bug#31138: Native json slower than json.el

[Dmitry Gutov]

On 24.04.2019 20:43, Eli Zaretskii wrote:

> > But what conversion primitives does that low-level code use?
> > code_convert_region?
>
> AFAICS, it uses decode_coding_c_string.  Incoming data doesn't have to
> be UTF-8, mind you, it could be anything, including an unknown
> encoding that needs detecting, and only the detection tells us it's
> UTF-8.

All right, thank you. If I ever have anything solid to propose, I will 
do so later.

> > Relying on the library is probably faster.
>
> Why faster?

Because the library will perform its validation anyway, during normal 
execution. Any extra validation work Emacs performs, will take time on 
top of that (of course, I don't know how much time).

> And more importantly, will the error indication be useful enough to
> the Lisp program that triggered it?  If we signal an error, we can
> make sure of that.

We still signal errors if the library returns an error code.

More importantly, we also perform additional validation ourselves if 
something goes wrong. See the pieces of code like

      if (json == NULL)
        {
          /* A failure can be caused either by an invalid string or by
             low memory.  */
          json_check_utf8 (encoded);
          json_out_of_memory ();
        }

Anyway, speeding up encoding is not as important as it was with 
decoding, because at least in this case Lisp programs can control how 
much data is sent. So let's not spend too much time and effort on it.