trio.socket.getaddrinfo (and some of its friends, like socket.resolve_*_address) internally spawn a thread. Right now there's no limited on this, so if you spawn 1000 tasks and they each make a socket connection, you'll briefly get 1000 threads at once. Probably it would be better if you instead, got, like, 20 threads at once, 50 times. Or maybe not, I haven't tried it!

The obvious thing would be to make a global (well, thread-local) semaphore and require getaddrinfo to hold it when calling run_in_worker_thread. Not so obvious how to allow the number of threads to be tuned etc. though.

See also: #6