org.hibernate.cache.redis.util.Timestamper Maven / Gradle / Ivy
/*
* Copyright 2011-2013 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.hibernate.cache.redis.util;
import java.util.concurrent.atomic.AtomicLong;
/**
* Generates increasing identifiers (in a single VM only).
* Not valid across multiple VMs. Yet, the identifier is based on time, so that the drifting
* across a cluster should not ever be large...
*/
public final class Timestamper implements CacheTimestamper {
private final AtomicLong VALUE = new AtomicLong();
private final int BIN_DIGITS = 12;
private final short ONE_MS = 1 << BIN_DIGITS;
@Override
public 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;
}
}
}
}
}