头文件：

class ConnectionManager

{ public:     static ConnectionManager *instance();

};

实现文件：

Q_GLOBAL_STATIC(ConnectionManager, connectionManager)

ConnectionManager *ConnectionManager::instance()

{     return connectionManager(); }

 

使用：

ConnectionManager::instance()

 

// POD for Q_GLOBAL_STATIC

template <typename T> class QGlobalStatic { public:     QBasicAtomicPointer<T> pointer;     bool destroyed; };

 

// Created as a function-local static to delete a QGlobalStatic<T>

template <typename T> class QGlobalStaticDeleter { public:     QGlobalStatic<T> &globalStatic;     QGlobalStaticDeleter(QGlobalStatic<T> &_globalStatic)         : globalStatic(_globalStatic)     { }

    inline ~QGlobalStaticDeleter()

    {         delete globalStatic.pointer;         globalStatic.pointer = 0;         globalStatic.destroyed = true;     } };

 

 

#define Q_GLOBAL_STATIC_INIT(TYPE, NAME)                              \

    static QGlobalStatic<TYPE > this_##NAME = { Q_BASIC_ATOMIC_INITIALIZER(0), false }

#define Q_GLOBAL_STATIC(TYPE, NAME)                                     \

    Q_GLOBAL_STATIC_INIT(TYPE, NAME);                                   \     static TYPE *NAME()                                                 \     {                                                                   \         if (!this_##NAME.pointer && !this_##NAME.destroyed) {           \             TYPE *x = new TYPE;                                         \             if (!this_##NAME.pointer.testAndSetOrdered(0, x))           \                 delete x;                                               \             else                                                        \                 static QGlobalStaticDeleter<TYPE > cleanup(this_##NAME); \         }                                                               \         return this_##NAME.pointer;                                     \     }

 

Q_GLOBAL_STATIC：

1、先通过Q_GLOBAL_STATIC_INIT声明一个静态的全局变量（this_##NAME ），并初始化为0

2、声明一个名字叫做全局变量（NAME）的static的函数，用来取得这个全局变量

3、如果这个变量没初始化且没删除，就通过testAndSetOrdered以原子方式创建

4、创建成功，再定义一个函数内的QGlobalStaticDeleter来清理这个全局变量

5、函数返回最后结果

 

qt在每个arch上面都实现了原子操作，移植时候修改src/corelib/arch/qatomic_ARCH.h

参考文档： Implementing Atomic Operations