/*
* Copyright 2005 JBoss Inc
*
* Licensed 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 org.drools.core.util;
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF 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.
*/
import org.drools.core.spi.Activation;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.util.Comparator;
import java.util.NoSuchElementException;
public class BinaryHeapQueue
implements
Queue,
Externalizable {
protected static final transient Logger log = LoggerFactory.getLogger(BinaryHeapQueue.class);
/** The default capacity for a binary heap. */
private final static int DEFAULT_CAPACITY = 13;
/** The comparator used to order the elements */
private Comparator comparator;
/** The number of elements currently in this heap. */
private volatile int size;
/** The elements in this heap. */
private Activation[] elements;
public BinaryHeapQueue() {
}
/**
* Constructs a new <code>BinaryHeap</code> that will use the given
* comparator to order its elements.
*
* @param comparator the comparator used to order the elements, null
* means use natural order
*/
public BinaryHeapQueue(final Comparator comparator) {
this(comparator,
BinaryHeapQueue.DEFAULT_CAPACITY);
}
/**
* Constructs a new <code>BinaryHeap</code>.
*
* @param comparator the comparator used to order the elements, null
* means use natural order
* @param capacity the initial capacity for the heap
* @throws IllegalArgumentException if <code>capacity</code> is <= <code>0</code>
*/
public BinaryHeapQueue(final Comparator comparator,
final int capacity) {
if (capacity <= 0) {
throw new IllegalArgumentException("invalid capacity");
}
//+1 as 0 is noop
this.elements = new Activation[capacity + 1];
this.comparator = comparator;
}
//-----------------------------------------------------------------------
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
comparator = (Comparator) in.readObject();
elements = (Activation[]) in.readObject();
size = in.readInt();
}
public void writeExternal(ObjectOutput out) throws IOException {
out.writeObject(comparator);
out.writeObject(elements);
out.writeInt(size);
}
/**
* Clears all elements from queue.
*/
public synchronized void clear() {
this.elements = new Activation[this.elements.length]; // for gc
this.size = 0;
}
public Activation[] getAndClear() {
Activation[] queue = ( Activation[] )this.elements;
this.elements = new Activation[this.elements.length]; // for gc
this.size = 0;
return queue;
}
/**
* Tests if queue is empty.
*
* @return <code>true</code> if queue is empty; <code>false</code>
* otherwise.
*/
public synchronized boolean isEmpty() {
return this.size == 0;
}
/**
* Tests if queue is full.
*
* @return <code>true</code> if queue is full; <code>false</code>
* otherwise.
*/
public synchronized boolean isFull() {
//+1 as Queueable 0 is noop
return this.elements.length == this.size + 1;
}
/**
* Returns the number of elements in this heap.
*
* @return the number of elements in this heap
*/
public synchronized int size() {
return this.size;
}
public synchronized Activation peek() {
return this.elements[1];
}
/**
* Inserts an Queueable into queue.
*
* @param element the Queueable to be inserted
*/
public synchronized void enqueue(final Activation element) {
if ( isFull() ) {
grow();
}
percolateUpMaxHeap( element );
element.setQueued(true);
if ( log.isTraceEnabled() ) {
log.trace( "Queue Added {} {}", element.getQueueIndex(), element);
}
}
/**
* Returns the Queueable on top of heap and remove it.
*
* @return the Queueable at top of heap
* @throws NoSuchElementException if <code>isEmpty() == true</code>
*/
public synchronized Activation dequeue() throws NoSuchElementException {
if ( isEmpty() ) {
return null;
}
final Activation result = this.elements[1];
dequeue(result.getQueueIndex());
return result;
}
public synchronized Activation dequeue(Activation activation) {
return dequeue(activation.getQueueIndex());
}
synchronized Activation dequeue(final int index) {
if ( index < 1 || index > this.size ) {
//throw new NoSuchElementException();
return null;
}
final Activation result = this.elements[index];
if ( log.isTraceEnabled() ) {
log.trace( "Queue Removed {} {}", result.getQueueIndex(), result);
}
setElement( index,
this.elements[this.size] );
this.elements[this.size] = null;
this.size--;
if ( this.size != 0 && index <= this.size ) {
int compareToParent = 0;
if ( index > 1 ) {
compareToParent = compare( this.elements[index],
this.elements[index / 2] );
}
if ( index > 1 && compareToParent > 0 ) {
percolateUpMaxHeap( index );
} else {
percolateDownMaxHeap( index );
}
}
result.setQueued(false);
result.setQueueIndex(-1);
return result;
}
/**
* Percolates element down heap from the position given by the index.
* <p>
* Assumes it is a maximum heap.
*
* @param index the index of the element
*/
protected void percolateDownMaxHeap(final int index) {
final Activation element = elements[index];
int hole = index;
while ((hole * 2) <= size) {
int child = hole * 2;
// if we have a right child and that child can not be percolated
// up then move onto other child
if (child != size && compare(elements[child + 1], elements[child]) > 0) {
child++;
}
// if we found resting place of bubble then terminate search
if (compare(elements[child], element) <= 0) {
break;
}
setElement( hole, elements[child] );
hole = child;
}
setElement( hole, element);
}
/**
* Percolates element up heap from from the position given by the index.
* <p>
* Assume it is a maximum heap.
*
* @param index the index of the element to be percolated up
*/
protected void percolateUpMaxHeap(final int index) {
int hole = index;
Activation element = elements[hole];
while (hole > 1 && compare(element, elements[hole / 2]) > 0) {
// save element that is being pushed down
// as the element "bubble" is percolated up
final int next = hole / 2;
setElement( hole, elements[next] );
hole = next;
}
setElement( hole, element );
}
/**
* Percolates a new element up heap from the bottom.
* <p>
* Assume it is a maximum heap.
*
* @param element the element
*/
protected void percolateUpMaxHeap(final Activation element) {
setElement( ++size, element );
percolateUpMaxHeap(size);
}
/**
* Compares two objects using the comparator if specified, or the
* natural order otherwise.
*
* @param a the first object
* @param b the second object
* @return -ve if a less than b, 0 if they are equal, +ve if a greater than b
*/
private int compare(final Activation a,
final Activation b) {
return this.comparator.compare( a,
b );
}
/**
* Increases the size of the heap to support additional elements
*/
private void grow() {
final Activation[] elements = new Activation[this.elements.length * 2];
System.arraycopy( this.elements,
0,
elements,
0,
this.elements.length );
this.elements = elements;
}
/**
*
* @param index
* @param element
*/
private void setElement(final int index,
final Activation element) {
this.elements[index] = element;
element.setQueueIndex(index);
}
public synchronized Object[] toArray(Object a[]) {
if ( a.length < this.size ) {
a = (Object[]) java.lang.reflect.Array.newInstance( a.getClass().getComponentType(),
this.size );
}
System.arraycopy( this.elements,
1,
a,
0,
this.size );
if ( a.length > this.size ) {
a[this.size] = null;
}
return a;
}
}