Should cider work with `--with-poll` emacs?

[jmckitrick]

There's a newish feature in emacs that swaps out select for poll to allow over 1024 file descriptors to be open, IIUC. It's supposedly a 'drop in' replacement. However, my first attempt to run emacs and cider with this option resulted in a hung connection during 'jack in'. Should this feature even work with cider at all? Or is it worth investigating?

[vemv]

Thanks for bringing attention over this!

We could expand our CI matrix and see which combinations succeed/fail.

(There aren't a lot of 'jack in' integration tests, but maybe a more basic test fails, giving us a hint)

[jmckitrick]

I build and run emacs HEAD every week and tinker with settings, so I'm happy to help with this.

[vemv]

I'll try out https://github.com/d12frosted/homebrew-emacs-plus which makes this option easy, apparently

(TIL about that distro)

[jmckitrick]

@vemv I use that one and https://github.com/daviderestivo/homebrew-emacs-head

[vemv]

I ran brew install emacs-head@30 --with-cocoa --with-poll and could repro the issue.

By running M-x toggle-debug-on-error and then cider-connecting I could see

• First:

[nREPL] Establishing direct connection to 127.0.0.1:64844 ...
[nREPL] Direct connection to 127.0.0.1:64844 established

• But later:

  signal(error ("Sync nREPL request timed out (op clone id 1 time-stamp 2023-09-26 16:32:21.439826000) after 10 secs"))
  error("Sync nREPL request timed out %s after %s secs" ("op" "clone" "id" "1" "time-stamp" "2023-09-26 16:32:21.439826000") 10)
  nrepl-send-sync-request(("op" "clone" "id" "1" "time-stamp" "2023-09-26 16:32:21.439826000") #<buffer *cider-uninitialized-repl*> nil nil)
  nrepl-sync-request:clone(#<buffer *cider-uninitialized-repl*>)
  nrepl--init-client-sessions(#<process nrepl-connection>)
  nrepl-start-client-process("127.0.0.1" 64844 nil #f(compiled-function (_) #<bytecode 0xf69663072ad1ccf>) nil)
  cider-nrepl-connect((:host "127.0.0.1" :port 64844 :project-dir "/Users/vemv/orchard/" :repl-init-function nil :session-name nil :repl-type clj))

This would require some investigation.

Perhaps the Emacs 30 changelog explains an adoption guide? i.e. the transition steps.

[jmckitrick]

@vemv I saw exactly the same thing. Yet every article I read on 'poll vs select' claimed it was a drop-in replacement that should be transparent to the user. At least, that was my impression.

I'll take a closer look at the emacs docs, but I'm pretty sure there was no migration guide or something similar.

[vemv]

It might be even an unofficial patch https://github.com/daviderestivo/homebrew-emacs-head/blob/master/patches/0011-Poll.patch - do you know where it comes from?

[jmckitrick]

@vemv Though I wouldn't be surprised if just a handful of simple changes in cider-nrepl solve the entire issue.

[vemv]

Those would be welcome as long that nothing was impacted for the vanilla ~patch~ path.

[jmckitrick]

@vemv The patch is for the macos build... but the feature itself is in the underlying emacs. Let me see if I can find it.

[jmckitrick]

But you're right.... this patch is more extensive than I initially thought. Maybe I'll try a vanilla terminal mode emacs and see if that works.

[jmckitrick]

@vemv I found the source of the patch!

https://lists.gnu.org/archive/html/emacs-diffs/2022-05/msg00142.html

I was mistaken in thinking this was in emacs master. It's actually on a feature branch. I wonder where the discussion would happen, if this is slated to become part of emacs.

[vemv]

Nice!

I can't promise we'll give this a try super soon (other than a quick look and trial/error - already done).

But leaving the issue open seems reasonable, for visibilty. I hear that this capability would be benefitial for LSP performance. OTOH, there's more than one LSP offering for Emacs itself (eglot, lsp-mode), so it wouldn't surprise me if the existent ones are good-enough for the vast majority of cases.

Which is to say, sometimes it's wise to stick to what the authors wanted us to use.

Note that https://lists.gnu.org/archive/html/emacs-diffs/2022-05/msg00142.html is a mailing list item. You can certainly try bumping that conversation or perhaps contacting the author.

[jmckitrick]

@vemv I emailed him yesterday. I'll report back what I find out.