Function run 

pub(crate) fn run(
    s: &Session,
    dirs: &Dirs,
    id: &str,
    ask: &TrainAsk,
    json: bool,
) -> Result<(), String>

The run itself, as its job: the lowest priority for every thread it starts, its power asked every half minute (unplugged or saving power: its own stop file, and it stops at its next step), its end kept for the settings and the next decision.