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

CHANGELOG.md

@@ -40,9 +40,8 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Jaeger Exporter: Ensure mapping between OTEL and Jaeger span data complies with the specification. (#1626)
 - The `otel-collector` example now correctly flushes metric events prior to shutting down the exporter. (#1678)
 - Synchronization issues in global trace delegate implementation. (#1686)
-
-### Fixed
 - Do not set span status message in `SpanStatusFromHTTPStatusCode` if it can be inferred from `http.status_code`. (#1681)
+- Reduced excess memory usage by global `TracerProvider`. (#1687)
 
 ## [0.18.0] - 2020-03-03
 

internal/global/trace.go

@@ -46,7 +46,7 @@ import (
 // configured.
 type tracerProvider struct {
 	mtx      sync.Mutex
-	tracers  []*tracer
+	tracers  map[il]*tracer
 	delegate trace.TracerProvider
 }
 
@@ -66,6 +66,11 @@ func (p *tracerProvider) setDelegate(provider trace.TracerProvider) {
 	defer p.mtx.Unlock()
 
 	p.delegate = provider
+
+	if len(p.tracers) == 0 {
+		return
+	}
+
 	for _, t := range p.tracers {
 		t.setDelegate(provider)
 	}
@@ -82,11 +87,31 @@ 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 := il{
+		name:    name,
+		version: trace.NewTracerConfig(opts...).InstrumentationVersion,
+	}
+
+	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
+}
+
 // tracer is a placeholder for a trace.Tracer.
 //
 // All Tracer functionality is forwarded to a delegate once configured.

internal/global/trace_test.go

@@ -195,3 +195,21 @@ func TestTracerDelegatesConcurrentSafe(t *testing.T) {
 
 	assert.LessOrEqual(t, int32(10), atomic.LoadInt32(&called), "expected configured TraceProvider to be called")
 }
+
+func TestTraceProviderDelegatesSameInstance(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")))
+}