GNU bug report logs - #76805
31.0.50; [PATH] Fix Emacs uses 100% CPU after switching graphic frame to inactive

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From: Lin Sun <sunlin7 <at> hotmail.com>
To: 76805 <at> debbugs.gnu.org
Subject: bug#76805: 31.0.50; [PATH] Fix Emacs uses 100% CPU after switching graphic frame to inactive
Date: Fri, 7 Mar 2025 08:17:31 +0000

[Message part 1 (text/plain, inline)]

Hi, 
Emacs sometimes takes 100% CPU after I switch emacs graphic frame to inactive.
This patch will fix the issue.

Reproduce steps:
1. Build Emacs with gtk3 and xinput2 on Ubuntu 22.04.
2. (setq x-use-fast-mouse-position 'really-fast) in early-init.el.
3. On a windows-host start a X11 server, and ssh -XY ubuntu-host:emacs to Start emacs with X11 forwared-frame, and open emacs "src/eval.c", enable the show-paren-mode in emacs.
4. On the windows host, move the mouse out of emacs-graphic frame first, the move the mouse in emacs-graphic frame and click.
5. On the windows host, switch the emacs-graphic frame to inactive (switch a native windows app to active).
Repeat steps 4,5 sometimes the emacs will takes 100% CPU.

The issue won't happen if set the x-use-fast-mouse-position to `t` or `nil` instead of the 'really-fast.

According to my debugging and tracking the variables, I found that
1. the xterm.c:21710 will let "dpyinfo->last_mouse_motion_frame = NULL;", then 
2. later calls `x_fast_mouse_position` will no chance to let "XX->mouse_moved = false", then 
3. the function some_mouse_moved() in keyboard.c always return true; then
4. the function timer_start_idle() in keyboard.c will be called again and again, which leads 100% CPU usage.

As contrast when setting the x-use-fast-mouse-position to `t`, the "XX->mouse_moved = false;" always run, then the issue won't happen.

Please help review the patch. Thanks

Best Regards, Lin

[0001-src-xterm.c-Mark-mouse_moved-to-false-in-x_fast_mous.patch (text/x-patch, attachment)]

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