add syncx.Guard func (#620)

core/syncx/barrier.go

@@ -9,7 +9,12 @@ type Barrier struct {
 
 // Guard guards the given fn on the resource.
 func (b *Barrier) Guard(fn func()) {
-	b.lock.Lock()
-	defer b.lock.Unlock()
+	Guard(&b.lock, fn)
+}
+
+// Guard guards the given fn with lock.
+func Guard(lock sync.Locker, fn func()) {
+	lock.Lock()
+	defer lock.Unlock()
 	fn()
 }