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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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*/ |
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|
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package java.util.concurrent; |
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|
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import java.util.concurrent.locks.*; |
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import java.util.*; |
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|
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/** |
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* An unbounded {@linkplain BlockingQueue blocking queue} that uses |
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* the same ordering rules as class {@link PriorityQueue} and supplies |
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* blocking retrieval operations. While this queue is logically |
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* unbounded, attempted additions may fail due to resource exhaustion |
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* (causing <tt>OutOfMemoryError</tt>). This class does not permit |
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* <tt>null</tt> elements. A priority queue relying on {@linkplain |
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* Comparable natural ordering} also does not permit insertion of |
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* non-comparable objects (doing so results in |
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* <tt>ClassCastException</tt>). |
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* |
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* <p>This class and its iterator implement all of the |
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* <em>optional</em> methods of the {@link Collection} and {@link |
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* Iterator} interfaces. The Iterator provided in method {@link |
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* #iterator()} is <em>not</em> guaranteed to traverse the elements of |
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* the PriorityBlockingQueue in any particular order. If you need |
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* ordered traversal, consider using |
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* <tt>Arrays.sort(pq.toArray())</tt>. Also, method <tt>drainTo</tt> |
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* can be used to <em>remove</em> some or all elements in priority |
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* order and place them in another collection. |
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* |
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* <p>Operations on this class make no guarantees about the ordering |
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* of elements with equal priority. If you need to enforce an |
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* ordering, you can define custom classes or comparators that use a |
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* secondary key to break ties in primary priority values. For |
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* example, here is a class that applies first-in-first-out |
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* tie-breaking to comparable elements. To use it, you would insert a |
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* <tt>new FIFOEntry(anEntry)</tt> instead of a plain entry object. |
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* |
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* <pre> |
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* class FIFOEntry<E extends Comparable<? super E>> |
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* implements Comparable<FIFOEntry<E>> { |
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* static AtomicLong seq = new AtomicLong(); |
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* final long seqNum; |
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* final E entry; |
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* public FIFOEntry(E entry) { |
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* seqNum = seq.getAndIncrement(); |
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* this.entry = entry; |
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* } |
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* public E getEntry() { return entry; } |
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* public int compareTo(FIFOEntry<E> other) { |
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* int res = entry.compareTo(other.entry); |
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* if (res == 0 && other.entry != this.entry) |
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* res = (seqNum < other.seqNum ? -1 : 1); |
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* return res; |
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* } |
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* }</pre> |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../guide/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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* @param <E> the type of elements held in this collection |
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*/ |
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public class PriorityBlockingQueue<E> extends AbstractQueue<E> |
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implements BlockingQueue<E>, java.io.Serializable { |
