Blinking window on multi-CPU machine

[Emmanuel Briot]

Hello all,

A customer of ours has reported the following problem on Emacs 21.1.
This is on linux, a machine with two CPUs.

It appears that after loading the compilation mode, and if left alone, Emacs
will start blinking, until the focus is moved out of the Emacs window.

Here is his report. It assumes that the file build.output is the result of a
make command, that contains some errors. His code is Ada, compiled with GNAT,
but I don't think it matters.


<<

After making your change I got blinking the first time with the following
sequence...

emacs build.output &
M-X compilation-mode
scrolled down to the last file I was working on
middle click on the error
-- window now split (build.output on top, truss_partition.2.ada on bottom)
compile file
-- top half now *compilation*. Runs for several seconds w/ a long output (I
have -gnatR enabled). Some minor blinking at the top during the compilation
and continued after the compilation complete.
go to next error
-- bottom half at "not referenced" warning [subject of another bug report]
no movement of mouse or keypresses
-- text on the screen blinks (as if being redraw over & over) with 10-20%
CPU load as seen on xosview
move the mouse outside the emacs window
-- the blinking stops and CPU time back to zero

I repeated this series of steps (w/o the oops) just now. The second time,
the blinking stopped at the same time I noticed the text
"Auto-saving...done" in the mini buffer. I repeated the compile file & got
to next error twice afterwards - no blinking.

Third time I repeated the initial steps - same result as first time. I let
the machine sit a while w/o moving cursor or typing keys while it was
blinking after the compile was complete - took about 60-70 seconds to
settle down and stop blinking (and stop burning CPU cycles). There was no
blinking when I did the "go to next error" command.

Somehow several different actions can cause the blinking to stop...
 - a time out of over a minute
 - moving the cursor to another window
 - "auto save" (unless I got really lucky...)
It does definitely start with the compile if I look closely. With the two
CPU's and xosview, I can see the blips on the idle CPU whenever emacs goes
and refreshes its display (other CPU is 100% loaded).

>>



If you need any more information, I would be happy to provide it (or get in
touch with our customer to ask for more information).

regards,
Emmanuel
(ada-mode.el and xml.el maintainer)