Re: Slightly OT: non-buffered stdin in Java

On Thu, Jun 8, 2023 at 9:22 PM Aryeh Friedman <aryeh.friedman@gmail.com>
wrote:

> On Thu, Jun 8, 2023 at 6:37 PM 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 PM 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 the
> > > > > 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 file
> 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 file
> > > > > version of stdin
> > > > >
> > > >
> > > > "stdbuf" might be what you look for:
> > > >
> > > > https://man.freebsd.org/cgi/man.cgi?query=stdbuf
> > >
> > > 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"
> disables linebuffer on input by itself, so you should use someting else for
> testing.
> >
> > Nik
> >
>
> I am pretty convinced by the following test it is not working as
> advertised:
>
> aryehl@neomarx:~/Desktop % cat foo.c
> #include <stdio.h>
> #include <fcntl.h>
> #include <unistd.h>
>
> int main()
> {
>     int in=fcntl(STDIN_FILENO, F_DUPFD, 0);
>     int out=fcntl(STDOUT_FILENO, F_DUPFD, 0);
>     char c=0;
>
>     do {
>         read(in,&c,1);
>         write(out,&c,1);
>     } while(c!=EOF);
> }
> 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.

~Paul

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