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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/publicdomain/zero/1.0/ |
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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.lang.ref.WeakReference; |
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import java.util.AbstractQueue; |
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import java.util.Arrays; |
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import java.util.Collection; |
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import java.util.Iterator; |
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import java.util.NoSuchElementException; |
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import java.util.Objects; |
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import java.util.Spliterator; |
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import java.util.Spliterators; |
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import java.util.concurrent.locks.Condition; |
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import java.util.concurrent.locks.ReentrantLock; |
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import java.util.function.Consumer; |
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import java.util.function.Predicate; |
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|
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/** |
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* A bounded {@linkplain BlockingQueue blocking queue} backed by an |
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* array. This queue orders elements FIFO (first-in-first-out). The |
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* <em>head</em> of the queue is that element that has been on the |
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* queue the longest time. The <em>tail</em> of the queue is that |
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* element that has been on the queue the shortest time. New elements |
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* are inserted at the tail of the queue, and the queue retrieval |
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* operations obtain elements at the head of the queue. |
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* |
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* <p>This is a classic "bounded buffer", in which a |
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* fixed-sized array holds elements inserted by producers and |
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* extracted by consumers. Once created, the capacity cannot be |
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* changed. Attempts to {@code put} an element into a full queue |
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* will result in the operation blocking; attempts to {@code take} an |
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* element from an empty queue will similarly block. |
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* |
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* <p>This class supports an optional fairness policy for ordering |
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* waiting producer and consumer threads. By default, this ordering |
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* is not guaranteed. However, a queue constructed with fairness set |
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* to {@code true} grants threads access in FIFO order. Fairness |
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* generally decreases throughput but reduces variability and avoids |
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* starvation. |
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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}/../technotes/guides/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 queue |
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*/ |
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public class ArrayBlockingQueue<E> extends AbstractQueue<E> |
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implements BlockingQueue<E>, java.io.Serializable { |
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|
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/** |
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* Serialization ID. This class relies on default serialization |
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* even for the items array, which is default-serialized, even if |
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* it is empty. Otherwise it could not be declared final, which is |
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* necessary here. |
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*/ |
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private static final long serialVersionUID = -817911632652898426L; |
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|
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/** The queued items */ |
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final Object[] items; |
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|
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/** items index for next take, poll, peek or remove */ |
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int takeIndex; |
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|
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/** items index for next put, offer, or add */ |
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int putIndex; |
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|
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/** Number of elements in the queue */ |
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int count; |
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|
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/* |
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* Concurrency control uses the classic two-condition algorithm |
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* found in any textbook. |
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*/ |
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|
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/** Main lock guarding all access */ |
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final ReentrantLock lock; |
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|
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/** Condition for waiting takes */ |
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private final Condition notEmpty; |
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|
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/** Condition for waiting puts */ |
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private final Condition notFull; |
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|
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/** |
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* Shared state for currently active iterators, or null if there |
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* are known not to be any. Allows queue operations to update |
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* iterator state. |
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*/ |
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transient Itrs itrs; |
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|
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// Internal helper methods |
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|
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/** |
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* Increments i, mod modulus. |
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* Precondition and postcondition: 0 <= i < modulus. |
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*/ |
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static final int inc(int i, int modulus) { |
