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Datei: Basic.java Sprache: Unknown

/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/

/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/

package java.util.concurrent;

import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.util.AbstractQueue;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.SortedSet;
import java.util.Spliterator;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Consumer;
import java.util.function.Predicate;
import jdk.internal.access.SharedSecrets;
import jdk.internal.util.ArraysSupport;

/**
* An unbounded {@linkplain BlockingQueue blocking queue} that uses
* the same ordering rules as class {@link PriorityQueue} and supplies
* blocking retrieval operations. While this queue is logically
* unbounded, attempted additions may fail due to resource exhaustion
* (causing {@code OutOfMemoryError}). This class does not permit
* {@code null} elements. A priority queue relying on {@linkplain
* Comparable natural ordering} also does not permit insertion of
* non-comparable objects (doing so results in
* {@code ClassCastException}).
*
* This class and its iterator implement all of the optional
* methods of the {@link Collection} and {@link Iterator} interfaces.
* The Iterator provided in method {@link #iterator()} and the
* Spliterator provided in method {@link #spliterator()} are not
* guaranteed to traverse the elements of the PriorityBlockingQueue in
* any particular order. If you need ordered traversal, consider using
* {@code Arrays.sort(pq.toArray())}. Also, method {@code drainTo} can
* be used to remove some or all elements in priority order and
* place them in another collection.
*
* Operations on this class make no guarantees about the ordering
* of elements with equal priority. If you need to enforce an
* ordering, you can define custom classes or comparators that use a
* secondary key to break ties in primary priority values. For
* example, here is a class that applies first-in-first-out
* tie-breaking to comparable elements. To use it, you would insert a
* {@code new FIFOEntry(anEntry)} instead of a plain entry object.
*
* <pre> {@code
* class FIFOEntry<E extends Comparable<? super E>>
* implements Comparable<FIFOEntry<E>> {
* static final AtomicLong seq = new AtomicLong();
* final long seqNum;
* final E entry;
* public FIFOEntry(E entry) {
* seqNum = seq.getAndIncrement();
* this.entry = entry;
* }
* public E getEntry() { return entry; }
* public int compareTo(FIFOEntry<E> other) {
* int res = entry.compareTo(other.entry);
* if (res == 0 && other.entry != this.entry)
* res = (seqNum < other.seqNum ? -1 : 1);
* return res;
* }
* }}</pre>
*
* This class is a member of the
* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
* Java Collections Framework</a>.
*
* @since 1.5
* @author Doug Lea
* @param <E> the type of elements held in this queue
*/
@SuppressWarnings("unchecked")
public class PriorityBlockingQueue<E> extends AbstractQueue<E>
 implements BlockingQueue<E>, java.io.Serializable {
 private static final long serialVersionUID = 5595510919245408276L;

 /*
 * The implementation uses an array-based binary heap, with public
 * operations protected with a single lock. However, allocation
 * during resizing uses a simple spinlock (used only while not
 * holding main lock) in order to allow takes to operate
 * concurrently with allocation. This avoids repeated
 * postponement of waiting consumers and consequent element
 * build-up. The need to back away from lock during allocation
 * makes it impossible to simply wrap delegated
 * java.util.PriorityQueue operations within a lock, as was done
 * in a previous version of this class. To maintain
 * interoperability, a plain PriorityQueue is still used during
 * serialization, which maintains compatibility at the expense of
 * transiently doubling overhead.
 */

 /**
 * Default array capacity.
 */
 private static final int DEFAULT_INITIAL_CAPACITY = 11;

 /**
 * Priority queue represented as a balanced binary heap: the two
 * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The
 * priority queue is ordered by comparator, or by the elements'
 * natural ordering, if comparator is null: For each node n in the
 * heap and each descendant d of n, n <= d. The element with the
 * lowest value is in queue[0], assuming the queue is nonempty.
 */
 private transient Object[] queue;

 /**
 * The number of elements in the priority queue.
 */
 private transient int size;

 /**
 * The comparator, or null if priority queue uses elements'
 * natural ordering.
 */
 private transient Comparator<? super E> comparator;

