refactor: batch observer to be independent from metric types (open-te…

…lemetry#1709)

* refactor: batch observer to be independent from metric types

- BatchObservers do not have to be created with names
- BatchObservers do not have instruments for their own

* fixup: nodejs v8 compatibilities

* fixup: replace all batch observer metric occurrences with batch observer

api/src/metrics/Meter.ts

@@ -20,8 +20,7 @@ import {
   Counter,
   ValueRecorder,
   ValueObserver,
-  BatchObserver,
-  BatchMetricOptions,
+  BatchObserverOptions,
   UpDownCounter,
   SumObserver,
   UpDownSumObserver,
@@ -108,15 +107,13 @@ export interface Meter {
   ): UpDownSumObserver;
 
   /**
-   * Creates a new `BatchObserver` metric, can be used to update many metrics
+   * Creates a new `BatchObserver`, can be used to update many metrics
    * at the same time and when operations needs to be async
-   * @param name the name of the metric.
    * @param callback the batch observer callback
-   * @param [options] the metric batch options.
+   * @param [options] the batch observer options.
    */
   createBatchObserver(
-    name: string,
     callback: (batchObserverResult: BatchObserverResult) => void,
-    options?: BatchMetricOptions
-  ): BatchObserver;
+    options?: BatchObserverOptions
+  ): void;
 }

api/src/metrics/Metric.ts

@@ -66,11 +66,16 @@ export interface MetricOptions {
   boundaries?: number[];
 }
 
-export interface BatchMetricOptions extends MetricOptions {
+export interface BatchObserverOptions {
   /**
    * Indicates how long the batch metric should wait to update before cancel
    */
   maxTimeoutUpdateMS?: number;
+
+  /**
+   * User provided logger.
+   */
+  logger?: Logger;
 }
 
 /** The Type of value. It describes how the data is reported. */
@@ -166,9 +171,6 @@ export type UpDownSumObserver = BaseObserver;
 /** Base interface for the SumObserver metrics. */
 export type SumObserver = BaseObserver;
 
-/** Base interface for the Batch Observer metrics. */
-export type BatchObserver = Metric;
-
 /**
  * key-value pairs passed by the user.
  */

api/src/metrics/NoopMeter.ts

@@ -23,7 +23,6 @@ import {
   Counter,
   ValueRecorder,
   ValueObserver,
-  BatchObserver,
   UpDownCounter,
   BaseObserver,
   UpDownSumObserver,
@@ -119,10 +118,9 @@ export class NoopMeter implements Meter {
    * @param callback the batch observer callback
    */
   createBatchObserver(
-    _name: string,
     _callback: (batchObserverResult: BatchObserverResult) => void
-  ): BatchObserver {
-    return NOOP_BATCH_OBSERVER_METRIC;
+  ): NoopBatchObserver {
+    return NOOP_BATCH_OBSERVER;
   }
 }
 
@@ -187,9 +185,7 @@ export class NoopBaseObserverMetric
   }
 }
 
-export class NoopBatchObserverMetric
-  extends NoopMetric<void>
-  implements BatchObserver {}
+export class NoopBatchObserver {}
 
 export class NoopBoundCounter implements BoundCounter {
   add(_value: number): void {
@@ -229,4 +225,4 @@ export const NOOP_SUM_OBSERVER_METRIC = new NoopBaseObserverMetric(
   NOOP_BOUND_BASE_OBSERVER
 );
 
-export const NOOP_BATCH_OBSERVER_METRIC = new NoopBatchObserverMetric();
+export const NOOP_BATCH_OBSERVER = new NoopBatchObserver();