Subject: 31.0.50; [PATH] Fix Emacs uses 100% CPU after switching graphic frame to inactive

From: Lin Sun <[email-masked]>
Date: Fri, 7 Mar 2025 08:17:31 +0000

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

From 4260ce23f260a58593bdbf02b251eb8077f0bedf Mon Sep 17 00:00:00 2001
From: Lin Sun <[email-masked]>
Date: Fri, 7 Mar 2025 06:50:03 +0000
Subject: [PATCH] * src/xterm.c: Mark mouse_moved to false in
 x_fast_mouse_position()

---
 src/xterm.c | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/src/xterm.c b/src/xterm.c
index 2ccf267bbd3..3fd9cb54ccf 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -14878,6 +14878,13 @@ x_fast_mouse_position (struct frame **fp, int insist, Lisp_Object *bar_window,
       return;
     }
 
+  FOR_EACH_FRAME (tail, frame)
+    {
+      if (FRAME_X_P (XFRAME (frame))
+	  && (FRAME_DISPLAY_INFO (XFRAME (frame)) == dpyinfo))
+	XFRAME (frame)->mouse_moved = false;
+    }
+
   if (!EQ (Vx_use_fast_mouse_position, Qreally_fast))
     {
       /* This means that Emacs should select a frame and report the
@@ -14886,14 +14893,6 @@ x_fast_mouse_position (struct frame **fp, int insist, Lisp_Object *bar_window,
 	 window beneath the pointer, and was borrowed from
 	 haiku_mouse_position in haikuterm.c.  */
 
-      FOR_EACH_FRAME (tail, frame)
-	{
-	  if (FRAME_X_P (XFRAME (frame))
-	      && (FRAME_DISPLAY_INFO (XFRAME (frame))
-		  == dpyinfo))
-	    XFRAME (frame)->mouse_moved = false;
-	}
-
       if (gui_mouse_grabbed (dpyinfo)
 	  && !EQ (track_mouse, Qdropping)
 	  && !EQ (track_mouse, Qdrag_source))
@@ -14964,14 +14963,6 @@ x_fast_mouse_position (struct frame **fp, int insist, Lisp_Object *bar_window,
 	  *bar_window = Qnil;
 	  *part = scroll_bar_nowhere;
 
-	  FOR_EACH_FRAME (tail, frame)
-	    {
-	      if (FRAME_X_P (XFRAME (frame))
-		  && (FRAME_DISPLAY_INFO (XFRAME (frame))
-		      == dpyinfo))
-		XFRAME (frame)->mouse_moved = false;
-	    }
-
 	  dpyinfo->last_mouse_motion_frame->mouse_moved = false;
 	}
     }
-- 
2.34.1