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private static final long serialVersionUID = 5595510919245408276L; |
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|
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private final PriorityQueue<E> q; |
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private final ReentrantLock lock = new ReentrantLock(true); |
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private final Condition notEmpty = lock.newCondition(); |
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|
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/** |
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* Creates a <tt>PriorityBlockingQueue</tt> with the default |
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* initial capacity (11) that orders its elements according to |
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* their {@linkplain Comparable natural ordering}. |
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*/ |
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public PriorityBlockingQueue() { |
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q = new PriorityQueue<E>(); |
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} |
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|
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/** |
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* Creates a <tt>PriorityBlockingQueue</tt> with the specified |
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* initial capacity that orders its elements according to their |
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* {@linkplain Comparable natural ordering}. |
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* |
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* @param initialCapacity the initial capacity for this priority queue |
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* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less |
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* than 1 |
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*/ |
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public PriorityBlockingQueue(int initialCapacity) { |
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q = new PriorityQueue<E>(initialCapacity, null); |
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} |
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|
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/** |
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* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial |
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* capacity that orders its elements according to the specified |
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* comparator. |
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* |
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* @param initialCapacity the initial capacity for this priority queue |
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* @param comparator the comparator used to order this priority queue. |
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* If <tt>null</tt> then the order depends on the elements' natural |
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* ordering. |
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* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less |
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* than 1 |
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*/ |
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public PriorityBlockingQueue(int initialCapacity, |
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Comparator<? super E> comparator) { |
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q = new PriorityQueue<E>(initialCapacity, comparator); |
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} |
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|
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/** |
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* Creates a <tt>PriorityBlockingQueue</tt> containing the elements |
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* in the specified collection. The priority queue has an initial |
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* capacity of 110% of the size of the specified collection. If |
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* the specified collection is a {@link SortedSet} or a {@link |
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* PriorityQueue}, this priority queue will be sorted according to |
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* the same comparator, or according to the natural ordering of its |
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* elements if the collection is sorted according to the natural |
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* ordering of its elements. Otherwise, this priority queue is |
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* ordered according to the natural ordering of its elements. |
125 |
* |
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* @param c the collection whose elements are to be placed |
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* into this priority queue. |
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* @throws ClassCastException if elements of the specified collection |
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* cannot be compared to one another according to the priority |
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* queue's ordering. |
