In what order are classes executed

Since A3 uses eventListeners, I’m assuming that this enables it to be multi-threaded in its execution. Or am I totally off track ?
So is there any way to give a thread, preference, or priority over another.
The Use in this (for me) is simply to have the foreground of focus area being updated with greater ability than the background.
Next is there anyway to determine when the same eventListenner, is used by multiple classes, eg the enter Frame event.
With one CPU there was a certainty that the order that imports and includes were arranged that the sequence wouldn’t change. But if A3 is multithreaded running on multiple processors.
Or again am I totally off track. ?