bug#75461: 30.0.93; Frequent (but inconsistent) hangs when creating frames

[Phil Sainty <psainty@orcon.net.nz>]

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I've recently switched my main instance of Emacs to 30.0 (firstly
30.0.93, and now the HEAD of the emacs-30 branch), and I've been
experiencing frequent hangs (with the CPU core spinning at 100% usage)
when creating new frames.

More specifically: when creating frames using a system I use with my
window manager when I want to interactively select a thing in a pop-up
Emacs frame.  (I've tried to replicate this with simply "C-x 5 2" but
didn't manage to do so thus far.)

If I spam a terminal with a large number of "kill -USR2 <pid>" commands
for the spinning Emacs process ID, then I'll get control back.

I'm experiencing this (inconsistently, but quite often) with using a
keybinding for my window manager (XMonad), which runs a command like:

  emacsclient --eval "(my-x-paste-example $(xdotool getactivewindow))"

With that command being something like:

  (defun my-x-paste-example (wid)
     (interactive)
     (my-x-paste #'my-example wid "*Example*" "Testing"))

  (defun my-example ()
    (interactive)
    (gui-backend-set-selection
     'CLIPBOARD (completing-read "Choose: " '(one two three))))

I've attached the definition of `my-x-paste' to this report.  It
creates a small floating frame for the interaction, and afterwards it
runs xdotool again to paste the clipboard contents into the X window
obtained by "xdotool getactivewindow", but I think the xdotool aspect
shouldn't be a factor, as it never gets that far -- Emacs creates the
frame and then immediately hangs before I can interact with it at all.
Perhaps the frame parameters used in that function are relevant,
though.

I've recompiled Emacs for debugging and run it under gdb, and have
reproduced a hang, so I have also attached some backtraces from gdb
(more than one because they're variable).  In each case I used
"kill -TSTP <PID>" to stop Emacs spinning and drop to the gdb prompt,
and then the "backtrace" command.  I then had to "continue" multiple
times before Emacs started running/spinning again, after which I
repeated the process.

(I also tried "xbacktrace" but that just said "Undefined command:
"xbacktrace".  Try "help".", and I'm afraid that I only just saw the
"bt full" recommendation in the report-emacs-bug template -- the
etc/DEBUG file doesn't actually mention that command -- and I've not
been able to reproduce the issue in the interim to try that one, so
I'm sending this as-is for now.)

The function I'm calling in lisp does a `completing-read', and I can
see Fread_from_minibuffer in the backtrace, so I *guess* it's getting
that far after creating the frame; but I'm not sure if that's a factor
as (I think) I've also seen this with a pop-up notification frame
I use for appt.el notifications -- and that one doesn't prompt me at
all (but it's creating frames in a fairly similar way).

I can't replicate this at will, but it happens often enough that I
*should* be able to recreate it again sometime soon, so let me know
if you want me to try other things (but note that I'm not familiar
with gdb and debugging C code, so step-by-step instructions will be
helpful for that).


-Phil




In GNU Emacs 30.0.93 (build 5, x86_64-pc-linux-gnu, X toolkit, cairo
  version 1.16.0, Xaw scroll bars) of 2025-01-09 built on phil-lp
Repository revision: 01464fc882dbb56d4271fbb89b7b847e8374d39c
Repository branch: emacs-30
Windowing system distributor 'The X.Org Foundation', version 
11.0.12101004
System Description: Ubuntu 22.04.5 LTS

Configured using:
  'configure --prefix=/home/phil/emacs/30.x/usr/local
  --without-native-compilation --with-x-toolkit=lucid --without-sound
  '--program-transform-name=s/^ctags$/ctags_emacs/'
  --enable-checking=yes,glyphs --enable-check-lisp-object-type
  'CFLAGS=-O0 -g3''

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
LCMS2 LIBSELINUX LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP
SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM
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