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* @throws NullPointerException if the specified collection or any |
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* of its elements are null |
133 |
*/ |
134 |
public PriorityBlockingQueue(Collection<? extends E> c) { |
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q = new PriorityQueue<E>(c); |
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} |
137 |
|
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/** |
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* Inserts the specified element into this priority queue. |
140 |
* |
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* @param e the element to add |
142 |
* @return <tt>true</tt> (as per the spec for {@link Collection#add}) |
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* @throws ClassCastException if the specified element cannot be compared |
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* with elements currently in the priority queue according to the |
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* priority queue's ordering |
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* @throws NullPointerException if the specified element is null |
147 |
*/ |
148 |
public boolean add(E e) { |
149 |
return offer(e); |
150 |
} |
151 |
|
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/** |
153 |
* Inserts the specified element into this priority queue. |
154 |
* |
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* @param e the element to add |
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* @return <tt>true</tt> |
157 |
* @throws ClassCastException if the specified element cannot be compared |
158 |
* with elements currently in the priority queue according to the |
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* priority queue's ordering |
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* @throws NullPointerException if the specified element is null |
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*/ |
162 |
public boolean offer(E e) { |
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if (e == null) throw new NullPointerException(); |
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final ReentrantLock lock = this.lock; |
165 |
lock.lock(); |
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try { |
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boolean ok = q.offer(e); |
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assert ok; |
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notEmpty.signal(); |
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return true; |
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} finally { |
172 |
lock.unlock(); |
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} |
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} |
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|
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/** |
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* Inserts the specified element into this priority queue. As the queue is |
178 |
* unbounded this method will never block. |
179 |
* |
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* @param e the element to add |
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* @throws ClassCastException if the specified element cannot be compared |
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* with elements currently in the priority queue according to the |
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* priority queue's ordering |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public void put(E e) { |
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offer(e); // never need to block |
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} |
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|
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/** |
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* Inserts the specified element into this priority queue. As the queue is |
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* unbounded this method will never block. |
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* |
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* @param e the element to add |
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* @param timeout This parameter is ignored as the method never blocks |
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* @param unit This parameter is ignored as the method never blocks |
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* @return <tt>true</tt> |
198 |
* @throws ClassCastException if the specified element cannot be compared |
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* with elements currently in the priority queue according to the |
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* priority queue's ordering |
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* @throws NullPointerException if the specified element is null |
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*/ |
203 |
public boolean offer(E e, long timeout, TimeUnit unit) { |
204 |
return offer(e); // never need to block |
205 |
} |
206 |
|
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public E poll() { |
208 |
final ReentrantLock lock = this.lock; |
209 |
lock.lock(); |
210 |
try { |
211 |
return q.poll(); |
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} finally { |
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lock.unlock(); |
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} |
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} |
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|
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public E take() throws InterruptedException { |