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if (++i >= modulus) i = 0; |
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return i; |
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} |
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|
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/** |
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* Decrements i, mod modulus. |
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* Precondition and postcondition: 0 <= i < modulus. |
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*/ |
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static final int dec(int i, int modulus) { |
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if (--i < 0) i = modulus - 1; |
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return i; |
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} |
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|
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/** |
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* Returns item at index i. |
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*/ |
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@SuppressWarnings("unchecked") |
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final E itemAt(int i) { |
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return (E) items[i]; |
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} |
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|
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/** |
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* Returns element at array index i. |
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* This is a slight abuse of generics, accepted by javac. |
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*/ |
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@SuppressWarnings("unchecked") |
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static <E> E itemAt(Object[] items, int i) { |
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return (E) items[i]; |
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} |
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|
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/** |
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* Inserts element at current put position, advances, and signals. |
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* Call only when holding lock. |
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*/ |
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private void enqueue(E x) { |
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// assert lock.getHoldCount() == 1; |
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// assert items[putIndex] == null; |
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final Object[] items = this.items; |
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items[putIndex] = x; |
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if (++putIndex == items.length) putIndex = 0; |
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count++; |
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notEmpty.signal(); |
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// checkInvariants(); |
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} |
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|
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/** |
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* Extracts element at current take position, advances, and signals. |
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* Call only when holding lock. |
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*/ |
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private E dequeue() { |
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// assert lock.getHoldCount() == 1; |
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// assert items[takeIndex] != null; |
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final Object[] items = this.items; |
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@SuppressWarnings("unchecked") |
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E x = (E) items[takeIndex]; |
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items[takeIndex] = null; |
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if (++takeIndex == items.length) takeIndex = 0; |
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count--; |
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if (itrs != null) |
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itrs.elementDequeued(); |
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notFull.signal(); |
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// checkInvariants(); |
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return x; |
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} |
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|
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/** |
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* Deletes item at array index removeIndex. |
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* Utility for remove(Object) and iterator.remove. |
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* Call only when holding lock. |
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*/ |
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void removeAt(final int removeIndex) { |
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// assert lock.getHoldCount() == 1; |
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// assert items[removeIndex] != null; |
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// assert removeIndex >= 0 && removeIndex < items.length; |
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final Object[] items = this.items; |
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if (removeIndex == takeIndex) { |
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// removing front item; just advance |
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items[takeIndex] = null; |
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if (++takeIndex == items.length) takeIndex = 0; |
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count--; |
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if (itrs != null) |
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itrs.elementDequeued(); |
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} else { |
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// an "interior" remove |
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|
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// slide over all others up through putIndex. |
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for (int i = removeIndex, putIndex = this.putIndex;;) { |
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int pred = i; |
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if (++i == items.length) i = 0; |
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if (i == putIndex) { |
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items[pred] = null; |
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this.putIndex = pred; |
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break; |
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} |
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items[pred] = items[i]; |
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} |
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count--; |
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if (itrs != null) |
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itrs.removedAt(removeIndex); |
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} |
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notFull.signal(); |
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// checkInvariants(); |
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} |
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|
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/** |
