/*
* Copyright (c) 2005, The Regents of the University of California, through
* Lawrence Berkeley National Laboratory (subject to receipt of any required
* approvals from the U.S. Dept. of Energy). All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* (1) Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* (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) Neither the name of the University of California, Lawrence Berkeley
* National Laboratory, U.S. Dept. of Energy nor the names of its contributors
* may be used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS 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 THE COPYRIGHT OWNER OR 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.
*
* You are under no obligation whatsoever to provide any bug fixes, patches, or
* upgrades to the features, functionality or performance of the source code
* ("Enhancements") to anyone; however, if you choose to make your Enhancements
* available either publicly, or directly to Lawrence Berkeley National
* Laboratory, without imposing a separate written license agreement for such
* Enhancements, then you hereby grant the following license: a non-exclusive,
* royalty-free perpetual license to install, use, modify, prepare derivative
* works, incorporate into other computer software, distribute, and sublicense
* such enhancements or derivative works thereof, in binary and source code
* form.
*/
package nux.xom.pool;
import java.lang.ref.SoftReference;
/**
* ThreadLocal utility that allows garbage collection of its value via a {@link SoftReference}.
* Typically used for static vars such as
*
* <pre>
* private static final ThreadLocal xyz = new SoftThreadLocal() { ... };
* </pre>
*
* To use it, override method initialSoftValue() instead of initialValue().
* <p>
* See http://java.sun.com/docs/hotspot/PerformanceFAQ.html#175 and
* http://java.sun.com/docs/hotspot/gc5.0/gc_tuning_5.html and
* http://www.theserverside.com/news/thread.tss?thread_id=29865 and
* http://www.theserverside.com/discussions/thread.tss?thread_id=26023
*
* @author whoschek.AT.lbl.DOT.gov
* @author $Author: hoschek3 $
* @version $Revision: 1.9 $, $Date: 2005/11/30 05:12:20 $
*/
abstract class SoftThreadLocal extends ThreadLocal {
/** Override this method instead of initialValue() */
protected abstract Object initialSoftValue();
protected final Object initialValue() { // lazy init
return wrap(initialSoftValue());
}
public Object get() {
Object value = ((SoftReference) super.get()).get(); // unwrap
if (value == null) { // reinitialize if it's been silently garbage collected
value = initialSoftValue();
set(value);
}
return value;
}
public void set(Object value) {
super.set(wrap(value));
}
private static SoftReference wrap(Object value) {
return new SoftReference(value);
}
}