Register/unregister in the fixed order (#1198)

- change the processors' map to array
- increase test coverage

Signed-off-by: Hui Kang <kangh@us.ibm.com>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

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

CHANGELOG.md

@@ -65,6 +65,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Rename `NewProvider` to `NewTracerProvider` in the `go.opentelemetry.io/otel/sdk/trace` package. (#1190)
 - Renamed `SamplingDecision` values to comply with OpenTelemetry specification change. (#1192)
 - Renamed Zipkin attribute names from `ot.status_code & ot.status_description` to `otel.status_code & otel.status_description`. (#1201)
+- The default SDK now invokes registered `SpanProcessor`s in the order they were registered with the `TracerProvider`. (#1195)
 
 ### Removed
 

sdk/trace/provider.go

@@ -109,13 +109,15 @@ func (p *TracerProvider) Tracer(name string, opts ...apitrace.TracerOption) apit
 func (p *TracerProvider) RegisterSpanProcessor(s SpanProcessor) {
 	p.mu.Lock()
 	defer p.mu.Unlock()
-	new := make(spanProcessorMap)
-	if old, ok := p.spanProcessors.Load().(spanProcessorMap); ok {
-		for k, v := range old {
-			new[k] = v
-		}
+	new := spanProcessorStates{}
+	if old, ok := p.spanProcessors.Load().(spanProcessorStates); ok {
+		new = append(new, old...)
 	}
-	new[s] = &sync.Once{}
+	newSpanSync := &spanProcessorState{
+		sp:    s,
+		state: &sync.Once{},
+	}
+	new = append(new, newSpanSync)
 	p.spanProcessors.Store(new)
 }
 
@@ -123,18 +125,33 @@ func (p *TracerProvider) RegisterSpanProcessor(s SpanProcessor) {
 func (p *TracerProvider) UnregisterSpanProcessor(s SpanProcessor) {
 	p.mu.Lock()
 	defer p.mu.Unlock()
-	new := make(spanProcessorMap)
-	if old, ok := p.spanProcessors.Load().(spanProcessorMap); ok {
-		for k, v := range old {
-			new[k] = v
+	new := spanProcessorStates{}
+	old, ok := p.spanProcessors.Load().(spanProcessorStates)
+	if !ok || len(old) == 0 {
+		return
+	}
+	new = append(new, old...)
+
+	// stop the span processor if it is started and remove it from the list
+	var stopOnce *spanProcessorState
+	var idx int
+	for i, sps := range new {
+		if sps.sp == s {
+			stopOnce = sps
+			idx = i
 		}
 	}
-	if stopOnce, ok := new[s]; ok && stopOnce != nil {
-		stopOnce.Do(func() {
+	if stopOnce != nil {
+		stopOnce.state.Do(func() {
 			s.Shutdown()
 		})
 	}
-	delete(new, s)
+	if len(new) > 1 {
+		copy(new[idx:], new[idx+1:])
+	}
+	new[len(new)-1] = nil
+	new = new[:len(new)-1]
+
 	p.spanProcessors.Store(new)
 }
 

sdk/trace/span.go

@@ -139,8 +139,8 @@ func (s *span) End(options ...apitrace.SpanOption) {
 	}
 	config := apitrace.NewSpanConfig(options...)
 	s.endOnce.Do(func() {
-		sps, _ := s.tracer.provider.spanProcessors.Load().(spanProcessorMap)
-		mustExportOrProcess := len(sps) > 0
+		sps, ok := s.tracer.provider.spanProcessors.Load().(spanProcessorStates)
+		mustExportOrProcess := ok && len(sps) > 0
 		if mustExportOrProcess {
 			sd := s.makeSpanData()
 			if config.Timestamp.IsZero() {
@@ -148,8 +148,8 @@ func (s *span) End(options ...apitrace.SpanOption) {
 			} else {
 				sd.EndTime = config.Timestamp
 			}
-			for sp := range sps {
-				sp.OnEnd(sd)
+			for _, sp := range sps {
+				sp.sp.OnEnd(sd)
 			}
 		}
 	})

