Qt 专门的宏Q_GLOBAL_STATIC，用来实现线程安全的单例模式

Qt本身就提供了专门的宏 Q_GLOBAL_STATIC。通过这个宏不但定义简单，还可以获得线程安全性。

1、先看官方文档

https://doc.qt.io/qt-5/qglobalstatic.html

https://doc.qt.io/qt-5/threads-reentrancy.html

2、再看使用方法

Q_GLOBAL_STATIC(Type, VariableName)

Q_GLOBAL_STATIC_WITH_ARGS(Type, VariableName, Arguments)

3、举例说明

rule.h

#ifndef RULE_H
#define RULE_H
#include <QGlobalStatic>
#define RULE Rule::instance()
class Rule
{
public:
    Rule() {}
    virtual ~Rule() {}
public:
    static Rule* instance();
public:
    void test();
};
#endif // RULE_H

rule.cpp

#include "rule.h"
Q_GLOBAL_STATIC(Rule, rule)
Rule* Rule::instance()
{
    return rule();
}
void Rule::test()
{
    //todo
}

在任何地方，引用头文件 include "rule.h"

就可以Rule::instance()->test();

或者使用宏RULE->test();