How to lazy load init files to speedup Emacs startup?

Question

My ~/.emacs.d/init.el file looks like this:

(package-initialize)

(require 'init-my-emacs-settings)
(require 'init-my-emacs-performance)
(require 'init-my-emacs-font)
(require 'init-my-emacs-color-theme)
(require 'init-my-emacs-appearance)

(require 'init-my-tool-calendar)
(require 'init-my-tool-dictionary)
(require 'init-my-tool-clock)
(require 'init-my-tool-speak)

(require 'init-my-prog-programming)
(require 'init-my-prog-license)
(require 'init-my-prog-code)
(require 'init-my-prog-comment)

;;; Programming Languages
(require 'init-my-prog-lang-lisp)
(require 'init-my-prog-lang-emacs-lisp)
(require 'init-my-prog-lang-common-lisp)
(require 'init-my-prog-lang-clojure)
(require 'init-my-prog-lang-ruby)
(require 'init-my-prog-lang-python)

I hope to load them only when needed. If for init files like init-my-emacs-settings can’t be lazy load. Then I hope lazy load for programming languages init files like init-my-prog-lang-lisp.

Here is my simple idea to load programming language init files only when load major-mode hook.

;;; TODO: convert code into an macro.

(defvar init-my-prog-lang-lisp-loaded nil)
(add-hook 'lisp-mode-hook
          (lambda ()
            (unless init-my-prog-lang-lisp-loaded
              (require 'init-my-prog-lang-lisp)
              (setq init-my-prog-lang-lisp-loaded t))
            ))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defun symbol-concat (symbol string)
  (intern (concat (symbol-name symbol) string)))

;; (type-of (symbol-concat 'ruby-mode-hook "-p"))

(defmacro my-lazy-load-init-file (init-file mode)
  "Lazy load my `INIT-FILE' only when `MODE' loaded."
  (let ((state (symbol-concat init-file "-loaded")))
    ;; state variable
    (defvar state nil)
    ;; load on major-mode hook
    (add-hook (symbol-concat mode "-hook")
              (lambda ()
                (unless state
                  (require init-file)
                  (setq state t)
                  )))
    )
  )

My questions: - how to improve this macro? - Do you have better solution? If have, please show me. Thanks

`C-h i g (elisp) Autoload` and also `(elisp) Hooks for Loading`. Using mode hooks is sometimes appropriate, too. — phils, Oct 18 '16 at 03:06
btw, `require` is very fast and its entire purpose is to load things *only when they are not already loaded*. Wrapping a lisp conditional around a call to `require` is pointless. — phils, Oct 18 '16 at 03:17
See also http://emacs.stackexchange.com/questions/2286/what-can-i-do-to-speed-up-my-start-up — npostavs, Oct 19 '16 at 11:37

score 4 · Accepted Answer · answered Oct 20 '16 at 02:44

Consider using John Wiegley's use-package if you really care about startup time that much. use-package provides built-in support for lazy/deferred loading.

Better yet, don't constantly restart your Emacs. The best way to avoid constantly restarting is to run an Emacs daemon; then you can create as many frames (both GUI and terminal) as you like that will all start instantly and, as an added benefit, share buffers, history, etc. because they're clients.

I use MJ Wall's scripts to easily start/stop the Emacs daemon, launch clients, etc. from the command line. I also set ec (described in the article) as a startup application so I never even notice the Emacs startup time, since it's part of the OS startup.

I use `use-package`, but don't know `:defer`. I add it now. And I use **Emacs daemon** before, but it has issue that color-theme not applied. Do you have this issue with your solution? — stardiviner, Oct 20 '16 at 02:55
My theme is applied just fine. Have you tried starting Emacs with the `emacs --debug-init` command to see if there are any errors? — Tianxiang Xiong, Oct 20 '16 at 03:40

score 3 · Answer 2 · answered Oct 18 '16 at 13:18

I'd recommend two things to speedup startup:

Merge your many init files into a single large file.
Look at the content of your init files and try to make sure that they don't require or load but instead, they should just use setq, add-hook, and eval-after-load.

How to lazy load init files to speedup Emacs startup?

2 Answers2