Fix issue #1490, apply same logic as in the SDK

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

internal/global/trace.go

@@ -45,8 +45,7 @@ import (
 // All TracerProvider functionality is forwarded to a delegate once
 // configured.
 type tracerProvider struct {
-	mtx      sync.Mutex
-	tracers  []*tracer
+	tracers  sync.Map
 	delegate atomic.Value
 }
 
@@ -63,12 +62,11 @@ var _ trace.TracerProvider = &tracerProvider{}
 // It is guaranteed by the caller that this happens only once.
 func (p *tracerProvider) setDelegate(provider trace.TracerProvider) {
 	p.delegate.Store(provider)
-	p.mtx.Lock()
-	defer p.mtx.Unlock()
-
-	for _, t := range p.tracers {
-		t.setDelegate(provider)
-	}
+	p.tracers.Range(func(key, value interface{}) bool {
+		value.(*tracer).setDelegate(provider)
+		p.tracers.Delete(key)
+		return true
+	})
 }
 
 // Tracer implements TracerProvider.
@@ -78,12 +76,26 @@ func (p *tracerProvider) Tracer(name string, opts ...trace.TracerOption) trace.T
 		return delegate.(trace.TracerProvider).Tracer(name, opts...)
 	}
 
-	p.mtx.Lock()
-	defer p.mtx.Unlock()
+	key := createKey(name, opts...)
+	if val, ok := p.tracers.Load(key); ok {
+		return val.(*tracer)
+	}
+
+	// Value not present, we cannot be sure that there is not any other concurrent
+	t, _ := p.tracers.LoadOrStore(key, &tracer{name: name, opts: opts})
+	return t.(*tracer)
+}
+
+type il struct {
+	name    string
+	version string
+}
 
-	t := &tracer{name: name, opts: opts}
-	p.tracers = append(p.tracers, t)
-	return t
+func createKey(name string, opts ...trace.TracerOption) il {
+	return il{
+		name:    name,
+		version: trace.NewTracerConfig(opts...).InstrumentationVersion,
+	}
 }
 
 // tracer is a placeholder for a trace.Tracer.

internal/global/trace_test.go

@@ -102,6 +102,25 @@ func TestTraceProviderDelegates(t *testing.T) {
 	assert.True(t, called, "expected configured TraceProvider to be called")
 }
 
+func TestTraceProviderDelegates_SameInstance(t *testing.T) {
+	global.ResetForTest()
+
+	// Retrieve the placeholder TracerProvider.
+	gtp := otel.GetTracerProvider()
+
+	tracer := gtp.Tracer("abc", trace.WithInstrumentationVersion("xyz"))
+	assert.Same(t, tracer, gtp.Tracer("abc", trace.WithInstrumentationVersion("xyz")))
+	assert.Same(t, tracer, gtp.Tracer("abc", trace.WithInstrumentationVersion("xyz")))
+
+	otel.SetTracerProvider(fnTracerProvider{
+		tracer: func(name string, opts ...trace.TracerOption) trace.Tracer {
+			return trace.NewNoopTracerProvider().Tracer("")
+		},
+	})
+
+	assert.NotSame(t, tracer, gtp.Tracer("abc", trace.WithInstrumentationVersion("xyz")))
+}
+
 func TestTraceProviderDelegates_MultiGoRoutines(t *testing.T) {
 	global.ResetForTest()