Major mode: IBuffer

Minor modes in effect:
   text-scale-mode: t
   hexl-follow-ascii: t
   magit-wip-initial-backup-mode: t
   magit-wip-before-change-mode: t
   magit-wip-after-apply-mode: t
   magit-wip-after-save-mode: t
   magit-wip-mode: t
   global-git-commit-mode: t
   magit-auto-revert-mode: t
   catalyst-directory-event-icalendar-sync-mode: t
   minibuffer-line-mode: t
   global-edit-server-edit-mode: t
   savehist-mode: t
   global-anzu-mode: t
   anzu-mode: t
   my-contextual-help-mode: t
   global-so-long-mode: t
   server-mode: t
   global-visible-mark-mode: t
   visible-mark-mode: t
   repeat-mode: t
   display-battery-mode: t
   my-visible-bell-mode: t
   global-display-fill-column-indicator-mode: t
   minibuffer-depth-indicate-mode: t
   which-key-mode: t
   winner-mode: t
   keep-buffers-mode: t
   global-subword-mode: t
   subword-mode: t
   global-hl-line-mode: t
   display-time-mode: t
   recentf-mode: t
   global-atomic-chrome-edit-mode: t
   my-global-keys-local-minor-mode: t
   my-keys-local-minor-mode: t
   windmove-mode: t
   url-handler-mode: t
   auto-compile-on-load-mode: t
   auto-compile-on-save-mode: t
   tooltip-mode: t
   global-eldoc-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tab-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   minibuffer-regexp-mode: t
   buffer-read-only: t
   column-number-mode: t
   line-number-mode: t
   transient-mark-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t

Load-path shadows:
/home/phil/.emacs.d/el-get/scratch/el-get hides 
/home/phil/.emacs.d/el-get/el-get/el-get
/home/phil/.emacs.d/el-get/avy/avy hides 
/home/phil/.emacs.d/elpa/avy-0.5.0/avy
/home/phil/.emacs.d/el-get/dash/dash hides 
/home/phil/.emacs.d/elpa/dash-2.19.1/dash
/home/phil/.emacs.d/el-get/iedit/iedit hides 
/home/phil/.emacs.d/elpa/iedit-0.9.9.9.9/iedit
/home/phil/.emacs.d/my-lisp/psysh hides 
/home/phil/.emacs.d/elpa/psysh-0.4.9/psysh
/home/phil/.emacs.d/elpa/transient-0.7.9/transient hides 
/home/phil/emacs/30.x/usr/local/share/emacs/30.0.93/lisp/transient
/home/phil/.emacs.d/el-get/which-key/which-key hides 
/home/phil/emacs/30.x/usr/local/share/emacs/30.0.93/lisp/which-key

Features:
(shadow sort ecomplete mail-extr emacsbug ibuf-ext ibuffer
ibuffer-loaddefs dired-aux face-remap pulse color help-fns xref project
hi-lock noutline outline find-func totp hexl executable magit-wip
magit-log which-func imenu magit-diff smerge-mode diff git-commit
log-edit message sendmail yank-media rfc822 mml mml-sec gnus-util
mm-decode mm-bodies mm-encode mailabbrev gmm-utils mailheader pcvs-util
add-log magit-core magit-autorevert autorevert filenotify magit-margin
magit-transient magit-process magit-mode transient edmacro compat
magit-git magit-section magit-utils crm dash mail-utils gnutls
network-stream url-cache epa-file epa epg rfc6068 epg-config view
holidays holiday-loaddefs cal-julian lunar solar cal-dst vc-git
diff-mode track-changes vc-dispatcher autoinsert bug-reference appt
diary-lib diary-loaddefs cal-menu calendar cal-loaddefs lexbind-mode
hl-sexp fic-mode elide-head idle-highlight-mode catalyst-directory
vtable mule-util url-http url-auth mail-parse rfc2231 rfc2047 rfc2045
mm-util ietf-drums mail-prsvr url-gw nsm puny goto-addr sockit tabify
minibuffer-line edit-server my-org my-projects my-session savehist
desktop frameset my-theme zenburn-theme my-mail my-libraries sudo anzu
my-version-control my-text my-programming so-long my-rectangles rect
my-utilities with-editor server browse-kill-ring derived term disp-table
shell pcomplete ehelp my-configuration visible-mark cus-edit pp cus-load
dired-details dired-x repeat highlight-parentheses format-spec battery
delight delsel ffap thingatpt display-fill-column-indicator mb-depth
which-key pcase easy-mmode winner keep-buffers cap-words superword
subword hl-line time recentf tree-widget wid-edit atomic-chrome
websocket bindat let-alist my-whitespace ws-trim my-externals .loaddefs
rainbow-mode notify dbus xml mo-git-blame cl iedit el-get cl-extra
help-mode autoload loaddefs-gen radix-tree lisp-mnt dired dired-loaddefs
my-holidays my-local kmacro my-mahara grep tks generic-x catalyst
redshift-indent my-keybindings framemove advice windmove my-startup-log
trace cl-print time-date adaptive-wrap-autoloads dape-autoloads
docker-autoloads dockerfile-mode-autoloads eat-autoloads
eldoc-box-autoloads elfeed-autoloads haskell-mode-autoloads
helpful-autoloads elisp-refs-autoloads f-autoloads iedit-autoloads rx
modus-themes-autoloads psysh-autoloads rfc-mode-autoloads s-autoloads
markdown-mode-autoloads tablist-autoloads info transient-autoloads
visual-fill-autoloads websocket-autoloads wtf-autoloads xr-autoloads
package browse-url url url-proxy url-privacy url-expand url-methods
url-history url-cookie generate-lisp-file url-domsuf url-util mailcap
url-handlers url-parse auth-source ...)

