restart: parallelize reconcile()

The only shared variable `m.client` is thread-safe, so we can safely
parallelize the loops.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

runtime/restart/monitor/monitor.go

@@ -19,6 +19,7 @@ package monitor
 import (
 	"context"
 	"fmt"
+	"sync"
 	"time"
 
 	"github.com/containerd/containerd"
@@ -164,19 +165,33 @@ func (m *monitor) reconcile(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
+	var wgNSLoop sync.WaitGroup
 	for _, name := range ns {
-		ctx = namespaces.WithNamespace(ctx, name)
+		name := name
+		wgNSLoop.Add(1)
+		go func() {
+			defer wgNSLoop.Done()
+			ctx := namespaces.WithNamespace(ctx, name)
 			changes, err := m.monitor(ctx)
 			if err != nil {
 				logrus.WithError(err).Error("monitor for changes")
-			continue
+				return
 			}
+			var wgChangesLoop sync.WaitGroup
 			for _, c := range changes {
+				c := c
+				wgChangesLoop.Add(1)
+				go func() {
+					defer wgChangesLoop.Done()
 					if err := c.apply(ctx, m.client); err != nil {
 						logrus.WithError(err).Error("apply change")
 					}
+				}()
 			}
+			wgChangesLoop.Wait()
+		}()
 	}
+	wgNSLoop.Wait()
 	return nil
 }