package org.javaldap.server.util;

/*
The JavaLDAP Server
Copyright (C) 2000  Clayton Donley (donley@linc-dev.com) - 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.

*/

/**
 * ObjectPool cleanup thread based on code from Javaworld
 * Issue: August, 1998
 * @author: Thomas E. Davis
 */
import java.util.Hashtable;
import java.util.Enumeration;

public abstract class ObjectPool {

	private long expirationTime;
	private long lastCheckOut;

	private Hashtable locked;
	private Hashtable unlocked;

	private CleanUpThread cleaner;



	/**
	 * ObjectPool constructor comment.
	 */
	public ObjectPool() {

		expirationTime = ( 1000 * 30 ); // 30 seconds

		locked = new Hashtable();
		unlocked = new Hashtable();

		lastCheckOut = System.currentTimeMillis();

		cleaner = new CleanUpThread( this, expirationTime );
		cleaner.start();
	}
	public synchronized void checkIn( Object o ) {
		if( o != null ) {
			locked.remove( o );
			unlocked.put( o, new Long( System.currentTimeMillis() ) );
		}
	}
	public synchronized Object checkOut() throws Exception {
		long now = System.currentTimeMillis();
		lastCheckOut = now;
		Object o;

		if( unlocked.size() > 0 ) {
			Enumeration e = unlocked.keys();

			while( e.hasMoreElements() ) {
				o = e.nextElement();

				if( validate( o ) ) {
					unlocked.remove( o );
					locked.put( o, new Long( now ) );
					return( o );
				} else {
					unlocked.remove( o );
					expire( o );
					o = null;
				}
			}
		}

		o = create();

		locked.put( o, new Long( now ) );
		return( o );
	}
	public synchronized void cleanUp() {
		Object o;

		long now = System.currentTimeMillis();

		Enumeration e = unlocked.keys();

		while( e.hasMoreElements() ) {
			o = e.nextElement();

			if( ( now - ( ( Long ) unlocked.get( o ) ).longValue() ) > expirationTime ) {
				unlocked.remove( o );
				expire( o );
				o = null;
			}
		}

		//System.gc();
	}
	public abstract Object create() throws Exception;
	public abstract void expire( Object o );
	public abstract boolean validate( Object o );
}