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Re: Keeping replace-buffer-contents runtime in bounds
From: |
Eli Zaretskii |
Subject: |
Re: Keeping replace-buffer-contents runtime in bounds |
Date: |
Sun, 17 Feb 2019 17:50:45 +0200 |
> From: Tassilo Horn <address@hidden>
> Date: Sat, 16 Feb 2019 21:09:40 +0100
>
> 1. There's some too_expensive field of the context struct passed to
> compareseq which has quite some effect on the speed. I couldn't find
> any negative sides in using a much lower value than we originally
> used (1,000,000). However, maybe it's just my use-case. This is now
> exposed as an optional argument of replace-buffer-contents.
>
> 2. The too_expensive field is not enough. If the buffer contents and
> the contents of the replacement buffer become too large and there are
> too many differences, it may still take ages.
>
> So now I added some code which allows compareseq to abort early if the
> difference computation is too costly. Initially I've tried to use the
> number of differences found so far plus a max value. However, after
> using that some days I noticed that this is not a too good measure.
> Sometimes there were gazillion of differences, yet the difference
> computation was quick. But other times the number of differences was
> lower but still it took ages (most probably because the json was
> larger).
>
> In the end I settled for a maximum number of seconds one can define by
> setting a new variable replace-buffer-contents-max-secs, so that you can
> define what's still acceptable in the respective use-case. (Actually,
> if you set that to 1.5 or so, it may still run for 2 or more seconds
> because the EARLY_ABORT expression isn't tested at regular intervals or
> rather it is, but the intervals don't take equally long.)
>
> If that number of seconds is over, compareseq returns early and
> replace-buffer-contents falls back to plain delete and insert.
The gotcha about aborting after more than the time-out value should be
mentioned in the doc string.
Thanks for working on this. My only other comment is that maybe we
should allow passing the time-out value via the function's arguments,
not via a global variable. It seems to me the time-out will be used
in more use cases than MAX-COSTS, and in any case treating these two
differently API-wise sounds strangely inconsistent.
> This is my first C encounter in emacs, so please feel free to nit-pick.
Nitpicking:
> + DEFVAR_LISP ("replace-buffer-contents-max-secs",
> + Vreplace_buffer_contents_max_secs,
> + doc: /* If differencing the two buffers takes longer than this,
> +`replace-buffer-contents' falls back to a plain delete and insert. */);
The first sentence of a doc string should not be longer than 79
characters. (But if you agree with me, this variable will go away, so
it's a moot point.)
- Keeping replace-buffer-contents runtime in bounds, Tassilo Horn, 2019/02/16
- Re: Keeping replace-buffer-contents runtime in bounds,
Eli Zaretskii <=
- Re: Keeping replace-buffer-contents runtime in bounds, Tassilo Horn, 2019/02/17
- Re: Keeping replace-buffer-contents runtime in bounds, Tassilo Horn, 2019/02/24
- Re: Keeping replace-buffer-contents runtime in bounds, Eli Zaretskii, 2019/02/24
- Re: Keeping replace-buffer-contents runtime in bounds, Philipp Stephani, 2019/02/24
- Re: Keeping replace-buffer-contents runtime in bounds, Tassilo Horn, 2019/02/25
- Re: Keeping replace-buffer-contents runtime in bounds, Tassilo Horn, 2019/02/25
- Re: Keeping replace-buffer-contents runtime in bounds, Stefan Monnier, 2019/02/25
- Re: Keeping replace-buffer-contents runtime in bounds, Tassilo Horn, 2019/02/26