/*
* JVSTM: a Java library for Software Transactional Memory
* Copyright (C) 2005 INESC-ID Software Engineering Group
* http://www.esw.inesc-id.pt
*
* This library 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 library 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 library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
* Author's contact:
* INESC-ID Software Engineering Group
* Rua Alves Redol 9
* 1000 - 029 Lisboa
* Portugal
*/
package jvstm;
import java.lang.reflect.Field;
public class VBoxBody<E> implements GarbageCollectable {
// this static field is used to change the non-static final field "next"
// see the comments on the clearPrevious method
private static final Field NEXT_FIELD;
static {
try {
NEXT_FIELD = VBoxBody.class.getDeclaredField("next");
NEXT_FIELD.setAccessible(true);
} catch (NoSuchFieldException nsfe) {
throw new Error("JVSTM error: couldn't get access to the VBoxBody.next field");
}
}
public final int version;
public final VBoxBody<E> next;
public volatile E value;
public VBoxBody(E value, int version, VBoxBody<E> next) {
this.version = version;
this.next = next;
this.value = value;
}
public VBoxBody<E> getBody(int maxVersion) {
VBoxBody result = this;
while (result.version > maxVersion) {
result = result.next;
}
return result;
}
public void clearPrevious() {
// we set the next field to null via reflection because it is
// a final field
// making the field final is crucial to ensure that the field
// is properly initialized (and visible to other threads)
// after an instance of MultiVersionBoxBody is constructed, as
// per the new Java Memory Model (JSR133)
// also, according to the Java specification, we may change a
// final field only via reflection and in some specific cases
// (such as object reconstruction after deserialization)
// even though this use is not the case, the potential
// problems that may occur do not affect the correcteness of
// the system: we just want to set the field to null to allow
// the garbage collector to do its thing...
try {
NEXT_FIELD.set(this, null);
} catch (IllegalAccessException iae) {
throw new Error("JVSTM error: cannot set the next field to null");
}
}
}