feat: add the UpDownCounter instrument

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

@@ -14,7 +14,13 @@
  * limitations under the License.
  */
 
-import { MetricOptions, Counter, ValueRecorder, Observer } from './Metric';
+import {
+  MetricOptions,
+  Counter,
+  ValueRecorder,
+  Observer,
+  UpDownCounter,
+} from './Metric';
 
 /**
  * An interface to allow the recording metrics.
@@ -40,6 +46,25 @@ export interface Meter {
    */
   createCounter(name: string, options?: MetricOptions): Counter;
 
+  /**
+   * Creates a new `UpDownCounter` metric. UpDownCounter is a synchronous
+   * instrument and very similar to Counter except that Add(increment)
+   * supports negative increments. It is generally useful for capturing changes
+   * in an amount of resources used, or any quantity that rises and falls
+   * during a request.
+   * Example uses for UpDownCounter:
+   * <ol>
+   *   <li> count the number of active requests. </li>
+   *   <li> count memory in use by instrumenting new and delete. </li>
+   *   <li> count queue size by instrumenting enqueue and dequeue. </li>
+   *   <li> count semaphore up and down operations. </li>
+   * </ol>
+   *
+   * @param name the name of the metric.
+   * @param [options] the metric options.
+   */
+  createUpDownCounter(name: string, options?: MetricOptions): UpDownCounter;
+
   /**
    * Creates a new `Observer` metric.
    * @param name the name of the metric.

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

@@ -48,12 +48,7 @@ export interface MetricOptions {
   disabled?: boolean;
 
   /**
-   * Asserts that this metric may only increase (e.g. time spent).
-   */
-  monotonic?: boolean;
-
-  /**
-   * (ValueRecorder only, default true) Asserts that this metric will only accept
+   * (Measure only, default true) Asserts that this metric will only accept
    * non-negative values (e.g. disk usage).
    */
   absolute?: boolean;
@@ -125,6 +120,13 @@ export interface Counter extends UnboundMetric<BoundCounter> {
   add(value: number, labels?: Labels): void;
 }
 
+export interface UpDownCounter extends UnboundMetric<BoundCounter> {
+  /**
+   * Adds the given value to the current value. Values can be negative.
+   */
+  add(value: number, labels?: Labels): void;
+}
+
 export interface ValueRecorder extends UnboundMetric<BoundValueRecorder> {
   /**
    * Records the given value to this value recorder.

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

@@ -22,6 +22,7 @@ import {
   Counter,
   ValueRecorder,
   Observer,
+  UpDownCounter,
 } from './Metric';
 import { BoundValueRecorder, BoundCounter } from './BoundInstrument';
 import { CorrelationContext } from '../correlation_context/CorrelationContext';
@@ -53,6 +54,15 @@ export class NoopMeter implements Meter {
     return NOOP_COUNTER_METRIC;
   }
 
+  /**
+   * Returns a constant noop UpDownCounter.
+   * @param name the name of the metric.
+   * @param [options] the metric options.
+   */
+  createUpDownCounter(name: string, options?: MetricOptions): UpDownCounter {
+    return NOOP_COUNTER_METRIC;
+  }
+
   /**
    * Returns constant noop observer.
    * @param name the name of the metric.

packages/opentelemetry-exporter-prometheus/src/prometheus.ts

@@ -191,10 +191,9 @@ export class PrometheusExporter implements MetricExporter {
 
     switch (record.descriptor.metricKind) {
       case MetricKind.COUNTER:
-        // there is no such thing as a non-monotonic counter in prometheus
-        return record.descriptor.monotonic
-          ? new Counter(metricObject)
-          : new Gauge(metricObject);
+        return new Counter(metricObject);
+      case MetricKind.UP_DOWN_COUNTER:
+        return new Gauge(metricObject);
       case MetricKind.OBSERVER:
         return new Gauge(metricObject);
       default:

packages/opentelemetry-exporter-prometheus/test/prometheus.test.ts

@@ -384,10 +384,9 @@ describe('PrometheusExporter', () => {
       });
     });
 
