bug#26525: `sit-for' in Flyspell slows typing down, hogs 90% of CPU

[Eli Zaretskii]

> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
> Date: Sat, 15 Apr 2017 16:33:56 -0400
> 
> The relevant piece of code seems to be this:
> 
>       (cond
>        ((get this-command 'flyspell-deplacement)
>       (not (eq flyspell-previous-command this-command)))
>        ((get this-command 'flyspell-delayed)
>       ;; The current command is not delayed, that
>       ;; is that we must check the word now.
>       (and (not unread-command-events)
>            (sit-for flyspell-delay)))
>        (t t)))
> 
> But the condition and the comment seem at odds, and it doesn't say much about 
> why it calls `sit-for`.

I'm not quite sure what needs to be explained.  I think the doc string
of flyspell-delay and flyspell-default-delayed-commands tell the whole
story; if something is unclear there, please say what is unclear.

If you want to see this feature in action, turn on Flyspell, then type
something like "ssss", and then wait _without_ typing any non-word
character.  You will see that the mis-spelled word is marked only
after 3 sec, the default value of flyspell-delay.  Then contrast that
with the same word with a space typed after it.

IOW, this is a feature designed to avoid annoying users who type
slowly or make short breaks after typing only part of a word.