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/*
 * 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 under the License.
 */
package org.apache.kafka.common.metrics.stats;

import java.util.ArrayList;
import java.util.List;

import org.apache.kafka.common.metrics.MeasurableStat;
import org.apache.kafka.common.metrics.MetricConfig;

/**
 * A SampledStat records a single scalar value measured over one or more samples. Each sample is recorded over a
 * configurable window. The window can be defined by number of events or elapsed time (or both, if both are given the
 * window is complete when either the event count or elapsed time criterion is met).
 * 

* All the samples are combined to produce the measurement. When a window is complete the oldest sample is cleared and * recycled to begin recording the next sample. * * Subclasses of this class define different statistics measured using this basic pattern. */ public abstract class SampledStat implements MeasurableStat { private double initialValue; private int current = 0; protected List samples; public SampledStat(double initialValue) { this.initialValue = initialValue; this.samples = new ArrayList<>(2); } @Override public void record(MetricConfig config, double value, long timeMs) { Sample sample = current(timeMs); if (sample.isComplete(timeMs, config)) sample = advance(config, timeMs); update(sample, config, value, timeMs); sample.eventCount += 1; } private Sample advance(MetricConfig config, long timeMs) { this.current = (this.current + 1) % config.samples(); if (this.current >= samples.size()) { Sample sample = newSample(timeMs); this.samples.add(sample); return sample; } else { Sample sample = current(timeMs); sample.reset(timeMs); return sample; } } protected Sample newSample(long timeMs) { return new Sample(this.initialValue, timeMs); } @Override public double measure(MetricConfig config, long now) { purgeObsoleteSamples(config, now); return combine(this.samples, config, now); } public Sample current(long timeMs) { if (samples.size() == 0) this.samples.add(newSample(timeMs)); return this.samples.get(this.current); } public Sample oldest(long now) { if (samples.size() == 0) this.samples.add(newSample(now)); Sample oldest = this.samples.get(0); for (int i = 1; i < this.samples.size(); i++) { Sample curr = this.samples.get(i); if (curr.lastWindowMs < oldest.lastWindowMs) oldest = curr; } return oldest; } protected abstract void update(Sample sample, MetricConfig config, double value, long timeMs); public abstract double combine(List samples, MetricConfig config, long now); /* Timeout any windows that have expired in the absence of any events */ protected void purgeObsoleteSamples(MetricConfig config, long now) { long expireAge = config.samples() * config.timeWindowMs(); for (Sample sample : samples) { if (now - sample.lastWindowMs >= expireAge) sample.reset(now); } } protected static class Sample { public double initialValue; public long eventCount; public long lastWindowMs; public double value; public Sample(double initialValue, long now) { this.initialValue = initialValue; this.eventCount = 0; this.lastWindowMs = now; this.value = initialValue; } public void reset(long now) { this.eventCount = 0; this.lastWindowMs = now; this.value = initialValue; } public boolean isComplete(long timeMs, MetricConfig config) { return timeMs - lastWindowMs >= config.timeWindowMs() || eventCount >= config.eventWindow(); } } }





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