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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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|
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package java.util.concurrent; |
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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} of |
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* <tt>Delayed</tt> elements, in which an element can only be taken |
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* when its delay has expired. The <em>head</em> of the queue is that |
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* <tt>Delayed</tt> element whose delay expired furthest in the |
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* past. If no delay has expired there is no head and <tt>poll</tt> |
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* will return <tt>null</tt>. Expiration occurs when an element's |
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* <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less |
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* than or equal to zero. This queue does not permit <tt>null</tt> |
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* elements. |
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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. |
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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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|
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public class DelayQueue<E extends Delayed> extends AbstractQueue<E> |
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implements BlockingQueue<E> { |
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|
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private transient final ReentrantLock lock = new ReentrantLock(); |
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private transient final Condition available = lock.newCondition(); |
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private final PriorityQueue<E> q = new PriorityQueue<E>(); |
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|
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/** |
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* Creates a new <tt>DelayQueue</tt> that is initially empty. |
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*/ |
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public DelayQueue() {} |
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|
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/** |
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* Creates a <tt>DelayQueue</tt> initially containing the elements of the |
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* given collection of {@link Delayed} instances. |
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* |
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* @param c the collection |
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* @throws NullPointerException if <tt>c</tt> or any element within it |
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* is <tt>null</tt> |
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* |
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*/ |
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public DelayQueue(Collection<? extends E> c) { |
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this.addAll(c); |
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} |
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|
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/** |
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* Inserts the specified element into this delay queue. |
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* |
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* @param o the element to add |
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* @return <tt>true</tt> |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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*/ |
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public boolean offer(E o) { |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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E first = q.peek(); |
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q.offer(o); |
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if (first == null || o.compareTo(first) < 0) |
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available.signalAll(); |
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return true; |
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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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|
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/** |
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* Adds the specified element to this delay queue. As the queue is |
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* unbounded this method will never block. |
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* @param o the element to add |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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*/ |
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public void put(E o) { |
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offer(o); |
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} |
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|
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/** |
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* Inserts the specified element into this delay queue. As the queue is |
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* unbounded this method will never block. |
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* @param o 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> |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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*/ |
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public boolean offer(E o, long timeout, TimeUnit unit) { |
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return offer(o); |
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} |
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|
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/** |
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* Adds the specified element to this queue. |
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* @param o the element to add |
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* @return <tt>true</tt> (as per the general contract of |
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* <tt>Collection.add</tt>). |
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* |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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*/ |
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public boolean add(E o) { |
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return offer(o); |
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} |
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|
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/** |
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* Retrieves and removes the head of this queue, waiting |
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* if no elements with an unexpired delay are present on this queue. |
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* @return the head of this queue |
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* @throws InterruptedException if interrupted while waiting. |
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*/ |
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public E take() throws InterruptedException { |
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final ReentrantLock lock = this.lock; |
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lock.lockInterruptibly(); |
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try { |
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for (;;) { |
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E first = q.peek(); |
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if (first == null) { |
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available.await(); |
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} else { |
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long delay = first.getDelay(TimeUnit.NANOSECONDS); |
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if (delay > 0) { |
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long tl = available.awaitNanos(delay); |
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} else { |
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E x = q.poll(); |
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assert x != null; |
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if (q.size() != 0) |
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available.signalAll(); // wake up other takers |
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return x; |
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|
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} |
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} |
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} |
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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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/** |
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* Retrieves and removes the head of this queue, waiting |
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* if necessary up to the specified wait time if no elements with |
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* an unexpired delay are |
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* present on this queue. |
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* @param timeout how long to wait before giving up, in units of |
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* <tt>unit</tt> |
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* @param unit a <tt>TimeUnit</tt> determining how to interpret the |
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* <tt>timeout</tt> parameter |
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* @return the head of this queue, or <tt>null</tt> if the |
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* specified waiting time elapses before an element with |
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* an unexpired dealy is present. |
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* @throws InterruptedException if interrupted while waiting. |
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*/ |
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public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
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final ReentrantLock lock = this.lock; |
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lock.lockInterruptibly(); |
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long nanos = unit.toNanos(timeout); |
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try { |
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for (;;) { |
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E first = q.peek(); |
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if (first == null) { |
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if (nanos <= 0) |
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return null; |
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else |
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nanos = available.awaitNanos(nanos); |
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} else { |
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long delay = first.getDelay(TimeUnit.NANOSECONDS); |
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if (delay > 0) { |
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if (delay > nanos) |
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delay = nanos; |
