Order of slots called on QObject

Question

I have a QObject that has multiple slots connected to one of its signals. Is there an order in which of each of these slots are called when the signal is emitted?

Answer 1

While the order is undefined, up to now, in all Qt versions it has been connect() order, except when Qt::QueuedConnection is used, in which case, of course, it's not even guaranteed that any or all slots have been executed when emit returns. Relying on the order is still discouraged, though.

Answer 2

In Qt v4.5 and earlier: No, the order is undefined as can be seen in the documentation here:

If several slots are connected to one signal, the slots will be executed one after the other, in an arbitrary order, when the signal is emitted.

Edit: From version 4.6 onwards this is no longer true. Now the slots will run in the order they are connected. The relevant paragraph of the current documentation:

If several slots are connected to one signal, the slots will be executed one after the other, in the order they have been connected, when the signal is emitted

Answer 3

Relying on what order the slots will be executed is a bad, bad idea, as it defeats both the spirit of the signals/slots connections and leaves you wide open for undesired behavior if you do any sort of programmatic connections of signals & slots.

Answer 4

According to Qt documentation:

If several slots are connected to one signal, the slots will be executed one after the other, in the order they have been connected, when the signal is emitted.

http://qt-project.org/doc/qt-4.8/signalsandslots.html