Function dochy::fs::history::save_history_file_nb_if_vacant

pub fn save_history_file_nb_if_vacant<F>(
    history_info: &HistoryInfo, 
    tag: Option<String>, 
    root: &RootObject, 
    callback: F
) -> bool where
    F: 'static + FnOnce(Result<FileNameProps, FsError>) + Send, 

Saves when no save-thread is runnning for the history_dir. Calling this function concurrently for the same history_dir can make the evaluation incorrect.