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* Creates an {@code ArrayBlockingQueue} with the given (fixed) |
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* capacity and default access policy. |
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* |
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* @param capacity the capacity of this queue |
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* @throws IllegalArgumentException if {@code capacity < 1} |
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*/ |
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public ArrayBlockingQueue(int capacity) { |
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this(capacity, false); |
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} |
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|
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/** |
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* Creates an {@code ArrayBlockingQueue} with the given (fixed) |
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* capacity and the specified access policy. |
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* |
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* @param capacity the capacity of this queue |
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* @param fair if {@code true} then queue accesses for threads blocked |
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* on insertion or removal, are processed in FIFO order; |
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* if {@code false} the access order is unspecified. |
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* @throws IllegalArgumentException if {@code capacity < 1} |
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*/ |
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public ArrayBlockingQueue(int capacity, boolean fair) { |
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if (capacity <= 0) |
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throw new IllegalArgumentException(); |
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this.items = new Object[capacity]; |
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lock = new ReentrantLock(fair); |
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notEmpty = lock.newCondition(); |
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notFull = lock.newCondition(); |
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} |
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|
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/** |
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* Creates an {@code ArrayBlockingQueue} with the given (fixed) |
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* capacity, the specified access policy and initially containing the |
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* elements of the given collection, |
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* added in traversal order of the collection's iterator. |
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* |
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* @param capacity the capacity of this queue |
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* @param fair if {@code true} then queue accesses for threads blocked |
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* on insertion or removal, are processed in FIFO order; |
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* if {@code false} the access order is unspecified. |
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* @param c the collection of elements to initially contain |
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* @throws IllegalArgumentException if {@code capacity} is less than |
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* {@code c.size()}, or less than 1. |
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* @throws NullPointerException if the specified collection or any |
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* of its elements are null |
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*/ |
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public ArrayBlockingQueue(int capacity, boolean fair, |
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Collection<? extends E> c) { |
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this(capacity, fair); |
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|
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final ReentrantLock lock = this.lock; |
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lock.lock(); // Lock only for visibility, not mutual exclusion |
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try { |
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final Object[] items = this.items; |
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int i = 0; |
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try { |
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for (E e : c) |
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items[i++] = Objects.requireNonNull(e); |
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} catch (ArrayIndexOutOfBoundsException ex) { |
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throw new IllegalArgumentException(); |
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} |
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count = i; |
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putIndex = (i == capacity) ? 0 : i; |
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// checkInvariants(); |
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} finally { |
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lock.unlock(); |
279 |
} |
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} |
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|
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/** |
283 |
* Inserts the specified element at the tail of this queue if it is |
284 |
* possible to do so immediately without exceeding the queue's capacity, |
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* returning {@code true} upon success and throwing an |
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* {@code IllegalStateException} if this queue is full. |
287 |
* |
288 |
* @param e the element to add |
289 |
* @return {@code true} (as specified by {@link Collection#add}) |
290 |
* @throws IllegalStateException if this queue is full |
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* @throws NullPointerException if the specified element is null |
292 |
*/ |
293 |
public boolean add(E e) { |
294 |
return super.add(e); |
295 |
} |
296 |
|
297 |
/** |
298 |
* Inserts the specified element at the tail of this queue if it is |
299 |
* possible to do so immediately without exceeding the queue's capacity, |
300 |
* returning {@code true} upon success and {@code false} if this queue |
301 |
* is full. This method is generally preferable to method {@link #add}, |
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* which can fail to insert an element only by throwing an exception. |
303 |
* |
304 |
* @throws NullPointerException if the specified element is null |
305 |
*/ |
306 |
public boolean offer(E e) { |
307 |
Objects.requireNonNull(e); |
308 |
final ReentrantLock lock = this.lock; |
309 |
lock.lock(); |
310 |
try { |
311 |
if (count == items.length) |
312 |
return false; |
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else { |
314 |
enqueue(e); |
315 |
return true; |
316 |
} |
317 |
} finally { |
318 |
lock.unlock(); |
319 |
} |
320 |
} |
321 |
|
322 |
/** |
323 |
* Inserts the specified element at the tail of this queue, waiting |
324 |
* for space to become available if the queue is full. |
325 |
* |
326 |
* @throws InterruptedException {@inheritDoc} |
327 |
* @throws NullPointerException {@inheritDoc} |
328 |
*/ |
329 |
public void put(E e) throws InterruptedException { |
330 |
Objects.requireNonNull(e); |
331 |
final ReentrantLock lock = this.lock; |
332 |
lock.lockInterruptibly(); |
333 |
try { |
