update

design_pattern/singleton/dcl_singleton.cpp

@@ -0,0 +1,42 @@
+//
+// Created by light on 20-2-7.
+//
+#include <iostream>
+
+using namespace std;
+
+#include <mutex>
+
+class singleton {
+private:
+    singleton() {}
+
+    static singleton *p;
+    static mutex lock_;
+public:
+    singleton *instance();
+
+    // 实现一个内嵌垃圾回收类
+    class CGarbo
+    {
+    public:
+        ~CGarbo()
+        {
+            if(singleton::p)
+                delete singleton::p;
+        }
+    };
+    static CGarbo Garbo; // 定义一个静态成员变量，程序结束时，系统会自动调用它的析构函数从而释放单例对象
+};
+
+singleton *singleton::p = nullptr;
+singleton::CGarbo Garbo;
+
+singleton* singleton::instance() {
+    if (p == nullptr) {
+        lock_guard<mutex> guard(lock_);
+        if (p == nullptr)
+            p = new singleton();
+    }
+    return p;
+}