bug#16875: python, comint-mode: Large output makes Emacs freeze

[fgallina@gnu.org (Fabián Ezequiel Gallina)]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: fgallina@gnu.org (Fabián Ezequiel Gallina)
>> Date: Sat, 26 Jul 2014 23:22:41 -0300
>> 
>> 
>> Emacs is still slow, but at least responds to commands.  I feel that
>> everything that could be optimized on the comint side is pretty much
>> there and that the slowness being experienced is in fact related to the
>> long-lines slowness bug mentioned before[0].
>
> That bug is about displaying long lines.  Is the code that is slow
> involved in displaying such lines?  If there's no display involved,
> then the discussion you point to is not relevant.
>
> Also, please tell how long are your lines, on the average.
>

Yes, such code outputs a long line consisting of 841601 chars.

One way to get that output in a file for testing is executing the
following shell command:

    python -c 'print ([[[False] * 200 for i in range(3)] for j in range(200)])' > /tmp/out.log

Even opening that file in fundamental-mode makes Emacs slow.  For
instance calling `previous-line' from the end of buffer several times
takes 1.1 seconds on average to complete.

    previous-line  30          33.263101639  1.1087700546

Next line is a bit more responsive though:

    next-line      30          14.028573178  0.4676191059

Operations seem to take longer and longer as point moves away from the
beginning of buffer.


Cheers,
Fabián