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Re: `format` slows down my function even though it shouldn't be called a
From: |
Joost Kremers |
Subject: |
Re: `format` slows down my function even though it shouldn't be called at all... |
Date: |
Sun, 15 Dec 2024 23:31:20 +0100 |
User-agent: |
mu4e 1.12.7; emacs 29.4 |
I did it again... Right after posting my message, I find the cause of the
problem. Sigh... Ignore please.
(For anyone wondering: the parser actually signals many errors, but most of
them are caught using `condition-case`...)
On Sun, Dec 15 2024, Joost Kremers wrote:
> Hi,
>
> I have a library for parsing `.bib` files[1] and today a user reported an
> issue[2] that lead me to a weird discovery. Basically, a call to `format`
> that is never even executed slows down execution tremendously.
>
> The reader part of the parser consists of a couple of functions that all
> have the following structure:
>
> ```
> (defun parsebib--chars (chars &optional noerror)
> "Read the character at point.
> CHARS is a list of characters. If the character at point matches
> a character in CHARS, return it and move point, otherwise signal
> an error, unless NOERROR is non-nil, in which case return nil."
> (parsebib--skip-whitespace)
> (if (memq (char-after) chars)
> (prog1
> (char-after)
> (forward-char 1))
> (unless noerror
> (signal 'parsebib-error (list (format "Expected one of %S, got %c at
> position %d,%d"
> chars
> (following-char)
> (line-number-at-pos)
> (current-column)))))))
> ```
>
> In short, after skipping whitespace, the reader functions try to read some
> element (character, keyword, etc. depending on the function), return it if
> it's found and signal an error if it's not found.
>
> The call to `signal` contains a call to `format` to provide a useful error
> message. It's this `format` that slows down parsing, even though no errors
> are ever signalled.
>
> This is an excerpt from a profiler report:
>
> ============================================================
> 17758 81% - parsebib--chars
> 17755 80% - if
> 17749 80% - if
> 17737 80% - signal
> 17737 80% - list
> 17515 79% format
> ============================================================
>
> This is from parsing a 28MB .bib file: The 79% of processing time spent in
> `format` seems very weird to me, given that the file contains no errors and
> no error is ever signalled.
>
> After removing the `format` calls, replacing them with a simple string, the
> parser runs much, much, much faster. To give an idea of the speed increase:
> without `format`, the 28MB .bib file I mentioned above is parsed in 1-2
> seconds (on my machine); with `format`, I don't even have enough patience
> to wait for parsing to finish... (I let it run for at least 20-30 seconds
> before interrupting it.)
>
> Anyone know what's going on here? Am I missing something, or could this be
> a bug in Emacs? (I'm running Emacs 29.4, BTW).
>
> TIA
>
> Joost
>
>
>
> Footnotes:
> [1] At https://github.com/joostkremers/parsebib
>
> [2] https://github.com/joostkremers/parsebib/issues/34
--
Joost Kremers
Life has its moments