-    it('should export a non-monotonic counter as a gauge', done => {
-      const counter = meter.createCounter('counter', {
+    it('should export a UpDownCounter as a gauge', done => {
+      const counter = meter.createUpDownCounter('counter', {
         description: 'a test description',
-        monotonic: false,
       });
 
       counter.bind({ key1: 'labelValue1' }).add(20);

packages/opentelemetry-metrics/src/BoundInstrument.ts

@@ -24,19 +24,16 @@ import { Aggregator } from './export/types';
 export class BaseBoundInstrument {
   protected _labels: api.Labels;
   protected _logger: api.Logger;
-  protected _monotonic: boolean;
 
   constructor(
     labels: api.Labels,
     logger: api.Logger,
-    monotonic: boolean,
     private readonly _disabled: boolean,
     private readonly _valueType: api.ValueType,
     private readonly _aggregator: Aggregator
   ) {
     this._labels = labels;
     this._logger = logger;
-    this._monotonic = monotonic;
   }
 
   update(value: number): void {
@@ -72,18 +69,17 @@ export class BoundCounter extends BaseBoundInstrument
   constructor(
     labels: api.Labels,
     disabled: boolean,
-    monotonic: boolean,
     valueType: api.ValueType,
     logger: api.Logger,
     aggregator: Aggregator
   ) {
-    super(labels, logger, monotonic, disabled, valueType, aggregator);
+    super(labels, logger, disabled, valueType, aggregator);
   }
 
   add(value: number): void {
-    if (this._monotonic && value < 0) {
+    if (value < 0) {
       this._logger.error(
-        `Monotonic counter cannot descend for ${Object.values(this._labels)}`
+        `Counter cannot descend for ${Object.values(this._labels)}`
       );
       return;
     }
@@ -93,7 +89,29 @@ export class BoundCounter extends BaseBoundInstrument
 }
 
 /**
- * BoundValueRecorder is an implementation of the {@link BoundValueRecorder} interface.
+ * BoundUpDownCounter allows the SDK to observe/record a single metric event.
+ * The value of single instrument in the `UpDownCounter` associated with
+ * specified Labels.
+ */
+export class BoundUpDownCounter extends BaseBoundInstrument
+  implements api.BoundCounter {
+  constructor(
+    labels: api.Labels,
+    disabled: boolean,
+    valueType: api.ValueType,
+    logger: api.Logger,
+    aggregator: Aggregator
+  ) {
+    super(labels, logger, disabled, valueType, aggregator);
+  }
+
+  add(value: number): void {
+    this.update(value);
+  }
+}
+
+/**
+ * BoundMeasure is an implementation of the {@link BoundMeasure} interface.
  */
 export class BoundValueRecorder extends BaseBoundInstrument
   implements api.BoundValueRecorder {
@@ -102,13 +120,12 @@ export class BoundValueRecorder extends BaseBoundInstrument
   constructor(
     labels: api.Labels,
     disabled: boolean,
-    monotonic: boolean,
     absolute: boolean,
     valueType: api.ValueType,
     logger: api.Logger,
     aggregator: Aggregator
   ) {
-    super(labels, logger, monotonic, disabled, valueType, aggregator);
+    super(labels, logger, disabled, valueType, aggregator);
     this._absolute = absolute;
   }
 
@@ -137,11 +154,10 @@ export class BoundObserver extends BaseBoundInstrument {
   constructor(
     labels: api.Labels,
     disabled: boolean,
-    monotonic: boolean,
     valueType: api.ValueType,
     logger: api.Logger,
     aggregator: Aggregator
   ) {
-    super(labels, logger, monotonic, disabled, valueType, aggregator);
+    super(labels, logger, disabled, valueType, aggregator);
   }
 }

packages/opentelemetry-metrics/src/Meter.ts

@@ -18,6 +18,7 @@ import * as api from '@opentelemetry/api';
 import { ConsoleLogger } from '@opentelemetry/core';
 import { Resource } from '@opentelemetry/resources';
 import { BaseBoundInstrument } from './BoundInstrument';
+import { UpDownCounterMetric } from './UpDownCounterMetric';
 import {
   Metric,
   CounterMetric,
@@ -72,10 +73,9 @@ export class Meter implements api.Meter {
       return api.NOOP_VALUE_RECORDER_METRIC;
     }
     const opt: MetricOptions = {
-      absolute: true, // value recorders are defined as absolute by default
-      monotonic: false, // not applicable to value recorder, set to false
       logger: this._logger,
       ...DEFAULT_METRIC_OPTIONS,
+      absolute: true, // value recorders are defined as absolute by default
       ...options,
     };
 
@@ -104,8 +104,6 @@ export class Meter implements api.Meter {
       return api.NOOP_COUNTER_METRIC;
     }
     const opt: MetricOptions = {
-      monotonic: true, // Counters are defined as monotonic by default
-      absolute: false, // not applicable to counter, set to false
       logger: this._logger,
       ...DEFAULT_METRIC_OPTIONS,
       ...options,
@@ -115,6 +113,41 @@ export class Meter implements api.Meter {
     return counter;
   }
 