 /**
 * Lock used for all public operations.
 */
 private final ReentrantLock lock = new ReentrantLock();

 /**
 * Condition for blocking when empty.
 */
 @SuppressWarnings("serial") // Classes implementing Condition may be serializable.
 private final Condition notEmpty = lock.newCondition();

 /**
 * Spinlock for allocation, acquired via CAS.
 */
 private transient volatile int allocationSpinLock;

 /**
 * A plain PriorityQueue used only for serialization,
 * to maintain compatibility with previous versions
 * of this class. Non-null only during serialization/deserialization.
 */
 private PriorityQueue<E> q;

 /**
 * Creates a {@code PriorityBlockingQueue} with the default
 * initial capacity (11) that orders its elements according to
 * their {@linkplain Comparable natural ordering}.
 */
 public PriorityBlockingQueue() {
 this(DEFAULT_INITIAL_CAPACITY, null);
 }

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

 /**
 * Creates a {@code PriorityBlockingQueue} with the specified initial
 * capacity that orders its elements according to the specified
 * comparator.
 *
 * @param initialCapacity the initial capacity for this priority queue
 * @param comparator the comparator that will be used to order this
 * priority queue. If {@code null}, the {@linkplain Comparable
 * natural ordering} of the elements will be used.
 * @throws IllegalArgumentException if {@code initialCapacity} is less
 * than 1
 */
 public PriorityBlockingQueue(int initialCapacity,
 Comparator<? super E> comparator) {
 if (initialCapacity < 1)
 throw new IllegalArgumentException();
 this.comparator = comparator;
 this.queue = new Object[Math.max(1, initialCapacity)];
 }

 /**
 * Creates a {@code PriorityBlockingQueue} containing the elements
 * in the specified collection. If the specified collection is a
 * {@link SortedSet} or a {@link PriorityBlockingQueue}, this
 * priority queue will be ordered according to the same ordering.
 * Otherwise, this priority queue will be ordered according to the
 * {@linkplain Comparable natural ordering} of its elements.
 *
 * @param c the collection whose elements are to be placed
 * into this priority queue
 * @throws ClassCastException if elements of the specified collection
 * cannot be compared to one another according to the priority
 * queue's ordering
 * @throws NullPointerException if the specified collection or any
 * of its elements are null
 */
 public PriorityBlockingQueue(Collection<? extends E> c) {
 boolean heapify = true; // true if not known to be in heap order
 boolean screen = true; // true if must screen for nulls
 if (c instanceof SortedSet<?>) {
 SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
 this.comparator = (Comparator<? super E>) ss.comparator();
 heapify = false;
 }
 else if (c instanceof PriorityBlockingQueue<?>) {
 PriorityBlockingQueue<? extends E> pq =
 (PriorityBlockingQueue<? extends E>) c;
 this.comparator = (Comparator<? super E>) pq.comparator();
 screen = false;
 if (pq.getClass() == PriorityBlockingQueue.class) // exact match
 heapify = false;
 }
 Object[] es = c.toArray();
 int n = es.length;
 if (c.getClass() != java.util.ArrayList.class)
 es = Arrays.copyOf(es, n, Object[].class);
 if (screen && (n == 1 || this.comparator != null)) {
 for (Object e : es)
 if (e == null)
 throw new NullPointerException();
 }
 this.queue = ensureNonEmpty(es);
 this.size = n;
 if (heapify)
 heapify();
 }

 /** Ensures that queue[0] exists, helping peek() and poll(). */
 private static Object[] ensureNonEmpty(Object[] es) {
 return (es.length > 0) ? es : new Object[1];
 }