218 |
final ReentrantLock lock = this.lock; |
219 |
lock.lockInterruptibly(); |
220 |
try { |
221 |
try { |
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while (q.size() == 0) |
223 |
notEmpty.await(); |
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} catch (InterruptedException ie) { |
225 |
notEmpty.signal(); // propagate to non-interrupted thread |
226 |
throw ie; |
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} |
228 |
E x = q.poll(); |
229 |
assert x != null; |
230 |
return x; |
231 |
} finally { |
232 |
lock.unlock(); |
233 |
} |
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} |
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|
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public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
237 |
long nanos = unit.toNanos(timeout); |
238 |
final ReentrantLock lock = this.lock; |
239 |
lock.lockInterruptibly(); |
240 |
try { |
241 |
for (;;) { |
242 |
E x = q.poll(); |
243 |
if (x != null) |
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return x; |
245 |
if (nanos <= 0) |
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return null; |
247 |
try { |
248 |
nanos = notEmpty.awaitNanos(nanos); |
249 |
} catch (InterruptedException ie) { |
250 |
notEmpty.signal(); // propagate to non-interrupted thread |
251 |
throw ie; |
252 |
} |
253 |
} |
254 |
} finally { |
255 |
lock.unlock(); |
256 |
} |
257 |
} |
258 |
|
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public E peek() { |
260 |
final ReentrantLock lock = this.lock; |
261 |
lock.lock(); |
262 |
try { |
263 |
return q.peek(); |
264 |
} finally { |
265 |
lock.unlock(); |
266 |
} |
267 |
} |
268 |
|
269 |
/** |
270 |
* Returns the comparator used to order the elements in this queue, |
271 |
* or <tt>null</tt> if this queue uses the {@linkplain Comparable |
272 |
* natural ordering} of its elements. |
273 |
* |
274 |
* @return the comparator used to order the elements in this queue, |
275 |
* or <tt>null</tt> if this queue uses the natural |
276 |
* ordering of its elements. |
277 |
*/ |
278 |
public Comparator<? super E> comparator() { |
279 |
return q.comparator(); |
280 |
} |
281 |
|
282 |
public int size() { |
283 |
final ReentrantLock lock = this.lock; |
284 |
lock.lock(); |
285 |
try { |
286 |
return q.size(); |
287 |
} finally { |
288 |
lock.unlock(); |
289 |
} |
290 |
} |
291 |
|
292 |
/** |
293 |
* Always returns <tt>Integer.MAX_VALUE</tt> because |
294 |
* a <tt>PriorityBlockingQueue</tt> is not capacity constrained. |
295 |
* @return <tt>Integer.MAX_VALUE</tt> |
296 |
*/ |
297 |
public int remainingCapacity() { |
298 |
return Integer.MAX_VALUE; |
299 |
} |
300 |
|
301 |
/** |
302 |
* Removes a single instance of the specified element from this queue, |
303 |
* if it is present. More formally, removes an element <tt>e</tt> such |
304 |
* that <tt>o.equals(e)</tt>, if this queue contains one or more such |
305 |
* elements. |
306 |
* Returns <tt>true</tt> if this queue contained the specified element |
307 |
* (or equivalently, if this queue changed as a result of the call). |
308 |
* |
309 |
* @param o element to be removed from this queue, if present |
310 |
* @return <tt>true</tt> if this queue changed as a result of the call |
311 |
*/ |
312 |
public boolean remove(Object o) { |
313 |
final ReentrantLock lock = this.lock; |
314 |
lock.lock(); |
315 |
try { |
316 |
return q.remove(o); |
317 |
} finally { |
318 |
lock.unlock(); |
319 |
} |
320 |
} |
321 |
|
322 |
/** |
323 |
* Returns <tt>true</tt> if this queue contains the specified element. |
324 |
* More formally, returns <tt>true</tt> if and only if this queue contains |
325 |
* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>. |
326 |
* |
327 |
* @param o object to be checked for containment in this queue |
328 |
* @return <tt>true</tt> if this queue contains the specified element |
329 |
*/ |
330 |
public boolean contains(Object o) { |
331 |
final ReentrantLock lock = this.lock; |
332 |
lock.lock(); |
333 |
try { |
334 |
return q.contains(o); |
335 |
} finally { |
336 |
lock.unlock(); |
337 |
} |
338 |
} |
339 |
|
340 |
/** |
341 |
* Returns an array containing all of the elements in this queue. |
342 |
* The returned array elements are in no particular order. |
343 |
* |
344 |
* <p>The returned array will be "safe" in that no references to it are |
345 |
* maintained by this queue. (In other words, this method must allocate |
346 |
* a new array). The caller is thus free to modify the returned array. |
347 |
* |
348 |
* <p>This method acts as bridge between array-based and collection-based |
349 |
* APIs. |
350 |
* |
351 |
* @return an array containing all of the elements in this queue |
352 |
*/ |
353 |
public Object[] toArray() { |
354 |
final ReentrantLock lock = this.lock; |
355 |
lock.lock(); |
356 |
try { |
357 |
return q.toArray(); |
358 |
} finally { |
359 |
lock.unlock(); |
360 |
} |
361 |
} |
362 |
|
363 |
|
364 |
public String toString() { |
365 |
final ReentrantLock lock = this.lock; |
366 |
lock.lock(); |
367 |
try { |
368 |
return q.toString(); |
369 |
} finally { |
370 |
lock.unlock(); |
371 |
} |
372 |
} |
373 |
|
374 |
/** |
375 |
* @throws UnsupportedOperationException {@inheritDoc} |
376 |
* @throws ClassCastException {@inheritDoc} |
377 |
* @throws NullPointerException {@inheritDoc} |
378 |
* @throws IllegalArgumentException {@inheritDoc} |
379 |
*/ |
380 |
public int drainTo(Collection<? super E> c) { |
381 |
if (c == null) |
382 |
throw new NullPointerException(); |
383 |
if (c == this) |
384 |
throw new IllegalArgumentException(); |
385 |
final ReentrantLock lock = this.lock; |
386 |
lock.lock(); |
