Update example instrumentation names (#5612)

Part of #5412 

- Use the recommended package name for the instrumentation exemplified
in the repository.
- Use the recommended detection of a `TracerProvider` from passed
context.

example/dice/rolldice.go

@@ -9,7 +9,7 @@ import (
 	"go.opentelemetry.io/otel/metric"
 )
 
-const name = "rolldice"
+const name = "go.opentelemetry.io/otel/example/dice"
 
 var (
 	tracer  = otel.Tracer(name)

example/namedtracer/foo/foo.go

@@ -18,7 +18,7 @@ var lemonsKey = attribute.Key("ex.com/lemons")
 func SubOperation(ctx context.Context) error {
 	// Using global provider. Alternative is to have application provide a getter
 	// for its component to get the instance of the provider.
-	tr := otel.Tracer("example/namedtracer/foo")
+	tr := otel.Tracer("go.opentelemetry.io/otel/example/namedtracer/foo")
 
 	var span trace.Span
 	_, span = tr.Start(ctx, "Sub operation...")

example/namedtracer/main.go

@@ -52,7 +52,7 @@ func main() {
 	}
 
 	// Create a named tracer with package path as its name.
-	tracer := tp.Tracer("example/namedtracer/main")
+	tracer := tp.Tracer("go.opentelemetry.io/otel/example/namedtracer")
 	ctx := context.Background()
 	defer func() { _ = tp.Shutdown(ctx) }()
 

example/opencensus/main.go

@@ -76,7 +76,8 @@ func tracing(otExporter sdktrace.SpanExporter) {
 	tp.ForceFlush(ctx)
 
 	log.Println("Creating OpenTelemetry span\n-- It should have the OpenCensus span as a parent, since the OpenCensus span was written with using OpenTelemetry APIs.")
-	ctx, otspan := tp.Tracer("simple").Start(ctx, "OpenTelemetrySpan")
+	tracer := tp.Tracer("go.opentelemetry.io/otel/example/opencensus")
+	ctx, otspan := tracer.Start(ctx, "OpenTelemetrySpan")
 	otspan.End()
 	tp.ForceFlush(ctx)
 

example/otel-collector/main.go

@@ -130,8 +130,9 @@ func main() {
 		}
 	}()
 
-	tracer := otel.Tracer("test-tracer")
-	meter := otel.Meter("test-meter")
+	name := "go.opentelemetry.io/otel/example/otel-collector"
+	tracer := otel.Tracer(name)
+	meter := otel.Meter(name)
 
 	// Attributes represent additional key-value descriptors that can be bound
 	// to a metric observer or recorder.

example/passthrough/handler/handler.go

@@ -30,7 +30,7 @@ func New(next func(r *http.Request)) *Handler {
 	// global progatators and tracer providers.
 	return &Handler{
 		propagators: otel.GetTextMapPropagator(),
-		tracer:      otel.Tracer("examples/passthrough/handler"),
+		tracer:      otel.Tracer("go.opentelemetry.io/otel/example/passthrough/handler"),
 		next:        next,
 	}
 }

example/passthrough/main.go

@@ -18,6 +18,8 @@ import (
 	"go.opentelemetry.io/otel/trace"
 )
 
+const name = "go.opentelemetry.io/otel/example/passthrough"
+
 func main() {
 	ctx := context.Background()
 
@@ -37,16 +39,22 @@ func main() {
 	// This is roughly what an instrumented http client does.
 	log.Println("The \"make outer request\" span should be recorded, because it is recorded with a Tracer from the SDK TracerProvider")
 	var span trace.Span
-	ctx, span = tp.Tracer("example/passthrough/outer").Start(ctx, "make outer request")
+	tracer := tp.Tracer(name)
+	ctx, span = tracer.Start(ctx, "make outer request")
 	defer span.End()
 	r = r.WithContext(ctx)
 	otel.GetTextMapPropagator().Inject(ctx, propagation.HeaderCarrier(r.Header))
 
 	backendFunc := func(r *http.Request) {
 		// This is roughly what an instrumented http server does.
-		ctx := otel.GetTextMapPropagator().Extract(r.Context(), propagation.HeaderCarrier(r.Header))
+		ctx := r.Context()
+
+		tp := trace.SpanFromContext(ctx).TracerProvider()
+		tracer := tp.Tracer(name)
+
+		ctx = otel.GetTextMapPropagator().Extract(ctx, propagation.HeaderCarrier(r.Header))
 		log.Println("The \"handle inner request\" span should be recorded, because it is recorded with a Tracer from the SDK TracerProvider")
-		_, span := tp.Tracer("example/passthrough/inner").Start(ctx, "handle inner request")
+		_, span := tracer.Start(ctx, "handle inner request")
 		defer span.End()
 
 		// Do "backend work"

example/prometheus/main.go

@@ -21,7 +21,7 @@ import (
 	"go.opentelemetry.io/otel/sdk/metric"
 )
 
-const meterName = "github.com/open-telemetry/opentelemetry-go/example/prometheus"
+const meterName = "go.opentelemetry.io/otel/example/prometheus"
 
 func main() {
 	rng := rand.New(rand.NewSource(time.Now().UnixNano()))

example/zipkin/main.go

@@ -21,6 +21,8 @@ import (
 	"go.opentelemetry.io/otel/trace"
 )
 
+const name = "go.opentelemetry.io/otel/example/zipkin"
+
 var logger = log.New(os.Stderr, "zipkin-example", log.Ldate|log.Ltime|log.Llongfile)
 
 // initTracer creates a new trace provider instance and registers it as global trace provider.
@@ -69,7 +71,7 @@ func main() {
 		}
 	}()
 
-	tr := otel.GetTracerProvider().Tracer("component-main")
+	tr := otel.GetTracerProvider().Tracer(name)
 	ctx, span := tr.Start(ctx, "foo", trace.WithSpanKind(trace.SpanKindServer))
 	<-time.After(6 * time.Millisecond)
 	bar(ctx)
@@ -78,7 +80,7 @@ func main() {
 }
 
 func bar(ctx context.Context) {
-	tr := otel.GetTracerProvider().Tracer("component-bar")
+	tr := trace.SpanFromContext(ctx).TracerProvider().Tracer(name)
 	_, span := tr.Start(ctx, "bar")
 	<-time.After(6 * time.Millisecond)
 	span.End()