Re: New optimisations for long raw strings in C++ Mode.

[Alan Mackenzie <acm@muc.de>]

Hello, Lars.

On Sun, Aug 07, 2022 at 14:49:40 +0200, Lars Ingebrigtsen wrote:
> Alan Mackenzie <acm@muc.de> writes:

> > I've just committed some optimisations to the savannah master branch
> > which should speed up the handling of long C++ raw strings in an Emacs
> > where font-locking is fully working.

> > On a megabyte long raw string in a normal build on a reasonably modern
> > machine, the response is slightly sluggish, but not unreasonable to
> > somebody who prefers correct fontification to instant response.

> I tried the same test case as before, yanking a 1MB long line into a raw
> string, and Emacs is still hanging after 20s (at which point I'm killing
> it).

Hmm.  Something is different on my setup from yours.  After my
optimisations, I do:
(i) Emacs -Q
(ii) M-: (setq long-line-threshold nil)
(ii) C-x C-f ~/long-line.cc RET; This is a file containing a 1MB raw
  string.
(iii) This loads and displays in somewhere between 1 and 2 seconds.
(iv) C-x 5 b long-line2.cc RET  M-x c++-mode RET
(v) Type in char long_line [] = R"foo(
(vi) Type in RET, twice
(vii) Type in )foo";

(ix) C-x 5 o
(x) Get the long line into the kill ring, with movement commands and
  M-w.
(xi) C-x 5 o.
(xii) Put point on the blank line 2.
(xiii) C-y.
(xiv) This takes less than a second to display.

What does your 1MB string look like?  Does it contain lots of "s?  CC
Mode needs to search through the yanked line for the first occurrence of
)foo", which is why it is not instantaneous.  It also has to put a
syntax-table text property on each " which isn't the terminating )foo",
which is another reason it's not instantaneous.

-- 
Alan Mackenzie (Nuremberg, Germany).