How do I start a span with no parent when another span is active?

[alevenberg]

I want to create a span with no parent.

Currently, when I call StartSpan(), the parent defaults to the current active span.

I want to do something like

  opentelemetry::trace::StartSpanOptions options;
  options.parent = null;
  auto span = tracer->StartSpan("span", {}, {} options);

But the parent needs to be SpanContext or context::Context. By default it uses, SpanContext::GetInvalid(), which will create a child of the active span. So, I'm not sure what I else I could use.

Is there a way to start a span with no parent?

Thanks, Anna

[lalitb]

For the root span, the parent_span_id field would contain the span_id of the current span. There is no way to make it null/empty/missing.

[lalitb]

Sorry, I think I misunderstood your question earlier. You want to create a root span, while a given span is already active - this is not possible, and not sure if this is the right use case either. All the span/log operations are bound to the current active span as a parent.

[alevenberg]

The use case is for asynchronous batching.

There are N spans that are initiating an async rpc, but the async rpc can occur during one of those spans. Instead of creating the parent/child relationship, we want to represent the relationship with links.

I think you can do this in other languages. I'm not sure about the specifics, but I think it would look like creating a new span context and then starting a new span with that context.

[lalitb]

Yes, on further thought this seems to be a valid requirement. When one can create a span that is a child to a non-active span, it should be possible to create a span with no parent. Would you like to create an issue for this? This can be an ABI-breaking change, so could be targeted for ABI v2.

[lalitb]

OK, have created an issue here - #2413. Feel free to further discuss there.

[alevenberg]

Thanks for making the issue!