void siftDownUsingComparator(int k, T x, Object[] array,
int n,
Comparator 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 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 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 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 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.
*
* The returned array will be "safe" in that no references to it are
* maintained by this queue. (In other words, this method must allocate
* a new array). The caller is thus free to modify the returned array.
*
*
This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this queue
*/
public Object[] toArray() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return Arrays.copyOf(queue, size);
} finally {
lock.unlock();
}
}
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 c) {
return drainTo(c, Integer.MAX_VALUE);
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public int drainTo(Collection 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.
*
*
If this queue fits in the specified array with room to spare
* (i.e., the array has more elements than this queue), the element in
* the array immediately following the end of the queue is set to
* {@code null}.
*
*
Like the {@link #toArray()} method, this method acts as bridge between
* array-based and collection-based APIs. Further, this method allows
* precise control over the runtime type of the output array, and may,
* under certain circumstances, be used to save allocation costs.
*
*
Suppose {@code x} is a queue known to contain only strings.
* The following code can be used to dump the queue into a newly
* allocated array of {@code String}:
*
*
{@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 ReentrantLock lock = this.lock;
lock.lock();
try {
int n = size;
if (a.length < n)
// Make a new array of a's runtime type, but my contents:
return (T[]) Arrays.copyOf(queue, size, a.getClass());
System.arraycopy(queue, 0, a, 0, n);
if (a.length > n)
a[n] = null;
return a;
} finally {
lock.unlock();
}
}
/**
* Returns an iterator over the elements in this queue. The
* iterator does not return the elements in any particular order.
*
* The returned iterator is a "weakly consistent" iterator that
* will never throw {@link java.util.ConcurrentModificationException
* ConcurrentModificationException}, and guarantees to traverse
* elements as they existed upon construction of the iterator, and
* may (but is not guaranteed to) reflect any modifications
* subsequent to construction.
*
* @return an iterator over the elements in this queue
*/
public Iterator iterator() {
return new Itr(toArray());
}
/**
* Snapshot iterator that works off copy of underlying q array.
*/
final class Itr implements Iterator {
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.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
lock.lock();
try {
// avoid zero capacity argument
q = new PriorityQueue(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).
*/
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;
}
}
// 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);
}
}
}