/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* Copyright (c) 2008-2011, Red Hat Inc. or third-party contributors as
* indicated by the @author tags or express copyright attribution
* statements applied by the authors. All third-party contributions are
* distributed under license by Red Hat Inc.
*
* This copyrighted material is made available to anyone wishing to use, modify,
* copy, or redistribute it subject to the terms and conditions of the GNU
* Lesser General Public License, as published by the Free Software Foundation.
*
* 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 Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this distribution; if not, write to:
* Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA 02110-1301 USA
*/
package org.hibernate.cache.internal;
import java.util.concurrent.atomic.AtomicLong;
/**
* Generates increasing identifiers (in a single VM only). Not valid across multiple VMs. Identifiers are not
* necessarily strictly increasing, but usually are.
*/
public final class Timestamper {
private static final int BIN_DIGITS = 12;
public static final short ONE_MS = 1<<BIN_DIGITS;
private static final AtomicLong VALUE = new AtomicLong();
public static long next() {
while (true) {
long base = System.currentTimeMillis() << BIN_DIGITS;
long maxValue = base + ONE_MS - 1;
for (long current = VALUE.get(), update = Math.max(base, current + 1); update < maxValue;
current = VALUE.get(), update = Math.max(base, current + 1)) {
if (VALUE.compareAndSet(current, update)) {
return update;
}
}
}
}
private Timestamper() {
}
}