HeadSamplingHistogramAlignedReservoir.cs

HeadSamplingHistogramAlignedReservoir.cs

using System.Diagnostics;
using OpenTelemetry.Metrics;

namespace Exemplars;

public class HeadSamplingHistogramAlignedReservoir(IReadOnlyList<double> bounds) : FixedSizeExemplarReservoir(bounds.Count + 1)
{
    private readonly bool[] _recordedWithSampledSpan = new bool[bounds.Count + 1];

    public override void Offer(in ExemplarMeasurement<long> measurement)
    {
        Debug.Fail("HeadSamplingHistogramAlignedReservoir shouldn't be used with long values");
    }

    public override void Offer(in ExemplarMeasurement<double> measurement)
    {
        var bucketIndex = GetBucketIndex(measurement.Value);
        
        if (_recordedWithSampledSpan[bucketIndex])
        {
            return;
        }

        UpdateExemplar(bucketIndex, in measurement);

        if (Activity.Current?.Recorded is true)
        {
            _recordedWithSampledSpan[bucketIndex] = true;
        }
    }

    protected override void OnCollected()
    {
        Array.Clear(_recordedWithSampledSpan);
    }
    
    private int GetBucketIndex(double value)
    {
        for (var i = 0; i < bounds.Count; i++)
        {
            if (value <= bounds[i])
            {
                return i;
            }
        }

        return bounds.Count;
    }
}