feat(api-metrics): async instruments spec compliance (#2569)

Co-authored-by: Valentin Marchaud <contact@vmarchaud.fr>

examples/metrics/metrics/observer.js

@@ -23,14 +23,14 @@ const meter = new MeterProvider({
   interval: 2000,
 }).getMeter('example-meter');
 
-meter.createObservableGauge('cpu_core_usage', {
-  description: 'Example of a sync observable gauge with callback',
-}, async (observableResult) => { // this callback is called once per each interval
+meter.createObservableGauge('cpu_core_usage', async (observableResult) => { // this callback is called once per each interval
   await new Promise((resolve) => {
     setTimeout(() => { resolve(); }, 50);
   });
   observableResult.observe(getRandomValue(), { core: '1' });
   observableResult.observe(getRandomValue(), { core: '2' });
+}, {
+  description: 'Example of a sync observable gauge with callback',
 });
 
 function getRandomValue() {

experimental/packages/opentelemetry-api-metrics/src/NoopMeter.ts

@@ -27,7 +27,6 @@ import {
   ObservableUpDownCounter,
 } from './types/Metric';
 import { ObservableResult } from './types/ObservableResult';
-import { Observation } from './types/Observation';
 
 /**
  * NoopMeter is a noop implementation of the {@link Meter} interface. It reuses
@@ -66,41 +65,41 @@ export class NoopMeter implements Meter {
   /**
    * Returns a constant noop observable gauge.
    * @param name the name of the metric.
+   * @param callback the observable gauge callback
    * @param [options] the metric options.
-   * @param [callback] the observable gauge callback
    */
   createObservableGauge(
     _name: string,
+    _callback: (observableResult: ObservableResult) => void,
     _options?: MetricOptions,
-    _callback?: (observableResult: ObservableResult) => void
   ): ObservableGauge {
     return NOOP_OBSERVABLE_GAUGE_METRIC;
   }
 
   /**
    * Returns a constant noop observable counter.
    * @param name the name of the metric.
+   * @param callback the observable counter callback
    * @param [options] the metric options.
-   * @param [callback] the observable counter callback
    */
   createObservableCounter(
     _name: string,
+    _callback: (observableResult: ObservableResult) => void,
     _options?: MetricOptions,
-    _callback?: (observableResult: ObservableResult) => void
   ): ObservableCounter {
     return NOOP_OBSERVABLE_COUNTER_METRIC;
   }
 
   /**
    * Returns a constant noop up down observable counter.
    * @param name the name of the metric.
+   * @param callback the up down observable counter callback
    * @param [options] the metric options.
-   * @param [callback] the up down observable counter callback
    */
   createObservableUpDownCounter(
     _name: string,
+    _callback: (observableResult: ObservableResult) => void,
     _options?: MetricOptions,
-    _callback?: (observableResult: ObservableResult) => void
   ): ObservableUpDownCounter {
     return NOOP_OBSERVABLE_UP_DOWN_COUNTER_METRIC;
   }
@@ -120,14 +119,7 @@ export class NoopHistogramMetric extends NoopMetric implements Histogram {
   record(_value: number, _attributes: Attributes): void {}
 }
 
-export class NoopObservableBaseMetric extends NoopMetric implements ObservableBase {
-  observation(): Observation {
-    return {
-      observable: this as ObservableBase,
-      value: 0,
-    };
-  }
-}
+export class NoopObservableBaseMetric extends NoopMetric implements ObservableBase {}
 
 export const NOOP_METER = new NoopMeter();
 

experimental/packages/opentelemetry-api-metrics/src/index.ts

@@ -19,7 +19,6 @@ export * from './NoopMeterProvider';
 export * from './types/Meter';
 export * from './types/MeterProvider';
 export * from './types/Metric';
-export * from './types/Observation';
 export * from './types/ObservableResult';
 
 import { MetricsAPI } from './api/metrics';

experimental/packages/opentelemetry-api-metrics/src/types/Meter.ts

@@ -81,36 +81,36 @@ export interface Meter {
   /**
    * Creates a new `ObservableGauge` metric.
    * @param name the name of the metric.
+   * @param callback the observable callback
    * @param [options] the metric options.
-   * @param [callback] the observable callback
    */
   createObservableGauge(
     name: string,
-    options?: MetricOptions,
-    callback?: (observableResult: ObservableResult) => void
+    callback: (observableResult: ObservableResult) => void,
+    options?: MetricOptions
   ): ObservableGauge;
 
   /**
    * Creates a new `ObservableCounter` metric.
    * @param name the name of the metric.
+   * @param callback the observable callback
    * @param [options] the metric options.
-   * @param [callback] the observable callback
    */
   createObservableCounter(
     name: string,
-    options?: MetricOptions,
-    callback?: (observableResult: ObservableResult) => void
+    callback: (observableResult: ObservableResult) => void,
+    options?: MetricOptions
   ): ObservableCounter;
 
   /**
    * Creates a new `ObservableUpDownCounter` metric.
    * @param name the name of the metric.
+   * @param callback the observable callback
    * @param [options] the metric options.
-   * @param [callback] the observable callback
    */
   createObservableUpDownCounter(
     name: string,
-    options?: MetricOptions,
-    callback?: (observableResult: ObservableResult) => void
+    callback: (observableResult: ObservableResult) => void,
+    options?: MetricOptions
   ): ObservableUpDownCounter;
 }

experimental/packages/opentelemetry-api-metrics/src/types/Metric.ts

@@ -14,10 +14,6 @@
  * limitations under the License.
  */
 
-import {
-  Observation,
-} from './Observation';
-
 /**
  * Options needed for metric creation
  */
@@ -112,13 +108,10 @@ export interface Histogram {
   record(value: number, attributes?: Attributes): void;
 }
 
+// ObservableBase has to be an Object but for now there is no field or method
+// declared.
 /** Base interface for the Observable metrics. */
-export interface ObservableBase {
-  observation: (
-    value: number,
-    attributes?: Attributes,
-  ) => Observation;
-}
+export type ObservableBase = Record<never, never>;
 
 /** Base interface for the ObservableGauge metrics. */
 export type ObservableGauge = ObservableBase;

experimental/packages/opentelemetry-api-metrics/src/types/ObservableResult.ts

@@ -20,5 +20,5 @@ import { Attributes } from './Metric';
  * Interface that is being used in callback function for Observable Metric
  */
 export interface ObservableResult {
-  observe(value: number, attributes: Attributes): void;
+  observe(value: number, attributes?: Attributes): void;
 }