCapacity, comparator);
113	dl	1.2	}
114
115			/**
116	dholmes	1.16	* Creates a <tt>PriorityBlockingQueue</tt> containing the elements
117	jsr166	1.52	* in the specified collection. If the specified collection is a
118			* {@link SortedSet} or a {@link PriorityQueue}, this
119			* priority queue will be ordered according to the same ordering.
120			* Otherwise, this priority queue will be ordered according to the
121			* {@linkplain Comparable natural ordering} of its elements.
122	dl	1.2	*
123	jsr166	1.52	* @param c the collection whose elements are to be placed
124			* into this priority queue
125	dl	1.2	* @throws ClassCastException if elements of the specified collection
126			* cannot be compared to one another according to the priority
127	jsr166	1.52	* queue's ordering
128	jsr166	1.42	* @throws NullPointerException if the specified collection or any
129			* of its elements are null
130	dl	1.2	*/
131	dholmes	1.14	public PriorityBlockingQueue(Collection<? extends E> c) {
132			q = new PriorityQueue<E>(c);
133	dl	1.7	}
134
135	dholmes	1.10	/**
136	jsr166	1.42	* Inserts the specified element into this priority queue.
137			*
138	jsr166	1.40	* @param e the element to add
139	jsr166	1.48	* @return <tt>true</tt> (as specified by {@link Collection#add})
140	dholmes	1.16	* @throws ClassCastException if the specified element cannot be compared
141	jsr166	1.42	* with elements currently in the priority queue according to the
142			* priority queue's ordering
143			* @throws NullPointerException if the specified element is null
144	dholmes	1.10	*/
145	jsr166	1.40	public boolean add(E e) {
146	jsr166	1.42	return offer(e);
147	dl	1.5	}
148
149	dholmes	1.16	/**
150	dl	1.24	* Inserts the specified element into this priority queue.
151	dholmes	1.16	*
152	jsr166	1.40	* @param e the element to add
153	jsr166	1.48	* @return <tt>true</tt> (as specified by {@link Queue#offer})
154	dholmes	1.16	* @throws ClassCastException if the specified element cannot be compared
155	jsr166	1.42	* with elements currently in the priority queue according to the
156			* priority queue's ordering
157			* @throws NullPointerException if the specified element is null
158	dholmes	1.16	*/
159	jsr166	1.40	public boolean offer(E e) {
160	dl	1.31	final ReentrantLock lock = this.lock;
161	dl	1.5	lock.lock();
162			try {
163	jsr166	1.40	boolean ok = q.offer(e);
164	dl	1.5	assert ok;
165			notEmpty.signal();
166			return true;
167	tim	1.19	} finally {
168	tim	1.13	lock.unlock();
169	dl	1.5	}
170			}
171
172	dholmes	1.16	/**
173	jsr166	1.42	* Inserts the specified element into this priority queue. As the queue is
174	dholmes	1.16	* unbounded this method will never block.
175	jsr166	1.42	*
176	jsr166	1.40	* @param e the element to add
177	jsr166	1.42	* @throws ClassCastException if the specified element cannot be compared
178			* with elements currently in the priority queue according to the
179			* priority queue's ordering
180			* @throws NullPointerException if the specified element is null
181	dholmes	1.16	*/
182	jsr166	1.40	public void put(E e) {
183			offer(e); // never need to block
184	dl	1.5	}
185
186	dholmes	1.16	/**
187	dl	1.24	* Inserts the specified element into this priority queue. As the queue is
188	dholmes	1.16	* unbounded this method will never block.
