using System;

using System.Collections.Generic;

using System.Diagnostics;

using OpenTelemetry;

using OpenTelemetry.Trace;

using OpenTelemetry.Exporter;

public class Program

{

    public static void Main()

    {

        var activitySource = new ActivitySource("MySource");

        var completedActivities = new List<Activity>();

        var traceExporter = new InMemoryExporter<Activity>(completedActivities);

        var traceProcessor = new SimpleActivityExportProcessor(traceExporter);

        var builder = Sdk.CreateTracerProviderBuilder()

                .AddSource("MySource")

                .AddProcessor(traceProcessor)

                .Build();

        using var firstActivity = activitySource.StartActivity("Item1");

​

        Console.WriteLine($"Activity.Current is {FormatSpan(Activity.Current)}");

        Activity.Current = null;

        // we are explicitly trying NOT to be a child of the Activity.Current here

        using var secondActivity = activitySource.StartActivity("Item2", ActivityKind.Consumer, parentContext: default);

        Activity.Current = firstActivity;

        Console.WriteLine($"Activity.Current is {FormatSpan(Activity.Current)}");

        using var thirdActivity = activitySource.StartActivity("Item3");

        // and this does not work, because unbeknowst to me - default(ActivityContext) is exactly what Activity.Create

        // is looking for in order to signal "make this activity a child of the current one"

        Console.WriteLine($"Activity.Current is {FormatSpan(secondActivity)}");

        Console.WriteLine($"Activity.Current is {FormatSpan(thirdActivity)}");

    }

    private static string FormatSpan(Activity x)

        {

            var parentOp = x.Parent != null ? $"({x.Parent.OperationName})" : string.Empty;

​

            return

                $"TraceId: {x.Context.TraceId}, Source: {x.Source.Name}, SpanId: {x.Context.SpanId}, ParentId: {x.ParentId}{parentOp}, Operation: {x.OperationName}";

        }

}