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Andrew Tropin

Today I learned: If you don't add (require 'server) before calling (daemonp), your Emacs daemon will silently hang.

The thing I don't actually want to learn at all, ever.

It took 3 hours to debug, I found solution completely accidentially: just forgot to remove it, when was playing with (server-running-p).

#til #emacs #cursedtech

14 June at 8:57 | Open on fosstodon.org
5 comments
zrzz

@abcdw Do you have a minimal test case to reproduce this? I don't see it with my config and emacs -Q --daemon -f daemonp and similar attempts don't hang for me either.

14 June at 14:41 | Open on emacs.ch
Andrew Tropin

@zrzz

~/tmp/init.el:
(defun test-fn ()
""
(message "fuuuck!")
(when (and (daemonp) (string= server-name "server"))
(message "everything is ok"))
(message "yeah!"))
(add-hook 'after-init-hook 'test-fn)

emacs --fg-daemon=test --no-site-lisp --no-site-file --init-directory=~/tmp

14 June at 15:02 | Open on fosstodon.org
Andrew Tropin

@zrzz Oh, my bad, it's cause of server-name, not daemonp. Today it's me, not a compiler or os. (Still silently hanging).

I thought I tried it in isolation and only later added server-name 🤔

14 June at 15:18 | Open on fosstodon.org
zrzz

@abcdw Looks like the current master correctly prints the error and doesn't hang. So I guess this was fixed sometime after 29.

14 June at 16:23 | Open on emacs.ch
zrzz

@abcdw Looks like this is actually triggered by the access to the server-name variable which is undefined since it's not autoloaded. Using (defun test-fn () foo) produces the same hang.

Access to the undefined variable throws an error and apparently if you signal an error in after-init-hook while in daemon mode it hangs instead of printing a backtrace. Not sure why that happens.

If I stick a (setq debug-on-error t) at the beginning of the original example then it does produce the expected backtrace:

Debugger entered--Lisp error: (void-variable server-name)
  (string= server-name "server")
  (and (daemonp) (string= server-name "server"))
  (if (and (daemonp) (string= server-name "server")) (progn (message "everything is ok")))
  test-fn()
  run-hooks(after-init-hook delayed-warnings-hook)
  command-line()
  normal-top-level()

@abcdw Looks like this is actually triggered by the access to the server-name variable which is undefined since it's not autoloaded. Using (defun test-fn () foo) produces the same hang.

Access to the undefined variable throws an error and apparently if you signal an error in after-init-hook while in daemon mode it hangs instead of printing a backtrace. Not sure why that happens.

14 June at 16:05 | Open on emacs.ch
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