189	jsr166	1.42	*
190	jsr166	1.40	* @param e the element to add
191	dholmes	1.16	* @param timeout This parameter is ignored as the method never blocks
192			* @param unit This parameter is ignored as the method never blocks
193	dl	1.22	* @return <tt>true</tt>
194	jsr166	1.42	* @throws ClassCastException if the specified element cannot be compared
195			* with elements currently in the priority queue according to the
196			* priority queue's ordering
197			* @throws NullPointerException if the specified element is null
198	dholmes	1.16	*/
199	jsr166	1.40	public boolean offer(E e, long timeout, TimeUnit unit) {
200			return offer(e); // never need to block
201	dl	1.5	}
202
203	jsr166	1.42	public E poll() {
204			final ReentrantLock lock = this.lock;
205			lock.lock();
206			try {
207			return q.poll();
208			} finally {
209			lock.unlock();
210			}
211			}
212
213	dl	1.5	public E take() throws InterruptedException {
214	dl	1.31	final ReentrantLock lock = this.lock;
215	dl	1.5	lock.lockInterruptibly();
216			try {
217	jsr166	1.55	E x;
218			while ( (x = q.poll()) == null)
219			notEmpty.await();
220	dl	1.5	return x;
221	tim	1.19	} finally {
222	dl	1.5	lock.unlock();
223			}
224			}
225
226			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
227	dholmes	1.10	long nanos = unit.toNanos(timeout);
228	dl	1.31	final ReentrantLock lock = this.lock;
229	dl	1.5	lock.lockInterruptibly();
230			try {
231	jsr166	1.55	E x;
232			while ( (x = q.poll()) == null) {
233	dl	1.5	if (nanos <= 0)
234			return null;
235	jsr166	1.55	nanos = notEmpty.awaitNanos(nanos);
236	dl	1.5	}
237	jsr166	1.55	return x;
238	tim	1.19	} finally {
239	dl	1.5	lock.unlock();
240			}
241			}
242
243			public E peek() {
244	dl	1.31	final ReentrantLock lock = this.lock;
245	dl	1.5	lock.lock();
246			try {
247			return q.peek();
248	tim	1.19	} finally {
249	tim	1.13	lock.unlock();
250	dl	1.5	}
251			}
252
253	jsr166	1.42	/**
254			* Returns the comparator used to order the elements in this queue,
255			* or <tt>null</tt> if this queue uses the {@linkplain Comparable
256			* natural ordering} of its elements.
257			*
258			* @return the comparator used to order the elements in this queue,
259			* or <tt>null</tt> if this queue uses the natural
260	jsr166	1.52	* ordering of its elements
261	jsr166	1.42	*/
262			public Comparator<? super E> comparator() {
263			return q.comparator();
264			}
265
266	dl	1.5	public int size() {
267	dl	1.31	final ReentrantLock lock = this.lock;
268	dl	1.5	lock.lock();
269			try {
270			return q.size();
271	tim	1.19	} finally {
272	dl	1.5	lock.unlock();
273			}
274			}
275
276			/**
277			* Always returns <tt>Integer.MAX_VALUE</tt> because
278	dholmes	1.16	* a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
279	dl	1.5	* @return <tt>Integer.MAX_VALUE</tt>
280			*/
281			public int remainingCapacity() {
282			return Integer.MAX_VALUE;
283			}
284
285	dl	1.37	/**
286	jsr166	1.42	* Removes a single instance of the specified element from this queue,
287	jsr166	1.52	* if it is present. More formally, removes an element {@code e} such
288			* that {@code o.equals(e)}, if this queue contains one or more such
289			* elements. Returns {@code true} if and only if this queue contained
290			* the specified element (or equivalently, if this queue changed as a
291			* result of the call).
292	jsr166	1.42	*
293			* @param o element to be removed from this queue, if present
294			* @return <tt>true</tt> if this queue changed as a result of the call
295	dl	1.37	*/
296	dholmes	1.14	public boolean remove(Object o) {
297	dl	1.31	final ReentrantLock lock = this.lock;
298	dl	1.5	lock.lock();
299			try {
300	dholmes	1.14	return q.remove(o);
301	tim	1.19	} finally {
302	dl	1.5	lock.unlock();
303			}
304			}
305
306	jsr166	1.42	/**
307	jsr166	1.52	* Returns {@code true} if this queue contains the specified element.
308			* More formally, returns {@code true} if and only if this queue contains
309			* at least one element {@code e} such that {@code o.equals(e)}.
310	jsr166	1.42	*
311			* @param o object to be checked for containment in this queue
312			* @return <tt>true</tt> if this queue contains the specified element
313			*/
314	dholmes	1.14	public boolean contains(Object o) {
315	dl	1.31	final ReentrantLock lock = this.lock;
316	dl	1.5	lock.lock();
317			try {
318	dholmes	1.14	return q.contains(o);
319	tim	1.19	} finally {
320	dl	1.5	lock.unlock();
321			}
322			}
323
324	jsr166	1.42	/**
325			* Returns an array containing all of the elements in this queue.