sdk/trace/span_processor.go

@@ -43,4 +43,8 @@ type SpanProcessor interface {
 	ForceFlush()
 }
 
-type spanProcessorMap map[SpanProcessor]*sync.Once
+type spanProcessorState struct {
+	sp    SpanProcessor
+	state *sync.Once
+}
+type spanProcessorStates []*spanProcessorState

sdk/trace/span_processor_test.go

@@ -45,47 +45,66 @@ func (t *testSpanProcesor) ForceFlush() {
 func TestRegisterSpanProcessort(t *testing.T) {
 	name := "Register span processor before span starts"
 	tp := basicTracerProvider(t)
-	sp := NewTestSpanProcessor()
-	tp.RegisterSpanProcessor(sp)
+	sps := []*testSpanProcesor{
+		NewTestSpanProcessor(),
+		NewTestSpanProcessor(),
+	}
+
+	for _, sp := range sps {
+		tp.RegisterSpanProcessor(sp)
+	}
 
 	tr := tp.Tracer("SpanProcessor")
 	_, span := tr.Start(context.Background(), "OnStart")
 	span.End()
 	wantCount := 1
-	gotCount := len(sp.spansStarted)
-	if gotCount != wantCount {
-		t.Errorf("%s: started count: got %d, want %d\n", name, gotCount, wantCount)
-	}
-	gotCount = len(sp.spansEnded)
-	if gotCount != wantCount {
-		t.Errorf("%s: ended count: got %d, want %d\n", name, gotCount, wantCount)
+
+	for _, sp := range sps {
+		gotCount := len(sp.spansStarted)
+		if gotCount != wantCount {
+			t.Errorf("%s: started count: got %d, want %d\n", name, gotCount, wantCount)
+		}
+		gotCount = len(sp.spansEnded)
+		if gotCount != wantCount {
+			t.Errorf("%s: ended count: got %d, want %d\n", name, gotCount, wantCount)
+		}
 	}
 }
 
 func TestUnregisterSpanProcessor(t *testing.T) {
 	name := "Start span after unregistering span processor"
 	tp := basicTracerProvider(t)
-	sp := NewTestSpanProcessor()
-	tp.RegisterSpanProcessor(sp)
+	sps := []*testSpanProcesor{
+		NewTestSpanProcessor(),
+		NewTestSpanProcessor(),
+	}
+
+	for _, sp := range sps {
+		tp.RegisterSpanProcessor(sp)
+	}
 
 	tr := tp.Tracer("SpanProcessor")
 	_, span := tr.Start(context.Background(), "OnStart")
 	span.End()
-	tp.UnregisterSpanProcessor(sp)
+	for _, sp := range sps {
+		tp.UnregisterSpanProcessor(sp)
+	}
 
 	// start another span after unregistering span processor.
 	_, span = tr.Start(context.Background(), "Start span after unregister")
 	span.End()
 
-	wantCount := 1
-	gotCount := len(sp.spansStarted)
-	if gotCount != wantCount {
-		t.Errorf("%s: started count: got %d, want %d\n", name, gotCount, wantCount)
-	}
+	for _, sp := range sps {
+		wantCount := 1
+		gotCount := len(sp.spansStarted)
+		if gotCount != wantCount {
+			t.Errorf("%s: started count: got %d, want %d\n", name, gotCount, wantCount)
+		}
 
-	gotCount = len(sp.spansEnded)
-	if gotCount != wantCount {
-		t.Errorf("%s: ended count: got %d, want %d\n", name, gotCount, wantCount)
+		gotCount = len(sp.spansEnded)
+		if gotCount != wantCount {
+			t.Errorf("%s: ended count: got %d, want %d\n", name, gotCount, wantCount)
+		}
 	}
 }
 

sdk/trace/tracer.go

@@ -58,9 +58,9 @@ func (tr *tracer) Start(ctx context.Context, name string, options ...apitrace.Sp
 	span.tracer = tr
 
 	if span.IsRecording() {
-		sps, _ := tr.provider.spanProcessors.Load().(spanProcessorMap)
-		for sp := range sps {
-			sp.OnStart(span.data)
+		sps, _ := tr.provider.spanProcessors.Load().(spanProcessorStates)
+		for _, sp := range sps {
+			sp.sp.OnStart(span.data)
 		}
 	}