Netscape used to start a new thread (or maybe it was a subprocess?) to handle DNS lookups, because the API at the time (gethostbyname) was blocking. It's kind of amazing that we're 30 years on and this is still a problem.
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.
>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.
To be precise, even on Linux getaddrinfo_a is not guaranteed to be present. It's a glibc extension. musl doesn't have it.
And MUSL's explicit policy of "do not implement essential features, just because the standards are falling behind" is a major reason why many programs choose to never support building against MUSL.
GetAddrInfoEx[0] has async support support since Windows 8 - it had the overlapped parameters earlier but didn't support them. I'm guessing that is what GP is referring to.
The system-provided API for getting DNS user/system preferences on Unix systems is to read /etc/resolv.conf. Every application is free to implement their own lookup from that.
This isn't even correct on Linux as it won't work if your user has anything other than or in addition to the dns module in their nsswitch.conf. You must use glibc's resolution on Linux for correct behavior. If it's software on your own systems then do what you want but you'll piss off some sysadmins deploying your software if you don't. Even Go farms out to cgo to resolve names if it detects modules it doesn't recognize.
In this case it isn't in the kernel, but in glibc. Could someone implement an equivalent alternative? Do any language runtimes re-implement DNS resolution?
