getaddrinfo_a is available, but not widely adopted (*BSD and Linux), probably because you can't guarantee it'll be available on every computer/phone/modem. This is only an issue if you're targeting POSIX rather than modern operating systems.
Windows 8 and above also have their own asynchronous DNS API on NON-POSIX land.
Windows 8 and above also have their own asynchronous DNS API on NON-POSIX land.