334 |
while (count == items.length) |
335 |
notFull.await(); |
336 |
enqueue(e); |
337 |
} finally { |
338 |
lock.unlock(); |
339 |
} |
340 |
} |
341 |
|
342 |
/** |
343 |
* Inserts the specified element at the tail of this queue, waiting |
344 |
* up to the specified wait time for space to become available if |
345 |
* the queue is full. |
346 |
* |
347 |
* @throws InterruptedException {@inheritDoc} |
348 |
* @throws NullPointerException {@inheritDoc} |
349 |
*/ |
350 |
public boolean offer(E e, long timeout, TimeUnit unit) |
351 |
throws InterruptedException { |
352 |
|
353 |
Objects.requireNonNull(e); |
354 |
long nanos = unit.toNanos(timeout); |
355 |
final ReentrantLock lock = this.lock; |
356 |
lock.lockInterruptibly(); |
357 |
try { |
358 |
while (count == items.length) { |
359 |
if (nanos <= 0L) |
360 |
return false; |
361 |
nanos = notFull.awaitNanos(nanos); |
362 |
} |
363 |
enqueue(e); |
364 |
return true; |
365 |
} finally { |
366 |
// checkInvariants(); |
367 |
lock.unlock(); |
368 |
} |
369 |
} |
370 |
|
371 |
public E poll() { |
372 |
final ReentrantLock lock = this.lock; |
373 |
lock.lock(); |
374 |
try { |
375 |
return (count == 0) ? null : dequeue(); |
376 |
} finally { |
377 |
lock.unlock(); |
378 |
} |
379 |
} |
380 |
|
381 |
public E take() throws InterruptedException { |
382 |
final ReentrantLock lock = this.lock; |
383 |
lock.lockInterruptibly(); |
384 |
try { |
385 |
while (count == 0) |
386 |
notEmpty.await(); |
387 |
return dequeue(); |
388 |
} finally { |
389 |
lock.unlock(); |
390 |
} |
391 |
} |
392 |
|
393 |
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
394 |
long nanos = unit.toNanos(timeout); |
395 |
final ReentrantLock lock = this.lock; |
396 |
lock.lockInterruptibly(); |
397 |
try { |
398 |
while (count == 0) { |
399 |
if (nanos <= 0L) |
400 |
return null; |
401 |
nanos = notEmpty.awaitNanos(nanos); |
402 |
} |
403 |
return dequeue(); |
404 |
} finally { |
405 |
// checkInvariants(); |
406 |
lock.unlock(); |
407 |
} |
408 |
} |
409 |
|
410 |
public E peek() { |
411 |
final ReentrantLock lock = this.lock; |
412 |
lock.lock(); |
413 |
try { |
414 |
return itemAt(takeIndex); // null when queue is empty |
415 |
} finally { |
416 |
lock.unlock(); |
417 |
} |
418 |
} |
419 |
|
420 |
// this doc comment is overridden to remove the reference to collections |
421 |
// greater in size than Integer.MAX_VALUE |
422 |
/** |
423 |
* Returns the number of elements in this queue. |
424 |
* |
425 |
* @return the number of elements in this queue |
426 |
*/ |
427 |
public int size() { |
428 |
final ReentrantLock lock = this.lock; |
429 |
lock.lock(); |
430 |
try { |
431 |
return count; |
432 |
} finally { |
433 |
lock.unlock(); |
434 |
} |
435 |
} |
436 |
|
437 |
// this doc comment is a modified copy of the inherited doc comment, |
438 |
// without the reference to unlimited queues. |
439 |
/** |
440 |
* Returns the number of additional elements that this queue can ideally |
441 |
* (in the absence of memory or resource constraints) accept without |
442 |
* blocking. This is always equal to the initial capacity of this queue |
443 |
* less the current {@code size} of this queue. |
444 |
* |
445 |
* <p>Note that you <em>cannot</em> always tell if an attempt to insert |
446 |
* an element will succeed by inspecting {@code remainingCapacity} |
447 |
* because it may be the case that another thread is about to |
448 |
* insert or remove an element. |
449 |
*/ |
450 |
public int remainingCapacity() { |
451 |
final ReentrantLock lock = this.lock; |
452 |
lock.lock(); |
453 |
try { |
454 |
return items.length - count; |
455 |
} finally { |
456 |
lock.unlock(); |
457 |
} |
458 |
} |
459 |
|
460 |
/** |
461 |
* Removes a single instance of the specified element from this queue, |
462 |
* if it is present. More formally, removes an element {@code e} such |
463 |
* that {@code o.equals(e)}, if this queue contains one or more such |
464 |
* elements. |
465 |
* Returns {@code true} if this queue contained the specified element |
466 |
* (or equivalently, if this queue changed as a result of the call). |
467 |
* |
468 |
* <p>Removal of interior elements in circular array based queues |
469 |
* is an intrinsically slow and disruptive operation, so should |
470 |
* be undertaken only in exceptional circumstances, ideally |
471 |
* only when the queue is known not to be accessible by other |
472 |
* threads. |
473 |
* |
474 |
* @param o element to be removed from this queue, if present |
475 |
* @return {@code true} if this queue changed as a result of the call |
476 |
*/ |
477 |
public boolean remove(Object o) { |
478 |
if (o == null) return false; |
479 |
final ReentrantLock lock = this.lock; |
480 |
lock.lock(); |
481 |
try { |
482 |
if (count > 0) { |
483 |
final Object[] items = this.items; |
484 |
for (int i = takeIndex, end = putIndex, |
485 |
to = (i < end) ? end : items.length; |
486 |
; i = 0, to = end) { |
487 |
for (; i < to; i++) |
488 |
if (o.equals(items[i])) { |
489 |
removeAt(i); |
490 |
return true; |
491 |
} |
492 |
if (to == end) break; |
493 |
} |
494 |
} |
495 |
return false; |
496 |
} finally { |
497 |
// checkInvariants(); |
498 |
lock.unlock(); |
499 |
} |
500 |
} |
501 |
|
502 |
/** |
503 |
* Returns {@code true} if this queue contains the specified element. |
504 |
* More formally, returns {@code true} if and only if this queue contains |
505 |
* at least one element {@code e} such that {@code o.equals(e)}. |
506 |
* |
507 |
* @param o object to be checked for containment in this queue |
508 |
* @return {@code true} if this queue contains the specified element |
509 |
*/ |
510 |
public boolean contains(Object o) { |
511 |
if (o == null) return false; |
512 |
final ReentrantLock lock = this.lock; |
513 |
lock.lock(); |
514 |
try { |
515 |
if (count > 0) { |
516 |
final Object[] items = this.items; |
517 |
for (int i = takeIndex, end = putIndex, |
518 |
to = (i < end) ? end : items.length; |
519 |
; i = 0, to = end) { |
520 |
for (; i < to; i++) |
521 |
if (o.equals(items[i])) |
522 |
return true; |
523 |
if (to == end) break; |
524 |
} |
525 |
} |
526 |
return false; |
527 |
} finally { |
528 |
// checkInvariants(); |
529 |
lock.unlock(); |
530 |
} |
531 |
} |
532 |
|
533 |
/** |
534 |
* Returns an array containing all of the elements in this queue, in |
535 |
* proper sequence. |
536 |
* |
537 |
* <p>The returned array will be "safe" in that no references to it are |
538 |
* maintained by this queue. (In other words, this method must allocate |
539 |
* a new array). The caller is thus free to modify the returned array. |
540 |
* |
541 |
* <p>This method acts as bridge between array-based and collection-based |
542 |
* APIs. |
543 |
* |
544 |
* @return an array containing all of the elements in this queue |
545 |
*/ |
546 |
public Object[] toArray() { |
547 |
final ReentrantLock lock = this.lock; |
548 |
lock.lock(); |
549 |
try { |
550 |
final Object[] items = this.items; |
551 |
final int end = takeIndex + count; |
552 |
final Object[] a = Arrays.copyOfRange(items, takeIndex, end); |
553 |
if (end != putIndex) |
554 |
System.arraycopy(items, 0, a, items.length - takeIndex, putIndex); |
555 |
return a; |
556 |
} finally { |
557 |
lock.unlock(); |
558 |
} |
559 |
} |
560 |
|
561 |
/** |
562 |
* Returns an array containing all of the elements in this queue, in |
563 |
* proper sequence; the runtime type of the returned array is that of |
564 |
* the specified array. If the queue fits in the specified array, it |
565 |
* is returned therein. Otherwise, a new array is allocated with the |
566 |
* runtime type of the specified array and the size of this queue. |
567 |
* |
568 |
* <p>If this queue fits in the specified array with room to spare |
569 |
* (i.e., the array has more elements than this queue), the element in |
570 |
* the array immediately following the end of the queue is set to |
571 |
* {@code null}. |
572 |
* |
573 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
574 |
* array-based and collection-based APIs. Further, this method allows |
575 |
