Re: We have a new standard!

From	Paavo Helde <eesnimi@osa.pri.ee>
Newsgroups	comp.lang.c++
Subject	Re: We have a new standard!
Date	2025-01-08 08:44 +0200
Organization	A noiseless patient Spider
Message-ID	<vll6rn$2lt27$1@dont-email.me> (permalink)
References	(1 earlier) <20250101182527.00004b2f@yahoo.com> <vl49dp$2uedm$1@dont-email.me> <86msg9a9t1.fsf@linuxsc.com> <vl5pte$3a2v3$1@dont-email.me> <86a5c1antv.fsf@linuxsc.com>

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On 08.01.2025 07:15, Tim Rentsch wrote:
> Paavo Helde <eesnimi@osa.pri.ee> writes:
> 
>> On 02.01.2025 10:39, Tim Rentsch wrote:
>>
>>> Paavo Helde <eesnimi@osa.pri.ee> writes:
>>>
>>> [...]
>>>
>>>> Half of the slowness of both in C printf() and C++ streams comes
>>>> from the locale support, [...]
>>>
>>> I find this assertion very hard to believe (specifically, for
>>> printf();  I might guess that C++ streams have similar
>>> performance characteristics, but I don't have nearly as much
>>> experience with C++ streams as I do with printf()).
>>>
>>> Is there anything else you can say about it besides an
>>> unsupported assertion?
>>
>> Probably you were misled by my vague word usage.  I said "half of the
>> slowness", not "half of the total time".  As "slowness" is nowhere
>> exactly defined, this was just a figure of speech, no need to get
>> overly upset about that.
> 
> I'm not upset, just disappointed.  I consider you one of the better
> contributors in the newsgroups, and so it's surprising to see a
> statement from you with zero information content.
> 
>> Anyway, I have profiled the writing of large CSV tables (multi-GB)
>> which was deemed too slow.  90% of time was spent in sprintf() calls,
>> from which 10% was spent in locale-related routines, presumably for
>> checking that the global process locale has not changed during the
>> last microsecond.  Considering that our CSV file format had to always
>> use the fixed C-locale format anyway, this locale checking was
>> something which was absolutely unneeded.
> 
> The 10% number is interesting, and disappointing.  Surely the authors
> of the standard library implementation could have done better.
> Incidentally, I did a measurement of the cost of localeconv() on my
> test server (running Ubuntu), and that gave a result in line with
> your 10% number.
> 
>> We tried to parallelize the writing, expecting to increase the speed N
>> times by using N threads, but alas, as the locale is a global
>> thread-shared object, now the threads started to fight over it and the
>> performance did not scale nowhere near to our expectations.  (The
>> thread-specific locales were not available an all needed platforms).
> 
> Does the C standard (or the C++ standard) allow locale information to
> be thread-specific?  I don't see anything in the C standard that looks
> like the <locale.h> functions can be anything but global.  I haven't
> looked at what C++ allows.

_configthreadlocale() is a MS extension.

"https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/configthreadlocale"

> 
>> We resolved it finally by using std::to_chars() for integer data and
>> Google's double-conversion library for floating-point data (our C++
>> implementations did not support std::to_chars() on floating-point data
>> on all needed platforms at that time).
> 
> It's disappointing that the C standard (and I assume also the C++
> standard) doesn't provide conversion functions that don't use global
> locale information.  Oh, come to think of it, I think I saw some C++
> functions (in which C++ standard I don't know) that pass locale
> information in explicitly, which is probably what you were alluding
> to above.

MSVC has _sprintf_l() which takes a locale explicitly, but this is again 
a non-standard extension.

Regardless if the locale is passed in implicitly or explicitly, the 
function would still need to process it, which might take non-zero time. 
We were aiming to use functions which would not consider locales at all.

C++ actually delivers that with std::to_chars() since C++17. I have not 
measured how fast it is nowadays, compared to Google's double-conversion.

Fast *and* accurate printing of floating-point numbers is not a trivial 
task. AFAIK last significant advances in this area were done as late as 
in 2010. See e.g. 
"http://www.serpentine.com/blog/2011/06/29/here-be-dragons-advances-in-problems-you-didnt-even-know-you-had/"

