Date: Thu, 8 Jun 2023 22:55:32 -0400 From: Aryeh Friedman <aryeh.friedman@gmail.com> To: Paul Procacci <pprocacci@gmail.com> Cc: "Dr. Nikolaus Klepp" <dr.klepp@gmx.at>, questions@freebsd.org, freebsd-java@freebsd.org Subject: Re: Slightly OT: non-buffered stdin in Java Message-ID: <CAGBxaXm6hP9YUCtbV2Cumvn=LWy7TgYctLA-tZU=GSrP8hg9Jw@mail.gmail.com> In-Reply-To: <CAFbbPuhvy=rtBU0iSJzyrxWdPYamXeFcGdBkUPYEvkLt46UyBA@mail.gmail.com> References: <CAGBxaX=muu6JbMsdZbop7mYa-LetXPHvO8_=kMZtF%2BzSAdiBYA@mail.gmail.com> <202306082039.36831.dr.klepp@gmx.at> <CAGBxaXnq%2BU9C7=Vepc4Poq8LaZCo8DnkPpMH5UT70dUsKrG3bw@mail.gmail.com> <202306090036.42118.dr.klepp@gmx.at> <CAGBxaXnVM=P%2B2r4o0UuEnOzhE6S9TTWbXyWFk2XGYqCsCdG44A@mail.gmail.com> <CAFbbPuhvy=rtBU0iSJzyrxWdPYamXeFcGdBkUPYEvkLt46UyBA@mail.gmail.com>
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On Thu, Jun 8, 2023 at 10:32=E2=80=AFPM Paul Procacci <pprocacci@gmail.com>= wrote: > > > > On Thu, Jun 8, 2023 at 9:22=E2=80=AFPM Aryeh Friedman <aryeh.friedman@gma= il.com> wrote: >> >> On Thu, Jun 8, 2023 at 6:37=E2=80=AFPM Dr. Nikolaus Klepp <dr.klepp@gmx.= at> wrote: >> > >> > Anno domini 2023 Thu, 8 Jun 17:22:38 -0400 >> > Aryeh Friedman scripsit: >> > > On Thu, Jun 8, 2023 at 2:39=E2=80=AFPM Dr. Nikolaus Klepp <dr.klepp@= gmx.at> wrote: >> > > > >> > > > Anno domini 2023 Thu, 8 Jun 14:01:19 -0400 >> > > > Aryeh Friedman scripsit: >> > > > > Under Java stdin (System.in) is a buffered stream not sent to th= e >> > > > > application until return is pressed. But, Java can read from >> > > > > files/sockets and other generic InputStreams unbuffered. So I = was >> > > > > wondering if there is a command that will make stdin go to a fil= e so >> > > > > that Java can open that file and read it unbuffered? >> > > > > >> > > > > I know I can do something like cat ->file but that makes it hard= to >> > > > > sync stdout and stderr (both are unbuffered in Java) with the fi= le >> > > > > version of stdin >> > > > > >> > > > >> > > > "stdbuf" might be what you look for: >> > > > >> > > > https://man.freebsd.org/cgi/man.cgi?query=3Dstdbuf >> > > >> > > Will likely need to play with it more but stdbuf -i 0 -o 0 cat -|cat >> > > didn't produce the expected immediate echo I still had to hit return >> > > >> > >> > Your console is linebuffered, so "cat" receives lines. IIRC "cat" disa= bles linebuffer on input by itself, so you should use someting else for tes= ting. >> > >> > Nik >> > >> >> I am pretty convinced by the following test it is not working as adverti= sed: >> >> aryehl@neomarx:~/Desktop % cat foo.c >> #include <stdio.h> >> #include <fcntl.h> >> #include <unistd.h> >> >> int main() >> { >> int in=3Dfcntl(STDIN_FILENO, F_DUPFD, 0); >> int out=3Dfcntl(STDOUT_FILENO, F_DUPFD, 0); >> char c=3D0; >> >> do { >> read(in,&c,1); >> write(out,&c,1); >> } while(c!=3DEOF); >> } >> aryehl@neomarx:~/Desktop % !cc >> cc foo.c >> aryehl@neomarx:~/Desktop % stdbuf -i 0 -o 0 ./a.out >> this is not echoing! >> this is not echoing! >> neither is this >> neither is this >> ^C >> aryehl@neomarx:~/Desktop % >> >> -- >> Aryeh M. Friedman, Lead Developer, http://www.PetiteCloud.org >> > > stdbuf only works for stdio buffering of which read(2) and write(2) aren'= t. I also tried it with System.in.read() in Java and it was also buffered but according to the openjdk source it appears that this is on purpose. --=20 Aryeh M. Friedman, Lead Developer, http://www.PetiteCloud.org
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