* precise control over the runtime type of the output array, and may, |
576 |
* under certain circumstances, be used to save allocation costs. |
577 |
* |
578 |
* <p>Suppose {@code x} is a queue known to contain only strings. |
579 |
* The following code can be used to dump the queue into a newly |
580 |
* allocated array of {@code String}: |
581 |
* |
582 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
583 |
* |
584 |
* Note that {@code toArray(new Object[0])} is identical in function to |
585 |
* {@code toArray()}. |
586 |
* |
587 |
* @param a the array into which the elements of the queue are to |
588 |
* be stored, if it is big enough; otherwise, a new array of the |
589 |
* same runtime type is allocated for this purpose |
590 |
* @return an array containing all of the elements in this queue |
591 |
* @throws ArrayStoreException if the runtime type of the specified array |
592 |
* is not a supertype of the runtime type of every element in |
593 |
* this queue |
594 |
* @throws NullPointerException if the specified array is null |
595 |
*/ |
596 |
@SuppressWarnings("unchecked") |
597 |
public <T> T[] toArray(T[] a) { |
598 |
final ReentrantLock lock = this.lock; |
599 |
lock.lock(); |
600 |
try { |
601 |
final Object[] items = this.items; |
602 |
final int count = this.count; |
603 |
final int firstLeg = Math.min(items.length - takeIndex, count); |
604 |
if (a.length < count) { |
605 |
a = (T[]) Arrays.copyOfRange(items, takeIndex, takeIndex + count, |
606 |
a.getClass()); |
607 |
} else { |
608 |
System.arraycopy(items, takeIndex, a, 0, firstLeg); |
609 |
if (a.length > count) |
610 |
a[count] = null; |
611 |
} |
612 |
if (firstLeg < count) |
613 |
System.arraycopy(items, 0, a, firstLeg, putIndex); |
614 |
return a; |
615 |
} finally { |
616 |
lock.unlock(); |
617 |
} |
618 |
} |
619 |
|
620 |
public String toString() { |
621 |
return Helpers.collectionToString(this); |
622 |
} |
623 |
|
624 |
/** |
625 |
* Atomically removes all of the elements from this queue. |
626 |
* The queue will be empty after this call returns. |
627 |
*/ |
628 |
public void clear() { |
629 |
final ReentrantLock lock = this.lock; |
630 |
lock.lock(); |
631 |
try { |
632 |
int k; |
633 |
if ((k = count) > 0) { |
634 |
circularClear(items, takeIndex, putIndex); |
635 |
takeIndex = putIndex; |
636 |
count = 0; |
637 |
if (itrs != null) |
638 |
itrs.queueIsEmpty(); |
639 |
for (; k > 0 && lock.hasWaiters(notFull); k--) |
640 |
notFull.signal(); |
641 |
} |
642 |
} finally { |
643 |
// checkInvariants(); |
644 |
lock.unlock(); |
645 |
} |
646 |
} |
647 |
|
648 |
/** |
649 |
* Nulls out slots starting at array index i, upto index end. |
650 |
* If i == end, the entire array is cleared! |
651 |
*/ |
652 |
private static void circularClear(Object[] items, int i, int end) { |
653 |
for (int to = (i < end) ? end : items.length; |
654 |
; i = 0, to = end) { |
655 |
Arrays.fill(items, i, to, null); |
656 |
if (to == end) break; |
657 |
} |
658 |
} |
659 |
|
660 |
/** |
661 |
* @throws UnsupportedOperationException {@inheritDoc} |
662 |
* @throws ClassCastException {@inheritDoc} |
663 |
* @throws NullPointerException {@inheritDoc} |
664 |
* @throws IllegalArgumentException {@inheritDoc} |
665 |
*/ |
666 |
public int drainTo(Collection<? super E> c) { |
667 |
return drainTo(c, Integer.MAX_VALUE); |
668 |
} |
669 |
|
670 |
/** |
671 |
* @throws UnsupportedOperationException {@inheritDoc} |
672 |
* @throws ClassCastException {@inheritDoc} |
673 |
* @throws NullPointerException {@inheritDoc} |
674 |
* @throws IllegalArgumentException {@inheritDoc} |
675 |
*/ |
676 |
public int drainTo(Collection<? super E> c, int maxElements) { |
677 |
Objects.requireNonNull(c); |
678 |
if (c == this) |
679 |
throw new IllegalArgumentException(); |
680 |
if (maxElements <= 0) |
681 |
return 0; |
682 |
final Object[] items = this.items; |
683 |
final ReentrantLock lock = this.lock; |
684 |
lock.lock(); |
685 |
try { |
686 |
int n = Math.min(maxElements, count); |
687 |
int take = takeIndex; |
688 |
int i = 0; |
689 |
try { |
690 |
while (i < n) { |
691 |
@SuppressWarnings("unchecked") |
692 |
E x = (E) items[take]; |
693 |
c.add(x); |
694 |
items[take] = null; |
695 |
if (++take == items.length) take = 0; |
696 |
i++; |
697 |
} |
698 |
return n; |
699 |
} finally { |
700 |
// Restore invariants even if c.add() threw |
701 |
if (i > 0) { |
702 |
count -= i; |
703 |
takeIndex = take; |
704 |
if (itrs != null) { |
705 |
if (count == 0) |
706 |
itrs.queueIsEmpty(); |
707 |
else if (i > take) |
708 |
itrs.takeIndexWrapped(); |
709 |
} |
710 |
for (; i > 0 && lock.hasWaiters(notFull); i--) |
711 |
notFull.signal(); |
712 |
} |
713 |
} |
714 |
} finally { |
715 |
// checkInvariants(); |
716 |
lock.unlock(); |
717 |
} |
718 |
} |
719 |
|
720 |
/** |
721 |
* Returns an iterator over the elements in this queue in proper sequence. |
722 |
* The elements will be returned in order from first (head) to last (tail). |
723 |
* |
724 |
* <p>The returned iterator is |
725 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
726 |
* |
727 |
* @return an iterator over the elements in this queue in proper sequence |
728 |
*/ |
729 |
public Iterator<E> iterator() { |
730 |
return new Itr(); |
731 |
} |
732 |
|
733 |
/** |
734 |
* Shared data between iterators and their queue, allowing queue |
735 |
* modifications to update iterators when elements are removed. |
736 |
* |
737 |
* This adds a lot of complexity for the sake of correctly |
738 |
* handling some uncommon operations, but the combination of |
739 |
* circular-arrays and supporting interior removes (i.e., those |
740 |
* not at head) would cause iterators to sometimes lose their |
741 |
* places and/or (re)report elements they shouldn't. To avoid |
742 |
* this, when a queue has one or more iterators, it keeps iterator |
743 |
* state consistent by: |
744 |
* |
745 |
* (1) keeping track of the number of "cycles", that is, the |
746 |
* number of times takeIndex has wrapped around to 0. |
747 |
* (2) notifying all iterators via the callback removedAt whenever |
748 |
* an interior element is removed (and thus other elements may |
749 |
* be shifted). |
750 |
* |
751 |
* These suffice to eliminate iterator inconsistencies, but |
752 |
* unfortunately add the secondary responsibility of maintaining |
753 |
* the list of iterators. We track all active iterators in a |
754 |
* simple linked list (accessed only when the queue's lock is |
755 |
* held) of weak references to Itr. The list is cleaned up using |
756 |
* 3 different mechanisms: |
757 |
* |
758 |
* (1) Whenever a new iterator is created, do some O(1) checking for |
759 |
* stale list elements. |
760 |
* |
761 |
* (2) Whenever takeIndex wraps around to 0, check for iterators |
762 |
* that have been unused for more than one wrap-around cycle. |
763 |
* |
764 |
* (3) Whenever the queue becomes empty, all iterators are notified |
765 |
* and this entire data structure is discarded. |
766 |
* |
767 |
* So in addition to the removedAt callback that is necessary for |
768 |
* correctness, iterators have the shutdown and takeIndexWrapped |
769 |
* callbacks that help remove stale iterators from the list. |
770 |
* |
771 |
* Whenever a list element is examined, it is expunged if either |
772 |
* the GC has determined that the iterator is discarded, or if the |
773 |
* iterator reports that it is "detached" (does not need any |
774 |
* further state updates). Overhead is maximal when takeIndex |
775 |
* never advances, iterators are discarded before they are |
776 |
* exhausted, and all removals are interior removes, in which case |
777 |
* all stale iterators are discovered by the GC. But even in this |
778 |
* case we don't increase the amortized complexity. |
779 |
* |
780 |
* Care must be taken to keep list sweeping methods from |
781 |
* reentrantly invoking another such method, causing subtle |
782 |
* corruption bugs. |
783 |
*/ |
784 |
class Itrs { |
785 |
|
786 |
/** |
787 |
* Node in a linked list of weak iterator references. |
788 |
*/ |
789 |
