bug#22519: 25.1.50; Emacs gets stuck while doing incremental search forward

[Vincent Belaïche]

Answers below:

Le 16/03/2016 17:08, Eli Zaretskii a écrit :
>> From: vincent.belaiche@gmail.com (Vincent Belaïche)
>> Cc: Vincent Belaïche <vincent.belaiche@gmail.com> ,
>>  22519@debbugs.gnu.org
>> Date: Wed, 16 Mar 2016 12:16:00 +0100
>>
>>> IOW, I still cannot reproduce the problem on my system.  I suspect
>>> some issue with your font configuration, but that's just a guess.
>>
>> I have the same type of suspicion that it has to do with the display. Ie
>> some code running outside Emacs in some standard system library of
>> Windows API. However, there may also be some suboptimal coding in the
>> ways that Emacs, or some graphic library used by Emacs, interacts with
>> these library fuctions.
>>
>> I have attached a picture of my display, as you see I have a few not
>> displayable characters. They are displayed with small retangles
>> containing the Unicode code point in 4 hexadecimal letters --- let us
>> call this an hexa-rectangle.
>>
>> My speculation is that every time MSWindows is requested for such not
>> displayable character, then it spends a lot of time seeking whether this
>> character can be displayed in any of the supported fonts, and if not, it
>> spends again time making on the fly the special hexa-rectangle
>> characters, or maybe those hexa-rectangle bitmaps are placed in some
>> memory area that is not fast enough...
>>
>> So, do you have also any hexa-rectangles displayed on your system ?
>
> Only one.  All the rest are displayed correctly.
>
> Do you have the Symbola font installed?  If not, I suggest to install
> it, then I expect your problem to go away.  If you need to work a lot
> with mathematical symbols, having Symbola installed is a must, IMO.
>

That was a good suggestion, I have just installed Symbola and here is
what I get:

$ ./emacs-bug22519.sh
mode: fundamental
latin-9=(0.234 0 0.0)
utf-8=(0.234 0 0.0)

That is a damatic change!

I think that I should maybe write some warning in the document for the
Info output. The slowdown would occur for anybody without appropriate
math font installed also for the English version when viewing the Info.

>> Maybe you could try and reproduce the problem by replacing in the file
>> some of the math symbols by characters that are not displayable on your
>> machine. E.g. you could do some `M-: (insert (string #xhhhh)) RET' with
>> hhhh in { FFF0, FFC0, FFD0, FFC1, FFD1, FFE7, FFC8, FFD8, FFC9, FFD9,
>> FFDD, FFDE, FFBF, FFDF, FFEF, 0380, 0381, 0382, 03A2, 0383, 0377, 0378,
>> 038B, 038D}, based on taking greyed cells from page 2 of these
>> documents:
>>
>>    http://www.unicode.org/charts/PDF/UFF00.pdf
>>    http://www.unicode.org/charts/PDF/U0370.pdf
>
> I don't see the point of such a test.  What would it demonstrate?
>

That would confirm that the not displayable characters are causing the
problem. But having Symbola installed solved the problem, seems to
confirm it per se.

>> BTW, even if we end up concluding that the problem is some sort of MSW
>> bug, I still think that there is also something in Emacs: now the `Emacs
>> stuck' does not happen so often, maybe this is due to this that there
>> has been some MSW update meanwhile, but still it can happen after system
>> wake-up.
>
> If you are talking about the fact that Emacs searches for a character
> in any fonts it thinks might be able to display it, then this isn't a
> bug.  What else could Emacs do, when presented with a character that
> cannot be displayed with fonts that are already loaded?

I don't this that _this_ as such is a bug, what is more annoying is that
the slow-down lasts longer than the first scroll into the area where
these characters are. I could stay on the same region for hours, and
whenever I made an edit it was slow --- loosing the WYSIWYGiness of the
edition, that is I was seeing the full result of what I had typed one or
two seconds after the typing had started.

Furthermore there was also this « Emacs stuck forever » problem which
was the original cause for opening bug #22519. This behaviour should not
happen, this clearly is a bug just like a crash is. It then became quite
less frequent after some MSW update, and now after Symbola installed
will probably remain as a silent bug, unless you try to reproduce the
problem by inserting undisplayable characters and understand why the
slowdown is lasting at any edit.

VBR,
        Vincent.