+  /**
+   * Creates a new `UpDownCounter` metric. UpDownCounter is a synchronous
+   * instrument and very similar to Counter except that Add(increment)
+   * supports negative increments. It is generally useful for capturing changes
+   * in an amount of resources used, or any quantity that rises and falls
+   * during a request.
+   *
+   * @param name the name of the metric.
+   * @param [options] the metric options.
+   */
+  createUpDownCounter(
+    name: string,
+    options?: api.MetricOptions
+  ): api.UpDownCounter {
+    if (!this._isValidName(name)) {
+      this._logger.warn(
+        `Invalid metric name ${name}. Defaulting to noop metric implementation.`
+      );
+      return api.NOOP_COUNTER_METRIC;
+    }
+    const opt: MetricOptions = {
+      logger: this._logger,
+      ...DEFAULT_METRIC_OPTIONS,
+      ...options,
+    };
+    const upDownCounter = new UpDownCounterMetric(
+      name,
+      opt,
+      this._batcher,
+      this._resource
+    );
+    this._registerMetric(name, upDownCounter);
+    return upDownCounter;
+  }
+
   /**
    * Creates a new observer metric.
    * @param name the name of the metric.
@@ -128,8 +161,6 @@ export class Meter implements api.Meter {
       return api.NOOP_OBSERVER_METRIC;
     }
     const opt: MetricOptions = {
-      monotonic: false, // Observers are defined as non-monotonic by default
-      absolute: false, // not applicable to observer, set to false
       logger: this._logger,
       ...DEFAULT_METRIC_OPTIONS,
       ...options,
@@ -188,7 +219,8 @@ export class Meter implements api.Meter {
    *
    * 2. The first character must be non-numeric, non-space, non-punctuation
    *
-   * 3. Subsequent characters must be belong to the alphanumeric characters, '_', '.', and '-'.
+   * 3. Subsequent characters must be belong to the alphanumeric characters,
+   *    '_', '.', and '-'.
    *
    * Names are case insensitive
    *

packages/opentelemetry-metrics/src/Metric.ts

@@ -31,7 +31,6 @@ import { hashLabels } from './Utils';
 /** This is a SDK implementation of {@link Metric} interface. */
 export abstract class Metric<T extends BaseBoundInstrument>
   implements api.UnboundMetric<T> {
-  protected readonly _monotonic: boolean;
   protected readonly _disabled: boolean;
   protected readonly _valueType: api.ValueType;
   protected readonly _logger: api.Logger;
@@ -44,7 +43,6 @@ export abstract class Metric<T extends BaseBoundInstrument>
     private readonly _kind: MetricKind,
     readonly resource: Resource
   ) {
-    this._monotonic = _options.monotonic;
     this._disabled = _options.disabled;
     this._valueType = _options.valueType;
     this._logger = _options.logger;
@@ -98,7 +96,6 @@ export abstract class Metric<T extends BaseBoundInstrument>
       unit: this._options.unit,
       metricKind: this._kind,
       valueType: this._valueType,
-      monotonic: this._monotonic,
     };
   }
 
@@ -119,7 +116,6 @@ export class CounterMetric extends Metric<BoundCounter> implements api.Counter {
     return new BoundCounter(
       labels,
       this._disabled,
-      this._monotonic,
       this._valueType,
       this._logger,
       // @todo: consider to set to CounterSumAggregator always.
@@ -130,8 +126,8 @@ export class CounterMetric extends Metric<BoundCounter> implements api.Counter {
   /**
    * Adds the given value to the current value. Values cannot be negative.
    * @param value the value to add.
-   * @param [labels = {}] key-values pairs that are associated with a specific metric
-   *     that you want to record.
+   * @param [labels = {}] key-values pairs that are associated with a specific
+   *     metric that you want to record.
    */
   add(value: number, labels: api.Labels = {}) {
     this.bind(labels).add(value);
@@ -156,7 +152,6 @@ export class ValueRecorderMetric extends Metric<BoundValueRecorder>
     return new BoundValueRecorder(
       labels,
       this._disabled,
-      this._monotonic,
       this._absolute,
       this._valueType,
       this._logger,
@@ -187,7 +182,6 @@ export class ObserverMetric extends Metric<BoundObserver>
     return new BoundObserver(
       labels,
       this._disabled,
-      this._monotonic,
       this._valueType,
       this._logger,
       this._batcher.aggregatorFor(this._descriptor)