private class Node extends WeakReference<Itr> { |
790 |
Node next; |
791 |
|
792 |
Node(Itr iterator, Node next) { |
793 |
super(iterator); |
794 |
this.next = next; |
795 |
} |
796 |
} |
797 |
|
798 |
/** Incremented whenever takeIndex wraps around to 0 */ |
799 |
int cycles; |
800 |
|
801 |
/** Linked list of weak iterator references */ |
802 |
private Node head; |
803 |
|
804 |
/** Used to expunge stale iterators */ |
805 |
private Node sweeper; |
806 |
|
807 |
private static final int SHORT_SWEEP_PROBES = 4; |
808 |
private static final int LONG_SWEEP_PROBES = 16; |
809 |
|
810 |
Itrs(Itr initial) { |
811 |
register(initial); |
812 |
} |
813 |
|
814 |
/** |
815 |
* Sweeps itrs, looking for and expunging stale iterators. |
816 |
* If at least one was found, tries harder to find more. |
817 |
* Called only from iterating thread. |
818 |
* |
819 |
* @param tryHarder whether to start in try-harder mode, because |
820 |
* there is known to be at least one iterator to collect |
821 |
*/ |
822 |
void doSomeSweeping(boolean tryHarder) { |
823 |
// assert lock.getHoldCount() == 1; |
824 |
// assert head != null; |
825 |
int probes = tryHarder ? LONG_SWEEP_PROBES : SHORT_SWEEP_PROBES; |
826 |
Node o, p; |
827 |
final Node sweeper = this.sweeper; |
828 |
boolean passedGo; // to limit search to one full sweep |
829 |
|
830 |
if (sweeper == null) { |
831 |
o = null; |
832 |
p = head; |
833 |
passedGo = true; |
834 |
} else { |
835 |
o = sweeper; |
836 |
p = o.next; |
837 |
passedGo = false; |
838 |
} |
839 |
|
840 |
for (; probes > 0; probes--) { |
841 |
if (p == null) { |
842 |
if (passedGo) |
843 |
break; |
844 |
o = null; |
845 |
p = head; |
846 |
passedGo = true; |
847 |
} |
848 |
final Itr it = p.get(); |
849 |
final Node next = p.next; |
850 |
if (it == null || it.isDetached()) { |
851 |
// found a discarded/exhausted iterator |
852 |
probes = LONG_SWEEP_PROBES; // "try harder" |
853 |
// unlink p |
854 |
p.clear(); |
855 |
p.next = null; |
856 |
if (o == null) { |
857 |
head = next; |
858 |
if (next == null) { |
859 |
// We've run out of iterators to track; retire |
860 |
itrs = null; |
861 |
return; |
862 |
} |
863 |
} |
864 |
else |
865 |
o.next = next; |
866 |
} else { |
867 |
o = p; |
868 |
} |
869 |
p = next; |
870 |
} |
871 |
|
872 |
this.sweeper = (p == null) ? null : o; |
873 |
} |
874 |
|
875 |
/** |
876 |
* Adds a new iterator to the linked list of tracked iterators. |
877 |
*/ |
878 |
void register(Itr itr) { |
879 |
// assert lock.getHoldCount() == 1; |
880 |
head = new Node(itr, head); |
881 |
} |
882 |
|
883 |
/** |
884 |
* Called whenever takeIndex wraps around to 0. |
885 |
* |
886 |
* Notifies all iterators, and expunges any that are now stale. |
887 |
*/ |
888 |
void takeIndexWrapped() { |
889 |
// assert lock.getHoldCount() == 1; |
890 |
cycles++; |
891 |
for (Node o = null, p = head; p != null;) { |
892 |
final Itr it = p.get(); |
893 |
final Node next = p.next; |
894 |
if (it == null || it.takeIndexWrapped()) { |
895 |
// unlink p |
896 |
// assert it == null || it.isDetached(); |
897 |
p.clear(); |
898 |
p.next = null; |
899 |
if (o == null) |
900 |
head = next; |
901 |
else |
902 |
o.next = next; |
903 |
} else { |
904 |
o = p; |
905 |
} |
906 |
p = next; |
907 |
} |
908 |
if (head == null) // no more iterators to track |
909 |
itrs = null; |
910 |
} |
911 |
|
912 |
/** |
913 |
* Called whenever an interior remove (not at takeIndex) occurred. |
914 |
* |
915 |
* Notifies all iterators, and expunges any that are now stale. |
916 |
*/ |
917 |
void removedAt(int removedIndex) { |
918 |
for (Node o = null, p = head; p != null;) { |
919 |
final Itr it = p.get(); |
920 |
final Node next = p.next; |
921 |
if (it == null || it.removedAt(removedIndex)) { |
922 |
// unlink p |
923 |
// assert it == null || it.isDetached(); |
924 |
p.clear(); |
925 |
p.next = null; |
926 |
if (o == null) |
927 |
head = next; |
928 |
else |
929 |
o.next = next; |
930 |
} else { |
931 |
o = p; |
932 |
} |
933 |
p = next; |
934 |
} |
935 |
if (head == null) // no more iterators to track |
936 |
itrs = null; |
937 |
} |
938 |
|
939 |
/** |
940 |
* Called whenever the queue becomes empty. |
941 |
* |
942 |
* Notifies all active iterators that the queue is empty, |
943 |
* clears all weak refs, and unlinks the itrs datastructure. |
944 |
*/ |
945 |
void queueIsEmpty() { |
946 |
// assert lock.getHoldCount() == 1; |
947 |
for (Node p = head; p != null; p = p.next) { |
948 |
Itr it = p.get(); |
949 |
if (it != null) { |
950 |
p.clear(); |
951 |
it.shutdown(); |
952 |
} |
953 |
} |
954 |
head = null; |
955 |
itrs = null; |
956 |
} |
957 |
|
958 |
/** |
959 |
* Called whenever an element has been dequeued (at takeIndex). |
960 |
*/ |
961 |
void elementDequeued() { |
962 |
// assert lock.getHoldCount() == 1; |
963 |
if (count == 0) |
964 |
queueIsEmpty(); |
965 |
else if (takeIndex == 0) |
966 |
takeIndexWrapped(); |
967 |
} |
968 |
} |
969 |
|
970 |
/** |
971 |
* Iterator for ArrayBlockingQueue. |
972 |
* |
973 |
* To maintain weak consistency with respect to puts and takes, we |
974 |
* read ahead one slot, so as to not report hasNext true but then |
975 |
* not have an element to return. |
976 |
* |
977 |
* We switch into "detached" mode (allowing prompt unlinking from |
978 |
* itrs without help from the GC) when all indices are negative, or |
979 |
* when hasNext returns false for the first time. This allows the |
980 |
* iterator to track concurrent updates completely accurately, |
981 |
* except for the corner case of the user calling Iterator.remove() |
982 |
* after hasNext() returned false. Even in this case, we ensure |
983 |
* that we don't remove the wrong element by keeping track of the |
984 |
* expected element to remove, in lastItem. Yes, we may fail to |
985 |
* remove lastItem from the queue if it moved due to an interleaved |
986 |
* interior remove while in detached mode. |
987 |
*/ |
988 |
private class Itr implements Iterator<E> { |
989 |
/** Index to look for new nextItem; NONE at end */ |
990 |
private int cursor; |
991 |
|
992 |
/** Element to be returned by next call to next(); null if none */ |
993 |
private E nextItem; |
994 |
|
995 |
/** Index of nextItem; NONE if none, REMOVED if removed elsewhere */ |
996 |
private int nextIndex; |
997 |
|
998 |
/** Last element returned; null if none or not detached. */ |
999 |
private E lastItem; |
1000 |
|
1001 |
/** Index of lastItem, NONE if none, REMOVED if removed elsewhere */ |
1002 |
private int lastRet; |
1003 |
|
1004 |
/** Previous value of takeIndex, or DETACHED when detached */ |
1005 |
private int prevTakeIndex; |
1006 |
|
1007 |
/** Previous value of iters.cycles */ |
1008 |
private int prevCycles; |
1009 |
|
1010 |
/** Special index value indicating "not available" or "undefined" */ |
1011 |
private static final int NONE = -1; |
1012 |
|
1013 |
/** |
1014 |
* Special index value indicating "removed elsewhere", that is, |
1015 |
* removed by some operation other than a call to this.remove(). |
1016 |
*/ |
1017 |
private static final int REMOVED = -2; |
1018 |
|
1019 |
/** Special value for prevTakeIndex indicating "detached mode" */ |
1020 |
private static final int DETACHED = -3; |
1021 |
|
1022 |
Itr() { |
1023 |
// assert lock.getHoldCount() == 0; |
1024 |
lastRet = NONE; |
1025 |
final ReentrantLock lock = ArrayBlockingQueue.this.lock; |
1026 |
lock.lock(); |
1027 |
try { |
1028 |
if (count == 0) { |
1029 |
// assert itrs == null; |
1030 |
cursor = NONE; |
1031 |
nextIndex = NONE; |
1032 |
prevTakeIndex = DETACHED; |
1033 |
} else { |
1034 |
final int takeIndex = ArrayBlockingQueue.this.takeIndex; |
1035 |
prevTakeIndex = takeIndex; |
1036 |
nextItem = itemAt(nextIndex = takeIndex); |
1037 |
cursor = incCursor(takeIndex); |
1038 |
if (itrs == null) { |
1039 |
itrs = new Itrs(this); |
1040 |
} else { |
1041 |
itrs.register(this); // in this order |
1042 |
itrs.doSomeSweeping(false); |
1043 |
} |
1044 |
prevCycles = itrs.cycles; |
1045 |
// assert takeIndex >= 0; |
1046 |
// assert prevTakeIndex == takeIndex; |
1047 |
// assert nextIndex >= 0; |