326			* The returned array elements are in no particular order.
327			*
328			* <p>The returned array will be "safe" in that no references to it are
329			* maintained by this queue. (In other words, this method must allocate
330			* a new array). The caller is thus free to modify the returned array.
331	jsr166	1.43	*
332	jsr166	1.42	* <p>This method acts as bridge between array-based and collection-based
333			* APIs.
334			*
335			* @return an array containing all of the elements in this queue
336			*/
337	dl	1.5	public Object[] toArray() {
338	dl	1.31	final ReentrantLock lock = this.lock;
339	dl	1.5	lock.lock();
340			try {
341			return q.toArray();
342	tim	1.19	} finally {
343	dl	1.5	lock.unlock();
344			}
345			}
346
347	jsr166	1.52
348	dl	1.5	public String toString() {
349	dl	1.31	final ReentrantLock lock = this.lock;
350	dl	1.5	lock.lock();
351			try {
352			return q.toString();
353	tim	1.19	} finally {
354	dl	1.5	lock.unlock();
355			}
356			}
357
358	jsr166	1.42	/**
359			* @throws UnsupportedOperationException {@inheritDoc}
360			* @throws ClassCastException {@inheritDoc}
361			* @throws NullPointerException {@inheritDoc}
362			* @throws IllegalArgumentException {@inheritDoc}
363			*/
364	dl	1.26	public int drainTo(Collection<? super E> c) {
365			if (c == null)
366			throw new NullPointerException();
367			if (c == this)
368			throw new IllegalArgumentException();
369	dl	1.31	final ReentrantLock lock = this.lock;
370	dl	1.26	lock.lock();
371			try {
372			int n = 0;
373			E e;
374			while ( (e = q.poll()) != null) {
375			c.add(e);
376			++n;
377			}
378			return n;
379			} finally {
380			lock.unlock();
381			}
382			}
383
384	jsr166	1.42	/**
385			* @throws UnsupportedOperationException {@inheritDoc}
386			* @throws ClassCastException {@inheritDoc}
387			* @throws NullPointerException {@inheritDoc}
388			* @throws IllegalArgumentException {@inheritDoc}
389			*/
390	dl	1.26	public int drainTo(Collection<? super E> c, int maxElements) {
391			if (c == null)
392			throw new NullPointerException();
393			if (c == this)
394			throw new IllegalArgumentException();
395			if (maxElements <= 0)
396			return 0;
397	dl	1.31	final ReentrantLock lock = this.lock;
398	dl	1.26	lock.lock();
399			try {
400			int n = 0;
401			E e;
402			while (n < maxElements && (e = q.poll()) != null) {
403			c.add(e);
404			++n;
405			}
406			return n;
407			} finally {
408			lock.unlock();
409			}
410			}
411
412	dl	1.17	/**
413	dl	1.37	* Atomically removes all of the elements from this queue.
414	dl	1.17	* The queue will be empty after this call returns.
415			*/
416			public void clear() {
417	dl	1.31	final ReentrantLock lock = this.lock;
418	dl	1.17	lock.lock();
419			try {
420			q.clear();
421	tim	1.19	} finally {
422	dl	1.17	lock.unlock();
423			}
424			}
425
426	jsr166	1.42	/**
427			* Returns an array containing all of the elements in this queue; the
428			* runtime type of the returned array is that of the specified array.
429			* The returned array elements are in no particular order.
430			* If the queue fits in the specified array, it is returned therein.
431			* Otherwise, a new array is allocated with the runtime type of the
432			* specified array and the size of this queue.
433			*
434			* <p>If this queue fits in the specified array with room to spare
435			* (i.e., the array has more elements than this queue), the element in
436			* the array immediately following the end of the queue is set to
437			* <tt>null</tt>.
438			*
439			* <p>Like the {@link #toArray()} method, this method acts as bridge between
440			* array-based and collection-based APIs. Further, this method allows
441			* precise control over the runtime type of the output array, and may,
442			* under certain circumstances, be used to save allocation costs.
