Lazily initialize the view package's default worker

stats/view/export.go

@@ -36,10 +36,12 @@ type Exporter interface {
 //
 // Binaries can register exporters, libraries shouldn't register exporters.
 func RegisterExporter(e Exporter) {
+	maybeInitDefaultWorker()
 	defaultWorker.RegisterExporter(e)
 }
 
 // UnregisterExporter unregisters an exporter.
 func UnregisterExporter(e Exporter) {
+	maybeInitDefaultWorker()
 	defaultWorker.UnregisterExporter(e)
 }

stats/view/export_test.go

@@ -0,0 +1,24 @@
+package view
+
+import "testing"
+
+// Exporting functionality is tested in `worker_test.go`. These are a trivial
+// set of tests to make sure that these package-level exports will correctly
+// initialize defaultWorker if necessary.
+func TestRegisterExporter(t *testing.T) {
+	stopAndClearDefaultWorker()
+
+	e := &countExporter{}
+	RegisterExporter(e)
+
+	if _, ok := defaultWorker.exporters[e]; !ok {
+		t.Errorf("exporter doesn't appear to be registered with the default worker")
+	}
+}
+
+func TestUnregisterExporter(t *testing.T) {
+	stopAndClearDefaultWorker()
+
+	e := &countExporter{}
+	UnregisterExporter(e)
+}

stats/view/worker.go

@@ -29,13 +29,6 @@ import (
 	"go.opencensus.io/tag"
 )
 
-func init() {
-	defaultWorker = NewMeter().(*worker)
-	go defaultWorker.start()
-	internal.DefaultRecorder = record
-	internal.MeasurementRecorder = recordMeasurement
-}
-
 type measureRef struct {
 	measure string
 	views   map[*viewInternal]struct{}
@@ -113,13 +106,28 @@ type Meter interface {
 
 var _ Meter = (*worker)(nil)
 
-var defaultWorker *worker
+var (
+	defaultWorker     *worker
+	defaultWorkerInit sync.Once
+)
+
+// Lazily initializes and starts the package's default worker. Should be invoked
+// before any exported functions in this package that use defaultWorker.
+func maybeInitDefaultWorker() {
+	defaultWorkerInit.Do(func() {
+		defaultWorker = NewMeter().(*worker)
+		go defaultWorker.start()
+		internal.DefaultRecorder = record
+		internal.MeasurementRecorder = recordMeasurement
+	})
+}
 
 var defaultReportingDuration = 10 * time.Second
 
 // Find returns a registered view associated with this name.
 // If no registered view is found, nil is returned.
 func Find(name string) (v *View) {
+	maybeInitDefaultWorker()
 	return defaultWorker.Find(name)
 }
 
@@ -138,6 +146,7 @@ func (w *worker) Find(name string) (v *View) {
 // Register begins collecting data for the given views.
 // Once a view is registered, it reports data to the registered exporters.
 func Register(views ...*View) error {
+	maybeInitDefaultWorker()
 	return defaultWorker.Register(views...)
 }
 
@@ -157,6 +166,7 @@ func (w *worker) Register(views ...*View) error {
 // It is not necessary to unregister from views you expect to collect for the
 // duration of your program execution.
 func Unregister(views ...*View) {
+	maybeInitDefaultWorker()
 	defaultWorker.Unregister(views...)
 }
 
@@ -180,6 +190,7 @@ func (w *worker) Unregister(views ...*View) {
 // RetrieveData gets a snapshot of the data collected for the the view registered
 // with the given name. It is intended for testing only.
 func RetrieveData(viewName string) ([]*Row, error) {
+	maybeInitDefaultWorker()
 	return defaultWorker.RetrieveData(viewName)
 }
 
@@ -229,11 +240,13 @@ func (w *worker) recordMeasurement(tags *tag.Map, ms []stats.Measurement, attach
 // duration is. For example, the Stackdriver exporter recommends a value no
 // lower than 1 minute. Consult each exporter per your needs.
 func SetReportingPeriod(d time.Duration) {
+	maybeInitDefaultWorker()
 	defaultWorker.SetReportingPeriod(d)
 }
 
 // Stop stops the default worker.
 func Stop() {
+	maybeInitDefaultWorker()
 	defaultWorker.Stop()
 }
 

stats/view/worker_test.go

@@ -89,7 +89,7 @@ func Test_Worker_ViewRegistration(t *testing.T) {
 
 	for _, tc := range tcs {
 		t.Run(tc.label, func(t *testing.T) {
-			restart()
+			stopAndClearDefaultWorker()
 
 			views := map[string]*View{
 				"v1ID": {
@@ -123,7 +123,7 @@ func Test_Worker_ViewRegistration(t *testing.T) {
 }
 
 func Test_Worker_MultiExport(t *testing.T) {
-	restart()
+	stopAndClearDefaultWorker()
 
 	// This test reports the same data for the default worker and a secondary
 	// worker, and ensures that the stats are kept independently.
@@ -239,7 +239,7 @@ func Test_Worker_MultiExport(t *testing.T) {
 }
 
 func Test_Worker_RecordFloat64(t *testing.T) {
-	restart()
+	stopAndClearDefaultWorker()
 
 	someError := errors.New("some error")
 	m := stats.Float64("Test_Worker_RecordFloat64/MF1", "desc MF1", "unit")
@@ -383,7 +383,7 @@ func TestReportUsage(t *testing.T) {
 	}
 
 	for _, tt := range tests {
-		restart()
+		stopAndClearDefaultWorker()
 		SetReportingPeriod(25 * time.Millisecond)
 
 		if err := Register(tt.view); err != nil {
@@ -436,7 +436,7 @@ func Test_SetReportingPeriodReqNeverBlocks(t *testing.T) {
 }
 
 func TestWorkerStarttime(t *testing.T) {
-	restart()
+	stopAndClearDefaultWorker()
 
 	ctx := context.Background()
 	m := stats.Int64("measure/TestWorkerStarttime", "desc", "unit")
@@ -487,7 +487,7 @@ func TestWorkerStarttime(t *testing.T) {
 }
 
 func TestUnregisterReportsUsage(t *testing.T) {
-	restart()
+	stopAndClearDefaultWorker()
 	ctx := context.Background()
 
 	m1 := stats.Int64("measure", "desc", "unit")
@@ -522,7 +522,7 @@ func TestUnregisterReportsUsage(t *testing.T) {
 }
 
 func TestWorkerRace(t *testing.T) {
-	restart()
+	stopAndClearDefaultWorker()
 	ctx := context.Background()
 
 	m1 := stats.Int64("measure", "desc", "unit")
@@ -638,11 +638,13 @@ func (e *vdExporter) ExportView(vd *Data) {
 	e.vds = append(e.vds, vd)
 }
 
-// restart stops the current processors and creates a new one.
-func restart() {
-	defaultWorker.Stop()
-	defaultWorker = NewMeter().(*worker)
-	go defaultWorker.start()
+// stopAndClearDefaultWorker stops defaultWorker's processors, clears it, and
+// resets its sync.Once so that it can be lazily initialized again.
+func stopAndClearDefaultWorker() {
+	if defaultWorker != nil {
+		defaultWorker.Stop()
+		defaultWorkerInit = sync.Once{}
+	}
 }
 
 // byTag implements sort.Interface for *metricdata.TimeSeries by Labels.