create design dir to learning design mode

.vscode/c_cpp_properties.json

@@ -0,0 +1,15 @@
+{
+    "configurations": [
+        {
+            "name": "Linux",
+            "includePath": [
+                "${workspaceFolder}/**",
+                "/usr/include/**"
+            ],
+            "defines": [],
+            "compilerPath": "/usr/bin/clang-18",
+            "intelliSenseMode": "linux-clang-x64"
+        }
+    ],
+    "version": 4
+}

.vscode/settings.json

@@ -0,0 +1,55 @@
+{
+    "files.associations": {
+        "cctype": "cpp",
+        "clocale": "cpp",
+        "cmath": "cpp",
+        "cstdarg": "cpp",
+        "cstddef": "cpp",
+        "cstdio": "cpp",
+        "cstdlib": "cpp",
+        "ctime": "cpp",
+        "cwchar": "cpp",
+        "cwctype": "cpp",
+        "array": "cpp",
+        "atomic": "cpp",
+        "bit": "cpp",
+        "*.tcc": "cpp",
+        "charconv": "cpp",
+        "compare": "cpp",
+        "concepts": "cpp",
+        "cstdint": "cpp",
+        "deque": "cpp",
+        "string": "cpp",
+        "unordered_map": "cpp",
+        "vector": "cpp",
+        "exception": "cpp",
+        "algorithm": "cpp",
+        "functional": "cpp",
+        "iterator": "cpp",
+        "memory": "cpp",
+        "memory_resource": "cpp",
+        "numeric": "cpp",
+        "optional": "cpp",
+        "random": "cpp",
+        "string_view": "cpp",
+        "system_error": "cpp",
+        "tuple": "cpp",
+        "type_traits": "cpp",
+        "utility": "cpp",
+        "initializer_list": "cpp",
+        "iosfwd": "cpp",
+        "iostream": "cpp",
+        "istream": "cpp",
+        "limits": "cpp",
+        "new": "cpp",
+        "numbers": "cpp",
+        "ostream": "cpp",
+        "span": "cpp",
+        "stdexcept": "cpp",
+        "streambuf": "cpp",
+        "typeinfo": "cpp",
+        "variant": "cpp",
+        "format": "cpp",
+        "text_encoding": "cpp"
+    }
+}

src/design/single.c

@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <stdatomic.h>
+
+struct Singleton
+{
+};
+
+struct Singleton *getInstance()
+{
+    static atomic_flag flag = ATOMIC_FLAG_INIT;
+
+    static struct Singleton *instance = NULL;
+
+    if (!instance)
+    {
+        if (atomic_flag_test_and_set(&flag) == 0)
+        {
+            instance = malloc(sizeof(struct Singleton));
+        }
+        while (!instance)
+            ;
+    }
+
+    return instance;
+}

src/design/single.cc

@@ -0,0 +1,19 @@
+#include <mutex>
+
+class Singleton
+{
+
+    Singleton(const Singleton &) = delete;
+    Singleton &operator=(const Singleton &) = delete;
+
+    static Singleton &getInstnce()
+    {
+        static Singleton instance;
+        return instance;
+        
+    }
+
+private:
+    Singleton() {}
+    ~Singleton() {}
+};