443			*
444			* <p>Suppose <tt>x</tt> is a queue known to contain only strings.
445			* The following code can be used to dump the queue into a newly
446			* allocated array of <tt>String</tt>:
447			*
448			* <pre>
449			* String[] y = x.toArray(new String[0]);</pre>
450			*
451			* Note that <tt>toArray(new Object[0])</tt> is identical in function to
452			* <tt>toArray()</tt>.
453			*
454			* @param a the array into which the elements of the queue are to
455			* be stored, if it is big enough; otherwise, a new array of the
456			* same runtime type is allocated for this purpose
457			* @return an array containing all of the elements in this queue
458			* @throws ArrayStoreException if the runtime type of the specified array
459			* is not a supertype of the runtime type of every element in
460			* this queue
461			* @throws NullPointerException if the specified array is null
462			*/
463	dl	1.5	public <T> T[] toArray(T[] a) {
464	dl	1.31	final ReentrantLock lock = this.lock;
465	dl	1.5	lock.lock();
466			try {
467			return q.toArray(a);
468	tim	1.19	} finally {
469	dl	1.5	lock.unlock();
470			}
471			}
472
473	dholmes	1.16	/**
474	dl	1.23	* Returns an iterator over the elements in this queue. The
475			* iterator does not return the elements in any particular order.
476	dl	1.51	* The returned <tt>Iterator</tt> is a "weakly consistent"
477			* iterator that will never throw {@link
478			* ConcurrentModificationException}, and guarantees to traverse
479			* elements as they existed upon construction of the iterator, and
480			* may (but is not guaranteed to) reflect any modifications
481			* subsequent to construction.
482	dholmes	1.16	*
483	jsr166	1.42	* @return an iterator over the elements in this queue
484	dholmes	1.16	*/
485	dl	1.5	public Iterator<E> iterator() {
486	dl	1.51	return new Itr(toArray());
487	dl	1.5	}
488
489	dl	1.49	/**
490			* Snapshot iterator that works off copy of underlying q array.
491			*/
492	dl	1.51	private class Itr implements Iterator<E> {
493	dl	1.49	final Object[] array; // Array of all elements
494	jsr166	1.54	int cursor; // index of next element to return;
495			int lastRet; // index of last element, or -1 if no such
496	jsr166	1.50
497	dl	1.49	Itr(Object[] array) {
498			lastRet = -1;
499			this.array = array;
500	dl	1.5	}
501
502	tim	1.13	public boolean hasNext() {
503	dl	1.49	return cursor < array.length;
504	tim	1.13	}
505
506			public E next() {
507	dl	1.49	if (cursor >= array.length)
508			throw new NoSuchElementException();
509			lastRet = cursor;
510			return (E)array[cursor++];
511	tim	1.13	}
512
513			public void remove() {
514	jsr166	1.50	if (lastRet < 0)
515	jsr166	1.54	throw new IllegalStateException();
516	dl	1.49	Object x = array[lastRet];
517			lastRet = -1;
518			// Traverse underlying queue to find == element,
519			// not just a .equals element.
520	dl	1.5	lock.lock();
521			try {
522	dl	1.49	for (Iterator it = q.iterator(); it.hasNext(); ) {
523			if (it.next() == x) {
524			it.remove();
525			return;
526			}
527			}
528	tim	1.19	} finally {
529	dl	1.5	lock.unlock();
530			}
531	tim	1.13	}
532	dl	1.5	}
533
534			/**
535	jsr166	1.52	* Saves the state to a stream (that is, serializes it). This
536	dl	1.5	* merely wraps default serialization within lock. The
537			* serialization strategy for items is left to underlying
538			* Queue. Note that locking is not needed on deserialization, so
539			* readObject is not defined, just relying on default.
540			*/
541			private void writeObject(java.io.ObjectOutputStream s)
542			throws java.io.IOException {
543			lock.lock();
544			try {
545			s.defaultWriteObject();
546	tim	1.19	} finally {
547	dl	1.5	lock.unlock();
548			}
549	tim	1.1	}
550
551			}