bug#58302: 29.0.50; browse-url-emacs is extremely slow (and I think always has been?)

[Phil Sainty]

browse-url-emacs has always been inexplicably slow for me,
since at least Emacs 24 (but maybe just 'always').

I've just done some basic benchmarking with:

(benchmark-run (save-selected-window
                 (browse-url-emacs "http://www.example.com";)))

;; If I delete the "www.example.com" buffer after each attempt, this
;; call takes nearly 3 seconds:

(2.819470404 1 0.046148434000000016)
(2.669529036 0 0.0)
(2.837350438 1 0.02421054800000011)

;; If I retain the "www.example.com" buffer, then each retry takes
;; <0.5 seconds:

(0.374270464 0 0.0)
(0.428719681 0 0.0)
(0.476068586 1 0.044311528999999794)

;; Whereas benchmarking only `url-retrieve-synchronously':

(benchmark-run (url-retrieve-synchronously "http://www.example.com";))

;; This takes <0.25 seconds.
(0.172364234 0 0.0)
(0.24314511600000002 0 0.0)
(0.19534228 0 0.0)

;; Deleting the network connection via M-x list-processes between
;; attempts adds about 0.25 seconds for all sets of benchmarks, so the
;; network connection time is not a factor.

;; eww is also fast:

(benchmark-run (save-window-excursion (let ((eww-retrieve-command 
'sync))
                                        (eww "http://www.example.com";))))
(0.197008672 0 0.0)
(0.25098304499999996 0 0.0)
(0.28419454299999997 0 0.0)


So something to do with browse-url-emacs is taking an additional 2.5s
on top of the basic URL request -- unless the buffer already exists,
in which case it's much faster (albeit still twice as slow as the
other options).

Presumably this could be improved?

If I benchmark-progn the final (funcall func url) in browse-url-emacs
I can see that this is where all the time is spent.  func is set to
`find-file-other-window'; so this is equivalent:

(benchmark-run
    (save-selected-window
      (let ((file-name-handler-alist
             (cons (cons url-handler-regexp 'url-file-handler)
                   file-name-handler-alist)))
        (find-file-noselect "http://www.example.com";)))
  (kill-buffer "www.example.com"))

If the buffer already existed, *Messages* says:
Contacting host: www.example.com:80
(0.408067329 0 0.0)

If the buffer did not already exist, *Messages* says:
Contacting host: www.example.com:80 [2 times]
File exists, but cannot be read
(2.617302471 0 0.0)

(The "[2 times]" is not on account of a previous test;
they are both generated by this single call.)


Benchmarking the end of `find-file-noselect' like so:

          (benchmark-progn
            (find-file-noselect-1 buf filename nowarn
                                  rawfile truename number))

Gives me:

Elapsed time: 1.876737s (0.057295s in 1 GCs) ;; find-file-noselect-1
(2.680159853 1 0.057295379000000146)         ;; the overall 
benchmark-run

And that's as far as I've gone.


-Phil



In GNU Emacs 29.0.50 (build 4, x86_64-pc-linux-gnu, X toolkit, cairo 
version 1.15.10, Xaw scroll bars)
 of 2022-07-15 built on phil-lp
Repository revision: 00eb894a56d63fad3573a53dd57c323289711512
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 
11.0.12008000
System Description: Ubuntu 18.04.6 LTS

Configured using:
 'configure --prefix=/home/phil/emacs/trunk/usr/local
 --with-x-toolkit=lucid --without-sound
 '--program-transform-name=s/^ctags$/ctags_emacs/''

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG JSON
LCMS2 LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP THREADS
TIFF TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM XINPUT2 XPM LUCID ZLIB

Important settings:
  value of $LC_MONETARY: en_NZ.UTF-8
  value of $LC_NUMERIC: en_NZ.UTF-8
  value of $LC_TIME: en_NZ.UTF-8
  value of $LANG: en_GB.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  savehist-mode: t
  windmove-mode: t
  winner-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug mule-util display-line-numbers dcl-mode
tempo mm-archive message sendmail yank-media rfc822 mml mml-sec epa
derived epg rfc6068 epg-config gnus-util mailabbrev gmm-utils mailheader
mm-decode mm-bodies mm-encode url-dav parse-time iso8601 cl-extra
cl-print debug backtrace find-func benchmark shortdoc url-about
url-handlers thingatpt help-fns radix-tree help-mode dabbrev time-date
textsec uni-scripts idna-mapping ucs-normalize uni-confusable
textsec-check mail-utils gnutls network-stream url-http mail-parse
rfc2231 rfc2047 rfc2045 mm-util ietf-drums mail-prsvr url-gw nsm
url-cache url-auth shr text-property-search pixel-fill kinsoku url-file
url-dired puny svg xml dom browse-url url url-proxy url-privacy
url-expand url-methods url-history url-cookie generate-lisp-file
url-domsuf url-util url-parse auth-source cl-seq eieio eieio-core
cl-macs password-cache json subr-x map byte-opt gv bytecomp byte-compile
cconv url-vars mailcap savehist windmove winner ring dired-aux
cl-loaddefs cl-lib dired dired-loaddefs advice rmc iso-transl tooltip
eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type
elisp-mode mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd
fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow
isearch easymenu timer select scroll-bar mouse jit-lock font-lock syntax
font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic
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romanian slovak czech european ethiopic indian cyrillic chinese
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
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base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo x-toolkit
xinput2 x multi-tty make-network-process emacs)

Memory information:
((conses 16 210718 27584)
 (symbols 48 9278 0)
 (strings 32 47429 2202)
 (string-bytes 1 1030861)
 (vectors 16 40826)
 (vector-slots 8 595360 31429)
 (floats 8 105 82)
 (intervals 56 1185 0)
 (buffers 992 38))