TIL: Async IO in Emacs

Stumbled on the emacs-aio library today and it's introduction post. What a great exploration into how async/await works under the hood! I'm not sure I totally grok the details, but I'm excited to dive more into Emacs generators and different concurrent programming techniques.

The article brings to mind Wiegley's async library, which is probably the more canonical library for handling async in Emacs. From a brief look at the README, async looks like it actually spawns independent processes, whereas emacs-aio is really just a construct for handling non-blocking I/O more conveniently.

Karthink on reddit comments on the usability of generators in Emacs:

I've written small-medium sized packages -- 400 to 2400 lines of elisp -- that use generators and emacs-aio (async/await library built on generator.el) for their async capabilities. I've regretted it each time: generators in their current form in elisp are obfuscated, opaque and not introspectable -- you can't debug/edebug generator calls. Backtraces are impossible to read because of the continuation-passing macro code. Their memory overhead is large compared to using simple callbacks. I'm not sure about the CPU overhead.

That said, the simplicity of emacs-aio promises is very appealing:

(defun aio-promise ()
  "Create a new promise object."
  (record 'aio-promise nil ()))

(defsubst aio-promise-p (object)
  (and (eq 'aio-promise (type-of object))
       (= 3 (length object))))

(defsubst aio-result (promise)
  (aref promise 1))