org.apache.gossip.accrual.FailureDetector.java Source code

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Here is the source code for org.apache.gossip.accrual.FailureDetector.java

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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.gossip.accrual;

import org.apache.commons.math.MathException;
import org.apache.commons.math.distribution.ExponentialDistributionImpl;
import org.apache.commons.math.distribution.NormalDistributionImpl;
import org.apache.commons.math.stat.descriptive.DescriptiveStatistics;
import org.apache.log4j.Logger;

public class FailureDetector {

    public static final Logger LOGGER = Logger.getLogger(FailureDetector.class);
    private final DescriptiveStatistics descriptiveStatistics;
    private final long minimumSamples;
    private volatile long latestHeartbeatMs = -1;
    private final String distribution;

    public FailureDetector(long minimumSamples, int windowSize, String distribution) {
        descriptiveStatistics = new DescriptiveStatistics(windowSize);
        this.minimumSamples = minimumSamples;
        this.distribution = distribution;
    }

    /**
     * Updates the statistics based on the delta between the last
     * heartbeat and supplied time
     *
     * @param now the time of the heartbeat in milliseconds
     */
    public synchronized void recordHeartbeat(long now) {
        if (now <= latestHeartbeatMs) {
            return;
        }
        if (latestHeartbeatMs != -1) {
            descriptiveStatistics.addValue(now - latestHeartbeatMs);
        }
        latestHeartbeatMs = now;
    }

    public synchronized Double computePhiMeasure(long now) {
        if (latestHeartbeatMs == -1 || descriptiveStatistics.getN() < minimumSamples) {
            return null;
        }
        long delta = now - latestHeartbeatMs;
        try {
            double probability;
            if (distribution.equals("normal")) {
                double standardDeviation = descriptiveStatistics.getStandardDeviation();
                standardDeviation = standardDeviation < 0.1 ? 0.1 : standardDeviation;
                probability = new NormalDistributionImpl(descriptiveStatistics.getMean(), standardDeviation)
                        .cumulativeProbability(delta);
            } else {
                probability = new ExponentialDistributionImpl(descriptiveStatistics.getMean())
                        .cumulativeProbability(delta);
            }
            final double eps = 1e-12;
            if (1 - probability < eps) {
                probability = 1.0;
            }
            return -1.0d * Math.log10(1.0d - probability);
        } catch (MathException | IllegalArgumentException e) {
            LOGGER.debug(e);
            return null;
        }
    }
}