Java tutorial
/* * 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; /** * 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}). * * <p>This class and its iterator implement all of the <em>optional</em> * methods of the {@link Collection} and {@link Iterator} interfaces. * The Iterator provided in method {@link #iterator()} and the * Spliterator provided in method {@link #spliterator()} are <em>not</em> * 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 <em>remove</em> some or all elements in priority order and * place them in another collection. * * <p>Operations on this class make no guarantees about the ordering * of elements with equal priority. If you need to enforce an * ordering, you can define custom classes or comparators that use a * secondary key to break ties in primary priority values. For * example, here is a class that applies first-in-first-out * tie-breaking to comparable elements. To use it, you would insert a * {@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(0); * final long seqNum; * final E entry; * public FIFOEntry(E entry) { * seqNum = seq.getAndIncrement(); * this.entry = entry; * } * public E getEntry() { return entry; } * public int compareTo(FIFOEntry<E> other) { * int res = entry.compareTo(other.entry); * if (res == 0 && other.entry != this.entry) * res = (seqNum < other.seqNum ? -1 : 1); * return res; * } * }}</pre> * * <p>This class is a member of the * <a href="{@docRoot}/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; /** * The maximum size of array to allocate. * Some VMs reserve some header words in an array. * Attempts to allocate larger arrays may result in * OutOfMemoryError: Requested array size exceeds VM limit */ private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; /** * 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. */ 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 PriorityQueue}, this * priority queue will be ordered according to the same ordering. * Otherwise, this priority queue will be ordered according to the * {@linkplain Comparable natural ordering} of its elements. * * @param c the collection whose elements are to be placed * into this priority queue * @throws ClassCastException if elements of the specified collection * cannot be compared to one another according to the priority * queue's ordering * @throws NullPointerException if the specified collection or any * of its elements are null */ public PriorityBlockingQueue(Collection<? extends E> c) { 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.toArray incorrectly doesn't return Object[], copy it. if (es.getClass() != Object[].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 newCap = oldCap + ((oldCap < 64) ? (oldCap + 2) : // grow faster if small (oldCap >> 1)); if (newCap - MAX_ARRAY_SIZE > 0) { // possible overflow int minCap = oldCap + 1; if (minCap < 0 || minCap > MAX_ARRAY_SIZE) throw new OutOfMemoryError(); newCap = MAX_ARRAY_SIZE; } if (newCap > oldCap && 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. * * <p>The returned array will be "safe" in that no references to it are * maintained by this queue. (In other words, this method must allocate * a new array). The caller is thus free to modify the returned array. * * <p>This method acts as bridge between array-based and collection-based * APIs. * * @return an array containing all of the elements in this queue */ public Object[] toArray() { final ReentrantLock lock = this.lock; lock.lock(); try { return 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. * * <p>If this queue fits in the specified array with room to spare * (i.e., the array has more elements than this queue), the element in * the array immediately following the end of the queue is set to * {@code null}. * * <p>Like the {@link #toArray()} method, this method acts as bridge between * array-based and collection-based APIs. Further, this method allows * precise control over the runtime type of the output array, and may, * under certain circumstances, be used to save allocation costs. * * <p>Suppose {@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. * * <p>The returned iterator is * <a href="package-summary.html#Weakly"><i>weakly consistent</i></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). * * <p>The returned spliterator is * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. * * <p>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); } } }