Is ReDim an atomic operation?

From my understanding functions called by GUI/Tray events have higher priority, i.e. can pause the execution, of functions called by AdlibRegister, which in turn have higher priority over the main program flow.

My question is: if I'm executing a (lengthy) ReDim operation and a GUI/Tray event is raised, would the ReDim be put on hold until the function linked to the event returns?

Thanks for any feedback.