Library instrumentation: hint if noop to minimize perf impact

[lmolkova]

While instrumenting libraries, if there is no OTel SDK/agent, I'd like to disable library instrumentation completely:

• no context propagation
• no collection of pre-sampled attributed

For this, I'd need some way on Global OpenTelemetry to check if it's noop (dynamically, since it can change at any moment). Is there a current mechanism for it or any existing issues on that - could not find any?

It seems my best bet currently is to check Tracer/SpanBuilder/Span implementation class name which is not great, but a reasonable hack.

Any practices in each language - e.g. .NET has ActivitySource (aka Tracer) with HasListeners hint.
Are there any other libraries interested in such capabilities?

[tbolon]

I am not sure I understand well, but in case of .NET if there is not listener, ActivitySource.StartActivity() will return null, and I am pretty sure that StartActivity has been build to have no perf impact when there is no listener. You only pay for having an ActivitySource instance.

There is also activity.IsAllDataRequested which will return true only if this activity has been marked as recorded for the current sampler.