From: Eli Zaretskii <eliz@gnu.org>
To: Philipp Stephani <p.stephani2@gmail.com>
Cc: emacs-devel@gnu.org
Subject: Re: JSON/YAML/TOML/etc. parsing performance
Date: Fri, 29 Sep 2017 22:55:54 +0300 [thread overview]
Message-ID: <83h8vl5lf9.fsf@gnu.org> (raw)
In-Reply-To: <CAArVCkRvSaS-orqHcVPtZ2etUnRiY39okHh+6sYV-mtQQRYs-g@mail.gmail.com> (message from Philipp Stephani on Thu, 28 Sep 2017 21:19:00 +0000)
> From: Philipp Stephani <p.stephani2@gmail.com>
> Date: Thu, 28 Sep 2017 21:19:00 +0000
> Cc: emacs-devel@gnu.org
>
> IIUC Jansson only accepts UTF-8 strings (i.e. it will generate an error some input is not an UTF-8 string), and
> will only return UTF-8 strings as well. Therefore I think that direct conversion between Lisp strings and C
> strings (using SDATA etc.) is always correct because the internal Emacs encoding is a superset of UTF-8.
> Also build_string should always be correct because it will generate a correct multibyte string for an UTF-8
> string with non-ASCII characters, and a correct unibyte string for an ASCII string, right?
I don't think it's a good idea to write code which has such
assumptions embedded in it. We don't do that in other cases, although
UTF-8 based systems are widespread nowadays. Instead, we make sure
that encoding and decoding UTF-8 byte stream is implemented
efficiently, and when possible simply reuses the same string data.
Besides, these assumptions are not always true, for example:
. The Emacs internal representation could include raw bytes, whose
representations (both of them) is not valid UTF-8;
. Strings we receive from the library could be invalid UTF-8, in
which case putting them into a buffer or string without decoding
will mean trouble for programs that will try to process them;
So I think decoding and encoding any string passed to/from Jansson is
better for stability and future maintenance. If you worry about
performance, you shouldn't: we convert UTF-8 into our internal
representation as efficiently as possible.
> > + /* LISP now must be a vector or hashtable. */
> > + if (++lisp_eval_depth > max_lisp_eval_depth)
> > + xsignal0 (Qjson_object_too_deep);
>
> This error could mislead: the problem could be in the nesting of
> surrounding Lisp being too deep, and the JSON part could be just fine.
>
> Agreed, but I think it's better to use lisp_eval_depth here because it's the total nesting depth that could cause
> stack overflows.
Well, at least the error message should not point exclusively to a
JSON problem, it should mention the possibility of a Lisp eval depth
overflow as well.
> > + Lisp_Object string
> > + = make_string (buffer_and_size->buffer, buffer_and_size->size);
>
> This is arbitrary text, so I'm not sure make_string is appropriate.
> Could the text be a byte stream, i.e. not human-readable text? If so,
> do we want to create a unibyte string or a multibyte string here?
>
> It should always be UTF-8.
How does JSON express byte streams, then? Doesn't it support data (as
opposed to text)?
> > + {
> > + bool overflow = INT_ADD_WRAPV (BUFFER_CEILING_OF (point), 1, &end);
> > + eassert (!overflow);
> > + }
> > + size_t count;
> > + {
> > + bool overflow = INT_SUBTRACT_WRAPV (end, point, &count);
> > + eassert (!overflow);
> > + }
>
> Why did you need these blocks in braces?
>
> To be able to reuse the "overflow" name/
Why can't you reuse it without the braces?
Thanks.
