--- jsr166/src/main/java/util/PriorityQueue.java 2003/08/30 11:44:53 1.37 +++ jsr166/src/main/java/util/PriorityQueue.java 2019/05/22 17:36:58 1.131 @@ -1,81 +1,110 @@ - package java.util; +/* + * Copyright (c) 2003, 2019, Oracle and/or its affiliates. All rights reserved. + * 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. + */ + +package java.util; + +import java.util.function.Consumer; +import java.util.function.Predicate; +// OPENJDK import jdk.internal.access.SharedSecrets; +import jdk.internal.util.ArraysSupport; /** * An unbounded priority {@linkplain Queue queue} based on a priority heap. - * This queue orders elements according to an order specified at construction - * time, which is specified in the same manner as {@link java.util.TreeSet} - * and {@link java.util.TreeMap}: elements are ordered either according to - * their natural order (see {@link Comparable}), or according to a - * {@link java.util.Comparator}, depending on which constructor is used. - *

The head of this queue is the least element with - * respect to the specified ordering. If multiple elements are tied for least - * value, the head is one of those elements. A priority queue does not permit - * null elements. - * - *

The {@link #remove()} and {@link #poll()} methods remove and - * return the head of the queue. - * - *

The {@link #element()} and {@link #peek()} methods return, but do - * not delete, the head of the queue. - * - *

A priority queue has a capacity. The capacity is the - * size of the array used internally to store the elements on the - * queue. - * It is always at least as large as the queue size. As - * elements are added to a priority queue, its capacity grows - * automatically. The details of the growth policy are not specified. - * - *

The Iterator provided in method {@link #iterator()} is not - * guaranteed to traverse the elements of the PriorityQueue in any - * particular order. If you need ordered traversal, consider using - * Arrays.sort(pq.toArray()). - * - *

Note that this implementation is not synchronized. - * Multiple threads should not access a PriorityQueue - * instance concurrently if any of the threads modifies the list - * structurally. Instead, use the thread-safe {@link + * The elements of the priority queue are ordered according to their + * {@linkplain Comparable natural ordering}, or by a {@link Comparator} + * provided at queue construction time, depending on which constructor is + * used. A priority queue does not permit {@code null} elements. + * A priority queue relying on natural ordering also does not permit + * insertion of non-comparable objects (doing so may result in + * {@code ClassCastException}). + * + *

The head of this queue is the least element + * with respect to the specified ordering. If multiple elements are + * tied for least value, the head is one of those elements -- ties are + * broken arbitrarily. The queue retrieval operations {@code poll}, + * {@code remove}, {@code peek}, and {@code element} access the + * element at the head of the queue. + * + *

A priority queue is unbounded, but has an internal + * capacity governing the size of an array used to store the + * elements on the queue. It is always at least as large as the queue + * size. As elements are added to a priority queue, its capacity + * grows automatically. The details of the growth policy are not + * specified. + * + *

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 priority queue in any particular order. If you need ordered + * traversal, consider using {@code Arrays.sort(pq.toArray())}. + * + *

Note that this implementation is not synchronized. + * Multiple threads should not access a {@code PriorityQueue} + * instance concurrently if any of the threads modifies the queue. + * Instead, use the thread-safe {@link * java.util.concurrent.PriorityBlockingQueue} class. * - * - *

Implementation note: this implementation provides O(log(n)) time - * for the insertion methods (offer, poll, - * remove() and add) methods; linear time for the - * remove(Object) and contains(Object) methods; and - * constant time for the retrieval methods (peek, - * element, and size). + *

Implementation note: this implementation provides + * O(log(n)) time for the enqueuing and dequeuing methods + * ({@code offer}, {@code poll}, {@code remove()} and {@code add}); + * linear time for the {@code remove(Object)} and {@code contains(Object)} + * methods; and constant time for the retrieval methods + * ({@code peek}, {@code element}, and {@code size}). * *

