Init map while initing stats

Signed-off-by: Rohit Nayak <rohit@planetscale.com>

go/vt/vttablet/tabletmanager/vdiff/engine.go

@@ -153,12 +153,12 @@ func (vde *Engine) openLocked(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
+
 	vde.ctx, vde.cancel = context.WithCancel(ctx)
 	vde.isOpen = true // now we are open and have things to close
 	if err := vde.initControllers(rows); err != nil {
 		return err
 	}
-	vde.updateStats()
 
 	// At this point we've fully and successfully opened so begin
 	// retrying error'd VDiffs until the engine is closed.
@@ -400,16 +400,4 @@ func (vde *Engine) resetControllers() {
 		ct.Stop()
 	}
 	vde.controllers = make(map[int64]*controller)
-	vde.updateStats()
-}
-
-// updateStats must only be called while holding the engine lock.
-func (vre *Engine) updateStats() {
-	globalStats.mu.Lock()
-	defer globalStats.mu.Unlock()
-
-	globalStats.controllers = make(map[int64]*controller, len(vre.controllers))
-	for id, ct := range vre.controllers {
-		globalStats.controllers[id] = ct
-	}
 }

go/vt/vttablet/tabletmanager/vdiff/stats.go

@@ -49,6 +49,7 @@ func (vds *vdiffStats) register() {
 	globalStats.ErrorCount = stats.NewCounter("", "")
 	globalStats.RestartedTableDiffs = stats.NewCountersWithSingleLabel("", "", "Table")
 	globalStats.RowsDiffedCount = stats.NewCounter("", "")
+	globalStats.controllers = make(map[int64]*controller)
 
 	stats.NewGaugeFunc("VDiffCount", "Number of current vdiffs", vds.numControllers)