feat(instrumentation): added synchronous gauge

Author: clintonb

api/CHANGELOG.md

@@ -8,6 +8,7 @@ All notable changes to this project will be documented in this file.
 
 ### :rocket: (Enhancement)
 
+* feat(metrics): added synchronous gauge [#4528](https://github.com/open-telemetry/opentelemetry-js/pull/4528) @clintonb
 * feat(api): allow adding span links after span creation [#4536](https://github.com/open-telemetry/opentelemetry-js/pull/4536) @seemk
   * This change is non-breaking for end-users, but breaking for Trace SDK implmentations in accordance with the [specification](https://github.com/open-telemetry/opentelemetry-specification/blob/a03382ada8afa9415266a84dafac0510ec8c160f/specification/upgrading.md?plain=1#L97-L122) as new features need to be implemented.
 * feat: support node 22 [#4666](https://github.com/open-telemetry/opentelemetry-js/pull/4666) @dyladan

api/src/index.ts

@@ -43,6 +43,7 @@ export { MeterProvider } from './metrics/MeterProvider';
 export {
   ValueType,
   Counter,
+  Gauge,
   Histogram,
   MetricOptions,
   Observable,

api/src/metrics/Meter.ts

@@ -17,6 +17,7 @@
 import {
   BatchObservableCallback,
   Counter,
+  Gauge,
   Histogram,
   MetricAttributes,
   MetricOptions,
@@ -45,6 +46,16 @@ export interface MeterOptions {
  * for the exported metric are deferred.
  */
 export interface Meter {
+  /**
+   * Creates and returns a new `Gauge`.
+   * @param name the name of the metric.
+   * @param [options] the metric options.
+   */
+  createGauge<AttributesTypes extends MetricAttributes = MetricAttributes>(
+    name: string,
+    options?: MetricOptions
+  ): Gauge<AttributesTypes>;
+
   /**
    * Creates and returns a new `Histogram`.
    * @param name the name of the metric.

api/src/metrics/Metric.ts

@@ -98,6 +98,15 @@ export interface UpDownCounter<
   add(value: number, attributes?: AttributesTypes, context?: Context): void;
 }
 
+export interface Gauge<
+  AttributesTypes extends MetricAttributes = MetricAttributes,
+> {
+  /**
+   * Records a measurement.
+   */
+  record(value: number, attributes?: AttributesTypes, context?: Context): void;
+}
+
 export interface Histogram<
   AttributesTypes extends MetricAttributes = MetricAttributes,
 > {

api/src/metrics/NoopMeter.ts

@@ -18,15 +18,16 @@ import { Meter } from './Meter';
 import {
   BatchObservableCallback,
   Counter,
+  Gauge,
   Histogram,
+  MetricAttributes,
   MetricOptions,
+  Observable,
   ObservableCallback,
   ObservableCounter,
   ObservableGauge,
   ObservableUpDownCounter,
   UpDownCounter,
-  MetricAttributes,
-  Observable,
 } from './Metric';
 
 /**
@@ -36,6 +37,13 @@ import {
 export class NoopMeter implements Meter {
   constructor() {}
 
+  /**
+   * @see {@link Meter.createGauge}
+   */
+  createGauge(_name: string, _options?: MetricOptions): Histogram {
+    return NOOP_GAUGE_METRIC;
+  }
+
   /**
    * @see {@link Meter.createHistogram}
    */
@@ -114,6 +122,10 @@ export class NoopUpDownCounterMetric
   add(_value: number, _attributes: MetricAttributes): void {}
 }
 
+export class NoopGaugeMetric extends NoopMetric implements Gauge {
+  record(_value: number, _attributes: MetricAttributes): void {}
+}
+
 export class NoopHistogramMetric extends NoopMetric implements Histogram {
   record(_value: number, _attributes: MetricAttributes): void {}
 }
@@ -140,6 +152,7 @@ export const NOOP_METER = new NoopMeter();
 
 // Synchronous instruments
 export const NOOP_COUNTER_METRIC = new NoopCounterMetric();
+export const NOOP_GAUGE_METRIC = new NoopGaugeMetric();
 export const NOOP_HISTOGRAM_METRIC = new NoopHistogramMetric();
 export const NOOP_UP_DOWN_COUNTER_METRIC = new NoopUpDownCounterMetric();
 

api/test/common/noop-implementations/noop-meter.test.ts

@@ -24,6 +24,7 @@ import {
   NOOP_OBSERVABLE_UP_DOWN_COUNTER_METRIC,
   NOOP_UP_DOWN_COUNTER_METRIC,
   createNoopMeter,
+  NOOP_GAUGE_METRIC,
 } from '../../../src/metrics/NoopMeter';
 import { NoopMeterProvider } from '../../../src/metrics/NoopMeterProvider';
 
@@ -116,6 +117,17 @@ describe('NoopMeter', () => {
     );
   });
 
+  it('gauge should not crash', () => {
+    const meter = new NoopMeterProvider().getMeter('test-noop');
+    const observableGauge = meter.createGauge('some-name');
+
+    // ensure the correct noop const is returned
+    assert.strictEqual(observableGauge, NOOP_GAUGE_METRIC);
+
+    const gaugeWithOptions = meter.createGauge('some-name', options);
+    assert.strictEqual(gaugeWithOptions, NOOP_GAUGE_METRIC);
+  });
+
   it('observable up down counter should not crash', () => {
     const meter = new NoopMeterProvider().getMeter('test-noop');
     const observableUpDownCounter =

packages/sdk-metrics/test/Instruments.test.ts

@@ -19,25 +19,25 @@ import * as sinon from 'sinon';
 import { InstrumentationScope } from '@opentelemetry/core';
 import { Resource } from '@opentelemetry/resources';
 import {
-  InstrumentType,
-  MeterProvider,
-  MetricReader,
   DataPoint,
   DataPointType,
   Histogram,
+  InstrumentType,
+  MeterProvider,
   MetricDescriptor,
+  MetricReader,
 } from '../src';
 import {
   TestDeltaMetricReader,
   TestMetricReader,
 } from './export/TestMetricReader';
 import {
-  assertMetricData,
   assertDataPoint,
-  commonValues,
+  assertMetricData,
   commonAttributes,
-  defaultResource,
+  commonValues,
   defaultInstrumentationScope,
+  defaultResource,
 } from './util';
 import { ObservableResult, ValueType } from '@opentelemetry/api';
 
@@ -764,6 +764,41 @@ describe('Instruments', () => {
       });
     });
   });
+
+  describe('Gauge', () => {
+    it('should record common values and attributes without exceptions', async () => {
+      const { meter } = setup();
+      const gauge = meter.createGauge('test');
+
+      for (const values of commonValues) {
+        for (const attributes of commonAttributes) {
+          gauge.record(values, attributes);
+        }
+      }
+    });
+
+    it('should record values', async () => {
+      const { meter, cumulativeReader } = setup();
+      const gauge = meter.createGauge('test');
+
+      gauge.record(1, { foo: 'bar' });
+      gauge.record(-1);
+
+      await validateExport(cumulativeReader, {
+        dataPointType: DataPointType.GAUGE,
+        dataPoints: [
+          {
+            attributes: { foo: 'bar' },
+            value: 1,
+          },
+          {
+            attributes: {},
+            value: -1,
+          },
+        ],
+      });
+    });
+  });
 });
 
 function setup() {