From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,68494635acddb77e
X-Google-Attributes: gid103376,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news2.google.com!eweka.nl!lightspeed.eweka.nl!82.197.223.104.MISMATCH!feeder4.cambrium.nl!feed.tweaknews.nl!193.141.40.65.MISMATCH!npeer.de.kpn-eurorings.net!npeer-ng1.kpn.DE!newsfeed.arcor.de!newsspool3.arcor-online.net!news.arcor.de.POSTED!not-for-mail
Date: Wed, 20 Aug 2008 15:19:56 +0200
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
User-Agent: Thunderbird 2.0.0.16 (Macintosh/20080707)
MIME-Version: 1.0
Newsgroups: comp.lang.ada
Subject: Re: File output and buffering
References: 
 <60a35fd4-e5a6-4aa0-a73f-6815ce7e92fc@f36g2000hsa.googlegroups.com>
 	<4af2f934-7458-4370-b325-c38e3a4068b8@s50g2000hsb.googlegroups.com>
 <b3f16c6a-742c-43c3-baec-9533db25e423@r66g2000hsg.googlegroups.com>
In-Reply-To: 
 <b3f16c6a-742c-43c3-baec-9533db25e423@r66g2000hsg.googlegroups.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Message-ID: <48ac19fc$0$11747$9b4e6d93@newsspool1.arcor-online.net>
Organization: Arcor
NNTP-Posting-Date: 20 Aug 2008 15:19:56 CEST
NNTP-Posting-Host: 524d8c03.newsspool1.arcor-online.net
X-Trace: 
 DXC=aL5Y6dnDPA0gP]QSEBQ^d4ic==]BZ:af>4Fo<]lROoR14nDHegD_]R5i>ZD03E=X21;9OJDO8_SK6NSZ1n^B98i:>@ldKe6I7Z2
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news2.google.com comp.lang.ada:7403
Date: 2008-08-20T15:19:56+02:00
List-Id: <comp.lang.ada>

Maciej Sobczak schrieb:

>> In particular: how can I *flush* the buffer?
> 
> By calling Ada.Text_IO.Flush.
> 
> Which means that Georg Bauhaus fell into the trap of my confusion. :-)

Sort of, but, as you say, the issue remains.
> Still valid question:
> 
>> 3. Why is buffered Ada.Text_IO as slow as non-buffered C's stdio? Who
>> is eating the 20x factor?


Text_IO is demonstrably slow. There are some speedy
shortcuts in the GNAT implementation of Put (e.g. Write_Buf).
But AFAICS there is (and has to be) a lot of protecting code
around the OS calls.

Using the following stupid programs for comparison,
and using strace, I get 3370 calls to write(2) from C,
but 50_000 from both C++ and Ada. Among other things open
to speculation (or open to inspection).  There are 4622
different lines in the 50_000 lines of output.

I think that if you have a formatted (constrained) string,
system I/O using fputs and flush might be a lot faster
(modulo threading issues).


#include <stdio.h>

int main()
{
    char s[68 + 1] =
"********************************************************************";

    for (int k = 0; k < 50000; ++k)
    {
        s[k % 68] = (char)(33 + k % 67);
        fputs(s, stdout), fputc('\n', stdout);
    }
    return 0;
}



#include <iostream>

int main()
{
    std::string s =
"********************************************************************";

    for (int k = 0; k < 50000; ++k)
    {
        s[k % 68] = static_cast<char>(33 + k % 67);
        std::cout << s << std::endl;
    }
    return 0;
}

with Ada.Text_IO;
procedure Ada_Wrt is
   S: String := (1 .. 68 => '*');
begin
   for K in 0 .. 50_000 - 1 loop
      S(1 + K rem 68) := Character'Val(33 + K rem 67);
      Ada.Text_IO.Put_Line(S);
   end loop;
end Ada_Wrt;

--
Georg Bauhaus
Y A Time Drain  http://www.9toX.de