bug#57207: 29.0.50; Fontification is slow after e7b5912b23 (Improvements to long lines handling)

[Ihor Radchenko <yantar92@gmail.com>]

Eli Zaretskii <eliz@gnu.org> writes:

> What I don't understand is why enlarging the value of the threshold
> causes Emacs to "hang".  If it really is some kind of infloop, I
> cannot understand how issues like outdated UNCHANGED_MODIFIED could
> cause that only for some value of the threshold, but not for a smaller
> value.  I thought perhaps there are lines longer than 10000
> characters, but none beyond 100000, but this turns out to be false, so
> with both values of the threshold that loop in redisplay_window should
> have scanned the entire buffer top to bottom in both cases...
>
> So I suspect something else is at work here.

Clarification: I was unable to trigger the hang again. I am not sure
what I did the first time (I played with long-line-threshold values
inside the same Org buffer), but I suspect that there were also some
errors raised in the Org fontification code - parts of the buffer got
wrong fontification just before the hang. Of course, these errors are
probably also an indication that something is going wrong, but the hang
may not be directly related to the slowdown.

Throughout my today's attempts to reproduce, I did not see any obvious
difference in the slowdown between 10000 and 100000 long-line-threshold
values.

-- 
Ihor Radchenko,
Org mode contributor,
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