[bug] Race condition in Tracer.StartSpan() can throw System.InvalidOperation

[gwest]

Package

OpenTelemetry.Api

Package Version

Package Name	Version
OpenTelemetry.Api	1.11.2
OpenTelemetry	1.11.2

Runtime Version

net9.0

Description

If calling Tracer.StartSpan() when Activity.Current has an item it is possible to hit the exception:

System.InvalidOperationException: 'Trying to set an Activity that is not running'

Currently, the Tracer.StartSpan() method does the following:

1. Captures the current Activity that is in Activity.Current as previousActivty.
2. Creates the new TelemetrySpan to be returned.
3. Puts previousActivity back into place as Activity.Current.

When trying to put previousActivity back into Activity.Current, if previousActivity has stopped whilst we were creating the new TelemetrySpan it will throw an error.

A simple way to avoid this seems to be by changing the following:

if (startSpanBehavior.HasFlag(StartSpanBehaviors.DeactivateNewSpan)
    && Activity.Current != previousActivity)
{
    Activity.Current = previousActivity;
}

to

if (startSpanBehavior.HasFlag(StartSpanBehaviors.DeactivateNewSpan)
    && Activity.Current != previousActivity)
{
    Activity.Current = previousActivity?.IsStopped == true ? null : previousActivity;
}

Steps to Reproduce

I've had difficulty recreating this race condition in a simple sample project.

Expected Result

No exceptions are thrown.

Actual Result

The following exception can sometimes be thrown.
System.InvalidOperationException: 'Trying to set an Activity that is not running'

Additional Context

No response

[TimothyMothra]

For context, the code being discussed is here:

opentelemetry-dotnet/src/OpenTelemetry.Api/Trace/Tracer.cs

Lines 225 to 232 in 1775968

	finally
	{
	if (startSpanBehavior.HasFlag(StartSpanBehaviors.DeactivateNewSpan)
	&& Activity.Current != previousActivity)
	{
	Activity.Current = previousActivity;
	}
	}

@gwest, do you have a simple app that can reproduce this?
The suggested fix seems reasonable to me, but I want to learn more about how you're hitting this exception.
I'm wondering if the OpenTelemetry.Api project has a testing gap.

[gwest]

Unfortunately I don't. I tried to create something but couldn't get it to hit the race condition I am experiencing in my fairly complex MAUI app.

In my app, I was able to debug the exception and see Activities unrelated to the one being started were the previous Activity and the IsStopped property was set to true.