fix(metric-reader): do not throw on multiple shutdown calls.

experimental/packages/opentelemetry-sdk-metrics-base/src/export/MetricReader.ts

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+import * as api from '@opentelemetry/api';
 import { AggregationTemporality } from './AggregationTemporality';
 import { MetricProducer } from './MetricProducer';
 import { MetricData } from './MetricData';
@@ -151,7 +152,8 @@ export abstract class MetricReader {
   async shutdown(options: ReaderForceFlushOptions): Promise<void> {
     // Do not call shutdown again if it has already been called.
     if (this._shutdown) {
-      throw new Error('Cannot call shutdown twice.');
+      api.diag.error('Cannot call shutdown twice.');
+      return;
     }
 
     await callWithTimeout(this.onShutdown(), options.timeoutMillis ?? 10000);

experimental/packages/opentelemetry-sdk-metrics-base/src/index.ts

@@ -17,4 +17,3 @@
 export { MeterProvider, MeterProviderOptions } from './MeterProvider';
 export * from './export/MetricExporter';
 export * from './export/MetricReader';
-export * from './export/ReaderResult';

experimental/packages/opentelemetry-sdk-metrics-base/test/export/PeriodicExportingMetricReader.test.ts

@@ -231,7 +231,7 @@ describe('PeriodicExportingMetricReader', () => {
 
       reader.setMetricProducer(new TestMetricProducer());
       await reader.shutdown({});
-      await assert.rejects(() => reader.shutdown({}));
+      await assert.rejects(() => reader.forceFlush({}));
     });
   });
 
@@ -270,8 +270,10 @@ describe('PeriodicExportingMetricReader', () => {
         thrown => thrown instanceof ReaderTimeoutError);
     });
 
-    it('should throw when called twice', async () => {
+    it('called twice should call export shutdown only once', async () => {
       const exporter = new TestMetricExporter();
+      const exporterMock = sinon.mock(exporter);
+      exporterMock.expects('shutdown').calledOnceWithExactly();
       const reader = new PeriodicExportingMetricReader({
         exporter: exporter,
         exportIntervalMillis: MAX_32_BIT_INT,
@@ -280,9 +282,11 @@ describe('PeriodicExportingMetricReader', () => {
 
       reader.setMetricProducer(new TestMetricProducer());
 
-      // first call should succeed.
+      // call twice, the exporter's shutdown must only be called once.
       await reader.shutdown({});
-      await assert.rejects(() => reader.shutdown({}));
+      await reader.shutdown({});
+
+      exporterMock.verify();
     });
 
     it('should throw on non-initialized instance.', async () => {