package org.apache.cassandra.stress.util;
/*
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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
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*/
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CountDownLatch;
// TODO: do not assume normal distribution of measurements.
public class Uncertainty
{
private int measurements;
private double sumsquares;
private double sum;
private double stdev;
private double mean;
private double uncertainty;
private CopyOnWriteArrayList<WaitForTargetUncertainty> waiting = new CopyOnWriteArrayList<>();
private static final class WaitForTargetUncertainty
{
final double targetUncertainty;
final int minMeasurements;
final int maxMeasurements;
final CountDownLatch latch = new CountDownLatch(1);
private WaitForTargetUncertainty(double targetUncertainty, int minMeasurements, int maxMeasurements)
{
this.targetUncertainty = targetUncertainty;
this.minMeasurements = minMeasurements;
this.maxMeasurements = maxMeasurements;
}
void await() throws InterruptedException
{
latch.await();
}
}
public void update(double value)
{
measurements++;
sumsquares += value * value;
sum += value;
mean = sum / measurements;
stdev = Math.sqrt((sumsquares / measurements) - (mean * mean));
uncertainty = (stdev / Math.sqrt(measurements)) / mean;
for (WaitForTargetUncertainty waiter : waiting)
{
if ((uncertainty < waiter.targetUncertainty && measurements >= waiter.minMeasurements) || (measurements >= waiter.maxMeasurements))
{
waiter.latch.countDown();
// can safely remove as working over snapshot with COWArrayList
waiting.remove(waiter);
}
}
}
public void await(double targetUncertainty, int minMeasurements, int maxMeasurements) throws InterruptedException
{
final WaitForTargetUncertainty wait = new WaitForTargetUncertainty(targetUncertainty, minMeasurements, maxMeasurements);
waiting.add(wait);
wait.await();
}
public double getUncertainty()
{
return uncertainty;
}
public void wakeAll()
{
for (WaitForTargetUncertainty waiting : this.waiting)
{
waiting.latch.countDown();
this.waiting.remove(waiting);
}
}
}