TracerProvider allows calling Tracer() while it's shutting down

CHANGELOG.md

@@ -33,6 +33,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Fixed
 
 - `TracerProvider` consistently doesn't allow to register a `SpanProcessor` after shutdown. (#3845)
+- `TracerProvider` allows calling `Tracer()` while it's shutting down. It used to deadlock.
 
 ### Removed
 

sdk/trace/provider.go

@@ -73,8 +73,10 @@ func (cfg tracerProviderConfig) MarshalLog() interface{} {
 // TracerProvider is an OpenTelemetry TracerProvider. It provides Tracers to
 // instrumentation so it can trace operational flow through a system.
 type TracerProvider struct {
+	tracerMu    sync.Mutex // separate mutex because Tracer() may be called while holding mu via Shutdown().
+	namedTracer map[instrumentation.Scope]*tracer
+
 	mu             sync.Mutex
-	namedTracer    map[instrumentation.Scope]*tracer
 	spanProcessors atomic.Value
 	isShutdown     bool
 
@@ -138,8 +140,6 @@ func NewTracerProvider(opts ...TracerProviderOption) *TracerProvider {
 func (p *TracerProvider) Tracer(name string, opts ...trace.TracerOption) trace.Tracer {
 	c := trace.NewTracerConfig(opts...)
 
-	p.mu.Lock()
-	defer p.mu.Unlock()
 	if name == "" {
 		name = defaultTracerName
 	}
@@ -148,14 +148,21 @@ func (p *TracerProvider) Tracer(name string, opts ...trace.TracerOption) trace.T
 		Version:   c.InstrumentationVersion(),
 		SchemaURL: c.SchemaURL(),
 	}
-	t, ok := p.namedTracer[is]
-	if !ok {
-		t = &tracer{
-			provider:             p,
-			instrumentationScope: is,
+	t, ok := func() (*tracer, bool) {
+		p.tracerMu.Lock()
+		defer p.tracerMu.Unlock()
+		t, ok := p.namedTracer[is]
+		if !ok {
+			t = &tracer{
+				provider:             p,
+				instrumentationScope: is,
+			}
+			p.namedTracer[is] = t
 		}
-		p.namedTracer[is] = t
-		global.Info("Tracer created", "name", name, "version", c.InstrumentationVersion(), "schemaURL", c.SchemaURL())
+		return t, ok
+	}()
+	if !ok {
+		global.Info("Tracer created", "name", name, "version", is.Version, "schemaURL", is.SchemaURL)
 	}
 	return t
 }

sdk/trace/provider_test.go

@@ -46,6 +46,33 @@ func (t *basicSpanProcessor) ForceFlush(context.Context) error {
 	return nil
 }
 
+type shutdownSpanProcessor struct {
+	shutdown func(context.Context) error
+}
+
+func (t *shutdownSpanProcessor) Shutdown(ctx context.Context) error {
+	return t.shutdown(ctx)
+}
+
+func (t *shutdownSpanProcessor) OnStart(context.Context, ReadWriteSpan) {}
+func (t *shutdownSpanProcessor) OnEnd(ReadOnlySpan)                     {}
+func (t *shutdownSpanProcessor) ForceFlush(context.Context) error {
+	return nil
+}
+
+func TestShutdownCallsTracerMethod(t *testing.T) {
+	stp := NewTracerProvider()
+	sp := &shutdownSpanProcessor{
+		shutdown: func(ctx context.Context) error {
+			_ = stp.Tracer("abc") // must not deadlock
+			return nil
+		},
+	}
+	stp.RegisterSpanProcessor(sp)
+	assert.NoError(t, stp.Shutdown(context.Background()))
+	assert.True(t, stp.isShutdown)
+}
+
 func TestForceFlushAndShutdownTraceProviderWithoutProcessor(t *testing.T) {
 	stp := NewTracerProvider()
 	assert.NoError(t, stp.ForceFlush(context.Background()))