[Feature]: Unregister Callbacks

[landonxjames]

Related Problems?

#958

Describe the solution you'd like:

Issue #958 implies the OTel-rust allows users to unregister callbacks as of 0.20.0. I do see the function for doing that in the 0.20 docs. But in the docs for the most recent version (0.26.0 currently) I cannot find anything about unregistering callback functions. I am not sure if the capability for doing that was moved or if it no longer exists. This functionality is in the spec and is present in other language libraries.

Considered Alternatives

N/A

Additional Context

N/A

[cijothomas]

We removed the ability to provide callbacks after instrument creation. Unregister is needed, only if an ability to register callback after instrument creation exists.
Currently, only way to provide callback is while instrument registration and not after.

Related: #2151

Can you share more details on how you are using callbacks, and why is unregister needed, so we can re-evaluate the priority for bringing back the ability to do so?

[landonxjames]

My use case is almost certainly too niche to warrant prioritizing this, but I will lay it out anyway.

I work on the AWS SDK for Rust and am currently implementing the observability portions of our spec (internal so unfortunately I can't share it). The spec is more or less a simplified version of the OTel interfaces, but they are not tied to an OTel implementation and users can implement their own observability provider using the interfaces we provide. You can see a WIP version of the Rust version of the interfaces here and the OTel based implementation of those interfaces here.

Our create_{someAsyncInstrument} methods all return an AsyncMeasurementHandle which allows the user to stop recording metrics and unregister the callback.

pub trait AsyncMeasurementHandle {
    /// Stop recording , unregister callback.
    fn stop(&self);
}

For reference here is the Kotlin version of this interface implemented for OTel.