Fix flaky test TestSimpleSpanProcessorShutdownHonorsContextCancel (#2290)

* Fix flaky test TestSimpleSpanProcessorShutdownHonorsContextCancel

* Add changes to changelog

* Prioritize return of exporter error

* Update changelog description

* Fix deadlock bug

CHANGELOG.md

@@ -26,6 +26,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Fixed
 
 - `semconv.NetAttributesFromHTTPRequest()` correctly handles IPv6 addresses. (#2285)
+- The simple span processor shutdown method deterministically returns the exporter error status if it simultaneously finishes when the deadline is reached. (#2290, #2289)
 
 ## [1.0.1] - 2021-10-01
 

sdk/trace/simple_span_processor.go

@@ -88,11 +88,25 @@ func (ssp *simpleSpanProcessor) Shutdown(ctx context.Context) error {
 
 		go shutdown()
 
+		// Wait for the exporter to shut down or the deadline to expire.
 		select {
 		case err = <-done:
 		case <-ctx.Done():
+			// It is possible for the exporter to have immediately shut down
+			// and the context to be done simultaneously. In that case this
+			// outer select statement will randomly choose a case. This will
+			// result in a different returned error for similar scenarios.
+			// Instead, double check if the exporter shut down at the same
+			// time and return that error if so. This will ensure consistency
+			// as well as ensure the caller knows the exporter shut down
+			// successfully (they can already determine if the deadline is
+			// expired given they passed the context).
+			select {
+			case err = <-done:
+			default:
 				err = ctx.Err()
 			}
+		}
 	})
 	return err
 }

sdk/trace/simple_span_processor_test.go

@@ -40,9 +40,15 @@ func (t *testExporter) ExportSpans(ctx context.Context, spans []sdktrace.ReadOnl
 	return nil
 }
 
-func (t *testExporter) Shutdown(context.Context) error {
+func (t *testExporter) Shutdown(ctx context.Context) error {
 	t.shutdown = true
+	select {
+	case <-ctx.Done():
+		// Ensure context deadline tests receive the expected error.
+		return ctx.Err()
+	default:
 		return nil
+	}
 }
 
 var _ sdktrace.SpanExporter = (*testExporter)(nil)