Re: elpa xclip 1.11.1: copying from emacs GUI hangs emacs terminal

[Madhu <enometh@meer.net>]

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* pinmacs <38c19494-4abb-4316-a307-5c9e2f43fe23@cas.cat> :
Wrote on Mon, 9 Dec 2024 17:59:32 +0100:
> I first contacted Leo, the maintainer privately, and she proposed me to
> discuss with you guys here broadly.
>
> Context: I am a Debian GNU/Linux 12 (bookworm) user that runs the
> i3wm.org desktop, but I use emacs compiled on my own [0] from banch
> emacs-30 commit 44c2614, I think this is unrelated for the issue because
> I am having the issue since long time but recently I dedicated some
> hours to see if I could fix it:
>
> Bug report: When I run an emacsclient sessions through X11 (named later,
> x11 emacs), and I copy (with common M-w) some text to the X11 clipboard
> and I paste (with common C-y) X11 clipboard it with Alacritty terminal
> (emacs running on terminal), then emacs hangs and I need to press C-g
> several times to kill the process that is being run and I don't get the
> clipboard content.


FWIW I'm attaching a patch I've been using for a long time, ever since
the the clipboard stuff was converted to elisp cl-generics. (I only
understood enough of it to work around the hangs at that time.  and
haven't reviewed it for mistakes before posting)


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From 28e7363314061e2a98ba29919146bf51e8f06770 Mon Sep 17 00:00:00 2001
From: Madhu <enometh@net.meer>
Date: Thu, 10 Mar 2016 14:37:20 +0530
Subject: [PATCH] initial fixes

;; <Thu Mar 22 13:07:37 2012 +0530> madhu 120322 1. avoid deadlock
;; when calling C-y (call-process("xclip-o")) in a terminal when an
;; emacs X frame owns the selection. 1a. (current-kill 0) when emacs
;; owns the primary. 2. a sit-for in xclip-select-text avoids deadlock
;; when calling C-y in a frame when xclip owns the selection. this
;; happens when M-w'ing a text which has text-properties and C-y'ing

sitfor workaround. (selection-value--internal): new dispatch to
(xclip-selection-value-synchrnous):new or gui-selection-value
internal.
---
 xclip.el | 45 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 39 insertions(+), 6 deletions(-)

diff --git a/xclip.el b/xclip.el
index 4fe07d3..c76e130 100644
--- a/xclip.el
+++ b/xclip.el
@@ -50,6 +50,15 @@
 ;; copy/pasting from an external application to Emacs and not from Emacs to
 ;; another application (for which it relies on the default code).
 
+;; <Thu Mar 22 13:07:37 2012 +0530> madhu 120322 1. avoid deadlock
+;; when calling C-y (call-process("xclip-o")) in a terminal when an
+;; emacs X frame owns the selection. 1a. (current-kill 0) when emacs
+;; owns the primary. 2. a sit-for in xclip-select-text avoids deadlock
+;; when calling C-y in a frame when xclip owns the selection. this
+;; happens when M-w'ing a text which has text-properties and C-y'ing
+;; it.
+;;
+
 ;;; Code:
 
 (defgroup xclip ()
@@ -156,7 +165,8 @@ (defun xclip-set-selection (type data)
               (method (error "Unknown `xclip-method': %S" method)))))
       (when proc
         (process-send-string proc data)
-        (process-send-eof proc))
+        (process-send-eof proc)
+	(sit-for .2))
       data)))
 
 (defun xclip-get-selection (type)
@@ -268,7 +278,13 @@ (defun xclip--hidden-frame ()
                                                &context (window-system nil))
         (if (not xclip-mode)
             (cl-call-next-method)
-          (xclip-get-selection selection-symbol)))
+          (cond ((fboundp 'x-selection-exists-p) ; X build
+		 (cond ((x-selection-exists-p selection-symbol)
+			(cond ((x-selection-owner-p selection-symbol)
+			       (cl-call-next-method))
+			      (t (xclip-get-selection selection-symbol))))
+		       (t (xclip-get-selection selection-symbol))))
+		(t (xclip-get-selection selection-symbol)))))
 
       (cl-defmethod gui-backend-set-selection (selection-symbol value
                                                &context (window-system nil))
@@ -311,10 +327,29 @@ (defun xclip--hidden-frame ()
       (xclip-set-selection 'clipboard text)
       (setq xclip-last-selected-text-clipboard text)))
 
