Not really. mkdir(2) is definitely sync, io_uring has been called asynchronous since the start, and its predecesor has asynchronous in the name: https://lwn.net/Articles/776703/

There is a difference between blocking and non-blocking, which is what I am asking about. Language runtimes apparently cannot provide non-blocking DNS (as evidenced by this article, and the other one I linked which was on HN a week or so ago).

DNS seems like it perfectly fits the model of "give me a buffer (to hold the resolved IP), and I will wake you up when it's filled". Maybe io_uring (/ IOCP?) already can support this, and these articles are just mistaken about the current (or soon-to-be) state-of-the-art? Or is there some fundamental reason about DNS that make writing a non-blocking resolver very very difficult?

It's just very odd to me that userspace apps are creating their own blocking thread pools just to run DNS stuff, when they can do seemingly everything else with just a single thread if they wanted to.

(edited a few times, sorry if I caught someone who was mid-reply)

> There is a difference between blocking and non-blocking

Not really.

"Blocking" means "tell the scheduler to mark the process idle until operation finishes", while "non-blocking" means "don't mark the process but flip a semaphore bit when operation finishes".

The point of view of the OS the difference is just which bit to flip.

On windows especially i/o is usually async, the sync apis serialize all the i/o on the file object(even across threads).

It has weird consequences, e.g. you can't use a named pipe in 2 threads doing read, write separately(without doing protcol level coordination say in a proxy). You need to use asynchornous i/o to get it right.