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/**
* Copyright Terracotta, Inc.
*
* 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 net.sf.ehcache.util.ratestatistics;
import java.util.concurrent.TimeUnit;
/**
* Abstract rate statistic implementation.
*
* Provides exponentially decaying moving average functionality to subclasses.
*
* @author Chris Dennis
*/
abstract class AbstractRateStatistic implements RateStatistic {
private final long rateAveragePeriod;
/**
* Create an abstract statistic using the specified time averaging period.
*
* @param averagePeriod average period
* @param unit period time unit
*/
AbstractRateStatistic(long averagePeriod, TimeUnit unit) {
this.rateAveragePeriod = unit.toNanos(averagePeriod);
}
/**
* Returns the time averaging period in nanoseconds.
*
* @return average period
*/
long getRateAveragePeriod() {
return rateAveragePeriod;
}
/**
* Combines two timestamped values using a exponentially decaying weighted average.
*
* @param nowValue current value
* @param now current value timestamp
* @param thenAverage previous value
* @param then previous value timestamp
* @return weighted average
*/
float iterateMovingAverage(float nowValue, long now, float thenAverage, long then) {
if (getRateAveragePeriod() == 0 || Float.isNaN(thenAverage)) {
return nowValue;
} else {
float alpha = (float) alpha(now, then);
return alpha * nowValue + (1 - alpha) * thenAverage;
}
}
private double alpha(long now, long then) {
return -Math.expm1(-((double) (now - then)) / getRateAveragePeriod());
}
}