next prev parent reply other threads:[~2017-09-29 19:55 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-16 15:54 JSON/YAML/TOML/etc. parsing performance Ted Zlatanov
2017-09-16 16:02 ` Mark Oteiza
2017-09-17 0:02 ` Richard Stallman
2017-09-17 3:13 ` Mark Oteiza
2017-09-18 0:00 ` Richard Stallman
2017-09-17 0:02 ` Richard Stallman
2017-09-18 13:46 ` Ted Zlatanov
2017-09-17 18:46 ` Philipp Stephani
2017-09-17 19:05 ` Eli Zaretskii
2017-09-17 20:27 ` Philipp Stephani
2017-09-17 22:41 ` Mark Oteiza
2017-09-18 13:53 ` Ted Zlatanov
2017-09-17 21:17 ` Speed of Elisp (was: JSON/YAML/TOML/etc. parsing performance) Stefan Monnier
2017-09-18 13:26 ` JSON/YAML/TOML/etc. parsing performance Philipp Stephani
2017-09-18 13:58 ` Mark Oteiza
2017-09-18 14:14 ` Philipp Stephani
2017-09-18 14:28 ` Mark Oteiza
2017-09-18 14:36 ` Philipp Stephani
2017-09-18 15:02 ` Eli Zaretskii
2017-09-18 16:14 ` Philipp Stephani
2017-09-18 17:33 ` Eli Zaretskii
2017-09-18 19:57 ` Thien-Thi Nguyen
2017-09-18 14:57 ` Eli Zaretskii
2017-09-18 15:07 ` Mark Oteiza
2017-09-18 15:51 ` Eli Zaretskii
2017-09-18 16:22 ` Philipp Stephani
2017-09-18 18:08 ` Eli Zaretskii
2017-09-19 19:32 ` Richard Stallman
2017-09-18 17:26 ` Glenn Morris
2017-09-18 18:16 ` Eli Zaretskii
2017-09-18 16:08 ` Philipp Stephani
2017-09-19 8:18 ` Philipp Stephani
2017-09-19 19:09 ` Eli Zaretskii
2017-09-28 21:19 ` Philipp Stephani
2017-09-28 21:27 ` Stefan Monnier
2017-09-29 19:55 ` Eli Zaretskii [this message]
2017-09-30 22:02 ` Philipp Stephani
2017-10-01 18:06 ` Eli Zaretskii
2017-10-03 12:26 ` Philipp Stephani
2017-10-03 15:31 ` Eli Zaretskii
2017-10-03 15:52 ` Philipp Stephani
2017-10-03 16:26 ` Eli Zaretskii
2017-10-03 17:10 ` Eli Zaretskii
2017-10-03 18:37 ` Philipp Stephani
2017-10-03 20:52 ` Paul Eggert
2017-10-04 5:33 ` Eli Zaretskii
2017-10-04 6:41 ` Paul Eggert
2017-10-04 8:03 ` Eli Zaretskii
2017-10-04 17:51 ` Paul Eggert
2017-10-04 19:38 ` Eli Zaretskii
2017-10-04 21:24 ` Paul Eggert
2017-10-05 1:48 ` Paul Eggert
2017-10-05 7:14 ` Eli Zaretskii
2017-10-08 22:52 ` Philipp Stephani
2017-10-09 5:54 ` Paul Eggert
2017-10-29 20:48 ` Philipp Stephani
2017-10-09 6:38 ` Eli Zaretskii
2017-10-05 7:12 ` Eli Zaretskii
2017-10-06 1:58 ` Paul Eggert
2017-10-06 7:40 ` Eli Zaretskii
2017-10-06 19:36 ` Paul Eggert
2017-10-06 21:03 ` Eli Zaretskii
2017-10-08 23:09 ` Philipp Stephani
2017-10-09 6:19 ` Paul Eggert
2017-10-29 20:48 ` Philipp Stephani
2017-10-29 22:49 ` Philipp Stephani
2017-12-09 23:05 ` Philipp Stephani
2017-12-10 7:08 ` Eli Zaretskii
2017-12-10 13:26 ` Philipp Stephani
2017-12-10 13:32 ` Ted Zlatanov
2017-10-08 23:04 ` Philipp Stephani
2017-10-09 6:47 ` Eli Zaretskii
2017-10-08 17:58 ` Philipp Stephani
2017-10-08 18:42 ` Eli Zaretskii
2017-10-08 23:14 ` Philipp Stephani
2017-10-09 6:53 ` Eli Zaretskii
2017-10-29 20:41 ` Philipp Stephani
2017-10-09 6:22 ` Paul Eggert
2017-10-01 18:38 ` Eli Zaretskii
2017-10-03 12:12 ` Philipp Stephani
2017-10-03 14:54 ` Eli Zaretskii
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