Calling a function on an QObject subclass that doesn't live in the current thread

[andyP]

According to the documentation :
"If you are calling a function on an QObject subclass that doesn't live in the current thread and the object might receive events, you must protect all access to your QObject subclass's internal data with a mutex; otherwise, you may experience crashes or other undesired behavior."
Consider the following class:

// Created on stack in main() => thread affinity = main thread
class Model : public QObject {
    Q_OBJECT
public:
   int getValue() const { // will be called from both main thread and non main thread
        return m_value;
   };
public slots:
    void incrementValue() { // will be called from both main thread and non main thread
        m_value++; 
    };
private:
    std::atomic<int> m_value = 0;
}

What is the internal data of Model?

std::atomic<int> m_value clearly is internal data.
It is already atomic and should not need to be protected by a mutex?

But what about the code generated by the Q_OBJECT macro?
Must I somehow synchronize access to data here as well? If so how?

[SGaist]

Hi,

In your class, there's nothing more to do.

As stated in the documentation, it's your internal data access that you must protect.

[andyP]

@SGaist: thank you for your help!