+  (defun xclip-selection-value--synchronous (type)
+    (with-output-to-string
+      (process-file xclip-program nil standard-output nil
+                    "-o" "-selection" (symbol-name type))))
+
+  (defun xclip-selection-value--internal (type)
+    (cond ((and (fboundp 'x-selection-exists-p)	; X build
+		;(eq window-system 'x)
+		)
+	   (cond ((x-selection-exists-p type)
+		  (cond ((x-selection-owner-p type)
+			 ;;thanks stefan monnier for spit cl-generic
+			 (let ((window-system 'x))
+			   (gui--selection-value-internal type)))
+			(t (xclip-selection-value--synchronous type))))
+		 (t
+		  (xclip-selection-value--synchronous type))))
+	  (t (xclip-selection-value--synchronous type))))
+
   (defun xclip-selection-value ()
     "See `x-selection-value'."
     (let ((clip-text (when xclip-select-enable-clipboard
-                       (xclip-get-selection 'CLIPBOARD))))
+		       (xclip-selection-value--internal 'CLIPBOARD))))
       (setq clip-text
             (cond                       ; Check clipboard selection.
              ((or (not clip-text) (string= clip-text ""))
@@ -329,9 +364,7 @@ (defun xclip--hidden-frame ()
              (t (setq xclip-last-selected-text-clipboard clip-text))))
       (or clip-text
           (when (and (memq xclip-method '(xsel xclip)) (getenv "DISPLAY"))
-            (let ((primary-text (with-output-to-string
-                                  (call-process xclip-program nil
-                                                standard-output nil "-o"))))
+            (let ((primary-text (xclip-selection-value--internal 'PRIMARY)))
               (setq primary-text
                     (cond               ; Check primary selection.
                      ((or (not primary-text) (string= primary-text ""))
-- 
2.46.0.27.gfa3b914457


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>
> More details:
>
> Everything else works perfectly, my config is simple on that matter:
>
> #+begin_src emacs-lisp
> ;; https://elpa.gnu.org/packages/xclip.html
> (use-package xclip :ensure nil
>    :config
>    (xclip-mode 1)
>    )
> #+end_src
>
>
> This problem is somehow well-known [1] (that does not mean that I
> understand what's going on, just reporting that this happens, not only
> in xclip context)
>
> Here, I am able to reproduce the hang with org-babel [1]:
>
> #+begin_src bash
> xclip -i /dev/null -selection clipboard
> xclip -o -selection clipboard
> #+end_src
>
> it also hangs with the built-in shell-command elisp function calls:
>
> (shell-command "echo 'clipboard content' | xclip -selection clipboard")
> (shell-command "xclip -o -selection clipboard")
>
>
> But I cannot reproduce the hang in a normal terminal (vterm, alacritty,
> even in a linux console; fails because cannot open display).
>
>
> Inside the xclip.el, a process-call with the xclip program is invoked,
> then hangs, and then you need to press C-g several times, this happens
> with the following configurations:
>
>      (setq xclip-method 'xclip)
>      (setq xclip-method 'xsel)
>
> Here, I suggest, to reduce UX-frustration throwing a timeout error; but
> I don't know how to do it. I just know the POSIX timeout command [2].
>
> There is a workaround, unrelated to emacs: using the typical terminal
> clipboard paste command Ctrl+Shift+V, but I don't like to think if I am
> in a terminal emacs buffer or X11 emacs buffer, I want to flow and have
> something that works everywhere flawlessly. In fact, I also like to
> access the whole previous kill ring with M-y.
>
>
> Then I found that the emacs xclip-method works fine for that corner case
> that I am describing, but then sometimes "looses the synchronization"
> (?) with the X11 clipboard and provides an old-wrong clipboard; so I end
> up copying and recopying from a random X11 app to emacs terminal without
> success (specially when doing it to the terminal window).
>
>      (setq xclip-method 'emacs)
>
>
> I also tried to hack on the xclip code, it is weird that when I override
> the function definition does not work, I think it would be nice to know
> the details/documentation on how to hack or change on this.
>
> Anyway, trying stuff, when I replaced the paste content with hello
> world, it does not hang and it works, so it is clearly a problem when
> tries to get the xclip content from terminal and the last content was
> put in clipboard by emacs X11.
>
> By the way, disabling xclip package, makes pasting the emacs X11 to
> emacs terminal work; but then, does not work with the rest of X11
> clipboard apps.
>
>
> Thanks for your attention,
> pinmacs
>
> [0] my compilation details:
>    ./configure --with-native-compilation --with-native-compilation=aot
> --with-x-toolkit=lucid
>    make -j4
>    make bootstrap
>
> [1]
> https://emacs.stackexchange.com/questions/39019/xclip-hangs-shell-command
> [2] https://orgmode.org/worg/org-contrib/babel/
> [3] https://pubs.opengroup.org/onlinepubs/9799919799/utilities/timeout.html