And how can I accomplish that? The data transfer is triggered by a button. So first thing that happens is that a signal (clicked()) is sent into a slot. Coming from Java Swing I was raised to return an event handler as quickly as possible, otherwise I will keep the gui thread busy and the gui itself will freeze. So this is why I decided to start a thread from there and to return the slot as quickly as possible. So unless Qt itself takes care of splitting out a thread to handle the slot, so that the gui is not blocked by my sluggish program, I don't see how I can solve it without a thread.