/*
* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package org.jboss.messaging.util.prioritylinkedlist;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
/**
* A basic priority linked list
*
* It implements this by maintaining an
* individual LinkedList for each priority level.
*
* @author <a href="mailto:tim.fox@jboss.com>Tim Fox</a>
* @version <tt>$Revision: 1174 $</tt>
*
* $Id: BasicPrioritizedDeque.java 1174 2006-08-02 14:14:32Z timfox $
*/
public class BasicPriorityLinkedList implements PriorityLinkedList
{
protected LinkedList[] linkedLists;
protected int priorities;
protected int size;
public BasicPriorityLinkedList(int priorities)
{
this.priorities = priorities;
initDeques();
}
public void addFirst(Object obj, int priority)
{
linkedLists[priority].addFirst(obj);
size++;
}
public void addLast(Object obj, int priority)
{
linkedLists[priority].addLast(obj);
size++;
}
public Object removeFirst()
{
Object obj = null;
//Initially we are just using a simple prioritization algorithm:
//Highest priority refs always get returned first.
//This could cause starvation of lower priority refs.
//TODO - A better prioritization algorithm
for (int i = priorities - 1; i >= 0; i--)
{
LinkedList ll = linkedLists[i];
if (!ll.isEmpty())
{
obj = ll.removeFirst();
break;
}
}
if (obj != null)
{
size--;
}
return obj;
}
public Object removeLast()
{
Object obj = null;
//Initially we are just using a simple prioritization algorithm:
//Lowest priority refs always get returned first.
//TODO - A better prioritization algorithm
for (int i = 0; i < priorities; i++)
{
LinkedList ll = linkedLists[i];
if (!ll.isEmpty())
{
obj = ll.removeLast();
}
if (obj != null)
{
break;
}
}
if (obj != null)
{
size--;
}
return obj;
}
public Object peekFirst()
{
Object obj = null;
//Initially we are just using a simple prioritization algorithm:
//Highest priority refs always get returned first.
//This could cause starvation of lower priority refs.
//TODO - A better prioritization algorithm
for (int i = priorities - 1; i >= 0; i--)
{
LinkedList ll = linkedLists[i];
if (!ll.isEmpty())
{
obj = ll.getFirst();
}
if (obj != null)
{
break;
}
}
return obj;
}
public List getAll()
{
List all = new ArrayList();
for (int i = priorities - 1; i >= 0; i--)
{
LinkedList deque = linkedLists[i];
all.addAll(deque);
}
return all;
}
public void clear()
{
initDeques();
}
public int size()
{
return size;
}
public boolean isEmpty()
{
return size == 0;
}
public ListIterator iterator()
{
return new PriorityLinkedListIterator(linkedLists);
}
protected void initDeques()
{
linkedLists = new LinkedList[priorities];
for (int i = 0; i < priorities; i++)
{
linkedLists[i] = new LinkedList();
}
size = 0;
}
}