fix(sdk-trace-base): always wait on pending export in SimpleSpanProcessor

CHANGELOG.md

@@ -26,6 +26,7 @@ For semantic convention package changes, see the [semconv CHANGELOG](packages/se
 * refactor(sdk-trace-base)!: remove `new Span` constructor in favor of `Tracer.startSpan` API [#5048](https://github.com/open-telemetry/opentelemetry-js/pull/5048) @david-luna
 * refactor(sdk-trace-base)!: remove `BasicTracerProvider.addSpanProcessor` API in favor of constructor options. [#5134](https://github.com/open-telemetry/opentelemetry-js/pull/5134) @david-luna
 * refactor(sdk-trace-base)!: make `resource` property private in `BasicTracerProvider` and remove `getActiveSpanProcessor` API. [#5192](https://github.com/open-telemetry/opentelemetry-js/pull/5192) @david-luna
+* fix(sdk-trace-base): always wait on pending export in SimpleSpanProcessor. [#5303](https://github.com/open-telemetry/opentelemetry-js/pull/5303) @anuraaga
 * feat(sdk-metrics)!: extract `IMetricReader` interface and use it over abstract class [#5311](https://github.com/open-telemetry/opentelemetry-js/pull/5311)
   * (user-facing): `MeterProviderOptions` now provides the more general `IMetricReader` type over `MetricReader`
   * If you accept `MetricReader` in your public interface, consider accepting the more general `IMetricReader` instead to avoid unintentional breaking changes

packages/opentelemetry-sdk-trace-base/src/export/SimpleSpanProcessor.ts

@@ -20,7 +20,6 @@ import {
   ExportResultCode,
   globalErrorHandler,
   BindOnceFuture,
-  ExportResult,
 } from '@opentelemetry/core';
 import { Span } from '../Span';
 import { SpanProcessor } from '../SpanProcessor';
@@ -38,16 +37,16 @@ import { Resource } from '@opentelemetry/resources';
  */
 export class SimpleSpanProcessor implements SpanProcessor {
   private _shutdownOnce: BindOnceFuture<void>;
-  private _unresolvedExports: Set<Promise<void>>;
+  private _pendingExports: Set<Promise<unknown>>;
 
   constructor(private readonly _exporter: SpanExporter) {
     this._shutdownOnce = new BindOnceFuture(this._shutdown, this);
-    this._unresolvedExports = new Set<Promise<void>>();
+    this._pendingExports = new Set<Promise<void>>();
   }
 
   async forceFlush(): Promise<void> {
-    // await unresolved resources before resolving
-    await Promise.all(Array.from(this._unresolvedExports));
+    // await pending exports
+    await Promise.all(Array.from(this._pendingExports));
     if (this._exporter.forceFlush) {
       await this._exporter.forceFlush();
     }
@@ -64,43 +63,26 @@ export class SimpleSpanProcessor implements SpanProcessor {
       return;
     }
 
-    const doExport = () =>
-      internal
-        ._export(this._exporter, [span])
-        .then((result: ExportResult) => {
-          if (result.code !== ExportResultCode.SUCCESS) {
-            globalErrorHandler(
-              result.error ??
-                new Error(
-                  `SimpleSpanProcessor: span export failed (status ${result})`
-                )
-            );
-          }
-        })
-        .catch(error => {
-          globalErrorHandler(error);
-        });
+    const pendingExport = this.doExport(span).catch(err =>
+      globalErrorHandler(err)
+    );
+    // Enqueue this export to the pending list so it can be flushed by the user.
+    this._pendingExports.add(pendingExport);
+    pendingExport.finally(() => this._pendingExports.delete(pendingExport));
+  }
 
-    // Avoid scheduling a promise to make the behavior more predictable and easier to test
+  private async doExport(span: ReadableSpan): Promise<void> {
     if (span.resource.asyncAttributesPending) {
-      const exportPromise = (span.resource as Resource)
-        .waitForAsyncAttributes?.()
-        .then(
-          () => {
-            if (exportPromise != null) {
-              this._unresolvedExports.delete(exportPromise);
-            }
-            return doExport();
-          },
-          err => globalErrorHandler(err)
-        );
+      // Ensure resource is fully resolved before exporting.
+      await (span.resource as Resource).waitForAsyncAttributes?.();
+    }
 
-      // store the unresolved exports
-      if (exportPromise != null) {
-        this._unresolvedExports.add(exportPromise);
-      }
-    } else {
-      void doExport();
+    const result = await internal._export(this._exporter, [span]);
+    if (result.code !== ExportResultCode.SUCCESS) {
+      throw (
+        result.error ??
+        new Error(`SimpleSpanProcessor: span export failed (status ${result})`)
+      );
     }
   }
 

packages/opentelemetry-sdk-trace-base/test/common/export/SimpleSpanProcessor.test.ts

@@ -216,7 +216,40 @@ describe('SimpleSpanProcessor', () => {
       );
     });
 
-    it('should await doExport() and delete from _unresolvedExports', async () => {
+    it('should await doExport() and delete from _pendingExports', async () => {
+      const testExporterWithDelay = new TestExporterWithDelay();
+      const processor = new SimpleSpanProcessor(testExporterWithDelay);
+      const spanContext: SpanContext = {
+        traceId: 'a3cda95b652f4a1592b449d5929fda1b',
+        spanId: '5e0c63257de34c92',
+        traceFlags: TraceFlags.SAMPLED,
+      };
+      const tracer = provider.getTracer('default');
+      const span = new SpanImpl({
+        scope: tracer.instrumentationScope,
+        resource: tracer['_resource'],
+        context: ROOT_CONTEXT,
+        spanContext,
+        name: 'span-name',
+        kind: SpanKind.CLIENT,
+        spanLimits: tracer.getSpanLimits(),
+        spanProcessor: tracer['_spanProcessor'],
+      });
+      processor.onStart(span, ROOT_CONTEXT);
+      processor.onEnd(span);
+
+      assert.strictEqual(processor['_pendingExports'].size, 1);
+
+      await processor.forceFlush();
+
+      assert.strictEqual(processor['_pendingExports'].size, 0);
+
+      const exportedSpans = testExporterWithDelay.getFinishedSpans();
+
+      assert.strictEqual(exportedSpans.length, 1);
+    });
+
+    it('should await doExport() and delete from _pendingExports with async resource', async () => {
       const testExporterWithDelay = new TestExporterWithDelay();
       const processor = new SimpleSpanProcessor(testExporterWithDelay);
 
@@ -247,11 +280,11 @@ describe('SimpleSpanProcessor', () => {
       processor.onStart(span, ROOT_CONTEXT);
       processor.onEnd(span);
 
-      assert.strictEqual(processor['_unresolvedExports'].size, 1);
+      assert.strictEqual(processor['_pendingExports'].size, 1);
 
       await processor.forceFlush();
 
-      assert.strictEqual(processor['_unresolvedExports'].size, 0);
+      assert.strictEqual(processor['_pendingExports'].size, 0);
 
       const exportedSpans = testExporterWithDelay.getFinishedSpans();