scroll-margin

scroll-margin

[Almer S. Tigelaar]

Dear maintainers,

I've found a bug in GNU Emacs 21.1. I've been able to reproduce both with the UNIX version as shipped with Debian GNU/Linux and the Windows binary version at the gnu ftp site.

Basically just set the "scroll-margin" variable to a positive number (e.g. 10). Open a file and then scroll up and down by whole screens (PgUp/PgDown). and navigate up/down line by line. After a while emacs will freeze consuming 100% CPU.

Yours sincerely,

Almer S. Tigelaar



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Re: scroll-margin

[Richard Stallman]

I can't reproduce this problem.  Would you please specify a single
*precise* test case?  Please read the Bugs section in the Emacs
manual, which provides guidelines on how to write a bug report to give
us the necessary information so we can fix the bug.

Re: scroll-margin

[Almer S. Tigelaar]

[-- Attachment #1: Type: text/plain, Size: 1190 bytes --]

Dear Mr. Stallman,

On Wed, 2002-03-27 at 00:17, Richard Stallman wrote:
> I can't reproduce this problem.  Would you please specify a single
> *precise* test case?  Please read the Bugs section in the Emacs
> manual, which provides guidelines on how to write a bug report to give
> us the necessary information so we can fix the bug.

My apologies for being vague about the issue. A retry :

I've attached something which can reproduce the problem. To try :
- Use the "dot-emacs" as init-file.
- After startup open "emacstest".
- Type "M-x hang-exec". (all it does it randomly scroll up and down)
- Sit back, let it scroll and wait :-)

I've tested with the following versions :
GNU Emacs 21.1.1 (i386-debian-linux-gnu, X toolkit, Xaw3d scroll bars)
of 2001-12-06 on raven, modified by Debian
GNU Emacs 21.1.1 (i386-MSVC-NT5.0.2195) of 2001-10-22 on Buffy
GNU Emacs 21.2.1 (i386-MSVC-NT5.0.2195) of 2002-03-19 on Buffy

(I define a "hang" as 100% CPU usage and Emacs not responding and
redrawing at all)

Observations :
- All of them "hang" within 3 minutes after the call to "hang-exec".
- The problem does not occur when scroll-margin is set to "0".

Yours sincerely,

Almer S. Tigelaar

[-- Attachment #2: dot-emacs --]
[-- Type: text/plain, Size: 545 bytes --]

(setq scroll-margin 10)

(defun hang-callback ()
  (setq hang-sequence (random 4))
  (setq hang-lines (1+ (random 24)))
  (if (> hang-sequence 1)
      (message "sequence %d lines %d" hang-sequence hang-lines)
      (message "sequence %d" hang-sequence))
  (if (equal hang-sequence 0) (next-line))
  (if (equal hang-sequence 1) (previous-line))
  (if (equal hang-sequence 2) (scroll-down hang-lines))
  (if (equal hang-sequence 3) (scroll-up hang-lines)))

(defun hang-exec ()
  (interactive)
  (run-at-time nil 1 'hang-callback))

[-- Attachment #3: emacstest --]
[-- Type: text/plain, Size: 319 bytes --]

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