Do not store TracerProvider or Tracer fields in SDK recordingSpan

sdk/trace/provider.go

@@ -74,10 +74,13 @@ type TracerProvider struct {
 	mu             sync.Mutex
 	namedTracer    map[instrumentation.Library]*tracer
 	spanProcessors atomic.Value
-	sampler        Sampler
-	idGenerator    IDGenerator
-	spanLimits     SpanLimits
-	resource       *resource.Resource
+
+	// These fields are not protected by the lock mu. They are assumed to be
+	// immutable after creation of the TracerProvider.
+	sampler     Sampler
+	idGenerator IDGenerator
+	spanLimits  SpanLimits
+	resource    *resource.Resource
 }
 
 var _ trace.TracerProvider = &TracerProvider{}

sdk/trace/span.go

@@ -126,14 +126,6 @@ type recordingSpan struct {
 	// childSpanCount holds the number of child spans created for this span.
 	childSpanCount int
 
-	// resource contains attributes representing an entity that produced this
-	// span.
-	resource *resource.Resource
-
-	// instrumentationLibrary defines the instrumentation library used to
-	// provide instrumentation.
-	instrumentationLibrary instrumentation.Library
-
 	// spanContext holds the SpanContext of this span.
 	spanContext trace.SpanContext
 
@@ -152,9 +144,6 @@ type recordingSpan struct {
 
 	// tracer is the SDK tracer that created this span.
 	tracer *tracer
-
-	// spanLimits holds the limits to this span.
-	spanLimits SpanLimits
 }
 
 var _ ReadWriteSpan = (*recordingSpan)(nil)
@@ -336,9 +325,9 @@ func (s *recordingSpan) addEvent(name string, o ...trace.EventOption) {
 	// Discard over limited attributes
 	attributes := c.Attributes()
 	var discarded int
-	if len(attributes) > s.spanLimits.AttributePerEventCountLimit {
-		discarded = len(attributes) - s.spanLimits.AttributePerEventCountLimit
-		attributes = attributes[:s.spanLimits.AttributePerEventCountLimit]
+	if len(attributes) > s.tracer.provider.spanLimits.AttributePerEventCountLimit {
+		discarded = len(attributes) - s.tracer.provider.spanLimits.AttributePerEventCountLimit
+		attributes = attributes[:s.tracer.provider.spanLimits.AttributePerEventCountLimit]
 	}
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -440,15 +429,15 @@ func (s *recordingSpan) Status() Status {
 func (s *recordingSpan) InstrumentationLibrary() instrumentation.Library {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	return s.instrumentationLibrary
+	return s.tracer.instrumentationLibrary
 }
 
 // Resource returns the Resource associated with the Tracer that created this
 // span.
 func (s *recordingSpan) Resource() *resource.Resource {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	return s.resource
+	return s.tracer.provider.resource
 }
 
 func (s *recordingSpan) addLink(link trace.Link) {
@@ -461,9 +450,9 @@ func (s *recordingSpan) addLink(link trace.Link) {
 	var droppedAttributeCount int
 
 	// Discard over limited attributes
-	if len(link.Attributes) > s.spanLimits.AttributePerLinkCountLimit {
-		droppedAttributeCount = len(link.Attributes) - s.spanLimits.AttributePerLinkCountLimit
-		link.Attributes = link.Attributes[:s.spanLimits.AttributePerLinkCountLimit]
+	if len(link.Attributes) > s.tracer.provider.spanLimits.AttributePerLinkCountLimit {
+		droppedAttributeCount = len(link.Attributes) - s.tracer.provider.spanLimits.AttributePerLinkCountLimit
+		link.Attributes = link.Attributes[:s.tracer.provider.spanLimits.AttributePerLinkCountLimit]
 	}
 
 	s.links.add(Link{link.SpanContext, link.Attributes, droppedAttributeCount})
@@ -514,10 +503,10 @@ func (s *recordingSpan) snapshot() ReadOnlySpan {
 	defer s.mu.Unlock()
 
 	sd.endTime = s.endTime
-	sd.instrumentationLibrary = s.instrumentationLibrary
+	sd.instrumentationLibrary = s.tracer.instrumentationLibrary
 	sd.name = s.name
 	sd.parent = s.parent
-	sd.resource = s.resource
+	sd.resource = s.tracer.provider.resource
 	sd.spanContext = s.spanContext
 	sd.spanKind = s.spanKind
 	sd.startTime = s.startTime

sdk/trace/tracer.go

@@ -122,18 +122,15 @@ func (tr *tracer) newRecordingSpan(psc, sc trace.SpanContext, name string, sr Sa
 	}
 
 	s := &recordingSpan{
-		parent:                 psc,
-		spanContext:            sc,
-		spanKind:               trace.ValidateSpanKind(config.SpanKind()),
-		name:                   name,
-		startTime:              startTime,
-		attributes:             newAttributesMap(tr.provider.spanLimits.AttributeCountLimit),
-		events:                 newEvictedQueue(tr.provider.spanLimits.EventCountLimit),
-		links:                  newEvictedQueue(tr.provider.spanLimits.LinkCountLimit),
-		tracer:                 tr,
-		spanLimits:             tr.provider.spanLimits,
-		resource:               tr.provider.resource,
-		instrumentationLibrary: tr.instrumentationLibrary,
+		parent:      psc,
+		spanContext: sc,
+		spanKind:    trace.ValidateSpanKind(config.SpanKind()),
+		name:        name,
+		startTime:   startTime,
+		attributes:  newAttributesMap(tr.provider.spanLimits.AttributeCountLimit),
+		events:      newEvictedQueue(tr.provider.spanLimits.EventCountLimit),
+		links:       newEvictedQueue(tr.provider.spanLimits.LinkCountLimit),
+		tracer:      tr,
 	}
 
 	for _, l := range config.Links() {