This class is a member of the - * + * * Java Collections Framework. + * * @since 1.5 - * @author Josh Bloch + * @author Josh Bloch, Doug Lea + * @param the type of elements held in this queue */ +@SuppressWarnings("unchecked") public class PriorityQueue extends AbstractQueue - implements Queue, java.io.Serializable { + implements java.io.Serializable { private static final long serialVersionUID = -7720805057305804111L; 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] 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[1], assuming the queue is - * nonempty. (A one-based array is used in preference to the traditional - * zero-based array to simplify parent and child calculations.) - * - * queue.length must be >= 2, even if size == 0. + * 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; + transient Object[] queue; // non-private to simplify nested class access /** * The number of elements in the priority queue. */ - private int size = 0; + int size; /** * The comparator, or null if priority queue uses elements' @@ -87,398 +116,439 @@ public class PriorityQueue extends Ab * The number of times this priority queue has been * structurally modified. See AbstractList for gory details. */ - private transient int modCount = 0; + transient int modCount; // non-private to simplify nested class access /** - * Creates a PriorityQueue with the default initial capacity - * (11) that orders its elements according to their natural - * ordering (using Comparable). + * Creates a {@code PriorityQueue} with the default initial + * capacity (11) that orders its elements according to their + * {@linkplain Comparable natural ordering}. */ public PriorityQueue() { this(DEFAULT_INITIAL_CAPACITY, null); } /** - * Creates a PriorityQueue with the specified initial capacity - * that orders its elements according to their natural ordering - * (using Comparable). - * - * @param initialCapacity the initial capacity for this priority queue. - * @throws IllegalArgumentException if initialCapacity is less - * than 1 + * Creates a {@code PriorityQueue} 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 PriorityQueue(int initialCapacity) { this(initialCapacity, null); } /** - * Creates a PriorityQueue with the specified initial capacity + * Creates a {@code PriorityQueue} with the default initial capacity and + * whose elements are ordered according to the specified comparator. + * + * @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. + * @since 1.8 + */ + public PriorityQueue(Comparator comparator) { + this(DEFAULT_INITIAL_CAPACITY, comparator); + } + + /** + * Creates a {@code PriorityQueue} 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 used to order this priority queue. - * If null then the order depends on the elements' natural - * ordering. - * @throws IllegalArgumentException if initialCapacity is less - * than 1 + * @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 PriorityQueue(int initialCapacity, + public PriorityQueue(int initialCapacity, Comparator comparator) { + // Note: This restriction of at least one is not actually needed, + // but continues for 1.5 compatibility if (initialCapacity < 1) throw new IllegalArgumentException(); - this.queue = new Object[initialCapacity + 1]; + this.queue = new Object[initialCapacity]; this.comparator = comparator; } /** - * Common code to initialize underlying queue array across - * constructors below. + * Creates a {@code PriorityQueue} containing the elements in the + * specified collection. If the specified collection is an instance of + * a {@link SortedSet} or is another {@code 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 */ - private void initializeArray(Collection c) { - int sz = c.size(); - int initialCapacity = (int)Math.min((sz * 110L) / 100, - Integer.MAX_VALUE - 1); - if (initialCapacity < 1) - initialCapacity = 1; - - this.queue = new Object[initialCapacity + 1]; + public PriorityQueue(Collection c) { + if (c instanceof SortedSet) { + SortedSet ss = (SortedSet) c; + this.comparator = (Comparator) ss.comparator(); + initElementsFromCollection(ss); + } + else if (c instanceof PriorityQueue) { + PriorityQueue pq = (PriorityQueue) c; + this.comparator = (Comparator) pq.comparator(); + initFromPriorityQueue(pq); + } + else { + this.comparator = null; + initFromCollection(c); + } } /** - * Initially fill elements of the queue array under the - * knowledge that it is sorted or is another