Support parallel A/AAAA queries. Likely implementation includes
Send & receive queue as either
simple, 2-packet queue integrated into struct dns_socket
complex queuing data structure supporting a shared socket among multiple resolvers
BUT complicates event polling contract--assumes event loop will wake up all pollers, or requires unique epoll/kqueue/socketpair descriptor per resolver
multiple sockets per resolver object
BUT complicates event polling contract--requires using epoll/kqueue descriptor to proxy multiple socket descriptors
2 execution stacks per resolver object, instead of 1.
Support parallel A/AAAA queries. Likely implementation includes