 /**
 * Tries to grow array to accommodate at least one more element
 * (but normally expand by about 50%), giving up (allowing retry)
 * on contention (which we expect to be rare). Call only while
 * holding lock.
 *
 * @param array the heap array
 * @param oldCap the length of the array
 */
 private void tryGrow(Object[] array, int oldCap) {
 lock.unlock(); // must release and then re-acquire main lock
 Object[] newArray = null;
 if (allocationSpinLock == 0 &&
 ALLOCATIONSPINLOCK.compareAndSet(this, 0, 1)) {
 try {
 int growth = (oldCap < 64)
 ? (oldCap + 2) // grow faster if small
 : (oldCap >> 1);
 int newCap = ArraysSupport.newLength(oldCap, 1, growth);
 if (queue == array)
 newArray = new Object[newCap];
 } finally {
 allocationSpinLock = 0;
 }
 }
 if (newArray == null) // back off if another thread is allocating
 Thread.yield();
 lock.lock();
 if (newArray != null && queue == array) {
 queue = newArray;
 System.arraycopy(array, 0, newArray, 0, oldCap);
 }
 }

 /**
 * Mechanics for poll(). Call only while holding lock.
 */
 private E dequeue() {
 // assert lock.isHeldByCurrentThread();
 final Object[] es;
 final E result;

 if ((result = (E) ((es = queue)[0])) != null) {
 final int n;
 final E x = (E) es[(n = --size)];
 es[n] = null;
 if (n > 0) {
 final Comparator<? super E> cmp;
 if ((cmp = comparator) == null)
 siftDownComparable(0, x, es, n);
 else
 siftDownUsingComparator(0, x, es, n, cmp);
 }
 }
 return result;
 }

 /**
 * Inserts item x at position k, maintaining heap invariant by
 * promoting x up the tree until it is greater than or equal to
 * its parent, or is the root.
 *
 * To simplify and speed up coercions and comparisons, the
 * Comparable and Comparator versions are separated into different
 * methods that are otherwise identical. (Similarly for siftDown.)
 *
 * @param k the position to fill
 * @param x the item to insert
 * @param es the heap array
 */
 private static <T> void siftUpComparable(int k, T x, Object[] es) {
 Comparable<? super T> key = (Comparable<? super T>) x;
 while (k > 0) {
 int parent = (k - 1) >>> 1;
 Object e = es[parent];
 if (key.compareTo((T) e) >= 0)
 break;
 es[k] = e;
 k = parent;
 }
 es[k] = key;
 }

 private static <T> void siftUpUsingComparator(
 int k, T x, Object[] es, Comparator<? super T> cmp) {
 while (k > 0) {
 int parent = (k - 1) >>> 1;
 Object e = es[parent];
 if (cmp.compare(x, (T) e) >= 0)
 break;
 es[k] = e;
 k = parent;
 }
 es[k] = x;
 }

 /**
 * Inserts item x at position k, maintaining heap invariant by
 * demoting x down the tree repeatedly until it is less than or
 * equal to its children or is a leaf.
 *
 * @param k the position to fill
 * @param x the item to insert
 * @param es the heap array
 * @param n heap size
 */
 private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
 // assert n > 0;
 Comparable<? super T> key = (Comparable<? super T>)x;
 int half = n >>> 1; // loop while a non-leaf
 while (k < half) {
 int child = (k << 1) + 1; // assume left child is least
 Object c = es[child];
 int right = child + 1;
 if (right < n &&
 ((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
 c = es[child = right];
 if (key.compareTo((T) c) <= 0)
 break;
 es[k] = c;
 k = child;
 }
 es[k] = key;
 }

 private static <T> void siftDownUsingComparator(
 int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
 // assert n > 0;
 int half = n >>> 1;
 while (k < half) {
 int child = (k << 1) + 1;
 Object c = es[child];
 int right = child + 1;
 if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
 c = es[child = right];
 if (cmp.compare(x, (T) c) <= 0)
 break;
 es[k] = c;
 k = child;
 }
 es[k] = x;
 }

 /**
 * Establishes the heap invariant (described above) in the entire tree,
 * assuming nothing about the order of the elements prior to the call.
 * This classic algorithm due to Floyd (1964) is known to be O(size).
 */
 private void heapify() {
 final Object[] es = queue;
 int n = size, i = (n >>> 1) - 1;
 final Comparator<? super E> cmp;
 if ((cmp = comparator) == null)
 for (; i >= 0; i--)
 siftDownComparable(i, (E) es[i], es, n);
 else
 for (; i >= 0; i--)
 siftDownUsingComparator(i, (E) es[i], es, n, cmp);
 }