PQ, in which - * case we can just place the elements in the order presented. + * Creates a {@code PriorityQueue} containing the elements in the + * specified priority queue. This priority queue will be + * ordered according to the same ordering as the given priority + * queue. + * + * @param c the priority queue whose elements are to be placed + * into this priority queue + * @throws ClassCastException if elements of {@code c} cannot be + * compared to one another according to {@code c}'s + * ordering + * @throws NullPointerException if the specified priority queue or any + * of its elements are null */ - private void fillFromSorted(Collection c) { - for (Iterator i = c.iterator(); i.hasNext(); ) - queue[++size] = i.next(); + public PriorityQueue(PriorityQueue c) { + this.comparator = (Comparator) c.comparator(); + initFromPriorityQueue(c); } /** - * Initially fill elements of the queue array that is not to our knowledge - * sorted, so we must rearrange the elements to guarantee the heap - * invariant. + * Creates a {@code PriorityQueue} containing the elements in the + * specified sorted set. This priority queue will be ordered + * according to the same ordering as the given sorted set. + * + * @param c the sorted set whose elements are to be placed + * into this priority queue + * @throws ClassCastException if elements of the specified sorted + * set cannot be compared to one another according to the + * sorted set's ordering + * @throws NullPointerException if the specified sorted set or any + * of its elements are null */ - private void fillFromUnsorted(Collection c) { - for (Iterator i = c.iterator(); i.hasNext(); ) - queue[++size] = i.next(); - heapify(); + public PriorityQueue(SortedSet c) { + this.comparator = (Comparator) c.comparator(); + initElementsFromCollection(c); } - /** - * Creates a PriorityQueue containing the elements in the - * specified collection. The priority queue has an initial - * capacity of 110% of the size of the specified collection or 1 - * if the collection is empty. If the specified collection is an - * instance of a {@link java.util.SortedSet} or is another - * PriorityQueue, the priority queue will be sorted - * according to the same comparator, or according to its elements' - * natural order if the collection is sorted according to its - * elements' natural order. Otherwise, the priority queue is - * ordered according to its elements' natural order. - * - * @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 c or any element within it - * is null - */ - public PriorityQueue(Collection c) { - initializeArray(c); - if (c instanceof SortedSet) { - // @fixme double-cast workaround for compiler - SortedSet s = (SortedSet) (SortedSet)c; - comparator = (Comparator)s.comparator(); - fillFromSorted(s); - } else if (c instanceof PriorityQueue) { - PriorityQueue s = (PriorityQueue) c; - comparator = (Comparator)s.comparator(); - fillFromSorted(s); + /** Ensures that queue[0] exists, helping peek() and poll(). */ + private static Object[] ensureNonEmpty(Object[] es) { + return (es.length > 0) ? es : new Object[1]; + } + + private void initFromPriorityQueue(PriorityQueue c) { + if (c.getClass() == PriorityQueue.class) { + this.queue = ensureNonEmpty(c.toArray()); + this.size = c.size(); } else { - comparator = null; - fillFromUnsorted(c); + initFromCollection(c); } } + private void initElementsFromCollection(Collection c) { + Object[] es = c.toArray(); + int len = es.length; + // If c.toArray incorrectly doesn't return Object[], copy it. + if (es.getClass() != Object[].class) + es = Arrays.copyOf(es, len, Object[].class); + if (len == 1 || this.comparator != null) + for (Object e : es) + if (e == null) + throw new NullPointerException(); + this.queue = ensureNonEmpty(es); + this.size = len; + } + /** - * Creates a PriorityQueue containing the elements in the - * specified collection. The priority queue has an initial - * capacity of 110% of the size of the specified collection or 1 - * if the collection is empty. This priority queue will be sorted - * according to the same comparator as the given collection, or - * according to its elements' natural order if the collection is - * sorted according to its elements' natural order. + * Initializes queue array with elements from the given Collection. * - * @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 c or any element within it - * is null + * @param c the collection */ - public PriorityQueue(PriorityQueue c) { - initializeArray(c); - comparator = (Comparator)c.comparator(); - fillFromSorted(c); + private void initFromCollection(Collection c) { + initElementsFromCollection(c); + heapify(); } /** - * Creates a PriorityQueue containing the elements in the - * specified collection. The priority queue has an initial - * capacity of 110% of the size of the specified collection or 1 - * if the collection is empty. This priority queue will be sorted - * according to the same comparator as the given collection, or - * according to its elements' natural order if the collection is - * sorted according to its elements' natural order. + * Increases the capacity of the array. * - * @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 c or any element within it - * is null + * @param minCapacity the desired minimum capacity */ - public PriorityQueue(SortedSet c) { - initializeArray(c); - comparator = (Comparator)c.comparator(); - fillFromSorted(c); + private void grow(int minCapacity) { + int oldCapacity = queue.length; + // Double size if small; else grow by 50% + int newCapacity = ArraysSupport.newLength(oldCapacity, + minCapacity - oldCapacity, /* minimum growth */ + oldCapacity < 64 ? oldCapacity + 2 : oldCapacity >> 1 + /* preferred growth */); + queue = Arrays.copyOf(queue, newCapacity); } /** - * Resize array, if necessary, to be able to hold given index + * Inserts the specified element into this priority queue. + * + * @return {@code true} (as specified by {@link Collection#add}) + * @throws ClassCastException if the specified element cannot be + * compared with elements currently in this priority queue + * according to the priority queue's ordering + * @throws NullPointerException if the specified element is null */ - private void grow(int index) { - int newlen = queue.length; - if (index < newlen) // don't need to grow - return; - if (index == Integer.MAX_VALUE) - throw new OutOfMemoryError(); - while (newlen <= index) { - if (newlen >= Integer.MAX_VALUE / 2) // avoid overflow - newlen = Integer.MAX_VALUE; - else - newlen <<= 2; - } - Object[] newQueue = new Object[newlen]; - System.arraycopy(queue, 0, newQueue, 0, queue.length); - queue = newQueue; + public boolean add(E e) { + return offer(e); } - - - // Queue Methods /** - * Add the specified element to this priority queue. + * Inserts the specified element into this priority queue. * - * @return true - * @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. + * @return {@code true} (as specified by {@link Queue#offer}) + * @throws ClassCastException if the specified element cannot be + * compared with elements currently in this priority queue + * according to the priority queue's ordering + * @throws NullPointerException if the specified element is null */ - public boolean offer(E o) { - if (o == null) + public boolean offer(E e) { + if (e == null) throw new NullPointerException(); modCount++; - ++size; - - // Grow backing store if necessary - if (size >= queue.length) - grow(size); - - queue[size] = o; - fixUp(size); + int i = size; + if (i >= queue.length) + grow(i + 1); + siftUp(i, e); + size = i + 1; return true; } - public E poll() { - if (size == 0) - return null; - return remove(); + public E peek() { + return (E) queue[0]; } - public E peek() { - return (E) queue[1]; + 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; } - // Collection Methods - the first two override to update docs + /** + * 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) { + int i = indexOf(o); + if (i == -1) + return false; + else { + removeAt(i); + return true; + } + } /** - * Adds the specified element to this queue. - * @return true (as per the general contract of - * Collection.add). + * Identity-based version for use in Itr.remove. * - * @throws NullPointerException {@inheritDoc} - * @throws ClassCastException if the specified element cannot be compared - * with elements currently in the priority queue according - * to the priority queue's ordering. - */ - public boolean add(E o) { - return super.add(o); - } - - - /** - * Adds all of the elements in the specified collection to this queue. - * The behavior of this operation is undefined if - * the specified collection is modified while the operation is in - * progress. (This implies that the behavior of this call is undefined if - * the specified collection is this queue, and this queue is nonempty.) - *

