/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
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/*
*
*
*
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*
* 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.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
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.PriorityQueue;
import java.util.Queue;
import java.util.SortedSet;
import java.util.Spliterator;
import java.util.function.Consumer;
/**
* 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()} is <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}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @since 1.5
* @author Doug Lea
* @param <E> the type of elements held in this collection
*/
@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;
/**
* Condition for blocking when empty
*/
private final Condition notEmpty;
/**
* 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.lock = new ReentrantLock();
this.notEmpty = lock.newCondition();
this.comparator = comparator;
this.queue = new Object[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) {
this.lock = new ReentrantLock();
this.notEmpty = lock.newCondition();
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[] a = c.toArray();
int n = a.length;
// If c.toArray incorrectly doesn't return Object[], copy it.
if (a.getClass() != Object[].class)
a = Arrays.copyOf(a, n, Object[].class);
if (screen && (n == 1 || this.comparator != null)) {
for (int i = 0; i < n; ++i)
if (a[i] == null)
throw new NullPointerException();
}
this.queue = a;
this.size = n;
if (heapify)
heapify();
}
/**
* 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 &&
UNSAFE.compareAndSwapInt(this, allocationSpinLockOffset,
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() {
int n = size - 1;
if (n < 0)
return null;
else {
Object[] array = queue;
E result = (E) array[0];
E x = (E) array[n];
array[n] = null;
Comparator<? super E> cmp = comparator;
if (cmp == null)
siftDownComparable(0, x, array, n);
else
siftDownUsingComparator(0, x, array, n, cmp);
size = n;
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.)
* These methods are static, with heap state as arguments, to
* simplify use in light of possible comparator exceptions.
*
* @param k the position to fill
* @param x the item to insert
* @param array the heap array
*/
private static <T> void siftUpComparable(int k, T x, Object[] array) {
Comparable<? super T> key = (Comparable<? super T>) x;
while (k > 0) {
int parent = (k - 1) >>> 1;
Object e = array[parent];
if (key.compareTo((T) e) >= 0)
break;
array[k] = e;
k = parent;
}
array[k] = key;
}
private static <T> void siftUpUsingComparator(int k, T x, Object[] array,
Comparator<? super T> cmp) {
while (k > 0) {
int parent = (k - 1) >>> 1;
Object e = array[parent];
if (cmp.compare(x, (T) e) >= 0)
break;
array[k] = e;
k = parent;
}
array[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 array the heap array
* @param n heap size
*/
private static <T> void siftDownComparable(int k, T x, Object[] array,
int n) {
if (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 = array[child];
int right = child + 1;
if (right < n &&
((Comparable<? super T>) c).compareTo((T) array[right]) > 0)
c = array[child = right];
if (key.compareTo((T) c) <= 0)
break;
array[k] = c;
k = child;
}
array[k] = key;
}
}
private static <T> void siftDownUsingComparator(int k, T x, Object[] array,
int n,
Comparator<? super T> cmp) {
if (n > 0) {
int half = n >>> 1;
while (k < half) {
int child = (k << 1) + 1;
Object c = array[child];
int right = child + 1;
if (right < n && cmp.compare((T) c, (T) array[right]) > 0)
c = array[child = right];
if (cmp.compare(x, (T) c) <= 0)
break;
array[k] = c;
k = child;
}
array[k] = x;
}
}
/**
* Establishes the heap invariant (described above) in the entire tree,
* assuming nothing about the order of the elements prior to the call.
*/
private void heapify() {
Object[] array = queue;
int n = size;
int half = (n >>> 1) - 1;
Comparator<? super E> cmp = comparator;
if (cmp == null) {
for (int i = half; i >= 0; i--)
siftDownComparable(i, (E) array[i], array, n);
}
else {
for (int i = half; i >= 0; i--)
siftDownUsingComparator(i, (E) array[i], array, 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[] array;
while ((n = size) >= (cap = (array = queue).length))
tryGrow(array, cap);
try {
Comparator<? super E> cmp = comparator;
if (cmp == null)
siftUpComparable(n, e, array);
else
siftUpUsingComparator(n, e, array, 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 (size == 0) ? null : (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) {
Object[] array = queue;
int n = size;
for (int i = 0; i < n; i++)
if (o.equals(array[i]))
return i;
}
return -1;
}
/**
* Removes the ith element from queue.
