is there an example out there of a batch source with splits that may or may not finish in a given

fetch

call? the source says

In either case, this method should be reentrant, meaning that
     * the next fetch call should just resume from where the last fetch call was waken up or
     * interrupted.

but how? what if a split is partially finished (and emitted) but the taskmanager dies? i don’t see a way to keep the partially progressed state of a split alive after emitting some records