Start Root Span Collects Current Active Span as Parent

[omamoo]

Bug Report

List of NuGet packages and version that you are using (e.g. OpenTelemetry 1.0.2):

• NuGet: OpenTelemetry.Api Version 1.2.0-rc1

Runtime version (e.g. net461, net48, netcoreapp3.1, net5.0 etc. You can find this information from the *.csproj file):

• dotnet 6.0.101

Symptom

I defined simple Api endpoint with the following code:

[HttpGet]
public async Task TestOtel()
{
    using (TracerProvider.Default.
               GetTracer(ActivitySourceProvider.ActivitySourceName, ActivitySourceProvider.Version).
               StartActiveSpan("FirstSpan"))
    {
        await Task.Delay(5.Seconds());
        var rootSpan = 
            TracerProvider.Default.
                GetTracer(ActivitySourceProvider.ActivitySourceName, ActivitySourceProvider.Version).
                StartRootSpan("MyRootSpan"); 
        using (Tracer.WithSpan(rootSpan))
        {
            Task.Delay(5.Seconds());
        }
    }
}

What is the expected behavior?

I'm expecting to see two different traces:

• First one is for incoming HTTP request (using AspDotNet instrumentation library) and one more nested span called "FirstSpan"
• Second is for the MyRootSpan which created by using CreateRootSpan and activated with WithSpan method.

What is the actual behavior?

One trace with all span see attached image.

Additional Context

Image with trace at Jaeger:

Thanks for the help.

[omamoo]

Anyone?

[alanwest]

Yes, this might be a bug. I created a test #2878 that I think models your situation.

[omamoo]

@alanwest Yes this is the exact case, thanks. How can I know if the test passes?

[alanwest]

We'll leave this issue open as I'm not yet sure what the best fix will be.

In my opinion, the problem is due in part to the behavior of the StartActivity method when it is passed an empty parent context (i.e., starting a root span). StartActivity is called from StartRootSpan and is not part of the OpenTelemetry .NET project - it is part of .NET's System.Diagnostics library.

I'll raise this issue for discussion in the .NET SIG meeting agenda next week.

In the meantime, a work around for you may be to set Activity.Current = null prior to calling StartRootSpan. It is the fact that Activity.Current is not null which is causing MyRootSpan to be a child of FirstSpan in your case.

---

Turns out there's another issue already tracking the underlying issue #984. Looks like there was discussion to follow up with the runtime team, but not sure if that happened or not.

[omamoo]

@alanwest Thanks for the update.

• We are using the workaround as you described, so it's don't urgent.
• I raised this issue because I couldn't find #984, they are the same.
• Yes, the problem is with .NET diagnostics library and activity which is not null. But you won't change the API of span creation am I right? If I'll call CreateActiveSpan with null span context it still will use the parent span if exist as a parent?

Thanks.

[Oberon00]

I don't think this is exactly the same as #984. While #984 is about the Activity API missing required basic functionality, this is about the OTel-specific StartRootSpan not doing what it says in its name.

[alanwest]

I don't think this is exactly the same as #984. While #984 is about the Activity API missing required basic functionality, this is about the OTel-specific StartRootSpan not doing what it says in its name.

We discussed in this week's SIG meeting fixing this for the StartRootSpan API since we control that in this project, so I agree we should keep this bug open for that.

Separately, I just opened https://github.com/dotnet/runtime/issues/65528 to address #984.