From 23a33739e9ca2e5bdab39b70d25a3c01c3a05b30 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <MrAlias@users.noreply.github.com>
Date: Tue, 19 Oct 2021 08:13:37 -0700
Subject: [PATCH] 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                            |  1 +
 sdk/trace/simple_span_processor.go      | 16 +++++++++++++++-
 sdk/trace/simple_span_processor_test.go | 10 ++++++++--
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index eb39b9e6dea..143a73bc5be 100644
--- a/CHANGELOG.md
+++ b/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
 
diff --git a/sdk/trace/simple_span_processor.go b/sdk/trace/simple_span_processor.go
index 9dc87f893b9..ecc45bc6c38 100644
--- a/sdk/trace/simple_span_processor.go
+++ b/sdk/trace/simple_span_processor.go
@@ -88,10 +88,24 @@ 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():
-			err = ctx.Err()
+			// 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
diff --git a/sdk/trace/simple_span_processor_test.go b/sdk/trace/simple_span_processor_test.go
index 688cc4703bd..4ac7124c5fc 100644
--- a/sdk/trace/simple_span_processor_test.go
+++ b/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
-	return nil
+	select {
+	case <-ctx.Done():
+		// Ensure context deadline tests receive the expected error.
+		return ctx.Err()
+	default:
+		return nil
+	}
 }
 
 var _ sdktrace.SpanExporter = (*testExporter)(nil)