update singleton

1. 修改mutex为sync.Once
2. 命名更加golang语言化

Author: xpzouying

03_singleton/singleton.go

@@ -5,16 +5,14 @@ import "sync"
 //Singleton 是单例模式类
 type Singleton struct{}
 
-var singletonInst *Singleton
-var singletonInstLock sync.Mutex
+var singleton *Singleton
+var once sync.Once
 
 //GetInstance 用于获取单例模式对象
 func GetInstance() *Singleton {
-	if singletonInst == nil {
-		singletonInstLock.Lock()
-		if singletonInst == nil {
-			singletonInst = &Singleton{}
-		}
-	}
-	return singletonInst
+	once.Do(func() {
+		singleton = &Singleton{}
+	})
+
+	return singleton
 }