1048 |
// assert nextItem != null; |
1049 |
} |
1050 |
} finally { |
1051 |
lock.unlock(); |
1052 |
} |
1053 |
} |
1054 |
|
1055 |
boolean isDetached() { |
1056 |
// assert lock.getHoldCount() == 1; |
1057 |
return prevTakeIndex < 0; |
1058 |
} |
1059 |
|
1060 |
private int incCursor(int index) { |
1061 |
// assert lock.getHoldCount() == 1; |
1062 |
if (++index == items.length) index = 0; |
1063 |
if (index == putIndex) index = NONE; |
1064 |
return index; |
1065 |
} |
1066 |
|
1067 |
/** |
1068 |
* Returns true if index is invalidated by the given number of |
1069 |
* dequeues, starting from prevTakeIndex. |
1070 |
*/ |
1071 |
private boolean invalidated(int index, int prevTakeIndex, |
1072 |
long dequeues, int length) { |
1073 |
if (index < 0) |
1074 |
return false; |
1075 |
int distance = index - prevTakeIndex; |
1076 |
if (distance < 0) |
1077 |
distance += length; |
1078 |
return dequeues > distance; |
1079 |
} |
1080 |
|
1081 |
/** |
1082 |
* Adjusts indices to incorporate all dequeues since the last |
1083 |
* operation on this iterator. Call only from iterating thread. |
1084 |
*/ |
1085 |
private void incorporateDequeues() { |
1086 |
// assert lock.getHoldCount() == 1; |
1087 |
// assert itrs != null; |
1088 |
// assert !isDetached(); |
1089 |
// assert count > 0; |
1090 |
|
1091 |
final int cycles = itrs.cycles; |
1092 |
final int takeIndex = ArrayBlockingQueue.this.takeIndex; |
1093 |
final int prevCycles = this.prevCycles; |
1094 |
final int prevTakeIndex = this.prevTakeIndex; |
1095 |
|
1096 |
if (cycles != prevCycles || takeIndex != prevTakeIndex) { |
1097 |
final int len = items.length; |
1098 |
// how far takeIndex has advanced since the previous |
1099 |
// operation of this iterator |
1100 |
long dequeues = (cycles - prevCycles) * len |
1101 |
+ (takeIndex - prevTakeIndex); |
1102 |
|
1103 |
// Check indices for invalidation |
1104 |
if (invalidated(lastRet, prevTakeIndex, dequeues, len)) |
1105 |
lastRet = REMOVED; |
1106 |
if (invalidated(nextIndex, prevTakeIndex, dequeues, len)) |
1107 |
nextIndex = REMOVED; |
1108 |
if (invalidated(cursor, prevTakeIndex, dequeues, len)) |
1109 |
cursor = takeIndex; |
1110 |
|
1111 |
if (cursor < 0 && nextIndex < 0 && lastRet < 0) |
1112 |
detach(); |
1113 |
else { |
1114 |
this.prevCycles = cycles; |
1115 |
this.prevTakeIndex = takeIndex; |
1116 |
} |
1117 |
} |
1118 |
} |
1119 |
|
1120 |
/** |
1121 |
* Called when itrs should stop tracking this iterator, either |
1122 |
* because there are no more indices to update (cursor < 0 && |
1123 |
* nextIndex < 0 && lastRet < 0) or as a special exception, when |
1124 |
* lastRet >= 0, because hasNext() is about to return false for the |
1125 |
* first time. Call only from iterating thread. |
1126 |
*/ |
1127 |
private void detach() { |
1128 |
// Switch to detached mode |
1129 |
// assert lock.getHoldCount() == 1; |
1130 |
// assert cursor == NONE; |
1131 |
// assert nextIndex < 0; |
1132 |
// assert lastRet < 0 || nextItem == null; |
1133 |
// assert lastRet < 0 ^ lastItem != null; |
1134 |
if (prevTakeIndex >= 0) { |
1135 |
// assert itrs != null; |
1136 |
prevTakeIndex = DETACHED; |
1137 |
// try to unlink from itrs (but not too hard) |
1138 |
itrs.doSomeSweeping(true); |
1139 |
} |
1140 |
} |
1141 |
|
1142 |
/** |
1143 |
* For performance reasons, we would like not to acquire a lock in |
1144 |
* hasNext in the common case. To allow for this, we only access |
1145 |
* fields (i.e. nextItem) that are not modified by update operations |
1146 |
* triggered by queue modifications. |
1147 |
*/ |
1148 |
public boolean hasNext() { |
1149 |
// assert lock.getHoldCount() == 0; |
1150 |
if (nextItem != null) |
1151 |
return true; |
1152 |
noNext(); |
1153 |
return false; |
1154 |
} |
1155 |
|
1156 |
private void noNext() { |
1157 |
final ReentrantLock lock = ArrayBlockingQueue.this.lock; |
1158 |
lock.lock(); |
1159 |
try { |
1160 |
// assert cursor == NONE; |
1161 |
// assert nextIndex == NONE; |
1162 |
if (!isDetached()) { |
1163 |
// assert lastRet >= 0; |
1164 |
incorporateDequeues(); // might update lastRet |
1165 |
if (lastRet >= 0) { |
1166 |
lastItem = itemAt(lastRet); |
1167 |
// assert lastItem != null; |
1168 |
detach(); |
1169 |
} |
1170 |
} |
1171 |
// assert isDetached(); |
1172 |
// assert lastRet < 0 ^ lastItem != null; |
1173 |
} finally { |
1174 |
lock.unlock(); |
1175 |
} |
1176 |
} |
1177 |
|
1178 |
public E next() { |
1179 |
// assert lock.getHoldCount() == 0; |
1180 |
final E x = nextItem; |
1181 |
if (x == null) |
1182 |
throw new NoSuchElementException(); |
1183 |
final ReentrantLock lock = ArrayBlockingQueue.this.lock; |
1184 |
lock.lock(); |
1185 |
try { |
1186 |
if (!isDetached()) |
1187 |
incorporateDequeues(); |
1188 |
// assert nextIndex != NONE; |
1189 |
// assert lastItem == null; |
1190 |
lastRet = nextIndex; |
1191 |
final int cursor = this.cursor; |
1192 |
if (cursor >= 0) { |
1193 |
nextItem = itemAt(nextIndex = cursor); |
1194 |
// assert nextItem != null; |
1195 |
this.cursor = incCursor(cursor); |
1196 |
} else { |
1197 |
nextIndex = NONE; |
1198 |
nextItem = null; |
1199 |
} |
1200 |
} finally { |
1201 |
lock.unlock(); |
1202 |
} |
1203 |
return x; |
1204 |
} |
1205 |
|
1206 |
public void remove() { |
1207 |
// assert lock.getHoldCount() == 0; |
1208 |
final ReentrantLock lock = ArrayBlockingQueue.this.lock; |
1209 |
lock.lock(); |
1210 |
try { |
1211 |
if (!isDetached()) |
1212 |
incorporateDequeues(); // might update lastRet or detach |
1213 |
final int lastRet = this.lastRet; |
1214 |
this.lastRet = NONE; |
1215 |
if (lastRet >= 0) { |
1216 |
if (!isDetached()) |
1217 |
removeAt(lastRet); |
1218 |
else { |
1219 |
final E lastItem = this.lastItem; |
1220 |
// assert lastItem != null; |
1221 |
this.lastItem = null; |
1222 |
if (itemAt(lastRet) == lastItem) |
1223 |
removeAt(lastRet); |
1224 |
} |
1225 |
} else if (lastRet == NONE) |
1226 |
throw new IllegalStateException(); |
1227 |
// else lastRet == REMOVED and the last returned element was |
1228 |
// previously asynchronously removed via an operation other |
1229 |
// than this.remove(), so nothing to do. |
1230 |
|
1231 |
if (cursor < 0 && nextIndex < 0) |
1232 |
detach(); |
1233 |
} finally { |
1234 |
lock.unlock(); |
1235 |
// assert lastRet == NONE; |
1236 |
// assert lastItem == null; |
1237 |
} |
1238 |
} |
1239 |
|
1240 |
/** |
1241 |
* Called to notify the iterator that the queue is empty, or that it |
1242 |
* has fallen hopelessly behind, so that it should abandon any |
1243 |
* further iteration, except possibly to return one more element |
1244 |
* from next(), as promised by returning true from hasNext(). |
1245 |
*/ |
1246 |
void shutdown() { |
1247 |
// assert lock.getHoldCount() == 1; |
1248 |
cursor = NONE; |
1249 |
if (nextIndex >= 0) |
1250 |
nextIndex = REMOVED; |
1251 |
if (lastRet >= 0) { |
1252 |
lastRet = REMOVED; |
1253 |
lastItem = null; |
1254 |
} |
1255 |
prevTakeIndex = DETACHED; |
1256 |
// Don't set nextItem to null because we must continue to be |
1257 |
// able to return it on next(). |
1258 |
// |
1259 |
// Caller will unlink from itrs when convenient. |
1260 |
} |
1261 |
|
1262 |
private int distance(int index, int prevTakeIndex, int length) { |
1263 |
int distance = index - prevTakeIndex; |
1264 |
if (distance < 0) |
1265 |
distance += length; |
1266 |
return distance; |
1267 |
} |
1268 |
|
1269 |
/** |
1270 |
* Called whenever an interior remove (not at takeIndex) occurred. |
1271 |
* |
1272 |
* @return true if this iterator should be unlinked from itrs |
1273 |
*/ |
1274 |
boolean removedAt(int removedIndex) { |
1275 |
// assert lock.getHoldCount() == 1; |
1276 |
if (isDetached()) |
1277 |
return true; |
1278 |
|
1279 |
final int takeIndex = ArrayBlockingQueue.this.takeIndex; |
1280 |
final int prevTakeIndex = this.prevTakeIndex; |
1281 |
final int len = items.length; |
1282 |
// distance from prevTakeIndex to removedIndex |
1283 |
final int removedDistance = |
1284 |
len * (itrs.cycles - this.prevCycles |
1285 |
+ ((removedIndex < takeIndex) ? 1 : 0)) |
1286 |
