/*
 * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
 *
 * This software is open source.
 * See the bottom of this file for the licence.
 */

package org.dom4j.util;

import java.lang.ref.WeakReference;

/**
 * <p>
 * <code>PerThreadSingleton</code> is an implementation of the
 * SingletonStrategy used to provide common factory access to a single object
 * instance based on an implementation strategy for one object instance per
 * thread. This is useful in replace of the ThreadLocal usage.
 * </p>
 * 
 * @author <a href="mailto:ddlucas@users.sourceforge.net">David Lucas </a>
 * @version $Revision: 1.3 $
 */

public class PerThreadSingleton<T> implements SingletonStrategy<T> {
    private String singletonClassName = null;

    private ThreadLocal<WeakReference<T>> perThreadCache = new ThreadLocal<WeakReference<T>>();

    public PerThreadSingleton() {
    }

    public void reset() {
        perThreadCache = new ThreadLocal<WeakReference<T>>();
    }

    public T instance() {
        T singletonInstancePerThread = null;
        // use weak reference to prevent cyclic reference during GC
        WeakReference<T> ref = (WeakReference<T>) perThreadCache.get();
        // singletonInstancePerThread=perThreadCache.get();
        // if (singletonInstancePerThread==null) {
        if (ref == null || ref.get() == null) {
            Class<T> clazz = null;
            try {
                clazz = (Class<T>) Thread.currentThread().getContextClassLoader().loadClass(
                        singletonClassName);
                singletonInstancePerThread = clazz.newInstance();
            } catch (Exception ignore) {
                try {
                    clazz = (Class<T>) Class.forName(singletonClassName);
                    singletonInstancePerThread = clazz.newInstance();
                } catch (Exception ignore2) {
                }
            }
            perThreadCache.set(new WeakReference<T>(singletonInstancePerThread));
        } else {
            singletonInstancePerThread = ref.get();
        }
        return singletonInstancePerThread;
    }

    public void setSingletonClassName(String singletonClassName) {
        this.singletonClassName = singletonClassName;
    }

}

/*
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided that the
 * following conditions are met:
 * 
 * 1. Redistributions of source code must retain copyright statements and
 * notices. Redistributions must also contain a copy of this document.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 * 
 * 3. The name "DOM4J" must not be used to endorse or promote products derived
 * from this Software without prior written permission of MetaStuff, Ltd. For
 * written permission, please contact dom4j-info@metastuff.com.
 * 
 * 4. Products derived from this Software may not be called "DOM4J" nor may
 * "DOM4J" appear in their names without prior written permission of MetaStuff,
 * Ltd. DOM4J is a registered trademark of MetaStuff, Ltd.
 * 
 * 5. Due credit should be given to the DOM4J Project - http://www.dom4j.org
 * 
 * THIS SOFTWARE IS PROVIDED BY METASTUFF, LTD. AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL METASTUFF, LTD. OR ITS CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
 */
