CopyOnWriteList.java

/*
 * Created on 15-Mar-2006
 * Created by Paul Gardner
 * Copyright (C) 2006 Aelitis, All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * This program 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 General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 * 
 * AELITIS, SAS au capital de 46,603.30 euros
 * 8 Allee Lenotre, La Grille Royale, 78600 Le Mesnil le Roi, France.
 *
 */

package com.aelitis.azureus.core.util;

import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

//import org.gudy.azureus2.core3.util.AEDiagnostics;
//import org.gudy.azureus2.core3.util.AEDiagnosticsEvidenceGenerator;
import org.gudy.azureus2.core3.util.IndentWriter;

public class 
CopyOnWriteList<T> 
implements Iterable<T>
{
	private static final boolean LOG_STATS = false;
	
	//private int mutation_count = 0;
	
	private List<T>	list = Collections.EMPTY_LIST;
	
	private boolean	visible = false;
	
	private int initialCapacity;
	
	private static CopyOnWriteList stats;
	
	static {
		if (LOG_STATS) {
			stats = new CopyOnWriteList(10);
//			AEDiagnostics.addEvidenceGenerator(new AEDiagnosticsEvidenceGenerator() {
//				public void generate(IndentWriter writer) {
//					writer.println("COWList Info");
//					writer.indent();
//					try {
//						long count = 0;
//						long size = 0;
//						for (Iterator iter = stats.iterator(); iter.hasNext();) {
//							WeakReference wf = (WeakReference) iter.next();
//							CopyOnWriteList cowList = (CopyOnWriteList) wf.get();
//							if (cowList != null) {
//								count++;
//								size += cowList.size();
//							}
//						}
//						writer.println(count + " lists with " + size + " total entries");
//						writer.println((size/count) + " avg size");
//					} catch (Throwable t) {
//					} finally {
//						writer.exdent();
//					}
//				}
//			});
		}
	}
	
	/**
	 * @param i
	 */
	public CopyOnWriteList(int initialCapacity) {
		this.initialCapacity = initialCapacity;
		if (stats != null) {
			stats.add(new WeakReference(this));
		}
	}

	/**
	 * 
	 */
	public CopyOnWriteList() {
		// Smaller default initial capacity as most of our lists are small
		// Last check on 7/24/2008: 444 lists with 456 total entries
		this.initialCapacity = 1;
		if (stats != null) {
			stats.add(new WeakReference(this));
		}
	}

	public void
	add(
		T	obj )
	{
		synchronized( this ){
			
			if ( visible ){
				
				List<T>	new_list = new ArrayList<T>( list );
				
				//mutated();
				
				new_list.add( obj );
			
				list	= new_list;
			
				visible = false;
				
			}else{
				if (list == Collections.EMPTY_LIST) {
					list = new ArrayList<T>(initialCapacity);
				}
				
				list.add( obj );
			}
		}
	}
	
	public boolean
	remove(
		T	obj )
	{
		synchronized( this ){
			
			if ( visible ){

				List<T>	new_list = new ArrayList<T>( list );
				
				//mutated();
				
				boolean result = new_list.remove( obj );
			
				list	= new_list;
						
				visible = false;
				
				return( result );
				
			}else{
				
				return( list.remove( obj ));
			}
		}
	}
	
	public void
	clear()
	{
		synchronized( this ){
								
			list	= Collections.EMPTY_LIST;
			
			visible = false;
		}
	}
	
	public boolean
	contains(
		T	obj )
	{
		synchronized( this ){

			return( list.contains( obj ));
		}
	}
	
	public Iterator<T>
	iterator()
	{
		synchronized( this ){

			visible = true;
			
			return( new CopyOnWriteListIterator( list.iterator()));
		}
	}
	
	public List<T>
	getList()
	{
			// TODO: we need to either make this a read-only-list or obey the copy-on-write semantics correctly...
		
		synchronized( this ){

			visible = true;
			
			return( list );
		}
	}
	
	public int
	size()
	{
		synchronized( this ){

			return( list.size());
		}
	}
	
	public boolean 
	isEmpty() 
	{
		synchronized( this ){

			return list.isEmpty();
		}
	}
	
	public Object[]
	toArray()
	{
		synchronized( this ){

			return( list.toArray());
		}
	}
	
	public T[]
  	toArray(
  		T[]	 x )
  	{
		synchronized( this ){

			return( list.toArray(x));
		}
  	}
	
	/*
	private void
	mutated()
	{
		mutation_count++;
		
		if ( mutation_count%10 == 0 ){
			
			System.out.println( this + ": mut=" + mutation_count );
		}
	}
	*/
	
	private class
	CopyOnWriteListIterator
		implements Iterator<T>
	{
		private Iterator<T>	it;
		private T			last;
		
		protected
		CopyOnWriteListIterator(
			Iterator<T>		_it )
		{
			it		= _it;
		}
		
		public boolean
		hasNext()
		{
			return( it.hasNext());
		}
		
		public T
		next()
		{
			last	= it.next();
			
			return( last );
		}
		
		public void
		remove()
		{
				// don't actually remove it from the iterator. can't go backwards with this iterator so this is
				// not a problem
			
			if ( last == null ){
			
				throw( new IllegalStateException( "next has not been called!" ));
			}
			
			CopyOnWriteList.this.remove( last );
		}
	}

	public int getInitialCapacity() {
		return initialCapacity;
	}

	public void setInitialCapacity(int initialCapacity) {
		this.initialCapacity = initialCapacity;
	}
}