bug#8235: 23.2; slow scrolling w/ multiple frames visiting same file

[Stefan Kangas]

Paul Vernaza <vernaza@stwing.upenn.edu> writes:

> Steps to reproduce:
> At an OS X terminal, run "open -a Emacs --args -Q".
> Open a large text file with C-x C-f.
> Open two new frames visiting the same buffer with C-x 5 2 C-x 5 2.
> Switch back to the original frame.
> Scroll down by holding C-n.
>
> Detailed description:
> In the OS X Cocoa version of Emacs, if multiple frames are visiting the
> same buffer, some of the frames visiting this buffer exhibit very slow 
> scrolling, while others scroll normally. Scrolling is slow in the sense
> that the display updates infrequently while scrolling (say, up to a
> second between updates).  CPU usage appears to be near normal, maybe at
> most slightly elevated while these symptoms are exhibited (possible
> concurrency issue?).
>
> Problem is consistent across major modes I've tested (fundamental, text, lisp,
> ocaml).  The problem seems to be specific to the Cocoa version of
> Emacs--the X11 version (23.3) compiled on the same platform does not have the
> issue. Although I'm reporting this from the Macports-compiled version,
> I have verified that the bug occurs compiling 23.3 with Cocoa on the
> same platform.
>
> Profiling with Shark shows abnormally high time spent in the
> redisplay_windows function (~50%) while slow scrolling is occurring.
> While scrolling normally, profiling shows an insignificant amount of 
> time spent in this function (< 1%).  

This was reported 9 years ago but unfortunately never got a reply at
the time.

I can't reproduce this using Emacs on macOS.  Are you still seeing
this bug?  If I don't hear back from you within a couple of weeks,
I'll just close this bug as unreproducible.

Best regards,
Stefan Kangas

> In GNU Emacs 23.2.1 (x86_64-apple-darwin10.4.0, NS apple-appkit-1038.32)
> of 2010-06-30 on seasnet-10-13.grasp.upenn.edu
> Windowing system distributor `Apple', version 10.3.1038
> configured using `configure  '--prefix=/opt/local' '--with-ns' '--without-x' 
> '--without-dbus' 'CC=/usr/bin/gcc-4.2' 'CFLAGS=-O2 -arch x86_64' 
> 'LDFLAGS=-L/opt/local/lib' 'CPPFLAGS=-I/opt/local/include''