 /**
 * Inserts the specified element into this priority queue.
 *
 * @param e the element to add
 * @return {@code true} (as specified by {@link Collection#add})
 * @throws ClassCastException if the specified element cannot be compared
 * with elements currently in the priority queue according to the
 * priority queue's ordering
 * @throws NullPointerException if the specified element is null
 */
 public boolean add(E e) {
 return offer(e);
 }

 /**
 * Inserts the specified element into this priority queue.
 * As the queue is unbounded, this method will never return {@code false}.
 *
 * @param e the element to add
 * @return {@code true} (as specified by {@link Queue#offer})
 * @throws ClassCastException if the specified element cannot be compared
 * with elements currently in the priority queue according to the
 * priority queue's ordering
 * @throws NullPointerException if the specified element is null
 */
 public boolean offer(E e) {
 if (e == null)
 throw new NullPointerException();
 final ReentrantLock lock = this.lock;
 lock.lock();
 int n, cap;
 Object[] es;
 while ((n = size) >= (cap = (es = queue).length))
 tryGrow(es, cap);
 try {
 final Comparator<? super E> cmp;
 if ((cmp = comparator) == null)
 siftUpComparable(n, e, es);
 else
 siftUpUsingComparator(n, e, es, cmp);
 size = n + 1;
 notEmpty.signal();
 } finally {
 lock.unlock();
 }
 return true;
 }

 /**
 * Inserts the specified element into this priority queue.
 * As the queue is unbounded, this method will never block.
 *
 * @param e the element to add
 * @throws ClassCastException if the specified element cannot be compared
 * with elements currently in the priority queue according to the
 * priority queue's ordering
 * @throws NullPointerException if the specified element is null
 */
 public void put(E e) {
 offer(e); // never need to block
 }

 /**
 * Inserts the specified element into this priority queue.
 * As the queue is unbounded, this method will never block or
 * return {@code false}.
 *
 * @param e the element to add
 * @param timeout This parameter is ignored as the method never blocks
 * @param unit This parameter is ignored as the method never blocks
 * @return {@code true} (as specified by
 * {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer})
 * @throws ClassCastException if the specified element cannot be compared
 * with elements currently in the priority queue according to the
 * priority queue's ordering
 * @throws NullPointerException if the specified element is null
 */
 public boolean offer(E e, long timeout, TimeUnit unit) {
 return offer(e); // never need to block
 }

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

 public E take() throws InterruptedException {
 final ReentrantLock lock = this.lock;
 lock.lockInterruptibly();
 E result;
 try {
 while ( (result = dequeue()) == null)
 notEmpty.await();
 } finally {
 lock.unlock();
 }
 return result;
 }

 public E poll(long timeout, TimeUnit unit) throws InterruptedException {
 long nanos = unit.toNanos(timeout);
 final ReentrantLock lock = this.lock;
 lock.lockInterruptibly();
 E result;
 try {
 while ( (result = dequeue()) == null && nanos > 0)
 nanos = notEmpty.awaitNanos(nanos);
 } finally {
 lock.unlock();
 }
 return result;
 }

 public E peek() {
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 return (E) queue[0];
 } finally {
 lock.unlock();
 }
 }

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

 public int size() {
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 return size;
 } finally {
 lock.unlock();
 }
 }

 /**
 * Always returns {@code Integer.MAX_VALUE} because
 * a {@code PriorityBlockingQueue} is not capacity constrained.
 * @return {@code Integer.MAX_VALUE} always
 */
 public int remainingCapacity() {
 return Integer.MAX_VALUE;
 }

 private int indexOf(Object o) {
 if (o != null) {
 final Object[] es = queue;
 for (int i = 0, n = size; i < n; i++)
 if (o.equals(es[i]))
 return i;
 }
 return -1;
 }