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long timeLeft = available.awaitNanos(delay); |
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nanos -= delay - timeLeft; |
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} else { |
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E x = q.poll(); |
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assert x != null; |
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if (q.size() != 0) |
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available.signalAll(); |
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return x; |
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} |
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} |
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} |
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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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|
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/** |
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* Retrieves and removes the head of this queue, or <tt>null</tt> |
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* if this queue has no elements with an unexpired delay. |
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* |
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* @return the head of this queue, or <tt>null</tt> if this |
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* queue has no elements with an unexpired delay. |
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*/ |
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public E poll() { |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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E first = q.peek(); |
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if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0) |
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return null; |
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else { |
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E x = q.poll(); |
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assert x != null; |
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if (q.size() != 0) |
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available.signalAll(); |
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return x; |
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} |
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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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/** |
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* Retrieves, but does not remove, the head of this queue, |
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* returning <tt>null</tt> if this queue has no elements with an |
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* unexpired delay. |
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* |
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* @return the head of this queue, or <tt>null</tt> if this queue |
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* has no elements with an unexpired delay. |
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*/ |
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public E peek() { |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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return q.peek(); |
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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 int size() { |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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return q.size(); |
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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 int drainTo(Collection<? super E> c) { |
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if (c == null) |
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throw new NullPointerException(); |
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if (c == this) |
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throw new IllegalArgumentException(); |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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int n = 0; |
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for (;;) { |
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E first = q.peek(); |
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if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0) |
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break; |
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c.add(q.poll()); |
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++n; |
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} |
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if (n > 0) |
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available.signalAll(); |
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return n; |
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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 int drainTo(Collection<? super E> c, int maxElements) { |
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if (c == null) |
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throw new NullPointerException(); |
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if (c == this) |
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throw new IllegalArgumentException(); |
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if (maxElements <= 0) |
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return 0; |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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int n = 0; |
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while (n < maxElements) { |
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E first = q.peek(); |
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if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0) |
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break; |
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c.add(q.poll()); |
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++n; |
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} |
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if (n > 0) |
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available.signalAll(); |
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return n; |
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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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/** |
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* Atomically removes all of the elements from this delay queue. |
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* The queue will be empty after this call returns. |
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*/ |
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public void clear() { |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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q.clear(); |
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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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/** |
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* Always returns <tt>Integer.MAX_VALUE</tt> because |
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* a <tt>DelayQueue</tt> is not capacity constrained. |
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* @return <tt>Integer.MAX_VALUE</tt> |
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*/ |
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public int remainingCapacity() { |
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return Integer.MAX_VALUE; |
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} |
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|
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public Object[] toArray() { |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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return q.toArray(); |
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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 <T> T[] toArray(T[] array) { |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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return q.toArray(array); |
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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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/** |
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* Removes a single instance of the specified element from this |
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* collection, if it is present. |
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*/ |
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public boolean remove(Object o) { |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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return q.remove(o); |
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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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/** |
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* Returns an iterator over the elements in this queue. The iterator |
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* does not return the elements in any particular order. The |
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* returned iterator is a thread-safe "fast-fail" iterator that will |
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* throw {@link java.util.ConcurrentModificationException} |
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* upon detected interference. |
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* |
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* @return an iterator over the elements in this queue. |
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*/ |
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public Iterator<E> iterator() { |
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final ReentrantLock lock = this.lock; |
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lock.lock(); |
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try { |
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return new Itr(q.iterator()); |
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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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private class Itr<E> implements Iterator<E> { |
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private final Iterator<E> iter; |
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Itr(Iterator<E> i) { |
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iter = i; |
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} |
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|
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public boolean hasNext() { |
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return iter.hasNext(); |
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} |
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|
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public E next() { |
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final ReentrantLock lock = DelayQueue.this.lock; |
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lock.lock(); |
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try { |
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return iter.next(); |
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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 void remove() { |
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final ReentrantLock lock = DelayQueue.this.lock; |
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lock.lock(); |
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try { |
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iter.remove(); |
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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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|
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} |