Thread

Re: We have a new standard! Michael S <already5chosen@yahoo.com> - 2025-01-01 18:25 +0200
  Re: We have a new standard! Muttley@dastardlyhq.com - 2025-01-01 16:33 +0000
    Re: We have a new standard! Ross Finlayson <ross.a.finlayson@gmail.com> - 2025-01-01 09:41 -0800
    Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-02 08:06 +0100
      Re: We have a new standard! Muttley@dastardlyhq.com - 2025-01-02 09:23 +0000
        Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-02 13:51 +0100
          Re: We have a new standard! Muttley@DastardlyHQ.org - 2025-01-02 14:07 +0000
            Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-02 17:54 +0100
              Re: We have a new standard! Muttley@DastardlyHQ.org - 2025-01-02 17:15 +0000
                Re: We have a new standard! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-01-02 13:58 -0800
                Re: We have a new standard! Muttley@DastardlyHQ.org - 2025-01-03 10:13 +0000
                Re: We have a new standard! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-01-03 11:22 -0800
                Re: We have a new standard! Muttley@dastardlyhq.com - 2025-01-04 10:17 +0000
                Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-04 12:31 +0100
                Re: We have a new standard! Muttley@dastardlyhq.com - 2025-01-04 11:34 +0000
                Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-04 14:01 +0100
                Re: We have a new standard! Muttley@dastardlyhq.com - 2025-01-04 15:49 +0000
                Re: We have a new standard! Ross Finlayson <ross.a.finlayson@gmail.com> - 2025-01-03 17:42 -0800
              Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-02 15:20 -0500
                Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-03 13:43 +0100
                Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-03 08:11 -0500
                Re: We have a new standard! Paavo Helde <eesnimi@osa.pri.ee> - 2025-01-03 16:33 +0200
                Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-03 10:50 -0500
                Re: We have a new standard! Muttley@DastardlyHQ.org - 2025-01-03 16:09 +0000
                Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-03 11:53 -0500
                Re: We have a new standard! Muttley@dastardlyhq.com - 2025-01-03 17:10 +0000
                Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-03 12:14 -0500
                Re: We have a new standard! Muttley@dastardlyhq.com - 2025-01-04 10:13 +0000
                Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-03 18:17 +0100
                Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-03 13:58 -0500
                Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-04 12:39 +0100
                Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-04 09:56 -0500
                Re: We have a new standard! Paavo Helde <eesnimi@osa.pri.ee> - 2025-01-03 21:46 +0200
                Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-03 21:06 -0500
                Re: We have a new standard! Ross Finlayson <ross.a.finlayson@gmail.com> - 2025-01-03 18:32 -0800
                Re: We have a new standard! Paavo Helde <eesnimi@osa.pri.ee> - 2025-01-04 20:08 +0200
                Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-04 14:46 -0500
                Re: We have a new standard! wij <wyniijj5@gmail.com> - 2025-01-05 07:14 +0800
                Re: We have a new standard! Muttley@DastardlyHQ.org - 2025-01-06 08:38 +0000
                Re: We have a new standard! Chris Ahlstrom <OFeem1987@teleworm.us> - 2025-01-07 08:40 -0500
                Re: We have a new standard! Muttley@DastardlyHQ.org - 2025-01-07 14:04 +0000
                Re: We have a new standard! Chris Ahlstrom <OFeem1987@teleworm.us> - 2025-01-08 14:52 -0500
                Re: We have a new standard! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-01-08 13:31 -0800
                Re: We have a new standard! Muttley@DastardlyHQ.org - 2025-01-09 08:39 +0000
                Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-07 21:32 -0500
                Re: We have a new standard! Ross Finlayson <ross.a.finlayson@gmail.com> - 2025-01-03 17:49 -0800
                Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-03 17:12 +0100
                Re: We have a new standard! Sam <sam@email-scan.com> - 2025-01-03 11:56 -0500
          Re: We have a new standard! Michael S <already5chosen@yahoo.com> - 2025-01-02 17:35 +0200
            Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-02 17:57 +0100
              Re: We have a new standard! Michael S <already5chosen@yahoo.com> - 2025-01-02 19:55 +0200
      Re: We have a new standard! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-01-02 13:40 -0800
        Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-03 09:42 +0100
    Re: We have a new standard! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-01-02 13:38 -0800
      Re: We have a new standard! Muttley@DastardlyHQ.org - 2025-01-03 10:09 +0000
        Re: We have a new standard! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-01-03 11:19 -0800
          Re: We have a new standard! Muttley@dastardlyhq.com - 2025-01-04 10:15 +0000
  Re: We have a new standard! Paavo Helde <eesnimi@osa.pri.ee> - 2025-01-01 22:43 +0200
    Re: We have a new standard! David Brown <david.brown@hesbynett.no> - 2025-01-02 07:56 +0100
    Re: We have a new standard! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-01-02 00:39 -0800
      Re: We have a new standard! Paavo Helde <eesnimi@osa.pri.ee> - 2025-01-02 12:31 +0200
        Re: We have a new standard! Michael S <already5chosen@yahoo.com> - 2025-01-02 14:59 +0200
          Re: We have a new standard! Paavo Helde <eesnimi@osa.pri.ee> - 2025-01-02 15:50 +0200
        Re: We have a new standard! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-01-07 21:15 -0800
          Re: We have a new standard! Paavo Helde <eesnimi@osa.pri.ee> - 2025-01-08 08:44 +0200
            Re: We have a new standard! Michael S <already5chosen@yahoo.com> - 2025-01-08 11:44 +0200
              Re: We have a new standard! James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-01-08 15:04 -0500
              Re: We have a new standard! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-01-14 08:49 -0800
            Re: We have a new standard! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-01-14 09:12 -0800
              Re: We have a new standard! Paavo Helde <eesnimi@osa.pri.ee> - 2025-01-14 19:53 +0200
          Re: We have a new standard! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-01-08 14:43 -0800
    Re: We have a new standard! scott@slp53.sl.home (Scott Lurndal) - 2025-01-02 20:51 +0000
  Re: We have a new standard! Michael S <already5chosen@yahoo.com> - 2025-01-02 16:47 +0200

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