- * This implementation iterates over the specified collection, and adds - * each object returned by the iterator to this collection, in turn. - * @throws NullPointerException {@inheritDoc} - * @throws ClassCastException if any element cannot be compared - * with elements currently in the priority queue according - * to the priority queue's ordering. + * @param o element to be removed from this queue, if present */ - public boolean addAll(Collection c) { - return super.addAll(c); + void removeEq(Object o) { + final Object[] es = queue; + for (int i = 0, n = size; i < n; i++) { + if (o == es[i]) { + removeAt(i); + break; + } + } } + /** + * 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) { + return indexOf(o) >= 0; + } /** - * Removes a single instance of the specified element from this - * queue, if it is present. More formally, - * removes an element e such that (o==null ? e==null : - * o.equals(e)), if the queue contains one or more such - * elements. Returns true if the queue contained the - * specified element (or equivalently, if the queue changed as a - * result of the call). + * Returns an array containing all of the elements in this queue. + * The elements are in no particular order. * - *

This implementation iterates over the queue looking for the - * specified element. If it finds the element, it removes the element - * from the queue using the iterator's remove method.

+ *

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 boolean remove(Object o) { - if (o == null) - return false; + public Object[] toArray() { + return Arrays.copyOf(queue, size); + } - if (comparator == null) { - for (int i = 1; i <= size; i++) { - if (((Comparable)queue[i]).compareTo((E)o) == 0) { - removeAt(i); - return true; - } - } - } else { - for (int i = 1; i <= size; i++) { - if (comparator.compare((E)queue[i], (E)o) == 0) { - removeAt(i); - return true; - } - } - } - return false; + /** + * 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 the queue fits in the specified array with room to spare + * (i.e., the array has more elements than the queue), the element in + * the array immediately following the end of the collection 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}: + * + * 