+ (removedIndex - prevTakeIndex); |
1287 |
// assert itrs.cycles - this.prevCycles >= 0; |
1288 |
// assert itrs.cycles - this.prevCycles <= 1; |
1289 |
// assert removedDistance > 0; |
1290 |
// assert removedIndex != takeIndex; |
1291 |
int cursor = this.cursor; |
1292 |
if (cursor >= 0) { |
1293 |
int x = distance(cursor, prevTakeIndex, len); |
1294 |
if (x == removedDistance) { |
1295 |
if (cursor == putIndex) |
1296 |
this.cursor = cursor = NONE; |
1297 |
} |
1298 |
else if (x > removedDistance) { |
1299 |
// assert cursor != prevTakeIndex; |
1300 |
this.cursor = cursor = dec(cursor, len); |
1301 |
} |
1302 |
} |
1303 |
int lastRet = this.lastRet; |
1304 |
if (lastRet >= 0) { |
1305 |
int x = distance(lastRet, prevTakeIndex, len); |
1306 |
if (x == removedDistance) |
1307 |
this.lastRet = lastRet = REMOVED; |
1308 |
else if (x > removedDistance) |
1309 |
this.lastRet = lastRet = dec(lastRet, len); |
1310 |
} |
1311 |
int nextIndex = this.nextIndex; |
1312 |
if (nextIndex >= 0) { |
1313 |
int x = distance(nextIndex, prevTakeIndex, len); |
1314 |
if (x == removedDistance) |
1315 |
this.nextIndex = nextIndex = REMOVED; |
1316 |
else if (x > removedDistance) |
1317 |
this.nextIndex = nextIndex = dec(nextIndex, len); |
1318 |
} |
1319 |
if (cursor < 0 && nextIndex < 0 && lastRet < 0) { |
1320 |
this.prevTakeIndex = DETACHED; |
1321 |
return true; |
1322 |
} |
1323 |
return false; |
1324 |
} |
1325 |
|
1326 |
/** |
1327 |
* Called whenever takeIndex wraps around to zero. |
1328 |
* |
1329 |
* @return true if this iterator should be unlinked from itrs |
1330 |
*/ |
1331 |
boolean takeIndexWrapped() { |
1332 |
// assert lock.getHoldCount() == 1; |
1333 |
if (isDetached()) |
1334 |
return true; |
1335 |
if (itrs.cycles - prevCycles > 1) { |
1336 |
// All the elements that existed at the time of the last |
1337 |
// operation are gone, so abandon further iteration. |
1338 |
shutdown(); |
1339 |
return true; |
1340 |
} |
1341 |
return false; |
1342 |
} |
1343 |
|
1344 |
// /** Uncomment for debugging. */ |
1345 |
// public String toString() { |
1346 |
// return ("cursor=" + cursor + " " + |
1347 |
// "nextIndex=" + nextIndex + " " + |
1348 |
// "lastRet=" + lastRet + " " + |
1349 |
// "nextItem=" + nextItem + " " + |
1350 |
// "lastItem=" + lastItem + " " + |
1351 |
// "prevCycles=" + prevCycles + " " + |
1352 |
// "prevTakeIndex=" + prevTakeIndex + " " + |
1353 |
// "size()=" + size() + " " + |
1354 |
// "remainingCapacity()=" + remainingCapacity()); |
1355 |
// } |
1356 |
} |
1357 |
|
1358 |
/** |
1359 |
* Returns a {@link Spliterator} over the elements in this queue. |
1360 |
* |
1361 |
* <p>The returned spliterator is |
1362 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
1363 |
* |
1364 |
* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT}, |
1365 |
* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}. |
1366 |
* |
1367 |
* @implNote |
1368 |
* The {@code Spliterator} implements {@code trySplit} to permit limited |
1369 |
* parallelism. |
1370 |
* |
1371 |
* @return a {@code Spliterator} over the elements in this queue |
1372 |
* @since 1.8 |
1373 |
*/ |
1374 |
public Spliterator<E> spliterator() { |
1375 |
return Spliterators.spliterator |
1376 |
(this, (Spliterator.ORDERED | |
1377 |
Spliterator.NONNULL | |
1378 |
Spliterator.CONCURRENT)); |
1379 |
} |
1380 |
|
1381 |
public void forEach(Consumer<? super E> action) { |
1382 |
Objects.requireNonNull(action); |
1383 |
final ReentrantLock lock = this.lock; |
1384 |
lock.lock(); |
1385 |
try { |
1386 |
if (count > 0) { |
1387 |
final Object[] items = this.items; |
1388 |
for (int i = takeIndex, end = putIndex, |
1389 |
to = (i < end) ? end : items.length; |
1390 |
; i = 0, to = end) { |
1391 |
for (; i < to; i++) |
1392 |
action.accept(itemAt(items, i)); |
1393 |
if (to == end) break; |
1394 |
} |
1395 |
} |
1396 |
} finally { |
1397 |
// checkInvariants(); |
1398 |
lock.unlock(); |
1399 |
} |
1400 |
} |
1401 |
|
1402 |
/** |
1403 |
* @throws NullPointerException {@inheritDoc} |
1404 |
*/ |
1405 |
public boolean removeIf(Predicate<? super E> filter) { |
1406 |
Objects.requireNonNull(filter); |
1407 |
return bulkRemove(filter); |
1408 |
} |
1409 |
|
1410 |
/** |
1411 |
* @throws NullPointerException {@inheritDoc} |
1412 |
*/ |
1413 |
public boolean removeAll(Collection<?> c) { |
1414 |
Objects.requireNonNull(c); |
1415 |
return bulkRemove(e -> c.contains(e)); |
1416 |
} |
1417 |
|
1418 |
/** |
1419 |
* @throws NullPointerException {@inheritDoc} |
1420 |
*/ |
1421 |
public boolean retainAll(Collection<?> c) { |
1422 |
Objects.requireNonNull(c); |
1423 |
return bulkRemove(e -> !c.contains(e)); |
1424 |
} |
1425 |
|
1426 |
/** Implementation of bulk remove methods. */ |
1427 |
private boolean bulkRemove(Predicate<? super E> filter) { |
1428 |
final ReentrantLock lock = this.lock; |
1429 |
lock.lock(); |
1430 |
try { |
1431 |
if (itrs == null) { // check for active iterators |
1432 |
if (count > 0) { |
1433 |
final Object[] items = this.items; |
1434 |
// Optimize for initial run of survivors |
1435 |
for (int i = takeIndex, end = putIndex, |
1436 |
to = (i < end) ? end : items.length; |
1437 |
; i = 0, to = end) { |
1438 |
for (; i < to; i++) |
1439 |
if (filter.test(itemAt(items, i))) |
1440 |
return bulkRemoveModified(filter, i, to); |
1441 |
if (to == end) break; |
1442 |
} |
1443 |
} |
1444 |
return false; |
1445 |
} |
1446 |
} finally { |
1447 |
// checkInvariants(); |
1448 |
lock.unlock(); |
1449 |
} |
1450 |
// Active iterators are too hairy! |
1451 |
// Punting (for now) to the slow n^2 algorithm ... |
1452 |
return super.removeIf(filter); |
1453 |
} |
1454 |
|
1455 |
/** |
1456 |
* Helper for bulkRemove, in case of at least one deletion. |
1457 |
* @param i valid index of first element to be deleted |
1458 |
*/ |
1459 |
private boolean bulkRemoveModified( |
1460 |
Predicate<? super E> filter, int i, int to) { |
1461 |
final Object[] items = this.items; |
1462 |
final int capacity = items.length; |
1463 |
// a two-finger algorithm, with hare i reading, tortoise j writing |
1464 |
int j = i++; |
1465 |
final int end = putIndex; |
1466 |
try { |
1467 |
for (;; j = 0) { // j rejoins i on second leg |
1468 |
E e; |
1469 |
// In this loop, i and j are on the same leg, with i > j |
1470 |
for (; i < to; i++) |
1471 |
if (!filter.test(e = itemAt(items, i))) |
1472 |
items[j++] = e; |
1473 |
if (to == end) break; |
1474 |
// In this loop, j is on the first leg, i on the second |
1475 |
for (i = 0, to = end; i < to && j < capacity; i++) |
1476 |
if (!filter.test(e = itemAt(items, i))) |
1477 |
items[j++] = e; |
1478 |
if (i >= to) { |
1479 |
if (j == capacity) j = 0; // "corner" case |
1480 |
break; |
1481 |
} |
1482 |
} |
1483 |
return true; |
1484 |
} catch (Throwable ex) { |
1485 |
// copy remaining elements |
1486 |
for (; i != end; i = inc(i, capacity), j = inc(j, capacity)) |
1487 |
items[j] = items[i]; |
1488 |
throw ex; |
1489 |
} finally { |
1490 |
int deleted = putIndex - j; |
1491 |
if (deleted <= 0) deleted += capacity; |
1492 |
count -= deleted; |
1493 |
circularClear(items, putIndex = j, end); |
1494 |
} |
1495 |
} |
1496 |
|
1497 |
/** debugging */ |
1498 |
void checkInvariants() { |
1499 |
// meta-assertions |
1500 |
// assert lock.isHeldByCurrentThread(); |
1501 |
// assert lock.getHoldCount() == 1; |
1502 |
try { |
1503 |
int capacity = items.length; |
1504 |
// assert capacity > 0; |
1505 |
// assert takeIndex >= 0 && takeIndex < capacity; |
1506 |
// assert putIndex >= 0 && putIndex < capacity; |
1507 |
// assert count <= capacity; |
1508 |
// assert takeIndex == putIndex || items[takeIndex] != null; |
1509 |
// assert count == capacity || items[putIndex] == null; |
1510 |
// assert takeIndex == putIndex || items[dec(putIndex, capacity)] != null; |
1511 |
} catch (Throwable t) { |
1512 |
System.err.printf("takeIndex=%d putIndex=%d count=%d capacity=%d%n", |
1513 |
takeIndex, putIndex, count, items.length); |
1514 |
System.err.printf("items=%s%n", |
1515 |
Arrays.toString(items)); |
1516 |
throw t; |
1517 |
} |
1518 |
} |
1519 |
|
1520 |
} |