Hi,
I’m having a bit of a hard time making sense of linking child spans from the Oban to the parent span and I hope somebody can clear that out for me.

Here is roughly the code from the first pass

span_ctx = OpenTelemetry.Tracer.start_span(:parent)
Task.async(fn ->
  link = OpenTelemetry.link(span_ctx) |> IO.inspect(label: "link")
  OpenTelemetry.Tracer.with_span :"my-task", %{links: [link]} do
    :hello
  end
end)
:otel_span.end_span(span_ctx, :undefined)

In the output, I can see that traced_id inside link matches the second item from the span_ctx tuple, but in Zipkin, those are two different traces and “my-task” doesn’t have a parent.

iex(5)> span_ctx = OpenTelemetry.Tracer.start_span(:parent)
{:span_ctx, 98688298365639109931104546606962518618, 12736530893077507678, 1, [],
 true, false, true,
 {:otel_span_ets, #Function<2.133377841/1 in :otel_tracer_server.on_end/1>}}
iex(6)> Task.async(fn ->
...(6)>   link = OpenTelemetry.link(span_ctx) |> IO.inspect(label: "link")
...(6)>   OpenTelemetry.Tracer.with_span :"my-task", %{links: [link]} do
...(6)>     :hello
...(6)>   end
...(6)> end)
link: %{
  attributes: %{},
  span_id: 12736530893077507678,
  trace_id: 98688298365639109931104546606962518618,
  tracestate: []
}
%Task{
  mfa: {:erlang, :apply, 2},
  owner: #PID<0.887.0>,
  pid: #PID<0.899.0>,
  ref: #Reference<0.3396824287.1941766146.188407>
}
iex(7)> :otel_span.end_span(span_ctx, :undefined)
{:span_ctx, 98688298365639109931104546606962518618, 12736530893077507678, 1, [],
 true, false, false,
 {:otel_span_ets, #Function<2.133377841/1 in :otel_tracer_server.on_end/1>}}
iex(8)>

image720×594 43.9 KB

Second pass

I attempted to start_span / end_span instead of with_span but the same result was the same - two uncorrelated spans

span_ctx = OpenTelemetry.Tracer.start_span(:parent) |> IO.inspect(label: "parent_ctx")
Task.async(fn ->
  link = OpenTelemetry.link(span_ctx) |> IO.inspect(label: "link")
  child_span_ctx = OpenTelemetry.Tracer.start_span(:child_async, %{links: [link]})  |> IO.inspect(label: "child span ctx")
  Process.sleep(20)
  :otel_span.end_span(child_span_ctx, :undefined)
end)
:otel_span.end_span(span_ctx, :undefined)

However I noticed that child span doesn’t have anything in relation to the parent span

image720×538 42.4 KB

Third pass

I briefly looked at the otel_span.erl and decided to put parent span as a current span before start a new span in the child process and it worked

span_ctx = OpenTelemetry.Tracer.start_span(:parent) |> IO.inspect(label: "parent_ctx")
Task.async(fn ->
  OpenTelemetry.Tracer.set_current_span(span_ctx)
  OpenTelemetry.Tracer.with_span(:child_third_pass) do
    Process.sleep(20)
  end
end)
:otel_span.end_span(span_ctx, :undefined)

image2393×508 46.9 KB

Am I confused about the role of the links?