 {@code String[] y = x.toArray(new String[0]);}
+ * + * 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[] toArray(T[] a) { + final int size = this.size; + if (a.length < size) + // 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, size); + if (a.length > size) + a[size] = null; + return a; } /** * Returns an iterator over the elements in this queue. The iterator * does not return the elements in any particular order. * - * @return an iterator over the elements in this queue. + * @return an iterator over the elements in this queue */ public Iterator iterator() { return new Itr(); } - private class Itr implements Iterator { - + private final class Itr implements Iterator { /** * Index (into queue array) of element to be returned by * subsequent call to next. */ - private int cursor = 1; + private int cursor; /** * Index of element returned by most recent call to next, * unless that element came from the forgetMeNot list. - * Reset to 0 if element is deleted by a call to remove. - */ - private int lastRet = 0; - - /** - * The modCount value that the iterator believes that the backing - * List should have. If this expectation is violated, the iterator - * has detected concurrent modification. + * Set to -1 if element is deleted by a call to remove. */ - private int expectedModCount = modCount; + private int lastRet = -1; /** - * A list of elements that were moved from the unvisited portion of + * A queue of elements that were moved from the unvisited portion of * the heap into the visited portion as a result of "unlucky" element * removals during the iteration. (Unlucky element removals are those - * that require a fixup instead of a fixdown.) We must visit all of + * that require a siftup instead of a siftdown.) We must visit all of * the elements in this list to complete the iteration. We do this * after we've completed the "normal" iteration. * * We expect that most iterations, even those involving removals, - * will not use need to store elements in this field. + * will not need to store elements in this field. */ - private ArrayList forgetMeNot = null; + private ArrayDeque forgetMeNot; /** * Element returned by the most recent call to next iff that * element was drawn from the forgetMeNot list. */ - private Object lastRetElt = null; + private E lastRetElt; + + /** + * The modCount value that the iterator believes that the backing + * Queue should have. If this expectation is violated, the iterator + * has detected concurrent modification. + */ + private int expectedModCount = modCount; + + Itr() {} // prevent access constructor creation public boolean hasNext() { - return cursor <= size || forgetMeNot != null; + return cursor < size || + (forgetMeNot != null && !forgetMeNot.isEmpty()); } public E next() { - checkForComodification(); - E result; - if (cursor <= size) { - result = (E) queue[cursor]; - lastRet = cursor++; - } - else if (forgetMeNot == null) - throw new NoSuchElementException(); - else { - int remaining = forgetMeNot.size(); - result = forgetMeNot.remove(remaining - 1); - if (remaining == 1) - forgetMeNot = null; - lastRet = 0; - lastRetElt = result; + if (expectedModCount != modCount) + throw new ConcurrentModificationException(); + if (cursor < size) + return (E) queue[lastRet = cursor++]; + if (forgetMeNot != null) { + lastRet = -1; + lastRetElt = forgetMeNot.poll(); + if (lastRetElt != null) + return lastRetElt; } - return result; + throw new NoSuchElementException(); } public void remove() { - checkForComodification(); - - if (lastRet != 0) { + if (expectedModCount != modCount) + throw new ConcurrentModificationException(); + if (lastRet != -1) { E moved = PriorityQueue.this.removeAt(lastRet); - lastRet = 0; - if (moved == null) { + lastRet = -1; + if (moved == null) cursor--; - } else { + else { if (forgetMeNot == null) - forgetMeNot = new ArrayList(); + forgetMeNot = new ArrayDeque<>(); forgetMeNot.add(moved); } } else if (lastRetElt != null) { - PriorityQueue.this.remove(lastRetElt); + PriorityQueue.this.removeEq(lastRetElt); lastRetElt = null; } else { throw new IllegalStateException(); } - expectedModCount = modCount; } - - final void checkForComodification() { - if (modCount != expectedModCount) - throw new ConcurrentModificationException(); - } } public int size() { @@ -486,60 +556,63 @@ public class PriorityQueue extends Ab } /** - * Remove all elements from the priority queue. + * Removes all of the elements from this priority queue. + * The queue will be empty after this call returns. */ public void clear() { modCount++; - - // Null out element references to prevent memory leak - for (int i=1; i<=size; i++) - queue[i] = null; - + final Object[] es = queue; + for (int i = 0, n = size; i < n; i++) + es[i] = null; size = 0; } - /** - * Removes and returns the first element from queue. - */ - public E remove() { - if (size == 0) - throw new NoSuchElementException(); - modCount++; - - E result = (E) queue[1]; - queue[1] = queue[size]; - queue[size--] = null; // Drop extra ref to prevent memory leak - if (size > 1) - fixDown(1); + public E poll() { + final Object[] es; + final E result; + if ((result = (E) ((es = queue)[0])) != null) { + modCount++; + final int n; + final E x = (E) es[(n = --size)]; + es[n] = null; + if (n > 0) { + final Comparator cmp; + if ((cmp = comparator) == null) + siftDownComparable(0, x, es, n); + else + siftDownUsingComparator(0, x, es, n, cmp); + } + } return result; } /** - * Removes and returns the ith element from queue. (Recall that queue - * is one-based, so 1 <= i <= size.) + * Removes the ith element from queue. * - * Normally this method leaves the elements at positions from 1 up to i-1, - * inclusive, untouched. Under these circumstances, it returns null. - * Occasionally, in order to maintain the heap invariant, it must move - * the last element of the list to some index in the range [2, i-1], - * and move the element previously at position (i/2) to position i. - * Under these circumstances, this method returns the element that was - * previously at the end of the list and is now at some position between - * 2 and i-1 inclusive. - */ - private E removeAt(int i) { - assert i > 0 && i <= size; + * Normally this method leaves the elements at up to i-1, + * inclusive, untouched. Under these circumstances, it returns + * null. Occasionally, in order to maintain the heap invariant, + * it must swap a later element of the list with one earlier than + * i. Under these circumstances, this method returns the element + * that was previously at the end of the list and is now at some + * position before i. This fact is used by iterator.remove so as to + * avoid missing traversing elements. + */ + E removeAt(int i) { + // assert i >= 0 && i < size; + final Object[] es = queue; modCount++; - - E moved = (E) queue[size]; - queue[i] = moved; - queue[size--] = null; // Drop extra ref to prevent memory leak - if (i <= size) { - fixDown(i); - if (queue[i] == moved) { - fixUp(i); - if (queue[i] != moved) + int s = --size; + if (s == i) // removed last element + es[i] = null; + else { + E moved = (E) es[s]; + es[s] = null; + siftDown(i, moved); + if (es[i] == moved) { + siftUp(i, moved); + if (es[i] != moved) return moved; } } @@ -547,129 +620,351 @@ public class PriorityQueue extends Ab } /** - * Establishes the heap invariant (described above) assuming the heap - * satisfies the invariant except possibly for the leaf-node indexed by k - * (which may have a nextExecutionTime less than its parent's). - * - * This method functions by "promoting" queue[k] up the hierarchy - * (by swapping it with its parent) repeatedly until queue[k] - * is greater than or equal to its parent. - */ - private void fixUp(int k) { - if (comparator == null) { - while (k > 1) { - int j = k >> 1; - if (((Comparable)queue[j]).compareTo((E)queue[k]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } - } else { - while (k > 1) { - int j = k >>> 1; - if (comparator.compare((E)queue[j], (E)queue[k]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } + * 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 + */ + private void siftUp(int k, E x) { + if (comparator != null) + siftUpUsingComparator(k, x, queue, comparator); + else + siftUpComparable(k, x, queue); + } + + private static void siftUpComparable(int k, T x, Object[] es) { + Comparable key = (Comparable) 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 void siftUpUsingComparator( + int k, T x, Object[] es, Comparator 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; } /** - * Establishes the heap invariant (described above) in the subtree - * rooted at k, which is assumed to satisfy the heap invariant except - * possibly for node k itself (which may be greater than its children). - * - * This method functions by "demoting" queue[k] down the hierarchy - * (by swapping it with its smaller child) repeatedly until queue[k] - * is less than or equal to its children. - */ - private void fixDown(int k) { - int j; - if (comparator == null) { - while ((j = k << 1) <= size && (j > 0)) { - if (j)queue[j]).compareTo((E)queue[j+1]) > 0) - j++; // j indexes smallest kid - - if (((Comparable)queue[k]).compareTo((E)queue[j]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } - } else { - while ((j = k << 1) <= size && (j > 0)) { - if (j 0) - j++; // j indexes smallest kid - if (comparator.compare((E)queue[k], (E)queue[j]) <= 0) - break; - Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; - k = j; - } + * 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 + */ + private void siftDown(int k, E x) { + if (comparator != null) + siftDownUsingComparator(k, x, queue, size, comparator); + else + siftDownComparable(k, x, queue, size); + } + + private static void siftDownComparable(int k, T x, Object[] es, int n) { + // assert n > 0; + Comparable key = (Comparable)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) 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 void siftDownUsingComparator( + int k, T x, Object[] es, int n, Comparator 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() { - for (int i = size/2; i >= 1; i--) - fixDown(i); + final Object[] es = queue; + int n = size, i = (n >>> 1) - 1; + final Comparator 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); } /** - * Returns the comparator used to order this collection, or null - * if this collection is sorted according to its elements natural ordering - * (using Comparable). - * - * @return the comparator used to order this collection, or