add DCL singleton implement

util/Singleton.go

@@ -0,0 +1,33 @@
+package util
+
+import "sync"
+
+// Singleton DCL singleton implement
+type Singleton[T any] struct {
+	value T
+	init  func() T
+	lock  sync.Mutex
+}
+
+func NewSingleton[T any](init func() T) *Singleton[T] {
+	if init == nil {
+		panic("nil singleton initializer")
+	}
+
+	return &Singleton[T]{
+		init: init,
+	}
+}
+
+func (s *Singleton[T]) Get() T {
+	if s.init != nil {
+		s.lock.Lock()
+		s.lock.Unlock()
+		if s.init != nil {
+			s.value = s.init()
+			s.init = nil
+		}
+	}
+
+	return s.value
+}