sdk/resource: Fix data race with emptyAttributes (#4409)

* Fix ASAN bug with emptyAttributes.

If mutliple instantiations of a Resources struct are happening
in parallel, they can end up modifying the same underlying resource.

* Capture literal

* add test

* remove unwanted change

* Update sdk/resource/resource_test.go

Co-authored-by: Robert Pająk <pellared@hotmail.com>

* Update sdk/resource/resource_test.go

Co-authored-by: Robert Pająk <pellared@hotmail.com>

* Update sdk/resource/resource_test.go

Co-authored-by: Robert Pająk <pellared@hotmail.com>

* Update sdk/resource/resource_test.go

Co-authored-by: Robert Pająk <pellared@hotmail.com>

* Add changelog.

* Update CHANGELOG.md

Co-authored-by: Robert Pająk <pellared@hotmail.com>

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

sdk/resource/resource.go

@@ -36,7 +36,6 @@ type Resource struct {
 }
 
 var (
-	emptyResource       Resource
 	defaultResource     *Resource
 	defaultResourceOnce sync.Once
 )
@@ -70,7 +69,7 @@ func NewWithAttributes(schemaURL string, attrs ...attribute.KeyValue) *Resource
 // 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 @@ func NewSchemaless(attrs ...attribute.KeyValue) *Resource {
 
 	// 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 @@ func Merge(a, b *Resource) (*Resource, error) {
 // 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 @@ func Default() *Resource {
 		}
 		// 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{}