Report data for a given view when it is unregistered.

This might help with census-instrumentation#773.

stats/view/worker.go

@@ -194,26 +194,30 @@ func (w *worker) tryRegisterView(v *View) (*viewInternal, error) {
 	return vi, nil
 }
 
+func (w *worker) reportView(v *viewInternal, now time.Time) {
+	if !v.isSubscribed() {
+		return
+	}
+	rows := v.collectedRows()
+	_, ok := w.startTimes[v]
+	if !ok {
+		w.startTimes[v] = now
+	}
+	viewData := &Data{
+		View:  v.view,
+		Start: w.startTimes[v],
+		End:   time.Now(),
+		Rows:  rows,
+	}
+	exportersMu.Lock()
+	for e := range exporters {
+		e.ExportView(viewData)
+	}
+	exportersMu.Unlock()
+}
+
 func (w *worker) reportUsage(now time.Time) {
 	for _, v := range w.views {
-		if !v.isSubscribed() {
-			continue
-		}
-		rows := v.collectedRows()
-		_, ok := w.startTimes[v]
-		if !ok {
-			w.startTimes[v] = now
-		}
-		viewData := &Data{
-			View:  v.view,
-			Start: w.startTimes[v],
-			End:   time.Now(),
-			Rows:  rows,
-		}
-		exportersMu.Lock()
-		for e := range exporters {
-			e.ExportView(viewData)
-		}
-		exportersMu.Unlock()
+		w.reportView(v, now)
 	}
 }

stats/view/worker_commands.go

@@ -88,6 +88,9 @@ func (cmd *unregisterFromViewReq) handleCommand(w *worker) {
 			continue
 		}
 
+		// Report pending data for this view before removing it.
+		w.reportView(vi, time.Now())
+
 		vi.unsubscribe()
 		if !vi.isSubscribed() {
 			// this was the last subscription and view is not collecting anymore.

stats/view/worker_test.go

@@ -362,9 +362,45 @@ func TestWorkerStarttime(t *testing.T) {
 	e.Unlock()
 }
 
+func TestUnregisterReportsUsage(t *testing.T) {
+	restart()
+	ctx := context.Background()
+
+	m1 := stats.Int64("measure", "desc", "unit")
+	view1 := &View{Name: "count", Measure: m1, Aggregation: Count()}
+	m2 := stats.Int64("measure2", "desc", "unit")
+	view2 := &View{Name: "count2", Measure: m2, Aggregation: Count()}
+
+	SetReportingPeriod(time.Hour)
+
+	if err := Register(view1, view2); err != nil {
+		t.Fatalf("cannot register: %v", err)
+	}
+
+	e := &countExporter{}
+	RegisterExporter(e)
+
+	stats.Record(ctx, m1.M(1))
+	stats.Record(ctx, m2.M(1))
+	stats.Record(ctx, m2.M(1))
+
+	Unregister(view2)
+
+	// Unregister should only flush view2, so expect the count of 2.
+	want := int64(2)
+
+	e.Lock()
+	got := e.totalCount
+	e.Unlock()
+	if got != want {
+		t.Errorf("got count data = %v; want %v", got, want)
+	}
+}
+
 type countExporter struct {
 	sync.Mutex
-	count int64
+	count      int64
+	totalCount int64
 }
 
 func (e *countExporter) ExportView(vd *Data) {
@@ -376,6 +412,7 @@ func (e *countExporter) ExportView(vd *Data) {
 	e.Lock()
 	defer e.Unlock()
 	e.count = d.Value
+	e.totalCount += d.Value
 }
 
 type vdExporter struct {