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bug#53798: 27.1; OSX: (redisplay) does not reliably redisplay
From: |
Eli Zaretskii |
Subject: |
bug#53798: 27.1; OSX: (redisplay) does not reliably redisplay |
Date: |
Sat, 05 Feb 2022 15:10:21 +0200 |
> From: Markus Triska <triska@metalevel.at>
> Date: Sat, 05 Feb 2022 13:42:58 +0100
>
>
> To reproduce this issue, please start Emacs with:
>
> $ emacs -Q
>
> and evaluate the following form:
>
> (while t
> (insert "\n" (make-string 50 ?a))
> (redisplay)
> (sit-for 0.1))
>
> At first, this works completely as intended: We see a growing number of
> lines in the buffer, and we are shown each fresh line as it appears:
>
> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
> ...
>
> However, as soon as any key is pressed, the output becomes erratic in
> the sense that for long stretches of time, we see no new lines at all,
> and then several of them appear immediately at the same time.
>
> The snippet uses (redisplay) after writing each line in order to show
> the line as it appears. I therefore expect to continue to see, also when
> a key is pressed, each line immediately after it is written in the
> buffer, not batches of multiple lines to be shown after several of them
> have already been written. Is there any way to obtain this behaviour?
sit-for exits immediately if some input is available, and pressing a
key makes input available. So the loop starts iterating much faster
than before, because sit-for no longer waits for 0.1 sec. And that is
what you see.
If I modify the snippet as below, it behaves the same no matter
whether you press a key or not.
(while t
(insert "\n" (make-string 50 ?a))
(redisplay)
(or (sit-for 0.1)
(read-char)))