[Qt-interest] How to use a QObject tracking QWeakPointer (thread-)safely?

[Stephen Kelly]

Hi,

QWeakPointer QObject tracking section has some cautions about tracking 
objects in other threads. I should call data() only if I can guarantee the 
contained pointer will never be deleted by another thread.

One way of providing that guarantee is to ensure that data() is only called 
if the contained QObject has affinity to the currentThread().

How can I guarantee that? It seems like the only thing I can do is document 
it? 

For example, how can this get more safety than the apidox provides?

class MyClass
{
  /**
    @p object must have the same thread affinity as the instance of MyClass.
    @p object must not be moved to another thread while this instance 
        of MyClass exists.
  */
  void setObject(QObject *object)
  {
    Q_ASSERT(object ? object->thread() == QThread::currentThread() : true);
    m_object = QWeakPointer(object);
  }

  void doSomething()
  {
    if (m_object) {
      // The object tracked by m_object might be deleted in another thread
      // at this point.
      Q_ASSERT(m_object.data()->thread() == QThread::currentThread());
      // Use m_object.data();
    }
  }
private:
  QWeakPointer<QObject> m_object;
};

Thanks,

Steve.