387 |
try { |
388 |
int n = 0; |
389 |
E e; |
390 |
while ( (e = q.poll()) != null) { |
391 |
c.add(e); |
392 |
++n; |
393 |
} |
394 |
return n; |
395 |
} finally { |
396 |
lock.unlock(); |
397 |
} |
398 |
} |
399 |
|
400 |
/** |
401 |
* @throws UnsupportedOperationException {@inheritDoc} |
402 |
* @throws ClassCastException {@inheritDoc} |
403 |
* @throws NullPointerException {@inheritDoc} |
404 |
* @throws IllegalArgumentException {@inheritDoc} |
405 |
*/ |
406 |
public int drainTo(Collection<? super E> c, int maxElements) { |
407 |
if (c == null) |
408 |
throw new NullPointerException(); |
409 |
if (c == this) |
410 |
throw new IllegalArgumentException(); |
411 |
if (maxElements <= 0) |
412 |
return 0; |
413 |
final ReentrantLock lock = this.lock; |
414 |
lock.lock(); |
415 |
try { |
416 |
int n = 0; |
417 |
E e; |
418 |
while (n < maxElements && (e = q.poll()) != null) { |
419 |
c.add(e); |
420 |
++n; |
421 |
} |
422 |
return n; |
423 |
} finally { |
424 |
lock.unlock(); |
425 |
} |
426 |
} |
427 |
|
428 |
/** |
429 |
* Atomically removes all of the elements from this queue. |
430 |
* The queue will be empty after this call returns. |
431 |
*/ |
432 |
public void clear() { |
433 |
final ReentrantLock lock = this.lock; |
434 |
lock.lock(); |
435 |
try { |
436 |
q.clear(); |
437 |
} finally { |
438 |
lock.unlock(); |
439 |
} |
440 |
} |
441 |
|
442 |
/** |
443 |
* Returns an array containing all of the elements in this queue; the |
444 |
* runtime type of the returned array is that of the specified array. |
445 |
* The returned array elements are in no particular order. |
446 |
* If the queue fits in the specified array, it is returned therein. |
447 |
* Otherwise, a new array is allocated with the runtime type of the |
448 |
* specified array and the size of this queue. |
449 |
* |
450 |
* <p>If this queue fits in the specified array with room to spare |
451 |
* (i.e., the array has more elements than this queue), the element in |
452 |
* the array immediately following the end of the queue is set to |
453 |
* <tt>null</tt>. |
454 |
* |
455 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
456 |
* array-based and collection-based APIs. Further, this method allows |
457 |
* precise control over the runtime type of the output array, and may, |
458 |
* under certain circumstances, be used to save allocation costs. |
459 |
* |
460 |
* <p>Suppose <tt>x</tt> is a queue known to contain only strings. |
461 |
* The following code can be used to dump the queue into a newly |
462 |
* allocated array of <tt>String</tt>: |
463 |
* |
464 |
* <pre> |
465 |
* String[] y = x.toArray(new String[0]);</pre> |
466 |
* |
467 |
* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
468 |
* <tt>toArray()</tt>. |
469 |
* |
470 |
* @param a the array into which the elements of the queue are to |
471 |
* be stored, if it is big enough; otherwise, a new array of the |
472 |
* same runtime type is allocated for this purpose |
473 |
* @return an array containing all of the elements in this queue |
474 |
* @throws ArrayStoreException if the runtime type of the specified array |
475 |
* is not a supertype of the runtime type of every element in |
476 |
* this queue |
477 |
* @throws NullPointerException if the specified array is null |
478 |
*/ |
479 |
public <T> T[] toArray(T[] a) { |
480 |
final ReentrantLock lock = this.lock; |
481 |
lock.lock(); |
482 |
try { |
483 |
return q.toArray(a); |
484 |
} finally { |
485 |
lock.unlock(); |
486 |
} |
487 |
} |
488 |
|
489 |
/** |
490 |
* Returns an iterator over the elements in this queue. The |
491 |
* iterator does not return the elements in any particular order. |
492 |
* The returned iterator is a thread-safe "fast-fail" iterator |
493 |
* that will throw {@link ConcurrentModificationException} upon |
494 |
* detected interference. |
495 |
* |
496 |
* @return an iterator over the elements in this queue |
497 |
*/ |
498 |
public Iterator<E> iterator() { |
499 |
final ReentrantLock lock = this.lock; |
500 |
lock.lock(); |
501 |
try { |
502 |
return new Itr(q.iterator()); |
503 |
} finally { |
504 |
lock.unlock(); |
505 |
} |
506 |
} |
507 |
|
508 |
private class Itr<E> implements Iterator<E> { |
509 |
private final Iterator<E> iter; |
510 |
Itr(Iterator<E> i) { |
511 |
iter = i; |
512 |
} |
513 |
|
514 |
public boolean hasNext() { |
515 |
/* |
516 |
* No sync -- we rely on underlying hasNext to be |
517 |
* stateless, in which case we can return true by mistake |
518 |
* only when next() will subsequently throw |
519 |
* ConcurrentModificationException. |
520 |
*/ |
521 |
return iter.hasNext(); |
522 |
} |
523 |
|
524 |
public E next() { |
525 |
ReentrantLock lock = PriorityBlockingQueue.this.lock; |
526 |
lock.lock(); |
527 |
try { |
528 |
return iter.next(); |
529 |
} finally { |
530 |
lock.unlock(); |
531 |
} |
532 |
} |
533 |
|
534 |
public void remove() { |
535 |
ReentrantLock lock = PriorityBlockingQueue.this.lock; |
536 |
lock.lock(); |
537 |
try { |
538 |
iter.remove(); |
539 |
} finally { |
540 |
lock.unlock(); |
541 |
} |
542 |
} |
543 |
} |
544 |
|
545 |
/** |
546 |
* Save the state to a stream (that is, serialize it). This |
547 |
* merely wraps default serialization within lock. The |
548 |
* serialization strategy for items is left to underlying |
549 |
* Queue. Note that locking is not needed on deserialization, so |
550 |
* readObject is not defined, just relying on default. |
551 |
*/ |
552 |
private void writeObject(java.io.ObjectOutputStream s) |
553 |
throws java.io.IOException { |
554 |
lock.lock(); |
555 |
try { |
556 |
s.defaultWriteObject(); |
557 |
} finally { |
558 |
lock.unlock(); |
559 |
} |
560 |
} |
561 |
|
562 |
} |