 /**
 * Removes the ith element from queue.
 */
 private void removeAt(int i) {
 final Object[] es = queue;
 final int n = size - 1;
 if (n == i) // removed last element
 es[i] = null;
 else {
 E moved = (E) es[n];
 es[n] = null;
 final Comparator<? super E> cmp;
 if ((cmp = comparator) == null)
 siftDownComparable(i, moved, es, n);
 else
 siftDownUsingComparator(i, moved, es, n, cmp);
 if (es[i] == moved) {
 if (cmp == null)
 siftUpComparable(i, moved, es);
 else
 siftUpUsingComparator(i, moved, es, cmp);
 }
 }
 size = n;
 }

 /**
 * Removes a single instance of the specified element from this queue,
 * if it is present. More formally, removes an element {@code e} such
 * that {@code o.equals(e)}, if this queue contains one or more such
 * elements. Returns {@code true} if and only if this queue contained
 * the specified element (or equivalently, if this queue changed as a
 * result of the call).
 *
 * @param o element to be removed from this queue, if present
 * @return {@code true} if this queue changed as a result of the call
 */
 public boolean remove(Object o) {
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 int i = indexOf(o);
 if (i == -1)
 return false;
 removeAt(i);
 return true;
 } finally {
 lock.unlock();
 }
 }

 /**
 * Identity-based version for use in Itr.remove.
 *
 * @param o element to be removed from this queue, if present
 */
 void removeEq(Object o) {
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 final Object[] es = queue;
 for (int i = 0, n = size; i < n; i++) {
 if (o == es[i]) {
 removeAt(i);
 break;
 }
 }
 } finally {
 lock.unlock();
 }
 }

 /**
 * Returns {@code true} if this queue contains the specified element.
 * More formally, returns {@code true} if and only if this queue contains
 * at least one element {@code e} such that {@code o.equals(e)}.
 *
 * @param o object to be checked for containment in this queue
 * @return {@code true} if this queue contains the specified element
 */
 public boolean contains(Object o) {
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 return indexOf(o) != -1;
 } finally {
 lock.unlock();
 }
 }

 public String toString() {
 return Helpers.collectionToString(this);
 }

 /**
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 */
 public int drainTo(Collection<? super E> c) {
 return drainTo(c, Integer.MAX_VALUE);
 }

 /**
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 */
 public int drainTo(Collection<? super E> c, int maxElements) {
 Objects.requireNonNull(c);
 if (c == this)
 throw new IllegalArgumentException();
 if (maxElements <= 0)
 return 0;
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 int n = Math.min(size, maxElements);
 for (int i = 0; i < n; i++) {
 c.add((E) queue[0]); // In this order, in case add() throws.
 dequeue();
 }
 return n;
 } finally {
 lock.unlock();
 }
 }

 /**
 * Atomically removes all of the elements from this queue.
 * The queue will be empty after this call returns.
 */
 public void clear() {
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 final Object[] es = queue;
 for (int i = 0, n = size; i < n; i++)
 es[i] = null;
 size = 0;
 } finally {
 lock.unlock();
 }
 }

 /**
 * Returns an array containing all of the elements in this queue.
 * The returned array elements are in no particular order.
 *
 * The returned array will be "safe" in that no references to it are
 * maintained by this queue. (In other words, this method must allocate
 * a new array). The caller is thus free to modify the returned array.
 *
 * This method acts as bridge between array-based and collection-based
 * APIs.
 *
 * @return an array containing all of the elements in this queue
 */
 public Object[] toArray() {
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 return Arrays.copyOf(queue, size);
 } finally {
 lock.unlock();
 }
 }

