I doubt non-blocking anything has guaranteed delivery on localhost if you don't account for full buffers. As long as there is a buffer, sure, why would UDP lose

I doubt non-blocking anything has guaranteed delivery on localhost if you don't account for full buffers. As long as there is a buffer, sure, why would UDP lose packets on localhost? In order to not block your program, you'll have to do it like one always has with non-blocking sockets: have a buffer and poll for the "write-able" event. Unix sockets would involve less overhead and provide more security if you only send to localhost. I really don't see a reason to use UDP on localhost at least if you are not running on Windows.