Avoid copying Activity tags and links when sampling - #135277

using System.Diagnostics;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

BenchmarkSwitcher.FromAssembly(typeof(PropagationDataBenchmarks).Assembly).Run(args);

[MemoryDiagnoser]
public class PropagationDataBenchmarks
{
    private static readonly KeyValuePair<string, object?>[] s_tags =
    [
        new("client.address", "192.0.2.1"), new("network.peer.address", "192.0.2.1"), new("network.peer.port", 50000),
        new("server.address", "localhost"), new("server.port", 5000), new("http.request.method", "GET"),
        new("user_agent.original", "Mozilla/5.0"), new("url.scheme", "https"), new("url.path", "/api/items"),
    ];

    private static readonly ActivityLink[] s_links = [new(new ActivityContext(ActivityTraceId.CreateRandom(), ActivitySpanId.CreateRandom(), ActivityTraceFlags.None))];

    private ActivitySource _source = null!;
    private ActivityListener _listener = null!;
    private ActivitySamplingResult _result;

    [Params(ActivitySamplingResult.PropagationData, ActivitySamplingResult.AllDataAndRecorded)]
    public ActivitySamplingResult Sampling { get; set; }

    [GlobalSetup]
    public void Setup()
    {
        Console.WriteLine("Assembly: " + typeof(Activity).Assembly.Location);
        _result = Sampling;
        _source = new ActivitySource("Bench");
        _listener = new ActivityListener
        {
            ShouldListenTo = s => ReferenceEquals(s, _source),
            Sample = (ref _) => _result,
        };
        ActivitySource.AddActivityListener(_listener);
    }

    [GlobalCleanup]
    public void Cleanup() { _listener.Dispose(); _source.Dispose(); }

    [Benchmark(Baseline = true)]
    public void NoTags() => Run(null, null);

    [Benchmark]
    public void NineTags() => Run(s_tags, null);

    [Benchmark]
    public void NineTagsAndLink() => Run(s_tags, s_links);

    private void Run(KeyValuePair<string, object?>[]? tags, ActivityLink[]? links)
    {
        var a = _source.CreateActivity("Request", ActivityKind.Server, default(ActivityContext), tags, links);
        a!.Start();
        a.Stop();
    }
}