 /**
 * Returns an array containing all of the elements in this queue; the
 * runtime type of the returned array is that of the specified array.
 * The returned array elements are in no particular order.
 * If the queue fits in the specified array, it is returned therein.
 * Otherwise, a new array is allocated with the runtime type of the
 * specified array and the size of this queue.
 *
 * If this queue fits in the specified array with room to spare
 * (i.e., the array has more elements than this queue), the element in
 * the array immediately following the end of the queue is set to
 * {@code null}.
 *
 * Like the {@link #toArray()} method, this method acts as bridge between
 * array-based and collection-based APIs. Further, this method allows
 * precise control over the runtime type of the output array, and may,
 * under certain circumstances, be used to save allocation costs.
 *
 * Suppose {@code x} is a queue known to contain only strings.
 * The following code can be used to dump the queue into a newly
 * allocated array of {@code String}:
 *
 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
 *
 * Note that {@code toArray(new Object[0])} is identical in function to
 * {@code toArray()}.
 *
 * @param a the array into which the elements of the queue are to
 * be stored, if it is big enough; otherwise, a new array of the
 * same runtime type is allocated for this purpose
 * @return an array containing all of the elements in this queue
 * @throws ArrayStoreException if the runtime type of the specified array
 * is not a supertype of the runtime type of every element in
 * this queue
 * @throws NullPointerException if the specified array is null
 */
 public <T> T[] toArray(T[] a) {
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 int n = size;
 if (a.length < n)
 // Make a new array of a's runtime type, but my contents:
 return (T[]) Arrays.copyOf(queue, size, a.getClass());
 System.arraycopy(queue, 0, a, 0, n);
 if (a.length > n)
 a[n] = null;
 return a;
 } finally {
 lock.unlock();
 }
 }

 /**
 * Returns an iterator over the elements in this queue. The
 * iterator does not return the elements in any particular order.
 *
 * The returned iterator is
 * <a href="package-summary.html#Weakly">weakly consistent</a>.
 *
 * @return an iterator over the elements in this queue
 */
 public Iterator<E> iterator() {
 return new Itr(toArray());
 }

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

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

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

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

 public void remove() {
 if (lastRet < 0)
 throw new IllegalStateException();
 removeEq(array[lastRet]);
 lastRet = -1;
 }

 public void forEachRemaining(Consumer<? super E> action) {
 Objects.requireNonNull(action);
 final Object[] es = array;
 int i;
 if ((i = cursor) < es.length) {
 lastRet = -1;
 cursor = es.length;
 for (; i < es.length; i++)
 action.accept((E) es[i]);
 lastRet = es.length - 1;
 }
 }
 }

 /**
 * Saves this queue to a stream (that is, serializes it).
 *
 * For compatibility with previous version of this class, elements
 * are first copied to a java.util.PriorityQueue, which is then
 * serialized.
 *
 * @param s the stream
 * @throws java.io.IOException if an I/O error occurs
 */
 private void writeObject(java.io.ObjectOutputStream s)
 throws java.io.IOException {
 lock.lock();
 try {
 // avoid zero capacity argument
 q = new PriorityQueue<E>(Math.max(size, 1), comparator);
 q.addAll(this);
 s.defaultWriteObject();
 } finally {
 q = null;
 lock.unlock();
 }
 }

 /**
 * Reconstitutes this queue from a stream (that is, deserializes it).
 * @param s the stream
 * @throws ClassNotFoundException if the class of a serialized object
 * could not be found
 * @throws java.io.IOException if an I/O error occurs
 */
 private void readObject(java.io.ObjectInputStream s)
 throws java.io.IOException, ClassNotFoundException {
 try {
 s.defaultReadObject();
 int sz = q.size();
 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, sz);
 this.queue = new Object[Math.max(1, sz)];
 comparator = q.comparator();
 addAll(q);
 } finally {
 q = null;
 }
 }

 /**
 * Immutable snapshot spliterator that binds to elements "late".
 */
 final class PBQSpliterator implements Spliterator<E> {
 Object[] array; // null until late-bound-initialized
 int index;
 int fence;

 PBQSpliterator() {}

 PBQSpliterator(Object[] array, int index, int fence) {
 this.array = array;
 this.index = index;
 this.fence = fence;
 }

 private int getFence() {
 if (array == null)
 fence = (array = toArray()).length;
 return fence;
 }

 public PBQSpliterator trySplit() {
 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
 return (lo >= mid) ? null :
 new PBQSpliterator(array, lo, index = mid);
 }

 public void forEachRemaining(Consumer<? super E> action) {
 Objects.requireNonNull(action);
 final int hi = getFence(), lo = index;
 final Object[] es = array;
 index = hi; // ensure exhaustion
 for (int i = lo; i < hi; i++)
 action.accept((E) es[i]);
 }

 public boolean tryAdvance(Consumer<? super E> action) {
 Objects.requireNonNull(action);
 if (getFence() > index && index >= 0) {
 action.accept((E) array[index++]);
 return true;
 }
 return false;
 }

 public long estimateSize() { return getFence() - index; }

 public int characteristics() {
 return (Spliterator.NONNULL |
 Spliterator.SIZED |
 Spliterator.SUBSIZED);
 }
 }

