At first I wondered if musl does it better, so I checked, and the version I have disables cancellation in the guts of `getaddrinfo`.

I've always thought APIs like `pthread_cancel` are too nasty to use. Glad to see well documented evidence of my crank opinion

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.

Maybe this is naive, but could there just be some amount of worker threads that run forever, wait for and take jobs when needed, and message when the jobs are done? Don't need to be canceled, don't block

Why is running the DNS resolution thread a problem? It should be dequeuing resolution requests and pushing responses and sleeping when there is nothing to do

When someone kills off the curl context surely you simply set a suicide flag on the thread and wake it up so it can be joined.