Do not store TracerProvider or Tracer fields in SDK recordingSpan (#2575)

* Do not store TracerProvider fields in span

Instead of keeping a reference to the span's Tracer, and therefore also
it's TracerProvider, and the associated resource and spanLimits just
keep the reference to the Tracer. Refer to the TracerProvider fields
when needed instead.

* Make span refer to the inst lib via the Tracer

Instead of holding a field in the span, refer to the field in the parent
Tracer.

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()
@@ -440,7 +429,7 @@ 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
@@ -448,7 +437,7 @@ func (s *recordingSpan) InstrumentationLibrary() instrumentation.Library {
 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() {