Start new Root Activity/Span, when Activity.Current is already present

ActivitySourceExtensions.cs

using System;
using System.Diagnostics;
using System.Collections.Generic;

// Author: https://github.com/arakis
// Inspired by https://github.com/open-telemetry/opentelemetry-dotnet/issues/984
// This is an usable implementation for the workaround in the above issue

namespace StartRootActivitySample
{

    public static class ActivitySourceExtensions
    {

        public static RootActivity StartRootActivity(this ActivitySource source,
            string name,
            ActivityKind kind = ActivityKind.Internal,
            IEnumerable<KeyValuePair<string, object?>>? tags = null)
        {
            var parent = Activity.Current;
            Activity.Current = null;
            var next = source.StartActivity(name, kind,
                parentContext: default,
                tags: tags,
                links: new[] { new ActivityLink(parent.Context) });

            return new RootActivity(next, parent);
        }

    }

    public class RootActivity : IDisposable
    {
        public Activity Activity { get; }
        public Activity ParentActivity { get; }

        public RootActivity(Activity activity, Activity parentActivity)
        {
            Activity = activity;
            ParentActivity = parentActivity;
        }

        private bool disposedValue;
        protected virtual void Dispose(bool disposing)
        {
            if (!disposedValue)
            {
                if (disposing)
                {
                    Activity.Dispose();
                    Activity.Current = ParentActivity;
                }

                disposedValue = true;
            }
        }

        public void Dispose()
        {
            Dispose(disposing: true);
            GC.SuppressFinalize(this);
        }
    }

}

Sample.cs

using (var root = MyActivitySource.StartRootActivity("new-root"))
{
    using (var child = MyActivitySource.StartActivity("in new root"))
    {
        Log.Error("in new root");
    }
}