QObject::deleteLater across a QThread

Question

I'm looking for a solution to schedule the deletion of an object across threads. The docs about how deleteLater behave are not entirely clear. Can I call this function in a thread which is not the object's owner?

For example, Object X is owned by Thread A, and in Thread B I would like to have Object X deleted. As the object may be inside event processing at the moment (in Thread A) I can't safely delete it until it gets back to the message loop. If I call deleteLater from Thread B however the docs seem to indicate it will delete as soon as Thread B gets back to the message loop.

Currently I take the approach of having a signal emitted in Thread A which is attached to a slot which calls deleteLater. I'm wondering if there is perhaps an easier way to do this -- if indeed I can just call deleteLater from any thread.

Answer 1

Looking at the Qt 4 code and Qt 5 code, deleteLater() just invokes QCoreApplication::postEvent() which is explicitly declared thread-safe. So, it should be fine to just call it directly. As the event queue is processed in the object's owner thread, deletion will happen in thread A.

Only Qt 5 QObject documentation explicitly lists deleteLater() as thread safe. If you want to completely rely on documented behaviour in Qt 4, use postEvent().