Memory information:
((conses 16 342345 195376) (symbols 48 38691 4)
  (strings 32 146239 28849) (string-bytes 1 3881004) (vectors 16 64057)
  (vector-slots 8 1530248 160628) (floats 8 907 8658)
  (intervals 56 9801 2166) (buffers 992 27))

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(defun my-x-paste (command wid &optional bufname header text)
  "Run COMMAND and paste the result into the original X window.

\(For use with programs where \"C-v\" is paste.)

The value returned from COMMAND will be set in the system clipboard,
and then the key \"C-v\" will be performed in the original X window.

The pop-up frame will initially display a temporary buffer named
BUFNAME which is displaying the `header-line-format' HEADER, and
buffer contents TEXT.  You can use these to give the user context
for the interaction.

Requires that \"xdotool\" is installed on your system.  E.g.:

 sudo apt-get install xdotool

To use, trigger the following command via your window manager:

 emacsclient --eval \"(my-x-paste-COMMAND $(xdotool getactivewindow))\"

With \(my-x-paste-COMMAND wid) being a wrapper for calling `my-x-paste'.

Example:

 \(defun my-x-paste-totp (wid)
   \"Paste `totp-as-clipboard' into X window WID (see `my-x-paste').\"
   (interactive)
   (my-x-paste #\\='totp-as-clipboard wid \"*TOTP\"
               \"Time-based One-time Password (TOTP)\"))

XMonad key binding (mod-T) for xmonad.hs:

 , ((modMask .|. shiftMask, xK_t), spawn \"emacsclient --eval \\
 \\\"(my-x-paste-totp $(xdotool getactivewindow))\\\"\")

Also for XMonad, include the following in your manageHook to make the
pop-up frame float over the other windows rather than being tiled:

 appName =? \"EmacsXPaste\" --> doFloat"
  (interactive)
  (with-temp-buffer
    (when bufname
      (rename-buffer bufname :unique))
    (when header
      (setq-local header-line-format header))
    (when text
      (insert text))
    (let* ((buf (current-buffer))
           (width 80)
           (height (max window-safe-min-height
                        (count-lines (point-min) (point-max))))
           (pxwidth (+ 3 (* width (default-font-width))))
           (pxheight (+ 3 (* height (default-font-height))))
           (fparams `((my-x-paste . t)
                      (name . "EmacsXPaste")
                      (fullscreen . nil)
                      (width . ,width)
                      (height . ,height)
                      (left . ,(- (/ (display-pixel-width) 2) (/ pxwidth 2)))
                      (top . ,(- (/ (display-pixel-height) 2) (/ pxheight 2)))
                      (menu-bar-lines . 0)
                      (tool-bar-lines . 0)
                      (auto-raise . t))))
      (select-frame (make-frame fparams))
      (pop-to-buffer buf)
      (delete-other-windows)
      (unwind-protect
          (let ((value (call-interactively command)))
            (and value
                 (integerp wid)
                 (gui-backend-set-selection 'CLIPBOARD value)
                 (call-process "xdotool" nil nil nil
                               "key"
                               "--clearmodifiers"
                               "--window" (number-to-string wid)
                               "ctrl+v")
                 t))
        ;; We need to give the target window time to talk to the Emacs frame to
        ;; extract the clipboard text before the frame is deleted.  This should
        ;; only take a moment; but as we don't know for sure how long we need, we
        ;; make the frame invisible and then sleep for a full second.  Note that
        ;; we need to redisplay to activate the visibility change.
        (set-frame-parameter (selected-frame) 'visibility nil)
        (redisplay)
        (sleep-for 1)
        (delete-frame)))))

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