Question about atomic operation and Qt's data sharing.

[The Storm]

Lets say I have this sample code:

class MyThead : public QThread
{
public:
      MyThead() {};
      ~MyThread {};
 
      QString getTheString() const { return m_someString; }
 
protected:
     void run()
     {
          // Do stuff with m_someString....
     }
 
private:
      QString m_someString;
}

class MyThead : public QThread
{
public:
      MyThead() {};
      ~MyThread {};

      QString getTheString() const { return m_someString; }

protected:
     void run()
     {
          // Do stuff with m_someString....
     }

private:
      QString m_someString;
}

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If for example I call getTheString() method using other thread context will I get crash or something nasty if I do not synchronize m_someString with mutex? I had read about the reentrant and atomic reference counter in Qt but I'm still not sure if I get it right.

On my project I have created an implicitly shared class using the QSharedData technique and I have lots of members that are mixed primitive types and Qt types. The big question here is can I share copy instances of my class without the need of mutex or other type locking?