Fix data race when registering views multiple times

Fixed by moving view canonicalization into worker.

stats/view/view_test.go

@@ -459,6 +459,18 @@ func TestViewRegister_negativeBucketBounds(t *testing.T) {
 	}
 }
 
+func TestViewRegister_zeroBucketBounds(t *testing.T) {
+	m := stats.Int64("TestViewRegister_negativeBucketBounds", "", "")
+	v := &View{
+		Measure:     m,
+		Aggregation: Distribution(0, 2),
+	}
+	err := Register(v)
+	if err != nil {
+		t.Errorf("Expected no error, got %v", err)
+	}
+}
+
 func TestViewRegister_sortBuckets(t *testing.T) {
 	m := stats.Int64("TestViewRegister_sortBuckets", "", "")
 	v := &View{

stats/view/worker.go

@@ -64,11 +64,6 @@ func 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 {
-	for _, v := range views {
-		if err := v.canonicalize(); err != nil {
-			return err
-		}
-	}
 	req := &registerViewReq{
 		views: views,
 		err:   make(chan error),

stats/view/worker_commands.go

@@ -58,6 +58,12 @@ type registerViewReq struct {
 }
 
 func (cmd *registerViewReq) handleCommand(w *worker) {
+	for _, v := range cmd.views {
+		if err := v.canonicalize(); err != nil {
+			cmd.err <- err
+			return
+		}
+	}
 	var errstr []string
 	for _, view := range cmd.views {
 		vi, err := w.tryRegisterView(view)