sdk/resource: Fix data race with emptyAttributes

CHANGELOG.md

@@ -63,6 +63,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Decouple `go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp/internal` from `go.opentelemetry.io/otel/exporters/otlp/internal` and `go.opentelemetry.io/otel/exporters/otlp/otlptrace/internal` using gotmpl. (#4401, #3846)
 - Do not block the metric SDK when OTLP metric exports are blocked in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc` and `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#3925, #4395)
 - Do not append _total if the counter already ends in total `go.opentelemetry.io/otel/exporter/prometheus`. (#4373)
+- Fix resource detection data race in `go.opentelemetry.io/otel/sdk/resource`. (#4409)
 
 ## [1.16.0/0.39.0] 2023-05-18
 

sdk/resource/resource.go

@@ -36,7 +36,6 @@
 }
 
 var (
-	emptyResource       Resource
 	defaultResource     *Resource
 	defaultResourceOnce sync.Once
 )
@@ -70,7 +69,7 @@
 // of the attrs is known use NewWithAttributes instead.
 func NewSchemaless(attrs ...attribute.KeyValue) *Resource {
 	if len(attrs) == 0 {
-		return &emptyResource
+		return &Resource{}
 	}
 
 	// Ensure attributes comply with the specification:
@@ -81,7 +80,7 @@
 
 	// If attrs only contains invalid entries do not allocate a new resource.
 	if s.Len() == 0 {
-		return &emptyResource
+		return &Resource{}
 	}
 
 	return &Resource{attrs: s} //nolint
@@ -195,7 +194,7 @@
 // Empty returns an instance of Resource with no attributes. It is
 // equivalent to a `nil` Resource.
 func Empty() *Resource {
-	return &emptyResource
+	return &Resource{}
 }
 
 // Default returns an instance of Resource with a default
@@ -214,7 +213,7 @@
 		}
 		// If Detect did not return a valid resource, fall back to emptyResource.
 		if defaultResource == nil {
-			defaultResource = &emptyResource
+			defaultResource = &Resource{}
 		}
 	})
 	return defaultResource

sdk/resource/resource_test.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"os"
 	"strings"
+	"sync"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -769,3 +770,29 @@ func TestWithContainer(t *testing.T) {
 		string(semconv.ContainerIDKey): fakeContainerID,
 	}, toMap(res))
 }
+
+func TestResourceConcurrentSafe(t *testing.T) {
+	// Creating Resources should also be free of any data races,
+	// because Resources are immutable.
+	var wg sync.WaitGroup
+	for i := 0; i < 2; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			d := &fakeDetector{}
+			_, err := resource.Detect(context.Background(), d)
+			assert.NoError(t, err)
+		}()
+	}
+	wg.Wait()
+}
+
+type fakeDetector struct{}
+
+func (f fakeDetector) Detect(_ context.Context) (*resource.Resource, error) {
+	// A bit pedantic, but resource.NewWithAttributes returns an empty Resource when
+	// no attributes specified. We want to make sure that this is concurrent-safe.
+	return resource.NewWithAttributes("https://opentelemetry.io/schemas/1.3.0"), nil
+}
+
+var _ resource.Detector = &fakeDetector{}