Stabilize synchronous gauge instrument API

[jack-berg]

Synchronous gauge support was added in #3540 (August 2023). This is a tracking issue for stability.

Below are the PRs / issues tracking prototyping of this in various languages.

• Java: Add experimental synchronous gauge opentelemetry-java#5506
• Go: How to implement Prometheus Gauge Set method in open-telemetry？ opentelemetry-go#3984
• C++: Add Synchronous Gauge instrument to the metrics API/SDK opentelemetry-cpp#2279
• Python: Synchronous gauge prototype opentelemetry-python#3462
• Erlang: Add sync gauge instrument opentelemetry-erlang#643
• Javascript: Add Synchronous Gauge instrument to the metrics API opentelemetry-js#4296, feat(api): added synchronous gauge opentelemetry-js#4528
• Dotnet
• Swift
• PHP
• Ruby
• Rust Add experimental synchronous gauge  opentelemetry-rust#1410

This comment seems to indicate that there may be prototypes available in C++ and .NET, but I couldn't find evidence of that.

Maintainers, please chime in on this issue with any relevant updates on prototypes.

[joaopgrassi]

I noticed the sync gauge is not listed in the table here: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#sum-aggregation. Should it?

[pichlermarc]

There is an API and SDK prototype for JavaScript now, we'll soon merge an experimental version of this.
open-telemetry/opentelemetry-js#4528

[jack-berg]

Thanks @pichlermarc - updated the issue descriptino to reflect that.

I noticed the sync gauge is not listed in the table here: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#sum-aggregation. Should it?

@joaopgrassi yes it should be.

[trask]

we have 3 prototypes now:

• Java - Add experimental synchronous gauge opentelemetry-java#5506
• Python - Synchronous gauge prototype opentelemetry-python#3462
• JS - feat(api): added synchronous gauge opentelemetry-js#4528

I think that may be enough to move forward with stabilization?

[jack-berg]

Its a bit of a grey area on whether something counts as a prototype if its a PR which hasn't been merged, or maybe the PR has been merged but it isn't consumable in a published artifact.

I'm inclined to say that this counts as a prototype, so long as the maintainers of that language confirm they didn't uncover any design issues along the way. After all, when we say that spec PRs much have associated prototypes, those are almost always just draft PRs or branches since a stronger requirement would cause a chicken and the egg problem.

@open-telemetry/javascript-maintainers can you comment on the JS PR linked above? Did you uncover any design issues along the way?

@open-telemetry/specs-metrics-approvers WDYT? Any objection to moving forward to stabilizing?

[reyang]

@open-telemetry/specs-metrics-approvers WDYT? Any objection to moving forward to stabilizing?

I don't see issue here - synchronous gauge is something we were hoping to add but got deprioritized as we wanted to ship the initial version of metrics API/SDK spec. It is just yet-another-instrument so I don't anticipate a lot of controversy.

[pichlermarc]

can you comment on the JS PR linked above? Did you uncover any design issues along the way?

No design issues. 🙂

In the JS SIG, we just don't have a proper mechanism in place yet to publish an experimental addition to the API, hence we cannot merge the PR until the spec stable or we've come up with such a mechanism.

Prototyping for experimental API features it is held up on a tooling update (open-telemetry/opentelemetry-js#4648)

[MrAlias]

Go PoC: open-telemetry/opentelemetry-go#5280

[cijothomas]

OTel Rust PoC (available under otel-unstable feature flags).
open-telemetry/opentelemetry-rust#1410
Tagging @lalitb who implemented the above as well.