Add experimental synchronous gauge

[jack-berg]

Adds experimental synchronous gauge, as described in spec PR #3540.

[mateuszrzeszutek]

Awesome 🚀

[codecov]

Codecov Report

Patch coverage is 100.00% of modified lines.

Files Changed	Coverage
.../incubator/metrics/ExtendedDoubleGaugeBuilder.java	ø
...on/incubator/metrics/ExtendedLongGaugeBuilder.java	ø
...a/io/opentelemetry/sdk/metrics/SdkDoubleGauge.java	100.00%
...ava/io/opentelemetry/sdk/metrics/SdkLongGauge.java	100.00%
...in/java/io/opentelemetry/sdk/metrics/SdkMeter.java	100.00%

📢 Thoughts on this report? Let us know!.

[jack-berg]

The corresponding spec PR for this feature has been merged and I've marked this PR as "Ready for Review"!

[jsuereth]

Yes.

[jack-berg]

I'm going to open an issue for this and solve in a separate PR. The synchronous use cases I'm aware of require the instrumentation to subscribe to notifications about change in some value, rather than fetching the current value which caters to async gauge. Not clear when context would be available in one of these notification event streams. I'm open to it being a use case, but its not as clear cut as what's in this PR.

[jack-berg]

@jkwatson planning on merging this for 1.30.0 release unless you have any reservations.

[MickaelCoquer]

Hi @jack-berg, I can't find a way to use the synchronous gauge with a public API. Do you have any working example to share? Currently I have to use reflexion to be able to use it. It's working but not so nice :)

[jack-berg]

@MickaelCoquer The synchronous gauge API is currently experimental and part of the opentelemetry-extension-incubator package, which is what we use to explore new APIs before committing to them.

Using APIs in the incubator is a bit awkward:

• Add a dependency on opentelemetry-extension-incubator
• Cast the DoubleGaugeBuilder / LongGaugeBuilder to ExtendedDoubleGaugeBuilder / ExtendedLongGaugeBuilder and call build() to obtain a synchronous DoubleGauge / LongGuage. See below for an example:

DoubleGauge gauge = ((ExtendedDoubleGaugeBuilder) meter.gaugeBuilder("my-gauge")).build();
gauge.set(1.0);

Once the specification stabilizes, we'll promote the API to opentelemetry-api and the ergonomics will improve.

[damnMeddlingKid]

This is awesome work, thanks for implementing a synchronous API. We need to use this in production and are trying to decide whether to use the experimental API or not. Do you know how long these kinds of things typically take ?.

[GabrielMulcahy]

Hi @jack-berg, I get a class cast exception:

io.opentelemetry.api.metrics.DefaultMeter$NoopLongGaugeBuilder cannot be cast to class io.opentelemetry.extension.incubator.metrics.ExtendedLongGaugeBuilder

with this example:

LongGauge gauge = ((ExtendedLongGaugeBuilder) GlobalOpenTelemetry.getMeter("default")
        .gaugeBuilder("gauge")
        .ofLongs())
        .build();

The same happens if I use a custom meter provider and try to cast from an instance of io.opentelemetry.sdk.metrics.SdkLongGauge$SdkLongGaugeBuilder

Does this implementation not work with certain versions of the libraries?

[trask]

Hi @GabrielMulcahy, can you open a new issue to make sure your question is seen? Thanks

[tongshushan]

Hi @jack-berg, I get a class cast exception:

io.opentelemetry.api.metrics.DefaultMeter$NoopLongGaugeBuilder cannot be cast to class io.opentelemetry.extension.incubator.metrics.ExtendedLongGaugeBuilder

with this example:

LongGauge gauge = ((ExtendedLongGaugeBuilder) GlobalOpenTelemetry.getMeter("default")
        .gaugeBuilder("gauge")
        .ofLongs())
        .build();

The same happens if I use a custom meter provider and try to cast from an instance of io.opentelemetry.sdk.metrics.SdkLongGauge$SdkLongGaugeBuilder

Does this implementation not work with certain versions of the libraries?

I met the same issue : #6378