Ondřej Kuzník authored May 10, 2017 and Ondřej Kuzník committed Nov 17, 2020

Several threads calling backend_select might reset current_backend to a
different place, there are two options to deal with that:
- just let the last rotation win (the current approach)
- detect whether first == current_backend and only replace then

Not sure which one is more useful, going with the simpler.