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/*
* Copyright 2015 The Netty Project
*
* The Netty Project licenses this file to you under the Apache License,
* version 2.0 (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package io.netty.util.internal;
import java.util.AbstractQueue;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;
import static io.netty.util.internal.PriorityQueueNode.INDEX_NOT_IN_QUEUE;
/**
* A priority queue which uses natural ordering of elements. Elements are also required to be of type
* {@link PriorityQueueNode} for the purpose of maintaining the index in the priority queue.
* @param The object that is maintained in the queue.
*/
public final class DefaultPriorityQueue extends AbstractQueue
implements PriorityQueue {
private static final PriorityQueueNode[] EMPTY_ARRAY = new PriorityQueueNode[0];
private final Comparator comparator;
private T[] queue;
private int size;
@SuppressWarnings("unchecked")
public DefaultPriorityQueue(Comparator comparator, int initialSize) {
this.comparator = ObjectUtil.checkNotNull(comparator, "comparator");
queue = (T[]) (initialSize != 0 ? new PriorityQueueNode[initialSize] : EMPTY_ARRAY);
}
@Override
public int size() {
return size;
}
@Override
public boolean isEmpty() {
return size == 0;
}
@Override
public boolean contains(Object o) {
if (!(o instanceof PriorityQueueNode)) {
return false;
}
PriorityQueueNode node = (PriorityQueueNode) o;
return contains(node, node.priorityQueueIndex(this));
}
@Override
public boolean containsTyped(T node) {
return contains(node, node.priorityQueueIndex(this));
}
@Override
public void clear() {
for (int i = 0; i < size; ++i) {
T node = queue[i];
if (node != null) {
node.priorityQueueIndex(this, INDEX_NOT_IN_QUEUE);
queue[i] = null;
}
}
size = 0;
}
@Override
public boolean offer(T e) {
if (e.priorityQueueIndex(this) != INDEX_NOT_IN_QUEUE) {
throw new IllegalArgumentException("e.priorityQueueIndex(): " + e.priorityQueueIndex(this) +
" (expected: " + INDEX_NOT_IN_QUEUE + ") + e: " + e);
}
// Check that the array capacity is enough to hold values by doubling capacity.
if (size >= queue.length) {
// Use a policy which allows for a 0 initial capacity. Same policy as JDK's priority queue, double when
// "small", then grow by 50% when "large".
queue = Arrays.copyOf(queue, queue.length + ((queue.length < 64) ?
(queue.length + 2) :
(queue.length >>> 1)));
}
bubbleUp(size++, e);
return true;
}
@Override
public T poll() {
if (size == 0) {
return null;
}
T result = queue[0];
result.priorityQueueIndex(this, INDEX_NOT_IN_QUEUE);
T last = queue[--size];
queue[size] = null;
if (size != 0) { // Make sure we don't add the last element back.
bubbleDown(0, last);
}
return result;
}
@Override
public T peek() {
return (size == 0) ? null : queue[0];
}
@SuppressWarnings("unchecked")
@Override
public boolean remove(Object o) {
final T node;
try {
node = (T) o;
} catch (ClassCastException e) {
return false;
}
return removeTyped(node);
}
@Override
public boolean removeTyped(T node) {
int i = node.priorityQueueIndex(this);
if (!contains(node, i)) {
return false;
}
node.priorityQueueIndex(this, INDEX_NOT_IN_QUEUE);
if (--size == 0 || size == i) {
// If there are no node left, or this is the last node in the array just remove and return.
queue[i] = null;
return true;
}
// Move the last element where node currently lives in the array.
T moved = queue[i] = queue[size];
queue[size] = null;
// priorityQueueIndex will be updated below in bubbleUp or bubbleDown
// Make sure the moved node still preserves the min-heap properties.
if (comparator.compare(node, moved) < 0) {
bubbleDown(i, moved);
} else {
bubbleUp(i, moved);
}
return true;
}
@Override
public void priorityChanged(T node) {
int i = node.priorityQueueIndex(this);
if (!contains(node, i)) {
return;
}
// Preserve the min-heap property by comparing the new priority with parents/children in the heap.
if (i == 0) {
bubbleDown(i, node);
} else {
// Get the parent to see if min-heap properties are violated.
int iParent = (i - 1) >>> 1;
T parent = queue[iParent];
if (comparator.compare(node, parent) < 0) {
bubbleUp(i, node);
} else {
bubbleDown(i, node);
}
}
}
@Override
public Object[] toArray() {
return Arrays.copyOf(queue, size);
}
@SuppressWarnings("unchecked")
@Override
public X[] toArray(X[] a) {
if (a.length < size) {
return (X[]) Arrays.copyOf(queue, size, a.getClass());
}
System.arraycopy(queue, 0, a, 0, size);
if (a.length > size) {
a[size] = null;
}
return a;
}
/**
* This iterator does not return elements in any particular order.
*/
@Override
public Iterator iterator() {
return new PriorityQueueIterator();
}
private final class PriorityQueueIterator implements Iterator {
private int index;
@Override
public boolean hasNext() {
return index < size;
}
@Override
public T next() {
if (index >= size) {
throw new NoSuchElementException();
}
return queue[index++];
}
@Override
public void remove() {
throw new UnsupportedOperationException("remove");
}
}
private boolean contains(PriorityQueueNode node, int i) {
return i >= 0 && i < size && node.equals(queue[i]);
}
private void bubbleDown(int k, T node) {
final int half = size >>> 1;
while (k < half) {
// Compare node to the children of index k.
int iChild = (k << 1) + 1;
T child = queue[iChild];
// Make sure we get the smallest child to compare against.
int rightChild = iChild + 1;
if (rightChild < size && comparator.compare(child, queue[rightChild]) > 0) {
child = queue[iChild = rightChild];
}
// If the bubbleDown node is less than or equal to the smallest child then we will preserve the min-heap
// property by inserting the bubbleDown node here.
if (comparator.compare(node, child) <= 0) {
break;
}
// Bubble the child up.
queue[k] = child;
child.priorityQueueIndex(this, k);
// Move down k down the tree for the next iteration.
k = iChild;
}
// We have found where node should live and still satisfy the min-heap property, so put it in the queue.
queue[k] = node;
node.priorityQueueIndex(this, k);
}
private void bubbleUp(int k, T node) {
while (k > 0) {
int iParent = (k - 1) >>> 1;
T parent = queue[iParent];
// If the bubbleUp node is less than the parent, then we have found a spot to insert and still maintain
// min-heap properties.
if (comparator.compare(node, parent) >= 0) {
break;
}
// Bubble the parent down.
queue[k] = parent;
parent.priorityQueueIndex(this, k);
// Move k up the tree for the next iteration.
k = iParent;
}
// We have found where node should live and still satisfy the min-heap property, so put it in the queue.
queue[k] = node;
node.priorityQueueIndex(this, k);
}
}
