Before, a DNS request was sent and the first thing appearing in the Lwt_mvar
was taken as reply. The issue with this was two-fold:
- it could be a reply for a different request
- there could be DNS replies being sent to the uplink stack leading to
Lwt_mvar.put being called, which blocks if there is already a value in the
mvar.
No, the separate task is a loop reading the mvar, using a Lwt_condition to
signal the receive of that ID (potentially discarding if there's no client
waiting). The DNS query registers itself (using the ID) in the map with a
Lwt_condition, and waits to be notified (or a timeout occurs).
