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

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

CHANGELOG.md

@@ -38,6 +38,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - `SamplingResult.TraceState` is correctly propagated to a newly created
   span's `SpanContext`. (#1655)
 - Jaeger Exporter: Ensure mapping between OTEL and Jaeger span data complies with the specification. (#1626)
+- Issue #1490, apply same logic as in the SDK. (#1687)
 
 ## [0.18.0] - 2020-03-03
 

internal/global/trace.go

@@ -44,9 +44,8 @@ import (
 // All TracerProvider functionality is forwarded to a delegate once
 // configured.
 type tracerProvider struct {
-	mtx     sync.Mutex
-	tracers []*tracer
-
+	mtx      sync.Mutex
+	tracers  map[il]*tracer
 	delegate trace.TracerProvider
 }
 
@@ -63,14 +62,15 @@ var _ trace.TracerProvider = &tracerProvider{}
 // Delegation only happens on the first call to this method. All subsequent
 // calls result in no delegation changes.
 func (p *tracerProvider) setDelegate(provider trace.TracerProvider) {
-	if p.delegate != nil {
-		return
-	}
-
 	p.mtx.Lock()
 	defer p.mtx.Unlock()
 
 	p.delegate = provider
+
+	if len(p.tracers) == 0 {
+		return
+	}
+
 	for _, t := range p.tracers {
 		t.setDelegate(provider)
 	}
@@ -87,11 +87,35 @@ func (p *tracerProvider) Tracer(name string, opts ...trace.TracerOption) trace.T
 		return p.delegate.Tracer(name, opts...)
 	}
 
+	// At this moment it is guaranteed that no sdk is installed, save the tracer in the tracers map.
+
+	key := createKey(name, opts...)
+
+	if p.tracers == nil {
+		p.tracers = make(map[il]*tracer)
+	}
+
+	if val, ok := p.tracers[key]; ok {
+		return val
+	}
+
 	t := &tracer{name: name, opts: opts}
-	p.tracers = append(p.tracers, t)
+	p.tracers[key] = t
 	return t
 }
 
+type il struct {
+	name    string
+	version string
+}
+
+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.
 //
 // All Tracer functionality is forwarded to a delegate once configured.

internal/global/trace_test.go

@@ -91,3 +91,22 @@ func TestTraceProviderDelegates(t *testing.T) {
 	gtp.Tracer("abc", trace.WithInstrumentationVersion("xyz"))
 	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")))
+}