 /**
 * Returns a {@link Spliterator} over the elements in this queue.
 * The spliterator does not traverse elements in any particular order
 * (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
 *
 * The returned spliterator is
 * <a href="package-summary.html#Weakly">weakly consistent</a>.
 *
 * The {@code Spliterator} reports {@link Spliterator#SIZED} and
 * {@link Spliterator#NONNULL}.
 *
 * @implNote
 * The {@code Spliterator} additionally reports {@link Spliterator#SUBSIZED}.
 *
 * @return a {@code Spliterator} over the elements in this queue
 * @since 1.8
 */
 public Spliterator<E> spliterator() {
 return new PBQSpliterator();
 }

 /**
 * @throws NullPointerException {@inheritDoc}
 */
 public boolean removeIf(Predicate<? super E> filter) {
 Objects.requireNonNull(filter);
 return bulkRemove(filter);
 }

 /**
 * @throws NullPointerException {@inheritDoc}
 */
 public boolean removeAll(Collection<?> c) {
 Objects.requireNonNull(c);
 return bulkRemove(e -> c.contains(e));
 }

 /**
 * @throws NullPointerException {@inheritDoc}
 */
 public boolean retainAll(Collection<?> c) {
 Objects.requireNonNull(c);
 return bulkRemove(e -> !c.contains(e));
 }

 // A tiny bit set implementation

 private static long[] nBits(int n) {
 return new long[((n - 1) >> 6) + 1];
 }
 private static void setBit(long[] bits, int i) {
 bits[i >> 6] |= 1L << i;
 }
 private static boolean isClear(long[] bits, int i) {
 return (bits[i >> 6] & (1L << i)) == 0;
 }

 /** Implementation of bulk remove methods. */
 private boolean bulkRemove(Predicate<? super E> filter) {
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 final Object[] es = queue;
 final int end = size;
 int i;
 // Optimize for initial run of survivors
 for (i = 0; i < end && !filter.test((E) es[i]); i++)
 ;
 if (i >= end)
 return false;
 // Tolerate predicates that reentrantly access the
 // collection for read, so traverse once to find elements
 // to delete, a second pass to physically expunge.
 final int beg = i;
 final long[] deathRow = nBits(end - beg);
 deathRow[0] = 1L; // set bit 0
 for (i = beg + 1; i < end; i++)
 if (filter.test((E) es[i]))
 setBit(deathRow, i - beg);
 int w = beg;
 for (i = beg; i < end; i++)
 if (isClear(deathRow, i - beg))
 es[w++] = es[i];
 for (i = size = w; i < end; i++)
 es[i] = null;
 heapify();
 return true;
 } finally {
 lock.unlock();
 }
 }

 /**
 * @throws NullPointerException {@inheritDoc}
 */
 public void forEach(Consumer<? super E> action) {
 Objects.requireNonNull(action);
 final ReentrantLock lock = this.lock;
 lock.lock();
 try {
 final Object[] es = queue;
 for (int i = 0, n = size; i < n; i++)
 action.accept((E) es[i]);
 } finally {
 lock.unlock();
 }
 }

 // VarHandle mechanics
 private static final VarHandle ALLOCATIONSPINLOCK;
 static {
 try {
 MethodHandles.Lookup l = MethodHandles.lookup();
 ALLOCATIONSPINLOCK = l.findVarHandle(PriorityBlockingQueue.class,
 "allocationSpinLock",
 int.class);
 } catch (ReflectiveOperationException e) {
 throw new ExceptionInInitializerError(e);
 }
 }
}

[ Original von:0.18Diese Quellcodebibliothek enthält Beispiele in vielen Programmiersprachen. Man kann per Verzeichnistruktur darin navigieren. Der Code wird farblich markiert angezeigt. Datei übertragen ]