SimpleWindowHistogramReservoir.java

package com.github.metricscore.hdr.histogram;

import com.codahale.metrics.Clock;
import com.codahale.metrics.Reservoir;
import com.codahale.metrics.Snapshot;
import com.codahale.metrics.WeightedSnapshot;
import com.github.metricscore.hdr.counter.SimpleWindowCounter;

import java.time.Duration;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class SimpleWindowHistogramReservoir implements Reservoir {
    private final long[] bucketOffsets;
    private final SimpleWindowCounter[] buckets;

    public SimpleWindowHistogramReservoir(Duration windowSize, int chunkCount, boolean smoothly, int numBuckets, Clock clock) {
        bucketOffsets = newOffsets(numBuckets);
        buckets = new SimpleWindowCounter[numBuckets];
        for (int i = 0; i < numBuckets; i++) {
            buckets[i] = new SimpleWindowCounter(windowSize, chunkCount, smoothly, clock);
        }
    }

    @Override
    public int size() {
        return buckets.length;
    }

    @Override
    public void update(long value) {
        //todo: check value range
        int index = Arrays.binarySearch(bucketOffsets, value);
        if (index < 0) {
            // inexact match, take the first bucket higher than n
            index = -index - 1;
        }
        // else exact match; we're good
        buckets[index].add(1);
    }

    @Override
    public Snapshot getSnapshot() {
        List<WeightedSnapshot.WeightedSample> weightedValues = new ArrayList<>(buckets.length);

        for (int i = 0; i < buckets.length; i++) {
            SimpleWindowCounter bucket = buckets[i];
            final long value = bucketOffsets[i];
            final long count = bucket.getSum();
            if (count>0){
                final WeightedSnapshot.WeightedSample weightedSample = new WeightedSnapshot.WeightedSample(value, count);
                weightedValues.add(weightedSample);
            }
        }

        return new WeightedSnapshot(weightedValues);
    }

    private static long[] newOffsets(int size) {
        long[] result = new long[size];
        result[0] = 0;
        result[1] = 1;
        for (int i = 1; i < result.length; i++) {
            long next = Math.round(result[i - 1] * 1.2);
            if (next == result[i - 1]) {
                next++;
            }
            result[i] = next;
        }

        return result;
    }
}