*/
private void removeAt(int i) {
Object[] array = queue;
int n = size - 1;
if (n == i) // removed last element
array[i] = null;
else {
E moved = (E) array[n];
array[n] = null;
Comparator<? super E> cmp = comparator;
if (cmp == null)
siftDownComparable(i, moved, array, n);
else
siftDownUsingComparator(i, moved, array, n, cmp);
if (array[i] == moved) {
if (cmp == null)
siftUpComparable(i, moved, array);
else
siftUpUsingComparator(i, moved, array, 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
*/
void removeEQ(Object o) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] array = queue;
for (int i = 0, n = size; i < n; i++) {
if (o == array[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();
}
}
/**
* 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();
}
}
public String toString() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
int n = size;
if (n == 0)
return "[]";
StringBuilder sb = new StringBuilder();
sb.append('[');
for (int i = 0; i < n; ++i) {
Object e = queue[i];
sb.append(e == this ? "(this Collection)" : e);
if (i != n - 1)
sb.append(',').append(' ');
}
return sb.append(']').toString();
} finally {
lock.unlock();
}
}
/**
* @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) {
if (c == null)
throw new NullPointerException();
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 {
Object[] array = queue;
int n = size;
size = 0;
for (int i = 0; i < n; i++)
array[i] = null;
} 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; // index of last element, or -1 if no such
Itr(Object[] array) {
lastRet = -1;
this.array = array;
}
public boolean hasNext() {
return cursor < array.length;
}
public E next() {
if (cursor >= array.length)
throw new NoSuchElementException();
lastRet = cursor;
return (E)array[cursor++];
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
removeEQ(array[lastRet]);
lastRet = -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();
this.queue = new Object[q.size()];
comparator = q.comparator();
addAll(q);
} finally {
q = null;
}
}
// Similar to Collections.ArraySnapshotSpliterator but avoids
// commitment to toArray until needed
static final class PBQSpliterator<E> implements Spliterator<E> {
final PriorityBlockingQueue<E> queue;
Object[] array;
int index;
int fence;
PBQSpliterator(PriorityBlockingQueue<E> queue, Object[] array,
int index, int fence) {
this.queue = queue;
this.array = array;
this.index = index;
this.fence = fence;
}
final int getFence() {
int hi;
if ((hi = fence) < 0)
hi = fence = (array = queue.toArray()).length;
return hi;
}
public Spliterator<E> trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid) ? null :
new PBQSpliterator<E>(queue, array, lo, index = mid);
}
@SuppressWarnings("unchecked")
public void forEachRemaining(Consumer<? super E> action) {
Object[] a; int i, hi; // hoist accesses and checks from loop
if (action == null)
throw new NullPointerException();
if ((a = array) == null)
fence = (a = queue.toArray()).length;
if ((hi = fence) <= a.length &&
(i = index) >= 0 && i < (index = hi)) {
do { action.accept((E)a[i]); } while (++i < hi);
}
}
public boolean tryAdvance(Consumer<? super E> action) {
if (action == null)
throw new NullPointerException();
if (getFence() > index && index >= 0) {
@SuppressWarnings("unchecked") E e = (E) array[index++];
action.accept(e);
return true;
}
return false;
}
public long estimateSize() { return (long)(getFence() - index); }
public int characteristics() {
return Spliterator.NONNULL | Spliterator.SIZED | Spliterator.SUBSIZED;
}
}
/**
* Returns a {@link Spliterator} over the elements in this queue.
*
* <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<E>(this, null, 0, -1);
}
// Unsafe mechanics
private static final sun.misc.Unsafe UNSAFE;
private static final long allocationSpinLockOffset;
static {
try {
UNSAFE = sun.misc.Unsafe.getUnsafe();
Class<?> k = PriorityBlockingQueue.class;
allocationSpinLockOffset = UNSAFE.objectFieldOffset
(k.getDeclaredField("allocationSpinLock"));
} catch (Exception e) {
throw new Error(e);
}
}
}