Use lock when retrieving span.Context() (jaegertracing#268)

Signed-off-by: Yuri Shkuro <ys@uber.com>

span.go

@@ -202,6 +202,8 @@ func (s *Span) FinishWithOptions(options opentracing.FinishOptions) {
 
 // Context implements opentracing.Span API
 func (s *Span) Context() opentracing.SpanContext {
+	s.Lock()
+	defer s.Unlock()
 	return s.context
 }
 

span_test.go

@@ -15,6 +15,7 @@
 package jaeger
 
 import (
+	"sync"
 	"testing"
 
 	"github.com/opentracing/opentracing-go"
@@ -121,3 +122,27 @@ type testThrottler struct {
 func (t testThrottler) IsAllowed(operation string) bool {
 	return t.allowAll
 }
+
+func TestBaggageContextRace(t *testing.T) {
+	tracer, closer := NewTracer("DOOP", NewConstSampler(true), NewNullReporter())
+	defer closer.Close()
+
+	sp1 := tracer.StartSpan("s1").(*Span)
+
+	var startWg, endWg sync.WaitGroup
+	startWg.Add(1)
+	endWg.Add(2)
+
+	f := func() {
+		startWg.Wait()
+		sp1.SetBaggageItem("x", "y")
+		sp1.Context().ForeachBaggageItem(func(k, v string) bool { return false })
+		endWg.Done()
+	}
+
+	go f()
+	go f()
+
+	startWg.Done()
+	endWg.Wait()
+}