tracer: minimize overhead on noop tracer usage

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

tracer/context.go

@@ -37,6 +37,15 @@ func NewContext(ctx context.Context, tracer Tracer) context.Context {
 
 type spanKey struct{}
 
+// SpanFromContext returns a span from context
+func SpanMustContext(ctx context.Context) Span {
+	sp, ok := SpanFromContext(ctx)
+	if !ok {
+		panic("missing span")
+	}
+	return sp
+}
+
 // SpanFromContext returns a span from context
 func SpanFromContext(ctx context.Context) (Span, bool) {
 	if ctx == nil {

tracer/memory/memory.go

@@ -25,6 +25,7 @@ func (t *Tracer) Start(ctx context.Context, name string, opts ...tracer.SpanOpti
 		name:      name,
 		ctx:       ctx,
 		tracer:    t,
+		labels:    options.Labels,
 		kind:      options.Kind,
 		startTime: time.Now(),
 	}
@@ -37,6 +38,14 @@ func (t *Tracer) Start(ctx context.Context, name string, opts ...tracer.SpanOpti
 	return tracer.NewSpanContext(ctx, span), span
 }
 
+type memoryStringer struct {
+	s string
+}
+
+func (s memoryStringer) String() string {
+	return s.s
+}
+
 func (t *Tracer) Flush(_ context.Context) error {
 	return nil
 }
@@ -52,14 +61,6 @@ func (t *Tracer) Name() string {
 	return t.opts.Name
 }
 
-type noopStringer struct {
-	s string
-}
-
-func (s noopStringer) String() string {
-	return s.s
-}
-
 type Span struct {
 	ctx        context.Context
 	tracer     tracer.Tracer
@@ -67,8 +68,8 @@ type Span struct {
 	statusMsg  string
 	startTime  time.Time
 	finishTime time.Time
-	traceID    noopStringer
+	traceID    memoryStringer
-	spanID     noopStringer
+	spanID     memoryStringer
 	events     []*Event
 	labels     []interface{}
 	logs       []interface{}

tracer/noop.go

@@ -2,6 +2,7 @@ package tracer
 
 import (
 	"context"
+	"time"
 
 	"go.unistack.org/micro/v3/util/id"
 )
@@ -23,6 +24,7 @@ func (t *noopTracer) Start(ctx context.Context, name string, opts ...SpanOption)
 		name:      name,
 		ctx:       ctx,
 		tracer:    t,
+		startTime: time.Now(),
 		labels:    options.Labels,
 		kind:      options.Kind,
 	}
@@ -31,7 +33,6 @@ func (t *noopTracer) Start(ctx context.Context, name string, opts ...SpanOption)
 	if span.ctx == nil {
 		span.ctx = context.Background()
 	}
-	t.spans = append(t.spans, span)
 	return NewSpanContext(ctx, span), span
 }
 
@@ -58,21 +59,16 @@ func (t *noopTracer) Name() string {
 	return t.opts.Name
 }
 
-type noopEvent struct {
-	name   string
-	labels []interface{}
-}
-
 type noopSpan struct {
 	ctx        context.Context
 	tracer     Tracer
 	name       string
 	statusMsg  string
+	startTime  time.Time
+	finishTime time.Time
 	traceID    noopStringer
 	spanID     noopStringer
-	events    []*noopEvent
 	labels     []interface{}
-	logs      []interface{}
 	kind       SpanKind
 	status     SpanStatus
 }
@@ -86,6 +82,7 @@ func (s *noopSpan) SpanID() string {
 }
 
 func (s *noopSpan) Finish(_ ...SpanOption) {
+	s.finishTime = time.Now()
 }
 
 func (s *noopSpan) Context() context.Context {
@@ -97,8 +94,6 @@ func (s *noopSpan) Tracer() Tracer {
 }
 
 func (s *noopSpan) AddEvent(name string, opts ...EventOption) {
-	options := NewEventOptions(opts...)
-	s.events = append(s.events, &noopEvent{name: name, labels: options.Labels})
 }
 
 func (s *noopSpan) SetName(name string) {
@@ -106,7 +101,6 @@ func (s *noopSpan) SetName(name string) {
 }
 
 func (s *noopSpan) AddLogs(kv ...interface{}) {
-	s.logs = append(s.logs, kv...)
 }
 
 func (s *noopSpan) AddLabels(kv ...interface{}) {