null - * if this collection is sorted according to its elements natural ordering. + * Returns the comparator used to order the elements in this + * queue, or {@code null} if this queue is sorted according to + * the {@linkplain Comparable natural ordering} of its elements. + * + * @return the comparator used to order this queue, or + * {@code null} if this queue is sorted according to the + * natural ordering of its elements */ public Comparator comparator() { return comparator; } /** - * Save the state of the instance to a stream (that - * is, serialize it). + * Saves this queue to a stream (that is, serializes it). * - * @serialData The length of the array backing the instance is - * emitted (int), followed by all of its elements (each an - * Object) in the proper order. * @param s the stream + * @throws java.io.IOException if an I/O error occurs + * @serialData The length of the array backing the instance is + * emitted (int), followed by all of its elements + * (each an {@code Object}) in the proper order. */ private void writeObject(java.io.ObjectOutputStream s) - throws java.io.IOException{ + throws java.io.IOException { // Write out element count, and any hidden stuff s.defaultWriteObject(); - // Write out array length - s.writeInt(queue.length); + // Write out array length, for compatibility with 1.5 version + s.writeInt(Math.max(2, size + 1)); - // Write out all elements in the proper order. - for (int i=0; iArrayList instance from a stream (that is, - * deserialize it). + * Reconstitutes the {@code PriorityQueue} instance 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 { // Read in size, and any hidden stuff s.defaultReadObject(); - // Read in array length and allocate array - int arrayLength = s.readInt(); - queue = new Object[arrayLength]; - - // Read in all elements in the proper order. - for (int i=0; ilate-binding + * and fail-fast {@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 {@code Spliterator} reports {@link Spliterator#SIZED}, + * {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}. + * Overriding implementations should document the reporting of additional + * characteristic values. + * + * @return a {@code Spliterator} over the elements in this queue + * @since 1.8 + */ + public final Spliterator spliterator() { + return new PriorityQueueSpliterator(0, -1, 0); + } + + final class PriorityQueueSpliterator implements Spliterator { + private int index; // current index, modified on advance/split + private int fence; // -1 until first use + private int expectedModCount; // initialized when fence set + + /** Creates new spliterator covering the given range. */ + PriorityQueueSpliterator(int origin, int fence, int expectedModCount) { + this.index = origin; + this.fence = fence; + this.expectedModCount = expectedModCount; + } + + private int getFence() { // initialize fence to size on first use + int hi; + if ((hi = fence) < 0) { + expectedModCount = modCount; + hi = fence = size; + } + return hi; + } + + public PriorityQueueSpliterator trySplit() { + int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; + return (lo >= mid) ? null : + new PriorityQueueSpliterator(lo, index = mid, expectedModCount); + } + + public void forEachRemaining(Consumer action) { + if (action == null) + throw new NullPointerException(); + if (fence < 0) { fence = size; expectedModCount = modCount; } + final Object[] es = queue; + int i, hi; E e; + for (i = index, index = hi = fence; i < hi; i++) { + if ((e = (E) es[i]) == null) + break; // must be CME + action.accept(e); + } + if (modCount != expectedModCount) + throw new ConcurrentModificationException(); + } + + public boolean tryAdvance(Consumer action) { + if (action == null) + throw new NullPointerException(); + if (fence < 0) { fence = size; expectedModCount = modCount; } + int i; + if ((i = index) < fence) { + index = i + 1; + E e; + if ((e = (E) queue[i]) == null + || modCount != expectedModCount) + throw new ConcurrentModificationException(); + action.accept(e); + return true; + } + return false; + } + + public long estimateSize() { + return getFence() - index; + } + + public int characteristics() { + return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL; + } + } + + /** + * @throws NullPointerException {@inheritDoc} + */ + public boolean removeIf(Predicate 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 filter) { + final int expectedModCount = ++modCount; + 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) { + if (modCount != expectedModCount) + throw new ConcurrentModificationException(); + return false; + } + // Tolerate predicates that reentrantly access the collection for + // read (but writers still get CME), 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); + if (modCount != expectedModCount) + throw new ConcurrentModificationException(); + 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; + } + + /** + * @throws NullPointerException {@inheritDoc} + */ + public void forEach(Consumer action) { + Objects.requireNonNull(action); + final int expectedModCount = modCount; + final Object[] es = queue; + for (int i = 0, n = size; i < n; i++) + action.accept((E) es[i]); + if (expectedModCount != modCount) + throw new ConcurrentModificationException(); + } }