Support for GLS and comment-based tracing

[ian-axelrod-sl]

Hi,

I would like to know if you are planning to implement a GLS-like solution, similar to orchestrion, to support tracing in codebases that have not followed the practice of including a Context in many function arguments.

Context (heh...): I want to add tracing to a collection of large codebases that have a fairly deep call stack for functions, many of which are not currently using a Context. It will take ages to refactor this codebase to add the contexts, as I'll need to add them all the way up the stack and then fix broken tests. I'll need to do this for each function (there are tens-to-hundreds per codebase) and each codebase (there are upwards of 10 codebases). I can use orchestrion temporarily to handle this, but I want a vendor-agnostic solution. Any plans here?

Comment-based tracing: Orchestrion has the idea of marking a function for tracing using //dd:span comments. This has been invaluable for quickly adding support for tracing to functions without significantly altering structs / interfaces / parameters. The tracing library I work with at the moment is an abstraction over opentelemetry and datadog, and does not use a global mutex. I am required to pass the tracer abstraction to the function somehow (similar to context, but in this case I can at least pass in a struct / in the receiver) so that I can create new spans or add span attributes/baggage. //dd:span has allowed me to get around this issue for functions where we do not need to add extra span tags at runtime; we just want a new span. This is most of the functions. It would be great to have a similar mechanism in otel. This has the additional benefit that you can manage span lifecycle for the developer by defering for them. Thoughts on this?

Thanks, fellas! And great project!

[y1yang0]

I believe the GLS feature should be included in the first version. Although it hasn't been developed yet, it has been on our high-priority to-do list for a long time. As for comment-based tracing, I don't think we will proactively include it in the first version, but if a solid community contribution comes along, it should be perfectly acceptable.

Thanks!

[ralf0131]

@RomainMuller Do you have any thoughts on the comment-based tracing?